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Study region: The current study was applied on two extensive and important regional aquifers: the first is the shallow aquifer of Gaza coastal aquifer (GCA), Palestine and the second is the deep aquifer of the Nile Delta (NDA), Egypt. The two sites are suffering from high stress water resource and contamination by saltwater intrusion (SWI). SWI is natural phenomena that damage the fresh groundwater in two sites and increase the aquifer. Shallow and deep aquifer plays a natural role for keeping the quality of freshwater from SWI in costal aquifers. This study aims to compare different methods for aquifer protection from SWI by analyzing their efficiency using numerical groundwater models in the two sites. Study focus: The finite difference for density dependent groundwater flow model SEAWAT was used on two sites to investigate the extension of SWI without management (base case) and the four methods to control SWI. The numerical models were calibrated for the base case using the other studies and field data to simulate the intrusion in GCA and NDA. The investigated four methods focused on (1) subsurface physical barriers of Cut-off walls), (2) subsurface physical barriers of subsurface dams, (3) the hydraulic method including Treatment and Recharge of collected wastewater, Abstraction and Desalination of low salinity by brackish water, and (4) the land reclamation using earth fill method. New hydrological insights for the region: The simulated results indicated for the base cases that the intrusion salt mass (NaCl) reached 6068 × 103 kg for GCA and 8863 × 1010 kg for NDA. Moreover, the percentage of aquifer salt mass was decreased and reached 17.60%;, 23.30%; 7.85% and 6.20% in for shallow aquifer while it reached 2.05%; 0.90%; 5.30% and 0.80% in deep aquifer for the physical subsurface dam of cut-off wall, subsurface dam, hydraulic method and land reclamation technique respectively. On the other side the control methods in shallow aquifers is more effective than the deep one. The subsurface barriers and land fill method isn’t effective for deep aquifer while the hydraulic of TRAD method has a positive effect on SWI in shallow and deep aquifers. The current study could be carried out around the world in different coastal hydrological groundwater thickness using the effective method to increase the mitigation of SWI and increase the fresh groundwater resources in coastal aquifers.

Meteoric groundwater discharge (MGD) to coastal regions transports terrestrial freshwater and nutrients that may alter coastal ecosystems by supporting harmful algal blooms. Estimation of MGD-driven nutrients is crucial to assess potential effects on coastal zones. These estimates require a reliable assessment of MGD rates and pore water nutrient concentrations below subterranean estuaries. To estimate nutrient delivery into a subterranean estuary in the Indian River Lagoon, FL., pore water and surface water samples were collected from nested piezometers along a selected transect on five sampling episodes. Groundwater hydraulic head and salinity were measured in thirteen onshore and offshore piezometers. Numerical models were developed, calibrated, and validated using SEAWAT to simulate MGD flow rates. Lagoon surface water salinity exhibits no spatial but mild temporal variation between 21 and 31. Pore water salinity shows tremendous variation in time and space throughout the transect except in the middle region of the lagoon which exhibits uniform but elevated salinities up to 40. Pore water salinity as low as that of freshwater happens to occur in the shoreline regions during most of the sampling episodes. Both pore water and surface water show remarkably higher total nitrogen TN than total phosphorus TP concentrations and most TN is exported as NH 4 , reflecting the effect of mangroves on the geochemical reactions that reduce NO 3 into NH 4 . Nutrient contributions of pore water and lagoon water exceed the Redfield TN/TP molar ratio in all sampling trips by up to a factor of 48 and 4, respectively. Estimated TP and TN fluxes receives by the lagoon via MGD are 41-106 and 113-1478 mg/d/m of shoreline. The molar TN/TP ratio of nutrient fluxes exceeds the Redfield ratio by a factor of up to 3.5 which indicates the potential of MGD-driven nutrients to alter the lagoon water quality and support harmful algal blooms., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Sustainable management of natural water resources and food security in the face of changing climate conditions is critical to the livelihood of coastal communities. Increasing inundation and saltwater intrusion (SWI) will likely adversely affect agricultural production and the associated beach access for tourism. This study uses an integrated surface-ground water model to introduce a new approach for retardation of SWI that consists of placing aquifer fill materials along the existing shoreline using Coastal Land Reclamation (CLR). The modeling results suggest that the artificial aquifer materials could be designed to decrease SWI by increasing the infiltration area of coastal precipitation, collecting runoffs from the catchment area, and applying treated wastewater or desalinated brackish water-using coastal wave energy to reduce water treatment costs. The SEAWAT model was applied to verify that it correctly addressed Henry's problem and then applied to the Biscayne aquifer, Florida, USA. In this study, to better inform Coastal Aquifer Management (CAM), we developed four modeling scenarios, namely, Physical Surface Barriers (PSB), including the artificial aquifer widths, permeability, and side slopes and recharge. In the base case scenario without artificial aquifer placement, results show that seawater levels would increase aquifer salinity and displace large amounts of presently available fresh groundwater. More specifically, for the Biscayne aquifer, approximately 0.50% of available fresh groundwater will be lost (that is, 41,192 m 3 ) per km of the width of the aquifer considering the increasing seawater level. Furthermore, the results suggest that placing the PSB aquifer with a smaller permeability of <100 m per day at a width of approximately 615 m increases the available fresh groundwater by approximately 45.20 and 43.90% per km of shoreline, respectively. Similarly, decreasing the slope on the aquifer-ocean side and increasing the aquifer recharge will increase freshwater availability by about 43.90 and 44.50% per km of the aquifer. Finally, placing an aquifer fill along the shallow shoreline increases net revenues to the coastal community through increased agricultural production and possibly tourism that offset fill placement and water treatment costs. This study is useful for integrated management of coastal zones by delaying aquifer salinity, protecting fresh groundwater bodies, increasing agricultural lands, supporting surface water