Estimation of the optimum yield in Yun-Lin area of Taiwan using loss function analysis

Safe yield is commonly defined as the largest quantity of water that can be withdrawn without causing any negative effects in the area of interest. When, negative effects are induced by over-pumping, the safe yield must be reinterpreted according to the present conditions. Therefore, the optimum yield, defined as the quantity of water that can be withdrawn from the groundwater aquifer with minimum expected losses, is introduced to balance the economic profit and environmental protection in groundwater management. A decision model based on the loss function concept is presented to estimate the optimum yield from a groundwater basin, which has experienced seawater intrusion and subsidence caused by over-pumping. The model employs loss functions, which account for environmental deterioration and economic profit according to the hydrogeological conditions and pumping rates. The optimum yield from a groundwater basin can thus be obtained by minimizing the expected value of the loss function. The method is applied to a groundwater basin in Yun-Lin, Taiwan. Analysis results indicate that the optimum yield of groundwater in this region is 619 million ton/yr, which is far lower than the current annual groundwater consumption. The method is more conservative than the conventional water balance method and is thus a more effective means of managing water resource conservation. Further environmental damage may be prevented if the loss function method proposed herein for determining the optimum yield can be applied to planning groundwater resources in the future.