Micro-Catchment-Water-Harvesting (MCWH) for arid zone development

Abstract

A micro-catchment consists of two elements: the runoff area A and the infiltration basin or basin area B. The water balance equations for A and B are discussed, and combined in the water balance of the micro-catchment. The water balance is used as a tool to analyze the performance of the system, and to locate problems in the water harvesting process. Water balance data were collected during the rainy season 1982/1983 from an experimental field in Sede Boqer, in the Northern Negev Desert, Israel. Eight micro-catchments of 125 m 2 and four control basins of 9 m 2 were used, each providing water for a single tree. Analysis of the water balance illustrates two problems: runoff production and soil water storage. Effective Micro-Catchment-Water-Harvesting (MCWH) occurs in storms with sufficient runoff to allow infiltration deep into the profile free from evaporation. Besides evaporation at the surface of the basin area, water is lost by deep percolation. Efficiencies for runoff and storage are defined, which express the relevant processes in two numbers. For the eight micro-catchments during the rainy season 1982/1983 average runoff efficiency e r = 0.19, and average storage efficiency e s = 0.18. The analysis shows the usefulness of the water balance approach, and the methods used to evaluate its terms. MCWH is especially suitable for application in desert fringes with about 250 mm annual rainfall and loess soils, which form a surface crust. Micro-catchments are an effective tool to scale down engineering activities. They are easy and cheap to construct, which allows active participation of the local population.