Experiment and Numerical Simulation of Seawater Intrusion under the Influences of Tidal Fluctuation and Groundwater Exploitation in Coastal Multilayered Aquifers

Abstract

The dynamic behavior of groundwater flow and salt transport is affected by tide and pumping in coastal multilayered aquifers. In this paper, two groups of experiments were conducted considering different constant head inland boundaries. The fluctuation of the groundwater level and the process of seawater intrusion in the multilayered aquifers were observed. A two-dimensional SEAWAT model is developed to simulate the seawater intrusion to coastal aquifers under the influences of tidal fluctuation and groundwater exploitation. The hydrogeological parameters in the model are calibrated by the records of the groundwater level and salinity measurements. The results showed that the simulated groundwater level and salt concentration match the observation well. The groundwater level has the characteristics of periodic fluctuation with tide. The lag time of the groundwater level fluctuation in each monitoring point increases slightly with the increasing distance from the saltwater chamber. For the low tide, the inland freshwater recharge has main effect on groundwater level fluctuation. The rising tide has a negative effect on the drawdown of the groundwater level induced by pumping. For the high tide, the tide plays a major role on groundwater level fluctuation, compared with the inland freshwater recharge. Compared with the condition of high head of inland recharge, larger saltwater intrusion lengths and area have been observed and simulated in the aquifer, which means that faster inland motion of the seawater wedge would occur when the inland recharge is small in the coastal aquifers. It revealed that inland recharge plays a major role in the seawater intrusion for the same pumping rate of groundwater in different seasons. The analysis provides insights into how the tide fluctuation, groundwater pumping, and inland recharge effect on the area and rates of seawater intrusion.

A Study on the Cause of Layered Seawater Intrusion in the Daqing River Estuary of Liaodong Bay, China

“…In the process of seawater intrusion, the external parameters such as local precipitation, pumping quantity, sea level and other related parameters such as permeability parameters and dispersion have an important impact on seawater intrusion. Laboratory experiments have shown that the differences in permeability parameters of different layers will cause different seawater intrusion in the multi-layered aquifers [21]. However, the reason for the differences in seawater intrusion between every two layers is not only the permeability parameters in the field.…”

“…The World Health Organization (WHO) indicated that freshwater is directly nonpotable when it is mixed with about 1% volume of seawater (250 mg/L chloride) [13]. There are two kinds of inducement factors for seawater intrusion, including natural factors (sea level rising, drought and tide) and human factors (groundwater pumping and mariculture) [14][15][16][17][18][19][20][21][22][23]. Compared with the minor equilibrium damage caused by sea level rise, seawater intrusion caused by a large imbalance of hydraulic gradient due to over-pumping groundwater is more important [1,18,[24][25][26][27].…”

“…Seawater intrusion is a density-dependent flow problem [4,28,29]. Several methods have been developed to address it, including analytical solution, experimental and simulation methods [18,21,23,24,[28][29][30][31][32]. Analytical solution is always used to locate a steady fresh-saltwater interface location under many assumed conditions [19,[33][34][35].…”

“…A coastal stratum deposit is affected by the alluvial-diluvial effects of coastal rivers and presents the stratification phenomenon. Some scholars have studied the law of seawater intrusion in the multi-layered aquifer system [7,19,21,42,[53][54][55][56][57]. A few studies have considered seawater intrusion under the influence of pumping in multi-layered aquifers.…”

“…A few studies have considered seawater intrusion under the influence of pumping in multi-layered aquifers. For example, Guo et al [21] studied saltwater intrusion in multi-layered aquifers in the laboratory, but only pumping in a confined aquifer. Chang et al [42] studied the interface change between brine and freshwater under pumping in multi-layered aquifers, but studies regard the complex ground-well pumping as a two-dimensional cross-section.…”