Geology Reference
In-Depth Information
Table 10.1.
Mean freeze-up and break-up dates on the Mackenzie River system, NWT, Canada,
1946-1955. *See Figure 10.1 for locations.
Location
Distance from Great
Freeze-up
Break-up
Slave Lake (km)
Fort Providence*
1
80
24 Nov.
18 May
Fort Simpson*
2
:
(i) Mackenzie above
335
27 Nov.
15 May
Fort Simpson
(ii) Mackenzie below
351
11 May
Fort Simpson
Tulita (Fort Norman)*
3
825
15 Nov.
14 May
Norman Wells*
4
909
10 Nov.
15 May
Fort Good Hope*
5
:
(i) Ramparts
1094
15 Nov.
22 May
(ii) Settlement
1101
12 Nov.
15 May
Tsiigehtchic (Arctic Red River) settlement*
6
:
(i) Arctic Red River
1445
8 Oct.
25 May
(ii) Mackenzie River
1445
1 Nov.
24 May
Aklavik*
7
1607
9 Oct.
28 May
Reindeer Station (north of Inuvik)*
8
1615
18 Oct.
27 May
Source: French and Slaymaker (1993). Reproduced by permission of McGill-Queens Press.
In Siberia, a number of similar large rivers fl ow northwards (Ob, Yenisei, Lena,
Indigirka, and Kolyma rivers), with the added advantage of a northern sea route along
the Siberian coast from Kolymsk (Cherskiy) in the Kolyma Delta in the Far East to
Archangel'sk on the White Sea in the west.
All these large rivers usually retain water in the main channel under the ice throughout
the winter. The river ice can be as much as 2.0 m thick and the channels are surprisingly
deep. Break-up usually begins with the fl ow of locally-derived meltwater over the ice
surface. Then, the ice rises as fl ow increases in the channel beneath and as shore leads
develop. Break-up is usually rapid, often accompanied by fl ooding. For example, in the
Mackenzie River basin, a major reason for the creation of Inuvik as a regional administra-
tive center in the mid-1950s was because Aklavik, the original center, was subject to
periodic fl ooding. Ice-jams, caused by large pieces of river ice becoming concentrated at
localities where the ice has yet to break-up, or where there are obstructions to fl ow, as at
bridge crossings, can accentuate fl ooding, causing serious damage (Gerard, 1990). Table
10.2 lists the direct costs associated with ice jams on the Mackenzie and Yukon River
systems between 1960 and 1990. In recent years, the continued relocation of settlements
and structures away from localities prone to fl ooding, and improved geotechnical
engineering has minimized this hazard (see Chapter 14). Comparable data for the large
Siberian rivers are not easily available but it is reasonable to assume that similar hydrograph
patterns and freeze-up/break-up conditions prevail. On the Lena and Kolyma Rivers,
annual ice damage to wharf facilities and settlements is an ongoing hazard.
10.2.2. Freeze-Up and Break-Up
We can distinguish between stream channels which are fed by both surface runoff and
groundwater and those which are fed almost entirely by surface runoff. The latter occur
in areas of continuous permafrost while the former occur in sub-arctic locations where
discontinuous permafrost permits springs to emerge from taliks and sub-permafrost aqui-
fers. In both types of channel the winter cold and abundance of snow and/or ice in the
