As noted earlier, historical trends indicate that the tim- outweigh costs associated with open-water floods
31
. The
ing of break up has advanced with warming but few at- economic costs of river ice jams in North America av-
tempts have been made to consider changes in the se- erage almost US$250 million per year
32,33
(converted
verity of break up
11,28
. Concern has been raised, however, to 2006 values), although this could be a conservative
about how large-scale patterns of warming might affect value considering that the cost of a single 2001 break-
thermal gradients along large northward-flowing rivers up season in Eastern Russia in 2001 exceeded US$100
– changes in these gradients can be expected to affect million
34
. They also pose significant risk to human life,
the incidence and magnitude of ice-induced flooding
29
particularly because they are less predictable and occur
(see box on river temperature gradients and floods). A more rapidly than open-water events.
related concern involves the increased potential for mid-
winter break ups, which are more unpredictable than Many northern settlements were established at the con-
spring events but can be just as severe
27,30
. fluence of rivers or where rivers enter lakes and these
sites are known to be highly susceptible to ice-jam for-
mation
4
(Figure 8.5). Damage by ice action and flood
Impacts on human economies and well- waters to such settlements by infrequent but severe ice
being jams can be costly. Freeze up, break up and changes in
ice thickness and production also cause regular prob-
The greatest impacts of freshwater ice on humans are as- lems for in-channel operations such as hydropower gen-
sociated with the dramatic ice and flooding that accom- eration, bridges and pipelines, and transportation
32
. All
pany dynamic freeze-up and break-up events. For many such freeze-up, break-up and ice-thickness related im-
cold regions, it is ice-induced flood events that regularly pacts will vary under changing climates.
Figure 8.5: Ice-jam flooding, Ounas-
joki River, Finland.
Photo: Esko Kuusisto
Figure 8.6: Loss of ice coverage re-
ducing ice transportation access to
northern communities, Liard River,
Canada.
Photo: T.D. Prowse
CHAPTER 8 RIVER AND LAKE ICE 207
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