scholarly journals A New Normalized Groundwater Age-Based Index for Quantitative Evaluation of the Vulnerability to Seawater Intrusion in Coastal Aquifers: Implications for Management and Risk Assessments

Water ◽  
2021 ◽  
Vol 13 (18) ◽  
pp. 2496
Author(s):  
Mohammed Adil Sbai ◽  
Abdelkader Larabi ◽  
Marwan Fahs ◽  
Joanna Doummar
Keyword(s):  
Steady State ◽  
Seawater Intrusion ◽  
Coastal Aquifers ◽  
Groundwater Age ◽  
Groundwater Resources ◽  
Age Distribution ◽  
Flow Simulation ◽  
Risk Assessments ◽  
Henry Problem ◽  
Variable Density Flow

The vulnerability of coastal aquifers to seawater intrusion has been largely relying on data-driven indexing approaches despite their shortcomings to depict the complex processes of groundwater flow and mass transport under variable velocity conditions. This paper introduces a modelling-based alternative technique relying on a normalized saltwater age vulnerability index post-processed from results of a variable density flow simulation. This distributed index is obtained from the steady-state distribution of the salinity and a restriction of the mean groundwater age to a mean saltwater age distribution. This approach provides a novel way to shift from the concentration space into a vulnerability assessment space to evaluate the threats to coastal aquifers. The method requires only a sequential numerical solution of two steady state sets of equations. Several variants of the hypothetical Henry problem and a case study in Lebanon are selected for demonstration. Results highlight this approach ability to rank, compare, and validate different scenarios for coastal water resources management. A novel concept of zero-vulnerability line/surface delineating the coastal area threatened by seawater intrusion has shown to be relevant for optimal management of coastal aquifers and risk assessments. Hence, this work provides a new tool to sustainably manage and protect coastal groundwater resources.

Prediction of seawater intrusion to coastal aquifers based on non-dimensional diagrams

2020 ◽  
Author(s):  
Charalampos Doulgeris ◽  
Evangelos Tziritis ◽  
Vassilios Pisinaras ◽  
Andreas Panagopoulos ◽  
Christoph Külls
Keyword(s):  
Hydraulic Conductivity ◽  
Case Studies ◽  
Seawater Intrusion ◽  
Coastal Aquifers ◽  
Variable Density ◽  
Real Case ◽  
Constant Thickness ◽  
Variable Density Flow ◽  
Density Flow ◽  
Dimensional Parameters

<p>A numerical analysis of the groundwater flow and contaminant transport equations, based on the variable density flow approach, is used for the construction of non-dimensional diagrams to predict seawater intrusion to confined coastal aquifers. The classical Henry’s seawater intrusion problem is analysed by using a finite element model. The model’s equations are written in non-dimensional form and the numerical solutions depend solely on three non-dimensional parameters:</p><p>α=q΄/Κ<sup>0</sup>, β=(bΚ<sup>0</sup>)/(nD<sub>m</sub>), α΄=bS<sup>0</sup>/n                                                                                           (eq. 1 a,b,c)</p><p>where q’ is the freshwater recharge rate (m/d), K<sup>0</sup> the freshwater hydraulic conductivity (m/d), b the aquifer thickness, n the porosity (-), D<sub>m</sub> the molecular diffusion coefficient (m<sup>2</sup>/d) and S<sup>0</sup> the freshwater specific storage (1/m). Please note that hydraulic conductivity appears in two of the non-dimensional parameters, α and β.</p><p>The non-dimensional formulation has led to the construction of non-dimensional diagrams of salt distribution for a homogeneous and isotropic confined aquifer with horizontal base and constant thickness that is uniformly recharged with freshwater. These diagrams illustrate the influence of the key hydrological and hydraulic parameters, and furthermore, can be used to predict the evolution of seawater intrusion in real case studies.</p><p>The numerical simulations were carried out up to the equilibrium state for different values of the non-dimensional parameters of equation 1. By decreasing the value of parameter α=q΄/Κ<sup>0</sup>, seawater intrusion is advancing inland and the width of dispersion zone is increasing. By increasing the parameter β=(bΚ<sup>0</sup>)/(nD<sub>m</sub>), the seawater-freshwater transition zone is narrowing and shifted to the seaside at the upper part of the aquifer, while the intrusion of saltwater is advancing inland at the lower part of the aquifer. The distribution of the salts in the aquifer was found essentially identical for different values of the parameter α΄=bS<sup>0</sup>/n; hence this parameter exhibits very low sensitivity, which makes it of low importance, especially for real case studies.</p><p>Overall, the non-dimensional diagrams – constructed by following the variable density flow approach and under specific assumptions – can be used for a quick and direct prediction of seawater intrusion in real aquifers. These diagrams would be useful for an initial prediction at the case studies of the PRIMA MEDSAL project (www.medsal.net), namely the coastal aquifers in Rhodope (Greece), Samos island (Greece), Bouficha (Tunisia), Bouteldja (Algeria), Tarsus (Turkey) and under specific assumptions to the karstic aquifer in Salento (Italy).</p>

