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Numerical modelling and control of seawater intrusion in coastal aquifers
Modélisation numérique et contrôle des intrusions d’eau de mer dans les aquifères côtiers
Javadi A.A., Hussain M.S.
University of Exeter, Exeter, UK
Abd-Elhamid H.F.
Zagazig University, Zagazig, Egypt
Sherif M.M.
United Arab Emirates University, Al Ain, UAE
ABSTRACT: This paper presents the results of an investigation into numerical modelling and control of seawater intrusion. A
coupled transient density-dependent finite element model has been used for modelling of seawater intrusion. Also, a new cost-
effective method is presented for effective control of seawater intrusion in coastal aquifers. This methodology ADR (Abstraction,
Desalination and Recharge) includes abstraction of saline water, desalination and recharge of a part of the excess desalinated water to
the aquifer while the rest of the desalinated water can be used for domestic consumption. The simulation model has been integrated
with an genetic algorithm (GA) to examine different scenarios to control seawater intrusion including different combinations of
abstraction, desalination and recharge. The main objectives of the model are to minimize the total capital and operational costs of the
abstraction and recharge wells and the salt concentrations in the aquifer. The results show that the proposed ADR system performs
significantly better than using abstraction or recharge wells alone as it gives the least cost and least salinity in the aquifer.
RÉSUMÉ : Cet article présente les résultats d’une étude sur la modélisation numérique et le contrôle des intrusions d’eau de mer. Un
couplage transitoire à densité variable par éléments finis a été utilisé pour modéliser les intrusions d’eau de mer. De plus, une nouvelle
méthode est présentée pour un contrôle optimisé des intrusions d’eau salée. Cette méthodologie ADR (Abstraction, Desalination and
Recharge) inclut l’extraction d’eau saline, le dessalement et la recharge dans l’aquifère d’une partie de l’excès d’eau dessalée tandis
que le reste d’eau dessalée peut être utilisée pour un usage domestique. Le modèle de simulation a été intégré à l’aide d’un algorithme
génétique (GA) dans le but d’examiner différents scénarios pour le contrôle des intrusions d’eau de mer incluant différentes
combinaisons d’extraction, de dessalement, et de recharge. L’objectif principal du modèle est de minimiser le coût total et le nombre
d’opérations pour l’extraction et la recharge des puits ainsi que la concentration en sel dans l’aquifère. Les résultats montrent que la
méthode ADR proposée donne de biens meilleurs résultats que l’extraction et la recharge des puits seules du fait qu’elle conduit à un
coût et une salinité dans l’aquifère minimaux.
KEYWORDS: numerical modelling, seawater intrusion, optimal management, abstraction, recharge
1 INTRODUCTION.
Seawater intrusion is a major problem threatening water
resources in many parts of the world. The intrusion of saline
water in groundwater is considered a special category of
pollution, making groundwater resources unsuitable for human,
industrial and irrigation uses. Mixing of 2-3% salinity would
render the fresh groundwater resources unsuitable for human
consumption. A 5% mixing of salinity with freshwater in an
aquifer is enough to make the aquifer unsuitable for any use
(Abd-Elhamid and Javadi, 2011). Seawater intrusion hence
reduces the freshwater storage in coastal aquifers and in
extreme cases can result in abandonment of freshwater supply
wells. Remediation of groundwater could be very costly and
could take a long time depending on the source and level of
salinization. As a result, groundwater resources should be
protected from saltwater intrusion, using suitable measures. To
control saline intrusion, a seaward hydraulic gradient should be
maintained and a proportion of the fresh-water should be
allowed to flow into the sea. Risks of saline intrusion clearly
limit the extent to which a coastal aquifer can be developed for
water supply. The management of a coastal aquifer is concerned
with deciding an acceptable ultimate landward extent of the
saline water and calculating the appropriate discharge of
freshwater necessary to maintain the seawater-fresh water
interface in that position. A number of methods have been
proposed to control seawater intrusion including:
reduction of
pumping rates, relocation of pumping wells, use of subsurface
barriers, natural recharge, artificial recharge, abstraction of
saline water and combination techniques (Todd, 1974). This
study presents a cost-effective methodology to control seawater
intrusion in coastal aquifers. This methodology (ADR -
Abstraction, Desalination and Recharge) consists of three steps;
abstraction of brackish water from the saline zone, desalination
of the abstracted brackish water using reverse osmosis (RO)
treatment process and recharge of the treated water into the
aquifer.
Generally, the seawater intrusion is a highly nonlinear
process. Spatial and temporal simulation of this process will
require numerical methods such as the finite element method or
finite difference method to solve the nonlinear governing
equations of flow and solute transport through
saturated/unsaturated porous media. Numerical simulation
models can be used to examine a limited number of design
options of these management methods, by trial and error (e.g.
Mahesha, 1996 and Rastogi et al., 2004
). However,
optimization tools can be combined with simulation models to
search for the optimal solution in a wide search space of design
variables.
