Modelling the effect of sediment and solid waste deposition on pluvial flood risk using high-resolution rainfall and water level measurements.

Pluvial flooding is a significant threat in many Sub-Saharan African cities, driven by rapid urbanisation, climate change, failures, and insufficient hydraulic capacity of existing urban drainage systems (UDSs). However, limited modelling studies have investigated the effect of sediment and solid waste accumulation on the performance of UDSs during extreme loading conditions. In this research, the influence of combined scenarios of sediment and solid waste deposition and extreme rainfall on urban flooding in the upper Lubigi catchment in Kampala was investigated. The collected high-resolution rainfall data and water level observations in combination with field observations were used for model calibration and validation. The results show three locations that account for over 50% of the flooded volume in the catchment, based on the existing conditions. A near-complete blockage of sediment and solid waste at three culvert crossings increased the flood volumes by up to 40% for higher (≥50 years) return periods and by up to 105% for low return periods (≤10 years). This research underscores the importance of using high-resolution rainfall data in flood modelling, as well as the necessity of improved UDS asset management, and effective solid waste and sediment management in order to achieve resilient and sustainable water management in cities.