Jökull - 01.12.1980, Blaðsíða 30

station in the receding phase of the jökul-
hlaup. For discharge in this jökulhlaup see Rist
(1976).
In the jökulhlaup of 1972 S3-samples only
were taken, at several places, including two
stations (the outlet and bridge sites), where
samples were collected in 1976. Fig. 5 presents
sediment rating for samples obtained in 1972.
The correlation coefficient of the rating curve
(equation (1)) for all the samples taken in that
jökulhlaup is 0.697. If a few points from an
abnormal sediment load peak are omitted the
correlation coefficient rises to 0.913. The cor-
relation coefficient for all the S3 taken in 1976
is 0.924, or not very much better than in 1972.
For discharge see Rist (1973).
The sediment transport curves for two grain
size fractions, coarse and fine silt, are shown in
Fig. 6. The curves indicate a certain regularity
in the sediment load of the jökulhlaup of 1972.
First the load gradually increased, almost
simultaneously with the discharge, and
having reached a maximum it receded in a
fairly regular manner. Concentration on the
other hand varied greatly from one place to
another both as regards coarse and fine grain
sizes. The sediment load reached its maximum
at the outlet, but at the bridge site the
concentration is far less at the western bank
than at the eastern one.
Two or three days after the peak in the
discharge a short but marked peak occurred in
the sediment load. The samples taken in this
peak (discussed by Tómasson 1974) are the
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16 l 8 20 Daga Da 22 m a ys of smár Mar 24 aðar h /9 1972 72 26 28 30
Fig. 6. Coarse (0.2—0.02 mm)
and fine (0.02—0.002 mm) silt
in suspended load in Skeiðará
jökulhlaup 1972. Key: 1. coarse
silt at glacier outlet and Skafta-
fell; 2. coarse silt at dikes and
bridge site, eastern shore; 3.
coarse silt at bridge site, western
Iceland; 4. fine silt at glacier
outlet and Skaftafell; 5. fine silt
at dikes and bridge site, eastern
shore; 6. fine silt at bridge site,
western shore. — Mynd 6. Aurrit
mós (0.2—0.02 mm) og mélu
(0.02—0.002 mm) í Skeiðarár-
hlaupi 1972. 1. Mór við Otfall og
Skaflafell. 2. Mór við garða og
brúarstáði austurland. 3. Mór við
brúarstœði vesturland. 4. Me'la við
Otfall og Skaftafell. 5. Méla við
garða og brúarstœði austurland. 6.
Méla við brúarstceði vesturland.
28 JÖKULL 30. ÁR