scholarly journals Management of Seawater Intrusion in Coastal Aquifers: A Review

Water ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 2467 ◽  
Author(s):  
Mohammed S. Hussain ◽  
Hany F. Abd-Elhamid ◽  
Akbar A. Javadi ◽  
Mohsen M. Sherif
Keyword(s):  
Seawater Intrusion ◽  
Coastal Aquifers ◽  
Arid Regions ◽  
Saline Water ◽  
Groundwater Resources ◽  
Management Strategies ◽  
Environmental Costs ◽  
Fresh Groundwater ◽  
Advantages And Disadvantages ◽  
And Control

Seawater intrusion (SWI) is one of the most challenging and widespread environmental problems that threaten the quality and sustainability of fresh groundwater resources in coastal aquifers. The excessive pumping of groundwater, associated with the lack of natural recharge, has exacerbated the SWI problem in arid and semi-arid regions. Therefore, appropriate management strategies should be implemented in coastal aquifers to control the impacts of SWI problems, considering acceptable limits of economic and environmental costs. The management of coastal aquifers involves the identification of an acceptable ultimate landward extent of the saline water body and the calculation of the amount of seaward discharge of freshwater that is necessary to keep the saline–freshwater interface in a seacoast position. This paper presents a comprehensive review of available hydraulic and physical management strategies that can be used to reduce and control SWI in coastal aquifers. Advantages and disadvantages of the different approaches are presented and discussed.

scholarly journals Modeling Seawater Intrusion to Coastal Aquifers in South Coast of Laizhou Bay, China

2018 ◽  
Vol 54 ◽  
pp. 00004
Author(s):  
Yawen Chang ◽  
Bill X. Hu ◽  
Xue Li
Keyword(s):  
Seawater Intrusion ◽  
Coastal Aquifers ◽  
Saline Water ◽  
Groundwater Resources ◽  
Water Area ◽  
Laizhou Bay ◽  
Precipitation Condition ◽  
Fresh Groundwater ◽  
Depression Cone ◽  
Error Method

In this study, a two-dimensional SEAWAT 2000 model is developed to simulate the seawater intrusion to coastal aquifers and brine water/fresh water interaction in the south of Laizhou Bay, Shandong Province, China and forecast the seawater intrusion and brine water/freshwater interface development in the coming years. The model profile is perpendicular to the coastal line, about 40 km long and 110 m in depth, and consists of two interfaces, freshwater-saline water interface and brine water-saline water-seawater interface. The parameters of aquifers in the SEAWAT-2000 model are calibrated by trial-error method repeatedly to fit the head and salinity measurements. Based on the historical groundwater and brine water exploration and natural precipitation condition, the prediction results indicate that equivalent freshwater head in shallow freshwater-saline water area will decrease year by year and decline 2.0 m in the forecasting period, caused by groundwater over-pumping for irrigating farmlands. The groundwater head in the brine-saline water area will also decrease about 1.8 m in forecasting period. A larger depression cone appears in the brine area, with smaller funnels in other areas. The salinity in the brine area finally drops below 105g/l. In the meanwhile, the salinity increases in other areas, damage fresh groundwater resources.

