Environmental Engineering Reference
In-Depth Information
appear in wells, degrading crops and soil over large areas. Furthermore the recycling of
irrigation water through salty soils continually increases the amount of dissolved solids in
the ground water.
There are several important aquifers around the Mediterranean, and many regions are
dependent upon them for their supplies of drinking water, and supplies for industry and
irrigation. Table 26.3 shows the importance of groundwater as part of the total water
resources of the Mediterranean part of four countries. Spain stands out as a country where
the annual consumption of water is higher than the total groundwater resource. Increased
pumping from an aquifer will cause a lowering of the groundwater level around the point
of abstraction, to cause a 'cone of dejection' in the water table. Upconing of saline water
occurs below boreholes, owing to pumping. In the worst cases of massive overpumping
from a large number of wells a regional reversal of hydraulic gradients takes place. The
process is slow but virtually irreversible, and once an aquifer has been invaded by saline
water it is extremely difficult to restore the quality of fresh water. A salt-water aquifer
has no value for irrigation or potable supplies. Serious intrusion has been reported from
all along the Spanish Mediterranean coastline (especially the Campo de Dalias in
Almeria), from Italy (Sardinia), from Greece (Argolides), from France (Roussillon and
Var), from Lebanon and from Libya (Tripolitania). Control of seawater intrusion can be
achieved by a modification of pumping (moving wells inland and/or reducing
abstraction) to re-establish a stronger seaward hydraulic gradient. Artificial recharge of
the aquifer is possible by constructing recharge barriers to cause surface spreading or by
digging recharge wells. These control measures are very costly, however, and in many
cases the only option is to cease using the aquifer and to develop entirely new sources. As
the lower reaches of rivers become controlled
Table 26.3 Water resources and consumption
(10
9
m
3
yr
−1
)
Country
Total resource
Groundwater resource
Total consumption
Spain
31·0
9·1
12·2
France
74·0
31·0
2·0
Greece
58·6
12·0
3·7
Italy
187·0
30·0
14·8
and diked, natural flooding is prevented, and thus a pathway of natural recharge is
removed.
The dominant factor behind water problems, however, has been the continual
intensification of agriculture since the 1960s. Agriculture has changed from the
traditional dry farming of cereals and olives, with some vegetable growing and sheep and
goat grazing, to dominance by vegetable and orchard fruit production, particularly citrus.
These new crops require irrigation. Agricultural technology has responded by using more
and more powerful water pumps - from hand, through animal to diesel and electrically
driven pumps; this technology has enabled water to be obtained from depths in excess of
400 m. Deeper and deeper wells are required to keep pace with declining water levels,
and there is increasingly a problem with the quality of this deeper water.
