Seawater Intrusion Model Research Articles

Adaptive machine learning surrogate based multiobjective optimization for scavenging residual saltwater behind subsurface dams

High-fidelity physically based groundwater flow and solute transport models have been limited for seawater intrusion remediation design because of computationally intensive evolutionary algorithms. Data-driven machine learning approaches are promising to substitute expensive-cost groundwater numerical models within optimization due to computing efficiency. However, machine learning surrogates may accumulate error of forecasting and thereby result in infeasible optimal solutions. To achieve desired fidelity level, this study proposes a novel adaptive machine learning surrogate based multiobjective optimization method for coastal aquifer desalination. An adaptive modeling algorithm is newly introduced to iteratively retrain poorly-performed machine learning models and enhance predicting accuracy. The method is demonstrated to seek optimal extraction and injection strategies for scavenging residual saltwater trapped in an upstream aquifer behind a subsurface dam. Two conflicting objectives of minimizing the total extraction-injection rate and maximizing saltwater removal effectiveness are considered. Three machine learning models including artificial neural network (ANN), Gaussian process (GP) and response surface regression model (RSR) are developed to replace a high-fidelity seawater intrusion model for predicting chloride concentration and salinity mass. Non-dominated Sorting Genetic Algorithm II (NSGA-II) is employed to derive Pareto fronts. Pareto optimal solutions obtained from machine learning models are compared against those from the seawater intrusion model. Results indicate that the developed machine learning models do not only have strong predicting capability, but also maintain good quality of Pareto optimal solutions, while achieving substantial computational saving up to 95%. Especially, the adaptively retrained RSR model inhibits error accumulation of forecasting and accelerates correct convergence to the true Pareto front. The proposed method is found superior performance in accurate convergence, widely-spread diversity as well as high computing efficiency than conventional methods.

Climatic Modeling of Seawater Intrusion in Coastal Aquifers: Understanding the Climate Change Impacts

The study examines the impacts of climate change and sea level rise on coastal aquifers, focusing on the influence of the components of the water cycle on seawater intrusion, and the evolution of the phenomenon in the future. The simulation of coastal water resources was performed using an integrated modeling system (IMS), designed for agricultural coastal watersheds, which consists of inter-connected models of surface hydrology (UTHBAL), groundwater hydrology (MODFLOW), and seawater intrusion (SEAWAT). Climatic models for the adverse impact scenario (RCP8.5) and the medium impact scenario (RCP4.5) of climate change were used. Transient boundary head conditions were set to the coastal boundary, to dynamically represent the rise in sea level due to climate change. The response of groundwater in the coastal Almyros Basin, located in central Greece, was simulated from 1991 to 2100. The findings indicate that seawater intrusion will be advanced in the future, in both climate change scenarios. The models show varying patterns in groundwater recharge, with varying uncertainty projected into the future, and sensitivity to time in the fluctuation of the components of the water cycle.

An ensemble-based approach for pumping optimization in an island aquifer considering parameter, observation and climate uncertainty

Abstract. In coastal zones, a major objective of groundwater management is often to determine sustainable pumping rates which avoid well salinization. Understanding how model and climate uncertainties affect optimal management solutions is essential for providing groundwater managers with information about salinization risk and is facilitated by the use of optimization under uncertainty (OUU) methods. However, guidelines are missing for the widespread implementation of OUU in real-world coastal aquifers and for the incorporation of climate uncertainty into OUU approaches. An ensemble-based OUU approach was developed considering parameter, observation and climate uncertainty and was implemented in a real-world island aquifer in the Magdalen Islands (Quebec, Canada). A sharp-interface seawater intrusion model was developed using MODFLOW-SWI2 and a prior parameter ensemble was generated containing multiple equally plausible realizations. Ensemble-based history matching was conducted using an iterative ensemble smoother which yielded a posterior parameter ensemble conveying both parameter and observation uncertainty. Sea level and recharge ensembles were generated for the year 2050 and were then used to generate a predictive parameter ensemble conveying parameter, observation and climate uncertainty. Multi-objective OUU was then conducted, aiming to both maximize pumping rates and minimize the probability of well salinization. As a result, the optimal trade-off between pumping and the probability of salinization was quantified considering parameter, historical observation and future climate uncertainty simultaneously. The multi-objective, ensemble-based OUU led to optimal pumping rates that were very different from a previous deterministic OUU and close to the current and projected water demand for risk-averse stances. Incorporating climate uncertainty into the OUU was also critical since it reduced the maximum allowable pumping rates for users with a risk-averse stance. The workflow used tools adapted to very high-dimensional, nonlinear models and optimization problems to facilitate its implementation in a wide range of real-world settings.

