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LARS 2007 Catchment and Lake Research An Assessment of Stream Discharges and Sediment Load and their Implications to the Environmental Health on Mt. Elgon, Eastern Uganda Bamutaze, Yazidhi Makerere University, Department of Geography Abstract The Mt. Elgon watershed in Eastern Uganda is undergoing environmental degradation, the most serious being soil erosion. This degradative process results in colossal economic losses through the various on-site damages especially reduction in land productivity. Unfortunately, the problems and damages transcend the onsite effects and are exported to the low land areas of Mt. Elgon and in the streams. For example it is a common feature to observe brown to reddish brown colored waters of rivers and streams Mt. Elgon, a visible manifestation of high concentration of sediment believed to be eroded from the farm lands. The gist of this study was to assess stream discharge and sediment load and relate to soil loss levels in the mountain catchment. Two Parshall flumes fabricated locally were calibrated and installed at the upper and lower reaches of the major stream draining Wanale micro-catchment where detailed erosion and land use studies were undertaken. Stream discharge measurements were taken and recorded before and after each study rainstorm using a graduated ruler that was dipped in water at a specific point in the flume. At the onset of the rainstorm, measurements were taken at intervals of 15 minutes for 1 hour as the stream water volume increased and color changed to brown then after very 30 minutes until when the stream volume declined. In addition, samples for sediment load and water quality determination were taken. Suspended and bed load sediments samples were taken using standard methods from the streams at the flume sites. The results showed that discharge and sediment load of streams increases downstream as well as with time to a peak following the on-set of a rainstorm. The base flow (before rainstorms) at the lower and upper stream reaches were 40 and 30cm, respectively. Peak discharge at the lower and upper gauging stations was 90 and 75 cm, respectively, and was attained between 30 and 45 minutes from the onset of the rainstorms. The total suspended sediment (TSS) for data taken on 12/11/2002 indicate increases with discharge (rising limb of hydrograph) to peaks of 80 and 61 mgTSS/L of water at 105 and 500o C, respectively. Results of TSS taken on 14/01/2003 and 16/01/2003 even reveals higher magnitudes for the lower stream gauging station. These observations dovetail the runoff and soil los measurements at plots requiring concerted conservation efforts for the sustainability of the Mt. Elgon watershed. Key words: Erosion, sedimentation, Mt. Elgon 30 Catchment and Lake Research LARS 2007 Notes: 31