river flooding case study uk

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Flood and coastal erosion risk management report: 1 April 2023 to 31 March 2024

Updated 3 September 2024

Applies to England

© Crown copyright 2024

This publication is licensed under the terms of the Open Government Licence v3.0 except where otherwise stated. To view this licence, visit nationalarchives.gov.uk/doc/open-government-licence/version/3 or write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email: [email protected] .

Where we have identified any third party copyright information you will need to obtain permission from the copyright holders concerned.

This publication is available at https://www.gov.uk/government/publications/flood-and-coastal-risk-management-national-report/flood-and-coastal-erosion-risk-management-report-1-april-2023-to-31-march-2024

The Environment Agency use this report to summarise activities carried out by risk management authorities ( RMAs ) in England. Producing this report is a requirement of Section 18 of the Flood and Water Management Act 2010 ( FWMA ). This report is for the period 1 April 2023 to 31 March 2024.

• Environment Agency
• lead local flood authorities ( LLFAs )
• district councils (where there is no unitary authority)
• internal drainage boards ( IDBs )
• water and sewerage companies
• highways authorities

RMAs work together to reduce the risk of flooding and coastal erosion. We also work with the regional flood and coastal committees ( RFCCs ).

The RFCCs :

• bring together RMAs and other local organisations to better understand flood and coastal erosion risks in their region
• make sure there are coherent plans to manage flood and coastal erosion risks across catchments and shorelines
• encourage efficient, targeted and risk-based investment that meets the needs of local communities
• assign funding through a local levy as set out in section 23 of the FWMA

1. Executive summary

This year (April 2023 to March 2024) has seen wet, windy and stormy weather across the country. The country has experienced 13 named storms, compared to just 1 in 2022 to 2023 and 7 in 2021 to 2022.

Overall, England has experienced in wettest 18-month period since records began in 1836. Met office figures show that just under 1,700 mm of rain fell from October 2022 to March 2024.

While flood defences across the country have protected nearly 250,000 properties, this weather has unfortunately resulted in more than 5,000 properties flooding. This flooding was mainly due to storms Babet, Ciaran, Henk and Gerrit.

Throughout the year, we have continued working with partners to better protect a further 29,000 properties from flooding and coastal erosion. This means that since April 2021 over 88,000 properties have benefited from better protection.

We have also continued to carry out the practical actions set out in the flood and coastal erosion risk management ( FCERM ) strategy roadmap . These actions will help us achieve the ambitions in the FCERM strategy . They recognise the importance of resilience, adaptation to flooding and working with natural processes to reduce risk.

Natural flood management ( NFM ) reduces local flood risk while at the same time improving habitats and biodiversity. The £25 million NFM programme that we launched in September is our single biggest investment in NFM . What we learn from this programme will help us mainstream NFM .

We have refreshed all the Shoreline Management Plans ( SMPs ) around England, in collaboration with coastal groups. These set out a range of management approaches for our coastline looking out to the end of century and beyond.

We have also developed the SMP Explorer , a new map-based digital tool. This makes SMPs easier to access, understand and use for policy makers and practitioners.

We are also taking a more active strategic leadership role to help support and enable others to plan for and adapt to surface water flood risks. We recognise that we are uniquely placed to bring together those working surface water flood risk management to share good practice and promote innovation.

This year’s storms have also had significant impacts on farmers and agricultural land around the country. We have worked with government to provide expert advice to help inform several initiatives this year, including:

• sustainable farming incentive
• countryside stewardship
• landscape recovery
• catchment sensitive farming programme

Many of these initiatives work with natural processes to benefit farmers and land managers. They also help to enhance the flood resilience of rural communities.

2. The year in context

This section describes:

• significant flooding and coastal events
• progress against strategic plans
• government policy announcements

2.1 Flooding between April 2023 and March 2024

2.1.1 storm babet – 18 to 21 october 2023.

Storm Babet caused severe and widespread disruption across much of the country. Heavy, persistent and widespread rain affected much of the country, with 100mm falling fairly widely. Overall, this was the third-wettest independent 3-day period for England and Wales since 1891.

The extensive flooding resulted in more than 750 flood warnings and alerts being issued. This included 5 severe warnings in the areas at highest risk.

We also deployed:

• more than a kilometre of demountable barriers
• 700m of temporary barriers
• high volume pumps and smaller pumps to remove water from flooded areas

Over 5,000 properties flooded from Storm Babet while flood defences protected around 97,000. Sadly, 7 people were reported to have died because of the storm.

Our flood digital services recorded some of their busiest periods ever:

• the Flood Warning System (FWS) recorded its busiest day ever - more than 5,500 new users registered for warnings and almost 400,000 messages were sent in a single day
• overall the FWS sent almost 800,000 messages over the course of the storm
• Floodline received over 1800 calls on one day – the highest daily number since December 2015
• check for flooding logged over 2 million visitors

2.1.2 Storm Ciarán – 1 to 3 November 2023

Storm Ciarán was an exceptionally severe storm for the time of year, with very high winds and significant rainfall. This rainfall made existing flooding problems worse and caused many rivers to overtop their banks. Plymouth recorded the lowest atmospheric pressure for November on record, at 953.3 hPa.

Storm Ciarán caused major disruption across the south of England:

• the port of Dover was temporarily closed
• ferry services were cancelled
• flights and rail services were cancelled
• hundreds of schools were shut
• almost 150,000 homes were left without power

Large waves affected the South Coast and a major incident was declared in Hampshire and on the Isle of Wight.

Around 300 properties flooded because of Storm Ciarán. Nearly 43,000 properties were protected by existing flood defences.

We carried out a range of activities to reduce the impact of the storm, including:

• installing temporary flood barriers in Exeter as part of the Exeter flood defence scheme
• operating flood gates
• replacing demountable barrier beams at Bewdley, Worcestershire
• using specialist equipment to check flow rates of the River Wey in Surrey

2.1.3 Storm Gerrit (27 to 28 December 2023) and Storm Henk (2 January 2024)

Storms Gerrit and Henk were the 7th and 8th named storms of the 2023 to 2024 season. Together, they brought heavy rainfall and high winds to most parts of England. Parts of the country had a month’s worth of rain in the first 4 days of January. Several river systems saw record levels or close to record levels, including:

This rainfall fell on already saturated catchments causing flooding which affected around 2,500 properties. Flood defences protected around 102,000 properties across the country.

Several major incidents were declared including in Nottingham due to flooding on the River Trent. The River Trent recorded some of its highest levels in over 20 years.

We carried out a range of activities to manage the impacts of the flooding including:

• pumping water away from affected areas in Nottinghamshire and Berkshire
• deploying demountable defences along the River Severn in Bewdley

These winter storms caused significant impacts to farmland and farming business across the country. As a result, the farming recovery fund was activated for eligible areas.

The number of properties flooded reflects the latest information as of April 2024. The numbers may change as we gather more data.

2.1.3 Recovery activities

Following flooding incidents, we carry out a range of recovery activities. These include:

• reviews of flood forecasting and warning
• inspecting assets
• gathering learning from events
• reviewing health, safety and wellbeing

The information we collect helps us improve how we respond to flood events in the future. 

As of May 2024, we have completed over 68,000 inspections of assets affected by this year’s storms. These inspections have identified around 1,800 damaged assets. Of these 1,400 are in Environment Agency high consequence systems. There were at least 13 breaches to flood embankments directly impacting farmland and nearby infrastructure.

We closely monitor any damaged defences and put in place mitigation measures. We also carry out any necessary urgent or emergency repairs.

2.1.4 Record of past flood events

Table 1: previous flood events, properties flooded and properties protected since 2020.

2.2 National Flood and Coastal Erosion Risk Management Strategy for England

The  FWMA states that we must develop, apply, maintain, and monitor a strategy for  FCERM  in England. The current FCERM  Strategy was adopted by Parliament and published on 25 September 2020.

The  FCERM  Strategy :

• contributes to our strategic overview role of all FCERM activities
• is a statutory framework to guide those involved in  FCERM  to achieve its ambitions on the ground

All  RMAs  have a duty to act consistently with the  FCERM  Strategy when carrying out their  FCERM  roles.

The  FCERM  Strategy’s long-term vision is for a nation ready for, and resilient to, flooding and coastal change – today, tomorrow and to the year 2100.

It has 3 ambitions:

• climate resilient places
• today’s growth and infrastructure resilient in tomorrow’s climate
• a nation ready to respond and adapt to flooding and coastal change

The 3 ambitions consist of 21 strategic objectives covering the next 10 to 30 years. The FCERM Strategy also contains 56 shorter term measures. These explain the immediate activities RMAs will take to achieve each objective.

2.2.1 Flood and Coastal Erosion Risk Management Strategy Roadmap to 2026

On 7 June 2022, we published the FCERM strategy roadmap to 2026 . This sets out the practical actions we will take to achieve the ambitions in the FCERM Strategy .

These actions will:

• help us tackle the growing threat of flooding from rivers, the sea, and surface water as well as coastal erosion
• provide a range of benefits, including local nature recovery, carbon reduction, improved water quality and more integrated water management – this will help with both flood and drought resilience

We developed the Roadmap in collaboration with 31 partners across multiple sectors.

This year we have completed several important actions that contribute towards achieving the FCERM Strategy ambitions. These achievements are described in more detail later in this report.

Climate resilient places

This year, we have:

• worked with coastal groups to refresh the SMPs , as well as reviewing the associated action plans and priorities
• published the SMP Explorer , which is an online map-based tool for SMP information
• invested £25 million in 40 natural flood management projects which use nature to increase the nation’s flood resilience
• expanded the Coastal Transition Accelerator Programme to include projects in Bude, Charmouth and Swanage – these help vulnerable communities explore innovative approaches to adapt to the effects of coastal erosion
• reviewed and updated the Thames Estuary 2100 Plan – this ensures that the Thames estuary remains resilient to a changing climate

Today’s growth and infrastructure resilient in tomorrow’s climate

• supported the development of skills and capabilities of local planners – this will make sure new developments are resilient to flooding and coastal change and encourages environmental net gain
• published a streamlined approach to developing and funding business cases for Property Flood Resilience ( PFR ) projects which will enable more PFR projects to be completed
• launched a new framework of suppliers for PFR which will result in a higher standard of PFR product and installation
• launched new biodiversity net gain guidance for capital projects which will help projects achieve biodiversity net gain and encourage other environmental benefits

A nation ready to respond and adapt to flooding and coastal change.

This year we:

• worked with partners and the insurance industry to review the recovery phase from a broad selection of historic major flood events and learn from other major civil emergencies
• led conversations with local resilience forums ( LRFs ) on the role of the third sector in responding to significant flood incidents across the country

LRFs are multi-agency partnerships made up of representatives from the emergency services, local authorities, NHS, Environment Agency and others.

2.3 Changes to government policy and announcements

The FCERM Strategy calls for the nation to embrace a broad range of resilience actions to better protect and prepare against flooding and coastal change.

Several important actions were achieved this year.

Property flood resilience repair grant scheme

The PFR repair grant scheme was activated twice this year for both Storm Babet and Storm Henk. The scheme lets eligible flood-hit property owners apply for up to £5,000 to help make their homes and businesses more resilient to future flooding.

Farming recovery fund

The farming recovery fund allows farmers who have suffered uninsurable damage to their land to apply for grants of up to £25,000. This money helps farmers with repair and reinstatement costs to return their land to the condition it was in before exceptional flooding. The fund was activated this year for eligible areas affected by Storm Henk.

These areas included:

• Gloucestershire
• Leicestershire
• Lincolnshire
• Nottinghamshire
• Warwickshire
• West Northamptonshire
• Worcestershire

Frequently flooded allowance

In April 2023, the first 53 communities in England to benefit from the £100 million frequently flooded allowance were announced. These communities have been allocated a total of £48 million, better protecting more than 2,300 households and businesses.

• Coastal transition accelerator programme

In September 2023, 3 further communities joined the Coastal Transition Accelerator Programme . These are:

Together, they will share £6 million to support adaptation to coastal erosion. This is in addition to North Norfolk and East Riding of Yorkshire previously announced.

The programme is exploring how best to support communities most affected by coastal erosion to plan for the long term. This includes through interventions such as improving and replacing damaged community infrastructure like beach access or coastal transport links.

We will share lessons from this programme to help other coastal communities and risk management authorities to prepare for a changing coastline.

National Audit Office and Public Accounts Committee reports

The National Audit Office ( NAO ) report on value for money in FCRM was published on 15 November 2023.

The Public Accounts Committee ( PAC ) met on 27 November 2023 to discuss the findings from the NAO report and other issues related to flood risk.

On 17 January 2024 the PAC published their report on the inquiry into resilience to flooding .

The previous government’s response to the Committee’s report was published on 31 March 2024.

Defra are working with the Environment Agency to develop a methodology for measuring and reporting ‘net’ change in flood risk at a national level. The new National Flood Risk Assessment ( NaFRA2 ) will introduce this capability. It will establish a new risk baseline against which change can be measured. The Environment Agency expects to be able to report “net” change in risk from 2025 onwards. This is in line with the timescales agreed with the National Audit Office following their 2020 report Managing Flood Risk.

Natural flood management programme

In February 2024 the Environment Agency announced the 40 projects that will benefit from the £25 million Natural Flood Management Programme. These projects will use natural processes such as planting trees and creating wetlands to slow and store water and dissipate wave energy. This helps reduce the risk of flooding.

Flood risk indicators

The Environment Agency will report on a national set of indicators to monitor long term trends over time in tackling flood and coastal erosion in England.

These indicators cover all sources of flood risk and will provide an improved understanding of progress to create a more resilient nation.

The indicators are:

• properties better protected from flooding through defences
• asset condition
• planning applications granted against flood risk advice
• availability and take up of flood warnings

The Environment Agency will report against these indicators annually through this report.

3. Current risk and investment

This section provides information on flood risk, investment and partnership working.

3.1 Properties in areas at risk of flooding

Overall, around 5.5 million homes and businesses in England are at risk from flooding. That risk can be from one or a combination of sources including:

• rising groundwater
• surface water
• overwhelmed drains and sewers

Some properties are at risk from more than one source of flooding.

Table 2: properties in areas at risk of flooding from rivers and the sea (as of December 2023), and from surface water as of (as of January 2024).

We have paused the updating of our national modelled flood risk products at present. This is because we are developing a new National Flood Risk Assessment ( NaFRA2 ), which is a significant update to our approach to mapping and modelling of flood risk.

Due to the complexity and nature of groundwater flooding, we are not able to assign a likelihood to it.

3.1.1 Changes in properties in areas at risk from flooding and coastal erosion

The numbers of properties in areas at risk from flooding and coastal erosion change over time. This is shown in table 3.

This is due to factors including:

• changes in land use
• changes to the natural environment
• the increasing impacts of climate change
• investment in building and maintaining flood and sea defences
• ageing defences that require maintenance or replacement

All these factors will influence the total number of properties at risk of flooding in any given year and in any given location.

Table 3: properties in areas at risk of flooding by source each year from 1 April to 31 March from 2019 to 2024

We continue to update our underlying property information. We updated and improved our national receptor dataset ( NRD ) in August 2023.

These improvements include:

• better identification of ancillary buildings, for example outbuildings - these were previously counted as separate properties but are now included with main buildings where appropriate
• better identification of properties in shared buildings, for example residential flats
• a large reduction in properties which we previously couldn’t classify and which when classified are not relevant to flood risk, for example covered walkways

This improved information means that overall, the number of properties identified as being at risk has decreased since last year.

This does not reflect a decrease in risk, but rather a better understanding of the level of risk. This change can be seen in the 2023 to 2024 risk values in table 3.

Table 3 shows that:

• 2.6m properties are at risk of flooding from rivers and the sea 
• 3.2m properties are in areas at risk of surface water flooding

Some properties are at risk from flooding from multiple sources. For example, around 642,000 properties are at risk from flooding from rivers, the sea, and surface water.

In addition, between 122,000 and 290,000 properties are estimated to be in areas at risk of groundwater flooding. This may include properties also in areas at risk of surface water flooding.

Overall, this means around 5.5 million homes and businesses in England are at risk from flooding.

We assess risk using flood modelling and mapping to understand the likelihood of flooding at national and local levels. We developed our current National Flood Risk Assessment ( NaFRA ) in the early 2000s. It provides risk information on flooding from rivers and the sea.

We are developing a new National Flood Risk Assessment ( NaFRA2 ).

We will publish a ‘National assessment of flood and coastal erosion risk in England 2024’ report in December 2024. This will use our new NaFRA2 data and our updated National Coastal Erosion Risk Map ( NCERM ).

Following this we expect to publish the new NaFRA2 data in early 2025.

3.2 Investment in FCERM

The finance figures included in this report may change subject to the completion of the NAO audit of the Environment Agency’s Annual Report and Accounts. This is due in October 2024. We will update the report once the audit has finished.

The current 6-year programme of FCERM projects runs from 1 April 2021 to 31 March 2027. April 2023 to March 2024 is the third year of this programme.

This year 28,920 properties have benefited from better protection from flooding and coastal erosion. Within this total, other RMAs have carried out works that better protect 10,650 properties.

Over 88,000 properties have benefited from better protection since April 2021.

Between April 2023 and March 2024, government invested £864 million of capital funding in FCERM .

This includes spend on:

• projects in 2023 to 2024 that better protect properties
• the development of future projects
• the flood and coastal resilience innovation programme

This means you should not directly compare overall spend with the number of properties protected in the same year.

Of this £864 million, £119 million was spent by other RMAs on FCERM projects. Other RMAs have also spent £11 million of local levy funding. Local levy funding is spent on local priority flood and coastal erosion projects. It is managed by RFCCs .

Funding for FCERM projects is allocated through the application of government’s partnership funding policy.

