Flood analysis for estimating the impact of rainwater harvesting system installation using hydrological models. Case study: Nyabugogo valley, Kigali

Abstract

Kigali, the capital city of Rwanda, is affected by frequent floods during rainy seasons. Nyabugogo valley, the downtown of the capital is the typical impacted area with devastating damage. Among the mitigation measures given by several research, is rainwater harvesting (RWH). This study’s objective is to analyze floods in Nyabugogo valley using hydrological models, for estimation of the impact of RWH systems installation. Nyabugogo river discharge was calculated using SWAT model, for a period of 3 years 2011-2013. The iRIC Nays2Dflood Model was used to simulate and visualize the flooded area with the input data of the discharge simulated by SWAT model. The flood event reported on March 2^nd and 3^rd, 2020 was successfully simulated. The maximum water depth of 2.56 m and the maximum velocity of 1.38 m/s were detected at the confluence of Nyabugogo river and Mpazi drainage channel; and flood extended throughout the valley. The accuracy of the flood simulation was visually checked by comparison with the sentinel2 satellite images. In further steps, the RWH system installation will be simulated using a developed model precipitation by statistical analysis based on maximum rainfall return periods. Therefore, the changes in water depth and spatial extent of the flood before and after the system installation will be detected and quantified.