Interaction Between River Water And Groundwater Under Influences Of Water Transfer

The upper Fenhe River is an important water conservation area and protection area in Taiyuan City.In recent years,in order to meet the demand for water supply,the Wanjiazhai Yellow River Diversion Project supplies 320 million m3 / yr to Taiyuan City through the Fen River,which will inevitably affect the local water resources.In order to find out the impact of water transfer,this article takes the section of Fenhe River receiving water from the Yellow River Diversion Project as an example.Through sampling and analysis of river water and groundwater during the water transfer period and interval,as well as setting observation / sampling sections in the riparian zone,placing long-term observations and sampling,and combining hydrological observation,hydrogeochemistry,mathematical statistics,and model simulation,the interactions between river water and groundwater are analyzed at the river section and riparian zone scales,the effects of water transfer are discussed,and the impacts of water transfer activities on the hydrology and water environment of the affected areas are analyzed.The results show that under the influence of water diversion from the Yellow River Diversion Project,the hydrologic and hydrochemical characteristics of the upstream reach of fen river are completely changed,the river valley groundwater is obviously affected,and the interaction between river and groundwater is obviously changed.Firstly,the hydrologic process and interaction between river and groundwater in the study area are obviously controlled by water diversion.Before the water diversion project is implemented,the water level of the river in the rainy season was higher than that in the dry season.However,after the implementation of the water transfer project,the water level of the rivers affected by the diversion is much higher than that of the rainy season.The natural hydrological process of the river is reversed by the diversion activity.The diversion raised river levels,which are almost always above groundwater levels throughout the year,allowing the water to continue to replenish groundwater.Affected by river water replenishment,a long-standing underground water mound directly connects to the river,distributes along the river,is formed in the riparian zone.Water transfer activities control the river water level,and the groundwater level in the valley also changes with the river water level.The further away from the river,the smaller the change range of the groundwater level,indicating that the influence of water diversion on the groundwater level decreased with the increase of the distance from the river.Secondly,the hydrochemical features of the water-receiving river are obviously changed by the transferred Yellow River water,and significantly affectes the hydrochemical characteristics of groundwater in the valley.Compared with the water from the upper reaches of fen river,the introduced water from the Yellow River has the hydrochemical characteristics of high EC value,Na+ and Cl-concentration,and the water quality is poor.Because the amount of water transferred is far greater than the amount of incoming water from the upper reaches of the Fenhe River,the water transfer has completely changed the hydrochemical characteristics of the river in the receiving river section,and the water quality of the river has been significantly degraded.At the same time,the amount of groundwater from river recharge in riparian zone is about 50%,so water diversion also has obvious influence on the hydrochemical characteristics of groundwater in riparian zone.The influence of water diversion on the hydrochemistry of groundwater in riparian zones did not subside during a hydrological year.Thirdly,the impact of water transfer on groundwater hydrochemistry is mainly concentrated in the riparian zone.Due to the influence of the terrain gradient of valley,the influence of the Yellow River water on the groundwater chemistry in the valley is mainly confined to the riparian zone and some low-reach transections.The longitudinal hydraulic gradient along the upstream of the reach is obviously greater than the lateral hydraulic gradient along the river to the valley edge,which is not conducive to the lateral groundwater flow from the river to both sides of the valley,and limits the influence scope of the river on the groundwater chemical characteristics.Under the action of lateral hydraulic gradient,the hydrochemical characteristics of groundwater in the river valley above some sections are affected by river water.Finally,groundwater still drains into rivers during a hydrological year.On the long view section of riparian zone,89.9% of the time the river water is in the state of discharge to groundwater.The discharge of groundwater into the river occurs only during the period when the diversion is suspended and the river level drops suddenly.In a hydrological year,the cumulative recharge of river water to groundwater per unit width of the river is 195.8m3,while the cumulative discharge of groundwater to river water is only 39.2m3.At the same time,the cumulative input of river water to groundwater solute is 125.0kg,while the cumulative discharge of groundwater to river water is only 25.3kg.