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Saltwater intrusion (SWI) has a negative environmental impact on groundwater quality in coastal areas. Therefore, effective management strategies are required to preserve fresh groundwater resources. Historically, vertical barriers have been exclusively considered in both numerical studies and practical applications. The novelty of this study consists in investigating the SWI mitigation effectiveness of inclined physical subsurface barriers (PSBs), and specifically cutoff walls (CWs) and subsurface dams (SDs). An initial benchmark analysis of the Henry problem was performed. Following verification, the proposed model was applied to a real case study - the Biscayne aquifer (Southeastern Florida, USA). The model simulations run for different scenarios considering the vertical placement of the PSB, an inclined placement of the PSB according to different slopes (1/4, 1/2 and 1/1, at sea- and landside) and the combination of the best scenario. The results showed that CWs are more effective in limiting SWI in comparison with SDs. The most positive impact in both cases was achieved for a slope of 1/4, indicating that a moderate vertical inclination of the PSB better preserve coastal groundwater resources. The model presented in this work can be a valuable tool for policy makers in predicting the coastal aquifer response. However, a comprehensive cost–benefit analysis is required to further account for the feasibility and the economic costs related to the construction of inclined PSBs.

Coastal aquifers are usually vulnerable to contamination by saltwater intrusion. The degree of contamination depends on the amount of former seawater intruding the aquifer as submarine groundwater discharge (SGD). A three-dimensional numerical SEAWAT model was developed to provide insights to the responses of saltwater intrusion and amount of seawater portion of SGD, to groundwater withdrawal from four wells at different spatial locations. The results showed that saltwater wedge encroachment varies with a withdrawal rate and well location. Increasing withdrawal rates from 0.165 m3/sec to 0.53166 m3/sec resulted in a noticeable increase in wedge encroachment into the aquifer from 589 m to 1319 m, respectively, regardless of the distance from the coastline. However, higher withdrawals from the wells closer to the coastline caused the hydraulic head near the seaside to drop below the terrestrial head, causing the saltwater wedge to be pushed back toward the sea. Simulations also showed that a coastal well might act as a hydraulic barrier that prevents the brackish zone from moving further inland, which is critically important in terms of groundwater management. Seawater contributed from 5% to above 33% in SGD. Although the withdrawal rates from Well 3 were 10 to 20 times larger than the Well 2 rates, the seawater contribution associated with Well 3 was about the same. This is attributed to the horizontal vicinity of Well 2 to the seacoast boundary compared to Well 3 even though Well 3 is deeper than Well 2, demonstrating that it is the horizontal location that governs the amount of abstracted former seawater.

This paper presents an integrated framework for management of aquifers threatened by saltwater intrusion (SI). In this framework, SEAWAT model is used for simulating the density dependent groundwater flow. Three meta-models based on the artificial neural network (ANN), M5 tree and random subspaces model (RSM) are developed, as surrogate models for SEAWAT to accurately simulate the groundwater response to different pumping and recharge scenarios. Various patterns of recharge to and discharge from aquifer are used to generate a database for training the mentioned surrogate models. To decrease the number of training parameters, the aquifer area is divided into different zones using k-means clustering technique (KMC). Additionally, a conjunctive model (CM) using a combination of the three surrogate models is proposed to enhance the accuracy of the simulation. It is then integrated with the Non-dominated Sorting Genetic Algorithm-II (NSGA-II) with the objectives of maximizing pumping rates and minimizing SI length. Next, the socially optimal scenarios are selected from the obtained Pareto-front using the Nash bargaining theory. The performance of the proposed model is evaluated by applying it to the Kahak aquifer, Iran, which is subjected to SI. The results show that the conjunctive model using KMC technique predicts SI length with a comparable accuracy and results in 95% reduction in runtime compared to a simulation-optimization (SO) model.

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

This paper provides a thorough investigation of the effect of a top low-permeability (TLK) layer on transient saltwater intrusion dynamics prompted by water table fluctuations and sea level rise. Laboratory experiments were conducted on a 2D-sandbox and numerical simulations were performed using the SEAWAT code. Four cases were investigated, including a homogeneous case and three cases, where the top layer thickness (Wtop) was equal to 0.2H, 0.33H and 0.5H, respectively, where H was the aquifer thickness. The experimental and numerical results show that the toe length decreases linearly with increasing the thickness of the TLK layer. The results also suggest that lowering the permeability of the upper part of the aquifer causes faster saltwater removal process. The sensitivity analysis shows that decreasing the top layer permeability causes further reduction of the intrusion length. Nonetheless, the results evidence that this method yields relatively little reduction of the saline water intrusion length if the upper layer thickness is inferior or equal to a fifth of the total aquifer thickness, regardless of the permeability value of the top layer. The field-scale modelling results demonstrate that the performance of the TLK layer weakens noticeably as the hydraulic gradient decreases. The results show that the TLK layer achieved a maximum saltwater wedge reduction of 31% in the case where Wtop = 0.75H, which means that lowering the permeability of three fourths of the aquifer thickness only induced a toe length reduction by nearly a third of its original length. In addition to providing a quantitative analysis of SWI dynamics in bi-layered coastal aquifers, this study questions the performance and practicality of the artificial reduction of the upper aquifer permeability as a countermeasure for seawater intrusion control.

A proper management of fresh groundwater lenses in small islands is required in order to avoid or at least limit uncontrolled saltwater intrusion and guarantee the availability of the resource even during drought occurrences. An accurate estimation of the freshwater volume stored in the subsoil is a key step in the water management decision process. This study focused on understanding the hydrogeological system behaviour and on assessing the sustainable use of the groundwater resource in Nauru Atoll Island (Pacific Ocean). A first phase, concerning the hydrogeological characterization of the island, highlighted the occurrence of few drought-resilient freshwater lenses along the seashore. The second part of the study focused on the characterization of a freshwater lens found in the northern coastal area and identified such area as the most suitable for the development of groundwater infrastructures for water withdrawal. The characterization activities allowed quantifying the freshwater lens thickness and volume in order to assess the capability to satisfy the population water demand. A geo-electrical tomography survey was carried out, and a 3D density-dependent numerical model was implemented in SEAWAT. The model results demonstrated that in small islands freshwater can unexpectedly accumulate underground right along the seashore and not in the centre of the island as is commonly believed. Furthermore, the model can constitute a useful tool to manage the groundwater resources and would allow the design of sustainable groundwater exploitation systems, avoiding saltwater intrusion worsening.

Laboratory and numerical experiments were conducted to provide a quantitative steady-state analysis of the effect of incremental variations of water level on saltwater intrusion. The purpose was to seek mathematical correlations relating both the wedge toe length and the height along the coastline to the boundary head difference. The laboratory experiments were completed in a 2D sand tank where both freshwater and seawater levels were varied. The experiments were conducted for two bead sizes having different hydraulic conductivities. The numerical model SEAWAT was used to validate the results and then to perform sensitivity analysis. The experimental results show that at steady-state conditions, the logarithmic toe length could be expressed as a linear function of the boundary head difference. The linear relationship was recorded in both advancing and receding wedge phases. The linearity of the correlation was also well demonstrated with analytical solutions. Similar relationships were also derived in the scenarios where the sea level fluctuated while the freshwater boundary head was constant. The height of the saltwater wedge along the coastline was also found to be a linear function of the boundary head difference. The sensitivity analysis shows that the regression coefficients were sensitive to the hydraulic conductivity, the dispersivity, and the saltwater density, while the porosity and the rate of boundary head change induced negligible effects. The existence of a linear relationship between the logarithmic toe length and the boundary head difference was also well evidenced in a field-scale aquifer model for all the different hydrogeological aquifer conditions tested. This study is the first attempt in identifying the underlying correlation between the boundary water level variations and the main seawater intrusion (SWI) external metrics under controlled laboratory conditions, which is of great relevance from a water resources management perspective.

Fresh groundwater reserves, being of vital importance for more than a billion people living in the coastal zone, are being threatened by saltwater intrusion due to anthropogenic activities and climate change. High resolution three-dimensional (3D), variable-density (VD), groundwater flow, and salt transport (FT) numerical models are increasingly being used to support water managers and decision-makers in their strategic planning and measures for dealing with the problem of freshwater shortages. However, these computer models typically require long runtimes and large memory usage, making them impractical to use without parallelization. Here, we parallelize SEAWAT and show that with our parallelization 3D-VD-FT modeling is now feasible for a wide range of hydrogeologists, since a) speedups of more than two orders of magnitude can be obtained as illustrated in this paper, and b) large 3D-VD-FT models are feasible with memory requirements far exceeding single machine memory.

