Excerpt from Environment Agency West Thames Fisheries Autumn Round-up 2015 – Low cost fish passes.
Many weirs represent a barrier to fish passage; including those within the Environment Agency’s hydrometric network. Most of the impounding structures within the H&T network are Crump or triangular-profile weirs.
Traditional solutions to fish passage problems at weirs and dams have normally been purpose-built to provide favourable hydraulic conditions for fish swimming in the upstream direction. Typical solutions include bypass channels, Larinier fish passes, brush passes and pool traverse passes. Such fish passes can be expensive to build, especially when added to an existing structure. They can also have a detrimental impact on the ability to gauge flows.
In response to the need for an alternative, low-cost strategy, which enables accurate flow gauging, a three-year research project into low cost modifications to the Crump weir to improve fish passage was undertaken.
This research led to the development of ‘low cost baffles’ which can be bolted on to existing structures to facilitate fish passage without any impacts on flow gauging. Low cost baffles can also be applied as an interim measure on ‘non-gauge’ weirs, or weirs where other fish pass solutions will be difficult to develop/achieve. In these instances low cost baffles provide a fish ‘easement’ until an opportunity for a alternative solution arises, or while a preferable, multi-species and multi-age class pass, is developed.
Pre-fabricated baffles can simply be retro-fitted to existing structures in a formation that is set using a standard equation. By gathering simple measurements from each impounding structure the low cost baffle solution can be applied to a wide range of crump weirs in a fashion that has been tried, tested, and approved by Fisheries and by Hydrometry & Telemetry Nationally.