Quantifying the contribution of ecological water replenishment on aquifer recovery using a refined groundwater model.

Due to its independent control and directly easy operation, ecological water replenishment (EWR) has been an important measure for restoring river ecosystems. However, the positive and negative contribution of the EWR activities to aquifer system are not fully understood under the combined influences of climate change and human activities across time scales. A refined groundwater flow model integrating an open channel flow at daily time scales is developed in a part of Northern China Plain to reproduce the dynamic process of groundwater level changes. After model calibration with groundwater level and runoff data, the changes of simulated groundwater level and river runoff have the Nash-Sutcliffe efficiency coefficient of 0.98 and 0.60, respectively. Results clearly demonstrate that the impulse response of aquifer recovery to runoff in three centralized EWRs. By using with and without EWR method, the simulated maximum contribution of EWR near river to aquifer recovery may be over 70 %. Scenario analysis method considering different precipitation, groundwater exploitation reduction and EWR activities are applied to evaluate the total quantities of aquifer recovery. The prediction of nine-year EWR activities under multiple scenarios shows that the increased groundwater level generally varies from 4.08 to 8.57 m, and the contribution of EWR accounts for 7.88 %-36.59 %. It is also noticed that 14 out of the 18 informal landfill sites will face potential groundwater pollution risks, indicating the negative influences of long-term EWR activities. This study can provide a method for quantifying the influences and contribution of EWR on aquifer recovery and can be referred to as a guideline for EWR evaluation with similar hydrogeological conditions.