The application of the Soil and Water Assessment Tool (SWAT) to the Olifants Basin in South Africa was the focus of our study with emphasis on calibration, validation and uncertainty analysis. The Basin was discretized into 23 sub-basins and 226 Hydrologic Response Units (HRUs) using 3 arc second (90 m × 90 m) pixel resolution SRTM DEM with stream gauge B7H015 as the Basin outlet. Observed stream flow data at B7H015 were used for model calibration (1988-2001) and validation (2002-2013) using the split sample approach. Relative global sensitivity analysis using SUFI-2 algorithm was used to determine sensitive parameters to stream flow for calibration of the model. Performance efficiency of the Olifants SWAT model was assessed using Nash-Sutcliffe (NSE), coefficient of determination (R 2 ), Percent Bias (PBIAS) and Root Mean Square Error-Observation Standard deviation Ratio (RSR). Sensitivity analysis revealed in decreasing order of significance, runoff curve number (CN2), alpha bank factor (ALPHA_BNK), soil evaporation compensation factor (ESCO), soil available water capacity (SOIL_AWC, mm H 2 O/mm soil), groundwater delay (GW_ DELAY, days) and groundwater “revap” coefficient (GW_REVAP) to be the most sensitive parameters to stream flow. Analysis of the model during the calibration period gave the following statistics; NSE = 0.88; R 2 = 0.89; PBIAS = -11.49%; RSR = 0.34. On the other hand, statistics during the validation period were NSE = 0.67; R 2 = 0.79; PBIAS = -20.69%; RSR = 0.57. The observed statistics indicate the applicability of the SWAT model in simulating the hydrology of the Olifants Basin and therefore can be used as a Decision Support Tool (DST) by water managers and other relevant decisions making bodies to influence policy directions on the management of watershed processes especially water resources.
KeywordsCalibrationValidationUncertainty AnalysisOlifants BasinSWAT Model
Betrie, G.D., Mohamed, Y.A., van Griensven, A. and Srinivasan, R. (2011) Sediment Management Modeling in the Blue Nile Basin Using SWAT Model. Hydrology and Earth System Sciences, 15, 807-818. http://dx.doi.org/10.5194/hess-15-807-2011
Panhalkar, S.S. (2014) Hydrological Modeling Using SWAT Model and Geoinformatic Techniques. The Egyptian Journal of Remote Sensing and Space Sciences.
Singh, V., Bankar, N., Salunkhe, S.S., Bera, A.K. and Sharma, J.R. (2013) Hydrological Stream Flow Modeling on Tungabhadra Catchment: Parameterization and Uncertainty Analysis Using SWAT CUP. Current Science, 104, 1187-1199.
Adeogun, A.G., Sule, B.F. and Salami, A.W. (2015) Simulation of Sediment Yield at the Upstream Watershed of Jebba Lake in Nigeria Using SWAT Model. Malaysian Journal of Civil Engineering, 27, 25-40.
DWAF (2005) Olifant River Water Resources Development (ORWRP) Environmental Impact Assessment (12/12/20/ 553). Infrastucture Development.
Obuobie, E. and Bernd, D. (2008) Using SWAT to Evaluate Climate Change Impact on Water Resources in the White Volta River Basin. West Africa Conference on International Research on Food Security, Natural Resource Management and Rural Development, University of Hohenheim, Tropentag, 7-9 October 2008.
Merrey, D.J., Drechsel, P., Penning de Vries, F.W.T. and Sally, H. (2005) Integrating “Livelihoods” into Integrated Water Resources Management: Taking the Integration Paradigm to Its Logical Next Step for Developing Countries. Regional Environmental Change, 5, 197-204. http://dx.doi.org/10.1007/s10113-004-0088-5
Setegn, S.G., Srinivasan, R. and Dargahi, B. (2008) Hydrological Modeling in the Lake Tana Basin, Ethiopia Using SWAT Model. The Open Hydrology Journal, 2, 49-62. http://dx.doi.org/10.2174/1874378100802010049
Chou, S., Russ, B. and Anne, W. (1997) Water Scarcity in River Basins as a Security Problem. Woodrow Wilson International Centre for Scholars, Environmental change and Security Project, Washington DC, 96-105.
