- 16th March 2018
- Posted by: Sophie Bunker
- Category: Projects
In 1978, Yorkshire Water constructed the Lobwood River Intake and Pumping Station on the River Wharfe near Bolton Abbey in West Yorkshire. The weir structure crosses the full width of the river and is a 35m wide reinforced concrete crump weir with a 750mm flat crest. A 300mm diameter PVC threader pipe extends along the full length of the weir structure carrying a water main. Scour protection in the form of grouted rock armour and gabion baskets is located immediately downstream of the structure.
The project involves the design of a fish and eel pass incorporated into the existing structure to allow the passage of migrating fish and eels over the weir. The design needed to ensure that the fish pass could be constructed safely within a river environment and also safely maintained and cleared of any debris in the future. The presence of shale at a relatively shallow depth also had to be considered when developing the design solution as well as the operational requirements of the client.
To enable the passage of fish and eels, a single flight Larinier pass has been designed. Larinier baffles are used to provide a suitable environment for the fish to negotiate the pass. The hydraulic design of the fish pass was completed by our specialist fish pass team in Saltaire and the engineering design was completed by our Tadcaster office.
To simplify construction, operation and maintenance, it was decided to locate the fish pass at the right bank of the river. An access ramp was included to allow plant to gain access to the fish pass and the river bed as a site enhancement to allow the client to maintain and clear the existing intake structure too.
The middle section of the existing weir has a vee notch and so, to ensure the fish pass works effectively, the design included a reinforced concrete detail to infill the vee notch and maintain a constant crest level across the weir.
Installing the fish pass means the top section of the existing weir crest is to be removed with the proposed fish pass structure founded on the remaining section of the weir structure.
Although the design of the fish and eel pass is relatively simple, the local constraints associated with the site, including the interaction with the existing weir structure, services and the client’s operational requirements at the site, added to the complexity of the design. From the start, the design was developed in 3D (as shown above) and so from an early stage the full impact of the local constraints became obvious. In addition, the 3D model made it simpler to demonstrate to the client how the installation would work and allowed them to determine if they were happy with it from an operational perspective.
Using 3D CAD allowed the client to request a change in the access arrangements to the fish pass. This allowed them to safely gain access to the river with plant in order to maintain other elements of the site – providing an improvement to the client beyond the installation of the fish pass.