A regional rain water (roof) catchment harvesting: case study of Kitui district, Kenya

Kitui district lies in the arid and semi-arid (ASA) climatic zone of Kenya. The surface water resources are scarce, mostly seasonal in occurrence and often polluted. The district is characterised by low ground water resources. The lack of adequate and suitable water supply hampers the development of the district, especially the rural areas. To supplement the existing water supply sources, rain water harvesting is practised in the district. Most of these rain water harvesting projects are initiated and financed by NGOsand church organisations with the assistance of the government and with participation of the benefiting communities. To homogenize the designs and provide basis for regional planning of these rain water catchment harvesting projects, it is important to establish regional design curves for the district. The objective of the study is presented under the above title, and will establish rainwater catchment harvesting design curves for Kitui district. The rain water catchment considered is roof catchment. This objective will be realised by firstly undertaking; delimitation of Kitui district into homogeneous seasonal rainfall regimes, estimation of mean area rainfall for the regimes, determination of the system capacities and finally establishing the design curves for the regimes thereof. The study reviews some of the methods and techniques proposed by various researchers. These vary in application, assumptions, complexity and consequently accuracy. By a method based on the principles of mass curve analysis method, sample rain water (roof} catchment harvesting design curves for Kitui district for a range cistern capacities, roof areas and demands based on the district rainfall patterns are presented. The method is versatile and can be easily modified to suit any conditions and region. The limitations and assumptions to the study are highlighted and recommendations for further studies and improvements to the study suggested