We review the programme of FCERM projects each year to make sure that we:

• get the best value for money
• better protect as many properties as possible
• invest in priority areas where the risk is highest

Table 4: FCERM capital investment from 1 April 2023 to 31 March 2024

Government funding is used to reduce flood and coastal erosion risk across all regions of the country. We do not have any regional investment targets. All schemes are carefully assessed to make sure they benefit the most people and property.

Table 5: government investment and properties protected in FCERM by Environment Agency area from 1 April 2023 to 31 March 2024 in £ millions

Government funding has helped benefit areas of higher socio-economic deprivation across the country. Areas of deprivation are measured using the indices of multiple deprivation.

Between April 2023 and March 2024 FCERM work better protected:

• 6,940 (24% of the 2023 to 2024 total) properties in the highest socio-economically deprived areas in England (0 to 20% index of multiple deprivation)
• 9,830 (34% of the 2023 to 2024 total) properties in the next highest socio-economically deprived areas (20 to 40% index of multiple deprivation)

3.2.1 Other benefits of FCERM investment

The focus of our current investment programme is to better protect properties from flooding and coastal change.

However, our investment programme will also provide other benefits to support local businesses, communities and economic growth.

Table 6 shows the flood risk reduction benefits our work provides to:

• agricultural land

Table 6: other benefits of  FCERM  investment from 1 April 2021 to 31 March 2024

3.2.2 Significant projects completed

Between April 2023 and March 2024, we worked with other  RMAs  to better protect 28,921 properties from flooding and coastal erosion through around 135 FCERM  capital projects.

These projects better protected people and properties from:

• sea and tidal flooding (15,719 properties from 29 projects)
• river flooding (7,575 properties from 60 projects)
• surface water flooding (927 properties from 39 projects)
• coastal erosion (4,700 properties from 7 projects)

A project can provide improved protection from more than one source of flooding. The number of properties protected by a project depends on the size of the project and the type of flooding it is providing protection from. For example, surface water projects are often lower cost and provide protection to fewer properties. 

Case Study 1 - Perry Barr and Witton and Bromford and Castle Vale schemes

The Perry Barr and Witton and the Bromford and Castle Vale areas are in north and north-east parts of central Birmingham. Both areas have a history of flooding from the River Tame. Both were badly affected by flooding in 2007.

The 2 projects together better protect nearly 2,500 properties:

• Perry Barr and Witton – 1,790 properties
• Bromford and Castle Vale – 703 properties

Perry Barr and Witton is a £50 million scheme that was completed in the summer of 2023. The work included the construction of a new flood storage reservoir at Forge Mill in the Sandwell Valley Country Park. This site is upstream of Perry Barr and Witton communities. It works by capturing excess water from the River Tame during times of heavy rainfall. 

The new reservoir can store 1.7 million cubic metres of water, the equivalent of 680 Olympic swimming pools. 

The scheme also includes: 

• new flood walls
• flood gates  
• flow conveyance improvements from Brookvale Road in Witton, down to Gravelly Park Industrial Estate in Aston

The project is supported by Birmingham City Council and Sandwell Council. 

The Bromford and Castle Vale project cost around £17 million and was also completed in 2023. It reduces the risk of flooding to residential and commercial properties and infrastructure.

The scheme includes: 

• a series of earth embankments 
• a low-level flood wall along the left bank of the River Tame 

Each section of flood wall was made using a type of lower carbon concrete which reduced the carbon footprint of each wall section by 35%. 

3.2.3 Partnership funding

Funding for  FCERM  projects is allocated in line with government partnership funding policy . The amount of funding a project is allocated depends on the damages avoided because of the project plus the benefits it will provide.

This is based on 4 measures:

• the overall benefits provided by a project less those valued under the other measures listed below – this could include damages avoided to hospitals, farms or transport infrastructure
• households moved from one category of flood risk to a lower category
• households better protected against coastal erosion
• environmental benefits provided through FCERM activities

Some projects will be fully funded by FCERM GIA, while others will need partnership funding contributions to go ahead. These contributions usually come from those benefiting from the project, including:

• local partners
• the local community
• other organisations or businesses

Partnership funding contributions allow more communities to benefit from local  FCERM  measures than could be funded directly by central government alone.

Table 7: Partnership funding spent between April 2021 and March 2024 on projects better protecting properties in 2021 to 2027 programme

3.2.4 Asset management

There are around 245,000 assets that have a FCERM purpose in England. Just over 240,000 manage risk from flooding. The remainder manage coastal erosion risk.

Of the flood risk management assets:

• around 160,000 are third party assets maintained by riparian owners who own the land next to the river – 96,000 of these are in high consequence systems
• around 80,000 are managed by the Environment Agency – 38,000 of these are in high consequence systems

High consequence systems are those where the assets protect a high concentration of properties. A system is where several different types of flood defences work together to reduce risk and better protect an area.

We allocated £197.4 million towards maintaining FCERM assets between April 2023 and March 2024.

This investment includes:

• inspecting assets and checking that they are operational
• clearing weeds and debris from assets to help ensure the free flow of water
• protecting embankments from erosion
• maintaining assets that support the free movement of eels and fish along watercourses
• clearing assets of invasive non-native species ( INNS ) which can harm other species, damage habitats and increase flood risk

The Environment Agency inspects and reports on 195,000 flood risk management assets. This includes our own and third-party assets. We inspect all flood risk assets that work together to protect people and property.

We do not maintain third party assets. However many are part of our schemes and connected to assets we do maintain. It is important we inspect and monitor these to understand their condition. This makes sure of the performance of the overall flood risk management system. We work with the third parties to make sure they are maintained and operated when required.

Inspection frequency is based on risk and varies from 6 months to 5 years. This means not all assets are inspected each year. At the start of 2023 we planned to carry out 107,000 inspections. Since the October 2023 storms we have carried out an extra 68,000 inspections to check the condition of our assets.

On 31st March 2024, 92.6% of our flood risk assets in high consequence systems were in the required condition.

Our long-term aim, with the appropriate level of investment, is for 98% of our high consequence assets to be at their required condition.

We publish details of planned maintenance activities in the river and coastal maintenance programme .

3.3 Public sector cooperation agreements

The FWMA requires RMAs to cooperate with each other when carrying out FCERM activities. RMAs should work together to provide flood risk maintenance and other activities.

One example of partnership working is through public sector cooperation agreements ( PSCAs ). These allow 2 public sector bodies to set out how they will work together to achieve public tasks of mutual benefit. The benefits of partnership working are well established.

We use PSCAs for a wide variety of work including:

• routine maintenance
• small improvement works
• incident response

Table 8: summary of Environment Agency PSCAs on 31 March 2024

3.4 Efficiency savings

We report to government about the efficiencies achieved through our FCERM investment programme. This is so that we achieve the best possible value for the investment of government funds.

We can achieve efficiencies through:

• national initiatives that allow operational improvements
• project specific activities

Savings are achieved through:

• value engineering
• longer-term planning and packaging of work

We aim to achieve 10% efficiencies in the current investment programme. These efficiencies are then reinvested in our investment programme.

Between April 2023 and March 2024, we achieved £46 million in efficiency savings. We have done this mainly by using different contract methods to gain greater value and risk sharing from our supply chain.

Efficiencies vary from year to year.

They depend on:

• the FCERM funding allocation for that year
• individual project completion dates

Case Study 2: Southsea Coastal Scheme 

The Southsea Coastal Scheme is a flood defence project across 4.5 km of Southsea seafront in Portsmouth. The aim of the scheme is to:

• better protect households, business and other buildings from flooding for the next 100 years
• take into account climate change
• improve urban public spaces

Southsea Castle is approximately 700m of coastal frontage located in the centre of the scheme. This is one of the most exposed peninsulas.

The original design included a steep rock revetment laid directly over the existing sea defences. However, a project review identified the opportunity to refine the design which significantly reduced the overall rock volume needed.

This resulted in an efficiency saving of £4.2 million. 

4. FCERM strategy ambition 1 - climate resilient places

This section explains how RMAs are working together to increase resilience to flooding and coastal change, both now and in the future.

4.1 Climate change

Our climate is changing, sea levels are rising, and we are experiencing more extreme weather. We are already seeing these changes.

Long term records show that in the UK:

• temperatures are rising
• more rainfall in winter is falling in intense rainfall events
• sea levels are rising more rapidly than in the past

The scale of potential future flooding and coastal change is significant. 1 in 6 people are already at risk of flooding from rivers and the sea. The risks will only increase with rising sea levels, more frequent and severe floods and storm surges.

There are 2 main ways we can tackle climate change:

• mitigation – reducing or limiting the effects of greenhouse gases to reduce the impacts of a changing climate
• adaptation – changing lifestyles, economy, and infrastructure to adapt to the unavoidable impacts of climate change

We need to prepare for the changes that are already happening. We need to take greater action to both mitigate and adapt to minimise risks from climate change.

The climate of the future depends on the actions we take now.

4.1.1 Mitigation

In May 2021 the Environment Agency set out our plan to achieve net zero by reducing emissions by 45% and offsetting the remaining 55%.

Since then, net zero science has continued to mature. This has led to a revised net zero definition by the Science Based Targets initiative ( SBTi ).

Therefore, in January 2024, we published an update to our net zero goal . In this, we have committed to increase our emissions reduction target to 90% between 2045 and 2050.

In FCERM , we remain committed to our pledge to reduce emissions by 45% by 2030. We have continued our work to achieve this, including:

• cross-sector collaboration to reduce carbon in our infrastructure - for example, we have made low carbon concrete a minimum requirement and business cases for any new flood schemes must contain a carbon assessment
• working on new innovations – for example low carbon steel reinforcement bar alternatives and using modelling to minimise the embedded carbon of our infrastructure schemes by design

We have also reduced our direct operational emissions by more than a third since 2019 by:

• switching a significant portion of our fleet to electric
• reducing the amount we travel
• investing in more efficient infrastructure

We have an action plan to support our net zero road map. This contains 92 actions which we track and report progress on every quarter.

In 2019 our work on  FCERM  projects accounted for around 54% of our corporate carbon emissions. This was the equivalent of around 148,000t CO2e .

Investment in  FCERM  projects has doubled since the last programme (2015 to 2021). This increase comes with an increased potential for more emissions. Currently we estimate that our emissions from our construction are greater than 70% of our overall carbon footprint.

However, our flood risk management projects also avoid using carbon. We estimate that 268,000t CO2e of carbon will be avoided through the operational life of  FCERM  projects completed between April 2021 and March 2023. This is through properties not flooding and livelihoods being protected.

We continue to prioritise reducing carbon during the construction of our flood risk management projects. The choices we make about the construction materials we use are very important.

For example, over 80% of our carbon emissions from construction are contained in materials we use such as concrete and steel. To reduce this, we have changed our technical requirements for suppliers. We now specify low carbon concrete by default where suitable.

Case study 3: Bridgewater Tidal Barrier Scheme

The Bridgwater Tidal Barrier ( BTB ) Scheme is a £100 million Environment Agency project to protect 13,000 homes and businesses from tidal flooding. The scheme design company was awarded funding from our net zero carbon innovation pathway fund 2022 to 2023.

This allowed them to trial their ‘Building Information Modelling ( BIM ) Analytics – Carbon’ workflow on the tidal barrier design.

This technology:

• integrates sustainability into BIM
• connects people, data and technology to support decision-making
• minimises the embodied carbon

We’re on track to achieve a 50% reduction in embodied carbon for the tidal barrier structure on the BTB Scheme. This is around 8,000 tCO2e.

Integrating sustainability with BIM provides a range of additional benefits including:

• encouraging carbon management behaviours through its regular use in carbon workshops
• analysing and accurately reporting embodied carbon with real-time carbon visualisations through data
• providing an audit trail of carbon changes through comments log
• providing learning and testing for the integration of carbon data within our Data Requirements Library and Carbon Calculator tool

Following this trial, we have provided more innovation funding to expand the use of the tool to the whole BTB project to the end of detailed design.

4.1.2 Adaptation and resilience

We are planning for a 2˚C global temperature increase by 2100 in our FCERM Strategy . However, it is also important that we prepare for more extreme scenarios of climate change and assess a range of climate impacts. This will make sure our approach to FCERM can adapt to a range of climate futures.

We’re doing this in both our planning advice for new developments and for the design of new FCERM projects, schemes and strategies . Our guidance reflects the latest climate science.

Guidance for RMAs on how to account for climate change in FCERM projects, schemes and strategies fits with our partnership funding and appraisal guidance .

Flood and coastal innovation programmes (FCIP)

We manage the Flood and coastal innovation programmes funded by Defra. This encourages innovation in flood and coastal resilience and adaptation to a changing climate. We’re investing £200 million to test and develop new ways to create a nation resilient to flooding and coastal change.

We’re doing this across three programmes:

• Flood and coastal resilience innovation programme
• Adaptive pathways programme

Flood and Coastal Resilience Innovation Programme (FCRIP)

£150 million of the  FCIP  funding is being used to develop 25 projects. In March 2021, government announced the 25 projects selected . These projects are led by local authorities with support from us.

Each project will show how practical innovative actions can help to improve resilience to flooding and coastal erosion. They will do this by developing, testing, and implementing resilience actions that are outside the scope of what central government usually funds.

The 25 projects include:

• projects piloting property flood resilience ( PFR ) to reduce the impacts of groundwater flooding
• developing nature-based solutions with rural land managers to improve resilience to floods and drought
• developing surface water flood warnings for remote communities
• creating new habitat to increase shoreline resilience and better protect local coastal economies
• trialling new and innovative financing to improve flood and coastal resilience and adaptation to coastal change

The programme will share evidence and learning to inform future approaches to, and investments in  FCERM .

We are working with Defra on an evaluation of the 25 projects.

Case study 4: Reclaim the Rain

The Reclaim the Rain project is led by Suffolk and Norfolk County Councils. It is investigating creative solutions for capturing floodwater which can then be reused for agriculture when there is too little water. The project will reduce flood risk and also benefit agriculture by improving water security for food production.

The project team are working with large scale food producers to identify where flood water can be stored upstream to reduce flood risk to downstream communities.

The learning from this innovation project will be used to identify:

• what doesn’t work
• how the approach could be replicated in future

Adaptive Pathways Programme (APP)

£8 million of the  FCIP  funding is being used to develop adaptation pathway plans for managing flooding and coastal change to 2100 and beyond.

The plans cover strategic locations including the:

• Thames Estuary
• Humber Estuary
• River Severn

They also include 2 locations in Yorkshire:

• a catchment scale project in South Yorkshire
• a community scale surface water project in West Yorkshire

We will work with partners to develop and explore:

• different resilience actions – these could help to better plan for, protect, respond to, and recover from flooding and coastal change over pathways to 2100 and beyond
• local land use and development choices – these could allow for more flood and climate resilient places
• better coordination of planning and investment cycles with infrastructure and utilities – these could unlock investment in flood resilient infrastructure and services
• integrated water level management – which could improve flood and coastal resilience whilst also enhancing water quality and the natural environment

These will help us achieve:

• the maximum benefit for people and places at the right time
• strategic objectives and measures in the  FCERM  Strategy

We have developed an  adaptation pathway knowledge hub  which contains information and tools to help  RMAs  develop adaptation pathways.

4.1.2.3 Coastal Transition Accelerator Programme

£36 million of the FCIP funding is being used for the Coastal Transition Accelerator Programme . This will:

• trial opportunities to transition and adapt to the impacts of coastal erosion
• cover 5 coastal areas at significant risk of coastal erosion
• cover the coastal areas with property most at risk of significant coastal erosion in the next 20 years
• produce an adaptation plan
• created practical actions that will support the long-term resilience of coastal communities and transition away from areas of coastal change

North Norfolk District Council and East Riding of Yorkshire Council were selected to receive £30 million of the funding to progress phase 1 of the project. This is because data shows up to 80% of the homes at risk in the next 20 years are within those 2 areas.

The £6 million of additional funding for phase 2 of the project will help support communities at risk of coastal erosion in the South West to transition and adapt to climate change. This is for projects in Bude in Cornwall and Charmouth and Swanage in Dorset.

The councils will work with residents, businesses and asset owners to prepare for the long term through:

• rolling back property and facilities at short term risk of coastal erosion
• improving and replacing damaged community infrastructure such as steps and ramps to the beach
• repurposing land where property has been removed for community and nature benefit
• trialling innovative moveable buildings
• working with planners and the financial sector to develop mechanisms and tools to support future adaptation and prevent inappropriate development in places at risk

The programme will run from 2022 to 2027 in East Riding of Yorkshire and North Norfolk and from 2024 to 2027 in Bude, Charmouth and Swanage.

We will share lessons from the programme with other coastal RMAs through existing groups, networks and workshops as required.

4.2 Coastal change

The  NCERM  shows that about 2,000 properties are at risk of being lost to coastal erosion by 2060. This assumes all current SMP approaches and actions are carried out.

We are currently updating our national coastal erosion predictions.

During 2023 to 2024 we have:

• used new climate change research to model the impacts of climate change on erosion
• completed extensive data checks and draft output reviews with over 80 local authorities along the English coast

Coast protection authorities ( CPAs ) lead on coastal erosion management. They have permissive powers, which allow them to carry out FCERM works.

Some CPAs in England use NCERM to develop local planning mechanisms. These include coastal change management area ( CCMAs ).

These mechanisms:

• ensure new development takes account of the changing coast
• support the transition of communities and infrastructure away from areas at risk of coastal erosion

We will be publishing the updated NCERM in December 2024. This will be included in the ‘National assessment of flood and coastal erosion risk in England 2024’ report alongside the new national flood risk assessment ( NaFRA2 ).

4.2.1 Shoreline management plans

SMPs set out the local approach to managing coastal flood and erosion risk into the next century. They identify the most sustainable management approach for each stretch of coastline in England.

