Deerness Feasibility Studies
The River Deerness catchment has had a long and productive industrial heritage, which has impacted heavily on the surrounding environment. Since the reclamation of coal mines in the area water quality has improved significantly and the Wear Rivers Trust is looking to make further improvements by addressing barriers to fish movement and enhancing in-stream habitat.
The River Deerness, a tributary of the River Browney, consists of four water bodies, of which three are failing to achieve the 'Good Ecological Status' (GES) required by the Water Framework Directive. One of the main reasons for this is low fish populations. The water body that does have GES is at top of the catchment and at risk of deteriorating due to downstream barriers to fish migration. WRT has used funds from Defra's River Improvement Fund to carry out feasibility studies relating to fish passage easement. Investigations have been carried out to identify suitable fish passage solutions and assess flood and hydromorphological effects.
Walkover surveys identified four separate barriers to migratory fish species: a culvert on Hedleyhope Burn at Cornsay Colliery; Broadgate Ford at Broadgate Farm on the River Deerness; Broadgate Weir, just downstream of the ford; and a road bridge at Ushaw Moor.
Feasibility studies have been carried out at each of the barriers by Pete Kerr of the Northumberland Rivers trust to assess easement options and propose solutions. Hydro-geomorphologist Professor Malcolm Newson also studied the barriers and assessed the proposed solutions for potential impacts on natural river processes. During this investigation stage, WRT have developed positive working partnerships with the Durham County Council Highways section, who own three of the structures, and also Durham University who have the resources to monitor the impact of proposed solutions.
Cornsay Colliery Culvert
Barrier: A circular steel ‘Armco’ culvert roughly 1.8m diameter and 25m long, with a drop into the downstream pool of probably 400mm in low flow conditions.
Proposed Solution: Create a ‘pre-barrage’ to raise the tailwater levels to drown out the culvert by 200mm in low flow conditions. A rock ramp with large keyed-in rocks would be cost-effective, possibly in conjunction with concrete or timber baffles in the culvert base. Velocities at the exit of the culvert are likely to be very high in flood conditions, and a key design requirement will therefore be durability in high flows.
This fish easement has now been installed. Click here to go to the project page.
Barrier: Ford designed to be dry in most flow conditions with flow passing through a series of 450mm diameter pipes under the ford. However, these pipes are frequently blocked by gravel and timber debris, resulting in the site becoming a ‘traditional ford’. This makes fish passage extremely difficult, and also has implications for nearby property due to frequently backed up levels.
Proposed Solution: Replace ford with a series of low, wide box culverts, without raising the road surface on top. This should increase channel area and reduce gravel blockages.
Barrier: The weir is 200m downstream of the ford. It presents a steeply sloping apron roughly 500mm high plus a vertical section of a similar height, impassable in low flow conditions and passable only by larger salmonids in high flows.
Proposed Solution: Removing the weir is likely to have an effect on the ford upstream, with incision possibly leading to increased erosion at the downstream side of the ford. The weir is holding back sediment up to roughly 100mm below the crest. Lowering the weir would therefore lead to significant material being released downstream. Options at the site include partially lowering the weir (by perhaps 500mm in the centre) in combination with either a rock ‘pre-barrage’ to raise tailwater levels or a rock ramp. Other alternatives include a pool and traverse pass or a larinier extending upstream within side walls. These later two options could be in conjunction with a separate eel pass.
Ushaw Moor Road Bridge
Barrier: A series of concrete steps result in very shallow flow in low flow conditions, and extend to a sloping concrete apron beneath the bridge structure. This apron is damaged in sections, with stone cobbles beneath.
Proposed Solutions: There are a number of possible options including rock ramps, baffles in conjunction with pools at the concrete steps, or larinier sections with resting pools. All of the options could be expensive, and also carry risks due to apparent gravel movement at the site (which could block a larinier), and high energy flood flows carrying woody debris (possibly damaging baffle systems or blocking pools). A solution would need to accommodate the bed level on the downstream side dropping further.
Defra's Catchment Restoration Fund was applied to for funding to implement the proposed fish-easement solutions at each barrier, carry out additional habitat improvements and carry out 'before and after' monitoring throughout. This bid was successful and the River Deerness Restoration Project will now be carried out over a three year period.
The implementation of these solutions will open up the whole of the Deerness catchment (over 25 km) for fish of all species. Access to excellent spawning habitat will increase recruitment and benefit the whole of the river ecosystem.
Funders and supporters of the project: