Effect of Approach Velocity on Impingement of Juvenile Northern Pike at Water Intake Screens

Abstract

Current guidelines with respect to the use of irrigation intakes limit Canadian operators to approach velocities (at the screen) of 3.8 cm/s; however, this value is based on relatively little data. To address this issue, I examined the ability of juvenile (2.3–7.4-cm fork length) northern pike Esox lucius to avoid impingement on irrigation intake screens under ambient environmental conditions in a swim tunnel (where water velocity was constant and uniform) and in a simulated intake where water velocity declined with distance from the test screen (as in real structures). The effects of impingement duration (in swim tunnel tests) and approach velocity (in both tests) on feeding and physical condition (abrasions, bruising, and scale loss) were also examined. Juvenile northern pike in the swim tunnel became impinged at speeds ranging from 10 to 28 cm/s. Injuries and mortalities from impingement up to 10 min in duration were nonexistent, although some short-term feeding disruptions were observed. Northern pike tested in the intake simulation apparatus never became impinged when the approach velocity was 15 cm/s; however, some impingement (but no feeding disruptions, injuries, or mortalities) was observed at an approach velocity of 25 cm/s. At higher velocities, impingement, feeding disruptions, injuries, and mortalities occurred. Environmental regulations pertaining to approach velocity at irrigation intake screens can be set as high as 15 cm/s without adversely affecting juvenile northern pike.