Download Climate change impact in a shallow coastal Mediterranean

Climate change impact in a shallow
coastal Mediterranean aquifer, at
Saïdia, Morocco
Júlio Carneiro, A. Correia
Geophysical Centre of Évora, Évora, Portugal
M. Boughriba, Y. Zarhloule
University Mohamed I, Oujda, Morocco
A. Rimi
Scientific Institute, Rabat, Morocco
‫م‬
B. El Houadi
Hydraulic Basin Agency of Moulouya, Oujda, Morocco
Location of the study area
Northeast Morocco, at the
border with Algeria
Mediterranean coast, the
Alboran sea
Coastal plain with about 30
km2
Atlantic
Saidïa
Algeria
Location of the study area
The Saïdia aquifer is exploited for irrigation
purposes.
Oued Moulouya
Salinity is too high for drinking water supply, usually
above 3000 mg/l.
Main pumping zones located close to the Kiss and
Moulouya.
The Mouluoya is an influent river. The Oued Kiss is
seasonal.
Mediterranean
Oued Kiss
Ain Chebbak
and Ain Zebda
Saïdia
Motivation for the study
The area is undergoing fast changes in land-use
Planning did not take into account sea-level rising and
likely salinity increase
Oued Moulouya
Several golf courses planned. Irrigated areas will
increase considerably
Mediterranean
Saïdia
Objectives and Methodology
Objective
1. The influence of climate changes in the goundwater level and in
salinity, due to:
a. Sea level rise
b. Changes in precipitation and temperature
Methodology
1. Build a density-dependent numerical model that matches hydraulic
head and concentration distributions in the aquifer;
2. Use changes in sea level, temperatures and precipitation fom IPCC
scenarios.
3. Estimate changes in recharge.
4. Sea level rise and changes in recharge applied in the groundwater
numerical model to make predictions.
Aquifer structure
dune
Mud layer
Marls with gypsum
dune
Sea
Mud layer
sands
Very simple structure - a single unconfined layer;
Sequence of alluvial and beach deposits: fine to medium
sands with remains of shells;
Thickness from 10 m to 25 m, with maximums at the two
sand dunes;
 Between those dunes, the sand layers are covered by a
mud layer up to 4 m thick.
Geometry and boundaries
Moulouya
flood plain
Ain Chebbak
and Ain Zebda
The aquifer overlay marls with gypsum layers, dating from the Miocene;
The marls outcrop at the Ouled Mansour hills, and are the impermeable south and
east boundary of the aquifer;
The oued Moulouya is the prescribed-head west boundary;
Recharge to the aquifer occurs mainly in the dunes strips and is about 23% of
precipitation (Melloul et al. 2006);
The Moulouya flood plain also receives recharge from the “Troueé” and from
springs (Ain Chebbak and Ain Zebda).
Wells and piezometers
Water level measurements in 45 wells and piezometers;
Samples collected in 18 of those wells and piezometers; in the others
measurements of electrical conductivity and conversion to salinity;
However, little information about the state of the existing wells and
unable to pump test any of those wells. Few data regarding hydraulic
conductivity.
Salinity sources
Based on chemical data Melloul et al. (2006) identifies three main sources of
salinity in the Saïdia aquifer:
1. Inflow from Triffa aquifer and Ain Chebbak and Ain Zebda springs;
2. Dissolution of evaporitic layers (mainly gypsum) in the marls, at the
southern limit of the aquifer. In some areas the nearly stagnant conditions
below the mud layers give rise to salinity values up to 10.5 g/l.
3. Mixing with sea water.
Numerical model
Mesh extended into the Mediterranean to fix a constant head, constant
concentration boundary; five vertical layers.
Only three zones of hydraulic conductivity values;
Recharge only along dunes;
Boundary with Triffa aquifer set as constant flux, constant concentration;
Boundary with marls set as constant concentration.
Steady state water table
Hydraulic head (m)
m
15
'
13
Computed
11
9
7
5
3
1
-1
-1
1
3
5
7
Observed
9
11
13
15
Salinity distribution
mg/l
Concentration (mg/l)
'
20000
Computed
15000
10000
5000
0
0
5000
10000
Observed
15000
20000
IPPC(2007) scenarios
Three IPCC emission scenarios were considered:
a) A1B scenario (the IPCC reference one); Business as usual;
b) B1 scenario, which shows the smallest variations in temperature and sea
level rise; renewables and energy efficiency;
c) A1FI scenario, which is the worst case scenario.
Changes in recharge rate
Present-day recharge estimated using a monthly water balance;
Rate of change of precipitation and temperature used to estimate the
changes in the evapotranspiration according to Turc’s equation;
Rate of change recharge found considering that run-off in the area is
negligible. The largest variation is found for scneario A1FI, with 47%
decrease in recharge.
Source: Melloul
(2007)
2
ETR   P 0.9  P 2  300  25T  0.05T 3  


1 2
Stresses imposed by Climate Change
a) sea level rise – the effect of which is incorporated by changing the
constant head value in the Mediterranean boundary;
b) advance of the seashore line – the new location of which is found
from a digital terrain model;
c) variation of recharge – input as linear decreases with time;
Table 1. Stresses imposed by climate change
IPPC
scenario
B1
A1B
A1FI
Temperature
change (ºC)
1.1
2.8
6.4
Sea level
rise (m)
0.18
0.35
0.59
Precipitation
decrease
6%
12%
38%
Recharge
decrease
9%
19%
47%
Observations
B1 lower values
A1B mean values
A1FI higher values
Decrease in groundwater level – 100 years
A1FI scenario
•Maximum decrease in groundwater level
around 0.9 m at the southern limit of the
aquifer;
•In the Saidia city and in the area of the
tourist resort, water levels with increase up
to 0.4 m;
Decrease in groundwater level – 100 years
•at the main pumping area close
to the Moulouya river, drawdown
will increase by 0.7 m.
'
0
-0.1
Hydraulic head (m)
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
-0.8
0
5000
10000
15000
20000
Time (days)
25000
30000
35000
Decrease in groundwater level – 100 years
A1B Scenario
Decrease in groundwater level – 100 years
B1 scenario
Changes in salinity
A1FI scenario
•Salinity increase is restricted to a very narrow area near the freshwater/saltwater
interface, with the remainder of the aquifer maintaining its mean salinity;
•Close to the Moulouya salinity may decrease, due to added contribution of
leakage from the river of the aquifer and decrease in discharge from the Triffa
aquifer.
Changes in salinity
A1FI scenario
Conclusions
main effect of the climate change in the Saïdia aquifer will be a decrease in
renewable resources of up to 48%, considering only the variation of recharge;
if changes in contribution for the Triffa aquifer is considered, renewable
resources could decrease by up to 60%;
water quality will be affected mostly in the area immediately adjacent to the
advancing seashore;
Localised areas may see a small decrease in salinity due to the added inflow
freshwater from the Moulouya and diminished inflow from high salinity springs
(Ain Chebaak and Ain Zebda).
But:
The situation in the field is changing considerably:
A field trip during last month, showed that groundwater level is rising in the area
close to Saidïa city. Problems of inflow to cellars have been reported.
This is probably an effect of land-use changes and irrigation pratices (to
maintain golf-courses?).