A procedure for reservoir sizing on intermittent rivers under high evaporation rate

Abstract

Most of the rivers located in arid and semi-arid areas at low latitudes have two well-defined seasons: a wet season where all flows occur, and a dry season with no flows. Another characteristic of these areas is the high evaporation rates -- ranging from two to three meters per year in some places -- reducing significantly the controllable release from surface reservoirs. The present research develops a procedure for sizing the storage capacity required for surface reservoirs located in areas with similar hydrologic conditions. The procedure has its theoretical support in the Stochastic Theory of Reservoirs, and consists of a collection of graphics linking the following three variables: the reservoir capacity, the annual release and the reservoir probability of failure. Others variables included in the sizing procedure are: the mean value of annual inflows, the coefficient of variation of annual inflows, the annual evaporation depth, and a parameter to take into account the shape of the lake. The main objective is to provide, quickly and with a certain accuracy, a tool for estimate the required reservoir capacity. As additional and related topics the research investigates: the reservoir behavior during the transient phase where the probability of emptiness depends on the initial storage as well as the relationship between the required capacity and the reservoir horizon life for several values of the initial storage, and the effect of annual and seasonal intermittence of inflows in the reservoir required capacity.