Response of groundwater regime to ecological water replenishment of the Yongding River

Ecological restoration of the Yongding River Basin is an important issue in the Coordinated Development of Beijing-Tianjin-Hebei Region, and the study of the response of groundwater regime to ecological water replenishment is one of key scientific issues. In this paper, based on the practice of ecological water replenishment of the Yongding River in 2020, multiple methods, including water balance analysis, correlation analysis and cluster analysis, are employed to analyze the loss rate of the river for different reaches, patterns of groundwater level changes and the controlling factors in detail. It is found that the river leakage loss rate (20%~40%) with large-flow ecological water replenishment in 2020 is lower than those with small-flow replenishment in 2016 (30%~60%)and 2019(41%~58%). At the same time, under the condition of ecological water replenishment, the groundwater dynamics of 77 observation wells in the study area showed the patterns with three types, which are the type of significant recovery, the type of no significant change and the type of continuous decline. According to the controlling factors, four types of groundwater changes are classified, which are the type of river leakage recharge, the type of river leakage recharge and precipitation, the type of distinct impacts under the controlling factors, and the type of unobvious impacts under the controlling factors. The groundwater level under the type of river leakage recharge gets rise rapidly, and the general increased water level is 1~19 m with the maximum of about 20 m.Meanwhile, obvious delay in the groundwater levels in monitoring wells with responses to leakage are also demonstrated.These findings may provide technical references for the formulation of scientific ecological water replenishment scheme.