An A Useful Model for Rainwater Catchment System Design

Abstract

Choosing a storage volume size for a rainwater catchment project is difficult because the overall volume needs to be large enough to meet the demand of users but not so high that it is never completely filled, which would waste money and space in the community. This newly developed Excel-based model can simplify choosing appropriate tank sizes for a rainwater catchment project by projecting the water availability in storage at multiple locations over the course of a year. For ease of use, the user can input monthly data or daily data for improved accuracy. This tool also incorporates the ability to include adjustable daily demand, to distribute demand over multiple structures, to account for tank overflow, and to increase demand at other locations if one of them runs out of water. The water level at each location over one year and the local storage volume are shown on a plot, making it easy to determine what storage volume is necessary to provide enough water for the community. This tool was originally developed to determine appropriate storage volumes for a rainwater catchment project in Mkutani, Tanzania and has been adapted for general use.