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University of Nairobi (2015)

Use of Geospatial technology in rainwater harvesting : case study of Karapul sub-location, Siaya county, Kenya

Gwena, Mary A O

Titre : Use of Geospatial technology in rainwater harvesting : case study of Karapul sub-location, Siaya county, Kenya

Auteur : Gwena, Mary A O

Université de soutenance : University of Nairobi

Grade : Master of Science (2015)

Kenya is currently experiencing growing pressure on water resources caused by increasing water demand for agricultural, domestic and industrial consumption. This has been brought about due the effects of climate change and has necessitated the need to maximize and augment the use of existing or unexploited sources of fresh water. Rain Water Harvesting (RWH) has been considered as the most promising among others with efforts currently being made world over to provide water to meet the growing need. The focus of this study was to use geo-information technology in assessing the potential of rooftop rainwater harvesting (RRWH). Rooftop rainwater harvesting is the technique through which rain water is captured from the roof catchments and stored in reservoirs for future use. The study was executed in Karapul sub-location in Siaya County, Kenya. The sub-location has had to contend with a water scarcity problem for decades owing to frequent droughts, changing climate pattern, fast growing population and the increasing demand for clean and safe drinking water. A total of 8,024 rooftops were digitized in the ArcGIS environment from ortho-rectified aerial photography of 40cm spatial resolution. Three different classes of rooftop types were captured in the digitization process, these were, iron sheets, tiles and grass thatched rooftop types. Run-off coefficients of 0.85, 0.6 and 0.2 were respectively assigned to the three rooftop classes. Estimated rainfall surfaces from the year 2000 - 2012 were used to extract mean monthly and mean annual rainfall. A local model combining, mean annual rainfall (Rt), rooftop run-off co-efficient (Rc) and average roof area (A) was used to estimate the rainwater harvesting potential. Results from this work showed that 89% (389,528 km²) of the area of study has a high potential for rainwater harvesting. The total estimated potential for the area of study was 588,301 m³ of rain water, with iron sheet rooftops accounting for 95.6% (562,869 m³) while grass-thatched rooftops accounted for 2.3% (13,276 m³) and tiled rooftop accounted for 2% (12,157 m³) of the potential. The outcome of this study highlighted the relevance of geospatial methods and tools in assessing rainwater harvesting potential. The results from this work are intended to aide in planning water provision and to help address the water scarcity problem in Karapul Sub-location. In addition, the methodology outlined in this study can be replicated in other areas in Kenya to determine the potential of rainwater harvesting and thus integrate rainwater as an alternative water source to ensure sustainable development. The use of existing wells to act as storage for rainwater and geological studies to investigate the reason for drying wells and the fluctuating water struck levels are some of the recommendations. Key words : Rainwater Harvesting Potential, Rooftop Rainwater Harvesting, Geospatial Technology, Runoff Coefficient


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