chosen as a matter of convenience, in terms of
from an airplane flying at about 65 mph at an
availability and cost. This report will discuss pre-
altitude of less than 20 ft. The accuracy of drop-
vious uses of explosives in Nebraska, steps to take
ping charges in this manner was not as good as
before and during blasting operations, selecting
when a helicopter is used, although accuracy im-
proper charge sizes and placement, and estimat-
proved with practice.
ing the quantity of explosives needed and the
An ice jam in DeSoto Bend (prior to the bend
time required.
cut-off) was broken up using T37 rockets (7.2-
The use of explosives to clear ice can be dated
inch demolition rockets) and hand charges of Com-
back to Germany in 1758, when bombs were af-
position C-3. The rockets carried a 32.5-lb charge
fixed below the ice and exploded (Bolsenga 1968).
of explosive in a steel casing, propelled by a
Several researchers have studied blasting effects
motor unit. The rockets had a maximum range of
on floating ice sheets (Van der Kley 1965, Mellor
300 yd and exploded upon impact. Eight rockets
1986, 1987), but there is little quantitative infor-
were used on 23 February to break up the ice jam.
mation available regarding blasting of ice jams.
Four rockets were used on sheet ice 68 inches in
Duego (1973) noted that thermally grown ice is
thickness. No appreciable effect was noticed from
relatively easy to break up by blasting, while fra-
the first three rockets, but immediately following
zil ice is more difficult to break up since it absorbs
the fourth rocket the sheet ice broke loose 1000 ft
much of the blast energy. The guidance available
upstream of the target area, and a 1500-ft section
for blasting ice sheets can be useful in designing
of sheet ice approximately 500 ft wide moved out.
an ice jam blasting plan, as long as the additional
Hand charges were then used on the remaining
difficulties posed by ice jams are taken into ac-
sheet ice below the jam. The ice was too rotten to
count. These include the fact that placement of
walk on, so the charges were cast out onto the ice
charges will be more difficult and hazardous, and
from the shore. One 10-lb charge and 13 charges
less exact, in an ice jam than in a stable ice sheet.
from 4.5 to 6.75 lb were tossed 50100 ft out onto
Also, the varying thickness, ice strength and po-
the ice at one- to five-minute intervals. Following
rosity in an ice jam will cause more of the explo-
a series of two to four charges, a crack would
sive energy to be absorbed than would be the case
open up across the channel at a distance 100300
in a uniform ice sheet, and therefore the crater
ft upstream of the last hole produced, and a large
size will be smaller. At a minimum, one would
section of ice would then break away. Rockets
expect to use more and larger charges to achieve
were then fired at the heavier jammed ice up-
the same effect in an ice jam as in an ice sheet.
stream (six hand charges had been tried but they
Explosives have been used to break up ice jams
had no discernible effect). The first two rockets
in Nebraska and surrounding states since at least
produced no discernible breaking effect, but the
the 1920s, with varying degrees of success. Some
third rocket started ice movement approximately
known applications of blasting for ice jam mitiga-
1500 ft upstream. A fourth rocket was used mere-
tion in Nebraska and the results, if known, are
ly to hasten the breakup.
presented below.
Rockets and hand charges were also used on
Missouri River, 1946. Tests were conducted in
an ice jam on 26 and 27 February at Tieville Bend
1946 by several agencies, including Corps of En-
near Decatur but with less success. The hand
gineers employees in the Omaha District, to test
charges were thrown from the bank and were used
the effectiveness of ice-jam removal on the
along a dike system. The ice was loosened but did
Missouri River by means of various explosives.
not move out. Charges were then placed from a
Moran (1946) described efforts to remove an ice
skiff, and the ice began moving through the dike
jam near Corning, Missouri, on 8 and 9 February
system. The next day fifty-two 18.5-lb charges were
1946. Weights and then live charges were dropped
used to break the ice clear of the dike system.
from a helicopter to demonstrate the feasibility
Hand charges were also used to clear 1.14 miles
and safety of such an operation. Following this,
of the main channel of sheet ice. The charges broke
15 charges of Composition C-3 ranging from 36 to
the ice, but the flow was very slow, so it was
160 lb were dropped on the ice jam from a heli-
necessary to start the broken ice downstream from
copter. However, the jam was resting on a bar,
the propeller wash of the outboard motor on the
and Moran observed "there was little or no flow
skiff. It was also necessary to place additional
under or through the ice to aid its movement when
charges downstream along the dike system to pre-
loosened." Following this, tests were conducted
vent the ice from jamming there. Additional charg-
to determine the accuracy of dropping charges
es were placed from the motorboat when the
47
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