Estimation of optimal yield in Yun-Lin area of Taiwan using decision analysis

Ground water is a vital resource in the Yun-Lin area of Taiwan. A substanti al amount is continuously extracted, creating adverse effects such as land subsidence and seawater intrusion. Minimizing these negative impacts depend s on regulating the rate of groundwater withdrawal. An optimal yield must b e determined to establish a sound water management policy. A wide range of safe yields for Yun-Lin have already been proposed based on constant hydrol ogical and hydrogeological parameters. By extending the results of those in vestigations, this study presents a decision analysis model. The optimal yi eld concept is introduced as well. The proposed model incorporates a probab ility density function for rainfall recharge and a loss function, derived f rom fluctuations in the ground water table. Through decision analysis, the optimum yield is obtained by minimizing the expected value of the loss func tion. The optimal yield varies monthly because the probability density func tion is time dependent. Analysis results suggest that the cumulative optimu m yield of ground water in the area is 1.26 x 10(8) m(3)/year. If the proba bility distribution function for rainfall recharge is modified as new preci pitation data become available, the above suggested yield may require revis ion in the future.