Jökull - 01.12.1986, Blaðsíða 29

freshwater resources of the Reykjanes peninsula must
be utilized in a well organised and coordinated
manner, which almost certainly implies some ad-
ministrative control.
CONCLUSIONS
The groundwater of the Reykjanes peninsula is very
important from a national point of wiev, because it is
the reservoir for the freshwater supply for 60% of the
population of Iceland i.e. 150.000 inhabitants (fig. 2).
This reservoir is also exploited by Suðurnes Regional
Heating (heated freshwater for 20,000 inhabitants)
and is in increasing demand for fishfarming and
various other industries. These demands have at pre-
sent reached several m3/s, while the communal ex-
ploitation is near to 2 m3/s.
This groundwater reservoir is plentiful because of
the high precipitation in the area (1000—3000 mm/y,
see fig. 4) and the high permeability of the young, vol-
canic rocks (hydraulic conductivity 10"4 — 10"’ m/s)
°f which the peninsula is composed (fig. 3). The
permeability is still enhanced by the fissure zones
running SW-NE across the volcanic zone stretching
WSW-ESE along the peninsula, as well as the fissure
zones alongside its northern margin (fig. 5). Some high
temperature geothermal fields are located in the vol-
canic zone. Where they have caused a strong alter-
ation of the rocks, the permeability is drastically
reduced. On the extensive lava fields in the western
Part of the peninsula and at its northern coast the
groundwater level is low, only 1—3 m asl., so that
there the freshwater is floating in a thin layer,
30-100 m thick, on sea water in the rocks (fig. 12).
By excessive pumping from the freshwater layer
upconing of the sea water can take place, resulting in
contamination of the freshwater.
East of lake Kleifarvatn the groundwater level rises,
probably up to 200 m asl., perhaps because of an up-
damming by the geothermally strongly altered rocks
to the west of the lake.
The freshwater is usually clean and of a good
Quality. The temperature is low, 3 —5°C. The chemi-
cal content is also rather low, with a marine factor
from the precipitation, expressed in the chloride con-
tent (10—60 ppm) and a factor from reactions with
the rocks (silica 10—20 ppm) (fig. 14). Higher concen-
trations are found in the off-flow zones from the
geothermal fields (fig. 15) where the temperature also
rises up to 7— 10°C, and near to the coast, where
salinity increases due to tidal effects on the thin fresh-
water layer (fig. 16). At present the bulk of the fresh-
water is not polluted because the settlements and
industrial activities are all located at the coast. On the
other hand the freshwater is very vulnerable against
pollution because a vegetation and soil cover is thin
or lacking on the peninsula. It is therefore urgent to
take some measures to prevent pollution from e.g.
quarrying and outdoor activities.
Some measures must also be taken regarding the
quantitative exploitation of the freshwater. The re-
sources are sufficient for decades to come for the
communal uses, but the increasing demands from
fishfarming and industries could turn the scale in a less
favourable way. Supply from outside the peninsula
would then be both very expensive and difficult so it
is necesssary to preserve the freshwater reservoir for
future supply to the municipalities. This could per-
haps be done with a long-term plan of exploitation,
where the supply of communal needs were preferen-
tial.
ACKNOWLEDGEMENTS
Thanks are due to the Suðurnes Regional Heating
and Iceland Salmon Ltd. for the kind permission to
use the data obtained in investigations on behalf of
these companies.
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