Xie, M. (2006) Integrated Water Resources Management (IWRM)—Introduction to Principles and Practices. World Bank Institute.
Carius, A., Dabelko, D.G. and Wolf, A.T. (2004) Water, Conflict and Cooperation, Policy Briefing Paper for United Nations and Global Security Initiative.
UNDP (2006) Summary Human Development Report. Beyond Scarcity: Power, Poverty and the Global Water Crisis.
Biswas, A.K. (2001) Management of International Waters: Opportunities and Constraints, in Sustainable Development of the Ganges-Brahmaputra-Meghna Basins. In: Biswas, A.K. and Uitto, J.I., Eds., United Nations University Press, Tokyo, 1-16.
Gleick, P.H. (2000) The Changing Water Paradigm: A Look at Twenty-First Century Water Resources Development. Water International, 25, 127-138. http://dx.doi.org/10.1080/02508060008686804
Ullrich, A. and Volk, M. (2009) Application of the Soil and Water Assessment Tool (SWAT) to Predict the Impact of Alternative Management Practices on Water Quality and Quantity. Agricultural Water Management, 96, 1207-1217. http://dx.doi.org/10.1016/j.agwat.2009.03.010
Schuol, J., Abbaspour, K.C., Srinivasan, R. and Yang, H. (2008) Estimation of Freshwater Availability in the West African Sub-Continent Using the SWAT Hydrologic Model. Journal of Hydrology, 352, 30-49. http://dx.doi.org/10.1016/j.jhydrol.2007.12.025
Yang, J., Reichert, P. and Abbaspour, K.C. (2007) Bayesian Uncertainty Analysis in the Distributed Hydrologic Modeling: A Case Study in the Thur River Basin (Switzerland). Water Resources Research, 43, W10401. http://dx.doi.org/10.1029/2006WR005497
Simic, Z., Milivojevic, N., Prodanovic, D., Milivojevic, V. and Perovic, N. (2009) SWAT-Based Runoff Modeling in Complex Catchment Areas—Theoretical Background and Numerical Procedures. Journal of the Serbian Society for Computational Mechanics, 3, 38-63.
Neitsch, S.L., Arnold, J.G., Kiniry, J.R. and Williams. J.R (2005) Soil and Water Assessment Tool Theoretical Documentation. Version 2005.
Arnold, J.G. and Fohrer, N. (2005) SWAT2000: Current Capabilities and Research Opportunities in Applied Watershed Modeling. Hydrological Processes, 19, 563-572. http://dx.doi.org/10.1002/hyp.5611
Obuobie, E. and Diekkrüger, B. (2008) Using SWAT to Evaluate Climate Change Impact on Water Resources in the Olifant River Basin, West Africa. Conference on International Research on Food Security, Natural Resource Management and Rural Development, University of Hohenheim, Stuttgart, 7-9 October 2008.
Li, Z., Liu, W., Zhang, X. and Zheng, F. (2009) Impacts of Land Use Change and Climate Variability on Hydrology in an Agricultural Catchment on the Loess Plateau of China. Journal of Hydrology, 377, 35-42. http://dx.doi.org/10.1016/j.jhydrol.2009.08.007
Neitsch, S.L., Arnold, J.G., Kiniry, J.R., Williams, J.R. and King, K.W. (2011) Soil and Water Assessment Tool Theoretical Documentation Version 2009. Grassland, Soil and Research Service, Temple.
Schultz, C.B. and Watson, M.D. (2002) WSAM: Water Situation Assessment Model Version 3: A Decision Support System for Reconnaissance Level Planning. Volume 1: Theoretical Guide. ARCUS-GIBB and DWAF, Republic of South Africa.
IWMI (2008) Baseline Report Olifants River Basin in South Africa: A Contribution to the Challenge Program Project 17 “Integrated Water Resource Management for Improved Rural Livelihoods: Managing Risk, Mitigating Drought and Improving Water Productivity in the Water Scarce Limpopo Basin”.
Schulze, R.E., Maharaj, M., Lynch, S.D., Howe, B.J. and Melvil-thomson, B. (1997) South African Atlas for Agrohydrology and Climatology. University of Natal, Pietermaritzburg.
