Determining the rooftop rainwater harvesting potential of Rwebisengo Sub county using the Gould and Nissen formula.

Abstract

Rainwater harvesting, which is arguably the best practice to curb water scarcity involves collection and storage of rainwater locally through different technologies, for future use. It is also useful for livestock, groundwater recharge and for irrigation practices. This study in particular focusses on rooftop rainwater harvesting where the rain water runoff from roof tops is collected and stored for use. Rooftop Rainwater harvesting potential refers to the capacity of an individual rooftop to capture the water falling on it during a particular time period putting rainfall into consideration. The present study deals with the identification of the boundary of Rwebisengo subcounty and marking it as a polygon in Google Earth Pro. Rooftops of various house entities were later digitized using the polygon command in Google Earth Pro within the boundary of the earlier created polygon of Rwebisengo subcounty. There were two types of rooftops that were digitized namely, iron rooftops and clay rooftops. A GIS (Geographic Information Systems) technique was employed for locating boundaries of the study area and for calculating the areas of the different types of rooftops. The rooftop rainwater harvesting potential was calculated using the Gould and Nissen formula with the application of GIS. The necessary parameters include rainfall data, runoff coefficient and area of rooftops which were all acquired successfully. The rooftop rainwater harvesting potential of Rwebisengo subcounty which was computed in a monthly manner was then assessed by comparing it with the monthly water demand so as to determine whether it would be a sufficient method for the population in the study area. The present study will therefore enable one to find out whether the rooftop rain water harvesting potential can be an efficient method for water collection that will enable availability of water in the study area for the whole year more so in the dry season.