Figur.∏ for
Figure 5. Lower basin of Cazenovia Creek and the site of the ice-control structures discussed here.
ICS DESIGN
ice to the design discharge (6000 cfs, which was also
Original ICS features and function
the maximum discharge possible in the model). Flood-
The original weir-with-piers ICS (see Fig. 2) was
way flow reduced the flow over the weir by about 20%
based on a similar structure installed on the Ste. Anne
at the design discharge, providing some safety margin.
River in St. Raymond, Quebec (Deck 1984). In early
For its final design, CELRB selected the 6-ft-high weir
winter, a low-flow opening would be closed to create a
with nine piers and the prepared floodway, reasoning
pool and form an ice sheet. The weir and excavated
that increased reliability outweighed the small incre-
pool were sized to reduce water velocities sufficiently
mental cost (U.S. Army 1986a). Existing trees were to
to store ice floes arriving from upstream during break-
be left intact along the floodway to prevent ice passage
up. Piers protruded above the weir to stabilize the ice
downstream at high flows.
sheet and prevent passage of ice floes over the weir. A
The weir-with-piers ICS would have required annual
prepared floodway helped reduce velocities over the
maintenance. All the estimated bed-load sediment and
weir at high flows.
some of the suspended sediment were expected to
Gooch and Deck (1990) conducted physical model
deposit in the pool upstream of the ICS. Dredging of
about 4000 ft3 of sediment annually would have been
tests to optimize this ICS. They determined that ice
breakup typically begins at about 1500 cfs and that the
needed to ensure adequate ice-storage volume (U.S.
seven ice-jam floods on Cazenovia Creek from 1971
Army 1986a).
82 had peak discharges less than 6000 cfs. The Corps
With the inclusion of a low-flow opening, no signif-
accepted this value as the design discharge for the orig-
icant long-term environmental impacts on water quality
inal ICS (U.S. Army 1986a), although the hydrographs
or stream ecosystems were expected to result from the
for the 1972 and 1985 events indicate that discharge
original ICS. Also, open-water flooding upstream was
can exceed this value during later stages of breakup
not expected to increase because increased water-
events (see Fig. 4).
surface elevations caused by the structure would extend
Gooch and Deck modeled about 4200 ft of river us-
no further than 4500 ft upstream (U.S. Army 1986a).
ing scales of 1:40 horizontal and 1:10 vertical, and used
Upstream effects with ice included were not examined,
urea-doped ice to scale ice flexural strength (prototype
based on the assumption that all upstream ice would
target 800 kPa or 120 psi). Test results indicated that a
collect within the ICS pool.
6-ft-high weir with piers retained ice more effectively
Physical model of cylindrical-pier ICS
than an 8-ft-high weir with no piers (U.S. Army 1986a).
For fewer than five piers, the ice sheet would extrude
The main requirement for the new, cylindrical-pier
past the piers, or break up in front of them, and the ice
ICS is to perform as well as the weir-with-pier ICS.
That is, it should arrest breakup ice runs and retain the
floes accumulated in the pool would spill over the weir
resulting ice jams (for ice thicker than about 0.8 ft) for
(Gooch and Deck 1990). Even with no floodway, the
the 6000-cfs design discharge (12-hour rise time). In
6-ft-high weir with five or nine piers was found to retain
4
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