The UNESCO-IHP project demonstrated a methodology for mapping the vulnerability of coastal aquifers to both vertical pollution from the surface and horizontal saltwater intrusion. The project mapped the comprehensive vulnerability of the Ghar El Melh coastal aquifer in Tunisia in a single parameter. It considered the aquifer's intrinsic properties that provide defense against these threats, such as groundwater levels and the aquifer's specific energy to resist saltwater intrusion. The resulting comprehensive vulnerability map integrated these factors with human activities data to provide a planning tool for safeguarding groundwater resources. The demonstrated methodology can be applied to other Mediterranean coastal aquifers.

1. UNESCO-IHP vulnerability mapping
demonstration project at the Ghar El
Melh coastal aquifer in Tunisia
Dott. Salvatore Carrubba
Consultant Geologist

2. Ghar El Melh Coastal Aquifer
Studied Area
UNESCO-IHP undertook this project to demonstrate the use of
vulnerability mapping at the Ghar El Melh coastal aquifer,
about 50 km North of Tunis

3. VULNERABILITY MAPPING IN COASTAL AREA
In coastal area we must consider two components of the evaluation of
aquifer vulnerability:
•vertical vulnerability against vertical pollution from surface
•and horizontal vulnerability due to the salt water intrusion phenomena.
Sea salt water is heavier than fresh water and in coastal area, it, can
intrude itself into the aquifer flowing under the fresh water (of the
aquifer) in a delicate equilibrium of weights
• At the moment there are many methods for
studying vertical vulnerability, but there are
no methods for studying horizontal and
vertical vulnerability at the same time.

4. VULNERABILITY MAPPING IN COASTAL AREA
The goal of the UNESCO-IHP project is to create a single
parameter – “comprehensive vulnerability” – able in
describing simultaneously these two types of vulnerabilities

5. Simplifying the hydro geological model, the main aquifer is constituted by the “Grès de
Porto Farina” (Upper Pliocene) that are sands and calcarenite, each other mixed.
This aquifer is a multilayer aquifer and this aquifer is in hydraulic connection with
the "younger" permeable deposits and sea water.
On the other hand the “Marnes de Raf Raf” (Pliocene) are impermeable clays
rocks and constitute the bed of the aquifer.
m3 - mc2 - mb2
- ma2 - mab2
m'1
P'a
P'b
a
D – qm2 – Aa
– qm1 – q"
SCHEMATIC HYDRO GEOLOGICAL MODEL
groundwater level
Ghar El Melh Coastal Aquifer

6. VULNERABILITY MAPPING IN COASTAL AREA
• Keeping in mind that vulnerability is an intrinsic
characteristic of the aquifer in defending itself from
an external threat that can be a pollutant or a
contaminant.
• we must look for the intrinsic characteristics of the
aquifer that can be able in opposing to a pollutant
from surface or to a contaminant like salt water
intrusion.

7. VERTICAL VULNERABILITY MAPPING
Ghar El Melh Coastal Aquifer
m3 - mc2 - mb2
- ma2 - mab2
m'1
P'a
P'b
a
D – qm2 – Aa
– qm1 – q"
SCHEMATIC HYDRO GEOLOGICAL MODEL
groundwater level
Elevate Vertical Vulnerability Grade
Low
Vulnerability
The natural intrinsic physical properties of an aquifer that can
protect it from a pollutant coming from surface
(VERTICAL VULNERABILITY) are:
Depth-to-Water,
Infiltration range,
Attenuation action
of unsaturated zone,
Soil attenuation capacity,
Aquifer types,
Hydraulic Conductivity,
Slope,
Other intrinsic characteristi

8. Ghar El Melh Coastal Aquifer

9. HORIZONTAL VULNERABILITY
MAPPING IN COASTAL AREA
The main “defence” that aquifer has in opposing sea
salt water intrusion is the aquifer specific energy that
is linked to groundwater level. In fact, more fresh
groundwater level is higher above sea level, and more
able the aquifer will be in opposing salt water
intrusion pushing out salt water

10. HORIZONTAL VULNERABILITY MAPPING IN
COASTAL AREA
Aquifer specific energy is the main “defence” that aquifer has in
opposing sea salt water intrusion
ElevateVulnerabilityGrade.
In this part of the aquifer
groundwater level is the
same of sea level. Aquifer is
fully exposed to the "threat"
and don't have any “means
of defence" for pushing out
salt water

11. HORIZONTAL VULNERABILITY
MAPPING IN COASTAL AREA
All the areas of the aquifer where
groundwater level is above sea level and
the bottom of the aquifer is under sea
level
ElevateVulnerability
Grade
High Vulnerability Grade
In this areas it is
probable that salt water
is naturally under fresh
water and human
activities can increase
salt water intrusion and
mix salt and fresh water.

12. HORIZONTAL VULNERABILITY
MAPPING IN COASTAL AREA
Naturally it is improbable that salt water can
contaminate fresh water but human
activities can induce salt water intrusion or
soil salinization.
Elevate
VulnerabilityGr.
High Vulnerability Grade
Medium
Vulnerability
Grade
Low
VeryLow

13. HORIZONTAL VULNERABILITY MAPPING
IN COASTAL AREA
GHAR EL MELH
COASTAL AQUIFER

14. VULNERABILITY MAPPING IN COASTAL AREA
1
1
4 0
0
2
3
4
7
6
1
1
8
COMPREHENSIVE VULNERABILITY MAP

15. COMPREHENSIVE VULNERABILITY MAP
GHAR EL MELH COASTAL AQUIFER
This map is an integrated vulnerability map because human activities data are also plotted:
the pollution sources (punctual or diffused);
subjects at contamination risk (target of pollution);
Drainage network.

16. COMPREHENSIVE VULNERABILITY MAP
GHAR EL MELH COASTAL AQUIFER
– Therefore, this map is a great instrument for territory planning and for safeguarding environment
and groundwater resources against pollution and overexploitation.
– The methodology developed for mapping the “comprehensive vulnerability” of this system is a
new concept and could be replicated at other Mediterranean coastal aquifers.

17. Thank you for your attention
Merci pour votre attention
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