The management approaches cover the:

• short-term (0 to 20 years)
• medium term (20 to 50 years)
• long-term (50 to 100 years)

CPAs and other important stakeholders have led the development of SMPs . This was done in 7 regional coastal groups across England, producing 20 SMPs .

We have worked with coastal authorities to refresh and update SMPs . This work has made sure SMPs are fit for purpose and continue to steer planning and investment decisions at the coast.

Through 2024 and beyond, coastal groups and SMP groups will be focusing on implementing the updated action plans.

 4.2.1.1 Shoreline Management Plan Explorer

On 30 January 2024, we launched the SMP Explorer. This new map-based digital tool makes plans for coastal management:

• easier to find, access and understand
• more useful for coastal practitioners and the public

SMP Explorer will also improve our ability to monitor and assure SMPs and the actions being taken to manage our changing coast.  

We will add new content regularly so the tool is up-to-date. This will include an improved NCERM in December 2024.  

We also commissioned an independent peer review to assess the state of  SMPs  and identify where further improvements can be made. The peer review panel was made up of 6 coastal experts including representatives from local government and academia.

The  peer review report  provides an objective view of how the updated SMPs contribute to the National Flood and Coastal Erosion Risk Management Strategy .

4.2.2 Coastal habitats

We work with other RMAs to find opportunities to reduce flood and coastal erosion risk through nature-based solutions. These are solutions that also create or enhance coastal habitats.

This can include:

• working with natural processes
• natural flood management, for example saltmarshes
• making space for wildlife by incorporating appropriate features into the design of FCRM projects

FCERM activities can also contribute to the loss of or reduction in the quality of protected coastal habitat. Most losses happen due to coastal squeeze . This is where flood and coastal erosion defences prevent the natural landward migration of intertidal habitats in response to sea level rise.

To meet our legal obligations, we create new habitat to replace what is lost due to coastal squeeze. We do this through the Habitat Compensation and Restoration Programme ( HCRP ). This carries out large-scale habitat creation projects, for example Steart Marshes in Somerset.

Overall, compensatory habitat created by the HCRP since the early 2000’s has successfully kept pace with losses. The HCRP creates:

• intertidal saltmarsh and mudflats
• freshwater and other coastal habitats

4.2.3 Intertidal saltmarsh and mudflats

Intertidal habitat includes saltmarsh and mudflats. Our knowledge of saltmarsh restoration and the benefits that this brings has improved significantly over time.

Saltmarshes can:

• reduce coastal flood and erosion risk
• store carbon
• filter out excess nutrients
• support fisheries
• provide health and well-being benefits

In total, the HCRP has created 1,601 hectares of intertidal habitat.

4.2.4 Freshwater and other coastal habitats

Other protected habitats may be lost due to coastal change and FCERM activities. These habitats include:

• coastal grazing marsh
• saline lagoons
• vegetated shingle

The loss of these habitats can also be caused by coastal squeeze. Where this happens, we replace the habitat that is lost.

Since the early 2000’s, the HCRP has created:

• 468 hectares of freshwater habitats
• 292 hectares of other coastal habitats

Most of these coastal habitats have been created on the east and south-east coasts.

4.3 Natural flood management

Nature-based solutions have an important contribution to play in achieving climate resilient places.

NFM describes interventions that reduce flood risk by using natural techniques. NFM can manage flood and coastal erosion risk by protecting, restoring and emulating the natural processes of:

• floodplains

NFM also provides a range of wider benefits, including:

• carbon capture
• increasing and improving habitats and biodiversity
• increasing water quality
• improving water resources
• improving health and wellbeing

There are 14 different NFM measures described in the working with natural processes evidence directory that was published in 2017.

These measures include:

• river and floodplain restoration
• leaky barriers
• offline storage areas
• targeted woodland planting
• soil and land management

We can better manage flood risk for communities by using a combination of nature-based solutions and engineered flood and coastal defences.

NFM Programme

The new £25 million NFM Programme launched in September 2023.

It aims to:

• reduce local flood risk using NFM
• provide wider benefits to the environment, nature, and society
• accelerate new and existing opportunities for NFM delivery and financing
• further improve evidence of NFM by filling knowledge gaps

The 40 successful packages of work were announced by ministers in February 2024. They will be carried out by a range of stakeholders including:

• risk management authorities
• non-governmental organisations (NGOs)
• other community organisations

The projects will carry out a mixture of NFM measures at a range of scales and across a variety of communities and landscapes.

These projects have now started the project development stage to write full business cases by September 2024.

During this time, they will:

• refine their designs
• strengthen partnerships
• progress landowner agreements
• define their cost estimates

They will also install monitoring equipment. This will help collect baseline data to meet the NFM monitoring requirements. We will analyse this data centrally.

We are also responsible for managing aspects of the NFM Programme and supporting projects through the development phase. What we learn from the NFM Programme will help us to mainstream NFM .

The programme will build on and embed learning from the £15 million NFM Pilot Programme. This programme, managed by the Environment Agency, supported 60 projects between 2017 and 2021.

Mainstream the use of natural flood management

We want people and places to make greater use of nature-based solutions to enhance flood and coast resilience and nature recovery.

This ambition is reflected in the aims of the:

• National FCERM Strategy for England
• FCERM Strategy Roadmap to 2026

At present there are:

• 94 projects in the 40 NFM programme packages of work
• 15 FCIP projects that include NFM measures
• around 70 NFM projects in the £5.6 billion flood and coastal defence programme, which use NFM in combination with traditional civil engineering approaches to reduce flood risk

We are also carrying out a range of work to develop support NFM projects including:

• streamlining business cases
• a new grant mechanism for non- RMAs
• work on a nationally consistent NFM benefits tool
• the development of a heat map to help target future investment
• an update to the Working with Natural Processes Evidence Directory
• improvements to the NFM hub in collaboration with the Rivers Trust

4.4 Improving the environment

We work with other RMAs to look for opportunities to create and improve habitat as part of our FCERM work. We also form partnerships with groups such as wildlife and rivers trusts.

Between April 2021 and March 2024 we have:

• created or enhanced 2,530 hectares of habitat
• enhanced 189 kilometres of rivers

Examples of these improvements include:

• removing or modifying weirs to make it easier for fish to migrate upstream
• implementing nature-based flood solutions that create and/or restore habitat and reduce flood risk downstream

Case Study 5: Tamar estuary habitat creation program (South Hooe)

The Tamar Valley is an area of outstanding natural beauty. It is a rare valley and water landscape that provides a unique wildlife resource.

South Hooe is a small peninsula in Devon, within a bend of the River Tamar. It is next to and includes part of the Tamar Tavy Estuaries Site of Special Scientific Interest (SSSI) and other environmental designations.

The Tamar estuary habitat creation programme (South Hooe) aims to restore the natural landscape of the area. We have worked closely with stakeholders including:

• the landowner
• Tamar Valley Area of Outstanding Natural Beauty (AONB)
• Natural England 

The project cost £1.7 million and was completed in October 2023. The work has created 14 hectares of intertidal habitat and 4 hectares of wetlands. These will provide habitat for many notable bird species including:

• little egret
• green sandpiper
• reed bunting

It will also provide suitable habitat for invertebrates and notable plant species.

4.5  Strategic planning: flood risk management plans

Flood risk management plans ( FRMPs ) set out how organisations, stakeholders and communities will work together to manage flood risk in England. They cover flooding from rivers, sea and surface water.

They also help achieve the ambitions of the National FCERM Strategy.

Future requirements to develop Flood Risk Management Plans no longer apply because of the Retained EU Law (Reform and Revocation) Act 2023.

It has been just over a year since we published FRMP plans. We have made good progress carrying out the action in the FRMPs this year. Around half of all our measures have started and are ongoing. There are over 1,100 projects currently in progress. This number will continue to increase in 2024.

Over the last year we have completed over 20 projects.

Some of our successes include:

• working with partners to install property resilience measures to reduce flood risk to over 400 homes that lie in the Thames Flood Risk Area
• working with the community in Rewe to install a new flood warning gauge to raise awareness of flood risk and increase community flood resilience in the East Devon Management Catchment
• improving the waterbody and its amenity value between Northampton and Peterborough in the Nene Catchment through The Nene Backwater Restoration project – this work also provided flood risk benefit
• working with Mid Devon District Council to establish a Critical Drainage Area in Cullompton – this will make sure development proposals increase community flood resilience and allow sustainable growth in the area
• carrying out a flood action campaign in Smallfield, Surrey to raise awareness of flooding and encourage residents to take action in the Thames Flood Risk Area

4.6 Agriculture and land management

Farming businesses in England were impacted by the prolonged wet weather over winter 2023 to 2024. There was exceptionally high rainfall across most parts of England with a particular concentration in mid and southern regions.

These exceptionally high rainfall totals have been associated with 11 named storms including Storms Babet (October 2023) and Henk (January 2024). Catchments in eastern parts of England were particularly impacted. 

We are working with Defra on the design and launch of 3 Environmental Land Management ( ELM ) schemes. This work will help to maximise the benefits for FCERM .

The FCERM Strategy recognises the importance of agriculture and land management. It makes it clear farmers have a role in mitigating flood risk whilst increasing the resilience of their own farms.

Between April 2023 and March 2024 we better protected around 7,000 hectares of Grade 1, 2 and 3 agricultural land from flooding. This work was carried out through the FCERM investment programme.

4.6.1 Catchment Sensitive Farming ( CSF )

Catchment Sensitive Farming ( CSF ) is a partnership programme. It was expanded in April 2022 to include providing advice on NFM practices.

In 2023, the Forestry Commission joined the partnership along with the existing organisations;

• Natural England

This advice provided by Catchment Sensitive Farming Advisers (CSFAs) includes both established and expanded CSF practices. These include:

• soil management to improve infiltration
• buffer strips to slow flow
• run-off attenuation features to store and slowly release water

CSFAs provide broad NFM advice as well as focused support in partnership to projects which are likely to have the greatest impact. These projects are prioritised using a catchment-based, nationally guided and locally determined approach.

We have worked with Natural England and the Forestry Commission to provide CSFAs with guidance and training courses. We have also carried out webinars to raise awareness of this work and encourage collaboration.

We have developed an evaluation strategy to assess the uptake and impact of NFM advice. The strategy builds on the established approach used in CSF Water Quality evaluation report . It will collect information on:

• implementation
• barriers to uptake
• farmer attitudes toward NFM and flood risk

In total, CSFAs have contributed to more than 50 NFM projects across England. They have worked with more than 50 partner organisations, including:

• the Environment Agency
• local flood authorities
• environmental non-governmental organisations ( eNGOs )
• universities

Contributions vary across the projects but include:

• providing targeted farm advice
• joint farm visits
• support for catchment sensitive specific options to benefit flood risk management
• engagement events
• contributing to project steering groups

This includes CSF NFM advice to 3 FCIP projects:

• Cumbria innovative flood resilience (CiFR)
• Devon resilience innovation programme (DRIP)

Between April 2023 and March 2024, CSFAs have provided one-to-one NFM advice more than 1,500 times to over 800 holdings.

Since CSF expanded its scope to include NFM advice in April 2022, it has provided this advice one-to-one more than 3,000 times to more than 1,500 holdings.

5. Ambition 2 – today’s growth and infrastructure resilient in tomorrow’s climate

This ambition is about making the right investment and planning decisions to secure sustainable growth and environmental improvements. It also supports infrastructure resilient to flooding and coastal change.

5.1 Promoting safe development resilient to flooding and coastal change

Our long term investment scenarios predict that the number of homes in the floodplain will almost double over the next 50 years.

Climate change will also increase the:

• size of flood risk areas
• frequency and severity of flooding
• complexity of the flood risk issues needing to be tackled

Spatial planning helps us minimise the flood damages that these trends could cause. The NPPF makes it clear that we should avoid inappropriate development in areas at risk of flooding.

Development that takes place in flood risk areas should:

• be designed to be safe throughout its lifetime
• not increase flood risk elsewhere

Development design should be flood resistant and resilient. This will minimise flood damage and speed up recovery in the event of flooding.

We have an important role as a statutory planning advisor to local planning authorities ( LPAs ). We support sustainable development by engaging with, and advising, developers and planners. By doing this, we help to support sustainable growth in the right places.

Investing in flood risk planning advice makes good economic sense. For every £1 we spend providing advice, around £12 of future flood damages are avoided.

We comment on development proposals:

• in areas that are currently at medium or high risk of flooding from rivers and the sea
• in areas with critical drainage problems
• within 20 metres of a main river

We are not a statutory consultee:

• on development in flood zone 1 which we expect to be at risk of flooding from rivers or the sea in the future
• when proposed development could be at risk from other sources of flooding such as groundwater or surface water

LLFAs are a statutory consultee on major development with surface water drainage.

We respond to approximately 9,000 planning applications each year. We provide detailed flood risk advice for around 6,000 planning applications. We know our flood risk planning advice this year has helped to avoid at least 60,000 homes from being permitted in potentially unsafe ways or locations.

Between April 2023 and March 2024:

• over 96% of all planning decisions were in line with our advice on flood risk
• over 99% of new homes proposed in planning applications complied with our advice on flood risk
• we are aware of planning permissions for 89 homes that were granted against our advice on flood risk

We record a sample of planning application outcomes. This:

• gives us an overview of how effective our advice is
• helps us focus our efforts on positively influencing development proposals

We recorded decisions for 2,391 planning applications where we lodged flood risk objections. These cases totalled 67,553 homes overall. Between 1 April 2016 and 31 March 2024, we recorded the LPA ’s final decision for around 64% of the applications we objected to on flood risk grounds.

We publish a list of all applications where we’ve lodged initial objections on flood risk grounds . Often, the issues are resolved before a final decision is made.

Table 9: planning applications reviewed by the Environment Agency between 1 April 2023 to 31 March 2024

5.1.1 Planning policy, guidance and research

This year, we have continued our work with the Town and Country Planning Association (TCPA) to provide training for local authority planners.

This includes:

• piloting face-to-face training for planning policy officers in the Winchester area in July 2023
• providing two training webinars to an audience of over 1,100 local planning authority officers in October 2023 - these sessions explained application of the sequential and exception tests to individual planning applications and set out best practice for undertaking site-specific flood risk assessment

We have also contributed to several CIRIA projects to support practitioners to provide sustainable drainage systems.

These projects include:

• getting sustainable urban drainage systems (SuDS) right from the start – this aims to encourage consideration of SuDS at the earliest stage of land acquisition or assessment for inclusion in the local plan
• producing a SuDS strategy template – this aims to help developers know what SuDS information should be included with planning applications
• updates to the SuDS Manual – this will update the guidance to reflect the latest evidence and best practice and make it more accessible

We remain a member of CIRIA Susdrain - a community that provides a range of resources for those involved in SuDS.

These resources include:

• tools such as the Benefits Estimation Tool (B£ST)
• guidance such as the SuDS Manual
• case studies

We published new guidance on using modelling for flood risk assessments in December 2023. This guidance helps developers understand when to use hydrological and hydraulic modelling as part of a flood risk assessment. It also explains the expected standards.

We supported the response to the Reinforced autoclaved aerated concrete ( RAAC ) crisis. We provided flood risk advice on its guidance for the installation of temporary buildings on affected school sites.

We responded to several public consultations related to flood risk and coastal change. These included:

• Levelling-up and Regeneration Bill: reforms to national planning policy
• Strengthening planning policy for brownfield development
• Planning for new energy infrastructure: revisions to National Policy Statements
• Environmental Outcomes Reports: a new approach to environmental assessment
• Operational reforms to the nationally aignificant infrastructure projects consenting process
• Approach to siting new nuclear power stations beyond 2025

5.2 Property Flood Resilience

Just under 700 properties were better protected by  PFR  measures between April 2023 and March 2024.

Between May and October 2023, we ran a joint PFR public awareness campaign alongside Flood Re. The aim of the Be Flood Smart campaign was to explain:

• what PFR measures are
• how they can help to reduce flood damage to homes

The campaign included:

• an online web portal          
• PFR case studies
• social media

It reached over 10 million people.

We launched new guidance in September 2023 to help RMAs develop and appraise PFR projects. We developed this guidance in response to feedback on PFR projects.

The guidance will help to:

• streamline PFR projects
• avoid disproportionate project development costs
• enable more PFR projects to be completed
• improve the resilience of hundreds more properties to flooding

It is available to all RMAs including:

• local councils
• water companies
• internal drainage boards

In December 2023, we launched a new supplier framework for PFR schemes. The framework can be accessed by RMAs in England. It will be used to provide survey and installation services for PFR projects for the next 4 years. This framework introduces new requirements for the quality of products used and installation following the industry led PFR Code of Practice .

5.3 Reservoir safety

We regulate large raised reservoirs ( LRRs ) in England. In April 2024, there were 2136 registered LRRs .

This regulation is a requirement of the Reservoirs Act 1975, which aims to ensure that dams and reservoirs are safe. Flooding from reservoir dam failure, although rare, can be very serious, putting lives at risk. Responsibility for the safety of reservoirs lies with their undertakers who are the owners or operators of the reservoir. 

As the enforcement authority, we must make sure undertakers follow the legal safety requirements. We report on our enforcement action in our biennial report .  

Owners and operators must report incidents at LRRs . Reservoir owners have 12 months following an incident to provide a full and comprehensive post incident report. 

Seventeen incidents were reported to us between April 2023 and March 2024, an increase from 7 last year.

