THE DISTRIBUTION OF RIVER INFILTRATED INTO SHALLOW POROUS AQUIFERS IN HUAIROU AREA, BEIJING

The interaction of river and groundwater is critical for understanding recharge and water quality for porous aquifer in the mountain front area, Huairou, Beijing. In this area groundwater level was greatly dropped due to heavy abstraction before the year of 2013, and alleviated from 2015 by the arrival and input of Yangtze River water under the south to north water division project. Transported river water could increasingly play roles for recharge into aquifers and help to restore groundwater storage. River and groundwater samples were taken from Huairou area and measured major ions and δD-δ¹⁸O to investigate the distribution of river infiltrated into shallow porous aquifers for understanding of effects on groundwater quality. The results demonstrate that:(1)δD-δ¹⁸O data indicate along river banks groundwater is a mixture with river water where the infiltrated river water has the signal of enriched oxygen-18. Consequently, a binary mixed model was established according to the balance of δ¹⁸O between two mixing components and used to estimate the fraction of infiltrated river water. Based on the spatial variation in δ¹⁸O values of groundwater near banks of rivers and estimated fraction of river water in the river and groundwater mixture, the area of river water infiltration was delineated; (2)Cl^- was taken as conservative tracer to reveal groundwater quality influenced by the river water infiltration. Groundwater Cl^- is closely related to Cl^- in river waters and unsaturated zone soils and can be used to assess the variation of quality in groundwater with the infiltration of river water. This work will benefit for evaluating river and groundwater interaction and water resources management.