Case Study: Wetland restoration, Goss Moor NNR

Flow deflectors on the River Fal


Willow faggots form the basis of a leaky dam


Leaky dam

 

Our contracting team undertook 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.

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.

Felling work was undertaken by traditional chain-saw work, but we minimised ground damage by using a mobile two-stroke engine winch, for extraction of willow used in the dams.  This minimised heavy plant access and damage to groundflora. 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.

During the contract we were able to improve and develop the design of both the leaky dams, and the flow deflectors.  This enabled the installation of more dams and better flow deflectors at no additional cost to Natural England.  Longer term, however, the site management team would quite like to see beavers undertaking the role in a more natural way!