Long-term variability in the thermal impact of river impoundment and regulation

A long-term study of the thermal impact of a reservoir in southwest England is reported, Detailed records collected from the regulated River Haddeo and the neighbouring (unregulated) River Pulham in a 14-year period following the attainment of top water level in the reservoir (Wimbleball Lake) show that the main thermal effects of impoundment and regulation have been to raise mean water temperature, eliminate freezing conditions, depress summer maximum values, delay the annual cycle and reduce diurnal fluctuation, However, the study also highlights pronounced year-to-year contrasts in the thermal impact of river impoundment and regulation, These can largely be explained with reference to inter-annual variations in both reservoir operation and weather conditions, which primarily control the amount of water released in summer months, and the volume of flow passing the spillway in the winter period, respectively. Copyright (C) 1996 Elsevier Science Ltd.