scholarly journals Groundwater withdrawal in randomly heterogeneous coastal aquifers

2018 ◽  
Vol 22 (5) ◽  
pp. 2971-2985 ◽  
Author(s):  
Martina Siena ◽  
Monica Riva
Keyword(s):  
Coastal Aquifers ◽  
Numerical Study ◽  
Groundwater Resources ◽  
Three Dimensional ◽  
Vertical Direction ◽  
Variable Density ◽  
Groundwater Withdrawal ◽  
Dimensional System ◽  
Mixing Zone ◽  
Variable Density Flow

Abstract. We analyze the combined effects of aquifer heterogeneity and pumping operations on seawater intrusion (SWI), a phenomenon which is threatening coastal aquifers worldwide. Our investigation is set within a probabilistic framework and relies on a numerical Monte Carlo approach targeting transient variable-density flow and solute transport in a three-dimensional randomly heterogeneous porous domain. The geological setting is patterned after the Argentona river basin, in the Maresme region of Catalonia (Spain). Our numerical study is concerned with exploring the effects of (a) random heterogeneity of the domain on SWI in combination with (b) a variety of groundwater withdrawal schemes. The latter have been designed by varying the screen location along the vertical direction and the distance of the wellbore from the coastline and from the location of the freshwater–saltwater mixing zone which is in place prior to pumping. For each random realization of the aquifer permeability field and for each pumping scheme, a quantitative depiction of SWI phenomena is inferred from an original set of metrics characterizing (a) the inland penetration of the saltwater wedge and (b) the width of the mixing zone across the whole three-dimensional system. Our results indicate that the stochastic nature of the system heterogeneity significantly affects the statistical description of the main features of the seawater wedge either in the presence or in the absence of pumping, yielding a general reduction of toe penetration and an increase of the width of the mixing zone. Simultaneous extraction of fresh and saltwater from two screens along the same wellbore located, prior to pumping, within the freshwater–saltwater mixing zone is effective in limiting SWI in the context of groundwater resources exploitation.

scholarly journals Groundwater age in the Wairarapa

2021 ◽  
Author(s):  
◽  
Ryan David Evison
Keyword(s):  
Land Use ◽  
Drinking Water ◽  
New Zealand ◽  
Groundwater Flow ◽  
Groundwater Age ◽  
Groundwater Resources ◽  
Age Distribution ◽  
Transport Processes ◽  
Age Assessment ◽  
The Mean

