Planning and design of cost-effective water harvesting structures for efficient utilization of scarce water resources in semi-arid regions of Rajasthan, India

Water-harvesting structures have the potential to increase the productivity of arable lands by enhancing crop yields and by reducing the risk of crop failure in arid and semi-arid regions, where water shortages are common because of scanty rainfall and its uneven distribution. In semi-arid regions of Rajasthan, India, existing practice of harvesting rainwater is through anicut and earthen embankments. Because of higher costs and higher technical skills involved in the construction of these structures, these structures have not been accepted by the resource-poor local people. Therefore, in the present paper, the detailed design of some low-cost water-harvesting structures using locally available materials and adaptable to the socio-economic conditions of the beneficiaries is discussed. Two types of cost-effective water-harvesting structures, which include dry stone masonry and upstream-wall cement masonry of heights 1, 2, and 2.5 m for catchments of less than 10, 10 to 20, and 20 to 30 ha, respectively are proposed and designed. The analysis of costs involved in constructing dry stone masonry and upstream-wall cement masonry water-harvesting structures, emergency spillway, anicuts and earthen embankments revealed that the earthen embankments have the least cost of construction whereas the anicuts have the highest construction costs for all the selected heights. However, based on the past experiences, earthen embankments are not suitable for the semi-arid regions of Rajasthan. The economic evaluation of the proposed structures indicated that the dry stone masonry structures are very cost-effective for the region with a benefit-cost ratio of 3.5:1 and the net present worth value of Rs. 102978. Although the economic indicators ranked the upstream-wall cement masonry structures lower than the dry stone masonry structures, the former has greater stability and strength compared to the latter. In practice, both the cost-effective water-harvesting structures (i.e., dry stone masonry and upstream-wall cement masonry) are gaining wide acceptance and popularity in the region through some nongovernmental organizations, which have adopted the design presented in this paper.