Construction of Rock Ramp Fish Easement, Hoghton Bottoms

Description

Blackburn's Rivers Important to Lancashire's Landscape and Natural Capital Economy (BRILLIaNCE) is an ambitious project supported with funding from the European Structual and Investment Fund to deliver physical improvements to the Rivers Darwen and Roddlesworth within Blackburn. We are seeking interest from suitable Civil Engineering Contractors to deliver the creation of a fish easement in the form of a rock ramp. Specifically the works are required to construct a fish easement on Hoghton Bottoms Weir on the River Darwen. The weir is a high vertical horse-shoe stone weir with an irregular bedrock outcrop on the left side. This is a complete barrier to the migration of fish such as trout and eels. The fish pass will be created by building a retaining wall up the bedrock outcrop on the (true) left of the weir. An embedded rock-ramp will be constructed between the new wall and the existing channel wall, enabling fish to swim up and over the weir. The rock ramp will have a rough surface to create a turbulent flow. It will include a central low-flow channel to enable fish passage in low flow conditions.