Quantitative Submarine Groundwater Discharges In Chongming Island

Groundwater hydrodynamics in coastal aquifers subject to tides and waves are an important topic in coastal hydrogeology as a consequence of the significant development of human activities near the shoreline. Numerical simulations of groundwater hydrodynamics in coastal aquifers have rapidly evolved over the last three decades.We investigated a zone which is located in south shore of Chongming Island. On the tidal flat we has chosen a vertical profile, using automatic sensor in the study area for obtaining the head, temperature and salinity. The tidal periodic changes of groundwater level in coastal aquifers contain important hydrogeological information.By collecting and analyzing the study area’s related data and information of the hydrogeology, sea tide, marine hydrology and weather, and using the two dimensional finite element model MARUN, the medium-scale numerical model was established to simulate the observed pressure of groundwater.With the analysis for the relevant data and observation data of groundwater level in the study area, we can conclude that:The water level of south branch of Yangtze river is influenced by the tide significantly due to the two irregular semidiurnal tides of different cycle and the spring-neap cycle of 15 days. The south branch water of the Yangtze River is fresh water, and its salinity is lower than the salinity of inland groundwater.In the south of Chongming Island, the aquifer in the tidal flat contents a lot of mud and its permeability is low, water level fluctuation decay quickly in the aquifer.This paper obtain and analysis the observations of the mudflat in the south of Chongming Island. The numerical model MARUN was used to simulate the field observations and adjust the hydrogeological parameter. Based on the field measurements and numerical simulations, we have the following findings:The estimated values of Kx,Kz,Ss,porosity of the aquifer in the study area aquifer, are 8×10-7m/s,4×10-7m/s,10-5 /m,0.4 respectively. The SGD of the mudflat in the study area in an entire spring-neap tide cycle is 0.46 m3d-1m-1and the net freshwater recharge from inland is 0.08 m3d-1m-1,about 17.6% of the total SGD.