Hydrologic study of flooding of district roads of Kilosa district, Tanzania

All the flooding locations on Mikumi, Mkata and Dumila roads were visited, and each location was studied and later on located on a large scale map 1: 50,000 to be able to identify more features. There are a number of possible causes of flooding of roads, including (a) insufficient discharge capacity of bridges and culverts. (b)The water level in the general area through which the road passes may rise due to downstream hydraulic control. (c)Water may be diverted onto the road and be forced to flow over the road for some distance before it can drain off the road. Most of the identified locations were studied for the above conditions. The TPRL East African Flood model was used to obtain the ten year design flood since rainfall data are the only data available for considerable length of time. The ten year daily rainfall study for Kilosa catchments was carried out to confirm the most important input data for the model and the results were found to be comparable. The principles of culverts hydraulics was also applied to estimate the capacity and compare with ten (10) years design flood. Generally most of the floods on the road are of limited extent and are caused by inadequate drainage of water under or from the road. The remedy is to improve the upstream drainage capacity of the culverts. Secondly, some of the flooding of the road are not because of any limitations of the culvert or bridge discharge but due to back-water effects from a downstream hydraulic control, the removal of which is usually prohibitively expensive. The remedy is to raise the level of the road.