Like the rest of the UK, Warwickshire is likely to face increased levels of flooding because of climate change. Mark Banning, Assistant Drainage Engineer in the Flood Risk and Water Management team at Warwickshire County Council (WCC), has written this blog to explain how he and his colleagues are working to find ways of working with the forces of nature, including water.
Working with developers
WCC already expects all developers to adopt the principals of Sustainable Drainage Systems (SuDS), when proposing or planning new developments.
As a statutory consultee on all major planning applications in the county, WCC works with developers to influence and guide this design and verify its appropriateness. We actively seek to manage risks in a number of ways and aim to ensure that any granted development is carried out in an appropriate and sustainable manner.
SuDS schemes are designed to control surface water run-off and mimic natural systems as closely as possible. Often you may see new developments built with attenuation, or storage, ponds. These aim to capture flows from the development site during a storm event, releasing them in a controlled manner after the storm.
Developers will be required to demonstrate as part of their planning submission that any such SuDS feature is adequately sized for various storm periods up to and including the one in 100-year event. Given we know that patterns of climate are changing there is also a requirement to make an allowance of 40% in this calculation for climate change.
New developments should not be viewed negatively and often provide wider benefits. In the case of SuDS it is no different, and WCC expects any developer within their proposed drainage strategy to demonstrate how multiple benefits will be delivered. Typically, benefits of a SuDS based drainage strategy will include not only provision for the control of flow volumes and rates, but also improvements in water quality, biodiversity and the creation of public amenable spaces.
Flooding within our communities
While much focus is often placed on maintaining watercourses and clearing drains, there are communities for which this will not prevent flooding.
As part of our duties as Lead Local Flood Authority, WCC has produced its Surface Water Management Plan (SWMP). This takes an evidenced based approach and blends both predicted flood risk against known events and reports, to produce a risk ranking of our most vulnerable communities. This has allowed us to prioritise locations for capital schemes, where typically DEFRA funding is bid for to deliver flood mitigation measured at a community level.
This funding is however highly competitive, and to access these funds, a detailed business case and design are required. It goes without saying that climate change must be considered in any design. Predictions for climate over the next century are that rainfall will increase. It is important that any flood schemes are designed with this change in mind, so that they remain effective throughout their life and do not become compromised or risk failure.
Depending on the design of a scheme, it is not uncommon for a structure to have an intended lifespan of many decades, if not longer. The vast number of Victorian culverts across the county highlight that major engineering projects are rarely a short-term endeavour.
All this work sits alongside Warwickshire’s investigations of reported flooding. From autumn to summer 2019/20 the Flood Risk Team received 480 separate reports of flooding, many of which related to internal property flooding. As a team, when we investigate, we aim to understand the causes and mechanisms of flooding, so that steps can be put in place to prevent or reduce the chances of it occurring again.
As a small team facing the pressures of receiving such volumes of reports, unfortunately we cannot investigate all reports as full as we would like to. We adopt a proportionate and risk-based approach, prioritising internal flooding to properties or flooding that creates a risk to life.
Often these investigations will centre around the maintenance of existing drainage assets. Where a landowner is felt to not be fulfilling their maintenance duty, the authority will step in with advice and guidance, or in the most serious cases, enforcement action. WCC can ask that drainage assets are maintained but cannot require landowners to undertake works to solve an existing problem. As such these reports are used to update our Surface Water Management Plan (SWMP) and where new and emerging areas of risk are identified, consideration will be given to the practicalities of delivering a wider flood mitigation scheme. Any such scheme should not be considered as a short-term solution, or a quick fix and most schemes delivered by Warwickshire have been developed over a number of years. All schemes that go forward to be delivered will need to be supported by a detailed and robust economic case and need to show that they are cost beneficial over the life of the scheme.
What you can do with our support
Many communities in Warwickshire are being empowered to reduce their own flood risk.
Several groups who are being supported by WCC and partners have taken the decision to deliver within the community natural flood management schemes (NFM). These schemes typically involve the creation of wetland areas, retention ponds and leaky dams in watercourses to replicate or restore natural landforms and processes.
These features are typically placed high up in the catchment and are intended to slow the flow, providing storage during storms. This means that whilst the total volume of water that ultimately passes through a town or village downstream remains the same, that volume of water should not pass through all at once and the peak of the flood should be reduced.
This perhaps shows how far flood management has come over the last few decades, as historically much effort has been placed on ensuring watercourses are kept clear, but in this instance real benefit is being achieve by actively obstructing upstream watercourses. NFM is unlikely to provide a complete solution in preventing flooding, but can reduce it, while offering an exciting opportunity to adapt for and mitigate our changing climate. The benefits do not stop there, NFM style flood schemes can have wide reaching wider benefits by reducing pollution, managing sediment transport and creating new areas of habitat.
To find out more about the risk of flooding where you live, the Environment Agency's Long Term Flood Risk map allows residents to quickly check the risk of their area. Information on how WCC manages flood risk can be found in the Local Flood Risk Management Strategy and Surface Water Management Plan.