Jonathan I. MATONDO
Member: IWRA, IET, IAHS. University of Swaziland. P/Bag Kwaluseni, Swaziland. Kennethy M. Msibi, Water Resources B ranch, Swaziland
The Usutu catchment which originates from South Africa traverses the four physiological regions before going into South Africa again and covers two thirds of the country. The population growth rate for Swaziland according to the 1996 census is 2.9% per year. The current population of about 1.0 million people was project to year 2075 using the continuous compound method and this, amounts to 8.802 million people. The domestic water demand for the country in year 2075 was estimated to be 17m3 /s which, translates to 12.75m3 /s, for Usutu catchment and this is equivalent to 0.092 mm/day. The irrigation water demand for the Usutu catchment in year 2075 has been estimated to be 0.058mm/day. Thus the total water demand in year 2075 is estimated to be 0.15 mm/day (1.8 million m3 per day of 20.833m3 /s).
The impact of climate change on water resources in the Usutu catchment was evaluated using General Circulation Models and hydrologic models. The results of GCM models (precipitation, temperature and potential evapotranspiration) were used as input to WatBall model to forecast stream flow for the Usutu catchment for the wet, dry and average conditions for year 2075. A comparison between observed and simulated stream flow reveals that all GCM models are simulating low flows from June to September for the wet years and from May to September for the dry and average year conditions. Rainfall runoff simulation results have shown a water reduction of 134.0 million cubic meters per year. Implementation of water demand measures in the catchment will save about 42 million m3 per year. This will leave a water deficit of 92 million m3 per year. This water deficit will have to be provided for by the construction of a water storage dam. It has been established that, the water that will be available for storage under climate change during the summer months (October to January) is 0.07mm/day which is equivalent to 98 million m3 per year. Therefore, there will be enough runoff to fill a reservoir with a capacity of 98 million m3 . Dam construction costs have been estimated to be 3500, 38,000 and 420,000 million Emalangeni for the construction periods of 2025, 2050 and 2075 years, respectively.