Our contracting team have recently completed a “Peatland Hydrological Restoration Project” for Natural England at Goss Moor National Nature Reserve in Cornwall. The aim was mainly to raise the water table locally, and also introduce some natural meandering processes in to the River Fal. The chosen methods on this occasion were a series of leaky dams on side drains and flow deflectors on the river channel. Longer term, the site manager, Steve Hall, would prefer to see beavers doing the work.
Leaky dams are getting a higher profile these days, as they are being tested and experimented with in a number of locations for flood alleviation: slow the peak flows upstream, and reduce flooding downstream. Experimental sites have included locations in North Yorkshire and around Stroud in Gloucestershire. We saw some of the Stroud trials two years ago, when working on the Ebworth Estate for the National Trust.
Goss Moor NNR has a long history of constant reworking for tin and then gravel. A very small River Fal flows through the reserve, and was canalised perhaps 40 years ago, to help with a rapid release of water from an old china clay reservoir. In recent years, ground disturbance has been much less than it used to be. The site has also dried out to an extent and willow and gorse have spread, to the detriment of some of the rarer species.
Natural England have tried some large scale willow clearance, and recently reintroduced grazing by cattle, but the focus of our work was raising water tables, and seeking to encourage the River Fal to return naturally to a more meandering course. Leaky dams were installed in some side drains, with a mix of willow cut on site and some soil. The willow was both bundled into faggots and packed down with earth. Some of the branches will root into the surrounding soil, helping form a permanent partial blockage and raise the local water table.
Our chain-saw operators had expert help from Mike in a wide tracked 13 tonne excavator, and of course in this sensitive habitat we all used biodegradable oils, excavator included. Having finished the works in good time and on schedule, we added a few scrapes for ephemeral aquatic plants (they like temporary puddles), and pushed back some sections of gorse, to increase access for the grazing cattle.
Areas of wet bog, meandering rivers and small ponds and pools have been largely lost as a result of centuries of agricultural improvement, and even perhaps misguided flood prevention schemes. Habitat loss in turn affects many native species, including the formerly native European Beaver. Beavers were hunted for fur and became extinct in Great Britain, the last recorded one being shot in Scotland in 1526. They were great for introducing small dams and creating boggy areas, which are now seen as possible solutions to soak up flood water and reduce the risk of flooding in downstream towns. There is a major scheme now underway to reintroduce beavers into Scotland, and an experimental site has run in North Devon for several years. A colony also lives wild on the River Otter in south Devon; perhaps in time Goss Moor will follow. Rewilding, using natural processes, is better than even the best excavator operator (sorry Mike!)