Author: Merle Brown.
In 2021 the condition of the SSSIs that are fed by the River Brue were re-assessed as unfavourable declining due to water quality. Issues of high phosphate levels were exacerbated by low summer water levels and flooding events.
The Brue Headwaters Multi-benefit Project was set up in 2020 in conjunction with FWAGSW and the Environment Agency (EA) with partnership funding from Somerset Rivers Authority (SRA) to work with farmers and landowners to deliver nature-based solutions in the Brue Headwaters.
Solutions included assessing soils and providing management advice on soil structure and nutrient applications. Running soil management events to enable farmer -farmer learning. Creation of attenuation features to slow the flow of run-off to capture sediment and slow impacts of flooding. This includes attenuation ponds, leaky dams, tree planting, river and stream corridor restoration.
This project focussed on a farm located on the outskirts of the village of Batcombe. The village experiences regular flooding events as a result of runoff from surrounding farmland.
The immediate catchment is prone to rapid runoff and flashy responses to rainfall due to the steep topography, short catchment and limited attenuation. The project sought to capture and slow down run off from the headwaters of one of the contributing valleys.
The catchment valley comprised a mixture of permanent pasture, herbal leys and arable land. The farmyard has experienced regular flooding before water moves on to the valley below. The farmer was keen to implement measures to alleviate flooding and safeguard water quality leaving the land.
Soil assessments were carried out by FWAG SW in 2023 on fields at highest risk of runoff. In general, the soils were in a good condition with little evidence of compaction or other obvious barriers to infiltration.
We then moved onto identifying opportunities to implement nature-based solutions to intercept flow paths of water across the farm.
The following opportunities were identified:
- Creation of a mosaic of wetland features above and below the farm to intercept overland run-off. The features are designed to drain from one feature to the next allowing the capture and settlement of sediment and to allow captured runoff to drain back into the watercourse within 24 hours.
- Creation of a clay lined freshwater wildlife pond designed to collect rainwater and not runoff from ditches and streams to provide high quality freshwater habitat for wildlife.
- Woodland management to infill current ditches and slow flow/capture sediment.
- Cross slope woodland planting to intercept run-off and increase infiltration.
A series of wetland features were completed in Autumn 2024. SCALGO software was used to model expected impact on runoff and capacity created. Based on rainfall event of 30mm and using generic infiltration rates for pasture the following data was calculated:
Site 1:
Before: Modelled Runoff_30mm rain event 1,157.42 m³
After: Modelled Runoff_30mm rain event 674.39 m³
Temporary Capacity Created: 517 m³
Site 2:
Before: Modelled Runoff_30mm rain event: 5,574.22 m³
After: Modelled Runoff_30mm rain event: 4,810.15 m³
Temporary Capacity Created: 159 m³
Newly installed features have been monitored using trail cameras to ensure they are filling and draining regularly and to identify improvements required. Data loggers have been installed downstream of features to monitor impact of interventions during similar climatic event before and after installation. Woodland work and tree planting to be conducted in February 2025.
The landowners are pleased with the results and are confident it will ease flooding issues on farm and create valuable wildlife habitat. They also hope the features and the wildlife value will provide opportunities to diversify on the farm and create additional income.
Unsettled weather making site work uncertain and time constraints due to funding.
Woodland work and tree planting to be conducted in March 2025.
- Nature based solution can ease flooding and reduce runoff of sediment loaded water whilst created valuable wildlife habitat.
- Nature based solutions should begin with soil assessments and management advice followed by implementation of mitigation features if required (attenuation features etc.)
- Attenuation features need to be monitored to ensure effective functioning and ongoing benefits.
- Management of new woodland in early years (1-10yrs) essential to effective functioning as NBS in future.
- Funding opportunities are available to help with the creation of similar features. Contact FWAG for more details.
Sources of further information: www.ciria.org
The natural flood management manual (C802F)