Browsing by Author "Bauwens, Willy"

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    Applications of the Soil Water Assessment Tool (SWAT) in Simiyu River Catchment
    (2005-11-14) Mulungu, Deogratias M. M.; Mtalo, Felix W.; Bauwens, Willy
    The physically based Soil Water Assessment Tool (SWAT) model is applied on the Simiyu river catchment at Ndagalu outfall, Tanzania. Input data are spatially distributed data set such as topographical, land cover and soil data, climatic and river flow time series data. The model was calibrated for the period 1970-1974 based on the availability of coinciding climatic data and validated in the period 1976-1983. The calibration involved fine-tuning the land coversoil parameters to match the observed discharge at Ndagalu flow gauging station. The weather generator tool of the SWAT was used to fill in the missing climatic data and enabled flow simulation in the periods with missing data. Several model fit techniques and water balance matching techniques were used to assess model performance. Results and analysis was presented to show model performances in calibration and validation periods. During model set-up it was found that the land use (especially vegetation types) classification was a sensitive issue for the river flow estimation. The study identified optimum parameters for better discharge simulations. However, since some model parameters were obtained manually by fine-tuning, in future study the more physical basis of the parameters need to be considered. Also, the analysis of observed and estimated hydrographs showed that the rainfall data used is not representative and more rainfall data is required especially in the headwaters of the catchment so as to have better rainfall representation, which may produce better model fits. Considering the good results of SWAT in this study and comprehensiveness of the model in land surface processes representation, the model is very promising for land and water management studies and expected to give valuable information to land and water resources managers.
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    Challenges of Modeling the Flows of the Nile River
    (University of Dar Es Salaam, 2005-11-14) Mutua, F. M.; Mtalo, Felix W.; Bauwens, Willy
    Perceptions and realities of water and conflict in basins such as the Nile vary widely. The river continues to be brought into debates about “water wars” by writers on the subject. One of the major problems with the “water wars” thesis is that it includes only a cursory understanding of “scarcity” issues, and of the actual facts and figures that underlie much of the analysis. This fact is as a result of the difficulties and subsequently the inability to be able to model the Nile flows satisfactorily due to the complexity of the geography, the hydrology and the climate – which are the major drivers of the hydrologic system of the Nile basin. One of the main features of the Nile basin is its varied geography. The second major feature of the of the basin is the hydrological diversity of the two major tributaries of the Nile River. The Blue Nile has a huge seasonality which yields flows mainly concentrated from July to October. The total flow of Blue Nile (including its tributaries) varies greatly from a high of 15.6 BCM in August to just 0.3 BCM in April. The White Nile’s average monthly maximum (October) and minimum (February) discharges var y only slightly from 1.4 billion cubic meters (BCM) to 1.2 BCM, A third major feature of the river system is caused by virtue of the river’s situation in hot, arid areas whe re evaporation losses are high. The north–south orientation of the River Nile on the African continent ensures extreme variability in climate between the extremes of the basin. The Nile Basin receives annually an average rainfall of about 650 mm, or a total of about 1,900 BCM per year. Long-term mean annual flow at Aswan is about 85 BCM per year, making the annual runoff coefficient of the basin to be very small (about 4.5 percent) compared to other basins of the same size in other parts of the world. This paper explores the challenges and opportunities of modeling the flows of the Nile.