Brackish to saline groundwater in arid environments encourages the development and sustainability of inland freshwater lenses (IFLs). While these freshwater resources supply much-needed drinking water throughout the Arabian Peninsula and other drylands, little is understood about their sustainability. This study presents a numerical model using the SEAWAT programming code (i.e., MODFLOW and the Modular Three-Dimensional Multispecies Transport Model (MT3DMS)) to simulate IFL transient evolution. The numerical model is based on a physical laboratory model and calibrated using results from simulations conducted in a previous study of the Raudhatain IFL in northern Kuwait. Data from three previously conducted physical model simulations were evaluated against the corresponding numerical model simulations. The hydraulic conductivities in the horizontal and vertical directions were successfully optimized to minimize the objective function of the numerical model simulations. The numerical model matched observed IFL water levels at four locations through time, as well as IFL thicknesses and lengths (R2 = 0.89, 0.94, 0.85). Predicted lens degradation times corresponded to the observed lenses, which demonstrated the utility of numerical models and physical models to assess IFL geometry and position. Improved understanding of IFL dynamics provides water-resource exploration and development opportunities in drylands throughout the Arabian Peninsula and elsewhere with similar environmental settings.

There is a close connection between saltwater intrusion into aquifers and groundwater extraction. Freshwater extraction in coastal aquifers is one of the most important reasons for the saltwater intrusion into these aquifers. Condition of extraction system such as well depth, discharge rate, saltwater concentration and etc. could affect this process widely. Thus, investigating different extraction conditions comprises many management advantages. In the present study, the effects of freshwater extraction on saltwater interface displacement have been investigated in a laboratory box. Three different well depths (H) were considered with combinations of 3 different extraction rates (Q) and 3 saltwater concentrations (C) for detailed investigation of the effects of these factors variations on saltwater displacement. SEAWAT model has been used to simulate all the scenarios to numerically study of the process. The experimental and numerical results showed that when the C and Q rates were small and the well depth was shallow, the saltwater interface wouldn’t reach the extraction well, so the extracted water remained uncontaminated. When the C and Q rates were increased and the well was deepened, the salinity of the extracted water became higher. When the Q and C rates were high enough, in the shallow well depth, the final concentration of the extracted water was low but a huge part of the porous media was contaminated by the saltwater, furthermore when the well was deepened enough, the final concentration of the extracted water was increased but a small part of the porous media was contaminated by the saltwater. Finally, the results showed that when the Q and H rates were high enough, the extraction well behaved like a barrier and didn’t allow the advancing saltwater wedge toe to be intruded beyond the wells.

The objective of this study was to examine the performance of cutoff walls in controlling saltwater intrusion in stratified heterogeneous coastal aquifers. Numerical and laboratory experiments were completed in laboratory-scale aquifer where the effectiveness of cutoff walls was assessed in three different configurations, including a homogeneous scenario, a stratified aquifer with high K–low K–high K pattern (case HLH) and another stratified aquifer with low K–high K–low K pattern (case LHL). The results show that the cutoff wall was effective in reducing the saltwater wedge in all the investigated cases of layered-aquifers with toe length reduction of up to 43%. The wall exhibited more wedge reduction in shallower than steeper hydraulic gradients. However, the soil stratification appeared to lessen the overall performance of the wall compared to the homogeneous case. The aquifer stratification disrupted the flow dynamics, and thus affected the freshwater velocity at the wall opening to various degrees, depending on the layering pattern. The presence of an interlayer of low k (case HLH) inhibited the downward movement of the freshwater towards the wall opening, and thus decreasing the repulsion ability of the wall. Moreover, the presence of an underlying low permeability layer (case LHL) was found to obstruct the freshwater flow in the lower part of the aquifer, thereby slowing down the velocity through the wall opening. Numerical analysis of other layering patterns of monotonically increasing/decreasing permeability from top to bottom showed that the cutoff wall remained effective in repulsing the seawater wedge.

Groundwater systems are considered major freshwater sources for many coastal aquifers worldwide. Seawater intrusion (SWI) inland into freshwater coastal aquifers is a common environmental problem that causes deterioration of the groundwater quality. This research investigates the effectiveness of using an injection through a well to mitigate the SWI in sloping beds of unconfined coastal aquifers. The interface was simulated using SEAWAT code. The repulsion ratios due to the length of the SWI wedge (RL) and the area of the saltwater wedge (RA) were computed. A sensitivity analysis was conducted to recognize the change in the confining layer bed slope (horizontal, positive, and negative) and hydraulic parameters of the value of the SWI repulsion ratio. Injection at the toe itself achieved higher repulsion ratios. RL and RA declined if the injection point was located remotely and higher than the toe of the seawater wedge. Installation at the toe achieved a higher RL in positive sloping followed by horizontal and negative slopes. Moreover, the highest value of RA could be reached by injecting at the toe itself with a horizontal bed aquifer, followed by negative and positive slopes. The recharge well is confirmed as one of the most effective applications for the mitigation of SWI in sloping bed aquifers. The Akrotiri case study shows that the proposed recharging water method has a significant impact on controlling SWI and declines in both SWI wedge length and area.

Gotland suffers from a shortage of drinking water at infrequent intervals which is onlypredicted to get worse with time. The problem is not a shortage of precipitation, the shortagelies in the combined problem of runoff and high water usage during the summer months.From September to March there is an abundance of water which mostly goes to runoff intothe sea surrounding Gotland. Due to the fact that Gotland is an island, a concave boundryis formed between the deeper saline groundwater and the fresh groundwater closer to thesurface. In an effort to possibly help in solving the water shortage, an idea was introducedto pump out the saline groundwater from the deep and thus creating an increase in storageof fresh groundwater.Firstly an investigation into suitable locations for modeling was conducted where two siteswere chosen. To test this concept and see if the idea was feasable a 2D-model was establishedusing GMS, MODFLOW, MT3DMS and SEAWAT with the aim of simulating the groundwaterat the well chosen sites on Sudret, Gotland. Two wells were implemented in the model,one for extracting fresh groundwater and one for extracting saline groundwater. The hopeswere to be able to simulate an increase of the storage of fresh water during the rechargeperiod and thus helping to solve the problem with insufficient water during the strenuoussummer months. Hopefully the results of the simultations can make up the foundations foran implementation of the concept at a location at Gotland.Results for site 1 indicate that the volume of fresh water in the akvifer can be increasedby 13of the extraction volume when only saline groundwater is removed. The maximumflow of only saline extraction at site 1 has been determined to 35m3år per meter. For example,with only an extraction of saline water of 35m3år at site 1 the fresh water in the aquifer willincrease by 340m3 per metre after 10 years.The model indicates that the volume of fresh water in the akvifer can be increased bya minimum of 15 of the saline extraction volume when only saline water is removed. Themaximum flow of only saline groundwater at site 2 was decided to be 65m3år per meter. Forexample, with only an extraction of saline water of 65m3år at site 1 the fresh water in theakvifer will increase by 940m3 per metre after 10 years. Gotland lider till och från av vattenbrist under sommaren, problemen förväntas även ökai samband med klimatförändringar och expanderande antropogen påverkan. Under vinterhalvåretfår Gotland mer än tillräckligt med sötvatten för att täcka efterfrågan, problemetuppkommer från att majoriteten av vattnet evapotranspireras samt går till ytavrinning tillÖstersjön. Ytterligare en orsak till vattenbristen beror på att Gotlands grundvatten omgesav saltvatten. Saltvattnet kring Gotland bildar en konkav gräns mellan sött och salt vatten igrundvattenmagasinet vilket väsentligt begränsar den möjliga lagringen av sött grundvatten.För att hjälpa till att lösa problemen med vattenbrist på Gotland introducerades en idé attutöka andelen sött vatten i grundvattenmgasinen genom att pumpa salt grundvatten fråndjupet under återhämtningsperioden.Arbetet påbörjades genom att undersöka en lämplig plats på Gotland, både ur en modelleringssynpunktsamt inför ett eventuellt fortsatt arbete. Två platser valdes slutligen dären 2D-grundvattenmodell skapades vid båda platserna med hjälp av GMS, MODFLOW,MT3DMS och SEAWAT. I modellen implementerades två uttagsbrunnar, en för salt grundvattenfrån djupet och en för sött grundvatten närmare ytan. Eftersom modellen skapats i 2Dinnebär det det en förenkling av geometrin och modellresultat motsvarar då en horisontelltborrad brunn, därför anges resultaten som flöde per meter horisontell brunn. Förhoppningenvar att genom simulering kunna påvisa en ökning av sötvatten i grundvattenmagasinet genomatt extrahera salt grundvatten under återhämtningsperioden. målet är att undersökningarnaska leda till en implementering av metoden i verkligheten i ett försök att minska vattenbristen.Modellresultat för plats 1 indikerar att volymen sött vatten i akviferen ökar med 13 avuttaget när endast salt vatten extraheras. Det maximala uttagsflödet vid plats 1 för endastsalt vatten bestämdes till 35m3år per meter. Vid ett saltvattenuttag på 35m3år vid plats 1 ökarsötvattenvolyem i akviferen t.ex. med 340m3 per meter efter 10 år.Modellresultat för plats 2 indikerar att volymen sött vatten i akviferen ökar med 15 avuttaget när endast salt vatten extraheras. Det maximala uttagsflödet vid plats 2 för endastsalt vatten bestämdes till 65m3år per meter. Vid ett saltvattenuttag på 65m3år vid plats 2 ökarsötvattenvolyem i akviferen t.ex. med 940m3 per meter efter 10 år. diva2:1345440