• one incident was a Level 2 (serious) incident, which is where emergency measures are required - we did not need to intervene in our regulatory role
• fifteen level 3 incidents occurred, which is when the undertaker takes precautionary measures
• one was recorded as a non-reportable incident, where the definition of a formal incident was not met but the undertaker reported the incident to help share some of the learning from the event to the industry

We are working on several reservoir safety reform s to strengthen and modernise reservoir safety management. We provide regular updates on our progress online. We have already made some changes including:

• introducing emergency flood plans
• updating and publishing flood maps for over 2000 large raised reservoirs

This year we updated our guidance for:

• inspecting engineers on inspections of high risk reservoirs
• undertakers (owners and operators of reservoirs) on making sure they appoint different people for each of their reservoir engineer appointments.  

We will continue to introduce non-legislative changes in 2024 and 2025.

5.4 Surface water management

Currently around 3.2 million properties in England are in areas at risk of surface water flooding. We know that this risk will increase over time due to climate change and population growth unless we act.

LLFAs have the principal role in managing flood risk from local sources such as surface water, ground water and ordinary watercourses.

The Environment Agency has a strategic overview role for all sources of flooding, which includes surface water. We show strategic leadership by playing an active role in supporting local authorities and other partners. We help them plan and adapt to current and future surface water flood risk.

This year, we reaffirmed our commitment to actively and boldly working in this strategic leadership space. We are uniquely placed to take a convening role, working with government, local authorities and water companies to share best practice and to promote innovation.

Between 2023 and 2024, we have:

• produced a suite of tools and guidance to help local authorities and partners deliver surface water projects more easily - this includes simplifying and speeding up business case approvals and bespoke guidance on small projects such as PFR measures
• co-hosted with the Met Office a national surface water risk roundtable on incident response – this brought together partners from national and local government and academia to discuss how we can be better prepared for this type of flooding
• convened a surface water flood forecasting and real-time communication symposium – this brought together the surface water flood forecasting community to identify priorities and new opportunities for delivering high quality research, innovative and practical solutions in this challenging space
• provided expert advice to inform the government response to the Infrastructure Commission’s 2022 reducing the risk of surface water flooding study
• worked with water companies, Ofwat and government to publish non-statutory Drainage and Wastewater Management Plans

5.5 Flood risk activities – environmental permitting

We regulate work on or near main rivers using environmental permits .

Our aim is to ensure our customer’s journey is positive and they get their permits in a timely and organised manner. We issue permits within a statutory two-month determination period. Between April 2023 and March 2024, we issued 1,403 bespoke permits and 34 standard rules permits. There were also 1,171 registered exemptions.

We continue to monitor and take enforcement action against unauthorised activity in rivers and floodplains. This can include illegal ground filling in the floodplain or taking material from within the river without the necessary permissions.

We continue to improve our service, to ensure our customers and partners receive value for money. During this reporting period we:

• reviewed the current demand for different types of activities within our rivers
• worked on refining our risk based regulatory approach

We continue to invest in digital and IT solutions to improve the service we provide to customers.

5.6 Water companies’ contribution to reducing risk

Water and sewerage companies are risk management authorities. Water companies:

• have a duty to maintain the water supply and sewer network
• must make sure public sewers effectively drain the areas they serve - this includes draining surface water
• manage the risk of flooding from their water main and sewer networks

Between April 2023 and March 2024, water and sewerage companies have:

• responded to flood incidents, including participating in multi-agency responses
• worked with partners to reduce flood risk and deliver wider benefits for communities, including water quality and amenity benefits
• used strategic partnerships, including with RFCCs , to align investment planning and funding
• finalised their Drainage and Wastewater Management Plans ( DWMPs ) and submitted their draft business plans to Ofwat in October 2023
• engaged with local communities, including local flood action groups, schools, farmers and others

Between April 2023 and March 2024, water companies invested:

• £87.8 million to reduce the risk of sewer flooding to properties
• £167.8 million to maintain the public sewer system to prevent blockages and flooding
• £12.9 million in property-level protection and mitigation measures to reduce the likelihood of customers’ homes experiencing sewer flooding

Winter 2023 to 2024 was one of the wettest on record for many areas of the country. Several water companies worked with other RMAs to mitigate flooding from multiple sources. They also improved their approach to incident management. Managing surface water flooding can mean fewer storm sewer overflows, which improves water quality.

Water companies published their first DWMPs in May 2023. These plans help build a resilient drainage system. This is one way to manage surface water and reduce the chances of surface water flooding. Through the DWMP process, water companies have worked with stakeholders and developed collaborative approaches to align with other flood alleviation projects. They have also worked with Defra on the next cycle of DWMPs .

There have been some good examples of partnership and integrated working this year. For example:

• Wessex Water partnered with Somerset Council and Somerset Rivers Authority to produce an integrated catchment model of Minehead – this includes surface water, sewers and drainage channels, as well as watercourses and tide levels, and has resulted in a pipeline of integrated flood management projects
• United Utilities worked with Bolton Council to install rain gardens and permeable surfaces at a new park in Bolton town centre – this will reduce surface water entering the sewer system

Other innovative approaches this year include:

• Southern Water installed additional sewer level monitors and temperature sensors to monitor infiltration and understand the relationship between groundwater and sewage, then used artificial intelligence to identify key points of infiltration
• Yorkshire Water have engaged with communities using an interactive digital game that allows residents to design streets with SuDS – this helps to understand their preferences and concerns
• South West Water have developed an ‘introductory course in catchment science and water quality’ for adult learners

6. Ambition 3 - a nation ready to respond and adapt to flooding and coastal change

This ambition is about ensuring local people understand:

• their risk of flooding and coastal change
• their responsibilities
• how to take action

6.1 Skills and capacity in LLFAs

Other Risk Management Authorities ( RMAs ) are delivering a large part of the £5.6 billion FCERM investment programme. It is important that they (and their suppliers) have the capacity and capability to lead the projects that achieve this ambition.

We are supporting them by:

• streamlining processes
• improving access to guidance, tools and training

This means that projects are approved more quickly and can access grant-in-aid funding more easily.

In April 2023 we launched the Supporting flood and coast projects SharePoint site. This is for all practitioners as a ‘one-stop-shop’ for:

• access to a community of practice

This site has over 1,000 subscribers from over 300 different organisations.

In June 2023 we launched improvements to simplify and strengthen project delivery, summarised in this short video.

([Streamlining processes to secure government grants to build flood resilience projects (youtube.com)[https://www.youtube.com/watch?v=vW3RJ97jYUI].

This focused on support for smaller projects, which make up most projects in the overall programme.

It includes:

• empowering local teams to assure and approve projects below £3 million 
• providing bespoke business case templates for different project types
• simplifying the process to access funding for property flood resilience
• providing a more pragmatic approach to tackle flooding from multiple sources including surface water

6.2 Using digital technology to warn and inform

The way we use digital technology continues to evolve. We have developed and improved our services in several ways, including:

• how we warn the public about expected flooding through our flood warning service
• our flood risk information services on GOV.UK
• making our flood information available as open data

6.2.1 Flood warning service

We have continued to improve our flood warning service based on user feedback. We focus on user-centred design and accessibility and have made several enhancements made during 2023.

These have:

• made the registration process easier
• improved usability
• made sure the service is accessible to all

We’ve received positive feedback from users which shows the success of these improvements. Government now recognises sign up for Flood Warnings as a ‘Great’ service. This means it reaches a high, measurable standard of both efficiency and usability.

We have completed the tender for the next warning service. This is to find a supplier to replace the current flood warning system by late 2025. We awarded the contact to Leidos, and their partners Intersec and Cogworx. Work started in early 2024.

The new service will be a direct replacement of the legacy flood warning system when initially launched. Improvements will continue to be made for up to eight years. 

The next warning service will be:

• user-centred
• designed to inspire action
• build resilience to flooding in a changing climate
• a net zero digital solution

Emergency Alerts , which is a central government-led capability, has been operationally live since March 2023. It warns of risk to life from severe flooding from the rivers and sea.

The pilot phase ended in March 2024 and the outcomes are now being evaluated.  We will continue to benefit from access to this capability in the short term.

6.2.2 Flood warnings issued and number of properties registered for them

Being prepared helps reduce the impacts of flooding and enables faster recovery. We encourage people to register for our free flood warning service . Alerts and warnings enable the public to take action to protect themselves and their possessions.

Our flood warning service covers:

• flooding from rivers and the sea
• some properties in areas at risk of groundwater flooding

The flood warning service does not cover surface water flooding. This is because it can be difficult to predict:

• where sudden rainstorms will occur
• their intensity and duration
• the effect the rain has on the ground

Our surface water management action plan includes an action to work with the Met Office to develop short range rapid forecasting. This would cover the type of rainfall that causes surface water flooding.

As of March 2024, there were over 1.58 million properties registered to receive free flood warnings . This includes phone numbers registered in areas at risk from flooding that are automatically opted-in.

6.2.3 Flood alerts, flood warnings and severe flood warnings issued

Between April 2023 to March 2024, we issued:

• 5,126 flood alerts
• 2,613 flood warnings
• 7 severe flood warnings

Find out what to do in a flood and what the different types of warnings mean.

Table 10: number of flood alerts, flood warnings and severe flood warnings for the period 1 April 2023 to 31 March 2024

Table 11: comparison of flood alerts, flood warnings and severe flood warnings issued 1 April to 31 March each year between 2018 and 2024

6.2.4 Messages sent

Between April 2023 and March 2024 we sent over 12.5 million messages to the public, partners and the media. These messages informed them of flooding in their area and the flood warning service they can receive.

This includes messages sent via text, email and automated telephone call.

Table 12: number of messages sent for the period 1 April 2023 to 31 March 2024

Table 13: comparison of messages sent 1 April to 31 March each year between 2018 and 2024

6.3 Flood risk information service

Between April 2023 and March 2024, we continued to improve the 3 main flood risk information services on GOV.UK.

• Check for flooding
• Check your long term flood risk for an area in England
• Flood map for planning

Table 14: Check for flooding service user totals each year from 1 January to 31 December between 2018 and 2023

In March 2024 we launched a trial of our Floodline webchat service. This new service connects our digital front-end Check for flooding service to our existing assisted digital support team at Floodline.

The purpose of this trial is to understand the current need and potential demand from users for a webchat. This will help define our future service offering. We will review user feedback to improve the service. We will also carry out operational reviews to define our future digital and assisted digital support channels.

6.4 FCERM Research and Development Programme

The FCERM Research and Development Programme is a collaborative partnership between:

• Welsh Government
• Natural Resources Wales

The research is used to:  

• understand and assess coastal and flood risks now and in the future  
• manage flood and coastal erosion risk management assets in an efficient and sustainable way  
• prepare for and manage flood events effectively  
• increase resilience to flooding and coastal erosion 
• meet policy and practical needs

This means that research is created and used to understand and manage flooding and coastal risks effectively in England and Wales. 

The FCERM research and development programme:   

• works with FCERM stakeholders to understand their needs and ensure research has a pathway to impact   
• works with research funders, research institutes and leading academics to explore our greatest challenges  
• carries out research and brings together evidence using our own expertise or by commissioning others  
• translates research into practical advice for risk management authorities in England and Wales   
• communicates research through the programme webpages FCERM research and development programme , conference papers seminars, webinars and scientific journals   

The research provides the evidence to support policy and practice in the partner organisations and flood and coastal risk management authorities.  This supports the FCRM Strategy Ambition 3. It also supports the Strategy Roadmap which says that world leading research and international best practice will underpin flood and coastal risk management.

6.5 Research publication highlights

6.5.1 published areas of research interest.

We work with universities, research councils and other partners to produce and access world leading research for the benefit of flood and coastal risk management.

We committed to publishing a research plan by Spring 2024 to provide focus for our future research programmes and academic partnerships.  

On 8 May, we published our areas of research interest which will guide our research work until 2028. This lists the pressing research issues and outcomes we need to achieve. They are used as a consistent way across government to express to others where we want to collate existing research in certain topics. 

We will use the areas of research interest to:

• concentrate our effort where research is needed most
• determine the research activity we do
• engage with the research community, industry partners and government
• connect people who have the operational problems with researchers who have solutions

6.5.2 Estimating flood peaks and hydrographs in small catchments

In March 2023, we published research describing our review of methods for estimating flood peaks and hydrographs in small catchments .

This work will help minimise uncertainties estimating the frequency of flooding, flood peaks, and hydrographs in small catchments.

We worked with the UK Centre for Ecology and Hydrology and research partners to:

• build an expanded data set of small catchments peak flow data
• developed improved methods to model flood flows in small ungauged catchments and plots of land

This information will be used by flood risk management authorities and developers when they design:

• flood risk management assets
• drainage systems
• flood mitigation in new development

6.5.3 Planning for the risk of widespread flooding

In March 2023, we published the Multivariate Event Modeller ( MEM ) tool code on GitHub. This is an update to research undertaken in 2017 on planning for the risk of widespread flooding .

This work developed methods and guidance to address the need for realistic planning scenarios that account for the:

• risk of widespread flooding across England and Wales
• flooding from multiple sources (river, surface water and sea)
• potential impacts of this flooding

It enables central government, emergency planners and responders to review their:

• planning assumptions
• emergency response
• mutual aid capabilities

This will help to increase the England and Wales preparedness for widespread flooding.

The MEM tool update allows others to contribute to developing the code via the  GitHub repository .

6.6 International learning 

We continue to have strong links and good relationships with several international organisations and agencies: 

These include the: 

• Dutch flood agency, Rijkswaterstaat ( RWS ) 
• Dutch regional water authority, Hoogheemraadschap Hollands Noorderkwartier 
• United States Army Corps of Engineers (USACE) 
• Australian Bureau of Meteorology 

We have worked with these organisations for many years, exchanging knowledge, research, innovations and technical expertise in flood and coastal risk management.  

The topics and issues covered include: 

• flood assets 
• nature-based solutions 
• coastal processes 
• incident management and response 
• sustainability 

International Engagement

Our work with international partners includes development of early career engineers through the I-Storm Next Generation group .

In April 2023 early career engineers from RWS joined our graduate engineers in the Lake District to share knowledge and experience. This was followed by a joint visit to the Maeslant barrier’s annual test closure in September 2023. This was part of the RWS 225th Anniversary events schedule. 

In 2023 we hosted a member of USACE on a 12-month technical exchange programme as part of our work with the Levee Safety Partnership. In July 2024 the second part of this exchange will begin. An Environment Agency technical lead will start a 12-month placement with USACE in the USA.  

We hosted international partners, including a keynote speaker from the New South Wales State Emergency Service (Australia), at the annual Flood and Coast conference in June 2023.  

In November 2023 a delegation of senior Environment Agency leaders attended the Rijkswaterstaat 225th Anniversary celebrations in the Netherlands. They gave a keynote speech and participated in workshops. 

Several international delegations visited the Thames Flood Barrier in 2023 and early 2024. These included:  

• a delegation from Hong Kong in October 2023 - to share flood risk management knowledge and explore opportunities for future collaboration
• an MSc student group from Sciences Po - Urban School, France in February 2024 - to find out more about our work towards climate adaptation in the Greater London Area

We have participated in numerous international events between March 2023 and April 2024.

We are continuing to develop our international network of contacts and strengthening relationships with our partners. Broadening the reach of our knowledge, experience, research, and innovations, will help us all better prepare, respond, and adapt to future flood and coastal risks.

The Environment Agency has worked with leading international partners on an International Handbook on Emergency Responses for Flood Defences. This shares best practices to manage risks during extreme flood events. These include during:

• preparedness

7. Looking ahead

This section lists some of the activities that we, government and other RMAs will be carrying out beyond March 2024.

National Flood Risk Assessment ( NaFRA2 )

The Environment Agency is developing a new National Flood Risk Assessment ( NaFRA2 ).

We will publish a “National assessment of flood and coastal erosion risk in England 2024’ report in December 2024. The report will identify national trends in terms of the source and characteristics of flood risk, the distribution of risk across England, and the potential for these to change in the future.

Nafra2 will:

• provide significant improvements including detail not currently available such as flood depth and climate change scenario information
• form a new baseline assessment of flood risk in England including updated estimates of properties at risk and average anticipated economic impacts of flooding

The NaFRA2 data will be published in early 2025.

Following that, we plan regular updates and will use the capabilities of NaFRA2 to help determine how flood risk is changing, including the impact of investment in flood resilience.

We are currently updating the full National Coastal Erosion Risk Map ( NCERM ) dataset based on a further 10 years of coastal monitoring data and the latest climate change evidence.

The updated NCERM will provide the best available information on coastal erosion risk. It will be used by coastal risk management authorities and the Environment Agency to inform coastal management investment and local planning decisions.

We plan to:

• publish a summary of the updated NCERM data in the “National assessment of flood and coastal erosion risk in England 2024” report in December 2024.
• at the same time, we will also publish the updated NCERM on SMP Explorer in December 2024

Section 19 Guidance

The 2020 Jenkins review outlined differences in:

• LLFA flood investigation (section 19) report content
• thresholds for triggering investigations
• type of evidence being collated

Defra is co-developing guidance, with users and LLFA , to bring more consistency to these reports, whilst preserving flexibility. The project will report in Autumn 2024.

Review of Flood and Coastal Erosion Risk Management Assets

The review of statutory powers and responsibilities to map, monitor, inspect and maintain all assets will be published in 2024. It covered coastal, fluvial, and surface water assets and examined riparian ownership. The aim was to make sure that responsibilities are clear and that there are effective powers in place.

It covers challenges and opportunities. Defra will consider the findings and act where necessary.

Rapid flood guidance service

The Rapid Flood Guidance service is provided by the Flood Forecasting Centre.

Rapid flooding is defined as any flooding:

• that starts within 6 hours of rain
• is caused by water getting trapped in urban low spots, overflowing drains, and flow from small streams and rivers

The service will give short notice updates for England and Wales to supplement the Flood Guidance Statement ( FGS ). It is aimed at responders who need to make decisions at a timescale of 0 to 6 hours.

It will initially run as a trial service from 14 May 2024 to 30 September 2024.