Two-Dimensional Resistivity Modeling of Seawater Intrusion Along the West Flood Canal, Semarang

The northern coastal area of Semarang City has significant problems with a decrease in groundwater quality due to seawater intrusion. Increasing groundwater extraction and subsidence due to the city growth worsen the condition. It is necessary to collect information on the contaminated location to develop a strategy to decrease the spreading of seawater intrusion. This study aims to identify the presence of seawater intrusion zones in groundwater and estimate the spread distance of seawater intrusion to the land. We applied the electrical resistivity tomography method to obtain the image of the subsurface. A geo-electric survey with a dipole-dipole multi-electrode configuration was completed along the West Flood Canal. The subsurface model result indicated that the identified seawater intrusion zone is associated with a low resistivity value of less than 3 Ohm.m. The zone is about 0 - 70 meters deep near the coast and is thinning to about 2600 meters to the south. The result confirms that seawater has penetrated long distances to the land.

Modeling of seawater intrusion into Salalah coastal plain aquifer, sultanate of Oman

Excessive groundwater pumping has become a concern in Salalah coastal aquifer in Oman causing seawater intrusion at different farms and abstraction wells near the shoreline. MODFLOW and MT3DMS were calibrated and validated for Salalah coastal aquifer to assess aquifer behavior and seawater intrusion pattern with new input data and fine grid spacing to improve the accuracy of predictions as compared to the previous modeling studies in this region. The study was conducted over an area of 640 km2 of Salalah Plain representing around 83% of its total area. Injection of tertiary treated wastewater, rainfall and dams were considered as sources of aquifer recharge while groundwater abstraction occurred for agricultural, domestic, and commercial uses. The calibration and validation of the models were done in steady and transient states using observed groundwater levels from year 2000–2019. The aquifer properties such as hydraulic conductivity, specific yield, and vertical anisotropy were calibrated. MODFLOW results were utilized by MT3DMS to simulate solute transport at transient state. The longitudinal dispersivity and porosity of the aquifer were obtained by calibration and validation of the model. Over the three aquifer layers, the hydraulic conductivity ranges from 10 m/day to 100 m/day, vertical anisotropy is 4 and the specific yield ranges from 0.01 to 0.1. The calibrated values of the longitudinal dispersivity and porosity range from 500 m to 50000 m, and 0.4, respectively. The study indicated a clear impact of seawater intrusion at coastal side of the Salalah plain. The predictive modeling indicated an average of 1.5 m drop in hydraulic head across the whole study area by 2040, while seawater intrusion effect was expected to increase near the coast with potential extension to the central area of the Salalah plain. The validated model can be used as a prediction tool by the decision makers to manage the aquifer considering different scenarios, for integrated water resources management in Salalah city.

An adaptive multi-fidelity optimization framework based on co-Kriging surrogate models and stochastic sampling with application to coastal aquifer management

Surrogate modelling has been used successfully to alleviate the computational burden that results from high-fidelity numerical models of seawater intrusion in simulation-optimization routines. Nevertheless, little attention has been given to multi-fidelity modelling methods to address cases where only limited runs with computationally expensive seawater intrusion models are considered affordable imposing a limiting factor for single-fidelity surrogate-based optimization as well. In this work, a new adaptive multi-fidelity optimization framework is proposed based on co-Kriging surrogate models considering two model fidelities of seawater intrusion. The methodology is tailored to the needs of solving pumping optimization problems with computationally expensive constraint functions and utilizes only small high-fidelity training datasets. Results from both hypothetical and real-world optimization problems demonstrate the efficiency and practicality of the proposed framework to provide a steep improvement of the objective function while it outperforms a comprehensive single-fidelity surrogate-based optimization method. The method can also be used to locate optimal solutions in the region of the global optimum when larger high-fidelity training datasets are available.

