Quantifying the Impact of Fish Ladders on River Flow Measurements
HR Wallingford is helping the UK Environment Agency to understand the impact of fish passes on flow gauging structures. How do these structures, and their positioning, impact on the accuracy of flow measurements in the river? Results of this research will allow better understanding of low cost options for fish passage and will ultimately lead to more accurate flood risk assessments.
Accurate information on the flow capacity of rivers and channels is critical for effective flood risk assessment; it is also essential for hydraulic and ecological management. The EU Water Framework Directive sets environmental goals for integrated river basin management, and one of the measures used to assess the status of a river is fish population. In order to encourage fish migration in rivers, more and more fishpasses are being built at weirs and other structures used for flow gauging. HR Wallingford is helping the Environment Agency to answer the following questions: do fish, elver and eel passes in weirs affect their measuring performance and, if so, by how much?
“The Environment Agency approached HR Wallingford to investigate the performance of low cost fish and eel passage in the laboratory in order to validate an initial CFD (Computational Fluid Dynamics) study and ongoing field trials,” explains HR Wallingford’s Project Director, Manuela Escarameia. “We have an extensive track record in this area. Our research on the hydraulic performance of Larinier fishpasses and “brush type” elver passes was used to develop the ISO Standard on fishpasses at flow measurement structures1.”
Low cost baffles and eel tiles have been installed in Flat V weirs which are commonly used for flow gauging purposes. These are three-dimensional structures with a triangular profile and a wide V shape formed on the crest. They allow measurement of low flows and also minimise afflux during flood conditions. HR Wallingford’s team is studying these structures in their Volumetric Flow Flume, which has the control and accuracy required for detailed hydrometric studies. HR Wallingford’s flume is unique in that its 36 m3 capacity volumetric tank has a BSI calibration of the level/volume relationship to an accuracy of 0.02 per cent. In addition, water levels are measured with precision micrometer gauges reading to ±0.01 mm, set in 150 mm diameter stilling wells.
The findings of this research will help the Environment Agency to understand the performance of low cost options for fish passage on gauging structures and provide advice on the positioning of these features to minimise their impact on flow measurements.
About HR Wallingford
HR Wallingford is an independent engineering and environmental hydraulics organisation. We deliver practical solutions to complex water-related challenges faced by our international clients. A dynamic research programme underpins all that we do and keeps us at the leading edge. Our unique mix of know-how, assets and facilities includes state of the art physical modelling laboratories, a full range of numerical modelling tools and, above all, enthusiastic people with world-renowned skills and expertise.