charge that establishes that WSE, and governing sur-
higher than even 100-year open-water ones, the jam
face condition (open-water or ice-jam) at each cross
length or volume essentially governs the upstream influ-
section.
ence of the structure. Insofar as possible, we have based
At the Winspear Subdivision and above, the 100-year
the terms that affect jam volume on data from the physi-
open-water profile dictates maximum water levels. That
cal model, the literature, or ice-jam events in Cazenovia
is, the ICS has no effect on water levels beyond about
Creek itself, and have selected values at the conservative
9600 ft upstream. From there to below the Leydecker
end of the ranges for each term. Consequently, the pre-
House, the 7000-cfs ice-jam profile dictates maximum
dicted maximum water levels caused by the ICS should
water levels. The governing ice-jam discharge then
be conservative.
increases with proximity to the ICS, such that 10,000
cfs dictates the maximum water level expected at
CONCLUSIONS
Kotecki Grove. Of the structures within the Cazenovia
Creek valley (Table 3), only Kotecki Grove and the
We recommend, as the new Cazenovia Creek ICS, a
structure consisting of nine 5-ft-diameter 10-ft-tall
Leydecker House are affected by ice jams at the ICS.
Note also that ice jams at the ICS do not contact the bridge
cylindrical piers spaced with 12-ft-gaps across the main
at Leydecker Road (low-steel elevation 666.00 ft).
channel. The treed floodplain should be left intact to
act as a flow-bypass channel. About 300 ft of riprap is
needed along the right bank near the structure to pre-
DISCUSSION
vent scour and to delay reentry of floodplain flow until
The cylindrical-pier ICS is a refinement of the
farther downstream. Comparison of the model results
sloped-block ICS installed in Hardwick, Vermont. These
indicates that the new ICS should have an ice-retention
wide-gap structures arrest breakup ice runs, retain the
capability at least as high as the original weir-with-piers
partially grounded ice jams, and use existing treed flood-
ICS. For ice thickness approximately 1 ft or greater,
plains to bypass flow. They function well without requir-
we would expect the ICS to arrest a breakup ice run
ing a weir or prepared floodway. Cylindrical piers with
and retain the ice jam for a discharge exceeding 7000
12-ft gaps should retain ice, particularly thin ice, at much
cfs. Slow washouts, rather than catastrophic releases,
higher discharge than sloped blocks with 14-ft gaps.
will likely be the release mode at higher discharges or
For breakup events that pose the greatest flood threat
with thinner ice. We saw no performance advantage
(thick, strong ice, heavy rain, or rapid snowmelt), the
for a cylindrical-pier ICS with 10-ft gaps, whereas one
cylindrical-pier ICS should retain ice until well after
with 14-ft gaps allowed ice washouts more easily.
ice has cleared from downstream reaches. Thus, this
Because the new ICS does not include a weir and exca-
new ICS should substantially reduce ice-jam flood dam-
vated pool, and makes use of the existing floodplain as
ages along Cazenovia Creek in West Seneca.
a bypass channel, it should be substantially cheaper than
Construction plans, specifications, and cost estimates
the original weir-with-piers ICS.
were completed for the original weir-with-piers ICS (US
Interestingly, the analysis for upstream effects has
Army 1986a). The most expensive items were com-
revealed the ice-retaining capacity of the ICS as a bal-
mon excavation, compacted fill, and concrete with
ance between two needs: the need to protect downstream
forming (for the upstream pool, prepared floodway, and
areas from natural ice-jam flooding with the need to
weir-with-piers structure, respectively). The new ICS
minimize upstream flooding by jams at the ICS. Melt-
eliminates the first two items and substantially reduces
ing and slow washout of ice through the ICS reduces
the third. We may estimate approximately 50% cost
extent of flooding upstream without endangering flood-
savings for the remaining items (e.g., clearing and grub-
ing downstream. Within our present capabilities
bing, roadways, riprap, engineering, supervision, land).
for physical and numerical modeling, the 12-ft-gap,
The construction cost for the new ICS might thus be
cylindrical-pier ICS appears to strike a good balance
about one-quarter to one-third of the cost of the origi-
of these competing needs.
nal ICS. The new ICS will not have a gate to operate
and will not require dredging to remove deposited sedi-
LITERATURE CITED
ment. Despite these lower costs, model results suggest
AASHTO (1998) LRFD Bridge Design Specifications.
that it should perform at least as well as the original
American Association of State Highway and Transpor-
concept.
tation Officials, Washington, D.C., Section 3.9.
The calibrated HEC-RAS model should provide
reliable estimates of the water-surface profiles expected
Beltaos, S., J.S. Ford, M. Pedrosa, N.K. Madsen, and
B.C. Burrell (1998) Remote measurements of tempera-
for both open-water and ice-jam events, with and with-
ture and surge levels in ice-laden rivers. In Ice in Sur-
out the ICS. Because ice-jam water levels are so much
21
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