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More than just a few bits of woody debris...

26/11/2020

5 Comments

 
Large Woody Debris (LWD), or leaky dams is one of the most utilised Natural Flood Management technique. In the right locations they can provide a cheap and easy way to reducing flood risk, particularly when applied at a catchment scale. The range of benefits these structures provide, is only matched by the diversity in their style and construction method. Ranging from naturalistic dams utilising materials from the site in which they sit, to heavily engineered structures made from fabricated materials. They all aim to reduce flood risk by intercepting the flow of water in watercourse and helping to restore river-floodplain connectivity, thereby reducing flood peaks, slowing water velocities and attenuating flow by storing water on the floodplain. 
At the Sussex Flow Initiative (SFI), we are interested in all of the benefits that leaky dams provide, but we are particularly excited about their potential for making our landscapes more resilient to the extreme and unpredictable events of climate change. The benefits wheels below (taken from the Environment Agency’s Working with Natural Processes evidence base) helps to illustrate just how many benefits leaky dams can have across a whole range of ecosystem services.
Picture
Types of benefits provided by LWD.
SFI aims to create naturalistic structures that blend into the landscape, utilising local material where possible. There are a variety of types of the LWD, the three main types used by the project are outline below. Further information on these can be found in 'SFI's Leaky Dam Guidance Document'.
Picture
SFI's Leaky Dam Guidance Document - Click image to open

Types of LWD 

Banktop diverters 
Large woody debris is positioned and fixed across the banktop in streams and ditches, engaging high flows, holding back water and encourage it out onto the floodplain.  
Picture
Banktop diverter backing up high flows and pushing water out into the wider woodland.
​Leaky dams 
​
In addition to a banktop diverter, woody material is added into and secured within the channel. This therefore means the structures are active earlier, at lower flow rates. The leaky construction maintains the watercourses base flow and ensure there is still fish passage.
Picture
Leaky dams still enabling fish passage and base flow, but engaging at lower flow rates.
​Gully stuffing 
​Woody materials is positioned and secured longitudinally within the channel to slow the flow of water and trap sediment. This type of LWD
 is typically used within relic drainage ditches within heathlands and woodlands.
These naturalistic structures emulate the natural process of wind blown trees or the dams that would have been created by beavers before they were lost from our landscape 400 years ago. The images below show how these structures can could just be a collection of sticks to fall length trees secured in place, but they are all:
  • Improving water quality and reducing sedimentation in streams,
  • Providing instream habitat and promoting new habitat formation,
  • Kick starting natural processes to restore more natural stream habitat,
  • Increasing drought resilience by holding back more water in the landscape; as well as
  • Reducing flood risk.
5 Comments
Iris Alban link
16/9/2022 11:59:25 am

Great ideas! This will certainly improve anyone's stamped concretes.

Reply
Sherwin Alvarez link
17/9/2022 06:37:56 am

Great article! Definitely going to save site for my future endeavors into planting.

Reply
Bane link
17/9/2022 07:02:23 am

Thank you so much for providing me with a great guide on why you can't just cut any branch you like when tree trimming.

Reply
Robin link
20/10/2022 08:07:58 am

Professionals have the proper equipment and tools to safely and effectively remove trees. Professionals can provide advice on how to properly care for trees and prevent future problems.

Reply
Donny link
24/10/2022 05:44:08 am

There are a lot of things to consider

Reply



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  • Home
  • About
    • Natural Flood Management
    • Beavers
    • Links and Resources
  • Our Work
    • Woodlands
    • Hedgerows
    • Wood in rivers
    • Flood Storage Ponds
    • Washland meadows
    • Annual Reports
  • Case Studies
  • Ouse Catchment
  • News
  • Get Involved
    • Volunteering
    • Research Projects
  • Contact Us