Receiving
Parties
Wire
Loop
Ice
Cover
Telephone
Plastic
AC
Dialer
Tie
Stick
Power
Unit
#22 AWG
Phone Wire Waterproof
Splice
Anchored
Loops
#28 AWG
Ice
Wire Loops
Cover
Figure 22. Ice motion detector.
signed to weaken it. Ice cutting must be carefully
spreaders than sand or coal dust. These materials
timed to avoid refreezing of the slots. This tech-
must be dry enough to flow freely for even distri-
nique may be used to cause a stable ice sheet to
bution and to avoid freezing. Wind can be a prob-
break up earlier than normal, preventing it from
lem, causing the fine materials to drift or the snow
obstructing the movement of upstream ice. Ice
to drift over the dust (Moor and Watson 1971).
cutting in selected locations can also create a flow
The dusting material is usually applied two to
path for ice and water at breakup, reducing the
three weeks prior to breakup. The degree of melt-
probability of jamming.
ing depends on the quantity and properties of the
Ice covers can be broken prior to natural break-
material deposited, solar radiation and snow-
up using icebreaking vessels or construction
storms. In areas where late snowstorms occur, sev-
equipment. The downstream movement of the
eral applications may be necessary, although snow
broken ice should be enhanced to prevent local-
of moderate depth over a dark material will melt
ized breakup ice jams. Air cushion vehicles (ACVs)
at an accelerated rate. The melting period may be
can be used to break large extents of relatively
too short for significant reduction in ice volume
smooth sheet ice covers, usually in areas where
or weakening if breakup occurs soon after appli-
cation. Whatever material is used, the possible
the sheet ice may stop the ice run and initiate a
adverse environmental impacts of dusting must
jam. The advantages of an ACV are its speed and
maneuverability and its ability to operate in shal-
be considered prior to application. The use of dust-
low areas. The disadvantages are that it simply
ing as a mitigation measure within the study area
breaks the ice but does not move it, it cannot
is discussed in detail below.
operate over rough ice accumulations because of
potential damages to its flexible skirts, and opera-
Emergency measures
Emergency measures are those that are taken
tions in cold weather can lead to severe icing of
the propulsion system. Also, the ACV must be
after an ice jam has formed and flooding is immi-
quite large; the smaller 2- or 4-person ACVs will
nent or already occurring. The effectiveness of
not break ice of average thickness in the Platte
emergency response may be reduced unless an
River.
emergency action plan exists that specifically re-
Dusting, or covering ice surfaces with a thin
fers to ice jams. Comprehensive emergency man-
layer of dark material, induces more rapid melt-
agement includes four phases: preparedness, re-
ing and ice weakening. Conventional materials
sponse, recovery and mitigation. Emergency
include coal dust, fly ash, topsoil, sand or river-
planners should have a clear line of command for
bed material. Initial tests with biodegradable ma-
multi-governmental management of ice-jam flood-
terials such as leaves, mulch and bark show prom-
ing events. Plans should be tested in advance to
ising results. This type of material is more easily
be sure that all phases can be carried out and that
spread by commercially available seeders and
all necessary materials and equipment are avail-
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