Slowing the flow to stop flooding
National Trust works with volunteer group on ‘leaky’ dams project to reduce risk to towns in Calder Valley
THE CALDER Valley has suffered more than most of Yorkshire from catastrophic flooding events in recent years.
Weather systems such as Storm Desmond in 2015 preyed on the area’s topography to wreak havoc in towns such as Hebden Bridge, Todmorden and Mytholmroyd at the bottom of the steep-sided valleys.
Yet the impact of the extreme weather has helped to raise awareness of the effects that land management has on increasing flood risk – and spurred landowners and members of the public alike to take action.
The National Trust is among the biggest landowners in the Calder Valley, along with Yorkshire Water, and they have been working with a volunteer group, Slow the Flow, to install natural flood mitigation measures at sites such as Hardcastle Crags, Hebden Water and Gorple Reservoirs.
The project, which began in 2019, has seen more than 800 ‘leaky’ dams built in woodland and on moorland to slow down the flow of rainfall and avoid sudden deluges onto the settlements below.
The majority of the £2.6m of funding came from the West Yorkshire Combined Authority – an unusual source as it normally focuses on transport schemes – with additional contributions from the Government.
Project manager Rosie Holdsworth attributes the scheme’s success in part to the level of interest in environmental issues in the famously ecoconscious Calder Valley, with large numbers of volunteers coming forward.
She said: “Flooding is a massive issue in the Calder Valley and we’re very aware there is a lot of work we can do to reduce the risk.
“The dambuilding has been so successful that we want to expand it across our and Yorkshire Water’s land holdings – there are vast opportunities in the Pennine corridor, in the Wassenden Valley and up to Marsden Moor where we have been planting new woodland.
“The causes of flooding are complex and it’s difficult to pinpoint one particular factor as being responsible. “Soil erosion, the degradation of vegetation, loss of tree cover all contribute. “But we have these steep-sided valley and huge uplands that just funnel rainfall down them really quickly. It’s about playing around with the ground cover and tinkering with the things we can control.”
The leaky dams are designed to hold small volumes of water over relatively short periods of time – between 12 and 24 hours – to reduce the peak of water and ‘flatten the curve’ before it is released down the valley.
Although each structure makes only a small contribution to the effort, with 860 now in operation, they will have a cumulative effect.
The University of Leeds has been monitoring each site with time lapse cameras, and although the multiple factors at play in the River Calder’s catchment mean it is difficult to assess their impact so far, the dams are working as intended.
The dambuilding has been so successful that we want to expand it. Project manager Rosie Holdsworth.