Jökull - 01.12.1980, Síða 25

SAMPLING AND QUANTITY OF
SUSPENDED SEDIMENT LOAD
Samples of suspended sediment load have
been taken in Skeiðará occasionally since 1956
as well as in the jökulhlaups of 1938, 1954,
1960, 1965, 1972 and 1976. From 1963 the
grain size distribution of the suspended load
has been measured; up to that time only the
total quantity of each sample was observed.
The samples can be divided into 3 classes
(F, S1 and S3) according to the mode of
sampling, see explanatory notes on Table 1.
The S1 samples expectedly yield the most
accurate measure of the load carried by the
river, while F-samples are the least reliable of
the three types.
Up to the end of 1965 only F-samples were
taken. During 1966 to 1973 very few samples
were collected except in the jökulhlaup of
1972; all samples were then of the S3 type.
Since the building of the bridge across Skeið-
ará in 1974 it has been possible to sample in
several vertical sections (Sl-samples) from the
bridge as well as from the riverbanks (S3- and
F-samples) enabling us to compare the dif-
ferent sampling methods.
Samples were taken in the 1976 jökulhlaup
both from the bridge and from land at the
bridge site as well as the outlet (at glacier) and
at 10 km distance downstream of the bridge.
All the S3-samples were collected at the west
bank. Furthermore, F-samples were taken at
the eastern bank at Skaftafell for comparison
TABLE 1 Quantity of suspended sediment in Skeiðará jökulhlaups.
TAFLA 1 Magn svifaurs í Skeibarárhlaupum.
Year and location of sampling Millions Sample Numbers of Estimated total
Ár og tökustaður tons type samples discharge
Milljónir Tegund Fjöldi Áœtlað heildar-
tonna sýna sýna rennsli, km3
1938 Skaftafell * co F 2 7 *
1954 Outlet/Útfall 29* F 9 3.5*
1960 Above Morsá tributary/ ofan Morsár 31* F 9 3*
1965 Above Morsá tributary/ ofan Morsár 17* F 11 3*
1972 Several locations/ nokkrir tókuslaðir 24 S3 34 2.4
1976 Outlet/Útfall 15 S3 8 2.4
1976 Skaftafell 11 F 15 —
1976 Bridge//ra 13 S3 10 —
1976 Bridge/brú 21 S1 15 —
1976 10 km downstream of bridge/ 10 km neðan brúar 14 S3 7
* Total for the Grímsvötn jökulhlaup. /öllu Grímsvatnahlaupinu.
Explanation of sample types: F-samples are collected near the river banks into bottles
without a sampler. S3-samples are collected near the river banks into bottles in a depth-
integrating sampler. Sl-samples are collected in several verticals from the bridge into
bottles in a depth-integrating sampler.
Skýrmgar á tegundum sýna: F-sýni eru tekin við bakka í venjulegar flöskur. S3-sýni eru tekin við
bakka í flöskur í sýnataka. Sl-sýni eru tekin í nokkrum lóðréttum sniðumfrá brúnni í flöskur í sýnataka.
JÖKULL 30. ÁR 23