Fish passes enable the movement of migrating fish, upstream and/or downstream, which would otherwise be impossible following the construction of a manmade river-wide obstacle such as a dam or pumping station.
Fish passes are normally complemented by fish screens at the water inlets; usually positioned at an angle to help direct fish to the bypass (there is some experimen-tation with behavioural barriers but none has so far proved to be reliably successful). Depending on the species, any water level change of more than 0.5m would require a fish pass, but one which is designed in such a way so as not to adversely affect the aquatic ecosystem. For significant changes in water levels fish locks or fish lifts (vertical lock chambers) might be used.
ADA (The UK Association of Drainage Authorities) reported in 2015 on the significant decline in the European eel population and the subsequent European and local regulations for eel management. The cost of installing eel passes retrospectively, even for modest pumping stations, has been estimated at £1m - £2m; in some cases as high as £20m. Ensuring a fish pass is included in the original design is not only good for freshwater biology but good for the asset owner’s budget too.
KGAL’s engineers have undertaken numerous fish, eel and elver pass projects. We understand the sensitivities of flow velocity, turbulence and head loss and, working with fish and marine biologists, the specific needs (including resting) of the relevant affected species.The image shows the eel pass at the Horseshoe Bridge Sluice in Ipswich, England. In contrast, our engineers are currently designing what is believed to be the largest fish pass in the world: the 70 gate fish pass on the Lower Mekong at Xayaburi.