Leaky dams

Leaky dams (also known as large woody debris dams or leaky barriers) are just one of a range of measures and techniques that belong under the banner of Natural Flood Management (NFM). Natural flood management involves implementing measures to:

Restore or mimic natural functions of rivers, floodplains and the wider catchment, or
Store water in the landscape, either in the river or in the soil, or
Intercept rainfall to prevent it from reaching the river in the first place, and/or
Slow the rate at which water runs off the land into rivers.

Leaky dams mimic the natural obstruction caused by trees and branches falling into the river. They range from a single large branch to several tree trunks tied together.

In the Eden catchment, our preferred method is to construct a type of leaky dam often known as a large woody dam. These are whole tree trunks sourced locally, placed across the stream and secured into place with stakes and wires on either side of the riverbank. The tree trunks are set above the normal stream/beck level, so normal flow and fish movement is not impeded.

Leaky by name, leaky by nature, even during high flows, they will only let a certain amount of water through, slowly draining the trapped water to reduce the flood peak.

They are suited to smaller watercourses less than 2m wide, so we focus on installing leaky dams on smaller becks and streams in upland areas.

The cost of installation and ongoing maintenance is low. Leaky dams do need to be cleared of debris and sediment occasionally so that water can still flow through the gaps. This reduces the likelihood of water flowing over the top of the barrier.

How you can help

We are currently working on Natural Flood Management initiatives in the following catchments: Cairn Beck, Trout Beck, (possibly future areas of Croglin and Renwick) areas. Please get in touch with us on 01768 866788 to talk to our NFM team and find out more about which NFM measures might be appropriate for your land.

Did you know?

As each dam will only hold back or slow a relatively small volume of water. They work best where a series of leaky dams are strategically placed along a stretch of river.

We have trialled laying large, single tree trunks horizontally on hillsides where storm channels develop to temporarily store water further up the hillside during heavy rain.

Leaky dams are also good for in-stream habitat – trapping sediment which improves water quality and providing habitat for fish through creating pools and cover.