The River Foss Pumping Station comprises eight pumps with a maximum capacity of 30.4 cumecs, and was built in 1989 as part of the Environment Agency’s flood alleviation scheme following the flooding of York in 1982. The pumping station is located south of the city centre at the lower end of the River Foss, just upstream of the convergence with the River Ouse.
The scheme is designed to protect the historic city centre by means of a barrier that closes off the lower end of the River Foss when flooding may occur. This prevents water from the River Ouse backing up into the River Foss, and potentially flooding the city centre. The pumping station transfers the water around the barrier from the River Foss into the River Ouse, which ensures the flooding is limited to the area south of the city, and the city centre is protected.
The initial operation of the scheme led to course fish from the River Foss being drawn into the water pumps and being injured and killed, but since the pumps are operated once a month for testing purposes the damage to the fish was not just confined to flood events. The Environment Agency concluded that finer physical screens on the intake could potentially block and would exacerbate the flood risk and so requested Fish Guidance Systems to provide a suitable acoustic system.
An initial demonstration trail was carried out in individual pumping chambers over the winter and autumn of 1993-4 and concluded the overall deflection efficiency of the system was 80%. The deflection efficiencies for the six key fish species were –
Chub (Leuciscus cephalus) – 88%
Dace (Leuciscus leuciscus) – 76%
Bream (Abramis brama) – 74%
Bleak (Alburnus alburnus) – 72%
Roach (Rutilus rutilus) – 68%
Perch (Perca fluviatilis) – 56%
The system was shown to be effective over the whole size range of fish present (20-150mm), and concluded that the low water temperatures (<1°C) may have reduced the ability of the fish to swim away from the pumps, so when higher water temperatures are present the deflection efficiency would be expected to be higher.
Following the success of the trials FGS was requested to provide a permanent system to protect all eight pumping chambers. A number of different configurations were modelled using FGS’s PrISM acoustic model to arrive at the final system that was installed in 1995.
Due to the pumping station being located close to the city centre, and adjacent to a large hotel complex, there was some concern about the potential for airborne noise from the system becoming a nuisance. However, once installed it was demonstrated that the sound is inaudible in air unless within a few metres of the system, and there have not been any noise issues with the surrounding properties.
