Developing ecologically acceptable river flow regimes: a case study of Kielder reservoir and the Kielder water transfer system

Kielder Reservoir and the Kielder water transfer scheme have been operational since the early 1980s. The hydro-ecological changes that occur in the River North Tyne and the River Wear as a result of Kielder operations are highlighted and release policy changes designed to minimize impacts on salmonid fish are described. The Kielder Reservoir release regime results in sudden and marked changes in flow in the North Tyne. These changes affect the availability of suitable habitat for newly emerged 0+ Atlantic salmon Salmo salar L. and potentially lead to the drying out of areas used for spawning. Physical Habitat Simulation (PHABSIM) models suggest that the reservoir compensation flow provides adequate habitat for older 0+ fish but limits the availability of spawning habitat. A seasonally variable compensation and hydroelectric power (HEP) release regime that limits impacts and increases suitable spawning and 0+ habitat is described. Transfers of water to the River Wear result in short-term changes in the abundance of certain invertebrate species, although there is no evidence that the river's invertebrate fauna has been permanently altered. Consequently, it is unlikely that fish are affected indirectly by transfers through reductions in the abundance of their invertebrate prey. Transfers allow abstractions for potable and industrial water supply to continue without breaching the river's statutory Minimum Maintained Flow (MMF). The PHABSIM models suggest that this augmentation helps avoid the loss of salmonid habitat during summer dry periods. Simulation of the impacts of some alternative regimes indicates that salmonid habitat could be increased further but at the expense of natural flow and habitat variation. Research findings do not suggest the need for changes to the transfer release regime.