Site selection for rainwater harvesting structures in Kiambu County-Kenya

In this study, a geospatial approach has been utilised to identify suitable sites and structures for rainwater harvesting in Kiambu County, Kenya. Based on an integrated use of remote sensing and GIS, ideal sites for five rainwater harvesting structures (bench terraces, check dams, percolation tanks, contour bunds and contour ridges) have been developed for potential runoff harvesting. SRTM GDEM and Landsat 8 are utilised to process thematic land-use layers in ENVI 4.7 environment and to map other thematic layers in ArcGIS environment. KENSOTER soil database and TRMM monthly precipitation data are also used in the study. The SCS-CN runoff generation technique is used to integrate land-use/cover and hydrologic soil group layers in a runoff depth determination. The lineaments used are analysed in the PCI Geomatics environment. All the thematic layers are assigned weight depending on the capacity of infiltration and runoff characteristics. A weighted overlay analysis is applied to obtain a layer showing suitable areas for rainwater harvesting structures by rank. The suitable areas’ layer is integrated further with other structural considerations layers to determine spatial positioning for each rainwater harvesting structure. Results show that 14, 9, 10, 8, and 14 locations in the entire County are suitable for check dams, percolation tanks, bench terraces, contour ridges, and contour bunds respectively.