In 2016, the EA secured a five-year funding package from the Thames Regional Flood & Coast Committee (RFCC) to trial a range of these NFM solutions for Littlestock Brook. The project used the Catchment Based Approach (CaBA), which involves collaboration between local communities and other partners. Increasingly popular, there are now over 100 catchments in the UK using catchment partnerships to deliver a range of environmental, social and economic benefits, and protect water environments, according to the CaBA website.
Jo Old, NFM project manager at the EA explains: “The RFCC funding was combined with Environment Agency environment and flood risk funding, as well as contributions from partners such as Thames Water and the Parish Council. We also received in-kind contributions of time and resources from many interested parties.
“Importantly, we were blessed with forward-thinking landowners, the Bruern Estate, owned by the Astor family. With all NFM projects, the power of a positive landowner relationship cannot be stressed enough. In this case, the enthusiasm and engagement of the farm manager, Matt Childs, was instrumental in delivering an effective scheme.”
For NFM schemes, supportive landowners are not only crucial because they need to agree to major works on their land, but also to ensure that NFM measures live on in the landscape well into the future. NFM needs to be integrated into agricultural businesses and, ideally, funded through associated land management schemes. In a future of ‘payment for public goods’ the services of improved water quality, flood storage, carbon capture and habitat creation could easily be delivered by landowners adopting NFM measures.
Matt Childs, farm manager at the Bruern Estate, explains what the project has helped achieve: “Getting involved in this scheme encompasses many of the values that are important to us in managing the Bruern Estate: helping the local community; improving soil and water quality; creating new habitat and increasing biodiversity. To be able to accomplish all these aims in one project highlights what can be achieved by working in partnership.”
In the project’s first year, key partners, including the Bruern Estate, the EA, Parish Council and Wild Oxfordshire, set up a tributary catchment trial for Littlestock Brook, using ‘opportunity mapping’ and site walkovers to plan and implement a suite of NFM measures. These included: creating temporary water retention ponds in field corners; constructing bunds and scrapes to store more floodwater on grassland areas; installing woody material in the brook’s channel to create leaky dams; and land management changes, including planting woodland in flood source areas and along flood pathways.
This was a great start, and Wild Oxfordshire and the EA were keen to use more technical analysis. And the timing couldn’t have been better, with HR Wallingford, the internationally renowned hydraulics organisation based in Oxfordshire, already setting out to prove the benefits of NFM, a question that has long needed an answer.
Spotting that there was very little evidence to demonstrate the actual performance of NFM, HR Wallingford wanted to see how useful NFM measures were in practice by using very detailed analysis, which could then be used to guide the design of future schemes. This is hugely advantageous as it allows those managing schemes to: quantify the impacts of NFM measures; estimate changes in flooding from schemes; and calculate savings from the reduction in flood damages.
In 2017, keen to employ its science-led approach to a real-life project, and hopefully demonstrate its success, HR Wallingford asked the EA to use Littlestock Brook as a test case. The initial work was part of HR Wallingford’s internally-funded research programme, which it uses to help solve the world’s most pressing water-related problems.
Wild Oxfordshire and the EA subsequently asked HR Wallingford to predict water flow throughout the catchment, and then, in 2019, to help develop and design NFM measures using the kind of rigorous engineering practice usually reserved for much bigger flood defence projects.
In this case, the approach for protecting the village from flooding was relatively simple – build a series of landscaped earthworks in the corners of fields to store excess rainwater and release it slowly back into the brook. However, the process for doing this was anything but straightforward.
On the modelling side, the team looked at rainfall across the catchment to map overland flow paths and identify where the field corner bunds could be built. The 2D model was extremely detailed, taking into account bridges, culverts and driveway drainage and used seven rainfall scenarios, two of which took climate change into account. An initial high-level investigation identified potential areas for NFM measures and this was followed by more detailed modelling of some of the recommended sites. The model was also able to show the benefits of reduced flow volumes in the brook to the areas around the residential properties.
Whilst other bunds had been built earlier in the project, those closest to the village were considered the most crucial and given special treatment. Working together, the catchment partnership and HR Wallingford identified various sites and then narrowed these down to two fields: New Field and Little Meadow, both located on the Bruern Estate. In 2019 the development of the two embankments was given the green light by the progressive landowner.
The team then looked at the viability of various structures for the two different fields, creating conceptual designs for mildly sloping clay bunds, before going on to develop them into detailed designs. These used a quantified and structured approach and took hydraulic, constructional and environmental considerations into account. They also looked at design criteria, such as whether there was sufficient freeboard, as well the location of overflow spillways to release surplus water, and drainage pipes for draining the areas after a flood.
Another consideration was ensuring that the volume of water stored behind each embankment was less than 10,000m3, to avoid the areas being classified as small dams under the Reservoirs Act. Small dams are subject to regular inspection requirements, causing additional complications and cost for the landowner. Using the model, HR Wallingford was able to show how much water would be stored behind the new bunds, ensuring the limit was not exceeded.