Ushaw Moor Bridge Easement
The bridge apron under Ushaw Moor road bridge acted as a significant barrier to fish moving both upstream and downstream. A nature-like fish pass know as a rock ramp was therefore built into the exisiting concrete apron to enable fish to pass the obstruction.
This particular easement was chosen as the most effective option due to the need to retain the integrity of the existing apron and to utilise the gradient of the concrete steps. Rock ramps are traditionally created using large boulders locked into position using nothing more than the stream bed, but at this site significant volumes of concrete, dowels and reinforcement were needed to secure everything into position.
The fish pass is a 4m section running along the right hand buttress; it is differentiated on the apron by means of a drop in level of 0.4m from the main apron section. This was achieved by raising the level of the main apron with new concrete. Large stones were dowelled and placed in the new channel section and embedded into the new concrete base. The stones act as baffles, concentrating the flow toward the middle of the channel. River cobbles were spread between the larger stones to roughen and naturlise the base and the channel edge.
Large 2 tonne blocks were placed on each step, forming the left edge of the fish pass. A concrete bed was laid down the steps beginning at a level with the new apron channel and running down the series of four steps at a slope of approximately 17.5% (0.96m fall over 5.5m).
Additional dowelled stones were placed on the front edges of steps two and three at depths of between 50 to 200mm in continuous concrete. River cobbles were scattered between the larger stones. A further line of large stones below the bottom of step four shows approximately 200mm above the new concrete base, extending the slope and reducing the final gradient.
An outlet pool was constructed, utilising large stones to construct rock armour edges and to reinforce the bottom of the pool. The pool exit was also reinforced by large stones which were well-buried to avoid the creation of a step either through the formation of a scour pool or scouring away the bed material. All the construction work was carried out by a team from Durham County Council.
Fish were observed making their way up the new easement within weeks of the project's completetion and local residents have reported very much enjoying the spectacle.
Funders and supporters of this project: