Making a Flood Simulation Model with Open Source Tools in Zanzibar. The Problem Most of the drainage systems in Zanzibar are blocked by impediments such as uncollected solid waste, accumulated rubbish materials, and informal buildings that prevent water from flowing along their streams and into drainage infrastructure. During data collection we also found that many communities dump waste directly into the drainage system, blocking its flow. The failure to control these blockages, results in major threats toward urban development and negatively impacts infrastructure in Zanzibar. There is no one place where the community or government can see the problem of flooding, understand it, and take appropriate measures. The Solution The solution is to create a web map, where people and communities in general can see