Groundwater sustainability: a review of the interactions between science and policy

Numerical simulation of seawater intrusion to coastal aquifers and brine water/freshwater interaction in south coast of Laizhou Bay, China

Since 1980s, seawater intrusion in coastal aquifers caused by groundwater over-abstraction has led to extensive deterioration in groundwater quality and quantity and has been fazing local residents in Zhoushuizi district of the metropolitan Dalian City in northern China. In this study, a three-dimensional (3D) density-dependent numerical model was constructed to simulate the seawater intrusion process in heterogeneous coastal aquifers in Zhoushuizi district of the metropolitan Dalian City. Considering that the groundwater flow in karst aquifers in northern China is relatively uniform, approximately following Darcy’s law, the fracture-karst aquifer in Zhoushuizi district of Dalian City was simplified as an equivalent porous medium. To further identify the hydrogeological parameters of the aquifers in the study area, the model was calibrated and validated using the observation heads and concentrations. Based on the current groundwater abstraction conditions of the study area, the calibrated and validated model was then applied to predict the dynamics and trend of seawater intrusion for the following 30 years from 2010 to 2040 under different rainfall scenarios. The overall extent of seawater intrusion in the future would be even more severe under different prediction scenarios. This 3D seawater intrusion model provides the theoretical basis for implementing a reasonable allocation of groundwater resource, which may significantly affect the sustainability of water resources.

Numerical modeling of seawater intrusion in Zhoushuizi district of Dalian City in northern China

Subsurface barriers have been used as one of the engineering measures to prevent saltwater intrusion in the coastal aquifers in China However, the effectiveness of those barriers has not been studied thoroughly In this research, comparative studies using sandbox test as a physical model and the FEFLOW-based groundwater numerical model were conducted for better understanding of the dynamic processes of saltwater intrusion with and without subsurface barriers Both laboratory tests and numerical simulation without subsurface barriers showed that the saltwater front intruded to 18, 55 and 63 in the aquifer in 10, 20 and 40 min, respectively The impact of the different permeability of the subsurface barriers to the migration distance and diffusion of saltwater front was also tested in the laboratory and simulated by using the two-dimensional numerical model Results showed the saltwater front could still pass through the subsurface barrier and continued moving forward when the permeability K of the subsurface barriers was 99 × 10−7 m/s When the K of the subsurface barriers was 13 × 10−7 m/s, the salt–front passed through the subsurface barrier in 40 min, and the migration rate of the salt–fresh water interface did not change in 70 min When the K was 37 × 10−8 m/s, the saltwater front could not go through the subsurface barriers These research results indicated that the subsurface barriers with low permeability (K = 37 × 10−8 m/s) could prevent the saltwater intrusion effectively The results of this case study provide important practical significance for the prevention of saltwater intrusion in coastal areas

Laboratory tests and numerical simulations on the impact of subsurface barriers to saltwater intrusion

Increasing impervious land cover has great impacts on groundwater regimes in urbanized areas. Low impact development (LID) is generally regarded as a sustainable solution for groundwater conservation. However, the effects of LID on the spatial-temporal distribution of groundwater are not yet fully understood. In this case study, a coupled Storm Water Management Model (SWMM) and Finite Element Subsurface FLOW system (FEFLOW) model was used to simulate surface and groundwater flow in an urbanized area in Shenzhen, China. After verification, the model was used to analyze the spatial-seasonal variations of groundwater head and hydrological processes under different LID scenarios. The results indicate that if the runoff from 7.5% and 15% of impervious area is treated by LID facilities, the annual surface runoff decreases by 5% and 9%, respectively, and the spatial average groundwater head relative to sea level pressure increases by 0.9 m and 1.7 m in the study area, respectively. The rise in groundwater head generally decreases from the recharge zones to the discharge zones surrounded by the streams and coastal waters. However, the groundwater head change is determined not only by the location in the catchment, but also by the hydraulic conductivity of underlying aquifer and LID infiltration intensity. Moreover, LID significantly enhances groundwater recharge and aquifer storage in the wet seasons; in turn it increases aquifer release and groundwater discharge in the dry seasons. However, LID has the potential to increase the risk of groundwater flooding during wet seasons in areas with poor aquifer drainage capacity and shallow groundwater depth. The findings from this study provide the basis for further assessing the benefit and risk of LID infiltration for groundwater supplementation in the urbanized areas.

https://www.mdpi.com/2073-4441/10/6/803/pdf

Modeling the Spatial and Seasonal Variations of Groundwater Head in an Urbanized Area under Low Impact Development

During the 1990s, groundwater overexploitation has resulted in seawater intrusion in the coastal aquifer of the Shenzhen city, China. Although water supply facilities have been improved and alleviated seawater intrusion in recent years, groundwater overexploitation is still of great concern in some local areas. In this work we present a three-dimensional density-dependent numerical model developed with the FEFLOW code, which is aimed at simulating the extent of seawater intrusion while including tidal effects and different groundwater pumping scenarios. Model calibration, using waterheads and reported chloride concentration, has been performed based on the data from 14 boreholes, which were monitored from May 2008 to December 2009. A fairly good fitness between the observed and computed values was obtained by a manual trial-and-error method. Model prediction has been carried out forward 3 years with the calibrated model taking into account high, medium and low tide levels and different groundwater exploitation schemes. The model results show that tide-induced seawater intrusion significantly affects the groundwater levels and concentrations near the estuarine of the Dasha river, which implies that an important hydraulic connection exists between this river and groundwater, even considering that some anti-seepage measures were taken in the river bed. Two pumping scenarios were considered in the calibrated model in order to predict the future changes in the water levels and chloride concentration. The numerical results reveal a decreased tendency of seawater intrusion if groundwater exploitation does not reach an upper bound of about 1.32 × 104 m3/d. The model results provide also insights for controlling seawater intrusion in such coastal aquifer systems.

/pdf/numerical-modelling-of-seawater-intrusion-in-shenzhen-china-1lp11qvs2k.pdf

Numerical modelling of seawater intrusion in Shenzhen (China) using a 3D density-dependent model including tidal effects

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Numerical modelling of seawater intrusion in Shenzhen (China) using a 3D density-dependent model including tidal effects