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Assessment of Groundwater Resources in Rmel Coastal
Aquifer (Morocco) by SEAWAT
A. Larabi, M. Faouzi and A. Cheng
LIMEN, Ecole Mohammadia d’Ingénieurs, Rabat
Department of Civil Engineering, University of Mississippi, USA
e-mail : [email protected]
www.emi.ac.ma/mawarid/
DEVELOPMENT OF A NUMERICAL MODEL
FOR SIMULATING SALT WATER
INTRUSION IN THE
RMEL COASTAL AQUIFER
USE OF THE MODEL AS A MANAGEMENT TOOL
FOR PLANNING AND WATER RESOURCES
MANAGEMENT IN THE AQUIFER
Location map of the study area.
area : 240 km2 ; 20 Km along the atlantic coast
HYDROCLIMATIC CONTEXT
 Semi-arid with oceanic influence;
 the average monthly temperature ranges from 12°c in
January to 24°c in August ;
The average annual precipitation: 695 mm.
 90% are recorded between November and April;
 The average ETP : 467 mm (DRPE, 1987)
Aquifer importance : used for drinking water supply for rural
areas, Larache and Ksar El Kebir cities, and Irrigation of the
Bas Loukkos plain
Overexploitation + Recurrent drought
 Important water table decrease
 Salt water intrusion advances
 aquifer’s Water quality degradation
 Hydro-agricultural development and drinking
supply threatened
 Need of optimum management
to protect water resources
water
• Work was commissioned by Direction de la
Recherche et de la Planification des Eau
Regular along the Atlantic coast
(located between - 25 and - 50 m
ASL);
 existence of a large basin (R'
hamna) in the East where the
depth of the substratum reaches
a value of - 90 m ASL;
In the south, the substratum of
the aquifer rises to form a high
bottom (watershed).
Map of the aquifer bottom
Piezometric map of the steady state (1972)
510000
508000
Océan Atlantique
Loukkos
506000
504000
 The flow is generally directed
South-west towards the North-East
with a component directed towards
the ocean;
502000
500000
498000
496000
494000
492000
490000
488000
424000 426000 428000 430000 432000 434000 436000 438000 440000
 General trend is modified on the
north by important local abstractions
of ONEP resulting in a cone of
depression) and along the rivers
and slopes where the aquifer is
drained permanently (presence of
springs and Merjas). ;
510000
Piezometric map 2000
508000
506000
Intensive local pumping near
the coast (field abstraction
of ONEP and SODEA)
504000
502000
500000
498000
inversion of the direction of
local fluxes from the sea
towards the continent,
resulting in a start of seawater
intrusion.
496000
494000
492000
490000
424000
426000
428000
430000
432000
434000
436000
438000
440000
SEAWATER INTRUSION MEASUREMENTS :
[NaCl]-Fo nd
[NaCl]-P ro f.
[NaCl]-P ro f
NP
-47.7
0.00
-48.2
[NaCl]-NP
[NaCl]-P ro f.
NP
Salinity and piezometry evolution in the coastal piezometers
NP (m)
0.20
janv-92
-47.2
janv-91
0.40
janv-90
-46.7
janv-88
0.60
janv-87
-46.2
janv-86
janv-92
janv-91
janv-90
janv-89
janv-88
janv-87
-34.0
janv-86
0.0
0.80
janv-85
-33.0
NaCl (g/l)
1.0
NP (m)
-32.0
janv-85
NaCl (g/l)
NP (m)
1536/3
1534/3
2.0
[NaCl]-NP
janv-92
janv-85
janv-92
[NaCl]-NP
NP
janv-89
[NaCl]-NP
janv-91
-39.6
janv-90
0.00
janv-89
-32.5
janv-88
0.0
janv-87
-39.0
janv-86
0.20
NaCl (g/l)
-32.0
NP (m)
1.5
janv-91
-38.4
janv-90
0.40
janv-89
-31.5
janv-88
3.0
janv-87
-37.8
janv-86
0.60
janv-85
NaCl (g/l)
-31.0
NP (m)
1535/3
1533/3
4.5
SEAWATER INTRUSION :
 Pz 1535/3 and 1536/3 don’t not show variation of the
concentration between the bottom and the top, however Pz
1533/3 and 1534/3 did;
 Peaks corresponding to January 1990 coinciding with the
intensive abstraction of the ONEP well field at the North (88-90)
associated to the beginning of reduced recharge of the aquifer
(period 91-95), due to droughts.
Modeling Processes
• Step 1: Identification of the information
required for making management decisions
• Step 2: Development of a conceptual model
• Step 3: Development of a mathematical
model
• Step 4: Development of a numerical model
and computer code
• Step 5: Code verification
• Step 6: Model validation
• Step 7: Model calibration and parameter
estimation
• Step 8: Model application
• Step 9: Sensitivity analysis
• Step 10: Stochastic analysis
DEVELOPMENT OF A MATHEMATICAL
MODEL FOR SIMULATING SEAWATER
INTRUSION
THE NUMERICAL CODE FOR MODELING
SEWATER INTRUSION
:
SEAWAT
A Computer Program For Simulation of Three-Dimensional
Variable-Density Ground-Water Flow (U.S.G.S.F)
MODFLOW
MT3DMS
Hydrodynamic Model for variable density
Solute Transport Model
-div (V ) +  qs =  Sp P + n  C
t
C t
V = -k ( grad P + g grad z)
µ
 = 0 (1 + )c
C =
t
N
 Dij C -  (Vi C) + qs Cs +  Rk
k=1
xi
xj
xi
n
Dispersion
Advection
Recharge/ Réactions
Décharge Chimiques
CONCEPTUAL MODEL
Mesh and Boundary conditions.
columns
Legend :
: Inactive Cells
: Cells with fixed potential and concentration
Drainage
The grid consists on 31 Columns, 42
Rows and 4 Layers generating 3216
regular square active cells of 500 m.
CONCEPTUAL MODEL
Control Network for the observation wells
Distribution of the piezometric observation
points in the modelled field
8 observation wells covering the field
are available and whose majority
concentrate in the North and the Center
of the study zone
compare the piezometric levels
simulated and measured vs
time
Calculated piezometry
Oc
éan
Atl
ant
iqu
e
Larache
Loukkos
The main piezometric structure of flow is well
represented;
The difference between calculated and measured
gw levels ranges between 1 and 1.5 m for
observation network;
The calibration is more reliable in the North-western
sectors and center-East where we have piezometric
data
: Piézométrie mesurée (m)
: Piézométrie calculée (m)
calibration of the R' mel aquifer model in
steady state (1972)
Correlation between measured and simulated values
Simulated water budget in SS
input
Balance components
Volumes
m3/day
discharge
l/s
recharge by precipitation
119978.35
1388.64
Return from irrigation
22852.80
264.50
Total
146206.50
1692.21
Agricultural withdrawls
31622.40
366.00
8640.00
100.00
30746.06
355.86
Domestic water supply
output
Error
(%)
Sea outflow
82% des entrées
28.2% des sorties
21.5% des sorties
50.3% des sorties
River drainage : Smid El
Ma-El Kihel-Sakh Sokh
71878.37
831.93
Total
142886.83
1653.78
3*10-4
Table 1: Calculated water balance in steady state (1972).
THE TRANSIENT MODEL
OBJECTIVES
Find out the starting period of Saltwater intrusion,
and follow-up its evolution and its extent
Identify the invaded zones by SWI and estimate the
contamination degree
Quantify the SWI inflow and the other balance terms
TRANSIENT MODEL
The model calibration was carried out over the period 1973-1984
A verification of the model was carried out over the period
1985-1996
Simulation of the model over the period 1997-2003 was carried
out by considering that the stresses are the same as those
characterizing the series 1985-1996
Transient water budget
Water budget terms
Mm3/an
1972
1975
1980
1985
1990
1995
2000
2003
0
8.787572
16.861682
1.039073
0.005411
13.364832
6.951049
3.885342
Return from irrigation
Return from irrigation
0.577109
0.577109
0.577109
16.466720
16.466720
16.466720
16.466720
16.466720
sea water Intrusion
0.000000
0.005670
0.012474
0.004097
0.000175
0.736463
2.116884
2.657511
Recharge by
precipitation
43.792099
12.648830
6.275535
22.521856
26.529291
3.924999
7.246354
7.246354
Total
44.369207
22.019181
23.726799
40.031746
43.001597
34.493013
32.781006
30.255927
0
0
0
5.282256
5.214287
0
0.000491
0
Net pumping
6.931613
6.931613
6.931613
6.182633
6.182633
11.985196
13.237976
13.237976
Sea outflow
11.222314
5.243754
5.114042
10.724994
12.006148
7.820600
7.386385
6.896315
River drainage : Smid El
Ma-El Kihel-Sakh Sokh
26.235607
9.842929
11.680025
17.839464
19.595962
14.670406
12.154008
10.119584
Total
44.389533
22.018297
23.725679
40.029348
42.999028
34.476201
32.778860
30.253875
0.046
0.046
0.004
0.005
0.006
0.006
0
0.007
Storage
I
n
p
u
t
O
u
t
p
u
t
destocking
Error en %
Reserve increases between 1972-1980: 2.93 Mm3/year between 1972-1975 and of 1.615
Mm3/year between 1975-1980;
Pronounced destocking between 1980-1985 of 4.22 Mm3/year, which continued until 1990
but with an average of 0.2 Mm3/year;
Transient water budget

1980-1985 : Reduction of the Recharge by precipitation (period of drought),
although water returns from surface irrigation increases (0.6
mm3 in 1980 to 16.5 mm3 in 1985);
 1985-1990 : decrease of the aquifer destocking because of the return to the
climate natural conditions of water supply, in addition to
contribution of surface water for the irrigation;
1990-1997: increase in the reserves (3.7 Mm3/year), although the development of
ONEP’s withdrawals (new pumping wells);

Increase in Sea outflow and River drainage
After 1997: destocking of the aquifer reserves,due to the increase in ONEP’s
withdrawals which increased from 184 l/s in 1995 to 223.72 l/s in 2000;

Sea water Intrusion
Quantitative evolution of seawater intrusion,
natural recharge and withdrawals in the R’mel
aquifer.
