Over the past year at Burrator, we have been creating leaky dams and willow bundles. Both act as a way to slow down the flow of water, as a method of natural flood management, and a means to create new habitats.

Willow Bundles

Willow bundle dams are easy to assemble and have many purposes. Our volunteers have spent many days coppicing willow and crafting bundles. Willow is easily twisted and wrapped into tight bundles, which allow little water through. These bundles can be staked into the ground using larger willow branches, which hold the bundle close to the ground. Over time, rainwater running off the hill will bring debris down with it, blocking the remaining gaps between the willow and the ground, helping to make a more impermeable barrier.


Bundles are placed in areas where water runoff is high and rainwater can be stored. This is important for both heavy rainfall events and drought periods. During periods of heavy rain, water will take longer to reach the reservoir and therefore this important resource will not be lost. In catchments where there is no reservoir, this will also alleviate flood risk down-stream. During droughts, pools of water may be retained behind the dams, which provide an important habitat for many species and create a slow-release system of water storage, allowing water resources to last longer.

Dams may be placed mid-stream were small tributaries run through wet grassland. This helps to slow down the flow of water, holding it in small pools. The first photo shows a dam when it was first installed, with a narrow stream of water running through. The second photo was taken in the same area this summer. As you can see, the dam has worked to create a boggy pool, with wetland species such as bog cotton grass. The willow from the dam has also begun to sprout. This will eventually connect surrounding areas of wet woodland, improving soil permeability by holding water between its roots.


This is the dam when it was first installed.                                   This the same area after a boggy pool has formed.

Another option is to place dams on open hillsides where rainwater gathers during flash flood events. The dams shown below have been placed alongside an acid flush with good quality peat characteristics. These include a diverse Sphagnum moss species, which hold up to 20 times their own weight in water, and extensive bog asphodel and bell heathers, which provide important nectar sources for pollinators. Alongside this flush is a drier area of peaty soil, which sees a vast amount of rainwater runoff. Here leaky dams have been placed ahead of flatter areas, to create pools of water. With time, pools may create an environment suitable for the nearby Sphagnum mosses to grow into, and the peatland flush may be expanded, with water storage capacity improved.


Leaky Log Dams

As well as willow dams on the flood plains and minor streams, we have been making leaky dams from logs and trees overhanging the river. Contractors spent two weeks in August carefully selecting and felling dead ash trees and conifers to use as dams. Similar to the willow dams, these will slow down the flow of water during peak flows, create new habitats for fish and move water onto the floodplain to increase catchment water storage capacity.

Dams are placed carefully so that during normal flows they are above the water level and during peak flows they hold back water. This works to slow the flow, and move water more regularly onto the floodplain, so that wetland habitats such as marshy grassland and wet woodland are created and maintained alongside the river. These habitats hold water and improve biodiversity by making many harbouring places for insects, which provide a food source for birds. Additionally, within the river, obstacles cause water to scour the river bed and banks, which in turn create habitats where fish can harbour and breed.


The below photos show where dams are in the river during normal flow and during a peak flow event. One photo show where the log is diverting water from the river onto the floodplain, reconnecting the wetlands, and the second shows water flowing over a log mid-stream.



This work is part of South West Water’s Green Recovery project, aiming to improve biodiversity throughout the catchment of Burrator Reservoir, and part of the wider Upstream Thinking project.