Adjustment of river channel capacity downstream from a reservoir

The construction of a reservoir may provide an opportunity to identify the way in which a changed pattern of river discharge below a dam results in an adjusted channel capacity. This is tested in the basin of the River Tone, Somerset, by comparing channel capacity above and below the Clatworthy reservoir, constructed in 1959. At a number of sites below the dam the channel cross section is multiple in form, the upper element represents the bank‐full stage prior to dam construction, and the lower element is the contemporary bank‐full level. The reduction of channel capacity downstream from the reservoir persists for a distance of 11 km until the catchment area contributing to the river is at least 4 times that draining to the reservoir. Peak discharge below the dam is deduced to be approximately 40% of the value that obtained prior to reservoir construction.