Interaction Between Yellow River Water And Groundwater In The Shanxi-Shaanxi Gorge

The Shanxi-Shaanxi Gorge is located in the middle reaches of the Yellow River.It is located in the Loess Plateau,with complex geology,and is the longest continuous canyon on the Yellow River.The Yellow River passes through the Shanxi-Shaanxi Gorge,receiving supplies from numerous tributaries on both sides of the river,and flows through the areas with the worst soil erosion.In recent years,the implementation of water conservancy and water conservation projects has significantly increased the vegetation coverage rate,resulting in changes in the underlying surface and the transformation relationship between different water bodies and significantly reducing the flow of tributaries flowing into the Yellow River.It is of great significance to study the transformation relationship between the Yellow River and groundwater in this region,identify the evolution and source of groundwater,and make rational use of local water resources and the high-quality development of the Yellow River.This article selectes the Fugu-Longmen Yellow River section.A total of 207 samples were collected in April,June and October 2021.Among them,there are 46 the Yellow River samples,42 tributary samples and 119 groundwater samples.The interaction between the Yellow River and groundwater is analyzed by means of hydrologic observation,hydrogeochemical method,water balance and radon model,to analyze the interaction between the Yellow River and groundwater and the influence of natural and human factors on the chemical evolution of groundwater is discussed.The following conclusions were drawn:1、The Yellow River discharge has been on the rise in the past 20 years,with a large amplitude after 2011,which may be the result of human water conservation projects such as afforestation,returning farmland to forest,and building silt dams.The section flow method shows that Fugu-Longmen Yellow River is a obtain reach,which is recharged by tributaries and groundwater.Fugu-wubao Yellow River is an obtain section and Wubao-Longmen Yellow River is a loss section.The operation of upstream reservoirs and seasonal variations complicate the exchange of water between groundwater in the valley and the Yellow River.Radon is a strong indicative tracer and is well suited for the study of the interaction between river and groundwater at the river section scale.The concentration of radon in groundwater is significantly higher than that in the Yellow River.The radon concentration in the Yellow River showed an alternating trend of ascending and descending along the Yellow River,indicating that there were sub-reaches of Fugu-Wubao and Wubao-Longmen of the Yellow River that had a large amount of groundwater recharge.The radon model is used to calculate the exchange of water volume,and the result is roughly the same as the section flow analysis.2、The groundwater in the valley along the Yellow River is affected by natural and human factors,which leads to the change of water type SO₄-Cl-Ca-Mg→HCO₃-Ca-Mg/HCO₃-Na→SO₄-Cl-Na.The ions in the water samples mainly come from the dissolution of silicite and evaporite.In the process of water flow,halite,gypsum,dolomite and calcite continuously dissolve,cation exchange and dedolomitization also occur.In addition,the groundwater in the valley will exchange water with the bedrock fissure water in the mountain area,the Yellow River water and the rain water.In the rainy season,all the water samples will be affected by the rain,resulting in heavy isotope dilution.3、By comparing the contribution of tributaries and groundwater to the discharge and solute of the Yellow River,it is concluded that the net discharge of groundwater into the Yellow River in dry season is 77 m³/s;The flow of tributaries into the Yellow River is 22m³/s and 72 m³/s during the rainy season.The net solute inflow of groundwater in dry season was 142 kg/s.The solubility of the tributaries is 49 kg/s in the rainy season and 13kg/s in the dry season.Today,the groundwater carries more water and solubility for the Yellow River than that of the tributaries.