Yinchuan Plain Yongning Irrigation District Research On Groundwater Circulation And Evolution

The Yongning Irrigation District is located in the south of Yinchuan City and is an important irrigation base for the Yellow River in the Yinchuan area.As the scale of production and domestic water use expands,groundwater resources become increasingly tense.Groundwater chemistry and isotope characteristics contain information on groundwater cycle evolution,and understanding the groundwater cycle process and evolution mechanism is the key to solving the shortage of water resources.This paper analyzes the isotope distribution of soil water before and after precipitation,regional isotope characteristics of groundwater and chemical distribution of groundwater to explore the recharge of groundwater by precipitation and the regional groundwater circulation and evolution.Get the following recognitions:?1?The isotope changes of soil water at different depths before and after precipitation have an important indicator on the analysis of the recharge mechanism of precipitation to groundwater.When precipitation of a general scale occurs,the isotope of soil water at a depth of 30 cm underground is significantly depleted after rain,and the isotope distribution of soil water is almost unchanged at a depth of 70 cm;when continuous large-scale rainfall occurs,the profile is 270 cm The soil water isotope at the depth can still respond effectively to precipitation.During rainfall,the soil at a depth of 70 cm below the ground can directly receive precipitation replenishment;the soil at a depth of 70 cm down mainly depends on the slow infiltration of the upper layer of original soil water mixed with rainwater,The response lags.The isotope variation characteristics of soil water at different depths can be used as an important basis for irrigation replenishment.The isotope distribution of the entire soil profile before and after irrigation shows significant changes.?2?Groundwater is recharged by precipitation,Yellow River water and irrigation water.Affected by evaporation in the groundwater flow,isotopes are gradually enriched,and the hydraulic connections between different geological units are close.The groundwater flow rate in the alluvial plain is slow,and the correlation of deuterium surplus becomes worse.The largest lake in the study area,Hequan Lake,is recharged by the groundwater and lake water on the east bank of the lake.The replenishment ratio is 75%and 25%respectively.?3?The correlation between the main ions in groundwater and TDS is good.With the increase of TDS,the Na⁺and Cl^-content in the water is relatively increased,and the proportion of Ca²⁺,Mg²⁺and HCO₃^-is relatively reduced.In the alluvial slope plain and river-lake accumulation plain,the evolution mechanism of groundwater chemical components is controlled by water-rock action.In the alluvial plain,groundwater is significantly affected by evaporation and concentration.The Na⁺content in groundwater is significantly higher than that of Cl^-.This is due to the dissolution of Glauber's salt in the alluvial slope plain,and alternating adsorption of cations in the river-lake accumulation and alluvial plain.In the groundwater circulation,rock salt and gypsum continue to dissolve,and calcite is supersaturated and precipitated.The groundwater on the west bank of the Yellow River is controlled by water and rock,and the main ion concentration and TDS decrease with the distance of the river bank.The groundwater on the east bank is controlled by water and rock and evaporation,and the ion content and TDS are richer than those in the west bank.