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th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
management model is the most cost effective strategy to control
the seawater intrusion in this hypothetical aquifer. The cost of
this model is about 50% of the abstraction only scenario and
25% of the recharge scenario. The reason for this lowest cost is
partly because the cost associated with the supply of water used
for recharge does not apply in this case as the required water is
provided primarily from the treatment of the abstracted saline
water. In addition, the excess treated water can be directly used
for other purposes. The other aspect of efficiency of this model
is about minimization of total concentration of salinity in the
aquifer as it reduced the total concentration in the system by
15% , while the first and second scenarios reduced it by 10-
11%. Figure (4) clearly shows the capability of third model in
controlling the further advance of the freshwater/seawater
interface in comparison with other models.
Table 2. Summary of the results obtained from the simulation-
optimization models for the hypothetical case study.
Figure 4. 0.5 isochlors from simulation-optimization models for the
hypothetical case.
6 CONCLUSIONS
This paper presented the development and application of a
simulation-optimization model to control seawater intrusion in
coastal aquifers. A coupled transient density-dependent finite
element model was used to simulate the seawater intrusion
problem. This simulation model was linked with a genetic
algorithm to optimize control arrangements for a hypothetical
aquifer using three management scenarios: abstraction of
brackish water, recharge of fresh water, and combination of
abstraction and recharge. The efficiencies of the proposed
management scenarios in controlling seawater intrusion in terms
of both the solute concentration in the aquifer and the total costs
(of construction and operation) of the management policy were
evaluated using this integrated model. The optimal locations,
depths, and rates of abstraction and/or recharge wells in each
scenario were determined. The results show that all three
scenarios could be effective in controlling sea intrusion but
using model 3 (a combination of abstraction and recharge wells)
resulted in the least cost and salt concentration in aquifers and
maximum movement of freshwater/saline water interface
towards the sea. The results also show that for the case study
considered in this paper, the amount of abstracted and treated
water is three times the amount required for recharge; therefore,
the remaining treated water can be used directly for different
purposes. Finally, ADR is an effective tool to control seawater
intrusion and can be applied in areas where there is a risk of
seawater intrusion.
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Model
L
(m)
D
(m)
Q
(m
3
/sec)
Total
C
Cost
($/year)
No
Management
-
-
-
167
-
Abstraction only
50
90
-0.083
149
2.62E+6
Recharge only
90
60
0.095
151
5.72E+6
Abstraction
and
Recharge
50
110
90
80
-0.048
0.018
142
1.32E+6
