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. RimiScientific Institute, Rabat, Morocco

B. El HouadiHydraulic Basin Agency of Moulouya, Oujda, Morocco

م

Algeria

SaidïaAtlantic

Mediterra

nean

Location of the study area

Northeast Morocco, at the border with Algeria

Mediterranean coast, the Alboran sea

Coastal plain with about 30 km2

Location of the study area

Mediterranean

Saïdia

Oued Moulouya

Oulad Mansour hills

The Saïdia aquifer is exploited for irrigation purposes.

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.

Ain Chebbak and Ain Zebda

Oued Kiss

Motivation for the study

Mediterranean

Saïdia

Oued Moulouya

Oulad Mansour hills

The area is undergoing fast changes in land-use

Planning did not take into account sea-level rising and likely salinity increase

Several golf courses planned. Irrigated areas will increase considerably

Objectives and MethodologyObjective

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

Marls with gypsum sands

Mud layerMud layer

Seadune

dune

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

First dune

Second dune

Mud layer

Mud layer

Moulouya flood plain

Marls with gypsum

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 sourcesBased 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)

-1

1

3

5

7

9

11

13

15

-1 1 3 5 7 9 11 13 15

Observed

Com

pute

d

'

m

mg/l Concentration (mg/l)

0

5000

10000

15000

20000

0 5000 10000 15000 20000

Observed

Com

pute

d

'

Salinity distribution

IPPC(2007) scenariosThree 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

1 222 30.9 300 25 0.05ETR P P T T

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)

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 Temperature change (ºC)

Sea level rise (m)

Precipitation decrease

Recharge decrease

Observations

B1 1.1 0.18 6% 9% B1 lower values A1B 2.8 0.35 12% 19% A1B mean values A1FI 6.4 0.59 38% 47% 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.

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0 5000 10000 15000 20000 25000 30000 35000

Time (days)

Hyd

raul

ic h

ead

(m)

'

Decrease in groundwater level – 100 years

A1B Scenario

Decrease in groundwater level – 100 years

B1 scenario

Changes in salinityA1FI 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

Conclusionsmain 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?).