Laboratory and numerical experiments were conducted to provide a quantitative steadystate analysis of the effect of incremental variations of water level on saltwater intrusion. The purpose was to seek mathematical correlations relating both the wedge toe length and the height along the coastline to the boundary head difference. The laboratory experiments were completed in a 2D sand tank where both freshwater and seawater levels were varied. The experiments were conducted for two bead sizes having different hydraulic conductivities. The numerical model SEAWAT was used to validate the results and then to perform sensitivity analysis. The experimental results show that at steady-state conditions, the logarithmic toe length could be expressed as a linear function of the boundary head difference. The linear relationship was recorded in both advancing and receding wedge phases. The linearity of the correlation was also well demonstrated with analytical solutions. Similar relationships were also derived in the scenarios where the sea level fluctuated while the freshwater boundary head was constant. The height of the saltwater wedge along the coastline was also found to be a linear function of the boundary head difference. The sensitivity analysis shows that the regression coefficients were sensitive to the hydraulic conductivity, the dispersivity, and the saltwater density, while the porosity and the rate of boundary head change induced negligible effects. The existence of a linear relationship between the logarithmic toe length and the boundary head difference was also well evidenced in a field-scale aquifer model for all the different hydrogeological aquifer conditions tested. This study is the first attempt in identifying the underlying correlation between the boundary water level variations and the main seawater intrusion (SWI) external metrics under controlled laboratory conditions, which is of great relevance from a water resources management perspective.

The quality of groundwater resources in coastal aquifers is affected by saltwater intrusion. Over-abstraction of groundwater and seawater level rise due to climate change accelerate the intrusion process. This paper investigates the effects of aquifer bed slope and seaside slope on saltwater intrusion. The possible impacts of increasing seawater head due to sea level rise and decreasing groundwater level due to over-pumping and reduction in recharge are also investigated. A numerical model (SEAWAT) is applied to well-known Henry problem to assess the movement of the dispersion zone under different settings of bed and seaside slopes. The results showed that increasing seaside slope increased the intrusion of saltwater by 53.2% and 117% for slopes of 1:1 and 2:1, respectively. Increasing the bed slope toward the land decreased the intrusion length by 2% and 4.8%, respectively. On the other hand, increasing the bed slope toward the seaside increased the intrusion length by 3.6% and 6.4% for bed slopes of 20:1 and 10:1, respectively. The impacts of reducing the groundwater level at the land side and increasing the seawater level at the shoreline by 5% and 10% considering different slopes are studied. The intrusion length increased under both conditions. Unlike Henry problem, the current investigation considers inclined beds and sea boundaries and, hence, provides a better representation of the field conditions.

This research investigated the effect of layered heterogeneity on transient saltwater upconing in a laboratory-scale coastal aquifer. The experiments were conducted in a 2D-laboratory flow tank, and the response of the saltwater wedge to pumping was analysed in a heterogeneous aquifer system, where a low permeability layer was constructed in the middle of the aquifer. The SEAWAT code was used for validation and to perform additional simulations to explore the sensitivity of the critical pumping rate and the critical time to the main parameters characterising the low-permeability layer, which included its permeability, thickness and position. The experimental results showed that the presence of layered heterogeneity noticeably altered the shape and the intrusion length of the upconing wedge without inducing a change in the abstraction rate “triggering” saltwater upconing mechanism compared to the homogeneous case. The numerical results of the layered aquifer provided excellent agreement with the experimental data for both the transient toe length and the shape of the steady-state saltwater wedges. The sensitivity analysis revealed that the critical pumping rate and the critical time was found to decrease considerably with decreasing hydraulic conductivity and thickness of the middle layer, which evidences the higher vulnerability of such layered aquifer systems to the saltwater upconing, in comparison to idealised homogeneous systems. The results nonetheless showed that varying the position of the interlayer induced very little change on the critical pumping rate, but the critical time would tend to decrease as the low permeability layer was moved deeper away from the pumping well, particularly for smaller middle layer thickness.

The Republic of Djibouti has an area of 23,000 km2, a coastline 370 km long and a population of 820,000 inhabitants. It experiences an arid climate characterized by high daytime temperatures and low and irregular rainfall (average of 140 mm/year), resulting in continuous periods of drought. These difficult climatic conditions and the absence of perennial surface water have progressively led to an intensive exploitation of groundwater to meet increasing water demands in all sectors (drinking water, agriculture and industries). In coastal areas, seawater intrusion constitutes a significant additional risk of groundwater degradation. This study is focused on the coastal aquifer of Tadjourah which supplies water to the city of Tadjourah, currently comprising 21,000 inhabitants. The main objective of this work is to assess the current resources of this aquifer, its capacity to satisfy, or not, the projected water demands during coming years, and to analyze its vulnerability to seawater intrusion within the frame of climate change. Three RCPs (Representative Concentration Pathway) were used to simulate different climate scenarios up to 2100. The simulated rainfall series allowed to deduce the aquifer recharge up to 2100. The code Seawat was used to model seawater intrusion into the aquifer, using the recharge data deduced from the climate scenarios. The results indicate that the risk of contamination of the Tadjourah coastal aquifer by seawater intrusion is high. The long-term and sustainable exploitation of this aquifer must take into consideration the impact of climate change.

We investigate the long-distance salinity in a dual permeability coastal karst aquifer with a double conduit network using a three-dimensional variable-density groundwater flow and multispecies transport SEAWAT model. Sensitivity analyses were used to evaluate the impact of the parameters and boundary conditions on the modeling saltwater wedge in a karstic aquifer situated in the Cuban land territory, including hydraulic conductivity, vertical anisotropy and salinity concentration, both in the conduits network and the fractured medium. These analyses indicated that hydraulic conductivity of the fractured medium and salt concentration were the ones that have a stronger effect on saltwater intrusion in a karstic aquifer. We also show results of the three-dimensional numerical simulations on groundwater salinity for different scenarios with the variabilities of the important parameters and compare results with electric conductivity profiles measured in a well.

The freshwater–saltwater interface position in groundwater at coastal aquifers is determined by the location of the coastline. Anthropogenic-driven changes as modification of the land uses in catchments or the engineering construction in rivers can alter the transport of sediments to the coastal areas affecting to the coastline shape in detrital systems. This is the case of the Motril-Salobreña aquifer where the rapid coastline progradation over the last 500 years generated new land previously covered by the sea at a fast rate, 3 m year−1 during hundreds of years. The effect of these changes in the salinity of the aquifer and the flushing time by freshwater has been examined with a paleo-hydrogeological model simulating the transient evolution of the groundwater salinity for the last 500 years with SEAWAT. The results of the model indicate a differentiated flushing time depending on the hydraulic properties in the region ranging from 50 years in the western sector to up to more than 200 years in the central sector for the shallower parts of the aquifer. In the deeper layers, the time can be highly increased but the uncertainties in the hydraulic properties generate different scenarios both in flushing time and water circulation in the aquifer. The sectors in the aquifer where changes took place at a faster rate are also the most sensitive to the effect of global changes, especially those associated to human activity as they occur at shorter time periods.

