Evaluating the effect of micro-catchment water harvesting on water and soil losses in the dryland catchment

Micro-catchment water harvesting (MCWH), by inducing and conserving surface runoff, can alleviate the water stresses in arid environments. It brings the changes in land surface, concentrates local runoff at plant location and reduces the downstream flows. It has serious implications on the water and soil losses as well as survival and growth of vegetative cover. This study evaluated the effects of the MCWH on the water, soil and vegetation in an area with an annual rainfall about 110 mm. A small catchment of 2.5 km2 was equipped with weather station, runoff stage sensors, runoff plots, bridge frames and Gerlach troughs to measure runoff and sediment loss at micro-catchment, site/rill and catchment scales. RUSLE2 model was used to compute the sediment delivery across the ridges. The results revealed that the rainfall is too low to support rainfed agriculture, but with 4 mm threshold value for runoff generation, the MCWH can capture a runoff between 5 and 80% of incidental rainfall that can help in rehabilitation of the range. At microcatchment scale, the annual runoff yield was between 200 and 400 m3 ha-1, which reduced to about half at the site scale and increased to 425 m3 ha-1 at the catchment scale. High contribution of the upper catchment raised the runoff yield at catchment scale. The annual sediment yield was about 1.6 times higher with MCWH (1.2 Mg ha-1 yr-1) than the control (0.77 Mg ha-1 yr-1). However, the sediment delivery across the ridges was less than 1/5th of the sediment loss. At the catchment scale, the annual sediment yield was about 1.5 Mg ha-1, which was due to the contribution of gully erosion. On an average, the sediment yield in the study area was below the soil loss tolerance limits set by the different studies elsewhere. The study estimated the effective life of the MCWH structures between 20 and 30 years. It concluded that the MCWH increased the shrub survival rate from less than 5% for control to about 70% with MCWH. It has been found that Atriplex halimus recorded high survival and growth rates and found best suited for this area. The study showed that the MCWH induced local runoff, but it did not affect the runoff yield at the catchment scale adversely. Keywords: Micro-catchment water harvesting, runoff, soil loss, soil-water, shrub survival and growth.