Hydrologic study of rivers Kikuletwa, Nduruma and Themi in Arusha region

The flood areas of Mbuguni, Majengo, Msitu wa Mbogo were visited. The area together is flooded by the three rivers i.e Kikuletwa, Nduruma, and Themi. The following are the cause of flooding established from this study; a} River Kikuletwa is the major river among the three river studied. The river disgorges from its deep cut in to flat plains. The river cross section area get reduced tremendously and therefore the river is unable to carry the whole water during rainy season and hence cause flooding. b) For river Nduruma when the river reaches flood prone areas it does not have a defined course and therefore during rainy season flooding is inevitable. c) Similar to river Nduruma Themi river has no defined course at the tail end which is the area been flooded. Most of catchment in Tanzania are ungauged and therefore when a planner or a designer of water resource want to plan a project at a s to they are faced with the problem of data not being available or not being enough. As such this was the problem chich was faced in this study. In order to be able to proceed with the study regional analysis was performed. A model to find out the mean max discharge in ungauged catchment was established using physical catchment characteristic. Then by using flood frequency curve the flood of different return period for the ungauged catchments of river Nduruma Kikuletwa and Themi were obtained. The multiple regression models obtained and regional flood frequency curve obtained from 15 selected catchment from Pangani river basin can also be used in any ungauged catchment in this basin. To minimise the effect of flood of river Nduruma and Themi it is proposed to construct/excavate a channel to connect this river with Kikuletwa River. Capacity of this channel will depend on the selected design floods which have already be computed in this study and made available for design purposes. River Kikuletwa should be able to carry its own water and to carry water which is diverted from Nduruma and Themi . River training works should be performed on this river Kikuletwa to a design capacity which will enable it to carry the water of the selected return period. Different design flood of selected return period for river Kikuletwa after joining this river with Themi and Nduruma are also presented in this study. It is also proposed to do sediment transport study in the river Kikuletwa Nduruma and Themi. It is observed that one of the reason of reduction of the river cross section is due to sedimentation which has resulted that even during rain season water cannot flow to the downstream area of the study area in Kikuletwa river. According to the people in the area ten years ago that was not the case. The benefit of following the above suggested points to alleviate the flood will be: i) People in the study area will be highly relieved from losses which is a result of floods which occur every rain season. ii) Water for irrigation will be available to the downstream people who have been missing it since ten years ago. iii) Training of the Kikuletwa river will also help in adding water to Nyumba ya Mungu reservoir which it used to get ten years ago because it have been observed that even during rainy season no flow passes downstream of study area.