TEZ12055 Tez (Yüksek Lisans) -- Çukurova Üniversitesi, Adana, 2019. Kaynakça (s. 63-66) var. XXV 67 s. :_res. (bzs. rnk.), tablo ;_29 cm. Deniz suyu girişimi kıyı bölgelerindeki yeraltı suyu kalitesine zarar veren önemli süreçlerden biridir. Bosaso Ovası’nda yeraltı suyunun aşırı çekimi deniz suyu girişimine neden olmaktadır. Yeraltı suyu modelleme çalışması ile Bosaso Ovası’na muhtemel deniz suyu girişimi etkileri çalışma konusu olarak alınmıştır. Bu araştırmada, SEAWAT yazılımı kullanarak farklı senaryoların deniz suyu girişimi üzerindeki etkilerini araştırmak amacıyla deniz suyu girişiminin potansiyel etkisini modellemektir. Analiz sonuçları, kıyı alanı boyunca elektriksel iletkenlik (EC), toplam çözünmüş katı madde (TDS), klorür, sodyum, kalsiyum ve magnezyum konsantrasyonunun yüksekliği ile çalışma alanında deniz suyu girişiminin bulunduğunu ortaya koymaktadır. Model 2013 yılı arazi verileri ile yeraltı suyu seviye ve TDS ortalama değeri kullanılarak kalibre edilmiştir. Yeraltısuyu çekim ve iklim değişikliğinin etkilerini araştırmak için dört farklı senaryo simüle edilmiştir. Sonuçlar, deniz suyu girişiminin sahil şeridine yakın yerlerde yüksek TDS seviyeleri ile yeraltı suyu konsantrasyonlarını önemli ölçüde etkilediğini göstermiştir. Artan yeraltısuyu çekim oranı deniz suyu girişimi arayüzünün 2040 yılına kadar yaklaşık 6,2 km kıyıdan içerilere doğru hareket edeceğini göstermiştir. Ayrıca, çekim oranındaki % 50'lik bir azalmanın, tatlı yeraltı suyunu koruyarak ve daha fazla deniz suyunun sızmasını önleyerek akiferlere rahatlama getireceğini ortaya koymuştur. Seawater intrusion is process that damage groundwater quality in the coastal regions. Groundwater overexploitation in the Bosaso Plain has resulted in seawater intrusion problem. Groundwater modelling were considered to study the effects of possible seawater intrusion into the Bosaso Plain. In this study, we present a three-dimensional variable–density numerical model developed with the SEAWAT code, which is aimed to predict the extent of seawater intrusion by different groundwater pumping scenarios. Results revealed the higher concentration of electrical conductivity (EC), total dissolved solids (TDS), chloride, sodium, calcium and magnesium along the coastal area which indicated the presence of seawater intrusion in the study area. The SEAWAT model was calibrated using both the average value of heads and TDS concentration for the 2013 field data. Four scenarios were simulated to understand the effects of pumping and climate change to the extent of seawater intrusion for a period of 27 years. The model results show that seawater intrusion significantly affects the groundwater concentrations near the coastline and demonstrated high levels of TDS. The predicted results reveal that increasing pump rate seawater intrusion interface will move about 6.2 km inland by 2040. Results also revealed that a 50% reduction in the pump rate will bring relief to the aquifer by protecting fresh groundwater and preventing any further seawater intrusion. This work was supported by Research Projects Center of Cukurova University Project No: FYL-2018-11190.

På grund av ökad brist och ökad efterfrågan efter vatten på Gotland undersöks möjligheten att genom pumpning av salt grundvatten, lokalt sänka gränsen mellan salt och sött grundvatten som ligger under ön samt öka grundvattenbildningen. Med saltvattengränsen längre ner i marken skulle djupare brunnar kunna borras och större uttag skulle kunna ske vid upprättande av en grundvattentäkt. För att undersöka konceptet skapades en grundvattenmodell över delar av Sudret, ett område på södra delen av ön Gotland. För att kunna simulera förhållanden med pumpning i ett grundvattensystem där blandning sker mellan salt och sött grundvatten av olika densitet, utvecklades modellen i grundvattenmodelleringsprogrammet GMS i kombination med modulerna MODFLOW, MT3DMS samt SEAWAT. Tillsammans med modulerna kunde modellen hantera densitetsskillnader, förändring av saltkoncentrationer och påverkan av pumpar. Som grund vid utvecklingen av modellen användes en geologisk tredimensionell modell framtagen av SGU. Då inga platsspecifika undersökningar vad gäller grundvattennivåer och flödes/spridningsparametrar fanns att tillgå valdes modellparametrar utifrån litteraturvärden och tidigare undersökningar från liknande förhållanden. Först skapades en modell utan pumpning för att simulera fram ett stabilt läge för saltvattengränsen och en stabil tjocklek på språngskiktet. Modellens parametrar anpassades till dess att grundvattennivån låg nära markytan och språngskiktet låg runt övergången från kalksten till sandsten. När en relativt stabil saltvattengräns simulerats fram utvecklades modellen vidare med pumpning från det salta grundvattnet. Resultaten från arbetet visar att det med pumpning går att sänka saltvattengränsen och att en ökning av grundvattenbildningen sker motsvarande 55 % av den bortpumpade volymen saltvatten. På grund av avsaknad av lokala materialparametrar bör resultaten inte ses som mer än en indikation på att konceptet fungerar. Vidare föreslås att lokala geohydrologiska undersökningar genomförs för att i framtiden kunna skapa en modell som bygger på lokalt uppmätta flödes- och spridningsparametrar vilket skulle generera mer pålitliga resultat. I en framtida modell bör även pumpning från den söta delen av grundvattnet adderas till modellen för att se hur utvinnande av färskvatten skulle påverka språngskiktets utbredning samt ge svar på hur stora uttag som skulle vara möjliga. Because of an increased shortage and an increased demand of fresh water on Gotland, the possibility to pump saline groundwater and thereby locally lower the saltwater interface and increase recharge was investigated. With the saltwater interface further down in the bedrock, deeper wells could be drilled and extraction of more fresh water would therefore be possible. To examine the concept, a groundwater model was created to simulate the idea on a region of the peninsula Sudret on the southern part of the island of Gotland, Sweden. To be able to simulate the idea of pumping groundwater in an aquifer with a mix of saline and fresh groundwater of variable density, a model was built using the groundwater modelling program GMS in combination with the modules/program codes MODFLOW, MT3DMS and SEAWAT. With these modules, the model can handle the complex situation with extraction by pumping from groundwater of variable density and changes of salt concentration over time. A three dimensional geological model over the area produced by SGU was used as a foundation for building the model. Since no site specific surveys considering groundwater levels and flow/dispersion parameters have been previously undertaken in the study area, the parameters of the model were chosen according to literature and findings from similar projects conducted in the past. First, a model was developed to simulate a stable saltwater interface without pumps. Parameters were changed until a groundwater level close to the surface of the model was given and the saltwater interface ended up around the transition between limestone and sandstone. When the model generated desirable results, it was further developed to include the extraction of saltwater by pumping. Results from the project showed that the concept of lowering the saltwater interface by pumping works, with an increased recharge corresponding to 55 % of the extracted saltwater volume. Because of a lack of site specific parameters, the results should not be seen as more than an indication that the concept works. Furthermore, geohydrological measures should be made to provide local parameters regarding flow and dispersion for more reliable future models. To gain a greater understanding of how well the concept would work in reality, further development should be undertaken to include fresh groundwater extraction to assess how that would affect the position of the saltwater interface.

The coastal regions of Pingtung Plain in southern Taiwan rely on groundwater as their main source of fresh water for aquaculture, agriculture, domestic, and industrial sectors. The availability of fresh groundwater is threatened by unsustainable groundwater extraction and the over-pumpage leads to the serious problem of seawater intrusion. It is desired to find appropriate management strategies to control groundwater salinity and mitigate seawater intrusion. In this study, a simulation–optimization model has been presented to solve the problem of seawater intrusion along the coastal aquifers in Pingtung Plain and the objective is using injection well barriers and minimizing the total injection rate based on the pre-determined locations of injection barriers. The SEAWAT code is used to simulate the process of seawater intrusion and the surrogate model of artificial neural networks (ANNs) is used to approximate the seawater intrusion (SWI) numerical model to increase the computational efficiency during the optimization process. The heuristic optimization scheme of differential evolution (DE) algorithm is selected to identify the global optimal management solution. Two different management scenarios, one is the injection barriers located along the coast and the other is the injection barrier located at the inland, are considered and the optimized results show that the deployment of injection barriers at the inland is more effective to reduce total dissolved solids (TDS) concentrations and mitigate seawater intrusion than that along the coast. The computational time can be reduced by more than 98% when using ANNs to replace the numerical model and the DE algorithm has been confirmed as a robust optimization scheme to solve groundwater management problems. The proposed framework can identify the most reliable management strategies and provide a reference tool for decision making with regard to seawater intrusion remediation.

The objective of this research was to examine the response of seawater intrusion and retreat to freshwater abstraction from a well in laboratory-scale coastal aquifer under transient conditions. This has been done experimentally and numerically through qualitative and quantitative analysis. The laboratory experiments were completed in a two-dimensional laboratory tank for two beads sizes, namely 1090 µm and 780 µm. The SEAWAT code was used for the numerical simulations. The experimental results showed that the vulnerability of the pumping well to salinization was higher for the low permeability aquifer, whereby the saltwater upconing process was observed at an abstraction rate 40 % smaller in the lower permeability aquifer compared to the high permeability aquifer. In the lower permeability scenario, the inland penetration of the saline plume was up to 41% larger than in the higher permeability scenario, for an equivalent pumping rate increment. In addition, the process of decay (after the abstraction had ceased) of the wedge was slower in the lower permeability aquifer, which suggests a slower retreat of the wedge. The qualitative comparison of the shape of the saline plume and the quantitative comparison of the transient toe length data between experimental and numerical results showed excellent agreement. The flow velocity field analysis revealed that the local reduction of the magnitude of the flow velocity along the upper part of the interface was a major factor contributing to the saltwater upconing mechanism.

