Evaluating drainage systems performance and Infiltration enhancement techniques as flood Mitigation measures in Nyabugogo Catchment, Rwanda

Abstract

Rapid urbanization contributes to the increase of impervious area which in return increases stormwater runoff peak and volumes. Nyabugogo catchment in Rwanda has been repeatedly subjected to a growing number of flooding events. The general objective of this research was to evaluate drainage systems performance and the impact of infiltration-based techniques in mitigating floods in Nyabugogo catchment. The United States Environmental Protection Agency’s Storm Water Management Model (EPA SWMM 5.1) and the Geographic Information Systems (ArcGIS) tool were used to model and analyse stormwater characteristics. Data from three meteorological stations and three hydrological stations were used to calibrate and validate EPA SWMM. The model performance was judged satisfactory for flow simulation in Nyabugogo catchment with the values of r2 greater than 0.6, NSE greater than 0.5 and d greater than 0.7. The indices of reliability, resiliency, vulnerability and sustainability were used to evaluate the performance of urban drainage systems of Nyabugogo catchment. The performance of the system decreased in reliability and resiliency, and increased in vulnerability as the design rainfall return period increased. Simulation results revealed the effectiveness of four infiltration-based techniques (IBTs); namely bio-retention ponds, infiltration trenches, vegetated swales and permeable pavement, on reducing floods in Nyabugogo catchment and the combination of four IBTs demonstrated a reduction of runoff quantity by 26.1 % using the index of unit-area peak discharge. The four IBTs are recommended to contribute in solving the flooding problems in Nyabugogo catchment.