<p>This dissertation focuses on the catchment-scale evaluation of groundwater age as a function of space and time in the 270 km² Middle Wairarapa catchment. The simulation of the mean age and point distribution of ages, contributing to a regional age estimate, is a novel demonstration of the recently developed groundwater software, Cornaton (2012). The Wairarapa is in the southern North Island of New Zealand and is a dynamic water catchment exhibiting complex interactions between its rivers and shallow aquifers. Groundwater has been widely utilized since the 1980s for agriculture, horticulture and drinking water; increasing land use development (i.e. irrigation and nutrient application) requires effective regional management of both the quantity and quality of water resources.  Groundwater age provides insights into groundwater flow and transport processes and thus enables better management of groundwater resources. Subsurface water age information enables the interpretation of recharge influence, zones of sensitivity for sustainable abstraction, as well as contamination risk from land-use intensification to drinking water supplies. It is accepted that groundwater is composed of a mixture of water with different ages, however, until very recently mean age has been the primary indicator for groundwater age assessment. Mean age alone can misrepresent the potential for contamination from young water; for example, a groundwater sample with an old mean age may still contain a significant fraction of young water; therefore, a fuller understanding of the age distribution in both time and space is important for groundwater management. The ability to simulate the full distribution of groundwater age within transient numerical groundwater models has only been very recently enabled, through implementation of the time-marching Laplace transform Galerkin technique (TMLTGT), and is demonstrated in this dissertation.  A transient finite-element groundwater flow model originally developed by Greater Wellington Regional Council was converted to simulate transport of the age tracer tritium and groundwater age using the Ground Water (GW) software. Observed tritium concentrations were utilized in the calibration using the Monte Carlo and Gauss-Marquardt-Levenberg methods. Following the calibration of the transport model the GW software was then used to derive pumping well capture zones and directly simulate age throughout the Middle Wairarapa Valley catchment. The advective dispersive equation and the TMLTGT were used for transient mean-age and transient simulations of the full distribution of groundwater age. The results are presented as maps and graphs of both mean age and age distributions throughout the Middle Valley, covering a 15 year simulation period.  The mean-age simulations indicated the groundwater age in the valley was strongly influenced by seasonal changes and extreme climatic events. Significant variations existed, from high rainfall recharge percolating young water throughout the domain, to dry extended droughts limiting recharge and increasing the age throughout large sections of the Middle Valley. Age distributions were shown to be strongly influenced by abstraction pressures, depth and geology. Abstractions were shown to skew the age distribution, creating both older and younger mean-ages depending on the location of the observation point, and several simulations indicated the potential misrepresentation of young (potentially contaminated) water quantified as old by mean-age assessment. These results show the dynamic nature of the Middle Valley groundwater system and its inherent vulnerabilities. The Wairarapa transient age distributions are one of the first such examples in New Zealand, and they demonstrate the potential of the information interpreted from age estimates to more effectively manage groundwater resources.</p>

Groundwater and salinization risk: tapping works and management experience in the Mediterranean Area

2021 ◽  
Author(s):  
Giorgio De Giorgio ◽  
Livia Emanuela Zuffianò ◽  
Maurizio Polemio
Keyword(s):  
Seawater Intrusion ◽  
Coastal Aquifers ◽  
Groundwater Resources ◽  
Regional Scale ◽  
Mediterranean Area ◽  
Management Approach ◽  
Fresh Groundwater ◽  
Groundwater Exploitation ◽  
Saline Groundwater ◽  
The Mediterranean