Seawater intrusion is a major problem to freshwater resources especially in coastal areas where fresh groundwater is surrounded and could be easily influenced by seawater. This study presents the development of a conceptual and numerical model for the coastal aquifer of Karareis region (Karaburun Peninsula) in the western part of Turkey. The study also presents the interpretation and the analysis of the time series data of groundwater levels recorded by data loggers. The SEAWAT model is used in this study to solve the density-dependent flow field and seawater intrusion in the coastal aquifer that is under excessive pumping particularly during summer months. The model was calibrated using the average values of a 1-year dataset and further verified by the average values of another year. Five potential scenarios were analyzed to understand the effects of pumping and climate change on groundwater levels and the extent of seawater intrusion in the next 10 years. The result of the analysis demonstrated high levels of electrical conductivity and chloride along the coastal part of the study area. As a result of the numerical model, seawater intrusion is simulated to move about 420 m toward the land in the next 10 years under “increased pumping” scenario, while a slight change in water level and TDS concentrations was observed in “climate change” scenario. Results also revealed that a reduction in the pumping rate from Karareis wells will be necessary to protect fresh groundwater from contamination by seawater., Scientific and Technological Research Council of Turkey (TUBITAK 113Y042)

The main purpose of this work was to examine how aquifer layering impacts the ability of subsurface dams to retain seawater intrusion (SWI) and to clean up contaminated coastal aquifers using both experimental and numerical techniques. Four different layering configurations were investigated, including a homogeneous case (case H), and three different layered cases where a low permeability layer was set at the top of the aquifer (case LH), at the middle part of the aquifer as interlayer (case HLH), and at the lower part of the aquifer (case HL). The subsurface dam was able to retain the saltwater wedge associated with a drop of the hydraulic gradient from 0.0158 down to 0.0095 in all the cases, thereby achieving up to 78% reduction in the saltwater toe length. In cases LH and HLH, the start of the saltwater spillage was delayed compared to the homogeneous case, and the time taken for the freshwater zone to be fully contaminated (post-spillage) was twice and three times longer, respectively. By contrast, the existence of a low K layer at the bottom of the aquifer (case HL) considerably weakened the ability of dams to retain the intrusion, allowing for quicker saltwater spillage past the wall. The natural cleanup of SWI-contaminated coastal aquifers was, for the first time, evidenced in heterogeneous settings. Depending on the stratification pattern, the presence of stratified layers however prolonged the cleanup time to various degrees, compared to the homogeneous scenario, particularly in case HL, where the cleanup time was nearly 50% longer.

Sustainable management of groundwater resources is essential for sound groundwater development, especially in sensitive salt-affected areas. In Northeast Thailand, the Central Huai Luang Basin, underlain by rock salt, is the source of groundwater and soil salinity. The future sustainable groundwater development yield was assessed under the plausible uncertainty of hydrogeological and projected climate scenarios that could impact the groundwater system. The SEAWAT and HELP3 models were used to simulate groundwater system. The four alternative scenarios of hydrogeological conceptual models were formulated to determine the impact on groundwater system and sustainable groundwater yield. In addition, impacts of projected climate conditions on each alternative model were explored. The results indicate that variable depths and thicknesses of rock salt layers have a higher impact on groundwater salinity distribution and sustainable yield estimations than model boundary conditions. Groundwater salinity, shallow water table areas, and sustainable yield projections vary substantially depending on the possible conceptual model scenarios. It is clear that the variable hydrogeological models affect groundwater sustainable yields.

Thesis (Master)--Izmir Institute of Technology, Environmental Engineering, Izmir, 2016, Includes bibliographical references (leaves: 85-88), Text in English; Abstract: Turkish and English, xv, 88 leaves, Seawater intrusion is a major problem to freshwater resources especially in coastal areas where fresh groundwater is surrounded and could easily be influenced by seawater. This study presents the development of conceptual and numerical model for the coastal aquifer of Karareis region in the western part of Turkey. The study also presents the interpretation and the analysis of the groundwater levels recorded by groundwater data loggers. Groundwater pumping from Karareis aquifer has increased significantly during the summer period to meet the agriculture and domestic water demands. Levels of groundwater were measured at nine locations in Karareis region; also water samples were collected and analyzed for some parameters. For this study SEAWAT code is used to solve the numerical model for the coupled density dependent flow system. The model was calibrated using the average of one-year dataset of collected groundwater levels. Model validation was handled using the average of groundwater levels measured over more one year. Five scenarios were tested to understand the effects of pumping and climate change on groundwater levels and seawater intrusion in the next ten years. The result of analysis demonstrated a high concentration of electrical conductivity and chloride along the coastal part of the study area. As a result of the numerical model, seawater intrusion will extent about 420 m towards the land in the next ten years of increased pumping scenario, while a little change in water level and TDS concentration was recognized in climate change scenario. Results also showed that reducing the pumping from Karareis wells will be necessary to protect the freshwater from contamination by seawater., Deniz suyu girişimi, özellikle deniz tarafından çevrelenen kıyı akiferlerde, tatlı su kaynaklarını tehdit eden en önemli problemlerden biridir. Bu çalışma kapsamında, Türkiye’nin batısında bulunan Karareis bölgesindeki kıyı akiferi için kavramsal ve numerik modelleme çalışmaları yapılmış olup ayrıca spesifik olarak deniz suyu girişimini dikkate alan değişken yoğunluklu yeraltı suyu akım modelleme çalışması sunulmuştur. Bununla beraber akiferdeki yeraltı suyu seviyelerinin ölçümü ve tahminine yönelik çalışmalar da bu tez kapsamında değerlendirilmiştir. Yapılan çalışmada, Karareis kıyı akiferinde yazın tarım ve günlük kullanıma bağlı olarak yeraltı suyu çekimi belirgin olarak artmakta olduğu saptanmıştır. Bölgenin hidrolojik ve hidrojeolojik parametrelerinin tayini için bölgede dokuz farklı lokasyonda yer alan sondaj kuyularında yeraltı suyu seviyesi ölçülmüştür. Kıyı akiferlerindeki deniz suyu girişimi etkisi altındaki yeraltı suyu akımları SEAWAT isimli matematiksel model sürümü ile belirlenmiştir. Model kalibrasyonu ve test için iki yıl boyunca kuyulardan düzenli ölçülen yeraltı suyu seviye verilerinden yararlanılmıştır. Gelecek on yıl için pompaj kuyularından su çekiminin, iklim değişiminin ve deniz suyu girişiminin yeraltı suyu seviyesine etkisini anlamak için beş senaryo test edilmiştir. Yapılan incelemelerde, çalışma alanının özellikle kıyı kesimlerinde, yüksek klorür konsantrasyonu ve elektriksel iletkenlik değerlerinin gözlendiği, deniz suyu girişiminin gelecek on yıllık artan su çekimi senaryosu kapsamında değerlendirilip modellenmesi sonucunda, bölgenin iç kesimlerine doğru 420 metreye kadar tuzlu su girişiminin ilerleyebileceği görülmüştür. Senaryo kapsamında yeraltı suyu seviyesinin veya TDS miktarının minimal düzeyde değişeceği ayrıca ortaya konulmuştur. Son olarak, Karareis bölgesi akiferinde yeraltı suyu çekiminin planlanması ile deniz suyu girişiminin tatlı suyu kaynaklarına etkisi azaltılmış olacak, bölgenin yeraltı suyu kaynaklarının niteliği ve niceliği korunmuş olacaktır., TUBITAK

The temperature inside wells used for gas, oil and geothermal energy production, as well as steam injection, is in general significantly higher than the groundwater temperature at shallower depths. While heat loss from these hot wells is known to occur, the extent to which this heat loss may result in density-driven flow and in mixing of surrounding groundwater has not been assessed so far. However, based on the heat and solute effects on density of this arrangement, the induced temperature contrasts in the aquifer due to heat transfer are expected to destabilize the system and result in convection, while existing salt concentration contrasts in an aquifer would act to stabilize the system. To evaluate the degree of impact that may occur under field conditions, free convection in a 50-m-thick aquifer driven by the heat loss from penetrating hot wells was simulated using a 2D axisymmetric SEAWAT model. In particular, the salinization potential of fresh groundwater due to the upward movement of brackish or saline water in a stratified aquifer is studied. To account for a large variety of well applications and configurations, as well as different penetrated aquifer systems, a wide range of well temperatures, from 40 to 100 °C, together with a range of salt concentration (1–35 kg/m3) contrasts were considered. This large temperature difference with the native groundwater (15 °C) required implementation of a non-linear density equation of state in SEAWAT. We show that density-driven groundwater flow results in a considerable salt mass transport (up to 166,000 kg) to the top of the aquifer in the vicinity of the well (radial distance up to 91 m) over a period of 30 years. Sensitivity analysis showed that density-driven groundwater flow and the upward salt transport was particularly enhanced by the increased heat transport from the well into the aquifer by thermal conduction due to increased well casing temperature, thermal conductivity of the soil, as well as decreased porosity values. Enhanced groundwater flow and salt transport was also observed for increased hydraulic conductivity of the aquifer. While advective salt transport was dominant for lower salt concentration contrasts, under higher salt concentration contrasts transport was controlled by dispersive mixing at the fresh-salt water interface between the two separate convection cells in the fresh and salt water layers. The results of this study indicate heat loss from hot well casings can induce density-driven transport and mixing processes in surrounding groundwater. This process should therefore be considered when monitoring for long-term groundwater quality changes near wells through which hot fluids or gases are transported.

