Jökull - 01.12.1988, Blaðsíða 38

is mainly from rainstorm floods and from snowmelt.
A heavy soil erosion is a problem of increasing con-
cem, as the vegetation cover is slowly but steadily
decreasing. Possible reservoirs for surface water
supply, mostly small lakes, are unreliable, and sea-
sonal variations in surface ranoff are fairly large.
Regional differences exist in the availability of
freshwater, mostly related to the pronounced hydro-
geological differences between the Late Quatemary
- Recent Volcanic Zones and the older, Tertiary and
Early Quatemary, formations. Local factors, as for
instance rock slides or fluvio-glacial sediments, can
also be decisive for the relative scarcity or abun-
dance of hamessible freshwater, as well as for the
methods of extraction.
As the difficulties in water supply have increased,
costs have been rising. At the same time the food
industry has made demands for higher quality clean
water. Recent investigations of groundwater have
been initiated primarily because of increased exploi-
tation. Consequently the vicinities of urban settle-
ments and other settlements with urgent needs are
the most explored (Sigurðsson, 1986).
As the present growth of water consumption
progresses, the necessity of an organized national
water administration is becoming evident. This
administration must encompass all necessary aspects
and means in order to protect this vital, national
resource from pollution, as well as providing means
for dividing it according to public interest, when and
if it gets limited locally. In view of previous experi-
ence in the industrialized countries, especially in
Westem Europe, this development is not at all
surprising. The first step is in sight, as a Ministry of
Environment will be formed in Iceland in 1989.
In the following chapter some aspects of the
groundwater hydrology and the hydrogeology of
Iceland are dealt with, as well as the principal
classification and distribution of the groundwater
regions. This serves as a basis for a separate chapter
dealing with an evaluation of the present state of
freshwater exploitation in Iceland and some aspects
of its possible future development.
GROUNDWATER REGIONS OF ICELAND
CLASSIFICAIION
The quantitative properties of the groundwater
basins in Iceland depend in the first place on the
hydrogeological stmcture of the area in question
(Fig. 1). In that sense the bedrock of the country
may be roughly divided into two groups: The Terti-
ary and Early Quatemary formations, with a rela-
tively low permeability, and the Late Quatemary
and Recent formations, with a relatively high per-
meability (Sigurðsson and Sigbjarnarson, 1985), as
further dealt with in the following chapters devoted
to the bedrock. Different sedimentary aquifers
accompany the bedrock groups at large, those on the
Tertiary - Early Quatemary formations being the
principal exploitable aquifers in the corresponding
regions (Fig. 2), discussed further in the following
chapters on sedimentary aquifers and the quantity of
the groundwater.
Hydrological regime — The precipitation is very
high in Iceland, exceeding 3,000 mm/year in the
mountainous parts of southem Iceland, although it
may be less than 600 mm/year over wide stretches in
the northem part of the country (Sigfúsdóttir, 1976;
Tómasson, 1982). In the Late Quatemary Zone
infiltration is relatively high and surface runoff is
limited (Fig. 1). On the borders of this formation, or
in connection with fissure swarms cutting through it
(Fig. 3), numerous springs are found with a very
strong discharge (Fig. 4). Infiltration is, on the other
hand, minimal over most of the Tertiary - Early
Quatemary regions, most of the precipitation
flowing off as surface runoff, especially during the
snowmelt season in spring and early summer.
Hydrogeological formations — In the Late Quater-
nary - Recent Volcanic Zones the bedrock is usually
highly permeable, the numerous swarms of open
fissures still enhancing the permeability as well as
creating a strong anisotropy. The result is, that
springs are common in these formations, having a
plentiful discharge and a high seasonal stability. In
the older formations, Tertiary and early Quatemary,
the bedrock usually has a low permeability, widely
36 JÖKULL, No. 38, 1988