*TCPA]: Town and Country Planning Association *[USACE]: United States Army Corps of Engineers

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Extreme UK flood levels are happening much more often than they used to, analysis shows

Professor of Hydroclimatology, University of Oxford

Principal Hydrologist, UK Centre for Ecology & Hydrology

Disclosure statement

Louise Slater is Professor of Hydroclimatology at Oxford University and a Future Leaders Fellow funded by UK Research and Innovation (UKRI). Slater leads the Hydroclimate Extremes research group which studies how floods and other extreme events are changing over time. She is also a member of the UK Flood Hydrology Scientific and Technical Advisory Group.

Jamie Hannaford is a Principal Hydrologist and Group Leader at the Centre for Ecology & Hydrology. He is also a visiting Associate Professor at the Irish Climate And Research Units (ICARUS) at Maynooth University, Ireland. Hannaford is the scientific lead for the UK Centre for Ecology and Hydrology’s water monitoring work in the programme UK-SCAPE. He is also the scientific lead for the UK National River Flow Archive (NRFA) and the UK Hydrological Outlook.

University of Oxford provides funding as a member of The Conversation UK.

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Heavy rain across southern Britain meant that most rivers in England swelled at the beginning of 2024, prompting widespread flooding.

The River Trent was among the most severely affected. Water levels at the Drakelow gauging station in the west Midlands reached 3.88 metres on January 4 – well above the previous record set less than four years earlier in February 2020.

Are floods growing larger and happening more often in the UK ? There are two ways to answer this question. One is to consult computer models which project Earth’s climate in the future, and the other is to search the historical record.

Climate projections are important but highly uncertain as they indicate a wide range of potential futures for any given river . Projections also only tell part of the story as they do not reflect the patterns of water use, changes to groundwater levels or to the urban environment that can decide flooding on a particular river.

That’s why we give equal importance to historical data, although we cannot project past changes directly into the future. Historical archives of river monitoring data can help us understand how the largest floods are changing on the River Trent.

For instance, how is the 50-year water level (the highest point a river would be expected to reach in 50 years on average) changing? On the River Trent at Drakelow, the 50-year water level has risen from about 3.46 metres in 1959 to 3.83 metres in 2024. This means the largest floods are indeed getting bigger.

How the January 2024 floods compare

The flood water level on the Trent at the start of January 2024 was actually higher than what scientists would consider a once-in-50-year event in today’s warmer climate.

Another way to understand how much floods have changed is to consider how often they happen today compared with the past. If we look at the 50-year level from 1959 (about 3.46 metres), how often would such a flood occur in today’s climate?

On the Trent, a 3.46-metre flood level would now be expected to occur every 9.38 years, on average, in 2024. This makes sense, considering there have already been six events in which the river level exceeded 3.5 metres since the 1980s. The historical data shows that extreme water levels are being reached more frequently on the Trent.

Our analysis of the Trent aligns with results from a previous study which looked at rivers across the rest of the UK . In many places, 50-year floods are now happening less than every ten years, on average.

This is partly due to climate change and also partly due to natural variations in the climate which see rivers cycle through spells of more and less flooding. The UK went through a “flood-poor” period in the 1960s, 70s and 80s, and has been going through a “flood-rich” period since then.

Prepare for worse

It is worth noting that there are caveats to this type of analysis which tries to assess how extreme events are changing over time. Caution must be exercised when looking at long records of river levels given changes in river management practices and measurement techniques over time.

It should also be noted that these results use a different methodology to the industry standard for flood estimation.

But what matters is not the precise changes in the frequency of major floods (from 50 years down to nine or even two-and-a-half years, according to some statistical methods). It is understanding that the frequency of large floods is changing fast.

For many UK rivers with more extensive historical archives of river level measurements, floods appear to be occurring far more frequently than before. In a smaller number of places, they are occurring less frequently.

We need to better understand how flood risk will evolve in response to further human-induced warming. The UK’s efforts to predict and prepare for future floods are supported by the Environment Agency’s flood hydrology roadmap , which is mobilising a wide community of researchers and practitioners.

Overall, the UK must prepare to live with bigger floods and be able to predict flood-rich periods several years ahead. This starts with an understanding of how the severity and frequency of such events is changing.

To support this effort, we are preparing a range of tools to guide flood planners, including an interactive map allowing users to explore how flood return periods are changing across the UK. Being better prepared for extreme events in a warming climate starts with understanding what it will mean for your local area.

Don’t have time to read about climate change as much as you’d like? Get a weekly roundup in your inbox instead. Every Wednesday, The Conversation’s environment editor writes Imagine, a short email that goes a little deeper into just one climate issue. Join the 30,000+ readers who’ve subscribed so far.

• Climate change
• UK flooding

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Improving UK’s resilience to floods and droughts

The first UK-wide floods and droughts research infrastructure will significantly improve our understanding of how, when and where floods and droughts occur in different parts of the country. This will inform action to improve our resilience to the increasing impacts of climate change on people, the economy and nature.

UKRI-Natural Environment Research Council (NERC) has confirmed £38 million funding for the ambitious programme, which it is jointly leading with the UK Centre for Ecology & Hydrology (UKCEH), in partnership with the British Geological Survey, Imperial College London and the University of Bristol.

The new Floods and Droughts Research Infrastructure (FDRI), comprising fixed and mobile measuring equipment in river catchments in different parts of the UK, will monitor the entire water environment–on a much bigger scale than previously. It will integrate data on evaporation, soil moisture, weather, groundwater and river flows for the first time, making them easily available for researchers.

The FDRI team will take advantage of cutting-edge technologies including advanced computer modelling, artificial intelligence and drone footage to deliver near real-time data and improve our understanding of floods and droughts. 

Impacts on people and wildlife

Millions of people in the UK are affected by floods and droughts, with various impacts on residents, farmers, businesses, transport and wildlife, and climate change is increasing the frequency and intensity of extreme weather events. The cost of damage caused by flooding alone is estimated at more than £700m a year.

Without significant investment in research infrastructure, there would be a lack of scientific evidence to support the UK's resilience to extreme weather, and the damage and costs would spiral upwards, say the team behind FDRI.

Dr Doug Wilson, UKCEH Science Director, says: “This exciting project will transform UK scientific research into floods and droughts, significantly enhancing our capability to prepare for and respond to extreme weather events. 

“Our improved understanding of how water flows through the environment and the impact of climate and land use change on the hydrological cycle, combined with faster, more easily accessible data, will greatly improve our predictions about the location and extent of floods and droughts. 

"This will inform future action to better protect communities and limit the impacts on people, the economy and the environment.”

The data and insights from FDRI will enable government agencies, local authorities water companies and landowners to develop better, cost-effective infrastructure and systems that are more resilient to extreme weather.

Digital technology

FDRI is initially testing a range of digital instrumentation and monitoring techniques in ‘outdoor labs’ on selected rivers – the upper Severn in mid-Wales, the Chess within the Thames catchment and the Tweed in Scotland to build up a UK-wide picture. 

In addition to fixed instruments, the team will have a variety of innovative, cutting edge mobile, digital measuring equipment to monitor upcoming and ongoing extreme weather events across the country. These include:

• drones to measure river volume and flow as well as land soil moisture.
• multi-spectral video that enables us to monitor surface temperatures and vegetation water loss.
• lidar mapping to measure how low a floodplain is around a river and amount of water it stores
• radio-controlled survey boats to monitor river flows.
• new sensing equipment such as fixed camera systems that use AI to interpret river flows.

NERC’s award of funding followed a scoping study that included consultation with a range of stakeholders to establish their requirements for FDRI.

Professor Louise Heathwaite, Executive Chair of NERC, says: “Earth’s changing climate means the number of extreme floods and droughts will increase in the UK, impacting homes, businesses and services. But predicting their location and measuring their intensity and impact needs the sort of scientific advances that this programme will bring, to overcome the data and analytical constraints that are currently very challenging.”

FDRI will be “using the power of science and tech to keep the public safe”, says Science and Technology Secretary Peter Kyle MP. “With climate change sadly making extreme weather events more common and adding an eye-watering cost to the economy, there is no time to waste in backing our researchers and innovators to ensure we are better prepared for floods and droughts,” he adds.

For more information on FDRI, see the website  and animation, below.

3.16 Case Study - Flooding in Somerset (2013-2014)

For a period of three months from December 2013 to February 2014, the Somerset Levels hit the national (United Kingdom) headlines as the area suffered from extensive flooding. At the height of the winter floods, 65 km2 of land on the Levels were under water. This was caused by human and physical factors. The floods were the most severe ever known in this area.

No one was prepared for the extent of damage brought by the floodwater. Several villages and farms were flooded and hundreds of people had to be evacuated. The risk of flooding is likely to increase in the future due to climate change. The government will need to invest in flood defences in order to protect areas at risk.

Flooding on the Somerset Levels - The News

Flooding on the Somerset Levels - Background Information

In December 2013, an unusually high amount of rainfall began to fall on the Somerset Levels and this continued into February 2014. With so much water, the ground became saturated, forcing both the river Parrett and the river Tone to flood. 

The physical characteristics of the Somerset Levels and Moors mean that flooding is a natural occurrence there. It is an area of low-lying farmland and wetlands between the Mendip and Blackdown Hills in central Somerset. This area forms the floodplain surrounding the river Parrett. 

Thousands of years ago the area was covered by the sea. It has since been drained to allow for agriculture, several villages and wetland conservation. It has become an area of social, economic and environmental importance. It covers an area of 650 km2 but has a low population density (the number of people per km2 ). The area may have had a natural vulnerability to floods but no one was prepared for the scale of the floods or the impacts that followed

What caused the flooding on the Somerset Levels?

A river flood is when the river bursts its banks and spills onto the surrounding floodplain. A floodplain is an area of low-lying ground next to a river, formed mainly of river sediments. A flood can last just a few days or several weeks. A flood event is often caused by a combination of physical and human factors.

Physical causes

Prolonged rainfall: In January 2014 in southern England, rainfall totalled 183.8 mm, which is approximately 200% higher than average for that month (Figure 2). That was the wettest since records began in 1910. 

Saturated ground: The long period of rainfall caused the ground to become saturated so that it could not hold any more water. 

Low-lying land: Much of the area lies at, or just a few metres above, sea level, putting it at risk of flooding. 

High tides and storm surges from the Bristol Channel: These prevent the floodwater from being taken to the sea, forcing it to back up the rivers.

Human Causes

Lack of dredging: Over the years the rivers had become clogged with sediment. The Environment Agency had decided to stop dredging the rivers some time earlier. Dredging increases the ability of a river to carry more water. 

Change in farming practices: Much of the land has been converted from grassland to grow maize. This more intensive use of the land means it is less able to retain water, causing it to run over the surface rather than being absorbed.

Impacts of the Somerset floods 

The widespread flooding on the Somerset Levels made the national headlines. Many people visited the affected areas to see the famous floods. Such people became known as ‘flood tourists’. Many of the people living on the Levels had experienced some form of flooding in the past but no one was quite prepared for the scale of these floods. Thankfully no one died, but many people suffered flood damage to their homes, possessions and farmland (Figure 3). 

Many people were evacuated and had to seek temporary accommodation elsewhere. More than 600 homes and 6880 hectares of farmland were flooded. Entire villages were cut off after roads became unusable. In the village of Muchelney, residents could only leave the island by a boat which left every two hours (Figure 4).

Isolated communities provided an opportunity for thieves. In January, 900 litres of fuel was stolen from a pumping station in Westonzoyland. By early February, there were reports of stolen heating oil and quad bikes from homes of flood victims. Many of the main roads were closed, such as the A361 which links Taunton and Street. Trains on the Bristol line between Bridgwater and Taunton were also disrupted. The economic costs soon started to rise. Fuel for emergency pumps used to reduce water levels cost £200 000 per week. Local businesses reported over £1 million in lost business. According to ‘Visit Somerset’ the floods on the Somerset Levels cost the county’s tourism industry £200 million. 

Farmers struggled to deal with flooded fields, ruined crops and the costs of moving livestock away from the affected areas. After nearly three months under millions of tonnes of water, much of the soil was damaged. It may take up to two years to restore the soil so that crops can be grown. Flood-hit home owners are likely to see their insurance costs increase in the future.

Management and Response

The response to the floods was rapid and well organised, as expected for an economically developed country (Figure 5). The Met Office issued an amber warning for heavy rain in South West England. They informed the public to be prepared for significant flooding. Many residents used sandbags to protect their homes and moved valuable items upstairs. One man even built a giant wall out of clay and soil around his house in Moorland to protect it from the floodwaters.

The fire brigade visited hundreds of properties, and rescue boats were used to help stranded people. In early February, rescue crews encouraged the residents of Moorland to evacuate. Owners of around 80 homes agreed but about 30 other residents chose to remain (Figure 6). Extra police patrols were brought in to respond to increased crime. By the end of January, the army had been sent in with specialist equipment. They delivered food and gave out sandbags. By 6 February they were joined by 40 Royal Marines. Sixty-five pumps were used to drain 65 million m3 of floodwater. 

There was a lot of local support for those affected by the floods, led by the organisation FLAG (Flooding on the Levels Action Group). Volunteers organised fundraising activities and collected and distributed supplies of food. They also used social media via Facebook and Twitter to communicate news.

The longer-term response focused on flood management to prevent a future flood of this scale. This took the form of ‘The Somerset Levels and Moors Flood Action Plan’. It included measures such as dredging, a tidal barrage, and extra permanent pumping sites, with a total cost of £100 million. A sum of £10 million was provided by the Conservative Government, a further £10 million came from the Department for Transport, and the Department for Communities and Local Government gave £500 000. It formed part of a 20-year plan for the Levels. It had the backing of Prime Minister David Cameron who stated: ‘We cannot let this happen again’. 

Future Considerations 

In November 2014, the Environment Agency (EA) kept its promise and completed the 8 km dredging of the rivers Parrett and Tone, costing £6 million. This will be a huge help in the protection of homes and farmland. Some people have argued that dredging alone is not the answer and it should be used alongside other forms of flood defence, such as flood relief channels. Can the government afford to spend so much money in a rural area with a low population? 

Climate change may mean that this area will receive more heavy rain in the future. The Met Office has predicted that sea levels around the UK will rise by 11–16 cm by 2030. It may be that spending money on hard engineering flood defences is not the best option for this area. The government may save money in the long term by moving people to higher land, and to pay them money for their homes and farms. However, this is unlikely to be a popular option. 

Conclusion 

The recent floods demonstrate how more people have put themselves at risk of flooding by living on this low-lying floodplain. Farming and settlement increased because people thought that flooding in the area was under control. This was clearly not the case and it is therefore not surprising that the local people felt so let down. There were many impacts of this flood, but they could have been far worse if it had not been for the effective and rapid response that followed.  

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• Flooding 3: Response to floods: Oxford Case Study

Suitable for GCSE

The Oxford Flood Alleviation Scheme is designed to reduce the impacts of a major flood in Oxford by diverting water down Hinksey Stream, which is a branch of the River Thames that flows between Botley and Kennington. Land use zoning means that much of the floodplain of Hinksey Stream is undeveloped. However, road, rail and energy infrastructure, as well as a number of homes are at risk on the margins of the floodplain.

This scheme uses a combination of hard and soft engineering strategies. Hard engineering, such as deepening the river channel and the replacement of culverts under roads, will ensure that the new channel has a greater capacity. Soft engineering (landscaping the floodplain and planting trees), will increase the flood storage capacity of the floodplain. At the same time, the network of footpaths and cycle paths along the floodplain will be improved, enhancing the environmental value of this commuter and leisure corridor through the urban landscape.

Specification requirements

Understanding flood management strategies including the role of flood plain zoning, flood relief channels and flood plain retention are requirements of all GCSE specifications. An understanding of urban land uses and the dilemmas of urban development is required by some.  Download the Specification audit .

Learning objectives

These activities can be used to develop an enquiry into the Oxford Flood Alleviation Scheme. This resource can be used to meet one or more of the following objectives:

• develop the skills required to conduct an enquiry – from setting an aim, sampling, collecting and analysing evidence to evaluating the quality of the data
• develop skills of extended writing as they evaluate the flood management scheme
• create a case study of the Oxford Flood Alleviation Scheme.

Download the Assessment Objectives .

Students should begin by reading the  brief document  published by Oxfordshire County Council which describes the scheme and outlines its potential benefits. The document includes a sketch map of the scheme but students should also become familiar with the location of the scheme and the area it is designed to protect. They should, therefore, study an OS map of the area – one is available on the  Bing map here .

Students can then investigate the area that will be protected by the Oxford Flood Alleviation Scheme in a virtual field trip – the student resource  Virtual fieldtrip . This investigation uses the same six steps that would be used in a real fieldwork enquiry and could be used to reinforce understanding of this process. However, it  cannot  be used as a substitute for one of the actual fieldwork enquiries conducted by your centre. The enquiry will help students explore the concept of risk and flood plain zoning and help to answer the following questions:

• What kinds of land uses are at risk of flooding in Oxford?
• Which land uses will be protected by the new flood alleviation scheme?

At this point students might want to watch the two videos about the scheme that have been created by the Environment Agency. The  first video  provides an outline of the scheme. The  second video  simulates a fly-through over the area affected by the scheme.

To conclude, students should be encouraged to use all of the evidence they have seen to create an evaluation of the Oxford Flood Alleviation Scheme. To do this, students might also want to consider these enquiry questions:

• Who will benefit?
• How might the scheme affect the economy of Oxford?
• What are the potential benefits for the environment?
• Does the scheme make Oxford a more sustainable city?

The Environment Agency publishes up to date information about the  flood scheme here . If students read this after they have completed the other activities then they can use it to assess the effectiveness of their own evaluation:

• What did I learn from the Environment Agency evaluation?
• What did I get right in my own evaluation?
• What did I miss?
• How was the Environment Agency evaluation structured?
• Could I improve the way that I write an evaluation next time?

