Development of Best Management Practices for Controlling the Non-PointSources of Pollution Around Lake Victoria Using SWAT Model: A Case ofSimiyu Catchment Tanzania

摘要

Recent studies carried out in Lake Victoria Basin have identified major sources of Non-Point Source (NPS) ofpollution in the Simiyu catchment of Lake Victoria using land-uses of 1975 and 2006 and compared the relative impact ofland-use change on sediment and nutrient load (P and N) into the Lake. The main aim of this study was to identify anddevelop Best Management Practices to control NPS pollution in the Simiyu Catchment. The SWAT model was used tostimulate and assess the Best Management Practices Scenario for the catchment. The catchment was divided into seven(7) sub-basins. The results show that there was no intensive use of artifical fertilisers in the catchment and manure is themajor type of fertiliser in use. Simulation was done for the period 2000 to 2005. High nutrient concentration was observedin Sub-basin 6; 0.558-0.779 kgN/ha/yr than in Sub-basin 7; 0.018-0.115 kgN/ha/yr, despite the larger area of coverage bythe latter. This is also irrespective of the fact that Sub-basin 7 covers a larger area, 3,426.52 km2 compared to Sub-basin 6(72.97 km2) and Sub-basin 4 (618.16 km2). Relatively, considering their size, Sub-basin 6 produces higher pollution thanSub-basin 7. It was also observed that the sediment yield from the whole catchment reduced from 81,222 ton/yr to98,400ton/yr.It was observed that to control the NPS pollution problem, Best Management Practices like reduced manureapplication rate, tillage and contour yielded a decrease of 1.4% in N load and 1.57% in sediment load. As a result, it wasconcluded that the SWAT modelling tool can be used in developing Best Management Practices because pollutant processesper sub-catchment had been fully understood. With good model performance, developing management strategies tocontrol NPS pollution around Lake Victoria can be achieved using the SWAT model. The BMPs have been devised dependingon the sub-basin, which has a big collective reduction and control in NPS pollution in the whole catchment.