Jökull - 01.12.1983, Síða 129

During the 30 years period of flow recording
dwelling houses in Selfoss have been flooded 5
times, three times in February, once in March and
once in April. It should be pointed out that two of
the largest floods in this century were before the
period of mesurements. They were on 2nd March
1930 and 5th March 1948. The figures 3000 and
2800 m'/s have been calculated. In neither case the
flow was hindered by ice but the main flood came
from the highland. Other damaging floods were the
winter floods of 1906 and 1934 and the autumn
flood of 1933, making a total of 10 in this
century.
From the previous century, large floods in 1864
and 1889 are well recorded. They were both winter
floods.
The flood period in the last days of February 1968
was first and foremost in the southwest part of the
country; less water came from the highlands inland
than in other floods. On the other hand there was a
sudden and dangerous flood from the highlands on
7th February 1960. However it was of such a short
duration that the water accumulation above the
first and second obstacles in Hvítá river (described
above) reduced the main peak of the flood before it
reached the Olfusá river.
The only flow control possible under the present
conditions is to close off the flow from Lake Thing-
vellir, which would reduce large floods in the Ölfusá
river by about 1/30. To understand properly to
what extent large íloods are greater than everyday
conditions it is not too farfetched to consider that in
flood run-off the Olfusá river transports the equi-
valent of a day’s water supply for Selfoss, a town of
3500 inhabitants, every 1/2 to 3/4 ofa second.
In the 30 year period the Hvítá river has flooded 5
times over the main road round Iceland 10 kilo-
meters east of Selfoss (see Figs. 1 and 4).
Very probably the Hvítá river will be allowed to
flush its way through Skeid and Flói until its flood
water is directed to the Thjórsá river. Selfoss can
protect itselfagainst this flood intrusion by building
a dyke on a section above and below Ölfusá bridge
on the east side. The local conditions next to the
river ofler easy walks and are suitable for bicycle
paths, and this area would be surmounted by the
protective dyke itself 1 to 2 meters high and planted
with trees for the pleasure of all.

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Fig. 6. Not all floods roar downstream as broken, noisy water. This peaceful water stretch in front of
Selfoss church on the leap year day’s flood of 1968 is a supplimentary water stage as a result of pack-ice
dam a short distance below Selfoss. (Photo. Sveinn Sveinsson).
6. mynd. Ekki beljar allt jlóðavatn fram með boðafóllum og látum. Þessi friðsæla vatnsfylla framan við Selfosskirkju í
hlaupárdagsflóðinu 1968 stafar meðal annars af ísstíflu í Ölfusá skammt fyrir neðan Selfoss. (Ljósm. Sveinn Sveinsson.)
JÖKULL 33. ÁR 127