Assessing the Influence of Nyabarongo River Catchment Characteristics on Flood Risk and Inundation in Rwanda

The Nyabarongo River Catchment in Rwanda is highly prone to flooding, posing serious threats to both the environment and nearby communities. This study examined how catchment characteristics influence flood risk and inundation across the region. The main objectives included identifying flood-prone zones, analyzing the extent of flooding, and evaluating how factors like topography, land use, soil, rainfall, and vegetation affect flood vulnerability. A mixed-methods approach was used, integrating geospatial and remote sensing data with field surveys for validation. Tools such as the Analytical Hierarchy Process (AHP) and Geographic Information Systems (GIS) were employed to map and assess flood risks. The analysis identified five flood risk zones: very high-risk (8.6%) in low-lying areas near rivers; high-risk (21.5%) within 200 meters of rivers affected by rainfall and poor drainage; moderate-risk (31.8%) areas 200–400 meters from rivers; low-risk (34.6%) zones in central and eastern regions with favorable soil and slope conditions; and very low-risk (3.5%) areas with high elevation and well-drained soils. Inundation mapping showed that croplands, wetlands, and built areas near the river were most affected. Key contributors to flood risk included rainfall distribution (22.5%), proximity to streams (16.3%), and land use/cover (15.7%), with urbanization and unsustainable agriculture worsening conditions. The study found strong correlations between catchment features and flood vulnerability. It recommends afforestation, improved urban drainage, and sustainable land management practices to reduce future flood risks. The findings offer crucial insights for integrated flood management strategies, emphasizing the need to address both environmental and human factors in reducing flood impacts