Natural Flood Management in the Cadoxton catchment

Periods of heavy rainfall over recent years have highlighted a flooding problem in Dinas Powys. In periods of high rainfall, the river channels, surface water drains and surface water sewers become overwhelmed causing flooding of roads, gardens and homes.  

One of our roles is to see what can be done to reduce the risks, especially in the face of climate change, which is likely to increase flood risk as time goes on.

The Cadoxton River and East Brook have a long history of flooding in the villages. Records dating back to 1903 show several instances of flooding, including on St Cadoc’s Avenue, Greenfield Avenue, Elm Grove Place and Cardiff Road.

The last significant flood event was on 23 December 2020. After an intense period of rain, water levels rose rapidly so that that 98 properties were flooded internally.  Many other “near-miss” events have occurred when the river has been very high but not caused flooding.

Climate change is causing more extreme weather conditions and putting increased pressure on the existing flood defences, rivers and drainage systems. As our climate continues to change, we will face more frequent storms and heavy rain, which is predicted to result in more frequent, and more significant, flood events. Studies predict that the number of properties at high risk of flooding may double over the next 100 years.

We've explored different flood risk management options. In 2021, we published the Outline Business Case (OBC) focusing on a flood water storage area adjacent to Cwm George, between Casehill Wood and Hales Wood. This option faced significant public opposition due to environmental and social factors such as tree loss. Acknowledging this, we decided not to proceed with this option. Therefore, alternative methods of flood alleviation are now being explored.

We are now exploring options to reduce the risks of flooding to people, property and infrastructure in Eastbrook and Dinas Powys, without adverse effects on communities downstream.

This includes considering the use of nature-based solutions to flood management and small-scale engineering solutions within the Cadoxton River catchment including its tributaries (East Brook, Cold Brook, Wrinstone Brook, Bullcroft Brook), taking account of previous feedback from consultation with the community and other stakeholders.

We have funding from Welsh Government to investigate the viability for Natural Flood Management “Plus” works. We aim to integrate this with helping nature recover through River Restoration of the Cadoxton River catchment.

Natural Flood Management (NFM) is when natural processes are used to reduce the risk of flooding through restoring bends in rivers, changing the speed water flows in rivers and the way land is managed so soil can absorb more water. 

It does not include using traditional flood defence infrastructure such as barriers or dams.

For more information about NFM, visit these links:

• Natural flood management – part of the nation’s flood resilience - GOV.UK (www.gov.uk)
• Natural Resources Wales / Maps for Natural Flood Management

In addition to NFM, there may be additional small-scale engineered solutions which can work alongside natural processes to help address the flooding issues.

Other plusses include the potential for additional local benefits, such as helping to restore and improve habitats, support agricultural practices, improving water and soil quality and enhancing the wellbeing and health of the local community.

• Our consultants, JBA, have created a River Restoration plan for the catchment.
• Working with the Woodland Trust we are exploring various Nature-based solutions, NFM and River Restoration opportunities on their land in the Case Hill and Cwm George woods.
• Mapping NFM opportunities in other areas of the catchment.
• Carrying out site visits and environmental surveys.
• Specialist consultants are conducting a review of the flood risk model including sensitivity testing.
• Attending engagement events and meetings with local farmers, landowners, and community to explore opportunities in the catchment.
• Ongoing stakeholder engagement via letter, face to face and meetings.
• Attendance at Dinas Powys Village show August 2024.
• Regular attendance at Community Council and Flood Action Group meetings.
• Collaboration with local authority and partner organisations.
• For more information about the project watch the Natural Flood Management Plus Landowner Webinar - May 2022.

Natural Flood Management in the Cadoxton catchment leaflet

Storing water

Ponds, scrapes, bunds and swales can temporarily store water, reduce water entering rivers and slow the flow of water overland.

Other benefits:

• retain water in times of drought
• land productivity
• less soil loss
• soil health
• supports invertebrate and plant species
• water quality

Large woody debris in river channels

This slows the flow by encouraging floodwater to temporarily spill onto the floodplain where suitable.

Other benefits:

• soil health
• land productivity
• diversity of river habitat features
• biodiversity
• improves channel structure
• traps sediment, improving water quality

Restoring floodplains, wetlands and meanders

Large volumes of water can be stored, slowing the flow by temporarily allowing floodwater to spill naturally onto land.

Other benefits:

• soil health
• land productivity
• diversity of river habitat features
• biodiversity
• water quality
• improves channel structure
• allows more natural lower energy flooding, stabilising river banks
• drains back into the river naturally

Restoring hedgerows and trees

This intercepts rainfall, water evaporates from leaves, and less water reaches the ground. Helps soil hold more water.

Other benefits:

• shelter and shade for animals
• slows surface water
• traps and filters runoff, stops loss of fertilisers, sediment and pesticides
• soil health
• biodiversity
• water quality
• absorbs and stores carbon

Planting next to rivers and across slopes

Shrubs, grass buffers, or trees can slow the flow, help soil soak up more water, and help stabilise river banks.

Other benefits:

• stabilise river banks
• less erosion
• shelter and shade for animals
• traps and filters runoff, stops loss of fertilisers, sediment and pesticides
• biodiversity and habitat
• water quality
• absorbs and stores carbon

Soil and land management

Managing soil compaction, crop and livestock rotations.

Other benefits:

• less soil loss
• soil health
• less waterlogged areas
• retain water in times of drought
• biodiversity
• water quality
• slows flow of water

Working closely with the local community, particularly property and landowners, is key in implementing NFM+ and reducing flood risk.

We are currently meeting with local farmers, landowners, and tenants to explore the opportunities.

We encourage all those with an interest in the project to share their local knowledge, ideas, and concerns, and get in touch with us.