With all the flooding events that have occurred across the UK this winter I thought it was pertinent to write about the work we have been doing with Stroud District Council ‘slowing the flow’ in the Sheepscombe and Cranham valleys. Work began at Ebworth in 2014 as one of the early adopters of the SDC project in the District. Chris Uttley the Project Officer has contributed the following article below:
Like other parts of Gloucestershire, the Stroud Valleys suffered extensive flooding during the summer of 2007. Every year since has seen flooding in some parts of the Stroud Valleys. Of particular concern to residents and the District Council is the designation by the Environment Agency of the Slad Valley as at risk of destructive flash flooding, of a similar type to the event that destroyed parts of Boscastle in Cornwall.
After the flooding in 2007, community flood action groups were established in the Slad and Painswick Valleys and also the lower Frome. They have campaigned for better protection for residents and properties from flooding, but over the years, communities and authorities have realised that the River Frome and its tributaries, are not suited to hard engineered solutions to the issue. This is in part due to the physical nature of the catchment and the distribution of the properties at risk, but also due to the heritage and aesthetic value of the Stroud valleys.
In 2012, the Environment Agency commissioned a report into the feasibility and potential benefits of implementing Natural Flood Management (also called Rural Sustainable Drainage) (RSuDS) throughout the catchment of the Frome and associated tributaries. This is an approach that attempts to slow down the rate at which flood peaks develop and move down the valleys by putting in place measures to keep as much water upstream as possible. We can do this by making it more difficult for water to move down the valley and allowing more time for it to soakaway into the ground.
To help achieve this, Stroud District Council has been working with the National Trust on the Ebworth estate. Together, we have been using timber felled as part of normal woodland management to construct large leaky log jams in the brook as it flows through the woodland. These log jams are fixed in place with reinforced steel bars. The log jams will do a number of things. Firstly, they will slow down the rate of flow of water through the woods, meaning the water will take longer to reach peak flows and will drain away at a slower rate. The log jams will trap soil and sediment, meaning there is less movement of silt down the stream. Build-up of silt can cause significant problems lower down the brooks and in the River Frome. The log jams are secured safely in place, but they will actually trap smaller twigs and branches that would otherwise move downstream and cause a problem.
You may also have noticed some larger trees have been felled and laid across the valley floor above the ponds. These trunks will divert high flows onto the woodland floor and increase the rate at which water will soak back into the ground here. We have also created a few temporary ponds, in which water will be stored during periods of high rainfall. All of the work is designed to slow the flow of flood water down the brook towards Painswick and Stroud and slow down the rate at which silt travels down the brooks.
One other piece of work we have carried out involves the installation of piped culverts where water courses across the forestry tracks within the wood. Normally a pipe increases the speed of flow however we have designed these installations to have a deep catch pit at the entrance of the pipe, in normal flow most often results in the water infiltrating back underground. At the exit of the pipe, another deep pit incorporates rocky boulders to reduce the erosive force of water flowing out of the pipe at speed and to spread the water into the forest floor beyond the track edge.
So there you have it, this article has hopefully explained more about those funny beaver-type constructions we have made within woods and fields at Ebworth. The National Trust is keen to be actively involved in a project such as this, where natural processes go far beyond ownership boundaries.
Matt Stanway, Area Ranger Ebworth Estate