supplies by harvesting rainfall and flash flooding, and desalinating saline water using wave energy. Also, the feasibility of freshwater storage and costs for CAM is achieved in this study., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Remediation measures are crucial to prevent or reverse seawater intrusion deteriorating coastal fresh groundwater resources. The mixed hydraulic barrier approach, as a combination of positive and negative hydraulic barriers, holds promising advantages especially for arid areas because extracted water provides a resource for injection after treatment. However, transient remediation mechanisms and impact of parameters are still unsatisfyingly understood. Therefore, the feasibility and optimal management of mixed hydraulic barriers as well as a comparison to single positive and negative barriers are explored with a synthetic 2D variable-density model of an already salinated, unconfined coastal aquifer using SEAWAT and FloPy. The hydraulic conductivity, porosity, injection and extraction rate, barrier locations, injection salt concentration, and reduction of pumping stress are varied jointly to determine the parameters' impact and interdependencies. The hydraulic conductivity controls the overall remediation potential as a hydrogeological component. Reduced inland abstractions of supply wells and the injection rates of the positive barrier show the largest remediation effects. However, locating the positive barrier within the salt wedge poses the risk of trapping salt landside. A sole negative barrier did not improve remediation substantially. This study thus shows that remediation with mixed hydraulic barriers can be feasible if implemented according to local conditions., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Climate change such as altered frequency and intensity of storm surge from tropical cyclones can cause saltwater intrusion into coastal aquifers. In this study, a reference SEAWAT model and a diagnostic SEAWAT model are developed to simulate the temporal variation of surficial aquifer total dissolved solids (TDS) concentrations after the occurrence of a storm surge for exploration of the effects of storm surge on the extent of saltwater intrusion into the surficial aquifer in coastal east-central Florida (USA). It is indicated from the simulation results that: (1) rapid infiltration and diffusion of overtopping saltwater resulting from storm surge could cause a significant and rapid increase of TDS concentrations in the surficial aquifer right after the occurrence of storm surge; (2) rapid infiltration of freshwater from rainfall could reduce surficial aquifer TDS concentrations beginning from the second year after the occurrence of storm surge in that the infiltrated rainwater could generate an effective hydraulic barrier to impede further inland migration of saltwater and provide a downgradient freshwater discharge for saltwater dilution and flushing counteracting the effects of storm surge on the extent of saltwater intrusion; and (3) infiltrated rainwater might take approximately eight years to dilute and flush the overwhelming majority of infiltrated saltwater back out to the surrounding waterbodies, i.e., the coastal lagoons and the Atlantic Ocean., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The Central Huai Luang Basin is one of the important rice producing areas of Udon Thani Province in Northeastern Thailand. The basin is underlain by the rock salt layers of the Maha Sarakham Formation and is the source of saline groundwater and soil salinity. The regional and local groundwater flow systems are the major mechanisms responsible for spreading saline groundwater and saline soils in this basin. Climate change may have an impact on groundwater recharge, on water table depth and the consequences of waterlogging, and on the distribution of soil salinity in this basin. Six future climate conditions from the SEACAM and CanESM2 models were downscaled to investigate the potential impact of future climate conditions on groundwater quantity and quality in this basin. The potential impact was investigated by using a set of numerical models, namely HELP3 and SEAWAT, to estimate the groundwater recharge and flow and the salt transport of groundwater simulation, respectively. The results revealed that within next 30years (2045), the future average annual temperature is projected to increase by 3.1°C and 2.2°C under SEACAM and CanESM2 models, respectively, while the future precipitation is projected to decrease by 20.85% under SEACAM and increase by 18.35% under the CanESM2. Groundwater recharge is projected to increase under the CanESM2 model and to slightly decrease under the SEACAM model. Moreover, for all future climate conditions, the depths of the groundwater water table are projected to continuously increase. The results showed the impact of climate change on salinity distribution for both the deep and shallow groundwater systems. The salinity distribution areas are projected to increase by about 8.08% and 56.92% in the deep and shallow groundwater systems, respectively. The waterlogging areas are also projected to expand by about 63.65% from the baseline period., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Seawater intrusion is a complex groundwater - seawater interaction process, and it is influenced by many factors from ground surface to underground, from groundwater to seawater. Generally, for seawater intrusion model, some model parameters and boundary conditions are always specified by model users' personal experiences or literature's reference value. The defective model would damage the groundwater management for controlling and preventing seawater intrusion when making decisions are based on this model. In order to improve the reliability of seawater intrusion model, the influences of model inputs on output should be identified prior at optimizing model inputs. Dagu river basin, Jiaozhou Bay is one of the most serious areas of seawater intrusion in China, and it is chosen as the study area in this study. The seawater intrusion model of Dagu river basin is built based on a general program SEAWAT4. The key influence factors of model output are analyzed by two sensitivity analysis methods, i.e., stepwise regression and mutual entropy. The results demonstrated that the most important influence factors which have largest sensitivities to groundwater Cl - concentration are the precipitation rate and groundwater pumping in agriculture area. In addition, the hydraulic conductivity of zone 1 has a non-negligible influence on seawater intrusion process. Stepwise regression analysis is capable of identifying most important influence factor, and it can't handle complicated nonlinear input-output relationship. Mutual entropy analysis is reliable for identifying the influence factors for complex seawater intrusion model., (Copyright © 2017 Elsevier Inc. All rights reserved.)