Study On The Effect Of Irrigation On Groundwater Recharge In The Oasis Plain Of The Kongque River Basin

The Kongque River Basin is located in the arid area of northwestern China.Rainfall is very scarce and evaporation is strong.Water shortage is serious.The local agricultural development often needs to use groundwater to irrigate to meet the growth needs of crops.Unreasonable irrigation methods often lead to many problems.Ecological and environmental issues.Therefore,in order to improve the efficiency of irrigation and utilization of water resources,it is urgent to explore the law of water infiltration and migration in the unsaturated zone of farmland under different irrigation methods,so as to provide a scientific basis for the determination of farmland irrigation quota and the efficient use of water resources in arid areas.Based on the geological survey project of the China Geological Bureau,this paper takes the oasis plain of the Kongque River Basin as the research area,and takes the local typical cash crop-cotton as the research object.It combines field in-situ experiments,indoor experiments and numerical simulations to analyze different rocks.The law of water infiltration and migration in the unsaturated zone under the conditions of nature and irrigation reveals the influence mechanism of irrigation methods on groundwater replenishment.The main results are as follows:(1)Through field in-situ tests,it was found that when the lithological structure of the aeration zone is coarse and fine,the infiltration rate of water after migration to the clay layer is drastically slowed down,and the irrigation water is enriched in the upper part of the clay layer,increasing irrigation water Recharge the groundwater lag time;when the lithological structure of the aeration zone is fine top and bottom coarse,the shallow soil is silt,and the deep is silt.The water holding capacity of the silt is strong,and the water is retained in the shallow loam after irrigation;Water penetrates the silt soil,and the silt fine sand has extremely poor water holding capacity,and the irrigation water is quickly supplied to the groundwater.During the test period,the lithology of the unsaturated zone controls the migration law of irrigation water in the unsaturated zone.(2)Comparing the influence of different irrigation volume,different irrigation methods and different lithology on groundwater replenishment,it is found that when the irrigation quota is less than 0.03m3/m2,the water can not effectively replenish groundwater with the coarse lithology structure at the top and bottom.Under the same irrigation conditions,the upper-fine and lower coarse lithological structure is more conducive to the infiltration of irrigation water than the upper coarse and lower fine lithological structure.The drip irrigation mode has a greater impact on the moisture of the unsaturated zone than the flood irrigation mode,and the time for the flood irrigation mode to restore the background value before irrigation is shorter.(3)Using the monitoring data of the in-situ test site,a numerical model of the vadose zone was established,and the coefficient of determination,Nash efficiency coefficient,and root mean square error were used to evaluate the results.The results show that HYDRUS-2D is effective in simulating field water migration under actual conditions.Higher accuracy.(4)Using numerical models to simulate groundwater replenishment laws under different irrigation methods,the simulation results found that: under flood irrigation,the irrigation replenishment rate for one irrigation with coarse lithological structures on top and bottom is24%,and the average irrigation replenishment rate during the growth period It is 32%.The irrigation replenishment rate for one-time irrigation of the coarse upper and lower fine lithology structure is 18.2%,and the average irrigation replenishment rate during the growth period is25%.Under the drip irrigation method,the irrigation replenishment rate for one irrigation of the upper fine and lower coarse lithology structure is 19.7%,the average irrigation replenishment rate during the growth period is 23%,and the irrigation replenishment rate for one irrigation of the upper coarse and lower fine lithology structure is 16.2 %,the average irrigation replenishment rate during the growth period is 21%.