1. Climate change impact on coastal aquifers in France –vulnerability of coastal aquifers due to sea level rise Nathalie Dörfliger Head of Water division per interim brgm, Orléans – France Workshop “Climat Change Impacts on Groundwater” Warsaw, Poland, 12th October 2011

2. Background Sea level rise
According IPCC (2007) respectively Cazenave & Llovel, (2009) at global level : : 3,1 ± 0,7 mm/year and 3,4 ± 0,4 mm/year for
According to IPCC (2007): 18 to 59 cm from scenario B1 to scenario A1FI for to
At French Metropolitan level: between 1 and 2,5 mm/year for period; for overseas territories: short time series (less than 10 years)
Selected sea level variations: 0,2cm, 0,6cm, 1m and + 2m to study the impact on coastal aquifers.
Source: LEGOS/GOHS
Spatial distribution of the sea level variation velocities ( ) based on Topex/Poseidon and Jason-1 : Zoom on the Mediterranean sea.
Source :
Spatial distribution of the sea level variation velocities ( ) based on Topex/Poseidon and Jason-1 data

3. Background
Which vulnerability on coastal aquifers in Metropolitan France and in the Overseas French territories ?
Which impact of sea level variation on sea water intrusion on coastal aquifers ?
How to identify vulnerable aquifers at national level considering various types of aquifers and > 5000km coastline length ?
Chang et al. 2011

4. Methodology at national and regional level
Coastal aquifers status
Metropolitain France and overseas territories
State of knowledge of coastal aquifers
Data base and mappping
Selection of coastal aquifers for modelling
Vulnerability mapping at various scales
Groundwater modeling at aquifer scale
Methodological development
Tests at regional scale
Groundwater modeling on two aquifers
Interpretation
Recommendations
Results interpretation
Recommendation in terms of management and survey before adaptation solutions 1 2 3
Considering:
Sea level rise scenarios
Not considered directly:
CC on recharge and precipitation patterns
Water demand increase on coastal areas

5. Vulnerability mapping of coastal aquifers at national level
Mapping of the coastal aquifer area (5km width)
Classification of sensitivity to present sea water intrusion
Mapping of point data of salinity of groundwater
Mapping of low elevation areas with Digital topography model
Impact of sea level rise considering two up to three classes
Demographical pressure mapping as well water supply works density
Vulnerability mapping of coastal aquifers at national level for sea level rise

6. Sensibility of coastal aquifers
BDLISA GW referential entities
Selection up to 8 regional areas to carry out GALDIT method and on one groundwater modeling
Caen coastal plain
Marais Poitevin
Garonne estuary
Roussillon plain
Crau aquifer – Rhône Delta
Var alluvial aquifer

7. Vulnerability mapping at regional scale
GALDIT method (Ferreira et al., 200; CHACHADI and LOBO-FERREIRA (2005))
Paramètres
Weight
Ranking
Very Low
Low
Middle
High
2.5 5
7.5 10
G : Groundwater occurrence – aquifer type 1
Bounded aquifer
Leaky confined
unconfined
confined
A : aquifer hydraulic conductivity (m/day) 3
< 5
5 - 10
10-40
> 40
L : GW level depth/ sea water level (m) 4
< 1
1 – 1.5
> 2
D : Distance to the coast (m) 2
< 500
> 1000
I : Impact of sea water intrusion (ppm)
T : Thickness of the aquifer (m)
5 – 7.5
7.5-10
> 10
Vulnerability classes
GALDIT index
High vulnerability
> 7.5
Mean vulnerability
5 – 7.5
Low vulnerability
< 5
D _ map
G_ map
Final vulnerability map

8. GW modeling Marais Poitevin
Similar GW abstraction volumes at present day
Only in first approximation hydrodynamic simulation + 1m for sea level increase
High water stage dry year
Low water stage dry year
Initial
+ 1 m
Impact on several kilometers inland
High impact for low water stage and dry years
Further GW modeling integrating salinity data, under progress

9. Vulnerability mapping at regional scale Example in Overseas Territories
GALDIT vulnerability classes
La Réunion Island
High vulnerability
Mean vulnerability
Low vulnerability
Impact of sea level rise on areas based on topography
< 0,6 m
0,6 to 2 m
> 2m to 4 m
> 1000 mS/cm

10. Comparison GW modeling and GALDIT method
Groundwater modeling
Reference
Groundwater modeling
Sea level + 1 m
Submersion areas
GALDIT – sea level + 1m
GALDIT– sea level + 2m

11. Conclusions and perspectives
Sea level rise will occur but demography pressure will play a major role on sea water intrusion on coastal aquifers
Uncertainties of climatic models on Overseas territories; less increase on Mediterranean Sea
Two levels of vulnerability mapping: national and regional
GALDIT method gives a first approximation in comparison to GW models; further works under progress to improve the method
Needs to link with demography pressure on water captures abstraction volumes
Focus on high vulnerability areas to implement dedicated GW salinity monitoring network
Thank you for your attention !