Evaluation of the Role of Green Infrastructure in Mitigating Stormwater Runoff: A Case Study of Kinamba Catchment, Kigali City

Floods are the most common natural disaster worldwide, and failing to evacuate flooded areas or entering flood waters can lead to injury or death. Kinamba catchment faces severe flood events that have led to loss of lives, crop destruction, and infrastructure damage. This study evaluated the impact of Green Infrastructure (GI) on stormwater runoff in the Kinamba Catchment, Kigali City, addressing the escalating challenges of urban flooding and water pollution exacerbated by rapid urbanization and climate change. The research aimed to assess the presence and coverage of GI, determine key factors contributing to stormwater runoff and analyze the effectiveness of GI in managing stormwater, ultimately reducing sewer overflows. Employing a mixed-methods approach, including cross-sectional, descriptive, and scenario-based modelling, the study integrated quantitative data from rainfall-runoff monitoring, GIS mapping, and hydrological modelling using the Rational methods, with qualitative insights from field observations and documentary reviews. The findings revealed a consistently low mean infiltration rate (0.38831) and high discharge variability, indicating a catchment prone to high runoff volumes and extreme events. The key findings from the Kinamba catchment showed the relationship between infiltration and discharge highlighted the complexity of hydrological interactions, while rainfall data from Gitega station underscored the importance of accurate spatial data for modelling. Land use analyses demonstrated a significant loss of green spaces, exacerbating runoff and compromising urban well-being. The study concluded that GI plays a critical role in mitigating stormwater runoff, enhancing infiltration, and reducing peak discharges, but its effectiveness is contingent upon soil properties, rainfall intensity, and maintenance. Therefore, the study recommends a comprehensive GI strategy tailored to high-risk zones, robust data collection and hydrological modelling using Gitega rainfall data, the integration of GI principles into urban planning and policy frameworks, community engagement, and sustainable funding mechanisms to enhance the resilience and sustainability of the Kinamba Catchment.