The impact of climate change on ground water recharge in karst and carbonate rocks: Task 5.3.4

The following activities will be developed at selected case studies

in the Mediterranean region:

a) Identification and analysis of ground water trends in the past decades

b) Application of selected climate scenario and forecast for the future decades

Groundwater trends in the past decades

The identification of case study will be performed on the basis of

• i) available data;• ii) significantly, as for hydrogeological

features and quantitative pressures.

Part of the effort will be devoted to the data collection (meteorological, hydrological, piezometric levels, etc). Data analysis will be supported by statistical methods

Aquifer levels recorded at 3 wells

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8

gen-66 set-66 mag-67 ge n-68 set-68 giu-69 feb-70 ott-70 giu-71 feb-72 nov-72 lug-73

m a

.s.l.

avilable data at 3 s ites with different elevations

What is the What is the response of groundwater response of groundwater to such a meteorological cycle?to such a meteorological cycle?

What is the quantitative What is the quantitative interplay between drought, recharge decrease and interplay between drought, recharge decrease and increased groundwater overexploitationsincreased groundwater overexploitations??

Aquifer levels Aquifer levels seem to have no particular recovery after the observed wet set.seem to have no particular recovery after the observed wet set.

Model forecast

Mathematical models will be run under different climate scenarios in order to forecast the future decades evolution of groundwater availability (discharge and storage) in relation to the selected case study.

The model will be able to define the reduction of coastal aquifer volumes due to the increase of seawater intrusion as a consequence of groundwater overexploitation.

Variation on groundwater storage during years

Microsoft Excel Worksheet showing the computation of the intrusion extent Li

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2000

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-5000 -2000 1000 4000

Xi (1999) m

Xi (1980) m

Dis

tanc

e pa

ralle

l y (m

)

y

Distance from coastline (m)

x

Xcoast

Plot of 50% saltwater/freshwater interface with respect to the coastline by using the model equations and its transformation to the position Xi by mean of the coordinates of the coastline (Xcoast).

Model development

z

x

Li=L-Lid

Lid= available length estimated by computational code (step 1)

L= minimum extent required to avoid seawater intrusion given by Eq. (8) (step 2)

Set of parallel fractures with the same mean aperture bm = seawater

intrusion extent Freshwater

Ghyben-Herzberg sharp interface model

X=L

Offshore spring Inland spring

Hs

Spring at coastline

Idealization of the parallel set of fractures and Ghyben-Herzberg sharp stationary interface under Dupuit assumption (horizontal motion).

Seawater extent, L:

δδφ

μγ

δ 2H)(

12b

n2

HBKLQ

2s

20

f

f2

m2s

2

0

• Hs (m) is the depth (below the sea surface) at the outflow section of the 50% sharp interface saltwater/freshwater. Obviously, Hs=0 can also be set for zero discharge;

•B(m) is the saturated aquifer thickness where =0 ;

bi (m) is the sum of the all horizontal apertures in the vertical aquifer column, while Nf is the total number of the horizontal fractures in the saturated thickness B.

δφγγ

γφ

fs

f)x(H

B

bn

fN

1ii

Evaluation of seawater intrusion extent into freshwater, in vertical plans ZX at distance y between them, in order to locate the three-dimensional development of the intrusion.

Preliminary flow solution:

Comparison of the freshwater outflow zones at Torre S. Isidoro: (a) springs monitored by Cotecchia (1977: 145-158); (b) springs visualized by Landsat Thematic Mapper photo (1997); (c) springs zones defined

by computational procedures (1980 and 1999).

Torre S. Isidoro

(a) (b) (c)

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1999 1980

x y

0 3 km o

Potential study areas

Geology

Monitored coastal springs

Trend of groundwater salinity