Geology Reference
In-Depth Information
After the snowmelt period, runoff progressively decreases and discharge becomes
dominated by storm runoff. The latter occurs after heavy cyclonic activity or following
periods of prolonged overcast and drizzly conditions. The hydrologic response is rapid,
refl ecting the presence of permafrost and the absence of vegetation. Superimposed upon
these short-term fl uctuations are diurnal fl uctuations; discharge usually increases in late
afternoons and early evenings, or following periods of uninterrupted solar radiation.
During late summer, many small streams are virtually without fl ow and, by freeze-back
time at the end of the summer, there is little or no runoff. Any stream fl ow that does exist
is maintained almost entirely by recession fl ow from either groundwater discharge or from
seepage through the active layer. Icing ablation augments stream fl ow, particularly after
snowmelt (Clark and Lauriol, 1997; Kane and Slaughter, 1972; Reedyk et al., 1995; Sokolov,
1978; van Everdingen, 1987, 1990). In general, icing ablation in warmer regions generates
high fl ows for a short period of time while icing ablation in colder regions sustains a longer
period of fl ow.
It is diffi cult to generalize about the magnitude and frequency of fl ow events because
there is a lack of long-term data. However, a number of catchment studies, undertaken in
northern Canada by governmental and other regulatory bodies (Table 10.3), suggest that
annual peak fl ows and fl ow variability are highest for mountainous catchments fed by
glaciers and for catchments underlain by continuous permafrost. They are least for lowland
catchments in discontinuous permafrost terrain that include numerous lakes and extensive
wetlands. Almost certainly, similar general relationships exist for the northern rivers of
Eurasia.
Long-term fl ow measurements are usually accompanied by observations upon precipi-
tation, snow cover, and evaporation. Together, these data can be analyzed within a water-
balance context in which the various water gains and losses within the basin are examined.
Typically, snowfall constitutes the bulk of annual precipitation in northern catchments,
most runoff results from snowmelt, and the importance of snow declines in areas where
Table 10.3.
Mean annual discharge (Q) and standard deviation of fl ow (S) of selected rivers in
northern Canada. Q and S are measured in m
3
s
−1
km
−2
River
Drainage
Mean
Standard
Years
Environment
area
discharge
deviation
of
(km
2
)
(
Q)
(S)
Record
Kluane
4 950
0.0148
0.0027
30
Mountainous, glacerized,
discontinuous permafrost
(below lake outlet)
Klondike
7 800
0.0078
0.0016
18
Mountainous, discontinuous
permafrost
Kakisa
14 900
0.0026
0.0010
19
Interior plain, discontinuous
permafrost (below lake
outlet)
Thoa
9 630
0.0037
0.0010
15
Canadian Shield,
discontinuous permafrost
Dubwant
67 600
0.0049
0.0008
15
Canadian Shield, continuous
permafrost (below lake
outlet)
Freshwater
1 490
0.0050
0.0013
8
Arctic Islands, continuous
permafrost
Source: Woo (1986).
