Study On The Interaction Between Groundwater And Surfacewater And Land-Sea Exchange Flux In Guangdong-Hong Kong-Macao Greater Bay Area Based On Coupled Model

The interaction between surface water and groundwater plays an important role in the global water cycle.The study on the interaction between groundwater and surface water is the key factor to accurately understand the evolutionary variation of water quantity and quality.Guangdong-Hong Kong-Macau Greater Bay Area is the fourth largest bay area in the world after New York Bay area,San Francisco Bay area and Tokyo Bay area.This Bay Area is an important space carrier for China to build world-class urban agglomeration and participate in global competition.River network is really dense along the bay,and the interaction between surface water and groundwater and the exchange of sea and land water quantity are remarkable.However,there is still a lack of research on the interaction between surface water and groundwater in this area,and systematic understanding of the temporal and spatial variation of surface water and groundwater and the exchange flux between sea and land are scarce.It is of great significance to study the interaction between groundwater and surface water in the Greater Bay Area and the interaction between sea and land in order to reveal the process of water cycle in the bay area and to realize the sustainable utilization of water resources.The main body of Guangdong-Hong Kong-Macau Greater Bay Area is located in the Pearl River Delta Basin.In this study,the surface water-groundwater coupling model GSFLOW,was used to construct the Pearl River Delta basin coupling model.The performance of the model was verified by using groundwater level observation data,remote sensing products of evapotranspiration and soil moisture.The coefficient of determination(R~2)is 0.7691 for simulated and remote sensed evapotranspiration and is0.8027 for simulated and remote sensed soil moisture.R~2for simulated and observed groundwater level is equal to 0.602.The verification results show that the performance of the calibrated model is acceptable.The calibrated model is used to study the process of Guangdong-Hong Kong-Macau Greater Bay Area's water cycle,the interaction between surface water and groundwater and the interaction between land and sea.The main conclusions are as follows:(1)the average annual surface fresh water discharge at the main eight outlets from 2000 to 2015 is 2812.44*10~8 m~3/yr.The Modaomen outlet ranks first in the average annual fresh water discharge,with an annual average of850.99*10~8 m~3/yr,then followed by Hengmen(589.74*10~8 m~3/yr),Humen,Hutiaomen,Hongqimen,Jitmen,Xiangjiaomen and Yamen;(2)from 2000 to 2015,the average fresh groundwater discharge and seawater invasion were 2.74*10~8 m~3/yr and 1.52*10~8 m~3/yr,respectively.The discharge area was mainly distributed on the east bank of Pearl River Estuary,the west bank of Huangmao Sea and around Daya Bay.The intrusion area was mainly located in Nansha to Zhongshan and the east coast of Huangmaohai in the west bank of Pearl River Estuary;(3)Based on the sensitivity analysis results,the flux between river and aquifer is most sensitive to the parameter of vertical hydraulic conductivity of the riverbed,and the other surface water-groundwater interaction fluxes are most sensitive to the parameter of maximum runoff area percentage.The discharge of underground fresh water from the seafloor and the amount of seawater intrusion are most sensitive to the maximum area of runoff production,and the discharge of fresh water from the surface of land is most sensitive to rainfall.