River regulation for the purposes of public water supply causes the flow
regime downstream of a dam to change. Traditionally, in the UK, such
regulation was accompanied by requirements for reservoir releases to
compensate downstream water users (e.g. industry) for the loss of
natural flow (compensation flows). In this article, we compare a unique
pre-impoundment macroinvertebrate data set for a regulated upland river
with survey data post-impoundment. This allows a longitudinal assessment
of the response of the system to regulation. The Derwent River,
Northumberland, was impounded in 1966. Impacts on the hydrological
regime were quantified by comparing long-term hydrographs, flow duration
curves, flow ranges and flashiness indices for the pre-impoundment and
post-impoundment periods. The comparison of changes in macroinvertebrate
richness and diversity post-impoundment showed that the change in flow
regime has had limited effect on the ecological community structure. The
flow regime of the Derwent River has become less flashy with fewer
extreme events, and the richness and the diversity of macroinvertebrates
have, in some cases, increased and at worst have not deteriorated. We
suggest that this reflects the strict compensation regime, which has
guaranteed minimum flows at all times. Copyright (c) 2012 John Wiley &
Sons, Ltd.