Other lessons in this series:

Flood risk and flood management: Introduction Flooding 1: Causes of river floods Flooding 2: Investigating the effects of river floods Flooding 4: Managing the upper drainage basin Flooding 5: Sustainable Drainage Systems (SuDS) Flooding 6: Managing river floods – exploring the role of the Environment Agency Flooding 7: Coastal flooding at Chiswell Flooding 8: Managed realignment Flooding 9: The role of the Environment Agency in coastal management and the development of shoreline management plans

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River Flooding ( Edexcel GCSE Geography: B (1GB0) )

Revision note.

Geography Lead

Risks from River Flooding

• River floods are one of the most common natural hazards
• The risk from river flooding around the world has increased over the past 50 years

Graph showing the increase in flood events over time

• Deforestation
• Agriculture
• Urbanisation
• These all increase overland flow/run off and decrease the lag time
• The result is that the river's capacity is more likely to be exceeded leading to a higher flood risk 
• Climate change may lead to increased rainfall or frequency of storms which increases the discharge
• River channel management upstream can increase discharge downstream for example straightening the channel will increase the speed the water moves downstream increasing the risk of the river capacity being exceeded

Impacts of increased flood risk

• There are a range of possible impacts of flooding
• These can be both social and environmental

Possible Impacts of Flooding 

Worked example

Explain one way in which human activity can increase the risk of river flooding.

• Building on floodplains/urbanisation (1) which can reduce infiltration and/or puts more people/property at risk (1)
• Deforestation (1) which reduces infiltration and so increases runoff making rivers ‘peakier’ (1)
• River channel management preventing river flooding upstream (1) so making river discharge larger downstream thus increasing risk (1)
• Climate change idea (1) increasing rainfall and/or making weather stormier increasing discharge (1)

Managing Flood Risk

• The key cause of flooding is the amount and duration of precipitation this cannot be altered
• There are a number of methods of managing floods and reducing the severity and/or impact
• Hard engineering involves building structures or changing the river channel
• Soft engineering works with natural processes of the river and surrounding environment
• Soft engineering is increasingly popular 
• Soft engineering is an example of mitigation where schemes aim to minimise damage rather than trying to prevent the flooding 

Cost and Benefits of Hard Engineering

Costs and Benefits of Soft Engineering

• Leaving the stubble on the fields after the crop is harvested helps to stabilise the soil and increase infiltration
• Contour ploughing which involves ploughing fields across the slope rather than up and down. This gives the water more time to infiltrate and stops the ploughed furrows becoming channels for water
• Improved forecasting and flood warnings

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• River Processes and Pressure
• Changing People and Places
• Dynamic UK Cities
• Investigating Coastal Change and Conflict
• Investigating River Processes and Pressures
• Investigating Dynamic Urban Areas
• Investigating Changing Rural Areas
• Biome Distribution
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Author: Bridgette

After graduating with a degree in Geography, Bridgette completed a PGCE over 25 years ago. She later gained an MA Learning, Technology and Education from the University of Nottingham focussing on online learning. At a time when the study of geography has never been more important, Bridgette is passionate about creating content which supports students in achieving their potential in geography and builds their confidence.

East Coast flooding in UK – 5th December 2013

On Thursday 5th December 2013 large areas of the east coast of England were affected by coastal flooding on a scale not seen since the  Great floods of 1953 . A combination of factors led to the storm surge that was responsible for flooding. This included a high spring tide, an area of low pressure and high northerly winds.

Tidal surge graph spurn 2013 – source: http://www.tides4fishing.com/uk/england/spurn-head

The  tidal coefficient  was 94(very high). The  tide heights  were 0.9 m, 7.1 m, 1.1 m and 7.2 m. We can compare these levels with the maximum high tide recorded in the tide tables for Spurn Head which is of 7.6 m and a minimum height of 0.3 m.

What is a storm surge and why does it happen?

Video from the BBC –  http://www.bbc.co.uk/news/uk-25229885  Met Office Article –  http://www.metoffice.gov.uk/learning/learn-about-the-weather/weather-phenomena/storm-surge  The Atlantic storm, which brought the coastal flooding and gale-force winds of up to 100mph, caused widespread disruption across the UK and claimed the lives of two men – in West Lothian, Scotland, and in Retford, Nottinghamshire.

The Environment Agency said 800,000 homes in England had been protected by flood defences and better forecasting had given people “vital time” to prepare. The agency said sea levels had peaked at 5.8m (19ft) in Hull – the highest seen by the East Yorkshire city since 1953 – and 4.7m (15ft) in Dover, Kent, the highest recorded there in more than 100 years.

Preparing for the 2013 storm surge:

Video report:  http://www.bbc.co.uk/news/uk-25237082 Thousands evacuated:  http://www.bbc.co.uk/news/uk-england-norfolk-25228834

Warnings issued:  http://www.metoffice.gov.uk/news/releases/archive/2013/storm-surge Preparing your home:  http://www.bbc.co.uk/news/science-environment-20497598 Thames Barrier raised:  http://now-here-this.timeout.com/2013/12/05/thames-barrier-to-close-tonight-as-forcasts-predict-the-biggest-storm-surge-for-30-years/ How the barrier works:   http://www.environment-agency.gov.uk/homeandleisure/floods/38359.aspx  The Environment Agency estimates that 800,000 homes and businesses were saved due to flood defence schemes.

Impacts of December 2013 floods:   Social Impacts

Thousands of people were evacuated from Britain’s east coast of England. Victims of the most serious tidal surge in 60 years have been warned to avoid direct contact with floodwater and beware of rats moving into homes.More detail and pictures here:  http://www.dailymail.co.uk/news/article-2519891/Beware-invasion-flood-rats-Homeowners-hit-tidal-surge-told-avoid-contact-water-amid-fears-pest-invasion.html

People Urged to remain vigilant:  http://www.independent.co.uk/news/uk/uk-weather-warnings-scotland-and-north-battered-by-100mph-winds-as-biggest-tidal-surge-in-60-years-threatens-east-coast-8984542.html

Impacts of the December 2013 floods:  Economic Impacts

Economic impact in North Norfolk –  http://www.northnorfolk.org/files/Tidal-surge-combined-info.pdf Seven Cliff Top Homes Collapse in Hemsby –  http://www.bbc.co.uk/news/uk-england-norfolk-25254808

1,400 homes were flooded, including 300 in Boston, Lincolnshire, according to Environment Agency (EA) figures.

Some good images and videos on the Daily Mail website:  http://www.dailymail.co.uk/news/article-2518340/Britain-battered-worst-tidal-surge-60-years-Sea-walls-breached-20ft-waves-smash-string-east-coast-towns.html

VIDEO – Bungalow falls off cliff in Norfolk  http://www.bbc.co.uk/news/uk-25258149 VIDEO – Thousands evacuated:  http://www.bbc.co.uk/news/uk-25253733 VIDEO – Homes in Whitby flooded:  http://www.bbc.co.uk/news/uk-25257747  plus: http://www.bbc.co.uk/news/uk-25258150 VIDEO – Cleaning up after the floods:  http://www.bbc.co.uk/news/uk-25257754 VIDEO – Aerial footages of flood aftermath:  http://www.bbc.co.uk/news/uk-25260863

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• Open access
• Published: 28 August 2024

Global insights on flood risk mitigation in arid regions using geomorphological and geophysical modeling from a local case study

• Adel Kotb   ORCID: orcid.org/0000-0002-8188-3188 1 ,
• Ayman I. Taha   ORCID: orcid.org/0000-0003-4526-1784 2 ,
• Ahmed A. Elnazer   ORCID: orcid.org/0000-0002-7338-0935 3 &
• Alhussein Adham Basheer   ORCID: orcid.org/0000-0001-5283-9201 1  

Scientific Reports volume  14 , Article number:  19975 ( 2024 ) Cite this article

Metrics details

• Environmental sciences
• Natural hazards

This research provides a comprehensive examination of flood risk mitigation in Saudi Arabia, with a focus on Wadi Al-Laith. It highlights the critical importance of addressing flood risks in arid regions, given their profound impact on communities, infrastructure, and the economy. Analysis of morphometric parameters ((drainage density (Dd), stream frequency (Fs), drainage intensity (Di), and infiltration number (If)) reveals a complex hydrological landscape, indicating elevated flood risk. due to low drainage density, low stream frequency, high bifurcation ratio, and low infiltration number. Effective mitigation strategies are imperative to protect both communities and infrastructure in Wadi Al-Laith. Geophysical investigations, using specialized software, improve the quality of the dataset by addressing irregularities in field data. A multi-layer geoelectric model, derived from vertical electrical sounding (VES) and time domain electromagnetic (TDEM) surveys, provides precise information about the geoelectric strata parameters such as electrical resistivity, layer thicknesses, and depths in the study area. This identifies a well-saturated sedimentary layer and a cracked rocky layer containing water content. The second region, proposed for a new dam, scores significantly higher at 56% in suitability compared to the first region’s 44%. The study advocates for the construction of a supporting dam in the second region with a height between 230 and 280 m and 800 m in length. This new dam can play a crucial role in mitigating flash flood risks, considering various design parameters. This research contributes to flood risk management in Saudi Arabia by offering innovative dam site selection approaches. It provides insights for policymakers, researchers, and practitioners involved in flood risk reduction, water resource management, and sustainable development in arid regions globally.

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Introduction.

Floods have long been recognized as one of the most devastating natural disasters, posing significant threats to communities worldwide 1 . In the Kingdom of Saudi Arabia (KSA), a region characterized by arid landscapes and sporadic rainfall, floods can have catastrophic consequences 2 . This paper aims to address the multifaceted issue of flood risks and their profound impact on the communities of KSA 3 , 4 . Furthermore, it underscores the critical importance of mitigating these risks through the judicious selection of dam sites, emphasizing the utilization of geophysical and geomorphological modeling techniques 5 .

Floods in KSA, while infrequent, are nonetheless devastating when they occur due to the arid nature of the region 6 . These events can lead to loss of life, damage to infrastructure, disruption of livelihoods, and economic losses 7 . Understanding the dynamics of flood risks is essential for safeguarding the well-being of KSA’s communities and ensuring the sustainable development of the region 8 . One pivotal approach to mitigating the impact of floods in KSA is through the strategic placement of dams 9 . These structures play a vital role in flood control, water resource management, and supporting agricultural activities 10 . Therefore, the selection of appropriate dam sites is paramount to the overall flood risk reduction strategy.

In this context, this paper centers its focus on the application of geophysical and geomorphological modeling techniques, specifically within the unique setting of Wadi Al-Laith in KSA 11 . Wadi Al-Laith, characterized by its intricate topography and hydrological features, serves as an exemplary case study to demonstrate the efficacy of these innovative approaches in dam site selection (Fig.  1 ). To contextualize our research, we present a comprehensive review of previous studies related to flood risks and dam site selection within the KSA region 12 . These studies provide valuable insights into the historical context and existing methodologies employed in flood risk management. Acknowledging the limitations and challenges of existing approaches is fundamental to driving innovation in flood risk mitigation 13 . By critically evaluating past strategies, we can identify areas where geophysical and geomorphological modeling can enhance the accuracy and effectiveness of dam site selection 14 , 15 .

location map of the study area, ( a ) spatial location of Saudi Arabia (red) relative to the world (gray) created by map chart, https://www.mapchart.net/world.html , ( b ) spatial location of Wadi Laith (green) relative to Makkah governorate (yellow) in Saudi Arabia created by map chart, https://www.mapchart.net/asia.html , ( c ) spatial location of Wadi Laith [created using 26 .

This study’s objective is toestablish a holistic framework for enhancing flood risk mitigation strategies in the region and contribute to the ongoing discourse on flood risk management in KSA by exploring innovative approaches to dam site selection, particularly through a promising solution of the application of geophysical and geomorphological modeling 16 , 17 . It endeavors to offer recommendations that can advance the planning and selection of optimal locations for new dams, as well as evaluate the performance and efficiency of existing dams 18 , 19 . Ultimately, this research is dedicated to ensuring the protection of both the communities and critical infrastructure within the Kingdom of Saudi Arabia (KSA).

The primary aim of this paper is to comprehensively address the multifaceted issue of flood risks in the Kingdom of Saudi Arabia (KSA), highlighting the unique challenges posed by the region’s arid landscapes and sporadic rainfall. The paper emphasizes the catastrophic consequences floods can have on communities, infrastructure, livelihoods, and the economy within KSA, while also considering global implications. It underscores the critical importance of mitigating flood risks through the judicious selection of dam sites, advocating for the use of advanced geophysical and geomorphological modeling techniques to enhance decision-making processes. Recognizing the devastating impact of floods in KSA despite their infrequency, the study promotes the strategic placement of dams as essential for flood control, sustainable water resource management, and supporting agricultural activities.

The paper specifically focuses on Wadi Al-Laith as a case study to illustrate the efficacy of geophysical and geomorphological modeling techniques in dam site selection. This area’s intricate topography and hydrological features serve as an exemplary setting for showcasing innovative flood risk mitigation strategies that could potentially inform similar efforts globally. To provide a comprehensive context, the paper conducts a thorough review of previous studies related to flood risks and dam site selection within KSA, aiming to offer insights into historical contexts, existing methodologies, and challenges faced in flood risk management.

Moreover, the study aims to contribute to the global discourse on flood risk management by exploring innovative approaches to dam site selection that improve accuracy and effectiveness through advanced modeling techniques. By establishing a holistic framework for enhancing flood risk mitigation strategies in KSA, the paper seeks to provide recommendations that can advance the planning and selection of optimal dam locations and evaluate the performance of existing infrastructure. Ultimately, the research aims to protect communities and critical infrastructure in KSA and beyond, thereby improving global resilience to floods and promoting sustainable development practices worldwide.

Area under investigation

Wadi Al-Laith, located in the Kingdom of Saudi Arabia (KSA), is a distinctive geographical feature within the western region of the country 20 . It is characterized by a variety of unique geographical attributes that shape its landscape and hydrology (Fig.  1 ).

Wadi Al-Laith can be described as a wadi, which is a typically dry riverbed or valley that experiences sporadic and often intense flash floods during the rare rainfall events in the arid region of KSA 21 . The geographical features of Wadi Al-Laith include a meandering topography with a pronounced channel that can expand dramatically during flood events. The valley exhibits a narrow and winding path, surrounded by rocky terrain and outcrops, with the nearby presence of limestone formations 22 .

The region’s hydrology is further influenced by its proximity to the Red Sea and the surrounding mountain ranges, which can contribute to localized weather patterns and rainfall variability 23 . Due to its geological composition and topographical characteristics, Wadi Al-Laith becomes particularly susceptible to flash flooding, making it a pertinent area for studying flood risk mitigation.

Wadi Al-Laith has witnessed several historical flood events, which have had significant repercussions for the surrounding communities and infrastructure 14 , 24 . These flood events are typically associated with the sporadic but intense rainstorms that occasionally occur in the region. Over the years, these floods have resulted in loss of life, damage to property, disruption of transportation networks, and agricultural losses. These historical flood events serve as poignant reminders of the urgent need to develop effective flood risk mitigation strategies in the area 20 , 21 , 25 .

Wadi Al-Laith assumes paramount importance as a case study for flood risk mitigation and dam site selection for several compelling reasons. Firstly, the unique topographical and geological characteristics of the region, such as the presence of limestone formations and rocky outcrops, make it an ideal testing ground for assessing the effectiveness of mitigation measures, including the strategic placement of dams. Secondly, the historical flood events in Wadi Al-Laith provide valuable data and insights into the vulnerabilities and risks associated with flash floods in arid regions, which can inform the development of targeted mitigation strategies. Thirdly, the lessons learned from Wadi Al-Laith can be extrapolated to other wadis and flood-prone areas within KSA and similar arid regions globally, making it a crucial reference point for policymakers, researchers, and practitioners engaged in flood risk management.

Briefly, Wadi Al-Laith in KSA serves as an exemplary study area for comprehensively examining the geographical characteristics, historical flood events, and the imperative role it plays in advancing flood risk mitigation and dam site selection strategies. The insights gained from this case study have the potential to enhance the resilience of communities and infrastructure in arid regions, safeguarding them against the adverse impacts of flash floods.

Geological settings

Wadi Al Lith, situated in the western region of Saudi Arabia, boasts a distinctive geological landscape characterized by its diverse features (Fig.  2 ). The prevailing geological composition of this area primarily consists of sedimentary rocks, prominently marked by the presence of extensive limestone formations 27 . These limestone formations are integral components of the sedimentary sequence affiliated with the Arabian Platform, with origins traceable to the Cretaceous and Paleogene epochs 26 , 28 . Specifically, the study area within Wadi Al-Lith assumes the form of a valley stream typified by a thin sedimentary layer, the close proximity of hard rock strata to the surface, and rocky outcrops flanking the valley’s margins 29 . Notably, in select regions, sediment thickness within the valley gradually increases until it interfaces with the underlying hard rock formations.

Geological map of the area under investigation and its surroundings. [Created using 34 .

The geological framework of the Wadi Al-Lith catchment area comprises four primary rock units, as detailed by 27 , 30 .

Quaternary, encompassing sand, gravel, and silt deposits: yhis unit exhibits the predominant presence of eolian sand-dune formations and sheet sand and silt deposits, with sand deposits covering a substantial portion of the region.

Late- to post-tectonic granitic rocks: represented by various plutonic rock types, including diorite, tonalite, granodiorite, and monzogranite, alongside serpentinite to syenite formations.

Lith suite, Khasrah complex, diorite, and gabbro: constituting a suite of mafic to intermediate plutonic rocks.

Baish and Baha groups: comprising rocks such as basalt–dacite and biotite-hornblende-schist-amphibolite.

