Thermal control
quite effective. However, the primary purpose of
Thermal ice control methods use either heat
blasting is to break an ice cover or to loosen an ice
obtained from a nearby source (such as power
jam so that it is free to move, and there must be
plant cooling water) or heat contained in the
enough flow passing down the river to transport
water body itself to melt ice. Because water reach-
the ice away from the site and an open-water area
es its maximum density at a temperature of about
downstream to receive the ice. Since the primary
39F, colder water in lakes tends to stratify above
driving force available to break ice by blasting is
warmer water. An ice cover can form on the water
the large gas bubble resulting from the blast and
surface even though the water at depth is still well
not the shock waves, the charges must be weight-
above freezing. When present, this warm water
ed and placed under the ice cover. Blasting is not
can be brought to the surface quite economically
a quick, easy solution. It requires planning, acqui-
using air bubblers, pumps or flow enhancers.
sition of explosives and hole-drilling equipment,
While this natural source of warm water is com-
and a crew of perhaps 11 people (USACE 1982a).
mon on lakes and reservoirs, warm water can ex-
A properly outfitted crew might be able to blast
ist at depth on some slow-moving rivers as well.
two rows of charges along about one-half mile of
Water even a fraction of a degree above freezing
river per day. Safety and environmental concerns
can be quite effective in melting ice over a period
must also be addressed.
of days or weeks. With water velocities on the or-
Removing an ice jam mechanically simply
der of 13 ft/s in the Missouri, however, such a
means taking the ice out of the river and placing it
warm water source is unlikely except down-
elsewhere. This method directly relieves the
stream in Lake Sakakawea.
cause of flooding but is neither cheap nor fast. In
External heat sources can include the cooling
February 1978 it cost approximately ,500 to
water effluent from fossil or nuclear power plants,
make a 2600-ft channel with a backhoe (USACE
or even groundwater. Recently a thermally based
1982a). Other mechanical removal operations
ice control solution was developed on the Kanka-
have employed such equipment as bulldozers,
kee River near Wilmington, Illinois (Deck 1986). A
excavators and draglines. Because of the time re-
siphon system was constructed to extract warm
quired to excavate ice with conventional equip-
water from a nuclear power plant's cooling pond
ment and safety concerns, this approach is nor-
and place it in the river through a system of diffus-
mally limited to midwinter jams on small
ers. Unfortunately no ready source of warm water
streams.
is available in the BufordTrenton area.
Mitigation techniques for the BufordTrenton
Emergency measures
Irrigation District
Predicting when, or even if, an ice jam will oc-
A number of ice-related flood mitigation tech-
niques have been reviewed in terms of technical,
cur at a given location in a given year is rarely pos-
but not economical, feasibility. Given the climate
sible. The section dealing with ice jam potential
of the Williston area and the characteristics of the
provides a scheme for predicting whether ice jams
river ice regime, a program of ice weakening
are likely in the BufordTrenton area based on
should be feasible as either a short-term advance
weather and flow conditions, but should ice jams
measure or a long-term ice control program. Ice
occur unexpectedly or in an area where no ad-
weakening efforts should be focused on the river
vance measures were taken, it may be necessary to
bendways near Ryder Point and the Hurley Bend,
resort to so-called emergency measures. Once a
which have been frequent jam locations in the
jam is in place, there are generally few mitigation
past. In terms of structural control measures,
alternatives available. The Ice Engineering Manu-
flood flow containment is already a reality for a
al (USACE 1982a) cites four methods: mechanical
flow approaching a five-year recurrence interval
removal, dusting, blasting and icebreaking with
spring breakup flood due to the existence of the
ships. Dusting has already been discussed as an
raised irrigation ditches along much of the river
advance measure, but because of the time re-
in the BufordTrenton Irrigation District. It might
quired for dusting to be effective, it is not normal-
be possible to improve the level of protection of-
ly effective once a spring breakup jam is in place.
fered by these ditches by raising low spots and
The use of icebreaking ships is highly effective but
requires suitable vessels present on-site, which is
ensuring their structural adequacy.
not the case in the BufordTrenton area.
The confluence area of the Missouri and Yel-
Blasting, in an appropriate application, can be
lowstone Rivers is considered to be a good poten-
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