The Response Of Groundwater To Tides In The Coastal Aquifer System

It is a worldwide problem that the marine ecological environment is deteriorated by the land-based pollution caused by groundwater discharge.Although hydrogeologists have done a lot of research on the analytical and numerical solutions of groundwater response to tide in the coastal aquifer system,the groundwater response to tide in the complex model is still unknown.In the coastal aquifer system,the response of groundwater to tide needs to be studied.There are many factors that affect the response of groundwater to tide,such as:hydraulic diffusivity,aquifer type,tide,bottom slope,leakage,etc.In order to better understand the propagation mechanism of groundwater in the coastal aquifer system,we set up the aquifer system model with leakage,slope,double frequency tide,confined and unconfined,expand the equation to the complex field,and use the superposition principle of the solution to obtain the analytical solution.On the basis of this model,three models are simplified to obtain the analytical solutions of groundwater response to tide.The results showed that if the hydraulic diffusivity is small or the leakage is large,the tide can only transport a limited distance towards inland.The least square fitting method can accurately identify the hydraulic diffusivity.If the thickness of aquifer and the radius of observation well are known,the permeability coefficient and storage coefficient can be separated.The attenuation rate of the tidal signal is linearly related to the cotangent function of the sea water oscillation.The slope and intercept in the linear relationship are both functions of the hydraulic diffusivity.The numerical simulation results showed that the method can accurately estimate the hydraulic diffusivity of aquifer.This paper mainly studies the response of groundwater to tide in four different aquifer systems in coastal area.In the first chapter,the development of groundwater response to tide in coastal aquifer system is introduced,followed by the current situation of aquifer research in coastal area,and finally the main work of this paper is proposed.In the second chapter,the response of groundwater to tide in the slope leakage aquifer system is studied,and the mathematical model is established.The model is extended to the complex field to separate variables,which is transformed into the fourth order ordinary differential equation.The analytical solution is obtained by using the Mathematica software and the superposition principle of the solution.In the third chapter,t.hree simplified models are studied,which are simplified model of bottom slope and aquifer,simplified model of bottom slope aquifer and leakage,simplified model of bottom slope,aquifer,leakage and tidal frequency.The analytic solutions of three simplified models are obtained by using the method of variable separation and the principle of superpositionIn the fourth chapter,the response of groundwater to tides in three simplified models is studied.The least square fitting method and the method of tidal signal attenuation rate are used to identify the hydraulic diffusivity of aquifer.The analytical solution of the aquifer system model with leakage,slope,double frequency tide and confined unconfined aquifer obtained in this paper can be used as a reference for hydrogeolo-gists.The method of attenuation rate of tidal signal is of great significance for pollution restoration and marine protection in coastal areas.