Natural Flood Management-LWDs

We have just finished installing ten Large-Woody Debris structures (LWDs) at a small beck near Windermere, as part of our Natural Flood Management (NFM) programme.

NFM aims to reduce or delay the arrival of flood waters downstream, allowing for increased time to prepare for flooding events. This is brought about by restricting the progress of water using natural features and a variety of different techniques- one being Large Woody Debris (LWDs).Other techniques include: creating wetlands, bank restoration, land and soil management, creating woodland, runoff storage and so on. LWDs are used because they mimic the woody debris that form naturally when trees and debris fall into a watercourse. They cause water to be forced out onto the flood plain in storm events, slowing the flow in channel and increasing the volume of water temporarily retained on the land next to it.

We have installed water recording equipment to monitor the effects that these LWDs have. The LWDs are all different and the information provided will help assess the efficiency of the different LWD designs used. We will be returning to develop and upgrade some of these in the near future.

Below are some photographs of the project and a great video showing just how the LWDs work and how the water reacts when the beck is in high flow.

UPDATE

Our NFM officer, Simon Johnson has been back to Bell Beck site this October to see how the LWDs have faired. He spent a day ‘topping-up’ and extending the leaky dams installed this time last year. It is really important to regularly evaluate the condition of these NFM features and tweak them accordingly, to ensure there effective in high flows. These tweaks have also allowed us to build in natural strength and minimise the need for excessive use of cable to secure the dams. As Simon put it, ‘..these ‘Shaggy’ dams blend into the landscape really well & are great for biodiversity too!’.