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Cong Burn Fish Easement

A weir on the Cong Burn, near its confluence with the River Wear, posed a significant barrier to migratory fish. In 2011 the Wear Rivers Trust carried out its first rock-ramp project to ease fish passage on this tributary.


The Cong Burn sub-catchment comprises approximately 41km2 of varied land including heathland around Waldridge Fell, woodland, many old mine workings and a large part of Chester-le-Street. The Burn is prone to flash flooding during periods of heavy rainfall but provides a top-quality spawning habitat for a wide range of fish species, including lamprey and trout.

Restricting access for migratory fish was a weir carrying the main sewer inlet to Chester-le-Street Sewage Treatment Works, located just 50 metres upstream from the confluence with the main river. As this obstruction could not be removed, an easement was designed to enable fish to get past it.

The easement took the form of a rock ramp: a series of pools and small cascades for fish to negotiate, designed to look as natural as possible. The rock ramp creates a 1:20 slope, raising the water level to drown out the existing weir. The weir is situated within the popular Riverside Park, with very restricted access for large vehicles, so equipment and 230 tonnes of stone were delivered to the site via the sewage treatment works. A storage area was created and segregated from the public by the temporary closure of a short section of public footpath including the lower footbridge, just above the confluence. Machinery and the stone to form the rock ramp were tracked up the stream bed and underneath the footbridge. Eden Stonework Ltd completed construction in one week in June 2011.

The series of high river levels and floods in 2012 caused serious erosion to both banks of the Cong Burn in the reach where the fish pass is located, washing out rock armour and scouring around the fish pass. The fish pass itself was left functional but the banks and surrounding footpaths needed reinstating. Wear Rivers Trust has worked with Durham County Council and Chester-le-Street Angling Club to repair damage. In Spring 2013 a log-jam was built into the south bank and planted with willow to secure the bank via soft revetment. This is the first time Wear Rivers Trust has tried the log-jam as a bank revetment technique and we are very pleased with the outcome. Durham County Council is now working to secure the banks further upstream.


 

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