Monitoring of Groundwater Recharge Facility and Result Evaluation Method Research in Choushui River.

By integrating several evaluation methods from domestic and foreign reference, this project has established a performance evaluation conceptual model of groundwater recharge suitable for the artificial recharge facilities. The model contains observed and simulated data to be validated.

Results from the performance evaluation concept models including: (1) Total recharge amount from the facilities is 40.88 million tons, Benefit/Cost Ratio of direct recharge efficiency is about 5.35, the ratio is higher than that of 2010(4.18); (2) According to the water level data from nearby observed wells, we found the direction of surface water infiltration includes horizontal also vertical component, the horizontal component flowed to downstream then infiltrated to aquifer; (3) Maximum infiltration distance from each embankment was between 850m and 1,150m after impounding river water; (4) After recharging surface water to the facilities, it should be able to recharge Changhua and Yunlin along with the direction of groundwater flow; (5) According to the results of oxygen stable isotope analysis, groundwater recharge ratio from the river at the northern highland beach near the facilities is about 0.69~0.93, and the ratio at the southern beach is 0.65, the results show that the major source of groundwater recharge in Changhua and Yunlin along the coast of Choushui River is river water; (6) In order to analyze the affects of 174-days long river impoundment, we utilized groundwater numerical model (MODFLOW) to simulate groundwater environment. The computation results show that the recharge caused by the embankment have strong impact on neighbor regional groundwater environment during operation. Additionally, 5 years cycle of the recharge form this facility has been simulated to evaluate the long term impact on the groundwater environment. Results show that by operating this embankment for five years of cycle could have a notable impact on the groundwater environment in Ershuei, , Sijhou Township of Changhua County and in Citong Township of Yunlin County.