Rainfall harvesting using sand ditches in Jordan

Abstract

Rainfall harvesting in rain-fed agricultural areas increases water availability for plants during the growing season, thus increasing crop production. Rainfall can be stored directly in the soil for crop production using terraces, rippers, contour ridges, and other types of water collection methods. However, the efficiency of these methods is limited by the infiltration characteristics of soil and climatic conditions. In the rain-fed agricultural areas of Northern Jordan soils are predominantly clay having very low infiltration rates. In such cases the depth of water infiltration is very small and water may remain in the upper layer of the soil profile. With high evaporation rates, collected water is lost to the atmosphere very rapidly and is therefore, unavailable for plants. Field experiments were initiated in Northern Jordan in 1996 to harvest rainfall and store it deeper in the soil profile thereby reducing the effect of evaporation. The experiment consisted of digging experimental trenches 80 cm deep, 5 m long and 1 m wide across the land slope between two rows of olive trees. The trenches were filled up to the original soil level using local deposits of fractured rock and river sand with large infiltration rate. These filled trenches, called sand ditches, were expected to collect rainfall, intercept runoff, and store water in the surrounding soil at greater depths to be used by plants for longer periods of time. It can be a very efficient method since it increases water infiltration and prevents evaporation during the growing season. The efficiency of sand ditches in storing water was assessed by monitoring soil moisture conditions and depth of infiltration in the sand ditch area, a 35 m 2 area located between four olive trees, and at a control area without a sand ditch, using an auger hole. The amount of water stored in the soil was calculated at each time interval and compared with total rainfall. Experimental results indicated that sand ditches increased both the percentage of rainfall stored in the soil matrix and the infiltration depth of water during the two winter seasons from 1996 to 1998. At one of the experimental areas on April 19, 1998 the infiltration depth and water content in the sand ditch area were 100 cm and 28%, respectively compared to only 68 m and 19% in the control area. During the same period, the calculated ratio of depth of water stored in the sand ditch area to rainfall was 73% compared to only 45% in the control area.