Modelling of Non-Point Source Pollution Around Lake Victoria Using SWAT Model: A Case of Simiyu Catchment Tanzania

Abstract

Pollutant loading in Lake Victoria is resulting from a wide range of anthropogenic activities. This study focused on Non-Point Sources (NPS) of pollution and it was carried out to identify and characterize land-use activities and to quantify the sediment and nutrient loads (nitrogen and phosphorus). The study was conducted in Simiyu catchment of Lake Victoria using land-use data of 1975 and 2006 and comparing the relative impact of land-use change on sediment and nutrient load (P and N) into the lake. Possible best management practices were also identified for those sub-basins with the highest pollution yield. Remote sensing using the package ILIWIS 3.0 was used to identify and characterize the land-use and the Soil and Water Assessment Tool (SWAT) model was used to quantify sediment and nutrient load from these two different land-use scenarios. Land use classification according to the SWAT model shows that Agricultural Land-Generic (AGRL) contributes about 73.43%, Range-brush (RNGB) contributes 24.42%, Pasture (PAST), 2.10% Savanna (SAVA) 0.03% and Water (WATR) 0.02% of the total catchment area of Simiyu. It was also found out that there was an expansion of agricultural land from covering 19.33% of the catchment to 73.43% at an annual change rate of 2.9%. However, average Nitrate load was higher for 1975 than 2006. The P load of 1975 was less compared to that in 2006. Model simulation at the catchment outlet for N gave 77.2 kg/km 2 .yr while observed values were 146 kg/km 2 .yr, simulated P was 47 kg/km 2 .yr while observed was 164 kg/km 2 .yr. Hence, the model underestimated nutrient yield in the catchment. Therefore, the applicability of the SWAT modelling tool in studying NPS pollution yields poor model performance due to the scantiness of data used for model calibration. More rigorous data campaigns have to be carried out along the two rivers of Duma and Simiyu for purposes of gaining enough information for model calibration and validation. With good model performance, developing management plans to control NPS pollution around Lake Victoria could be achieved using the SWAT model.

Modeling of runoff pollution load in a data scarce situation using swat, Sondu watershed, Lake Victoria Basin

“…However the validation iteration captured the low and high flow seasons reasonably well and insynchrony with rainfall pattern (Figures 2a and b). The simulations compared favorably with similar studies on Lake Victoria such as Kimwaga et al (2011) and Opere and Okello (2011) (Figures 3a, b and c). These high water yielding areas not only receive higher precipitation but also have higher slope and the two characteristics mainly explain the water yield.…”

“…The study assessed the impact on change in land cover driven by adoption of modern technology for smallholder dairy industry (Cheruiyot and Muhandiki, 2014b). Kimwaga et al (2011) modeled non-point source pollution in Simiyu watershed in Tanzania using the SWAT model. The study used the model to quantify sediment and nutrient from two land cover scenarios.…”

“…The study used the model to quantify sediment and nutrient from two land cover scenarios. From the literature reviewed, Kimwaga et al (2011) was the only study which aimed to predict and quantify non-point source pollution (sediments and nutrients) going into Lake Victoria using the SWAT model. Although the studies were faced with the problem of data scarcity due to detailed model data requirements, more similar studies are needed in Lake Victoria.…”

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

“…The relationship between poor land-use practices and NPS pollution was recently established [9][10][11]. Identifying and quantifying NPS hotspots and establishing a relationship between land-use change and water quality deterioration will contribute to the development of strategies for catchment management to control impacts related to the same.…”

“…Several studies have identified point source pollution as one of the largest problems causing water quality deterioration in Lake Victoria [9][10][11]. Though enormous attention had been invested in tackling the pollution problem based on point source pollution, recent studies have reported on quantification of Non Point Source (NPS) of pollution into Lake Victoria [9][10][11]. Studying the NPS hot spots and their contribution to lake pollution and relating this to land-use change in the catchment is an important move to set measures for the best management of the catchment land-uses and reduction in deterioration of the lake water quality.…”