Multiple duration limited water level and dynamic limited water level for flood control, with implications on water supply

With water shortages occurring in semi-arid areas of the world, the need for multipurpose reservoirs that can, under the requirement of reservoir safety, store sufficient water for supply during dry seasons is becoming egregious. In order to increase water storage of a reservoir while maintaining its security for flood control, two approaches, multiple duration limited water level and dynamic limited water level, are proposed in this study. Contrary to traditional annual limited water level, multiple duration limited water level employs a multiple duration design storm. When a large storm takes place in the first part of multiple duration, the likelihood of another large storm to be occurring in the next part of the duration diminishes. Based on this intuitive reasoning, this study proposes a dynamic limited water level for flood control based on conditional probabilities of large storms. In order to obtain these conditional probabilities, a multivariate autoregressive model with lag one [AR(1)] is chosen for extending multiple duration rainfall series. Using Menlou drainage area in China as an example, multiple duration limited water level and dynamic limited water level for flood control are applied and their benefits for water supply are discussed.