The coastal aquifer salinization is an urgent problem caused by groundwater resources overexploitation and climate change. This phenomenon is enhanced in areas lying below the sea level, like the polders in the Netherlands or the Po River lowland in Italy. In these reclaimed lands the saltwater intrusion is usually controlled by a network of irrigation canals that supplies freshwater to the shallow aquifer, maintaining soil salinity at acceptable levels. The 2012 was dramatic in terms of agricultural water supply, since the Po River plain experienced a prolonged drought. Despite this, continuous monitoring of piezometric heads and total dissolved solids (TDS) near a canal (Canale della Gronda) demonstrated that freshening was occurring in the shallow portion (first 4 m) of the unconfined aquifer, while the bottom part was characterized by elevated relic salinity. The two-dimensional model SEAWAT was calibrated using piezometric heads and TDS depth profiles measured along a transect perpendicular to the canal. The calibrated model was then used to predict the behaviour of this cross section using a multiple scenario approach: increase in evapotranspiration induced by temperature increase; increase in the frequency of extreme high rainfall events; extreme drought conditions; and canal dewatering due to salinization of the water courses. Moreover, for each scenario, two sub-scenarios were run to account for projected sea level rise. The first three scenarios had only a minor influence on the aquifer salinization rate, while the fourth one predicted serious upward flux of the high salinity groundwater actually residing in the bottom of the unconfined aquifer. The scenarios quantified the possible future effects on groundwater salinization and could be useful to find adaptation strategies to manage the water resources of this and similar areas.

Διερευνώνται επιμέρους θέματα διαχείρισης παράκτιων υδροφορέων που αφορούν στην διασφάλιση της αειφορίας των υπόγειων αποθεμάτων μέσω (α) της προστασία τους έναντι στην υποβάθμιση της ποιότητάς τους που μπορεί να προέλθει από τη διείσδυση του θαλασσινού νερού και από ανθρωπογενείς δραστηριότητες και (β) της διασφάλισης της κάλυψης των αναγκών σε υπόγειο νερό κατά τις περιόδους αυξημένης ζήτησης. Η διερεύνηση βασίζεται στη χρήση δύο αριθμητικών μοντέλων υπόγειας ροής που λαμβάνουν υπόψη τις διαφορές πυκνότητας μεταξύ γλυκού και αλμυρού νερού και περιλαμβάνει τα ακόλουθα: Παρουσιάζεται ο τρόπος με τον οποίο διατυπώνονται και επιλύονται οι εξισώσεις που περιγράφουν την υπόγεια ροή υπό την επιρροή διαφορών πυκνότητας σε δύο ευρέως χρησιμοποιούμενα αριθμητικά μοντέλα, που είναι το μοντέλο SEAWAT-2000 (Langevin et al., 2003) και το μοντέλο SUTRA v2.2 (Voss & Provost, 2010). Βάσει των ανωτέρω και της εμπειρίας που αποκτήθηκε από την παράλληλη εφαρμογή τους, οι δύο κώδικες αξιολογούνται συγκριτικά και διατυπώνονται κριτήρια, στα οποία μπορεί να βασιστεί η επιλογή του κατά περίπτωση προσφορότερου κώδικα. Γίνεται η ρύθμιση αριθμητικού μοντέλου, το οποίο είναι βασισμένο στον κώδικα SEAWAT-2000, για τον παράκτιο υδροφορέα του Γλαύκου π., ο οποίος βρίσκεται στα νότια της πόλης των Πατρών και αποτελεί σημαντικό υδατικό πόρο για την περιοχή. Η ρύθμιση του μοντέλου βασίζεται σε μετρήσεις της υπόγειας στάθμης που προέρχονται από ένα σχετικά πυκνό δίκτυο γεωτρήσεων παρατήρησης το οποίο όμως έχει χρονικά περιορισμένη διάρκεια λειτουργίας. Το δίκτυο κατασκευάστηκε στα πλαίσια του προγράμματος INTERREG Ελλάδα – Ιταλία, 2000 – 2006, σε συνεργασία του Εργαστηρίου Υδραυλικής Μηχανικής του Πανεπιστημίου Πατρών και της Δημοτικής Επιχείρησης Ύδρευσης και Αποχέτευσης της Πάτρας (Δ.Ε.Υ.Α.Π.) και ολοκληρώθηκε στα μέσα του 2008. Η διαδικασία ρύθμισης του μοντέλου περιλαμβάνει τα εξής: (α) Τη συστηματική οργάνωση, συνδυασμό και αξιολόγηση των διαθέσιμων πληροφοριών σε λογισμικό συστημάτων γεωγραφικών πληροφοριών. (β) Την εφαρμογή υδραυλικών και στατιστικών μεθόδων σε συνδυασμό με την τροποποίηση και εφαρμογή μεθόδων αριθμητικής προσομοίωσης αντλητικών δοκιμών για τον προσδιορισμό των υδραυλικών χαρακτηριστικών του υδροφορέα. (γ) Τη συνδυαστική ανάλυση υδρολογικών δεδομένων και χρονοσειρών της υπόγειας στάθμης για την εκτίμηση των συνιστωσών του υδρολογικού ισοζυγίου. (δ) Τον καθορισμό κατάλληλων κριτηρίων αξιολόγησης των προσομοιώσεων. (ε) Την εμπειρική ρύθμιση των παραμέτρων του μοντέλου, η οποία επειδή έγινε παράλληλα με την συλλογή των μετρήσεων της υπόγειας στάθμης πραγματοποιήθηκε για δύο περιόδους, κατ’ αρχήν για την περίοδο 2008-2010 και εν συνεχεία για την περίοδο 2010-2012 και (στ) την εκτέλεση προσομοιώσεων Monte Carlo για την πραγματοποίηση καθολικής ανάλυσης ευαισθησίας (global sensitivity analysis, βλ. Saltelli et al., 2004) και τη διερεύνηση ύπαρξης περισσοτέρων συνδυασμών των τιμών των παραμέτρων του μοντέλου που οδηγούν σε παρόμοια αποτελέσματα (equifinality thesis, Beven, 2006). Από τη ρύθμιση του μοντέλου με τη βοήθεια των μετρήσεων της υπόγειας στάθμης που συλλέχτηκαν με το δίκτυο παρατήρησης προέκυψαν πληροφορίες για τους μηχανισμούς εμπλουτισμού του υδροφορέα στις διάφορες περιοχές, κάτι που είναι σημαντικό για τη διαχείρισή του. Το ρυθμισμένο μοντέλο του παράκτιου υδροφορέα του Γλαύκου χρησιμοποιήθηκε για την εξέταση θεμάτων διαχείρισης του υδροφορέα: (α) Προσδιορίστηκαν οι ζώνες τροφοδοσίας των γεωτρήσεων της ΔΕΥΑΠ με χρήση του κώδικα MODPATH v3 (Pollock, 1994) και εκτιμήθηκε η τρωτότητα αυτών των γεωτρήσεων. Διαπιστώθηκε ότι οι γεωτρήσεις που βρίσκονται κοντά στην κοίτη του Γλαύκου, όπως συμβαίνει με πολλές από τις γεωτρήσεις της ΔΕΥΑΠ, αντλούν σχεδόν αποκλειστικά νερό που προέρχεται από τον ποταμό. Έτσι είναι δυνατόν να προσβληθούν από ρυπάνσεις του νερού του ποταμού καθώς επίσης και από ανθρωπογενείς δραστηριότητες στις παρόχθιες ζώνες. (β) Εκτιμήθηκε ο κίνδυνος διείσδυσης θαλασσινού νερού σε περίπτωση εμφάνισης περιόδων ξηρασίας, για δύο διαφορετικά σενάρια αντλήσεων: ένα σύμφωνα με το σημερινό καθεστώς χρήσης του υπόγειου νερού και ένα για την αύξηση των αντλήσεων κατά 50%. Διαπιστώθηκε ότι για ξηρασία διάρκειας τεσσάρων ετών και αύξηση των αντλούμενων ποσοτήτων τα φαινόμενα υφαλμύρισης θα είναι έντονα. Με την επάνοδο όμως των μέσων υδρολογικών συνθηκών ο υδροφορέας ανακάμπτει. (γ) Για συνθήκες ξηρασίας εξετάστηκε η αποτελεσματικότητα του τεχνητού εμπλουτισμού για τον περιορισμό της διείσδυσης του θαλασσινού νερού. Ως μέθοδος εμπλουτισμού εξετάστηκε η εποχιακή αύξηση της στάθμης του νερού στον ποταμό με τη βοήθεια φουσκωτών φραγμάτων (βλ. Κωτσοβίνος, 1999). Διαπιστώθηκε ότι με τη μέθοδο αυτή μπορεί να επιτευχθεί σημαντική αύξηση των υπόγειων αποθεμάτων. Τέλος, εξετάζεται ως μέτρο προστασίας έναντι της διείσδυσης του θαλασσινού νερού η τεχνική των υπόγειων φραγμών. Επειδή στις μελέτες της τεχνικής αυτής που έχουν παρουσιαστεί στη βιβλιογραφία (π.χ. Luyun et al., 2011) έμφαση δίνεται μόνο στην επιρροή των γεωμετρικών χαρακτηριστικών των φραγμών (απόσταση από την ακτή, βάθος φραγμού), έγινε στην παρούσα εργασία συστηματική διερεύνηση της συναρτησιακής σχέσης ανάμεσα στην αποτελεσματικότητα της μεθόδου και τα χαρακτηριστικά τόσο των φραγμών όσο και του υδροφορέα (υδραυλική αγωγιμότητα, ανισοτροπία, υδρομηχανική διασπορά, παροχή γλυκού νερού προς τη θάλασσα, αντλήσεις στην παράκτια ζώνη, υλικό κατασκευής του φραγμού). Η διερεύνηση έγινε με τη βοήθεια του αριθμητικού μοντέλου SUTRA 2.2 (Voss and Provost, 2010), για δύο τύπους υπόγειων φραγμών: τους διαφραγματικούς τοίχους και τα υπόγεια φράγματα. Δίδονται διαγράμματα και αναλυτικές σχέσεις με χρήση αδιάστατων μεταβλητών και για εύρος τιμών των μεταβλητών αυτών που μπορούν να χρησιμοποιηθούν για τη διαστασιολόγηση φραγμών σε εφαρμογές πεδίου. Βάσει των αποτελεσμάτων που προκύπτουν από τη διερεύνηση της προαναφερθείσας συναρτησιακής σχέσης και χρησιμοποιώντας και το μοντέλο του Γλαύκου, εξετάστηκε η αποτελεσματικότητα της κατασκευής ενός φραγμού περιορισμένου μήκους στον υδροφορέα. Διαπιστώθηκε ότι πέραν του περιορισμού της διείσδυσης αλμυρού νερού σε περιόδους ξηρασίας που επιτυγχάνεται, ο φραγμός επιταχύνει την υποχώρηση της αλμυρής σφήνας όταν επανέλθουν οι συνήθεις υδρολογικές συνθήκες. In the present study coastal aquifer management issues are investigated. These issues concern measures which ensure the sustainability of the coastal groundwater and particularly: (a) protective measures against the degradation of groundwater caused by saltwater intrusion and human activities and (b) measures allowing the availability of sufficient volumes of fresh groundwater during periods of high demand. The investigation is based on the application of two numerical codes, which are suitable for simulating the groundwater flow under the influence of density differences. The investigation procedure is as follows. The application of the equations of groundwater flow with density differences and transport, the limitations and the advantages are presented for two widely used numerical models, the SEAWAT-2000 code (Langevin et al., 2003) and the SUTRA v.2.2 code (Voss & Provost, 2010). Based on the analysis above and on the experience acquired through the parallel use of the two codes, basic criteria are derived that allow for the selection of the code that best suits the needs of a certain problem. The investigation focuses on the Glafkos coastal aquifer, which is located at north Peloponnese (Greece), south of the city of Patras and is an important source of freshwater for the region. For this aquifer the SEAWAT-2000 code is implemented and calibrated. The model calibration is based on groundwater level time series that were registered by a relatively dense monitoring network, whose operation time, however, is limited. The network of the monitoring wells was constructed during 2007-2008 in cooperation of the Hydraulic Engineering Laboratory (Department of Civil Engineering, University of Patras) and the Municipal Enterprise of Water Supply and Sewage of Patras (DEYAP), in the frame of the project INTERREG IIIA GREECE-ITALY. The calibration procedure is based on: (a) The application of a G.I.S. system to organize, combine, analyse and evaluate the available information. (b) The application of hydraulic and statistical methods combined with the modification and application of pumping tests simulation methods, for the estimation of the hydraulic parameters of the coastal aquifer. (c) The combined analysis of hydrological data and groundwater level time series for the estimation of the aquifers water budget components. (d) The establishment of appropriate criteria for the evaluation of simulation results. (e) The empirical calibration of the model is performed for two periods, i.e. the period 2008-2010 and the period 2010-2012. This procedure is due to the availability of the groundwater level time series which were registered parallel to the model calibration. (f) The application of the Monte-Carlo method in order to investigate the probability that different combinations of model parameters give similar or better simulation results. The model calibration led to a better understanding of the aquifers recharge mechanisms which is crucial for the development of a groundwater management policy and the implementation of a management plan. The calibrated groundwater model of the Glafkos coastal aquifer is used for the investigation and evaluation of coastal aquifer management applications: (a) The capture zones of the municipal production wells are delineated by applying the MODPATH v3 code (Pollock, 1994). It is found out that the production wells that are located close to the Glafkos River, as it is the fact for the majority of the municipal production wells, pump water that originates almost exclusively from the river. Consequently, polluted water from the river or polluting human activities close to the riverbank can affect the quality of the pumped water. (b) The saltwater intrusion risk is estimated, in case of a prolonged drought period. Two cases are investigated; the first considers the current pumping rates of groundwater while the second considers a 50% increased pumping. It is found out that a four-year drought period combined with an increase of the groundwater exploitation will lead to significant saltwater intrusion problems. (c) The applicability and effectiveness of in-channel artificial recharge with the use of rubber dams, as a countermeasure against the saltwater intrusion, which may be induced by a four-year drought period, is investigated. It is found that the method is applicable and effectively reduces the intrusion of saltwater. Further it increases the groundwater storage in the aquifer. Finally, the construction of a cutoff wall which covers only a small part of the aquifers width, is evaluated as a countermeasure to saltwater intrusion problems which may arise in Glafkos coastal aquifer. Due to the fact that existing studies on the technique of the subsurface barriers focus only on the influence of the geometrical characteristics of barriers covering the whole width of the aquifer, a systematic investigation is curried out on the functional relationship between the effectiveness of the barriers and all the parameters influencing it, i.e. the geometrical characteristics of the barriers, the aquifer parameters (the hydraulic conductivity, anisotropy, hydromechanical dispersion, groundwater flow towards the sea) and the pumping rate. The investigation is curried out by the use of the finite element code SUTRA v.2.2 and concerns two types of barriers; the subsurface dams and the cutoff walls. The results include graphs and functional relationships for the assessment of the effect of subsurface dams and cutoff walls and the design of such structures. The results are presented in terms of dimensionless variables, with ranges suitable for field applications. Based on these results, a cutoff wall of small width is designed for the Glafkos coastal aquifer. Its effectiveness is evaluated by applying the calibrated SEAWAT-model of the coastal aquifer. It is shown that the cutoff wall not only reduces the saltwater intrusion during drought periods, but also it reduces the retreat time of the saltwater front under normal hydrological conditions.