Seepage Analysis and the Reservoir Water Pollution Potential under Vertical Dam Structure Planning

A prospective resolution to the intricate predicaments of flooding, sanitation, and the availability of unprocessed water for the populace of Jakarta residents is the implementation of the coastal reservoir paradigm. This paradigm entails harnessing the latent capacity of the Cisadane River flow and its subsequent storage within a retention pond, and then subjecting it to reprocessing to serve as a viable source of raw water. The selection of a vertical seawall design was based on the objective of creating an effective barrier between the reservoir and the sea, while also considering several environmental factors. This design was selected with the aim of minimizing the need for extensive soil excavation and rock placement. However, it is important to note that the risks of construction failure associated with seepage under hydraulic structure and dam stability pose significant challenges. Besides preventing saltwater intrusion and maintaining the integrity of the reservoir as a freshwater source, dam must be designed to mitigate potential seepage failure and intrusion issues. To address these concerns, this study employed numerical simulation using the SEEP/W and CTRAN/W software. The simulation was carried out to analyze seepage discharge under a vertical dam and predict potential seawater intrusion into the reservoir. The dam was examined over a ten-year period, with varying embankment widths of 10m, 20m, and 30m. The analysis considered changes in water level (ΔH) and the addition of a cut-off wall at depths of 5m, 10m, and 15m. The obtained results showed that seepage discharge rates amounted to 3,14x10-4 m3 s-1, 2,67x10-4 m3 s-1, and 2,50x10-4 m3 s-1 for embankment widths of 10m, 20m, and 30m, respectively, under a 1m level difference condition. Following this, the safety factor for piping on vertical embankment was determined as 1.10, 1.34, and 1.39 for widths of 10m, 20m, and 30m, respectively. This factor was found to increase to 4.03 when the embankment distance was widened, and a 15m deep cut-off wall was installed. It is important to note that the seawater intrusion model predicted a seawater concentration of 65,12 g m-3 at the bottom for an embankment width of 10m, while no intrusion was observed at widths of 20m and 30m with ΔH=1m. This study aims to assess potential risks of piping due to seepage and seawater contamination at the Cisadane Estuary.

Review: Assessment and modeling of seawater intrusion in coastal aquifers of the Arabian Peninsula

Review: Assessment and modeling of seawater intrusion in coastal aquifers of the Arabian Peninsula

Efficient uncertainty quantification for seawater intrusion prediction using Optimized sampling and Null Space Monte Carlo method

Uncertainty in environmental modeling predictions, stemming from parameter estimation, is a crucial challenge that must be addressed to ensure effective decision-making. Limited field measurements, high computational costs, and a lack of guidance in estimating measurement uncertainty further compound this challenge, particularly for highly parameterized complex models. In this study, we propose a novel and computationally efficient framework for quantifying predictive uncertainty that can be applied to a range of environmental modeling contexts. The novel components of the framework include efficient parameter space sampling using an Optimized Latin hypercube sampling strategy, and applying the Null Space Monte Carlo method (NSMC) along with a developed filtering technique. The NSMC generates sample sets to calibrate the model while exploring the null space. This space contains parameter combinations that are not sufficiently supported by observations. The filtering technique omits low-potential parameter sets from undergoing model calibration. The framework was tested on the seawater intrusion (SWI) model of Wadi Ham aquifer in the United Arab Emirates (UAE) to investigate aquifer sustainability in 2050. Our results demonstrate the importance of incorporating direct and indirect measurements of heads, salinity, and geophysical survey data into the calibration dataset to reduce uncertainty in salinity predictions. The extent of SWI for multiple calibrated parameter sets varied by 4.5% to 11% relative to their means at two main pumping fields. We conclude, with a moderate to a high degree of certainty, that SWI is a serious threat to these fields, and actions are needed to protect the aquifer from salinization. Additionally, variations in SWI length under different geological conditions illustrate regions of high uncertainty that require further data collection. Our framework effectively reduced and quantified prediction uncertainty and provides decision-makers with critical information to inform risk management strategies.

Assessing the impact of groundwater abstractions on aquifer depletion in the Cauvery Delta, India

Many of the world’s deltas are highly productive areas for agriculture as well as important places of socio-economic development but are currently under stress. This study assesses the impacts of stresses on groundwater pumping, changing cropping patterns, and saltwater intrusion on groundwater resources in the Cauvery Delta in Tamil Nadu, India. A transient groundwater flow model of the delta was constructed for this assessment. The historical changes in groundwater resources in response to decreasing irrigation canal flows and increasing groundwater abstractions were assessed for the past 30 years. Furthermore, the model was used to formulate and analyze future sustainable groundwater development scenarios. Farmers’ narratives about a drying delta, as they experience water scarcity and quality issues most closely, were ascertained in the research. Farmers have abandoned many shallow wells in their fields. The model simulation shows groundwater levels are decreasing and aquifer storage depleting. Furthermore, salinization has increased, with continuous declining groundwater levels in the deep aquifer from 1990 to 2019. A more robust hydro-chemical assessment and further modeling of seawater intrusion are needed to better assess the sources and distribution of groundwater salinity. The pathway for future sustainability requires enhancing groundwater recharge in the shallow aquifer and controlling groundwater abstraction in the deep aquifers.

Numerical Modeling of Seawater Intrusion in Wadi Al-Jizi Coastal Aquifer in the Sultanate of Oman

The Sultanate of Oman is an arid country in the Arabian Peninsula suffering from insufficient freshwater supplies and extremely hot weather conditions. The only source of recharge is rainfall, which is scarce and varies with space and time, for the aquifers being overexploited for the last few decades. This has led to depleting groundwater levels and seawater intrusion into coastal aquifers. In the present study, Ground Modeling System (GMS) was employed in Wadi Al-Jizi, which is one of the important aquifers in the Al Batinah coastal plain that caters to the needs of the country’s 70% agriculture. MODFLOW and MT3DMS were used to simulate the groundwater levels and solute transport, respectively. These models were calibrated under steady and transient conditions using observed data from twenty monitoring wells for a period of seventeen years (year 2000–2016). After validation, the model was utilized to predict the salinity intrusion due to changes in groundwater abstraction rates and sea level rise owing to climatic change. These predictions show that, by the year 2040, salinity intrusion (TDS > 12,800 mg/L) will transgress by 0.80 km inland if the current abstraction rates are allowed to be maintained. Further deterioration of groundwater quality is anticipated in the following years due to the increased pumping rates. The models and the results from the present study may be utilized for the effective management of groundwater resources in the Wadi Al-Jizi aquifer.

Pumping Optimization Under Uncertainty in an Island Freshwater Lens Using a Sharp‐Interface Seawater Intrusion Model

AbstractPumping optimization under uncertainty is a powerful approach for the management of groundwater resources, and its implementation would be valuable in island aquifers where freshwater lenses are affected by seawater intrusion. Sharp‐interface numerical models are especially well suited for the task as they offer fast simulation times, but to date they have not been used because of a lack of guidelines and due to the specific challenges associated with this approach. This study presents a methodology for pumping optimization under uncertainty for island freshwater lenses using a sharp‐interface model (MODFLOW‐SWI2) and demonstrates it for a real case (Magdalen Islands, Quebec, Canada). The total pumping in a well field was maximized while avoiding well salinization due to upconing. To do so, the sharp interface simulated below the pumping wells was corrected successively for cell‐to‐well upconing and for dispersion. Pumping optimization under uncertainty was then conducted using PESTPP‐OPT, considering parameter and observation uncertainty, and was repeated for 23 reliability levels to illustrate a large range of risk‐averse, tolerant and neutral stances. The maximum pumping was obtained as a function of risk of well salinization. This approach enabled quantification of the tradeoffs between pumping and risk, allocation of pumping amongst wells, and an examination of the ability of the well field to meet the water demand while maintaining an acceptable level of risk. Ultimately, this framework allows groundwater managers to select the final pumping scenario themselves, depending on their attitude toward risk.

Analysis of coastal groundwater hydrochemistry evolution based on groundwater flow system division

Groundwater hydrochemistry evolution in carbonated coastal aquifers is impacted by seawater intrusion. A well-documented groundwater flow system division is the premise and the key of hydrochemistry evolution or seawater intrusion research under complex geological and topographical conditions. In this research, the regional groundwater system in the study area is divided into three groundwater flow systems, according to topographic, geological, and hydrodynamic conditions. The hydrogeochemistry evolution in the Daweijia coastal aquifer is characterized on the basis of the groundwater flow system division. The results show that the groundwater hydrochemistry evolution varies in different groundwater flow systems in the Daweijia area: (1) Hydrochemistry evolution in groundwater flow system I (SI) is controlled by lateral recharge, dissolution of evaporates, and seawater intrusion. The hydrochemistry presents characteristic HCO3-Ca·Mg, Cl·HCO3-Ca, and Cl-Na·Ca along the runoff path, and seawater intrusion is found 1.3 km inland. (2) Hydrochemistry composition in groundwater flow system II (SII) is influenced by water–rock interaction, freshwater-seawater mixing, evaporation, and reverse cation exchange. Additionally, human activities are potentially a primary factor in the hydrochemical evolution of SII and cause NO3 type groundwater. Seawater intrusion is found 2.8 km inland, with a mixing proportion of < 5%. (3) Hydrochemistry evolution in groundwater flow system III (SIII) is influenced by seawater intrusion, local precipitation, and a short runoff path. A classic seawater intrusion model is present in SIII. The hydrochemical distribution presents a regular changing pattern following the order: HCO3-Ca and HCO3·Cl-Ca (freshwater) and Cl-Mg·Ca/Na·Ca (brackish water). The degree of seawater intrusion in SIII is more serious than that in the SI and SII. Isotopic results generally reveal that the groundwater is primarily derived from the combination of local precipitation and lateral recharge from the system boundary. The study proposes an effective method to analyze groundwater hydrochemical evolution under complex geological conditions in coastal areas.

Modeling of seawater intrusion into coastal aquifers in laboratory conditions

Modeling of seawater intrusion into coastal aquifers in laboratory conditions

A framework for parameter estimation using sharp-interface seawater intrusion models

Sharp-interface seawater intrusion models present shorter run times than variable density codes, which makes them practical for regional, decision-support groundwater modeling. Although parameter estimation and uncertainty analyses are essential steps for model-based decision making, their implementation in seawater intrusion models has remained limited. Few guidelines are available and it is unclear which observations should be used, what processing they require and what weighting strategy should be used. A framework has been developed for parameter estimation using a regional sharp-interface decision-support model applied to a real-world example in the Magdalen Islands (Quebec, Canada). This framework included the assimilation of head observations collected from shallow wells, deep open wells and pumping wells, as well as freshwater-seawater interface observations derived from deep open wells, TDEM (time-domain electromagnetic) and ERT (electrical resistivity tomography) geophysical surveys. A model was developed using MODFLOW-SWI2 in which fast model run times allowed the estimation of numerous parameters, including a heterogeneous hydraulic conductivity field with pilot points. Following parameter estimation with PEST, the uncertainty of several model forecasts, i.e. the volume of freshwater and the interface elevation near municipal pumping wells, was examined with the first-order second moment (FOSM) approach and a data worth analysis was carried out. While the observations presented a low signal-to-noise ratio, parameter estimation was effective to reduce the uncertainty of model forecasts. Interface observations, and particularly geophysical observations, were most useful to reduce predictive uncertainties. Head and interface observations from deep open wells were biased and could not be suitably reproduced by the model. The framework developed here is relatively straightforward and could be implemented more systematically. The study also provides recommendations to guide future data collection strategies in coastal aquifers.

Application of artificial intelligence deep learning in numerical simulation of seawater intrusion.

Seawater intrusion not only causes fresh water shortages in coastal areas, but also has a negative impact on regional economic and social development. Global climate change will affect precipitation, sea level, and many other factors, which will in turn affect the simulation and prediction results for seawater intrusion. By combining groundwater numerical simulation technology, an atmospheric circulation model, artificial intelligence methods, and simulation optimization methods, this study coupled a numerical simulation model of seawater intrusion with an optimization model to optimize the groundwater exploitation scheme in the study area under the condition of climate change. As a result, a groundwater exploitation scheme was obtained for a typical study area, which provided a scientific basis and a reference for the rational development of effective groundwater resource solutions. The results of this study can be described as follows. (1) By introducing the theory and method of deep learning from artificial intelligence, the problem of complex nonlinear mapping between the inputs and outputs of a three-dimensional variable-density seawater intrusion numerical simulation model under the condition of limited number of training samples is effectively solved, and the approximation accuracy of the surrogate model with respect to the simulation model is improved. (2) By solving the optimization model, a reasonable groundwater exploitation scheme was obtained, which provided a scientific basis for the rational development and efficient use of groundwater resources in the study area.