In recent years, a number of simulation models have been
combined with optimization techniques to address groundwater
management problems. The combined simulation and
optimization model can identify an optimal management
strategy by considering appropriate management objectives and
constraints. The genetic algorithm (GA) optimization tool has
the capability to deal with a wide range of optimization
problems. These techniques have been applied by a number of
researchers to coastal aquifer problems. Different simulation
models (or Meta models) have been integrated with GA to
optimize different management schemes to limit seawater
u ric l
lli
a c tr l f se ater intrusion in coastal aquifers
odélisation nu érique et contrôle des intrusions d’eau de er dans les aquifères côtiers
A. A. Javadi & M. S. Hussain
University of Exeter, Exeter, UK
H. F. Abd-Elhamid
Zagazig University, Zagazig, Egypt
M. M. Sherif
United Arab E irates University, Al Ain, UAE
ABSTRACT: This paper presents the results of an investigation into numerical modelling and control of seawater intrusion. A
coupled transient density-dependent finite element model has been used for modelling of seawater intrusion. Also, a new cost-
effective method is presented for effective control of seawater intrusion in coastal aquifers. This methodology ADR (Abstraction,
Desalination and Recharge) includes abstraction of saline water, desalination and recharge of a part of the excess desalinated water to
the aquifer while the rest of the desalinated water can be used for domestic consumption. The simulation model has been integrated
with an genetic algorithm (GA) to examine different scenarios to control seawater intrusion including different combinations of
abstraction, desalination and recharge. The main objectives of the model are to minimize the total capital and operational costs of the
abstraction and recharge wells and the salt concentrations in the aquifer. The results show that the proposed ADR system performs
significantly better than using abstraction or recharge wells alone as it gives the least cost and least salinity in the aquifer.
RÉSUMÉ : Cet article présente les résultats d’une étude sur la modélisation numérique et le contrôle des intrusions d’eau de mer. Un
couplage transitoire à densité variable par éléments finis a été utilisé pour modéliser les intrusions d’eau de mer. De plus, une nouvelle
méthode est présentée pour un contrôle optimisé des intrusions d’eau salée. Cette méthodologie ADR (Abstraction, Desalination and
Recharge) inclut l’extraction d’eau saline, le dessalement et la recharge dans l’aquifère d’une partie de l’excès d’eau dessalée tandis
que le reste d’eau dessalée peut être utilisée pour un usage domestique. Le modèle de simulation a été intégré à l’aide d’un algorithme
génétique (GA) dans le but d’examiner différents scénarios pour le contrôle des intrusions d’eau de mer incluant différentes
combinaisons d’extraction, de dessalement, et de recharge. L’objectif principal du modèle est de minimiser le coût total et le nombre
d’opérations pour l’extraction et la recharge des puits ainsi que la concentration en sel dans l’aquifère. Les résultats montrent que la
méthode ADR proposée donne de biens meilleurs résultats que l’extraction et la recharge des puits seules du fait qu’elle conduit à un
coût et une salinité dans l’aquifère minimaux.
KEYWORDS: numerical modelling, seawater intrusion, optimal management, abstraction, recharge
1 INTRODUCTION.
Seawater intrusion is a major problem threatening water
resources in many parts of the world. The intrusion of saline
water in groundwater is considered a special category of
pollution, making groundwater resources unsuitable for human,
industrial and irrigation uses. Mixing of 2-3% salinity would
render the fresh groundwater resources unsuitable for human
consumption. A 5% ixing of salinity with freshwater in an
aquifer is enough to make the aquifer unsuitable for any use
(Abd-Elhamid and Javadi, 2011). Seawater intrusion hence
reduces the freshwater storage in coastal aquifers and in
extreme cases can result in abandonment of freshwater supply
wells. Remediation of groundwater could be very costly and
could take a long time depending on the source and level of
salinization. As a result, groundwater resources should be
protected from saltwater intrusion, using suitable measures. To
control saline intrusion, a seaward hydraulic gradient should be
maintained and a proportion of the fresh-water should be
allowed to flow into the sea. Risks of saline intrusion clearly
limit the extent to which a coastal aquifer can be developed for
water supply. The management of a coastal aquifer is concerned
with deciding an acceptable ultimate landward extent of the
saline water and calculating the appropriate discharge of
freshwater necessary to maintain the seawater-fresh water
interface in that position. A number of methods have been
proposed to control seawater intrusion including:
reduction of
pumping rates, relocation of pumping wells, use of subsurface
barriers, natural recharge, artificial recharge, abstraction of
saline water and combination techniques (Todd, 1974). This
study presents a cost-effective methodology to control seawater
intrusion in coastal aquifers. This methodology (ADR -
Abstraction, Desalination and Recharge) consists of three steps;
abstraction of brackish water from the saline zone, desalination
of the abstracted brackish water using reverse osmosis (RO)
treatment process and recharge of the treated water into the
aquifer.
Generally, the seawater intrusion is a highly nonlinear
process. Spatial and temporal simulation of this process will
require numerical methods such as the finite element method or
finite difference method to solve the nonlinear governing
equations of flow and solute transport through
saturated/unsaturated porous media. Numerical simulation
models can be used to examine a limited number of design
options of these management methods, by trial and error (e.g.
Mahesha, 1996 and Rastogi et al., 2004
). However,
optimization tools can be combined with simulation models to
search for the optimal solution in a wide search space of design
variables.
In recent years, a number of simulation models have been
combined with optimization techniques to address groundwater
management problems. The combined simulation and
optimization model can identify an optimal management
strategy by considering appropriate management objectives and
constraints. The genetic algorithm (GA) optimization tool has
the capability to deal with a wide range of optimization
problems. These techniques have been applied by a number of
researchers to coastal aquifer proble s. Different simulation
