Stoke Brook Flood Alleviation and Habitat Enhancement

Background The Stoke Brook (upstream of the A418), is very disconnected from its floodplain. It has also been significantly straightened. This leaves the channel very uniform in terms of habitat. The channel is very wide for the low flows in the summer.

The increased gradient caused by the straightening and the lack of connection with the floodplain, means that the stream power under high flows is more than would naturally occur. This has led to erosion along large sections. Some of the reach runs very close to the houses and in these places the erosion poses a real risk to property.

The channel is trying to reach a more natural state through erosion and deposition and there are pool and riffle features developing especially in the upper section.

It is evident that the channel vegetation is heavily managed – macrophytes and marginal vegetation were virtually non-existent. Removal of vegetation can be crucial for places of critical flood risk but removal of anymore than 50-60% macrophyte cover generally provides little extra flood benefit.  Through this project it might be possible to work with the local community to try and influence this management.

In February 2014, 79 properties on the Willows Estate, adjacent to the Stoke Brook, flooded.  In the Buckinghamshire County Council Flood Investigation Report, it states ‘the flooding appears to have been from the river overtopping the banks at low spots along the banks across the green area adjacent to Dormer Close and Parrot Close’.  There are several reasons for the flooding to have occurred including; the undersized culvert where the Stoke Brook flows under the A418, surface water outfalls being blocked and a saturated catchment.

There are multiple issues associated with the watercourse – flood risk, proximity to the housing, erosion risk, lack of habitat diversity etc. Given the land use on the left hand bank is extensive pasture/grazing and that HS2 are looking for opportunities that may provide multiple benefits – there is a very feasible project opportunity. This project could potentially improve flood risk and biodiversity – helping achieve WFD objectives.