Early warning Simulation for flood risk areas of Msimbazi River

Floods are natural disasters as overflow of a large amount of water beyond the normal limits, especially over what is normally dry land. The most important element of disaster risk reduction is the early warning because it significantly prevents loss of life, reduces the economic and material disturbances resulting from disasters. Msimbazi River flows across Dar es Salaam City through valleys such as Jangwani from the higher areas of Kisarawe in the Coastal region into the Indian Ocean. Tanzania government is concerned about the activities in the riparian areas of the Msimbazi River valley due to floods and therefore hydrologic and hydrauric tools for simulating the early warning are Important so that communities such as DART, Muhimbili Hospital and Jangwani dwellers can prepare and survive the destruction of properties, infrastructures and deaths of people when it floods. Hydrologic modeling with TRRL East African flood model was used to estimate flows using 30 years’ time series of annual daily maximum rainfall between 1982 and 2012 from two rainfall stations Dar es salaam International Airport (DIA) and Kisarawe. The highest and lowest annual daily maximum at Kisarawe station were 175 mm in 2012 and 51.3 mm in 1982 respectively while Dar es Salaam International airport station, they were 156.4 mm in 2011 and 55.7 mm in 1987 respectively. The estimated discharges were 151.3m3/s, 191.0 m3/s, 251.6 m3/s, 276.9 m3/s, and 302.2 m3/s for 2-years, 5 year, 10-year, 25-year, 50-year and 100- flood inundation and later simulate the flood warning. About 80% of buildings in the evacuation centers, 14% stay in premises and 22% moving to friends houses. 65% of the assessed population does not get any flood early warning. Hydraulic modeling resulted into an inundation of 422939. 8 m2, 575369.5 m2, 645542.7 m2, 719402.6 m2, 764567.4 m2, 810661.5 m2 for floods of 2 years, 5 year, 10 year, 25 year, 50 year and 100 year return period respectively. Tabata residences have 48 minutes as flood warning time to escape flood impacts, whereas residences at Buguruni ward have 62 minutes (1 hour and 2 minutes) as flood warning lead time.