DAR ES SALAAM, May 15, 2019 – During the first few months of each year in Tanzania, the mood around urban centres like Dar es Salaam is one of dread due to the impending arrival of the rainy season. Around this time, headlines report a toll of losses related to flooding - of assets, of critical infrastructure, and of life.
Recent World Bank studies have identified many contributing factors to the increasing impact of flooding in Dar es Salaam. Soil erosion, historically under-addressed, plays a major role. Plaguing the Msimbazi River basin that snakes through the city’s centre, soil erosion enables water to escape the confines of the river’s natural borders. It also produces sedimentation, which obstructs river flow and increases flooding over time. This has disastrous effects on settlements along the river banks – many of which are informal and low-income. Community-led efforts to reinforce the collapsing riverbanks have involved the intentional dumping of solid waste, a makeshift solution that has further exacerbated the issue.
To analyze the extent of erosion along the river and better visualize the impact of potential interventions, the Tanzania Urban Resilience Programme, a DfID-funded initiative jointly implemented by the World Bank and the Government of Tanzania, is conducting flood modelling for the city. With accurate flood models, decision makers will be better able to design sustainable solutions for the basin. However, experts have noted that modelling accuracy has been hindered by an outdated soil map.
“Flood modelling has not often shown the whole story for Dar es Salaam as the soil map does not reflect the impact of urbanization,” said Mussa Natty, an engineer and former municipal director supporting program activities. “Only one general soil type has been considered by decision makers in the past – this severely limits accuracy of analysis as it doesn’t account for how soil in different areas reacts differently to water.”