Using community mapping for flood modelling

Published: 16 November 2017

Dar Es Salaam’s community mapping projects, Ramani Huria (“Open Map”) and Zuia Mafuriko (“Stop Floods”), convened by the World Bank and the Tanzania Red Cross Society, have collected a vast amount of data, detailing the city’s most vulnerable wards for floods in openly accessible maps. As a hydrologist working in Dar Es Salaam, I am interested to see if the data available can tell us how water moves through the city at ward scale (not including the streams flowing through the city) and if we can use it to set up detailed flood models.

Flooding at Jangwani bridge on 26 October 2017, photo taken by Daudi Fufuji — World Bank

As part of a Challenge Fund project, Deltares (a Dutch research institute) started to assess what can be done with this vast amount of OpenStreetMap (OSM) data to increase the understanding of flood risk.

Movement of water within the wards is particularly determined by detailed conveying elements such as drains, culverts and roads equipped with sidewalks, but also elements that block water such as elevated roads that do not have a significant facility for drainage, or conditions that lead to impeded drainage such as blockage by solid waste. A second block of information related to flood risks is the exposure of people, their livelihoods, assets as well as critical infrastructure to flooding. Especially during flooding, people depend on roads to move to safe places, churches, schools and central open spaces for relief, health centres for treatment, and police stations for security.

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