The coastal karst aquifers are known to be highly vulnerable to anthropogenic and natural changes, and in particular to the overexploitation of groundwater resources. They are of strategic relevance, especially for the coastal areas of Asia, USA and Mediterranean Countries, where the urbanization and human activities are highly developed. In these coastal zones, densely populated areas and intensive agricultural activities always demand greater quantities of water to support their economy. Climate change may particularly aggravate these requirements, especially in the Mediterranean areas, due to the combined effects of reduced recharge and consequent increase of discharge. In addition, the seawater intrusion processes involve a deterioration of the water resource quality. These problems highlight the importance of a serious reflection on water resources management to ensure agricultural sustainability and good fresh water supply of the coastal areas. In Italy, Apulia, with its coastline extending over 800 km, is the region with the largest coastal karst aquifer. The predominant karst Apulian features make the region extremely poor of surface water resources but, at the same time, rich of groundwater resources, which allow the improvement of agricultural activitiejknbews in the whole region. In particular we focus on a coastal groundwater system that is already threatened by a high seawater level: Salento Peninsula. The aim of this paper is to simulate the effects of climate change on recharge, sea level rise and increase of crop water demand, using density-depending numerical codes MODFLOW and SEAWAT. A large-scale approach was chosen to assess the efficacy of modelling as a new management tool, and to develop predictive scenarios taking into account the irrigation needs.

A case study of hydrogeological characterization and heat transport modeling for the design of a low enthalpy system in the Province of Treviso (Italy) is here presented. It is an open loop system that pumps and re-injects groundwater from a confined aquifer of the high Veneto plain. This type of systems is the most efficient in terms of yield, but its construction is highly conditioned by the availability of groundwater resource and by the environmental laws related to groundwater exploitation. Groundwater flow modeling with MODFLOW 2005 led to a good aquifer parameters estimation, by means of the quantitative calibration of a pumping test made on the pumping well and an observation piezometer. Then, with the heat transport modeling with SEAWAT 4 the distance between pumping well and re-injecting well has been optimized, avoiding so the thermal feedback effect. The lack of sitespecific data for dispersivity parameters has been solved through a sensitivity analysis on the main dispersivity parameters of heat transport. Finally, in order to comply with the environmental laws, a long-term forecasting simulation (duration of 20 years) has been set up in order to evaluate the open loop system thermal impact on the aquifer. The obtained results put in evidence that the design of low enthalpy systems strongly needs a detailed hydrogeological characterization of the aquifer interested by the pumping and that numerical modeling is the most effective tool in support of the definition of the optimal distance between pumping and re-injecting wells in the open loop systems.

