Study On The Influence Of Precipitation And Mining On The Hydrochemical Composition Of Groundwater In Irrigation Area

The People’s Victory Canal Irrigation Area is an important grain production area in China.As an important irrigation water source,groundwater plays an important role in the development of agricultural production.The long-term high-intensity mining led to the continuous decline of the groundwater level in the People’s Victory Canal Irrigation Area,and a large area of falling funnels appeared.In the process of groundwater level fluctuation,the chemical composition of groundwater also changes..In order to study the effects of precipitation and exploitation on the chemical composition of groundwater,the inter-annual and intra-annual characteristics of the chemical composition of groundwater in the high-salinity area and low-salinity area of the study area in the wet and dry seasons with precipitation and groundwater level were studied.analysis and by calculating its relevance.Then,a simulation experiment was designed and carried out to simulate the influence of rainfall and mining on the chemical composition of groundwater,to analyze the change law of the chemical composition of groundwater under different rainfall infiltration scenarios and mining conditions,and to further explore the internal impact mechanism.Finally,a numerical model under rainfall infiltration recharge and artificial mining is constructed by numerical simulation method,and the influence of rainfall infiltration and artificial mining on the chemical composition of groundwater is quantitatively analyzed.The following main conclusions are drawn:（1）By analyzing the inter-annual and intra-annual variation trends of precipitation and the chemical composition of groundwater,it is found that the ion concentration is roughly negatively correlated with precipitation in the period with more average precipitation,and the period with less average precipitation Precipitation is positively correlated.Based on the observation well data of 10villages in the study area from 1996 to 2010,the correlation degree between precipitation and groundwater level and each ion in high and salinity areas were calculated respectively.And the influence degree of the low salinity area is greater than that of the high salinity area.The change of groundwater level in the high salinity area mainly has a large impact on anions,and a small impact on cations.The change of groundwater level in the low salinity area mainly has a large impact on cations,and a small impact on anions.（2）According to the simulation experiment analysis of the influence of precipitation and exploitation on the hydrochemical composition of groundwater,it is found that the media in the vadose zone,the characteristics of precipitation and the initial depth of the aquifer are different,and the influence of precipitation on the hydrochemical composition of groundwater is different.When the vadose zone is a soil-sand medium,a large amount of soluble salts in the soil enter the aquifer with the infiltration water flow,and precipitation has a greater impact on the chemical composition of groundwater than when the vadose zone is a sand medium;,the longer the seepage path,the larger the interaction area between water and rock and soil,and the greater the influence of precipitation on the chemical composition of water;when the precipitation is light rain,when the water level of the aquifer rises to the same height,the ratio of the action time of water flow to rock and soil during light rain The moderate rain time is long,and the impact on the chemical composition of groundwater is more obvious.Different groundwater exploitation intensity and cumulative exploitation amount have different effects on the chemical composition of groundwater.With the increase of mining volume,the water flow update speed becomes faster,the dissolution and filtration effect becomes stronger,and the concentration of cations in the aquifer generally increases,and the concentration of cations is higher than that in the non-mining area.（3）In the process of precipitation infiltration to recharge groundwater,the hydrochemical composition of groundwater is mainly affected by the content of soluble salt in the vadose zone and the effect of leaching,and is weakly affected by the alternating adsorption of cations.The influence of mining on the chemical composition of groundwater is mainly affected by the water quality of the recharge water source and the effect of leaching.（4）The groundwater solute transport models in the process of precipitation infiltration recharge and artificial exploitation were constructed using Hydrus-1D and Hydrus-2D,respectively.The simulation of Ca²⁺and Cl^-under the conditions of 0.5times,1.5 times,and 2 times of precipitation intensity and mining intensity found that the precipitation intensity was positively correlated with the changes of Ca²⁺and Cl^-concentrations.The change was about 26.3 mg/L,and the average change of Cl^-concentration was about 9.3 mg/L.Over time,the effect of rain intensity on the change of ion concentration gradually weakened;The mining intensity has a positive correlation with the changes of Ca²⁺and Cl^-concentrations.For every 320ml/min change in mining intensity,the average change of Ca²⁺concentration is about 3 mg/L,and the average change of Cl^-concentration is about 2.6 mg/L.The time of ion concentration change under different mining intensities is different,and the mining intensity is negatively correlated with the time of ion concentration change.