Study On Wellhead Protection Area Along The Yellow River In Zhengzhou By Numerical Simulation Method

The Jiuwutan and Beijiao wellheads are representative riverside groundwater sources which located on the south bank of the Yellow River,northern suburb of Zhengzhou.This two wellheads mainly exploit the shallow groundwater and solve the intensive situation of water supply in Zhengzhou,ensuring the water resource safety to some extent.On the basis of relevant data collecting and hydrogeology survey,we have divided the groundwater,placing depth above 300 meters,into two aquifer groups,including shallow phreatic aquifer group and middle-deep confined aquifer group.The numerical simulation model,dating from 1995.1.1 to 2013.12.31,is established by the GMS.After calibrating the model in the trial-and-error method,we have got a receivable fitting in the flow field and hydrograp level.The established model has resonable hydrogeological structure,sensible parameters and proper boundary conditions,which basically reflects the hydraulic characteristics of groundwater and its connection between the Yellow River.We set up a four-year prediction model of particle tracing,dating from 2014.1.1 to 2017.12.31,according to the aboved long-sequence numerical simulation model.Through the comparative study of particle tracing under different exploiting yield and different well spacing,we find that the increasing exploiting can lead to a faster movement and a longer path of the particle.That is a result of hydrodynamic conditions change and inseasing hydraulic gradient,after the drop of ground water level under the condition of riverside mining.Meanwhile,the well spacing can influence the shape of the particle migration path.Take the particle tracing results,well spacing and exploitation planning into consideration,we delimit the wellhaed protection area of Jiuwutan and Beijiao synthetically.Fot the Jiuwutan wellhead,the primary and second protection zone which including the Yellow River reach is defined on the basis of the particle tracing result under the largest yield.And to Beijiao wellhaed,the primary protection zone is confirmed by the tracing length of 100 days under maximum exploition,while the second protection zone combined the tracing length of 1000 days under present exploition with the consideration of fish-pond production together.Wellhead protection area,as an important technical method of water quality control,should be fully applied to the water source management and pollution prevention.