River barriers made up of natural materials like trees, branches, logs and leaves can reduce flooding in at-risk communities by storing water upstream, new research has found.
The study, led by scientists from Cardiff University and the University of Worcester, assessed the impact of leaky barriers at a natural flood management site on a small Shropshire river over a period of two years.
Human-made leaky barriers, which are designed to imitate beaver dams, work in units of 50-100, deliberately raising water levels upstream to slow down river flow through storage and diversion, providing ecological benefits to the river corridor and on nearby farmland.
Until now scientists have used numerical modelling based on multiple assumptions to measure their impact, but the Cardiff and Worcester team gathered real data from 105 leaky barriers over a distance of three miles to understand how they operate when they are overtopped by flood waters.
Their study, published in the Journal of Hydrology, found the site's leaky barriers could store enough water to fill at least four Olympic-sized swimming pools during significant weather events such as Storm Dennis.
The team recorded raised water levels up to 0.8 metres at each barrier, which they say slowed the flow of the river during these storm events taking between seven and nine days to return to normal and protecting communities from flooding downstream.
Dr Catherine Wilson, a Reader at Cardiff University's School of Engineering and one of the study's authors, said: "In recent years, we've seen a significant increase in flood risk across the UK and internationally due to greater storm intensity and other climate change-related factors.
"Where flooding does occur, we often see extreme human and socio-economic cost. And so, it's vital that we better understand how to combat these events in the most effective way possible."
The team placed monitoring equipment on three channel-spanning leaky barriers to measure their effects on water levels upstream and downstream over time.
Further data was extracted from drone images of the site using a technique known as photogrammetry, which enabled the team to make extremely accurate measurements of the land elevation in areas of the river covered by trees and other flora.
