Loss of reservoir volume by sediment deposition and its impact on water availability in semiarid Brazil

Abstract

A methodology is presented to assess the impact of reservoir silting on water availability for semiarid environments, applied to seven representative watersheds in the state of Ceará, Brazil. Water yield is computed using stochastic modelling for several reliability levels and water yield reduction is quantified for the focus areas. The yield—volume elasticity concept, which indicates the relative yield reduction in terms of relative storage capacity of the reservoirs, is presented and applied. Results show that storage capacity was reduced by 0.2% year−1 due to silting, that the risk of water shortage almost doubled in less than 50 years for the most critical reservoir, and that reduction of storage capacity had three times more impact on yield reduction than the increase in evaporation. Average 90% reliable yield—volume elasticity was 0.8, which means that the global water yield (Q 90) in Ceará is expected to diminish yearly by 388 L s−1 due to reservoir silting.