The following information was provided by: The River Restoration Centre
Historically a degraded river due to its industrial heritage, water quality on the Calder has been significantly improved over the last 20 years allowing coarse fish populations to return. However, in-channel obstructions have prevented the migration of fish, including eels, to approximately 20km of spawning grounds and habitat further upstream.
The ambitious River Calder Fish Migration Improvement project was led by the Environment Agency and the Ribble Rivers Trust to link isolated sections of watercourse. The project aim was to restore fish passage on the River Calder. This was achieved by reducing the height of the existing weir as well as installing a rock ramp.
Padiham Weir was built in the 1950s to provide water to teh now demolished power station. At 1.85m, it was the largest weir on the Calder and created a total barrier to all fish migration. Since 2000, Padiham Weir had been the subject of a number of different fish passage proposals including a pool-and-traverse scheme, the installation of a technical Larinier fish pass, and even a white water canoe course. An initial hydromorphological assessment concluded that the impact of the weir removal on sediment transport, water levels and the flow regime would be beneficial.
Three bed check weirs, all 0.3m high, were installed in phases using an excavator, working from downstream up towards the existing weir. Once the installation of the bed check weirs was complete, the existing weir was partially deconstructed and now effectively acts as a fourth check weir.
Upstream migration of fish species has been achieved with adult Atlantic salmon and sea trout observed upstream of the site. Juvenile population numbers are yet to be recorded upstream of the weir but have been identified immediately downstream.
Electrofishing surveys and redd counts were carried out following the completion of the works in the summer of 2010. RRT have conducted surveys every year for 11 years upstream. At 2 locations they found salmon fry where they couldn’t get to before! The excitement, is that both the locations are upstream of fish passage projects RRT delivered on different tributaries! One through a technical fish pass, and the other through a weir removal and two rock ramps! Grayling Numbers have also swelled upstream as a result.
The total cost amounted to £406,000. The project was funded by Lancashire Environmental Fund (a grant giving trust, that disperses landfill tax funds), River Improvement Fund (The Rivers Trust) and The Environment Agency.
The Environment Agency have confirmed that if the weir hadn’t been removed, during the boxing day floods of 2015, many more properties and a large industrial estate would have flooded. Causing misery and jobs to be lost. So weir/dam removal is important to the whole of society not just fish.