&lt;p&gt;The progressive population growth in coastal areas constitutes a huge worldwide problem, particularly relevant for coastal aquifers of the Mediterranean basin.&lt;/p&gt;&lt;p&gt;The increasing use of groundwater and the effect of seawater intrusion makes the study of coastal aquifers extremely relevant.&lt;/p&gt;&lt;p&gt;There are various measures, practices, and actions throughout the world for managing groundwater when this natural resource is subject to salinization risk.&lt;/p&gt;&lt;p&gt;This research focused on the seawater intrusion, classifies the different practical solutions protecting the groundwater through salinization mitigation and/or groundwater salinity improvements along the Mediterranean Area.&lt;/p&gt;&lt;p&gt;The literature review was based on 300 papers, which are mainly international journal articles (76%). The rest includes conference papers (11.8%), reports and theses (7%), and books or chapters of a book (25%).&lt;/p&gt;&lt;p&gt;Three main schematic groundwater management approaches can be distinguished for the use of groundwater resources at risk of salinization.&lt;/p&gt;&lt;p&gt;The &lt;strong&gt;engineering approaches&lt;/strong&gt; pursue locally the discharge increase avoiding or controlling the salinity increase.&lt;/p&gt;&lt;p&gt;The most recent experiences of tapping submarine springs were realized using underground concrete dams, tools shaped like a parachute or tulip, or a fiberglass telescopic tube-bell, especially in the case of karstic aquifers.&lt;/p&gt;&lt;p&gt;The current widespread form of the engineering approach is to address the issue of groundwater exploitation by wells.&lt;/p&gt;&lt;p&gt;More complex solutions use subhorizontal designs. Subhorizontal tapping schemes were realized using tunneling and/or boring in combination with wide-diameter wells or shafts.&lt;/p&gt;&lt;p&gt;These works include horizontal drains or radial tunnels bored inside the saturated aquifer, shafts excavated down to the sea level with radial galleries or drains realized together with weirs to improve the regulation of the discharge rate and of salinization. Application of these solutions in areas where a thin fresh groundwater lens floats on the saline groundwater, as in the case of narrow and highly permeable islands, can yield high discharges, thus causing a very low drawdown over very wide areas. These solutions were successfully applied in Malta Islands.&lt;/p&gt;&lt;p&gt;The &lt;strong&gt;discharge management approach&lt;/strong&gt; encompasses at least an entire coastal aquifer and defines rules concerning groundwater utilization and well discharge.&lt;/p&gt;&lt;p&gt;A multi-methodological approach based on monitoring networks, spatiotemporal analysis of groundwater quality changes, and multiparameter well logging is described in Apulian karstic coastal aquifers (Italy). The core is the definition of the salinity threshold value between pure fresh groundwater and saline groundwater mixture. The basic tools were defined to be simple and cost-effective to be applicable to the widest range of situations.&lt;/p&gt;&lt;p&gt;The &lt;strong&gt;water and land management approach&lt;/strong&gt; should be applied on a regional scale. The main choice for this approach is pursuing water-saving measures and water demand adaptation. A multiple-users and multiple-resources-water supply system model was implemented to evaluate the effectiveness of the increasing maximum capacity of the surface reservoir and managed aquifer recharge in Apulia, a semi-arid region of Southern Italy.&lt;/p&gt;

scholarly journals Effects of Aquifer Bed Slope and Sea Level on Saltwater Intrusion in Coastal Aquifers

Hydrology ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 5 ◽  
Author(s):  
Hany F. Abd-Elhamid ◽  
Ismail Abd-Elaty ◽  
Mohsen M. Sherif
Keyword(s):  
Sea Level ◽  
Groundwater Level ◽  
Coastal Aquifers ◽  
Saltwater Intrusion ◽  
Groundwater Resources ◽  
The Other ◽  
Henry Problem ◽  
Dispersion Zone ◽  
Bed Slope

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.

scholarly journals Efficient Stochastic Simulation of Seawater Intrusion, With Mixing, in Confined Coastal Aquifers

2021 ◽  
Vol 3 ◽  
Author(s):  
Evangelos Rozos ◽  
Katerina Mazi ◽  
Antonis D. Koussis
Keyword(s):  
Seawater Intrusion ◽  
Coastal Aquifers ◽  
High Efficiency ◽  
Flow Region ◽  
Variable Density ◽  
Tracer Transport ◽  
Advection Dispersion ◽  
Variable Density Flow ◽  
Density Flow ◽  
Principal Directions

We present a high-efficiency method for simulating seawater intrusion (SWI), with mixing, in confined coastal aquifers based on uncoupled equations in the through-flow region of the aquifer. The flow field is calculated analytically and the tracer transport numerically, via spatial splitting along the principal directions (PD) of transport. Advection-dispersion processes along streamlines are simulated with the very efficient matched artificial dispersivity (MAD) method of Syriopoulou and Koussis and the system of discretized transverse-dispersion equations is solved with the Thomas algorithm. These concepts are embedded in the 2D-MADPD-SWI model, yielding comparable solutions to those of the uncoupled SWI equations with the state-of-the-art FEFLOW code, but faster, while 2D-MADPD-SWI achieves an at least hundredfold faster solution than a variable-density flow model. We demonstrate the utility of the 2D-MADPD-SWI model in stochastic Monte Carlo simulations by assessing the uncertainty on the advance of the 1,500 ppm TDS line (limit of tolerable salinity for irrigation) due to randomly variable hydraulic conductivity and freshwater flow rate.

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