1 Optimization of Rainwater Catchment Systems Design Parameters in the Arid and Semiarid Lands of Kenya

It is evident from experiences in Kenya that rainwater could be the long awaited answer to water scarcity in the next millennium. However, some technical and policy hindrances need to be addressed. Lack of appropriate technical designs, among other factors, has led to low adoption of rainwater harvesting technology, especially in Arid and Semiarid Lands (ASAL), where rainwater is one of the most viable water supply. This calls for optimisation of Rain Water Catchment Systems (RWCS) design parameters and formulation of comprehensive water policy. Therefore, to address this problem, the paper focus on the hydrological criteria for determining RWCS design parameters, especially storage capacity and catchment area, using historical rainfall records of Kibwezi rainfall station. Specifically, a design procedure for determining optimal design parameters and developing design curves is outlined. The mass curve analysis was adopted for the determination and optimisation of the design parameters due to outlined inadequacies of most empirical formulae. The strength of the design procedure is the determination of optimal design parameters at various reliability levels of rainfall amount and distribution. The analysis of design parameters revealed that the catchment area and the storage capacity are affected by variations in rainfall amount and distribution respectively