Evaluation of Sustainable Water Demand in a Coastal Environment using WEAP Model
Ogun river basin, located in southwestern Nigeria, is one of the major river basins under the management of Ogun-Oshun River Basin Development Authority. Different water uses, including domestic, commercial, industrial and agricultural takes place within the basin. As population and economic activities increase, water demand also increases, which makes it imperative for water resources planners to take into account the consequent water demand challenges. In this study, Water Evaluation and Planning (WEAP) model is used to evaluate the impacts of possible water demands on the water resources of Ogun river basin up to the year 2020. Two scenarios were simulated: the first concerns the previous and current accounts of water demand in the basin from 2006 to 2011 while the second simulates the future water demand in the basin from 2012 to 2020. The water demand utilization, unmet demand, demand site coverage, supply delivered, stream flows and water storage were analysed for each scenario by integrating various hydrological components, such as hydrological year cycles, precipitation and dams. Each scenario also made key assumptions with respect to the gross domestic product, population growth rate, irrigation efficiency and complementary sources of water. The results of the model for the previous and current scenarios indicate that the water demand for domestic, commercial, industrial and agricultural uses are 4.7 x 109 m3, 9.5 x 108 m3, 6.8 x 108 m3 and 3.4 x 104 m3 respectively while the corresponding values for the total water demand, supply required and supply delivered are 6.7 x 109 m3, 7.7 x 109 m3 and 3.6 x 109 m3, thereby making the unmet total water demand to be 4.1 x 109 m3.The model prediction for the years 2012-2020 indicates that the water demand for domestic uses will be the highest at 5.3 x 1010 m3. The demand from commercial, industrial and agricultural uses are 1.1 x 1010, 2.5 x 109 and 1.4 x 109 m3 respectively. The total water demand, supply required and supply delivered are 6.8 x 1010 m3 , 7.9 x 1010 m3 and 10 x 109 m3 respectively resulting in unmet total water demand of 6.9 x 1010 m3, at an average annual rate of 7.7 x 109 m3. The Ogun River therefore, may not be able to satisfy the future water demand of water users in the basin. To reduce unmet demand, waste water treatment, introduction of water meters to check wastage, building of new dams or increasing the capacities of existing ones, groundwater development, information dissemination and development of manpower in the field of water resources are recommended.