deployment of a freestanding fence boom or "ice
United States and southern Canada. There has
fence" on the Penkeniuppi River on the Japanese
been a marked increase in ice jam flood frequen-
island of Hokkaido. Inspired by Perham's fence
cy on smaller rivers as small mill dams fall into
boom, this structure is made up of 3-ft-wide in-
disrepair and are removed.
dividual steel frames supporting 3.3-ft-long, 2-
2-in. wood pieces, inclined away from the flow
Removable weirs
at 60. The gap width is 2.8 in. and the frames
Experimental tension weirs placed in small
are connected by steel pipe. Figure 14 shows the
rivers have successfully created pools and ice
units spanning a 90-ft-wide riffle section of river
covers for the purpose of limiting frazil produc-
1000 ft upstream of a small power dam. Since
tion. Researchers at CRREL initially used a struc-
ture consisting of vertical wood 2 4s attached to
installed in 1991, the ice fence has eliminated the
previously frequent interruptions to power pro-
top and bottom cables, referred to as a fence
duction resulting from frazil accumulations at
boom (Fig. 13) (Perham 1986). The intent was for
the intakes. The frazil accumulation that forms
frazil to accumulate in the gaps, creating an ice
behind the structure at the channel center diverts
dam and an impoundment. Field tests were rela-
water flow towards the banks, where velocities
tively successful but scour was a problem in un-
armored riverbeds. Other materials such as
reach 3.5 ft/s, resulting in some bed scour. To
reduce the scour, the banks are armored with
chain link fence were tried with relative success
stone-filled gabions. The structure was devel-
(Foltyn 1990).
oped through a cooperative effort between engi-
Mineta et al. (1994) reported the successful
a. Installed condition of the ice fence, 24 December
a. Installed condition.
1991.
b. Ice cover formed behind the ice fence, 23 January
b. After ice cover formation.
1992.
Figure 13. Fence boom installed on the Mascoma
Figure 14. Ice fence on the Penkeniuppi River in
River, Lebanon, New Hampshire.
northern Japan. (Photos courtesy of Ken-ichi Hiraya-
ma and the Hokkaido Electric Co.)
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