Response of groundwater to different water resource allocation patterns in the Sanjiang Plain, Northeast China

Study region: The Sanjiang Plain, located at the confluence of Heilong, Songhua, and Wusuli Rivers, Northeast China. Study focus: Due to the low and flat terrain, wetlands and swamps were widely distributed in plain areas in history. After decades of reclamation, farmland has replaced wetland as the dominant landscape. The competition of water resources between wetland ecological health and food security is very fierce, which is mainly reflected in the serious overexploitation of groundwater. This study used a new coupled surface water-groundwater model with an innovative function of irrigation and drainage simulation to research the changes of groundwater in the Sanjiang Plain under different water resource allocation schemes and paddy development scale in the future, which may provide a scientific basis for the planning of water resource allocation projects related to the restoration of groundwater and wetlands in this region. New hydrological insights for the region: We established four prediction models for different water resource allocation schemes and paddy areas by replacing the water supply data and planting structure of the baseline model in the Sanjiang Plain. By comparing the groundwater balance and level of various schemes simulated by prediction models, it was found that the complete water diversion scheme covering the plain areas would greatly reduce groundwater exploitation, increase groundwater recharge, and turn groundwater storage from deficit to surplus, which would increase by 853 million m3/a. It would gradually compensate for the historical debts due to groundwater overexploitation while achieving a balance between groundwater recharge and discharge; thus, the groundwater depth in most part of the plain areas would be restored to less than 5 m. However, the scheme also had a defect, that is, it may cause soil secondary salinization in shallow groundwater areas. Therefore, the scheme needs to be further optimized to make full use of the low-cost groundwater.