Jökull - 01.01.2009, Side 27

Chemical and mechanical fluvial denudation in cold environments
Table 5. Peak runoff events and fluvial suspended sediment transport in Kidisjoki. – Leysing og aurburður í
Kidisjoki.
Year Runoff Reason Total Percent of Total Percent of SSC max SSC mean Percent of
peak for sediment annual runoff mean annual during during annual mean
runoff yield mechanical during runoff peak peak mechanical
peak during denudation peak (324 mm) denudation
peak
[t km!2] [mm] [mg l!1] [mg l!1] (0.25 t km!2)
2002 1 Snow 0.23 85 85 26 21.22 2.79 92
melt
2003 1 Snow 0.21 95 68 21 16.74 3.07 84
melt
2004 1 Snow 0.21 95 79 24 13.79 2.78 84
melt
2005 1 Snow 0.24 77 98 30 18.44 2.50 96
melt
2006 1 Snow 0.20 91 71 22 22.54 3.39 80
melt
2007 1 Snow 0.22 88 81 25 20.32 2.72 88
melt
Annual mean
2002 – 2007 0.22 89 80 25 18.84 2.88 87
the snow pack, infiltration of melt water and storage
are inhibited at the time of most intensive snowmelt
(Dankers, 2002; Beylich and Gintz, 2004; Beylich et
al., 2006b). The resulting peak runoff mobilises the
debris pavement of the main creeks within the catch-
ment. An additional sediment source of significance
is a gravel road through the valley (Beylich et al.,
2006b). The total suspended sediment yields during
snowmelt generated peak runoff in the years 2002–
2007 in the Kidisjoki catchment are presented in Table
5. The maximum suspended sediment concentration
during the annual snowmelt generated peak runoff
events was 17–28 times higher than the mean annual
suspended sediment concentration in 2002–2007. Be-
tween 80 and 96% of the mean annual total mechani-
cal denudation occurred during the annual snowmelt-
generated peak runoff. Summer rainfall events only
moderately increased runoff due to infiltration and
storage in the forested areas of the catchment.
In the Latnjavagge catchment, the snowmelt- and
rainfall-generated runoff peaks show significant dif-
ferences in the mean and maximum suspended sed-
iment concentrations (Table 6). These differences
are mainly caused by still-existing ground frost be-
low the snow pack during the snowmelt generated
runoff peaks (Beylich and Gintz, 2004). The frozen
ground, preventing the infiltration of melt- and rain-
water, causes a concentrated surface runoff in creeks
and channels and, as in the Kidisjoki catchment, a
mobilisation of channel debris pavements exposing
fine sediments. In addition, permanent ice patches
and material mobilised by slush flows and ground
avalanches are relevant sediment sources during the
snowmelt period (Beylich and Gintz, 2004; Beylich
et al., 2006a). During heavy summer rainfall events
in 2000, 2002 and 2005 rainwater infiltrated the partly
frozen regolith. However, the saturation overlandflow
observed in the lower slope areas did not show a
concurrent increase of suspended sediment concen-
trations in the creeks due to the continuous and sta-
ble vegetation cover of the slope systems (Beylich and
Gintz, 2004).
The geomorphic effects of a rare rainfall event on
July 20–21, 2004, triggering debris flows and other
erosive processes within the catchment are discussed
in detail in Beylich and Sandberg (2005), Beylich
et al. (2006a) and Beylich (2008). The relative im-
portance of the different runoff peaks for suspended
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