A Study of Conjunctive Use of Surface and Groundwater Reservoirs in Taiwan

Surface reservoirs are important water resources measures in Taiwan. However, high amount of sedimentation had decreased the reservoir capacity and threaten the reservoirs operation life. The groundwater reservoirs are important alternatives to reduce the water shortage risk by conjunctive operation with the conventional surface water reservoir.

The study proposed an optimal conjunctive model by integrating groundwater simulation model MODFLOW with surface water allocation model. A non-linear programming is used to solve the optimal conjunctive use problem. The storage volume in surface and groundwater reservoirs are divided into different zones to implement the water use priority among the two type of reservoirs. For sustainable operation of groundwater reservoir, the usable volume of groundwater aquifer is constrained by a permissible groundwater level drawdown.

The model was applied to the Zhoushui River alluvial fan in Taiwan. The groundwater aquifer under the upstream section of the river was selected as groundwater reservoirs to supply the water. The groundwater reservoir was conjunctively operated with the existing complex surface water system that consists of three surface water reservoirs and an in stream water supply dam. Simulation results revealed that the conjunctive operation of groundwater reservoir with a surface water system can effectively reduce the water shortage and maintaining the groundwater level within a permissible drawn.