River-groundwater Conversion And Its Ecological Effects In The Laohe River Basin

In arid and semi-arid areas of China,rivers and groundwater are frequently transformed,and their conversion rules play a crucial role in the rational development and utilization of water resources and the maintenance of aquatic ecosystem functions.This article is based on national natural science foundation of China and the key research and development plan of Shaanxi Province,and the Laohe River Basin as a typical research area.On the basis of fully collecting previous research results and field hydrogeological surveys and experiments,Analyze the conversion relationship between rivers and groundwater in the study area,discuss the evolution of the river basin's ecological pattern induced by the river-groundwater conversion under the influence of climate change and human activities,using the base flow separation and numerical simulation method to calculate river basin and the transformation of quantity of groundwater,and Simulate of the relationship between river and groundwater conversion and its ecological effects in a changing environment.The main research results are as follows:(1)The river and groundwater have undergone three transformations in total,and the geological and geomorphic conditions control the basic pattern of the river and groundwater conversion in the Laohe River Basin.In the bedrock mountainous area upstream of the basin,groundwater is discharged into the river along the fissures,and the river and groundwater are completed.The first transformation;in the middle and upper part of the alluvial fan in the middle of the basin,the river leaked to recharge groundwater,completing the second transformation of the river and groundwater;at the front edge of the alluvial fan and the Weihe alluvial plain downstream of the basin,groundwater was discharged In the river,the third transformation of river and groundwater was completed.Affected by climate change and human activities,the amount of groundwater conversion in the middle reaches of the river decreases,resulting in insufficient recharge of groundwater in the lower reaches of the river basin,the location of the frontal overflow zone of the alluvial fan,and the area of groundwater replenishment lakes shrinking or even disappearing.(2)A three-dimensional geological structure model,a hydrogeological conceptual model and a three-dimensional heterogeneous groundwater flow numerical model were established in the plain area of the Laohe River Basin.The groundwater flow numerical model was solved using GMS software.After model identification and verification,the groundwater level was dynamically fitted The errors are all less than 0.5m,the groundwater flow field is well fitted at the end,and the hydrogeological parameters are in line with the actual situation,indicating that the model has good reliability and simulation.(3)Through the comparative analysis between the three types of five base flow segmentation methods,combined with the groundwater flow numerical model,the conversion amount of river and groundwater is calculated,and the annual change of conversion amount and its main influencing factors are analyzed.(1)In the Qinling Mountain section,groundwater is discharged into the river along the fissures,the conversion amount is3431×10⁴m³,the base flow index is 0.32,the base flow modulus is 2.62L·km^-2·s^-1;affected by atmospheric precipitation,its annual distribution follows the abundance The dry season has obvious changes,and the conversion during the high water season from July to October accounts for 69.3%of the total conversion amount during the year.(2)In the middle and upper part of the alluvial and alluvial fan,the Laohe River Outlet-Luoshi Village section,the river water leakage recharges the groundwater,and the conversion amount is 5672×10⁴m³,accounting for 40.6%of the groundwater resources in the plain area of the river basin;the conversion amount changes within the year with the river The runoff fluctuates and increases or decreases.The conversion during the high water period from July to October accounts for63.5%of the total conversion during the year.(3)In the front of alluvial and alluvial fans and alluvial plains,the total amount of groundwater to river conversion is 6011×10⁴m³,and the annual change is affected by the upstream river runoff,precipitation in the area and artificial exploitation.At the front edge of the alluvial and alluvial fan of the Laohe River,the conversion amount is concentrated in the high water period;while the conversion amount in the alluvial plain is larger than that in the high water period.(4)Based on climate change and human activities,the relationship between river and groundwater conversion and its ecological effect under simulated changing environment are simulated.The results show that:increased groundwater extraction and reduced rainfall will reduce the conversion of groundwater to the river and cause the overflow zone to move down;the effect of the total amount of river runoff on the conversion of river and groundwater is not absolute,and the annual distribution of runoff is also One of the important factors affecting the conversion of river water and groundwater.