Náttúrufræðingurinn - 1998, Side 30

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■ SUMMARY
Groundwater in the StraumsvíkArea
At Straumsvík, immediately southwest of the capi-
tal area of Iceland, about 10 m3/s of groundwater
issue into the sea from highly permeable lavas. The
flow into the Straumsvík bay alone is approx. 5 m3/
s. This groundwater constitutes a natural resource
of vital interest to the capital area, where 60% of
the total population live. The Straumsvík bay is a
remnant of a former bay, stretching probably about
4 km inland, which has been filled with basaltic and
very permeable lavas in postglacial times. This
former bay continues as a lava-filled depression,
cut by active fissure swarms with a SW-NE trend
and extending far to both sides. These direct the
groundwater flow towards the depression, where it
gathers in a very strong groundwater current, issu-
ing at Straumsvík (Freysteinn Sigurðsson 1976,
1986).
The groundwater basin has an areal extension of
150-200 km2, probably closer to the lower margin.
The precipitation ranges from 1,000 mm/year at
the coast to over 3,000 mm/year in the mountains.
The area is mostly covered by postglacial or inter-
glacial lavas and hyaloclastite hills and mountains,
all highly permeable. Surface runoff is practically
absent, the precipitation being almost completely
infiltrated. The runoff rate of the groundwater is
correspondingly high, resulting in a total runoff of
8-14 m3/s, presumably close to or exceeding 10 m3/s.
A similar value is obtained from the estimate of the
coastal outflow, or 6-15 m3/s, most probably 10-
11 m3/s. The very same valuc is obtained from hy-
drological models of the the Reykjanes peninsula
(Vatnaskil 1991).
The quality of the water is excellent. The water
basin is almost completely uninhabitated, though
only sparsely vegetated. The chief sources of pos-
sible pollution are the various enterprises and rec-
reation sites located on the fiat lava fields south of
Straumsvík. An aluminium plant (Icelandic Alu-
minium Company, ISAL) on Straumsvík bay has
not been shown to pollute the groundwater farther
inland; as for other enterprises and the rallye-cross
fields l'urther upstream from the bay, there is no
certain knowledge about this. The least damage
would be done by siling potential pollution sources
as close as possible to the coast, which should be
included in all future planning of the area, to en-
sure proper conservation and exploitation of the
unique groundwater source at Straumsvík.
PóSTFANG HÖFUNDAR/AuTHORSAdDRESS
Freysteinn Sigurðsson
Orkustofnun
National Energy Authority
Grensásvegi 9
1S-108 Reykjavík
188