Cornsay Colliery Fish Easement
The fish easement at Cornsay Colliery was the first to be delivered as part of the River Deerness Restoration Project. A road culvert on Hedleyhope Burn, a tributary of River Deerness, was addressed in September 2012.
The Hedleyhope Burn measures 9.2km in length and flows down from Tow Law into the Deerness at Esh Winning. The road culvert at Cornsay Colliery had been cutting off access to over 5km of good quality habitat under most flow conditions as the culvert, a 30m corrugated steel pipe, had rapid and very shallow uniform flows when water levels were low and extremely fast, concentrated high velocity flows at high water. The extensive erosion pool immediately downstream of the culvert was evidence of the force of the water leaving the culvert. A wide concrete step, normally rising 150 to 200mm above the surface of the water, obstructed fish from gaining access to, and attempting to run, the culvert itself.
The corrugated iron cladding running through the culvert meant it was not possible to install baffles to create rest areas within the culvert itself without seriously affecting its structural integrity. The solution agreed was to replace the scour pool with a series of rock pools which would provide a variety of flows for different fish species and drown out the concrete step by increasing the water level to create slower, deeper flow through the culvert. Backing up water does not increase flood risk under any flow conditions as the site lies within a deep depression with no vulnerable residential or industrial buildings upstream or downstream.
The site is owned by Durham County Council, who contributed half of the cost of the easement as match funding. The Highways Department cleared the site, and the Bridges Team worked with the Wear Rivers Trust to construct the fish pass. An access road was constructed into the burn with straw bales placed downstream to trap any disturbed sediment. Large rocks were buried and keyed-in to create a series of pools and coarse gravel and sandbags full of quick-setting concrete were used to plug gaps. Surplus rock armour was used along the northern bank to reduce erosion and willow spiling will be installed at a later stage to further protect the banks from high flows.
Funders and supporters of this project: