Seawater Intrusion

Numerical modeling of land subsidence induced by groundwater extraction considering unsaturated effects and using element-free Galerkin (EFG) method
Document Type : Article

Authors

A. Tourei  1  A. Pak  2  M. A. Iranmanesh 3
1 Civil Engineering Department, Sharif University of Technology, Tehran, Iran

2 Civil Engineering Department, Sharif University of Technology, Tehran, Iran.

3 Civil Engineering Department, Khajeh Nasir Toosi University of Technology, Tehran, Iran

10.24200/j30.2023.59625.3256
Abstract

This study aims to provide a coupled flow-deformation model for simulating land subsidence associated with groundwater extraction in aquifers. For this simulation, we have adopted the element-free Galerkin (EFG) method and considered the unsaturated effects in the aquifers based on the aquifer's hydrologic and geotechnical characteristics. This model gives us a better understanding of the aquifer's hydrogeological characteristics, enabling us to forecast changes in the hydraulic head and land subsidence. To ensure the credibility of our model and to verify the code, we modeled unsaturated hydromechanical benchmark problems. Then, using the EFG method as a numerical tool, we modeled an isotropic aquifer to investigate the effects of groundwater pumping on land subsidence and hydraulic changes in the aquifer. To ascertain the reliability of the modeling, we compared the results obtained from the EFG method with those from the Finite Element Method (FEM). The comparative analysis of EFG and FEM models demonstrates discrepancies of 5.51% in land subsidence and 13.35% in hydraulic head reduction, which are satisfying. The land subsidence and hydraulic head profiles demonstrate that the EFG method is capable of land subsidence simulation caused by water pumping. Furthermore, our findings highlight the nonlinear correlation between groundwater extraction and the subsequent decrease in hydraulic head and land subsidence augmentation. Finally, we conducted a parametric study to better understand the effect of various characteristics of aquifers and observe the effect of the aquifer's parameters, such as hydraulic conductivity, elastic modulus, and Poisson's ratio. We investigated the effect of each parameter on land subsidence increase and hydraulic head decline. The results show that elastic modulus and Poisson's ratio have the most significant effect on land subsidence. Although hydraulic conductivity controls the hydraulic decrement and land subsidence increase time, it slightly affects the ultimate hydraulic head and land subsidence at the steady-state stage. These results highlight the importance of in-situ measurement of elastic modulus and Poisson's ratio paraeters with acceptable accuracy for groundwater extraction projects, as these parameters play a significant role in the feasibility studies.
Keywords

Land subsidence  Groundwater extraction  Numerical modeling  Coupled hydromechanical analysis  Element-free Galerkin (EFG)  Unsaturated effects

The hydrogeochemical characterization of groundwater helps to assess the trend of salinization and freshening of the groundwater. The present study was carried out to understand the lateral and vertical variation of groundwater salinity and the process of salinization and freshening of the groundwater in a coastal aquifer comprising a freshwater lens. The partially isolated unconfined aquifer selected for the present study is lying just south of the Chennai City, one of the densely populated cities on the east coast of South India. Critical problems affecting this aquifer include a thin aquifer which is connected/surrounded by saltwater on all the sides, overexploitation of the groundwater, surface impermeabilization due to increasing residential areas, and destruction of existing dune morphology by conversion of barren land to the residential area which causes a reduction in their barrier effect to seawater intrusion. The process of salinization and freshening of the groundwater was studied and monitored by using electrical resistivity survey and hydrogeochemical analysis. The vertical electrical sounding was carried out at 17 locations, and 400 water samples were collected and analyzed from 50 locations during the period from August 2008 to May 2010 for this study. The apparent resistivity values were analyzed and compared with groundwater quality to demarcate the zone of seawater intrusion. The regional flow direction of the groundwater is westward and eastward with respect to the central stretch and groundwater level ranges from 4.96 m MSL at the dune morphology to 0 m MSL along the boundary on all the sides. Base exchange index indicates that salinization trend in the northern part of the study area is due to the extensive groundwater pumping which increases the possibility of seawater intrusion. The increase of base exchange index towards southern part indicates a better groundwater quality of the aquifer due to proper land use practices. A strong trend of quality alteration is clearly visible from the base exchange index in response to the seasonal change between monsoon and dry season. In the western side, the monsoonal variation in the salinization and freshening of the groundwater was not noticed; however, the salinity is slightly higher than freshwater due to the presence of clay.

This paper addresses the sustainable abstraction rate and depth, and the corresponding salinity, in a coastal aquifer as a result of abstraction from beach wells, which is applied on the coastal Nile Delta aquifer as a case study. The field measurements were conducted at West Port Said (WP site) Egypt, and included site visits, topographic survey, drilling of exploratory wells with depths ranging from 60 m to 500 m, pumping tests, water sampling and chemical analysis to identify the physical settings, geological, hydrogeological, and environmental characteristics of the study area and the surroundings. A conceptual model was developed for abstraction from WP site, with the aquifer, comprising five water-bearing layers spreading over three sub-aquifers separated by two clay confining layers. It also includes a surface coastal lake. Consequently, a numerical model was developed and validated to simulate drawdown and salinity at abstraction rates from 50,000 m 3 /d to 500,000 m 3 /d over a period of 50 years, which resulted in drawdowns of 9-84.2 m, and salinity levels range from 39,835 to 40,272 mg/L for abstraction rates of 50,000 m 3 /d and 500,000 m 3 /d, respectively. The model also included simulation of oil concentration at abstraction wells because of accidental oil spill in the sea. To generalize the conclusions for abstraction over the entire Nile Delta coastal aquifer, the numerical model developed for WP site is used to simulate abstraction at any site within the coastal aquifer with different settings, including presence or absence of coastal lake and clay confining units. It also addressed the impact of improved salinity of the coastal lake on the abstraction, mainly for salinity. Among all these scenarios at 50 year and abstraction rate of 500,000 m3/d, it was found that drawdown varies from lowest value of 54 m to highest value of 86.65 m, as well as salinity varies from lowest value of 38,629 mg/L to highest value of 41,878 mg/L. This leads to identify abstraction depth, salinity, drawdown and the daily maximum recommended sustainable abstraction rate from the subject coastal aquifer, when compared to the daily abstraction as per Egyptian government plan 2050, it was found that the Nile Delta aquifer could serve 50 % of the demand.

Seawater Intrusion (SI) is a critical problem as a consequence of climate change. The progression of the salt wedge inland compromises the quality and quantity of groundwater, seriously damaging agriculture and gradually desertifying the territory. The alluvial aquifer of the Lower Val Magra (LVM) is one of the most important in Liguria (Italy). It supplies drinking water to the city of La Spezia. The main objective of this research is to determine the severity of the SI phenomenon in the LVM aquifer and in the River Magra estuary. Data from different databases (ACAM, Aral, Ispra) and new original data were used for this purpose. The analytical methods focused on multivariate statistics (HAC, PCA and PLS). It was found that the migration pattern of SI along the estuary is mainly controlled by river discharge and wind speed. The weir in Romito (8.5 km from the sea coast) is the current limit of the SI in the R. Magra. About the groundwater, the most salinized wells are concentrated in the Marinella plain. For the other part of the LVM, aquifer water quality is good, but will be deteriorate in the next years as a consequence of climate change.

Multisecular land use change and difficulties in water management lead to changes in soil properties, but the slow kinetics, the spatio-temporal variability of soils, land use and water quality makes these changes difficult to decipher. The method used here combines geomodelling (gOcad geomodel) and geochemical modelling (PHREEQC) to integrate multiple sources of information. The gOcad geomodel has long been recognized as an appropriate tool to reconstruction of 3D architectures in fundamental geology and geology engineering for minerals and oil prospection. It is used here to interpolate soil data, land use data and outputs of the geochemical model. The groundwater quality is the input of PHREEQC geochemical model. The output of the geochemical model is the saturation index (SI) of water with respect to calcite. By using classical data such as soil, hydrogeological and land use maps (Figures ), soil profiles, piezometric water analyses in time and combining the tools gOcad and PHREEQC (Figure ) on a demonstration area in the Crau's plain, it is shown that: i) multisecular irrigation modifies soil properties by a recarbonatation process which counterbalances the general geochemical tendency towards decarbonatation; this results in the presence of active limestone in the topsoil; ii) water shortage for irrigation during dry years results in smaller SI (smaller oversaturation or slight undersaturation) in grasslands, and larger SI in land used for orchards, where groundwater was used for irrigation; iii) the presence in the subsoil of a "poudingue" of pedogenetic origin (pebbles cemented by a calcrete), thick, but fractured and discontinuous, does not prevent the land use to impact directly the water quality of the underground water.

Studies on lymphatic filariasis (LF) in Indonesia have mostly focused on the disease determinants with limited focus on spatial-based and the determinants of implementing ivermectin, diethylcarbamazine citrate, and albendazole (IDA). This study aimed to identify the causes of program failure. A cross-sectional survey was conducted from November to December 2022 in nine urban villages with high endemic records and one sentinel village in Pekalongan City, Central Java, Indonesia. The analysis using Quantum Geographical Information System (QGIS) and Pearson correlation. Slum settlements were linked to the presence of open sewers (p=0.000; r=0.974) and overcrowding (p=0.033; r=0.672), while the first round of IDA medication adherence correlated with knowledge of medication (p=0.054; r=-0.623) and willingness to take the medication in the second round (p=0.051, r=0.603). Adverse effects of the treatment are strongly correlated with drug boredom from taking medication (p=0.003; r=0.828) and assistance from health workers (p=0.027; r=0.791). We identified gaps in slum settlements, open sewers, overcrowding and medication adherence, including low knowledge of medication, unwillingness to take second-round medication, adverse effects, and boredom with taking medication. We recommend effective strategies by engaging health education between health workers, local leaders, and private sectors as key to ensuring elimination program.

Statistical and geochemical methods validate each other, showing comparable results. • Both methods outline recharge areas and those subject to salinization processes. • The proposed approach enabled to outline areas with different salinization dynamics. • The integrated methodology was used to create groundwater salinization hazard maps.

Seawater intrusion is the primary cause of groundwater salinisation in coastal aquifers. However, attributing salinisation solely to seawater intrusion may not always be accurate, given the likely presence of other sources. To understand if salinisation comes from seawater intrusion and its onset is crucial for groundwater management, but there are no definite threshold values for common indicators such as chlorides. Based on 1662 groundwater analyses from five Mediterranean coastal aquifers, the study aimed to distinguish the effects of mixing with present-day seawater from those caused by other sources. The trend analysis of cumulative probability plots of chloride (and total dissolved solids) is a key method for discriminating different groundwater salinisation sources and processes. Results establish that chloride, as a non-reactive tracer, is a more reliable indicator of seawater intrusion than total dissolved solids, a reactive indicator.
A chloride concentration threshold of 200 mg/L identifies the seawater intrusion onset. The threshold validation comes from groundwater salinisation facies, as provided by groundwater-type codification.
Fresh groundwater (Cl < 200 mg/L) anomalous total dissolved solids highlight the input of non-chloride salts and pollutants, providing caution regarding using total dissolved solids to recognise seawater intrusion. Beyond the threshold (Cl > 200 mg/L), data disclose emergent signals of salinisation sources and water–rock interaction processes overlapping seawater intrusion or the involvement of saline fluids different from present-day seawater. The threshold and a new categorisation of groundwater in coastal aquifers according to salinisation processes provide a benchmark for identifying and managing seawater intrusion in the Mediterranean area.

This study aims to identify groundwater salinization origin and to determine seawater intrusion extension toward the inland in Chaouia, Morocco. To reach these objectives, firstly, 46 groundwater samples were analyzed for major chemical elements during January 2012 and, secondly, 10 electrical resistivity tomography (ERT) profiles were performed perpendicularly to the coastal fringe. Statistical analysis provided the distinction between three Clusters reflecting different hydrochemical processes. Cluster I and Cluster II-a showed a high water electrical conductivity (EC) (from 2.3 to 11.2 mS/cm) with the dominance of Na + (668 mg/L on average) and Cl -(1735 mg/L on average) ions as a consequence of seawater intrusion. However, Cluster II-b presented low ECs (from 0.5 to 1.7 mS/cm) and Ca 2+ (99.6 mg/L on average) and HCO 3 2-(235.2 mg/L on average) ions dominance. Water chemistry in these wells was controlled by water-rock interaction, cation exchange, and anthropogenic activities. The Hydrochemical Facies Evolution Diagram highlighted the succession of different water facies developed between intrusion and freshening phases. The formation of Na-HCO 3 facies, which characterizes the last facies of freshening phase, followed the succession of Na-Cl, MixNa-MixCl, MixCa-MixCl, MixCa-MixHCO 3 , and Na-HCO 3 . In contrast, Na-Cl facies formation, which characterizes the last facies of intrusion phase, followed the evolution of Ca-HCO 3 , Ca-MixHCO 3 , Ca-MixCl, MixCa-MixCl, MixCa-Cl, and Na-Cl. Moreover, the obtained ERT results allowed determining the extent of different hydrochemical facies and provided more details about seawater intrusion extension. The conductive level assigned to seawater contamination showed a resistivity less than 36 Ω.m, which remains limited to 3000 m from the ocean, where Na-Cl water type dominates. The seawater intrusion depth varied between 5 and 40 m from the surface. Overall, this original study in Chaouia region demonstrated the effectiveness of combining hydrochemical

This study presents the differences and similarities between the MODFLOW-USG (Unstructured Grid version of MODFLOW) and traditional structured versions of MODFLOW 2005 in simulating a three-dimensional multilayer groundwater flow model in Quaternary aquifer east Nile delta in Egypt. A 390-borehole dataset was used to build a three-dimension stratigraphic model of the Quaternary aquifer. GIS-based conceptual model is mapping to represent the different boundary conditions such as lakes, river, drains, aquifer recharge, and discharge. The conceptual model is exported to the stratigraphic model; therefore, boundary conditions data are automatically arranged in arrays identical with the grid cells. MODFLOW 2005 and MODFLOW USG are combined with the computer-based program PEST to calibrate groundwater head distribution through the aquifer system. Groundwater levels measured in 1991 are used for the steady-state calibration and are employed then as initial conditions for the transient calibration between 1991 and 2004. The heads measured in 2015 are used for more model verification. The results show that MODFLOW-USG provides flexibility in grid design, including the capability to use nonrectangular cell shapes. Also, it can be used with simple grids and nested grids that allow for the solution to be focused in areas of interest. Also, the results show that the MODFLOW-2005 simulation takes about 20 times longer to complete the run and uses about 6 times more cells number than the MODFLOW-USG simulation.

This study focuses on the application of the new method, GALDIT, for the cartography of aquifer vulnerability due to seawater intrusion in the area of Chaouia coast (Morocco) which is characterized by intense agricultural activity and low depth of the groundwater. The method was developed by Chachadi and Lobo-Ferreira in 2001 after that modified in 2005 and is specific for coastal aquifers. The computing of the GALDIT index (GI) is based on six parameters: Groundwater occurrence (aquifer type); Aquifer hydraulic conductivity; Depth to groundwater level above the sea; Distance from the shore (distance inland perpendicular from shoreline); Impact of existing status of seawater intrusion in the area; and Thickness of the aquifer. This GALDIT is the indicator scores and summing them and dividing by the total weight for determining the relative role of each one. The results of this study show a vulnerability of the aquifer to the seawater intrusion with a high risk in the fringe littoral...

This study investigates the replacement of traditional surface irrigation methods with modern irrigation systems (MIS) including horizontal sprinkler, central pivot, surface drip, and subsurface drip aimed at improving water efficiency in the Nile Delta, Egypt. The primary objectives were to determine the optimal agricultural area for implementing MIS and to assess the effects of these systems on groundwater quantity and quality in the region. To achieve this, the LINDO software was employed to optimize land allocation for each irrigation method. At the same time, the SEAWAT code was utilized to simulate saltwater intrusion (SWI) in the Nile Delta aquifer. The transition from traditional surface irrigation to MIS resulted in significant water savings, reaching 2.15 × 10^9 m 3. However, groundwater modeling indicated a decrease in groundwater levels, leading to an 8 % increase in aquifer salinity due to reduced infiltration of recharge water. These findings underscore the urgent need to revise outdated irrigation practices and enhance water management strategies in the Nile Delta to mitigate salinity issues in coastal aquifers. This research's outcomes are crucial for decision-makers and stakeholders in selecting appropriate irrigation methods, particularly in arid and semi-arid regions, to ensure sustainable water use and agricultural productivity.

This study has investigated the potential impact of human activities and climate change on the groundwater budget, water levels, and seawater intrusion in the coastal aquifer of the Gaza Strip (State of Palestine) over the next two decades. The impact of a proposed measure to use alternative freshwater provision from desalinated seawater on the future groundwater quantity and quality was also analyzed. Following extensive analysis of available observed data, a three-dimensional groundwater flow model, coupled with variable-density saltwater flow and transport components, was utilized for the investigations. Compared with the benchmark scenario (SC0), the climate change scenario (SC1) suggests that over the next two decades, an average annual aquifer recharge of 6.3 Mm3 can be expected, while the human activities scenario (SC2) indicates that the groundwater levels will decline at a rate of 0.09 m/year with expected urban area expansion. The combined human activities and climate chan...

Sumur resapan merupakan bangunan rekayasa yang dibuat untuk konservasi air sebagai tempat menampung dan meresapkan air permukaan. Konservasi air diperlukan untuk mengurangi intrusi air laut di daerah pesisir. Air tanah dangkal di Kelurahan Pohe yang terletak di daerah pesisir dipengaruhi oleh intrusi air laut. Penelitian ini bertujuan dalam upaya konservasi air tanah di daerah pesisir untuk mengurangi limpasan air hujan yang langsung mengalir ke saluran drainase dan mereduksi intrusi air laut. Penelitian dilakukan pada daerah pesisir yang berbatasan langsung dengan Teluk Tomini di Kelurahan Pohe. Data yang digunakan dalam penelitian ini adalah data primer berupa data laju infiltrasi dan permeabilitas tanah dan data sekunder berupa data curah hujan tahun 2009-2020. Data laju infiltrasi diperoleh dengan alat Double Ring Infiltrometer dan dianalisis menggunakan metode Horton. Untuk pengujian permeabilitas tanah menggunakan alat constant head. Analisis intensitas hujan menggunakan metode Mononobe dan analisis debit menggunakan metode Rasional. Perencanaan dimensi sumur resapan menggunakan metode Sunjoto 1988. Hasil penelitian diperoleh laju infiltrasi nyata (ft) di lokasi penelitian sebesar 3,89 cm/jam atau 38,90 mm/jam tergolong pada kriteria laju infiltrasi sedang. Koefisien permeabilitas tanah (k) sebesar 0,07 cm/detik. Intensitas hujan (I) menggunakan metode Mononobe sebesar 38,94 mm/jam. Berdasarkan data luas Kelurahan Pohe (A) seluas 4,83 km 2 dan koefisien aliran gabungan (C) diperoleh 0,21. Analisis debit (Q) yang diperoleh sebesar 10,86 m 3 /detik. Dimensi sumur resapan yang direncanakan menggunakan sumur resapan berbentuk silinder berdiameter tanpa isian/kosong, (D) sebesar 1 m dan kedalaman (H) sebesar 58,90 m dibagi menjadi 31 buah sumur dengan kedalaman 1,90 m.

This paper aims to understand the general background of groundwater quality that must be considered for the 'smart city' planning of Surat city. Twenty-Six water samples collected from bore wells of the city were analyzed. The results showed that water is alkaline, as pH varies from 7.6 to 9.2. The concentration of Cl À and Na þ are correlated with EC. The highest levels of Cl À and Na þ are found near the coastal region (predominantly northwestern); Piper trilinear diagram shows 52% of samples are Na-HCO 3 À type and 48% NaCl type. WQI shows that most samples are potable for drinking, but a few samples from the western part are not suitable for drinking. SAR, Na%, and PI results show that most samples are suitable for irrigation. The corrosivity index indicates that 50% of samples have a CR . 1(unsafe zone), and the rest are within the safe limit. The relationship of WQI with different water quality parameters revealed that groundwater quality has deteriorated in the city's western part, which may be due to seawater intrusion in the aquifer. This work gives a basic idea of groundwater quality, which will help make Surat a smart city.

Thirty-one groundwater samples were collected from Jiwani, Ganz, Pishukan, Gwadar and Sur Bander, coastal towns of Gwadar District, Balochistan Province, Pakistan. The overall average trend of cationic and anionic distributions is found in the order of Na respectively. Average ionic composition on Stiff diagram shows (Na + +K + )-Cl -as one of the principal ionic pair, while ionic balance among Mg 2+ -SO 2- 4 and Ca 2+ -(HCO - 3 + CO 2- 3 ) have shown an imbalance. On Piper diagram, majority of the groundwater samples in the study area are of NaCl type. The Na + versus Cl -, Na + /Na + + Cl -versus Cl -/ anions, and Cl versus Cl/HCO 3 ratios signify influence of seawa-B Shahid Naseem

PIER LUIGI VERCESI * ASPETTI QUALI-QUANTITATIVI DELLE RISORSE IDRICHE SOTTERRANEE DEL BRESCIANO** RIASSUNTO-Vengono compendiati gli aspetti idrogeologici della provincia di Brescia attraverso l'analisi sintetica delle sue principali caratteristiche geologiche e idrogeomorfologiche. Il quadro geologico tratteggiato definisce i lineamenti della regione in studio nei suoi aspetti orografici, descrivendo i vari ambiti: montani, dei conoidi, vallivi, morenici e di pianura, evidenziando i tipi litologici presenti nelle varie zone che fungono da serbatoi e da mezzi trasrnissivi della risorsa idrica sotterranea. Di detti corpi vengono riportate valutazioni sui principali parametri idrogeologici al fine di caratterizzare le modalità della circolazione idrica alloro interno e di definirne il grado di vulnerabilità. La caratterizzazione generale che viene fornita compendia pertanto gli elementi salienti della zona esaminata, utilizzando peraltro valori e informazioni di carattere puntuale desunti da aree campione rappresentative, attraverso l'acquisizione di dati locali mediante specifici e dettagliati studi. Dal complesso degli elementi conoscitivi di carattere generale che sono forniti, e che rappresentano un preliminare momento fondamentale della ricerca, si evince la necessità di acquisire dati puntuali (informazioni sui circuiti idrici, sul quadro di fratturazione e fessurazione, sulla distribuzione spaziale della permeabilità e porosità delle rocce, ecc.) che costituiscono i pilastri su cui basare modelli matematici di simulazione, al fine di arrivare ad una completa ed esauriente conoscenza degli acquiferi. Di conseguenza le caratteristiche litologiche e tettoniche di un'area sono gli elementi che rendono possibile la ricostruzione idrogeologica di una determinata zona e che permettono, attraverso opportune elaborazioni quali modelli ed integrazioni (localizzazione dei punti d'acqua, dei centri di pericolo ecc.), di definire la potenzialità idrica, il quadro di vulnerabilità delle risorse, l'evoluzione dei fenomeni di eventuali inquinamenti. SUMMARY -Qualitative and quantitative aspects oj water resources in the area of Brescia. The hydrogeologic aspects of the province of Brescia are briefly discussed, through the concise analysis of its main geologica! and hydrogeologic morphologic characteristics. The geologica! structure defines the orographic aspects of the area, characterizing the different environments: mountains, alluvial fans, valleys, morains and plain. This highlights the lithologic types which act as tanks and transmission media of the underground water resources in the various area. The above mentioned structures are evaluated relative to the main hydrogeologic parameters in order to characterize the patterns of water circulation inside them and their degree of vulnerability. The resulting generai characterization sums up the main components of the area. 1t is based on detailed values and information gathered from rapresentative sample areas where specific researches were carried out. From the preliminary knowledge gathered, it becomes evident that it will be necessary to collect more detailed data (information concerning water circulation, breaking and cracking patterns, permeability and porosity of rocks) which are the basis of mathematical models of simulation for a complete knowledge of the acuifers. Consequently the lithologic and tectonic features of an area are the components that allow the hydrogeologic reconstruction of a certain area and that permit, through opportune elaborations like models and integrations (localization of water points, of danger centres, etc.) to define the water capacity, the picture of vulnerability of the resources and the evolution of possible pollutions.

PurposeThis paper aims to define the current and potential extent of seawater intrusion in Manukan Island under different scenarios of varying recharge and pumping rates. The calibrated model was also used to predict the extent of seawater intrusion in low lying area of Manukan Island for two years with all conditions assumed to remain the same as those in December 2009.Design/methodology/approachDifferent scenarios of varying recharge and pumping rates based on threats received by Manukan Island were investigated. El‐Nino events and overpumping are represented by varying recharge and pumping rates. Simulation was done using SEAWAT‐2000, the latest modeling software available in groundwater modeling that couples flow and transport together.FindingsThe seawater‐freshwater mixing ratio moves landwards after two years of simulation in Scenario 1. In order to control overpumping in this study area, Scenario 2 has resulted in backward movement of the 1.4 percent seawater‐freshwater mixin...

This study aimed to analyze seawater intrusion by measuring TDS, DHL and Salinity in dug well water on the coast of Pasir Nan Tigo Village. Sampling was carried out in December on the third week. TDS concentration measurements showed that there were three wells that indicated seawater intrusion, Well 1 (1526.4 mg/L), Well 2 (2500.1 mg/L) and Well 3 (2733 mg/L). DHL value measurements showed that there were three wells that indicated seawater intrusion Well 1 (1765 uS/cm), Well 2 (1556.1 uS/cm) and Well 3 (2002.3 uS/cm). Salinity values showed that there were four wells which indicated seawater intrusion Well 1 (12.7 o/oo), Well 2 (15 o/oo), Well 3 (17.9 o/oo) and Well 4 (10.02 o/oo). The effect of the distance of the well from the shoreline on the concentration of TDS and DHL had an effect of 33% while on the Salinity value of 44%. The results showed that there were several wells that indicated seawater intrusion along the coast in Pasir Nan Tigo Village.

Marine intrusion phenomenon is the main phenomenon threatening the groundwater quality in coastal aquifers around the world. This phenomenon is generally caused by the overexploitation of aquifers, decline in the piezometric level and the rise in sea level under the climate change effect. There are several approaches to study and assess the marine intrusion phenomenon. For this study, the crossing of piezometric, hydrochemical and isotopic approaches was adopted to highlight the state of this phenomenon within the Plio-quaternary aquifer of the Essaouira basin. The couples (Na, Cl), (Ca, Mg), (Br, Cl), (δ 2 H, δ 18 O), (δ 18 O, Cl) were determined for 24 samples capturing the shallow aquifer of the Essaouira basin. The piezometric approach shows that negative piezometric levels are registered. The ionic ratios Br/Cl close to 1.5 and 1.7‰, Na/Cl close to 0.86, Mg/Ca and SO 4 /Cl weak showed that the seawater begins to invade the freshwater of the Plio-quaternary aquifer of Essaouira basin. This intrusion demonstrated by ionic ratios and corroborated by isotopic approach and the combined use of oxygen-18 contents and chlorides has a mixing rate of 15.9% at the well 11/51, 14.5% at the sample 45/51, 13.2% at the well 149/51, 13.3% at point O114 and 12.8% at the well O94. However, the results of the hydrogeochemical and isotopic approach suggest intrusion up to 2 km from the sea; this reflects a warning sign about the groundwater deterioration of the study area.

La complejidad de los medios geológicos, así como el que cada vez más se requieran estudios de mayor detalle, ha provocado un gran auge en el empleo de modelos numéricos en hidrogeología, fundamentalmente de flujo de agua, pero también de forma creciente de transporte de solutos. Debido a esta complejidad y a la dificultad de disponer de medidas directas de los parámetros físicos de flujo y transporte (conductividad, difusión, porosidad, etc.), resulta necesaria una calibración. Este proceso de calibración se puede llevar a cabo de forma manual o automática. Aunque actualmente se dispone de un buen número de códigos que permiten la calibración automática, todavía se sigue empleando la calibración manual. En este artículo se presenta brevemente la teoría del problema inverso y se muestra su aplicación a dos ejemplos mostrando algunas de las posibilidades de la calibración automática. Palabras clave: calibración, función objetivo, modelos, problema inverso The inverse problem in hydrogeology. Applications

Minecraft, sonsuz olasılıkları ve yaratıcı özgürlüğü ile bilinen küresel bir sansasyon haline geldi. Orijinal PC ve konsol sürümleri efsanevi olsa da, mobil sürüm olan Minecraft APK, tüm bloklu evreni avucunuzun içine getiriyor. İster yüksek kaleler inşa ediyor, ister toprağın derinliklerinde madencilik yapıyor veya çetelerle savaşıyor olun, mobil sürüm tüm heyecanı ve daha fazlasını sunuyor.

Increasing usage of ground water tends to cause sea water intrusion. Sea water intrusion often happens in coastal areas. This study was conducted to determine the spread, levels of intrusion and factors that affect sea water intrusion in the research area. The sampling technique was carried out using interval random sampling, where 30 samples were taken with a distance of 2 km each, and then chemical analysis was carried out including the parameters of Cl-, HCO3-, CO3 = , and electrical conductivity (EC). The method used to determine the level of seawater intrusion was the method of Chloride Bicarbonate Ratio and then the types of water were classified based on chloride content and electrical conductivity. The determination of the distribution of seawater intrusion was done by mapping analysis using the ArcGis application program. To determine the factors that affected sea water intrusion, multivariate regression analysis with the "backward elimination" method was used. The results showed that on several sample points the shallow aquifer had been intruded by sea water with a ratio of 1.02 to 102.16 which were included in the category of intrusion of slightly to high. Chloride concentrations ranged from 2 mg/L to 31,160 mg/L and were classified as fresh water to salt water. Electrical conductivity ranged from 186 μmhos/cm to 26,400 μmhos/cm and generally above 200 μmhos/cm which meant that the sea water had been disturbed. Factors that significantly affected sea water intrusion were water usage debit and aquifer permeability with an adjusted coefficient R 2 of 0.797.

Many coastal agricultural regions are at risk of sea-level rise and groundwater overdraft, which lead to saltwater intrusion of underlying aquifers. Increased salinity levels in irrigation water can lead to crop yield reductions and degraded land quality. This paper considers the value of groundwater quality in agricultural production using micro-level data from California's central coast. We combine panel measurements of groundwater salinity and fine spatial land use data with property ownership boundaries to predict the likelihood that farmers shift crops in response to a change in groundwater salinity. This allows us to estimate marginal damages associated with changing salinity while incorporating the adaptive response of crop switching. We find that growers shift away from crops if they are both salt-sensitive and require long-term investments. Results inform our understanding of the social marginal cost of groundwater extraction, the potential impacts of sea-level rise to coastal agriculture, and the benefits of investing in alternative water sources for irrigation.

Reverse osmosis (RO) seawater desalination is a widely applied technological process to supply potable water worldwide. Recently, saline groundwater (SGW) pumped from beach wells in coastal aquifers that penetrate beneath the freshwater-seawater interface is considered as a better alternative water source to RO seawater desalination as it is naturally filtered within the sediments which reduces membrane fouling and pre-treatment costs. The SGW of many coastal aquifers is anoxic -and thus, in a low redox stage -has elevated concentrations of dissolved manganese, iron and sulfides. We studied the influence of the SGW redox stage and chemistry on the performance -permeate flux and fouling properties -of RO desalination process. SGWs from three different coastal aquifers were sampled and characterized chemically, and RO desalination experiments were performed under inert and oxidized conditions. Our results show that all three aquifers have anoxic saline groundwater and two of them have intensive anaerobic oxidation of organic matter. Two aquifers were found to be in the denitrification stage or slightly lower and the third one in the sulfate reduction stage. Our results indicate that the natural redox stage of SGWs from coastal aquifers affects the performance of RO desalination. All SGW types showed better RO performance over seawater desalination. Furthermore, air oxidation of the SGW was accompanied with pH elevation, which increased the membrane fouling. Hence, keeping the feed water unexposed to atmospheric conditions for maintaining the natural reducing stage of the SGW is crucial for low fouling potential. The observed benefits of using naturally reduced SGW in RO desalination have significant implications for reduction in overall process costs.

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Water availability is a fundamental concern for coastal areas in arid and semiarid regions such as Jerba Island, southeastern Tunisia. In these areas, the water demand is steadily increasing and putting pressure on water resources. These pressures are maintained by excessive pumping to meet the needs of various agricultural, domestic, industrial and tourism sectors. The effects on the groundwater are expressed by a quantitative and qualitative deterioration of the regional ecosystem. An assessment of groundwater salinization and seawater intrusion in Jerba aquifer are therefore needed. Physical parameters were measured in situ in one hundred and three boreholes and major ions were analyzed and several diagram were used to model groundwater mineralization. Geochemical analysis revealed that Cl-Na-Mg-Ca-SO 4 was the dominant water type indicating rockwater interaction and saltwater intrusion. Na + /Cl -, Ca 2+ /Cl -, Br -/Cl -, Ca 2+ /Na + , Mg 2+ /Ca 2+ and Cl -/ HCO 3 -ratios versus chloride confirms the double influence of mixing mechanisms of fresh and saline waters and the water-rock interactions. Computed seawater fraction for sampled water shows that the average mixing rate of seawater intrusion reached 10.5%, confirming the marine intrusion in the aquifer. The highest values were registered in coastal wells. The statistical analyses reveal that high groundwater mineralization is due to rockwater interaction associated with mixture of groundwater and seawater in many areas.

Highlights  Seawater intrusion is the mechanism controlling the interaction between groundwater and aquifer materials.  Lithium content and groundwater abnormal salinizationAre highly correlated.  Lithium is a tracer for the processes associated to seawater intrusion.

Highlights  Seawater intrusion is the mechanism controlling the interaction between groundwater and aquifer materials.  Lithium content and groundwater abnormal salinizationAre highly correlated.  Lithium is a tracer for the processes associated to seawater intrusion.

Saltwater intrusion is generally related to seawater-level rise or induced intrusion due to excessive groundwater extraction in coastal aquifers. However, the hydrogeological heterogeneity of the subsurface plays an important role in (non-)intrusion as well. Local hydrogeological conditions for recharge and saltwater intrusion are studied in a coastal groundwater system in Vietnam where geological formations exhibit highly heterogeneous lithologies. A three-dimensional (3D) hydrostratigraphical solid model of the study area is constructed by way of a recursive classification procedure. The procedure includes a cluster analysis which uses as parameters geological formation, lithological composition, distribution depth and thickness of each lithologically distinctive drilling interval of 47 boreholes, to distinguish and map well-log intervals of similar lithological properties in different geological formations. A 3D hydrostratigraphical fence diagram is then generated from the constructed solid model and is used as a tool to evaluate recharge paths and saltwater intrusion to the groundwater system. Groundwater level and chemistry, and geophysical direct current (DC) resistivity measurements, are used to support the hydrostratigraphical model. Results of this research contribute to the explanation of why the aquifer system of the study area is almost uninfluenced by saltwater intrusion, which is otherwise relatively common in coastal aquifers of Vietnam.

In coastal aquifers which are exploited for agricultural purposes, salinisation by salt recycling from irrigation is superimposed on the effects of seawater intrusion. Water quality degradation of irrigation pumping wells caused by seawater intrusion further enhances salinisation by irrigation, as the extracted solute mass is recycled and is not withdrawn from the system. The main objective of this study is the investigation and quantification of the impact of solute recycling from irrigation relative to seawater intrusion. A solute mass budget was established by expressing the solute mass return flow as fraction of the extracted solute mass from wells by means of a solute mass return flow ratio ðr r Þ: The obtained expression for the relative contribution of solute recycling from irrigation is an exponential function of the return flow ratio r r and normalised time t only (time versus system turnover time). This expression was applied to an example, the Kiti aquifer (Southern Cyprus), where field observations suggest that solute return flow is a superimposed salinisation mechanism. The contribution from solute recycling normalised with the solute mass flux entering from the sea after 20 years was found to be 1.5-8.5% in the extracted solute mass flux, depending on the estimation of the system turnover time. Subsequently, a coupled finite element model, reflecting the main features of the Kiti aquifer was used as a possible 'synthetic reality', to test the relative impact of solute recycling on the spatial salinity distribution in a complex hydrogeological and geometrical setting. This was done by running two simulation scenarios: (1) recycling all the extracted solute back into the system and (2) leaving solute recycling aside and comparing the results of these two scenarios relative to each other and to patterns observed in the field. The results showed, that by introducing solute recycling into the numerical model as coupled boundary condition does not only respect the overall solute mass balance but can have an important impact on the salinity distribution, leading to a significant spreading of the mixing zone, similar to what was observed in the field.

A framework for a process-based salinisation risk assessment methodology is proposed that allows separation and mapping of areas prone to primary salinisation, such as seawater intrusion, agrochemical pollution or geogenic contamination and secondary salinisation derived from irrigationinduced solute recycling. By adaptation of the boundary conditions, the bulk salinity distribution is decomposed into components derived from the different salinisation processes. To obtain the respective risk index distributions, both the 'present state' and salinisation potentials (steady state salinity distributions) have to be simulated. The respective salinisation risk indices are defined as the potential of further salinisation induced by the respective salinisation process and are obtained by deducting the components of the 'present state' salinity distributions from the respective salinisation potentials. The risk index distribution maps are then overlaid with a defined threshold salinity, revealing areas requiring remediation or conservation measures. The risk index distributions are strictly related to a given exploitation scheme. Modification of an exploitation scheme leads therefore to modified risk index distributions which highlight areas that will suffer further salinisation from areas for which the modified exploitation scheme will have a remediating effect. The risk maps obtained for a real case site (Akrotiri aquifer, Southern Cyprus) are then presented, revealing the outcomes of the approach, as well as its limitations.

A framework for a process-based salinisation risk assessment methodology is proposed that allows separation and mapping of areas prone to primary salinisation, such as seawater intrusion, agrochemical pollution or geogenic contamination and secondary salinisation derived from irrigationinduced solute recycling. By adaptation of the boundary conditions, the bulk salinity distribution is decomposed into components derived from the different salinisation processes. To obtain the respective risk index distributions, both the 'present state' and salinisation potentials (steady state salinity distributions) have to be simulated. The respective salinisation risk indices are defined as the potential of further salinisation induced by the respective salinisation process and are obtained by deducting the components of the 'present state' salinity distributions from the respective salinisation potentials. The risk index distribution maps are then overlaid with a defined threshold salinity, revealing areas requiring remediation or conservation measures. The risk index distributions are strictly related to a given exploitation scheme. Modification of an exploitation scheme leads therefore to modified risk index distributions which highlight areas that will suffer further salinisation from areas for which the modified exploitation scheme will have a remediating effect. The risk maps obtained for a real case site (Akrotiri aquifer, Southern Cyprus) are then presented, revealing the outcomes of the approach, as well as its limitations.

In coastal aquifers which are exploited for agricultural purposes, salinisation by salt recycling from irrigation is superimposed on the effects of seawater intrusion. Water quality degradation of irrigation pumping wells caused by seawater intrusion further enhances salinisation by irrigation, as the extracted solute mass is recycled and is not withdrawn from the system. The main objective of this study is the investigation and quantification of the impact of solute recycling from irrigation relative to seawater intrusion. A solute mass budget was established by expressing the solute mass return flow as fraction of the extracted solute mass from wells by means of a solute mass return flow ratio ðr r Þ: The obtained expression for the relative contribution of solute recycling from irrigation is an exponential function of the return flow ratio r r and normalised time t only (time versus system turnover time). This expression was applied to an example, the Kiti aquifer (Southern Cyprus), where field observations suggest that solute return flow is a superimposed salinisation mechanism. The contribution from solute recycling normalised with the solute mass flux entering from the sea after 20 years was found to be 1.5-8.5% in the extracted solute mass flux, depending on the estimation of the system turnover time. Subsequently, a coupled finite element model, reflecting the main features of the Kiti aquifer was used as a possible 'synthetic reality', to test the relative impact of solute recycling on the spatial salinity distribution in a complex hydrogeological and geometrical setting. This was done by running two simulation scenarios: (1) recycling all the extracted solute back into the system and (2) leaving solute recycling aside and comparing the results of these two scenarios relative to each other and to patterns observed in the field. The results showed, that by introducing solute recycling into the numerical model as coupled boundary condition does not only respect the overall solute mass balance but can have an important impact on the salinity distribution, leading to a significant spreading of the mixing zone, similar to what was observed in the field.

Demand for freshwater is rising with factors, such as population growth, land use change and climate variations, rendering water availability in the future uncertain. Groundwater resources are being increasingly exploited to meet this growing demand. The aim of this study is to identify the influence of population growth induced by land use change and climate change on the future state of freshwater resources of Lamu Island in Kenya where a major port facility is under construction. The results of this study show that the "no industrial development" population scenario (assuming the port was not constructed) would be expected to reach ~50,000 people by 2050, while the projected population upon completion is expected to reach 1.25 million in the same year when the Lamu Port-South Sudan-Ethiopia Transport Corridor Program (LAPSSET) port reaches its full cargo-handling capacity. The groundwater abstraction in 2009 was 0.06 m 3 daily per capita, while the demand is expected to raise to 0.1 m 3 by 2050 according to the "LAPSSET development" projection. The modelling results show that the Shela aquifer in Lamu, which is the main source of water on the island, will not experience stress by 2065 for the "no industrial development"

In coastal groundwater aquifer, seawater intrusion is seen as a significant issue. Increasing the groundwater pumping rate enhances seawater intrusion into groundwater in the coastal aquifers. In Egypt, the Nile Delta aquifer (NDA) is extremely vulnerable to Mediterranean Sea seawater intrusion. The study's major goal was to create a three-dimensional groundwater model that included main branches of the irrigation system and their groundwater recharges into the NDA. The NDA model was built by using the SEAWAT program. The model validation was achieved by comparing its results with the observation data and results from previous models. Three scenarios were proposed considering: 1) sea level rise, 2) changes in the rate of groundwater abstraction, and 3) a combination of the conditions of the two previous scenarios' conditions. A rise in Mediterranean Sea levels by 25, 50, 75 and 100 cm caused additional saltwater intrusion to distances of 5.11 km, 7.10, 7.62 and 8.2 km, respectively. Moreover, in comparison to the base situation, a decrease in the lower boundary's groundwater head by 25, 50, 75 and 100 cm caused the saltwater to advance further inland to distances of 5.30, 5.47, 5.52 and 5.75 km, respectively. The third scenario proved to be the worst case, in which saltwater intrusion increased to a distance of 7.22, 7.73, 8.20 and 10.20 km, respectively. Compared with previous model studies, the results showed that saltwater intrusion length decreases by 4.0 km after including all branches of the irrigation network.

Groundwater quality is an essential factor restricting regional sustainable development owing to water resource scarcity, especially in coastal regions. Coastal groundwater is affected by natural conditions and strong human activities, and the evolution of water quality is extremely complex. Information on the hydrochemistry evolution and nitrate contamination status of coastal groundwater under the conjunctive effects of natural processes and human activities is a vital requirement for groundwater resource management in coastal regions. Thus, this study integrated traditional hydrochemical analysis approaches, the entropy-weight water quality index (EWQI), and the health risk assessment model to analyze hydrochemical characteristics, quality, and nitrate health risks in a typical coastal region (i.e., southern Laizhou Bay) simultaneously affected by seawater intrusion and anthropogenic activities, as well as to explore the dominant mechanisms controlling groundwater quality. The results indicated that the concentrations of major hydrochemical constituents in groundwater exhibited wide variability. The NO − 3 concentration varied from 0.59 to 824.80 mg/L; it surpassed the WHO drinking water standard (50 mg/ L) at 89.47% of sampling sites. The predominant hydrochemical types of groundwater were SO 4 •Cl-Ca•Mg and HCO 3-Ca•Mg. Governing factors influencing groundwater chemistry were recognized as rock weathering, inverse cation exchange and anthropogenic activities, and nitrate contents were largely controlled by agricultural practices. The computed EWQI showed that 55.26% of groundwater samples possessed EWQI values greater than 57, which is relatively poor-quality groundwater. The poor-quality groundwater was concentrated in the southwestern part of the study area. Non-cancer risks of nitrate in 96.71%, 94.74%, 89.47%, and 89.47% of the groundwater samples were unacceptable for infants, children, teens, and adults, and the spatial distribution of the hazard quotient (HQ) was in accordance with the spatial pattern of nitrate concentration. These findings can guide the exploitation and utilization of groundwater resources and water quality conservation in coastal regions.

Resumen-El problema inverso en hidrología subterránea consiste en la estimación de los parámetros de un modelo, a partir de las respuestas del sistema (niveles, concentraciones, etc.) y de información previa sobre los propios parámetros, tanto físicos (conductividad hidráulica, almacenamiento específico, etc.) como empíricos asociados a alguna función no lineal, también empírica, que controla la evolución de los parámetros físicos en función de la variable de estado. Su uso es poco frecuente

School of Water Resources Engineering, Jadavpur University, Kolkata-700 032, India Department of Civil Engineering, Dr. Sudhir Chandra Sur Degree Engineering College, Kolkata-700 074, India &lt;em&gt;E-mail&lt;/em&gt;: [email protected]; [email protected]; [email protected]; [email protected] &lt;em&gt;Manuscript received online 27 January 2020, revised 24 February 2020, accepted 03 March 2020&lt;/em&gt; India has a long coastline. Compared to the western coastline, the eastern coast line is severely affected by seawater intrusion. The Contai town is located in Purba Medinipur district of West Bengal on the eastern coastline of India. The soil of the region is mainly of fresh alluvials. There are few rivers flowing through the region, but this surface water is not sufficient to meet the domestic, industrial, agricultural demand. With the increasing population, urbanization, industrialization, the demand for water is increasing. To meet up such water...