Unplanned exploitation of groundwater from coastal aquifers may cause salt water intrusion in coastal aquifers. Coastal areas are generally overpopulated with fertile agricultural lands and diversified irrigated farming activities. The objective of this study was to develop a model to control/prevent seawater intrusion into the coastal aquifer with a case study of the Silifke-Goksu Deltaic Plain. A computer program for the simulation of three-dimensional variable density groundwater flow, SEAWAT, is used to model the seawater intrusion mechanism of the Goksu Deltaic Plain along the Mediterranean coast of Turkey. The calibration analysis of the developed seawater intrusion model is performed using field measured data in the water-year of 2008 including static groundwater head, electrical conductivity, total dissolved solid (TDS), and chloride concentration values collected from 23 observation wells and the existing data which were compiled and reviewed. The main objectives for applying the seawater intrusion model to the Goksu Deltaic Plain were (1) to determine the hydraulic and hydrogeologic parameters of the aquifer, (2) to estimate the spatial variation of the salt concentration in the aquifer and (3) to investigate the impact of the increase and decrease in groundwater extractions. The simulation results show that the Goksu Deltaic Plain aquifer is especially sensitive to the increase in groundwater extraction. © 2012 Elsevier B.V. Firat University Scientific Research Projects Management Unit This work was supported by the Cukurova University Scientific Research Project Unit, Grant No. MMF2006D6.

Variable-density groundwater models require extensive computational resources, particularly for simulations representing short-term hydrologic variability such as tidal fluctuations. Saltwater-intrusion models usually neglect tidal fluctuations and this may introduce errors in simulated concentrations. The effects of tides on simulated concentrations in a coastal aquifer were assessed. Three analyses are reported: in the first, simulations with and without tides were compared for three different dispersivity values. Tides do not significantly affect the transfer of a hypothetical contaminant into the ocean; however, the concentration difference between tidal and non-tidal simulations could be as much as 15%. In the second analysis, the dispersivity value for the model without tides was increased in a zone near the ocean boundary. By slightly increasing dispersivity in this zone, the maximum concentration difference between the simulations with and without tides was reduced to as low as 7%. In the last analysis, an apparent dispersivity value was calculated for each model cell using the simulated velocity variations from the model with tides. Use of apparent dispersivity values in models with a constant ocean boundary seems to provide a reasonable approach for approximating tidal effects in simulations where explicit representation of tidal fluctuations is not feasible.

Nüfusun yoğunlaştığı, çoğu zaman verimli arazilere sahip olan ve sulu tarım yapılan kıyı akiferlerinden plansızca aşırı olarak kullanılan su, kıyı akiferlerine deniz suyu girişimine sebep olabilir. Bu çalışmada deniz suyu girişiminin kontrolü/önlenmesine yönelik Silifke?Göksu deltası örneği ile model geliştirilmesi amaçlanmıştır. Akdeniz bölgesi kıyı şeridinde bulunan Göksu Deltasındaki deniz suyu girişim mekanizmasını tanımlayabilmek için üç boyutlu değişken yoğunluklu yeraltı suyu akımının simülasyonunu yapan SEAWAT programı kullanılmıştır. Geliştirilen deniz suyu girişim modelinin kalibrasyon çalışmalarında arazi verileri olarak önceki çalışmalardaki veriler ve 2008 su yılına ait 23 gözlem noktasında ölçülmüş statik yeraltı su seviyesi, elektriksel iletkenlik, toplam çözünmüş madde ve klorür değerleri kullanılmıştır. Deniz suyu girişimi modelinin Göksu deltasına uygulanmasının başlıca amaçları: (1) akiferin hidrolik ve hidrojeolojik parametrelerinin belirlenmesi, (2) akiferdeki tuz konsantrasyonunun uzaysal dağılımını tahmin etmek, (3) yeraltı suyu çekiminin artış ve azalışının akifere etkilerini araştırmak ve (4) iklim değişikliğinin kıyı akiferlerindeki yeraltı su kaynaklarına etkilerini değerlendirmektir. İklim değişikliğinin etkilerinin önlenmesi ya da en aza indirilmesi bakımından gelecekteki olması muhtemel üç senaryo için simülasyonlar yapılmış ve Göksu deltası akiferinin özellikle pompaj miktarındaki artışa duyarlı olduğu görülmüştür. Unplanned exploitation of water from coastal aquifers which have generally over population and fertile agricultural land and irrigated farming activities may cause salt water intrusion in coastal aquifers. The objective of this study was to develop a model to control/prevent the seawater intrusion into the coastal aquifer with a case study at Silifke?Goksu deltaic plane. A computer program for simulation of three?dimensional variable density groundwater flow, SEAWAT, is used to model the seawater intrusion mechanism of Goksu deltaic plane along the Mediterranean coast of Turkey. The calibration analysis of the developed seawater intrusion model is performed using actual data measured in the field which included static groundwater head, electrical conductivity, total dissolved solid and chloride concentration values of 23 observation wells taken in the water year of , 2008 and the existing data were compiled and reviewed. The main objectives of application of the seawater intrusion model to the Goksu deltaic plane are (1) to determine the hydraulic and hydro geologic parameters of the aquifer, (2) to estimate the spatial variation of the salt concentration in the aquifer, (3) to investigate the impact of the increase and decrease in the groundwater extractions and (4) to evaluate the effects of the climate changes on the groundwater resources in coastal aquifer. In the Goksu deltaic plane, to prevent or decrease the impacts of the climate changes has been simulated by three different climate change scenarios and the Goksu deltaic plane aquifer is sensitive especially to the increase in groundwater extraction. 156

Il lavoro tratta di una modellizzazione di flusso a densità variabile, tramite MODFLOW-SEAWAT, per valutare l'impatto ambientale, in termini di salinizzazione dell'acquifero, di un progetto di cava in sabbia di paleo-alveo nella bassa pianura Ferrarese

A comprehensive conceptual regional model for the Nile Delta aquifer has been composed in terms of the actual perspective of aquifer heterogeneity using all the new field data of drilled quality monitoring points in the Nile Delta aquifer. The study used the recently acquired configuration of the aquifer system which shows that the northern part the quaternary aquifer is devolved into multi-layered aquifer system while in the southern part; the aquifer consist of sand and gravel facies. The numerical modeling uses the finite difference SEAWAT program. The model is calibrated, both in terms of hydraulic heads and salt concentration, for the 2013 field data. The calibrated model is validated for the period 2013⿿2015. The model water balance reveals that seawater intrusion into the aquifer takes place at shallow to medium depths (up to 400 m), whereas groundwater fluxes in the deeper layers are moving toward the sea. The majority of the fluxes toward the sea help retaining old brine water in the deep zones and thus preventing seawater intrusion in these deep layers of the aquifer. This emphasizes the conclusion that the Nile Delta aquifer is not losing fresh groundwater flux to the sea. The study has achieved reliable necessary baseline simulation modeling and delineation of fresh/saline water interfaces as basis for decision-making and future management scenarios for controlled development of groundwater in the Nile Delta coastal aquifer. Keywords: Nile Delta aquifer, Sea water intrusion modeling, SEAWAT, Aquifer heterogeneity, Multi-layered aquifer system

PHWAT is a new model that couples a geochemical reaction model (PHREEQC-2) with a density-dependent groundwater flow and solute transport model (SEAWAT) using the split- operator approach. PHWAT was developed to simulate multi- component reactive transport in variable density groundwater flow. Fluid density in PHWAT depends not on only the concentration of a single species as in SEAWAT, but also the concentrations of other dissolved chemicals that can be subject to reactive processes. Simulation results of PHWAT and PHREEQC-2 were compared in their predictions of effluent concentration from a column experiment. Both models produced identical results, showing that PHWAT has correctly coupled the sub- packages. PHWAT was then applied to the simulation of a tank experiment in which seawater intrusion was accompanied by cation exchange. The density dependence of the intrusion and the snow- plough effect in the breakthrough curves were reflected in the model simulations, which were in good agreement with the measured breakthrough data. Comparison simulations that, in turn, excluded density effects and reactions allowed us to quantify the marked effect of ignoring these processes. Next, we explored numerical issues involved in the practical application of PHWAT using the example of a dense plume flowing into a tank containing fresh water. It was shown that PHWAT could model physically unstable flow and that numerical instabilities were suppressed. Physical instability developed in the model in accordance with the increase of the modified Rayleigh number for density-dependent flow, in agreement with previous research.