FAO (2002) Major Soils of the World. Land and Water Digital Media Series. Food and Agricultural Organization of the United Nations. FAO, Rome.
FAO (2005) Digital Soil Map of the World and Derived Soil Properties of the World. Food and Agricultural Organization of the United Nations. FAO, Rome.
Batjes, N.H. (2002) ISRIC-WISE Global Data Set of Derived Soil Properties on a 0.5 by 0.5 Degree Grid (Version 2.0). Report 2002/03. International Soil Reference and Information Centre (ISRIC), Wageningen.
Anderson, J.R., Hardy, E.E., Roach, J.T. and Witmer, W.E. (1976) A Land Use and Land Cover Classification System for Use with Remote Sensing Data. USGS Professional Paper 964, 138-145.
Neitsch, S.L., Arnold, J.G., Kiniry, J.R., Srinivasan, R. and William, J.R. (2002) Soil and Water Assessment Tool User’s Manual. Version 2000.
FAO (2003) The Digital Soil Map of the World. Version 3.6.
Abbaspour, K.C. (2012) SWAT-CUP-2012.SWAT Calibration and Uncertainty program—A User Manual. Swiss Federal Institute of Aquatic Science and Technology, Dübendorf.
Faramarzi, M., Abbaspour, K.C., Schulin, R. and Yang, H. (2009) Modelling Blue and Green Water Resources Availability in Iran. Hydrological Processes, 23, 486-501. http://dx.doi.org/10.1002/hyp.7160
Schuol, J., Abbaspour, K.C., Yang, H., Srinivasan, R. and Zehnder, A.J.B. (2008) Modeling Blue and Green Water Availability in Africa. Water Resources Research, 44, W07406. http://dx.doi.org/10.1029/2007wr006609
Abbaspour, K.C., Yang, J., Maximov, I., Siber, R., Bogner, K., Mieleitner, J., Zobrist, J. and Srinivasan, R. (2007) Modelling Hydrology and Water Quality in the Pre-Alpine/Alpine Thur Watershed Using SWAT. Journal of Hydrology, 333, 413-430. http://dx.doi.org/10.1016/j.jhydrol.2006.09.014
Abbaspour, K.C., Johnson, C.A. and van Genuchten, M.T. (2004) Estimating Uncertain Flow and Transport Parameters Using a Sequential Uncertainty Fitting Procedure. Vadose Zone Journal, 3, 1340-1352. http://dx.doi.org/10.2136/vzj2004.1340
Coffey, A.E., Workman, S.R., Taraba, J.L. and Fogle, A.W. (2004) Statistical Procedures for Evaluating Daily and Monthly Hydrologic Model Predictions. Transaction of the American Society of Agriculture Engineers, 47, 59-68. http://dx.doi.org/10.13031/2013.15870
Moriasi, D.N., Arnold, J.G., van Liew, M.W., Bingner, R.L., Harmel, R.D. and Veith, T.L. (2007) Model Evaluation Guidelines for Systematic Quantification of Accuracy in Watershed Simulations. Transactions of the ASABE, 50, 885-900. http://dx.doi.org/10.13031/2013.23153
Vaghefi, S.A., Mousavi, S.J., Abbaspour, K.C., Srinivasan, R. and Yang, H. (2013) Analyses of the Impact of Climate Change on Water Resources Components, Drought and Wheat Yield in a Semi-Arid Regions: Karkheh River Basin in Iran. Hydrological Processes, 28, 2018-2032. http://dx.doi.org/10.1002/hyp.9747
Yang, H., Reichert, P., Abbaspour, K.C., Xia, J. and Yang, H. (2008) Comparing Uncertainty Analysis Techniques for SWAT Application to the Chaohe Basin in China. Journal of Hydrology, 358, 1-23. http://dx.doi.org/10.1016/j.jhydrol.2008.05.012
Midgley, D.C., Pitman, W.V. and Middleton, B.J. (1994) Surface Water Resources of South Africa, Volumes I, II, III, IV, V and VI. Reports No’s. 298/1.1/94, 298/2.1/94, 298/3.1/94, 298/4.1/94, 298/5.1/94 and 298/6.1/94, Water Research Commission, Pretoria.