Additionally, Wadi Al-Lith encompasses volcanic rocks, notably basalt and andesite, remnants of ancient volcanic activity 2 . These volcanic formations are associated with the Red Sea rift system, a significant geological phenomenon that has profoundly influenced the region’s topographical characteristics 31 .

Structurally, the geology of the Wadi Al-Lith region is shaped by faulting and folding processes. Underlying the sedimentary rocks is the Arabian Shield, a Precambrian-age basement complex 31 . Characterized by its rugged and mountainous terrain, this geological foundation contributes significantly to the diverse topography evident in the area 27 , 32 .

The presence of a multitude of rock types and geological structures within Wadi Al-Lith holds significant implications for water resources and the occurrence of flash floods. Impermeable rock formations, such as limestone, can expedite surface runoff during intense precipitation events, augmenting the susceptibility to flash floods 27 , 32 . Consequently, a profound comprehension of the geological attributes of the region assumes paramount importance in facilitating effective water resource management and the implementation of appropriate mitigation measures aimed at mitigating the impact of flash floods 31 , 32 .

Methodology

The hydrogeological method in this study primarily involves using hydrological models to predict and map regions prone to flash floods. The geophysical methods employed include electrical resistivity sounding (VES) and time-domain electromagnetic (TDEM) methods to investigate subsurface layers. Combining hydrogeological and geophysical methods offers a comprehensive understanding of the factors influencing flash floods. Hydrological models derived from detailed morphometric and land cover analyses are augmented with subsurface information obtained from geophysical measurements. This integrated approach allows for more accurate predictions of flash flood-prone areas by considering both surface characteristics and subsurface conditions, ultimately enhancing flood risk mitigation strategies.

Hydrogeological method

In this study, hydrological models assume a pivotal role in the anticipation and mapping of flash flood-prone regions. The hydrological models used in this study are advanced and multifaceted, incorporating: (a) morphometric analysis which are utilizing parameters like drainage density, stream frequency, and rainage intensity, (b) topographic data derived from high-resolution topographic maps, (c) land cover data (integrated using the ASTER GDEM dataset), (d) subsurface information (enhanced with data from geophysical methods), and e) GIS Software: ArcGIS 10.4.1(for comprehensive data analysis).

These models work together to predict specific locales susceptible to flash floods, considering both surface and subsurface characteristics, to provide a holistic approach to flood risk mitigation in arid regions like the Kingdom of Saudi Arabia. These models find their genesis in morphometric analyses, which entail a comprehensive examination of the terrain's spatial characteristics and configurations. Topographic maps, boasting a horizontal posting resolution of approximately 30 m at the equatorial belt, serve as the primary data source for these morphometric inquiries. This level of detail facilitates an exhaustive comprehension of the landscape’s morphology and its ensuing influence on the hydrological patterns governing water flow.

To bolster the precision of the hydrological models, supplementary data regarding land cover is incorporated into the analytical framework. The research team leverages the ASTER Global Digital Elevation Model (GDEM) Version 3 33 , a dataset that furnishes a worldwide digital elevation model of terrestrial regions. This dataset boasts a spatial resolution of 1 arcsecond, equating to approximately 30 m on the ground. By integrating this land cover information into the hydrological models, the research endeavor accommodates pertinent factors such as vegetation types, soil compositions, and land use patterns, all of which exert substantial influences on the hydrological dynamics across the landscape.

Subsequently, hydrological models are brought into action to predict the specific locales susceptible to flash floods. These models simulate the water’s flow trajectory predicated on the amalgamation of topographic particulars and land cover attributes. In so doing, these models pinpoint areas where the confluence of terrain features and land cover characteristics renders them predisposed to the occurrence of flash floods. To further bolster the predictive capacity of these models, subsurface information procured through geophysical measurements is incorporated.

For the comprehensive analysis of data, including morphometric assessments, ArcGIS 10.4.1 software 34 is employed. This software platform facilitates data visualization, manipulation, and morphometric analyses, enabling a detailed exploration of the study area’s pertinent parameters. Key morphometric parameters essential to this study are presented in Table 1 , encompassing metrics such as drainage density (Dd), stream frequency (Fs), drainage intensity (Di), and infiltration number (If). These parameters, as outlined by 35 , 36 , form the cornerstone of the morphometric analyses undertaken in this investigation.

Geophysical methods

Geophysical methods, including electrical resistivity sounding (VES) and time-domain electromagnetic (TDEM) methods, are employed to investigate subsurface layers. The number of measurements were 157 VES and the same number of TDEM have been conducted in the same place to cover the whole area under investigation (Fig.  3 a). VES measures subsurface electrical resistivity at various points, yielding insights into subsurface composition and properties. In contrast, TDEM employs electromagnetic pulses to assess subsurface characteristics. These geophysical measurements inform the development of subsurface models.

( a ) Geographical distribution of VES and TDEM soundings’ site in the area under investigation [created using 26 , ( b ) example of VES no. 1 interpretation [extracted from 51 , ( c ) example of TDEM sounding no. 1 interpretation [extracted from 52 .

Geoelectrical method

Geoelectrical surveys, also known as the “DC method,” entail injecting direct electric current into the ground using surface-based current and voltage electrodes. The current’s direction is alternated to mitigate natural ground interference.

The vertical electrical sounding (VES) technique, utilizing continuous direct current (DC), is widely employed for groundwater exploration. It gauges values influenced by water content in rocks; higher values are characteristic of unsaturated rocks, while lower values indicate saturation, with salinity influencing measurements 37 .

The method of measuring ground electrical resistance relies primarily on Ohm's law, which states that the electric current flowing through a conductor is directly proportional to the voltage across it Eq. ( 1 ).

Ground electrical resistance is measured in accordance with Ohm’s law, where electric current is injected into the ground via two conductive electrodes (A and B) 38 , 39 Eqs. ( 2 ), ( 3 ).

The apparent electrical resistance (ρa) is determined by dividing the product of the potential difference (∆V) by the current strength (I) and multiplying it by a geometric constant (K), which varies based on the distance between the current and voltage electrodes. This process is conducted using the Schlumberger configuration, which allows for deeper measurements compared to other configurations 40 , 41 .

Simultaneously, the potential difference across two additional electrodes (M and N) within the ground is measured. Apparent electrical resistance (ρa) is calculated by dividing the product of potential difference (∆V) by current strength (I) and multiplying by a geometric constant (K), contingent on the electrode distance. The Schlumberger configuration is employed for deeper measurements Eqs. ( 2 ),( 3 ) 42 .

The geoelectrical survey in the study area was performed using the ARES II/1 43 device, manufactured in the Czech Republic, which has a high capacity to transmit a current of up to 5 A, a voltage of 2000 V, and a capacity of up to 850 W, enabling measurements to be taken until reaching the solid base rocks.

Time domain electromagnetic method (TDEM)

TDEM relies on electromagnetic induction principles, creating a varying magnetic field and measuring induced electrical currents in the subsurface.

A transmitter coil carrying a strong current generates a changing magnetic field penetrating the subsurface. This field induces secondary electrical currents (eddy currents) in conductive materials beneath the surface, resulting in secondary magnetic fields. Upon deactivating the transmitter coil, the eddy currents decay, and the associated magnetic fields diminish. A receiver coil captures changes in the magnetic field over time, known as the decay curve or decaying electromagnetic response, providing subsurface resistivity distribution insights 44 .

Key equations utilized in TDEM include Faraday’s law of electromagnetic induction, Maxwell’s equations Eq. ( 4 ), governing electromagnetic wave propagation, and Ampere’s law, accounting for electric currents and the displacement current.

where ( ∇  × B) is the curl of the magnetic field vector (B), (μ 0 ) is the permeability of free space, a fundamental constant, (J) is the electric current density, and (∂E/∂t) is the rate of change of the electric field vector (E) with respect to time. This equation relates magnetic fields to electric currents and the displacement current (the term involving ∂E/∂t), which accounts for the changing electric field inducing a magnetic field 45 , 46 .

The Cole–Cole model represents complex electrical conductivity in subsurface materials, incorporating parameters (σʹ, σʹʹ, and α) to account for frequency-dependent conductivity Eq. ( 5 ).

where the complex conductivity (σ*) and angular frequency (ω) and (j) is the imaginary unit (√(− 1)) 40 , 41 .

Inversion algorithms, based on forward modeling and optimization techniques, interpret TDEM data and construct subsurface resistivity models. The inversion process involves comparing predicted data with measured data and adjusting the resistivity model to minimize discrepancies. Iterations continue until a satisfactory match is achieved, yielding the best-fitting resistivity distribution. These methodologies enable the estimation of subsurface properties, valuable in groundwater exploration, mineral assessment, and geological formation characterization 47 . Figure  3 b, c illustrates an example of these interpretations.

By combining hydrological models derived from topographic and land cover data with the subsurface model obtained from geophysical measurements, a comprehensive understanding of the factors affecting the occurrence of flash floods can be achieved. This integrated approach allows for more accurate prediction of locations vulnerable to flash floods, as it takes into account surface characteristics and subsurface conditions.

In a clearer and more summarized sense, the hydrological models used in this study are derived from detailed morphometric studies based on topographic maps and land cover data. ASTER’s Global Digital Elevation Model (GDEM) version 3 is used to obtain land cover information. These models, along with subsurface information obtained through geophysical measurements and interpretation using VES and TDEM methods, contribute to predicting locations vulnerable to flash floods through a more comprehensive and accurate understanding of the contributing factors.

Hydrogeological modeling

In this study, a comprehensive analysis of the study area’s topography, hydrology, and precipitation patterns was conducted using various geospatial data sources and techniques. The digital elevation model (DEM) played a central role in extracting valuable insights.

The DEM was employed to delineate the drainage network within the study area, specifically focusing on the Wadi Lith watershed (Fig.  4 a). By assessing stream orders within this watershed, a significant observation emerged. It was noted that as the stream order increased, the number of associated stream segments decreased. Notably, the first-order stream (SU1) displayed the highest frequency, indicating that lower-order streams are more prevalent in the area. This observation underscores the heightened susceptibility of Wadi Lith to drainage-related hazards (Fig.  4 b).

( a ) Digital elevation map of the area under investigation, ( b ) drainage network map of the area under investigation. Created using 34 .

The DEM dataset yielded critical information concerning the topography and hydrology of the study area. Elevation data, flood flow directions, and identification of vulnerable regions were among the key findings derived from the DEM analysis. The elevation levels captured by the DEM ranged from 0 to 2663 m within the study area (Fig.  4 a).

The researchers employed ArcGIS software to generate three essential maps using the DEM data: slope, aspect, and hill shade maps to gain a deeper understanding of the topographic features. These maps provided distinct perspectives on the terrain’s characteristics. The slope map (Fig.  5 a) vividly illustrated the steepness of the rocks in the study area, with higher slope values indicating more pronounced inclinations. The aspect map (Fig.  5 b) revealed that slopes predominantly faced southward within the study area. Furthermore, the hill shade map (Fig.  5 c), employing shading techniques, effectively portrayed the topographical features of hills and mountains. It accentuated relative slopes and mountain ridges, notably highlighting the valley of Al-Lith as particularly susceptible to flood hazards (Table 2 ).

( a ) Slope map of the area under investigation, ( b ) aspect map of the area under investigation, ( c ) Hill shade map of the area under investigation. [created using 34 .

Monthly precipitation data (Table 3 ) were scrutinized to understand the precipitation patterns in the Al-Lith area. The analysis revealed that the average annual precipitation in the area amounted to approximately 9.3 mm. Notably, January, November, and December were identified as the months with the highest recorded rainfall levels, as per data sourced from climate-data.org. The combination of these factors suggests that while Al-Lith typically experiences low annual precipitation, the region is highly susceptible to flash floods during specific months which are January, November, and December. This primary flood risk occurs due to significantly higher precipitation levels during these months, where rainfall is significantly higher. The last historical floods happened in November 2018 and December 2022.

As a combined result of the above, this study harnessed the power of the DEM to conduct an in-depth analysis of the study area's drainage network, stream orders, and topographical features. ArcGIS software facilitated the creation of informative slope, aspect, and hill shade maps, shedding light on the terrain’s characteristics and emphasizing flood vulnerabilities in Al-Lith Valley. Furthermore, the examination of monthly precipitation data unveiled the region’s average annual rainfall patterns, highlighting specific months of heightened precipitation (Table 4 ). These integrated findings contribute to a comprehensive understanding of the study area's hydrological and topographic dynamics, which are crucial for flood risk assessment and mitigation efforts.

Morphometric parameters analysis

In the assessment of the study area’s morphometric characteristics, several key parameters were examined to gain valuable insights into its drainage network and hydrological behavior.

Drainage density (Dd)

Drainage density (Dd) serves as a fundamental metric, calculated as the total length of streams within a drainage basin divided by its area (A). In the present research region, a notably low drainage density of 1.19 km −1 is observed, indicative of a scarcity of streams relative to the area’s expanse. This characteristic can be primarily attributed to the presence of erosion-resistant, fractured, and rough rock formations that facilitate accelerated water flow within the wadi 26 .

Stream frequency (Fs)

Stream frequency (Fs) signifies the abundance of streams within a specific area, quantified as the number of streams per unit area. In the studied domain, the stream frequency is calculated to be 3.32 km 2 , revealing a relatively low stream density. This implies a scarcity of streams per square kilometer, a phenomenon influenced by factors such as modest relief, permeable subsurface materials, and a heightened capacity for infiltration. These conditions collectively contribute to the profusion of streams within the region 48 , 49 .

Bifurcation ratio (Rb)

The bifurcation ratio (Rb) provides insights into the branching pattern within a watershed’s stream network. It is computed as the ratio of the number of streams of a given order to the number of streams of the order directly above it. The mean bifurcation ratio (Mbr) in the study area is determined to be 1.96, signifying a notable degree of branching within the watershed’s stream network 49 .

Infiltration number (If)

The infiltration number (If) represents a comprehensive metric evaluating the infiltration capacity of a watershed, factoring in both drainage density and stream frequency. In the research region, the calculated infiltration number is 3.95, categorizing it as exhibiting low infiltration numbers and high runoff potential. This observation underscores the area’s propensity for high runoff rates due to its limited infiltration capacity 49 .

Flood risk assessment and site suitability

The interplay of drainage density, stream frequency, bifurcation ratio, and infiltration number impart significant insights into the watershed's characteristics and hydrological behavior. Notably, the low drainage density, low stream frequency, high bifurcation ratio, and low infiltration number in the study area collectively contribute to elevated flood risk and heightened potential for runoff. This assessment underscores the imperative necessity for the implementation of effective flood mitigation measures within the region.

Furthermore, a holistic approach was applied by 50 involving the interrelationship of bifurcation ratio, drainage frequency, and drainage density to evaluate the basin’s hazard potential. Based on this analysis, the studied basin is identified as having a considerable likelihood of experiencing flash floods.

Briefly, the comprehensive analysis of morphometric parameters reveals critical insights into the study area’s hydrological behavior and flood risk. The observed characteristics necessitate diligent attention to flood risk mitigation strategies and effective management practices within the region.

Geophysical data processing and interpretation

In the aftermath of an extensive field survey conducted within the study area, a meticulous and structured data processing sequence is enacted. This sequence encompasses several crucial steps geared toward enhancing data consistency and reliability.

Data quality assessment

The initial phase of data processing revolves around the generation of apparent resistance curves employing the field data. These curves serve the pivotal function of identifying and rectifying any irregularities, with particular emphasis on anomalies encountered during the onset of electrical and electromagnetic tests. Aberrant readings undergo rigorous scrutiny and, where necessary, are expunged from the dataset to elevate the overall precision and fidelity of the information.

Utilization of data processing software

Subsequently, specialized data processing software tools come into play, specifically the “Interpex 1DIV” 51 and “ZondTEM1D” 52 programs. These meticulously designed programs take on the responsibility of processing data originating from electrical probes. The dataset encompasses critical information, including electrical resistance, and, in applicable scenarios, resistance and inductive polarization. The primary probe data collected from the study site serves as the foundational data set for this comprehensive processing (Fig.  3 b, c).

Development of a multi-layers model

The third phase in the data processing continuum is marked by efforts to streamline the representation of multi-layered data into a more coherent and manageable form. This procedure necessitates the amalgamation of groups of closely associated resistance values into unified composite resistance layers. The primary objective is to streamline the dataset’s complexity while preserving its intrinsic geoelectric attributes and characteristics.

Characterization of geoelectric layers

The ultimate stage of data processing culminates in the meticulous characterization of geoelectric layers. This encompasses the precise determination of electrical resistivity values, layer thicknesses, and the depths of the discrete geoelectric strata. These defined parameters offer a comprehensive understanding of the geological and geophysical attributes of the study area.

Geophysical insights

The geophysical investigation, with a specific focus on the vicinity proximate to the groundwater dam and the Wadi Al-Leith water station within Wadi Al-Laith, has yielded valuable insights. The primary aim was to harness the dam’s influence on nearby wells, thus mitigating the necessity for extensive station-to-well extensions. Concurrently, the presence of a fractured layer and the heterogeneous topography of the solid base rocks were meticulously documented.

The amalgamated findings underscore the existence of a substantial and adequately saturated sedimentary layer at select locations, coexisting alongside a cracked rocky layer harboring a discernible water content. It is pertinent to note that the predominant characteristic across the valley’s expanse is the prevalence of a notably thin sedimentary layer, characterized by limited water saturation (Fig.  6 ). It is clear from the interpretations that the depth of groundwater in the investigation area ranges from 0.5 to 14 m (Fig.  6 a), and the thickness of the layer containing the water ranges between 0.3 and 33.63 m (Fig.  6 b). The inference of the presence of groundwater was confirmed by an actual review of the results of the electrical resistance values, which ranged from 33.9 to 145 Ω.m (Fig.  6 c).

