News
Water Friendly Farming research has shown which leaky dam design features give the best chance of reducing flooding after multiple storm events. The study highlights the importance of increasing a dam’s permeability and positioning the gap at the base of the barrier well above winter flows to maximise water storage.
The research team, led by the University of York, focused on 27 leaky barriers, which were installed in the headwater of the Eye Brook, part of the Water Friendly Farming demonstration site, between 2016 and 2018. The team used water level data, which has been captured by monitoring the headwater catchment outlet every 15 minutes since 2012. They were then able to model flow data from before and after leaky barrier installation. The team also analysed time-lapse photography taken during storm events.
The researchers used this data to simulate the performance of the leaky dams for a range of storm events over a three-year period. This enabled them to assess the storage capacity of the dams and the effect of their performance on downstream flow.
Across 11 recorded storm events, the dams provided up to 17,700 cubic metres of water storage and delayed peak flow by up to five hours. The analysis showed that barriers need to be permeable to speed-up the time it takes for each dam to drain down and mitigate the risk of flooding caused by consecutive storm events.
The gap at the base of the barriers proved to be particularly important. The study showed that a vertical gap that is higher than average winter flows allows the barrier to retain water only during the largest flow events. This increases storage availability during flood events, reduces channel erosion and increases the lifespan of the leaky barriers.
This is the first study of its kind to focus on multiple storms, rather than single peak flow events. Storm events and flooding are expected to become more frequent as a result of climate change. Natural flood management techniques, including the installation of leaky dams, are increasingly popular and have been incentivised through various stewardship schemes.
The study was carried out by the University of York, Game & Wildlife Conservation Trust’s Allerton Project and Freshwater Habitats Trust. It was published in the journal River Research and Applications.