An Integrated Modeling System for the Evaluation of Water Resources in Coastal Agricultural Watersheds: Application in Almyros Basin, Thessaly, Greece

This study presents an integrated modeling system for the evaluation of the quantity and quality of water resources of coastal agricultural watersheds. The modeling system consists of coupled and interrelated models, including (i) a surface hydrology model (UTHBAL), (ii) a groundwater hydrology model (MODFLOW), (iii) a crop growth/nitrate leaching model (REPIC, an R-ArcGIS-based EPIC model), (iv) a groundwater contaminant transport model (MT3DMS), and (v) a groundwater seawater intrusion model (SEAWAT). The efficacy of the modeling system to simulate the quantity and quality of water resources has been applied to the Almyros basin in Thessaly, Greece. It is a coastal agricultural basin with irrigated and intensified agriculture facing serious groundwater problems, such as groundwater depletion, nitrate pollution, and seawater intrusion. Irrigation demands were estimated for the main crops cultivated in the area, based on precipitation and temperature from regional weather stations. The models have been calibrated and validated against time-series of observed crop yields, groundwater table observations, and observed concentrations of nitrates and chlorides. The results indicate that the modeling system simulates the water resources quantity and quality with increased accuracy. The proposed modeling system could be used as a tool for the simulation of water resources management and climate change scenarios.

Global sensitivity analysis on a numerical model of seawater intrusion and its implications for coastal aquifer management: a case study in Dagu River Basin, Jiaozhou Bay, China

Seawater intrusion (SWI) has triggered an accelerating process of freshwater contamination and significantly affected the soil fertility and local groundwater supply in the coastal area of Jiaozhou Bay, Shandong Province, China. This study establishes a three-dimensional numerical model based on SEAWAT code to simulate transient regional SWI to coastal aquifers in Dagu River Basin (DRB) adjacent to Jiaozhou Bay. The hydrogeological parameters in the SEAWAT model are calibrated and validated with the observed data of groundwater level and chloride (Cl−) concentration from 1 January 2010 to 1 June 2018. Also, global sensitivity analysis is used to evaluate the impacts of hydrogeological parameters (aquifer hydraulic conductivity and specific yield), along with sources/sinks consisting of recharge from precipitation infiltration and groundwater abstraction, on the SWI model. The sensitivity analysis results indicate that the progression of SWI is sensitive to the groundwater recharge from precipitation infiltration and the groundwater abstraction in the study area, while the hydraulic conductivity is of secondary importance. Furthermore, the baseline SWI model is applied to predict the extent of SWI under different scenarios considering the possible future precipitation and groundwater abstraction. It is shown that increased recharge and reduced groundwater abstraction could effectively lessen the extent of future SWI. As a case study, the research efforts on the regional SWI model are of critical importance for investigating the occurrence of SWI, identifying the factors most influential on the SWI process, and providing useful predictive information for SWI management in the DRB aquifer of Jiaozhou Bay.

3D modeling of tsunami-induced seawater intrusion and aquifer recovery in Niijima Island, Japan, under the future tsunami scenario

3D modeling of tsunami-induced seawater intrusion and aquifer recovery in Niijima Island, Japan, under the future tsunami scenario

Convergence of a positive nonlinear control volume finite element scheme for an anisotropic seawater intrusion model with sharp interfaces

AbstractWe study a sharp interface model in the context of seawater intrusion in an anisotropic unconfined aquifer. It is a degenerate parabolic system with cross‐diffusion modeling the flow of fresh and saltwater. We study a nonlinear control volume finite element scheme. This scheme ensures the nonnegativity of the discrete solution without any restriction on the transmissibility coefficients. Moreover, it also provides a control on the entropy. The existence of a discrete solution and the convergence of this scheme are obtained, based on nonlinear stability results.