The mechanism governing salinization of ground water discharging into the Sea of Galilee in Israel has been the subject of debate for several decades. Because the lake provides 25% of the water consumed annually in Israel, correct identi®cation of the salt sources is essential for the establishment of suitable water-management strategies for the lake and the ground water in the surrounding aquifers. Existing salinization models were evaluated in light of available and newly acquired data including general chemistry, and O, H, C and Cl isotopes. Based on the chemical and isotopic observations, the proposed salt source is an ancient, intensively evaporated brine (21-to 33-fold seawater) which percolated through the valley formations from a lake which had formed in the Rift Valley following seawater intrusion during the late Miocene. Low Na:Cl and high Br:Cl values support the extensive evaporation, whereas high Ca:Cl and low Mg:Cl values indicate the impact of dolomitization of the carbonate host rock on the residual solution. Based on radiocarbon and other isotope data, the dilution of the original brine occurred in two stages: the ®rst took place H30 000 a ago by slightly evaporated fresh-to-brackish lake water to form the Sea of Galilee Brine. The second dilution phase is associated with the current hydrological regime as the Sea of Galilee Brine migrates upward along the Rift faults and mixes with the actively circulating fresh ground water to form the saline springs. The spatially variable chemical and isotopic features of the saline springs suggest not only dierential dilution by fresh meteoric water, but also dierential percolation timing of the original brine into the tectonically disconnected blocks, registering dierent evaporation stages in the original brine. Consequently, various operations to reduce the brine contribution to the lake may be dierentially eective in the various areas.

In coastal areas, obtaining groundwater is not easy due to the lack of geological support conditions that cause water in the area to have poor quality such as groundwater that becomes salty. The coastal area of Sayung Subdistrict has geomorphological conditions whose surface tends to be flat with elevations 0-5 m higher than sea level and is dominated by alluvial material so that it can cause seawater infiltration to increase. The purpose of this research was to determine the distribution of salinity of groundwater in the coastal area of Sayung Subdistrict and to determine the cause of groundwater becoming salty. The method used in this research is the electrical conductivity (DHL) approach which is then classified based on the level of saltiness of groundwater. And then, well water from the sample points was tested using a hydrochemical test with the parameters used, namely the content of cations (Na, K, Mg, Ca) and anions (Cl, CO3, HCO3, SO4, NO3). This research was conducted at 33 well points spread across Sayung sub-district. The results of this study show that the electrical conductivity value obtained is between the range of 928-7,199 μS/cm which is divided into 3 classifications namely fresh water, fresh-brackish water, and brackish water. The analysis of the Trilinier Piper diagram shows that the saltiness of the groundwater is due to indications of seawater mixing characterized by a chloride (Cl) content that is increasingly greater towards the sea.

The detailed characterization of salt water intrusion is a key to understand both submarine groundwater discharge and manage often intensively exploited groundwater resources in coastal areas. With the objective to study the response of a coastal aquifer to a series of boundary conditions, a new experimental site has been developed through a clastic aquifer located north of Barcelona (Spain). This hectometer scale site is located 50 m from the seashore and equipped with 17 nearby shallow holes, with depths ranging from 15 to 28 m.

We study the effect of heterogeneity in the hydraulic conductivity field on the three-dimensional dynamics of seawater intrusion in a coastal aquifer with a pumping well. In order to test whether the mean behavior of this setup can be approximated with effective parameters we ran a Monte Carlo type series of numerical simulations. Variable-density groundwater flow and solute transport simulations were carried out within several random realizations of heterogeneous permeability fields. We determine the mean critical pumping rate by averaging over the ensemble of random conductivity fields and compare the result to the analytical solution derived by Strack (1976) for a homogeneous medium. Further, we evaluate the impact heterogeneity has on the seawater mass flux, the width of the mixing zone and the salinity of the water arriving at the well.

Salinity intrusion is a problem in many coastal estuarine and waterways in various parts of the world. Brisbane is a river city close to the coast and as such the condition of the river influences the surrounding groundwater quality. The data gathered by various agencies relating to the river system are used in this paper to develop and calibrate a 3D model of tidal intrusion into the river and surrounding groundwater. The FEMWATER finite element package is used to solve the model equations. Model simulations showed that salinity as far as15-25km from the coast. The model simulations show tidal effects on Brisbane River and surrounding groundwater and water quality deterioration appear to be related to coastal seawater intrusion over time.

Semi-arid coastal zones often suffer water-stress, as water demand is high and markedly seasonal, due to agriculture and tourism. Driven by scarcity of surface water, the communities in semi-arid coastal regions turn to aquifers as prime water source; but intensive exploitation of coastal aquifers causes seawater intrusion, which degrades the quality of groundwater. The cost-efficient and sustainable development of coastal aquifers can be achieved through a holistic management scheme which combines two non-traditional water sources: (a) saltwater, to be treated to the desired quality, and (b) wastewater, to be reclaimed to augment aquifer recharge for control of seawater intrusion, and also to meet certain demands. This management scheme is based on the idea that it is costadvantageous to: (i) desalt brackish groundwater, instead of seawater, as the former requires far less energy, and (ii) to re-use wastewater at only the differential cost to any treatment already practiced. In this paper, we present the general framework of the proposed management scheme, and a decision aid tool (DAT) which has been developed to assist decision makers to explore the scheme's decision space. The DAT uses cost as optimization criterion to screen various management scenarios, via modelling of the dynamic natural-engineered system behaviour, and identifies those cost-efficient ones that meet the water demand and achieve aquifer protection.

The increased use of reclaimed water for artificial groundwater recharge purposes has led to concerns about future groundwater quality, particularly as it relates to the introduction of new organic and inorganic contaminants into the subsurface. Here we review the integrated application of isotopic characterization and numerical modeling techniques for assessing the migration of reclaimed water that is used for artificial groundwater recharge in the coastal aquifer underlying Orange County, California. The Orange County Water District (OCWD) manages a groundwater basin that currently provides 70% of the domestic water supply for approximately 2 million residents in the northern, urbanized part of Orange County, California (OCWD, 1991, 1994, 1995). The remaining 30% is imported from outside the district. On an average annual basis, roughly 270,000 acre-feet (3.3 x 108 m3) of water are extracted from several hundred production wells located within the middle production aquifer of a 20...