Volume d'intrusion marine (Mm3/an)
2.5
2
1.5
1
0.5
 Reduction of the seawater intrusion between 1995-1998
: wet period
1997
1992
1987
1982
Années
350
300
Infiltration des pluies mm/an)
 Seawater intrusion started since 1992 following the
increased development of ONEP’s withdrawals for the
Drinking water supply of Larache;
1977
1972
0
250
200
150
100
50
1987
1992
1997
1987
1992
1997
Années
25
20
15
1982
1977
10
1972
Volume de pompage (Mm3/an)
Seawater intrusion is very sensitive to the fluctuations
of water supply and the increase in withdrawals
1982
 From 1998, development of the seawater intrusion,
because of the recharge reduction associated with
increase of the ONEP pumping
1977
1972
0
Années
a) Calculated salinity in 1996 for layer 2
seawater intrusion
 zone located at the immediate West of ONEP
well field and pumping increased since 1992
 salinity exceeds 2 g/l in layer 2 where the well
filters are located
b) Calculated salinity in 2000 for layer 2
seawater intrusion
 Extension of the invaded zone by seawater
intrusion which becomes 2 times between 1996
and 2000
Satisfactory Model Results
Support Tool for Water Resources Planning and
Management in the area
SIMULATING PREVISIONAL SCENARIOS FOR
WATER RESOURCES MANAGEMENT OF THE
AQUIFER
3 scenario schemes have been applied in order to assess quantitative and
qualitative impact of the aquifer :
Scenario 1 : Keeping the present aquifer exploitation. The exploitation Volume is
about 13.24 Mm3/year untill 2020.
Scenario 2 : ONEP’s withdrawals from the existing well field which should satisfy
DWS demand of the Larache agglomerations projected for 2020;
Scenario 3 : Satisfy the maximum demands projected for the DWS for Larache
and Ksar El Kebir cities until 2020.
a) Calculated salinity for
Scenario1 in layer 2
b) Calculated salinity for
Scenario1 in layer 4
 Results are in agreement with observations and show that the contaminated zone by seawater
intrusion continues to extend more;
 Salinity in water is much higher on the level of layer 2 than layer 4 and this due to the
overexploitation in layer 2 (location of the filters);
c) Transversal section of simulated salinity in row 9 of the model for Scenario 1 (2020)
ONEP’s well field will be reached by seawater intrusion and the
concentration would be of 1g/l
Volume (Mm3/an)
year
Scenarios
2004
2005
2010
2015
2020
Scenario 1
1.5068
1.2480
0.7908
0.4492
0.3905
Scenario 2
2.9996
3.7544
4.5457
4.7273
4.9428
Scenario 3
3.0139
3.8145
4.7860
5.0961
5.7462
Previsional Volumes of seawater
intrusion
Seawater intrusion volume would decrease in scénario 1 since 2003 to reach a steady
state beyond the year 2020
a) Calculated Salinity for Scenario 2 in layer
2 (2010)
b) Calculated salinity for Scenario 2 in layer 4
 Considerable increase in the salinity in layer 2 (values generally range between 15 and 25 g/l);
 ONEP’s well field would be already reached by the seawater intrusion front in 2010 and the
concentration would be of 1.5 g/l;
a) Calculated salinity for Scenario 3 in layer 3
(2010)
b) Calculated salinity for Scenario 3 in layer 4
(2010)
Plume distribution is almost identical for scenario 2 and 3, but the RADEEL’s well field (to
supply the city of Ksar El Kebir), located at the south of the ONEP wells would not be
contaminated, although with the pumping increase, because it is far from the coast;
C/C : Simulated results
For scenario 1 (maintenance of the current conditions), the ONEP well
field would be already contaminated by seawater around 2020;
Groundwater quality varies badly in the Western Northern coastal part
of the aquifer;
Impact of these scenarios on the groundwater quality: pumping increase
in scenario 2 and 3 would accelerate seawater intrusion advance, which
would reach the ONEP well field in 2010; and would more accentuate the
deterioration of groundwater quality to higher concentrations.
We conclude that the water demand projected in 2020 would
lead to negative impact, resulting in seawater intrusion at the
noth western part of the studied area. If no measures and
actions are taken, the ONEP well field and the coastal
agricultural area will be abundoned.
Improvement of the situation will be reinforced by the surface
water use for irrigation of the coastal sectors and artificial
recharge of the aquifer. This will improve significantly the
groundwater quality in the coastal sectors of the aquifer and
will protect freshwater from seawater intrusion.