Vertical Slot Fish Pass

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Group Design Project
Hydraulic design, analysis and optimisation of a vertical slot fish pass for the Diglis Weir on the River Severn
Group Members
Serban Berariu Adam Curran Tobyn Dawson Matthew Gorvett Xiaohan Mei Tim Pellew Richard Saunders

Dr. Gerald Müller Dr. Gustavo de Almeida

Fishtek Consulting Ltd

After the installation of weirs along the River Severn, the once thriving shad population had largely disappeared. Plans are underway to reopen the river to shad, through the construction of four fish passes, including three vertical slot fish passes. This project sought to physically test the flow conditions within the lower region of the designed vertical slot fish pass at Diglis Weir, near Worcester, through the creation of 1:15 scale models in two flumes, to ascertain whether the design performed as desired.

After conducting tests at both 50% and 95% exceedance flow rates, the client’s design was determined to perform inadequately. This was primarily because high flows exiting the downstream region of the gallery channels would attract shad away from the main channel. Eddy currents were also found to form within the junction pool which could confuse the fish further.

As a result, considerations were made to improve the design. These consisted of, but were not limited to, installing ‘column arrangements’ and ‘deflection curves’ behind the gallery screens to improve the uniformity of and minimise the effect of eddy currents on the outflow through the screens. In improving the flow uniformity through the screen, the high flows at its downstream end would be reduced. These two modifications were chosen as those to be studied further.

By assessing the flow through the screen with these modifications, it was found that they were able to improve the uniformity of the flow through the screen in the higher of the two flow conditions.

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