( a ) Depth map to groundwater bearing layer, ( b ) thickness map of groundwater bearing layer, ( c ) resistivity distributions map of groundwater bearing layer, ( d ) map of hypothetical score calculation by geophysical weighted decision matrix [created using 26 .

In summation, the comprehensive geophysical investigation has unveiled the coexistence of well-saturated sedimentary layers and fractured rocky substrates across the study area. These findings constitute a pivotal resource for groundwater assessment and the judicious utilization of resources within the Wadi Al-Laith region.

Matrix of comparative assessment of dam site suitability

Matrix of the effective geoelectrical model for dam site suitability.

Matrices have been mentioned, as one of the means of evaluating the preference for identifying areas, in many studies that deal with environmental and water assessment processes for proposing or evaluating areas for constructing dams, such as 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 . The matrices differed in many of them depending on the parameters used and the data available (Tables S1 and S2 supplementary information documents). In this research, a somewhat unique matrix was designed based on the availability of data and the amount of correlation and complementarity between them.

In the comprehensive assessment of the geoelectric model of sublayers as an effective parameter in the suitability matrix for both the first and second regions, a series of parameters were carefully considered, each assigned a weight percentage to reflect its relative importance in the decision-making process. These parameters encompassed critical aspects of the geoelectrical model of sublayers and related factors, including layer resistivity (ρ), layer thickness (h), layer geometry, layer boundaries, electrode configuration, data quality and error estimation, inversion algorithm, geological constraints, and hydrogeological properties (Tables S3 and S4 supplementary information documents).

The weighted decision matrices for both regions were constructed by evaluating the effectiveness of each parameter for its effective power in site suitability. A hypothetical score calculation was then performed by multiplying the weight percentage by the effectiveness score for each parameter and summing these values for each region (Table 5 , Fig.  6 d). The results revealed that the second region excelled in suitability, achieving an impressive score of 60%, whereas the first region scored lower at 40%. This suggests that the second region is significantly more favorable for dam construction, as determined by the geoelectrical model of sublayers and its associated suitability parameters.

Matrix of dam site suitability

In the evaluation of suitable locations for building a dam within the first and second regions, a set of parameters and their respective weightings were considered. These parameters included bifurcation ratio (Mbr), aspect, slope, hill shade of the study area, annual average precipitation, stream length (Lu), drainage density (Dd), stream frequency (Fs), drainage intensity (Di), infiltration number (If), flood possibilities, and the geoelectrical model of sublayers (Table 6 ). Each parameter was assigned a weight percentage reflecting its relative importance in the decision-making process. Subsequently, weighted decision matrices were created for both regions, where the quality of each parameter was assessed for each location.

The hypothetical score calculation was performed by multiplying the weight percentage by the quality score for each parameter and summing these values for each region. Based on this analysis, the first region, where the old dam was located, received a suitability score of 44%, while the second region scored higher at 56%, suggesting that the second region may be a more suitable option for building a dam according to the specified criteria (Fig.  7 ).

Map of hypothetical score calculation by hydrogeological and geophysical weighted decision matrix. Created using 26 .

Evaluating dam site suitability

The assessment conducted through matrix analysis has yielded valuable insights into the suitability of potential dam sites in the specified regions. These findings are rooted in a meticulous evaluation of various parameters and their weighted contributions to the overall suitability score. In this context, the first region emerged with a suitability score of 44%, while the second region demonstrated a notably higher score of 56%. This discrepancy in scores underscores a critical distinction between the two regions in terms of their potential for dam construction (Fig.  7 ).

The higher score awarded to the second region suggests that it may hold distinct advantages when measured against the specific criteria used for evaluation. These criteria, which include factors like bifurcation ratio (Mbr), aspect, slope, hill shade of the study area, annual average precipitation, stream length (Lu), drainage density (Dd), stream frequency (Fs), drainage intensity (Di), infiltration number (If), flood possibilities, and the geoelectrical model of sublayers depended on geoelectrical properties, geological constraints, and hydrogeological considerations, collectively indicate a higher level of suitability for dam construction in the second region. This implies that the second region offers a more promising and feasible prospect for establishing a dam infrastructure, aligning closely with the predefined objectives and prerequisites of the project. As such, the findings of this analysis provide a compelling rationale for considering the second region as the preferred choice for future dam construction endeavors.

Parameters of proposed dam

Although it is impossible to completely eliminate the risk of flash floods, there are a variety of strategies to lessen it. For example, it is possible to identify the areas that are most vulnerable to the hazard by analyzing the drainage system, hydrologic modeling, and the local geology. Dams and canals are suggested solutions to the issue in addition to assisting in collecting and replenishing water for various reasons.

The Al-Lith earthen dam in the study area collapsed on November 23, 2018, as a result of repeated rainstorm events in the upper part of Wadi Al-Lith in western Saudi Arabia 64 . An old Al-Lith dam was built as an altocumulus dam to solve this issue. Its height terminates at the earth's surface and its goal is to store groundwater to supply the wells dug above this dam. To supply a purification plant next to the old dam, a number of wells needed to be sunk at the top of the old dam (Fig.  8 ).

Map of the calculated storage-capacity volume of the proposed dam which is suggested for the area under investigation. Created using 34 .

Based on the morphological analysis of the watershed and to reduce the risk of flash flooding 50 , the study of work suggests improving the proposed dam so that it can have a storage capacity of about 38,187,221.4 m 3 and an area behind the dam of about 3,567,763.9 m 2 . Additionally, it may advocate building a supporting dam around 5 km south of the old Al-Lith Dam. Geologically, the site of the proposed and projected new Dam will be constructed on the two wadi sides with hard rock of quartz–diorite and no faults. The newly proposed dam will have a storage capacity of 114,624,651.1 m 3 , and its size will be 5,104,646.8 m 2 (Fig.  8 ). According to GIS analysis, if the elevation map of the study area ranges from 122 to 617 m, the suggested proposed dam should measure between 230 and 280 m in height and 800 m in length.

The hydrogeological modeling conducted in this study leverages Digital Elevation Model (DEM) data to delineate the drainage network of Wadi Lith, revealing key insights into the region's susceptibility to flood hazards. The DEM analysis underscores the dominance of first-order streams (SU1) in the area, indicating a heightened vulnerability to drainage-related issues. The slope, aspect, and hill shade maps generated using ArcGIS further enhance our understanding of the region’s topography. The slope map highlights areas of steep inclinations, the aspect map shows a predominance of south-facing slopes, and the hill shade map vividly portrays the valley’s topographical features, emphasizing the Al-Lith Valley’s susceptibility to floods.

The analysis of morphometric parameters offers a comprehensive understanding of the drainage characteristics and flood risks within the study area. Drainage density (Dd) shows a value of 1.19 km −1 , the low drainage density indicates a scarcity of streams, attributed to erosion-resistant rock formations that facilitate rapid water flow, contributing to flood risk. Stream Frequency (Fs) shows at 3.32 km 2 , the relatively low stream frequency suggests limited stream presence, influenced by modest relief and high infiltration capacity. The bifurcation ratio (Rb) shows a mean value of 1.96 reflecting significant branching within the stream network, crucial for understanding flood dynamics. Infiltration number (If) illustrates the low infiltration number of 3.95 highlights a high runoff potential, underlining the area’s vulnerability to flash floods. These parameters collectively indicate an elevated flood risk and necessitate effective mitigation strategies.

The geophysical investigation, focusing on the area around the groundwater dam and Wadi Al-Leith water station, reveals the coexistence of well-saturated sedimentary layers and fractured rocky substrates. This duality is crucial for groundwater assessment and highlights the potential for utilizing these resources effectively. The identified groundwater depths (0.5–14 m) and layer thicknesses (0.3–33.63 m) are significant for planning water extraction and management strategies.

The matrix analysis for dam site suitability compares two regions, considering various hydrological, geological, and geoelectrical parameters. The geoelectrical model illustrates that the second region scores higher (60%) compared to the first (40%), indicating better suitability for dam construction based on geoelectrical properties. Overall suitability containing factors like bifurcation ratio, aspect, slope, and precipitation illustrates that the second region again scores higher (56%) versus the first (44%). This comprehensive evaluation suggests that the second region is more favorable for dam construction due to its advantageous geoelectrical and topographical characteristics.

Considering the historical collapse of the Al-Lith Dam in November 2018 and December 2022, the study proposes improvements to the dam structure to enhance its storage capacity and flood mitigation capability. The proposed dam should have a storage capacity of approximately 114,624,651.1 m 3 , with a height of 230–280 m and a length of 800 m. This strategic enhancement aims to bolster the region's flood resilience and water management efficiency.

The integrated hydrogeological, geophysical, and morphometric analyses provide a holistic understanding of the flood risks and water management challenges in Wadi Al-Lith. The proposed mitigation strategies, including the construction of a new dam, are grounded in comprehensive geospatial and geophysical data, ensuring their effectiveness in enhancing the region’s flood resilience and water resource management. This study underscores the importance of leveraging advanced geospatial techniques and comprehensive data analysis for effective flood risk mitigation in arid regions.

The study offers a comprehensive evaluation of flood risk mitigation strategies in Wadi Al-Laith, Kingdom of Saudi Arabia (KSA), emphasizing the critical need to address flood risks in arid regions due to their severe impact on communities, infrastructure, livelihoods, and the economy.

By using the hydrological analysis, the investigation of the morphometric parameters revealed low drainage density, low stream frequency, a high bifurcation ratio, and a low infiltration number, indicating elevated flood risk and high runoff potential in Wadi Al-Laith. These characteristics highlight the need for effective flood risk management to protect communities and infrastructure.

By using geophysical investigation, data processing used specialized software 51 , 52 to process electrical and electromagnetic probe data, ensuring accuracy by correcting field data irregularities. The “multi-layer model” was developed by consolidating resistance values and providing detailed information on electrical resistivity, layer thicknesses, and depths of geoelectric strata. Findings include a well-saturated sedimentary layer and a cracked rocky layer with water content, though a thin, less saturated sedimentary layer is predominant. The study area was divided into two regions for dam construction, with the proposed new dam site scoring 56% in suitability, higher than the old dam sites at 44%.

The study indicates the encouragement and support of combining hydrogeological and geophysical data to offer a thorough understanding of factors contributing to flash floods, including topography, drainage characteristics, and subsurface properties.

Long-term implications of constructing dams have environmental Impacts like (1) dams significantly alter natural water flow, which can impact downstream ecosystems. By regulating water flow, dams can reduce the frequency and severity of floods, but they may also reduce sediment transport, affecting riverine habitats and delta formations. (2) The creation of a reservoir can lead to the submersion of land, affecting local flora and fauna. In arid regions like Wadi Al-Laith, this could disrupt unique desert ecosystems (3) Stagnant water in reservoirs can lead to reduced water quality, promoting the growth of algae and affecting aquatic life.

Also, the long-term implications of constructing dams have a morphological response like (1) the dam will trap sediments, leading to sediment accumulation in the reservoir. This can reduce the dam’s storage capacity over time and necessitate periodic dredging. (2) downstream of the dam, reduced sediment supply can lead to channel erosion, altering the geomorphology of the riverbed and potentially impacting infrastructure and habitats.

While acknowledging the potential long-term environmental implications, the decision to propose dam construction is based on a comprehensive assessment of the specific context of Wadi Al-Laith a recommended advice for building an 800 m-long auxiliary dam with a height of 230–280 m, utilizing quartz–diorite rock. Our analysis of morphometric parameters indicates a high flood risk due to low drainage density, low stream frequency, high bifurcation ratio, and low infiltration number. A strategically placed dam can significantly mitigate these risks. Additionally, the selected dam site in the second region, utilizing sturdy quartz–diorite rock without faults, provides a stable foundation for the proposed structure, ensuring its long-term stability and effectiveness. The proposed auxiliary dam, with a detailed design considering height, diameter, relief holes, surface inclinations, and well placements, aims to enhance flood resilience while addressing the specific hydrological and geological conditions of the area.

In addition to proposing dam construction, our study considered several non-structural and nature-based solutions to mitigate flood risk in Wadi Al-Laith, The study underscores the need for a holistic approach to enhance water resource management and support agriculture, and flood risk mitigation in arid regions like KSA, where infrequent but devastating floods can occur. A holistic approach to flood risk mitigation in arid regions like Wadi Al-Lith in the Kingdom of Saudi Arabia should combine structural and non-structural measures to address both immediate flood threats and long-term resilience, considering the unique hydrological and climatic conditions. Key strategies include (1) integrated watershed management, involving catchment area analysis, land use planning, and soil and water conservation; (2) structural measures, such as building dams, flood channels, and retention basins; (3) non-structural measures, including advanced flood forecasting, community engagement, and sustainable water management policies; (4) geophysical and hydrological monitoring through continuous data collection and geophysical surveys; (5) ecosystem-based approaches, such as restoring natural floodplains and promoting green infrastructure; and (6) adaptive management and research to allow flexibility in strategies and support ongoing research. By integrating these measures, advanced monitoring, and active community involvement, a holistic approach can significantly enhance flood resilience in arid regions like Wadi Al-Lith, addressing immediate risks and building long-term sustainability and adaptability to climate change.

The research contributes to flood risk management discourse in KSA by presenting innovative approaches to dam site selection using geophysical and geomorphological modeling. While our study acknowledges the potential long-term environmental implications of dam construction, it also highlights the necessity of such infrastructure in the specific context of Wadi Al-Laith to ensure effective flood risk mitigation. It offers valuable insights and recommendations to protect communities and infrastructure in arid regions prone to flash floods, promoting sustainable development. Findings can guide policymakers, researchers, and practitioners in KSA and similar arid regions globally.

Data availability

All data generated or analyzed during this study are included in this mnuscript.

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Acknowledgements

Special thanks to Dr. Nihal Adel ([email protected]), Associate Professor of English, Department of English Language, Faculty of Al-Alsun, Minya University, Egypt, for reviewing the linguistic, grammar, and scientific moral context of the current research.

Open access funding provided by The Science, Technology & Innovation Funding Authority (STDF) in cooperation with The Egyptian Knowledge Bank (EKB).

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Adel Kotb & Alhussein Adham Basheer

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Ayman I. Taha

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All authors contributed to all sections and work stages, field measurements, data collection and measurements using geophysical equipment and reviewed the manuscript. A. K. wrote the theoretical part, research methods, removed the deficiencies that appeared after the interpretation, and strengthened the main parts of the research, wrote the summary and conclusions part, reviewed the research parts, maintained a reduction in the percentage of plagiarism, made tables and arranged the forms to match the idea and form of the research, prepare files to confirm the journal requirements and then submitted the research to the journal after approval rest of the authors. A. I. T. developed the field work plan and acquired the data. A. A. E. contributed to the data interpretation, reviewed the research and arranged its parts. A. A. B wrote the text of the manuscript, developed the field work plan with the first and second authors, coordinated the text, wrote the summary and conclusions part with the first author, reviewed the research parts, maintained a reduction in the percentage of plagiarism with the first author, made tables and arranged the forms to match the idea and form of the research with the first author.

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Kotb, A., Taha, A.I., Elnazer, A.A. et al. Global insights on flood risk mitigation in arid regions using geomorphological and geophysical modeling from a local case study. Sci Rep 14 , 19975 (2024). https://doi.org/10.1038/s41598-024-69541-x

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DOI : https://doi.org/10.1038/s41598-024-69541-x

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The River Severn Case Study - landforms of erosion and deposition

The River Severn Case Study – landforms of erosion and deposition

The River Severn (Afon Hafren) is the UK’s longest river at 354 km (220 miles) long.

The upper, middle and lower course of the River Severn

The source of the River Severn is on the slopes of Plynlimon (the highest point of the Cambrian Mountains) in mid-Wales at around 600 metres above sea level. The hills in this part of Wales receive about 2,650 mm of rainfall annually (compared to the average annual precipitation in the UK, which typically ranges from approximately 800 mm to 1,400 mm). The rain which falls on Plynlimon is stored in thick layers of peat and is slowly released into the River Severn.

Source: https://commons.wikimedia.org/wiki/File:Source_of_the_river_Severn-Tarddiad_Afon_Hafren_-_geograph.org.uk_-_228886.jpg

Source: https://www.geograph.org.uk/photo/772159

From its source, the River Severn flows over alternating mudstone, siltstone and sandstone layers. The river erodes vertically into its bed by hydraulic action and abrasion . Rapids have formed as the sandstone is more resistant to erosion than mudstone and siltstone.

Around 6km from its source, the River Severn plunges over a narrow band of sandstone at a waterfall called Water-break-its neck (Hafren-Torri-Gwddf). It is located in the Hafren Forest. It has formed due to a layer of harder rock (sandstone) lying over a softer rock (mudstone). The river erodes the mudstone through hydraulic action in the plunge pool. This causes an overhang to form. Eventually, this collapses, and the waterfall retreats upstream, forming a gorge downstream.

Water break its neck waterfall (Hafren Torri Gwddf)

After Llanidloes, the gradient of the River Severn is much more gentle. The river flows east and northeast through mid-Wales, past Newtown and Welshpool and then into Shropshire, where it flows through Shrewsbury and Ironbridge.

There are a considerable number of meanders along the middle and lower course of the River Severn.

OS Map showing meanders at Shrewsbury

The image below shows the River Severn at Shrewsbury.

There are a series of oxbow lakes on the River Severn east of Berriew at the Dolydd Hafren Nature Reserve.

Oxbow lakes at the Dolydd Hafren Nature Reserve – Source: Ordnance Survey

Towards the mouth of the Severn, the river becomes very wide. The relief is very flat, where the River Severn flows into the Bristol Channel, forming an estuary . There is significant deposition here, forming large sand and silt banks.

The Lower Course of the River Severn

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