In September 2020, we successfully installed two fish passes on a weir on the River Ock in Abingdon. The River Ock is a small tributary of the Thames and owes its name to the pre-Saxon word “Ock” meaning young salmon. Salmon were a common sight on the Ock and a staple part of local diets in the middle ages. So why are these migratory majesties no longer present on the river?
Aside from other more global issues, barriers to migration such as the weir at Abingdon would present challenges to upstream migration of all fish species, not just salmon. The weir results in fragmented habitat which in turn can create bottlenecks at varying life stages. As a result, the survival and success of fish is compromised. It was therefore in the river’s best interest to implement fish passage on this weir.
The weir is a standard crump gauging weir, used by the Environment Agency’s Hydrometry and Telemetry’s team to monitor flows in order to help predict downstream flooding and manage abstraction licenses. It is 5.7m long and split into two channels. The left hand channel (as you look downstream) feeds the River Ock and the right hand channel feeds the Sandford Brook. The design of the weir, coupled with the fact that it was a gauging station, added several complexities.