干旱区生态环境知识资源中心

The performance of a small runoff-basin water-harvesting system (negarim) was evaluated under a typical Mediterranean arid environment in Jordan. Rainfall, runoff, catchment area, soil water storage, and crop evapotranspiration were analyzed as elements of one system. Three micro-catchment areas (25,50, and 75 m(2)) and three surface treatment methods (natural, plastic cover, and compaction) were used. Runoff efficiency was evaluated for 16 storms. Storage efficiency was evaluated for eight periods by monitoring soil water balance in the crop root zone. The overall efficiency of the water-harvesting system was determined as the ratio of the amount of water stored and used by the crop to the amount of rainfall received in the catchment area. The overall efficiency of the system varied from over 85% to as low as 7% depending on the size of the catchment and the root zone capacity. Gains in runoff improvement were lost when the soil moisture in the cultivated area was near field capacity. The required ratio of the catchment area to the cultivated area was found to be strongly related to the root zone storage capacity and the rate of consumptive use as well as rainfall-runoff characteristics.