EP 1110-2-11
30 Nov 94
gate, which allows for sediment and fish passage as well as recreational use by canoeists and fishermen. Two low-flow
pipes also provide fish passage. Levees were constructed on both upstream banks to contain the Standard Project Flood.
The project cost was .2 million for a unit cost of approximately ,300/ft (Wuebben, Gagnon, and Deck 1992). No
damaging ice jam has occurred in Oil City since the Allegheny River ice boom and Oil Creek ice control structure were
put into use.
5-4. Lancaster, NH - Weir, Ice Retention, Storage
a. Lancaster experienced ice jams every year due to breakup of the ice cover on the Israel River. Broken ice passage
is impeded by a natural frazil deposit that forms at the change in slope, which occurs at the upper end of the backwater
formed by the confluence with the Connecticut River. Few ice jams were reported prior to 1936, probably because four
dams that have been removed since that time decreased frazil production, provided frazil ice storage, decreased the down-
stream transport of frazil ice, and delayed the downstream passage of broken ice.
b. The Corps' New England Division and Cold Regions Research and Engineering Laboratory (CRREL) designed
and built an ice control project to reduce the production and transport of frazil ice and decrease the volume of ice avail-
able to ice jams downstream. Environmental and financial constraints limited the scope of the project, which ideally
would have provided the same protection as the four dams. The project consists of two parts: a submarine net to capture
surface ice and a 36.6-m-long by 2.7-m-high (120-ft-long by 9-ft-high) permanent weir located several miles downstream
(Figure 5-5). The submarine net is a form of suspended ice retention structure that allows water to flow through but cap-
tures floating ice pieces, which are then stored in overbank flood plains.
c. The ice control weir includes four 1.2-m-wide by 2.4-m-deep (4-ft-wide by 8-ft-deep) sluiceways for fish passage.
During the winter, stop logs or metal bar racks are placed in the sluiceways to develop an ice retention pool. The pool
forms an ice cover, and frazil ice generated upstream deposits beneath the ice cover. After the ice cover has formed, two
of the gates are opened, allowing the pool level to drop. This creates additional water storage in the pool area, provides
additional discharge capacity through the weir, and slightly delays the breakup and movement of ice through the pool as
well. The project, which cost 0,000 (approximately
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,800/ft) was completed in 1982. Although costs constrained
the size of the project to less than ideal, no major flooding has occurred since this relatively inexpensive, innovative
project was constructed (Axelson 1991).
5-5. Idaho Falls, ID - Land Acquisition
In 1982, two hydroelectric dams were removed and rebuilt on the Snake River near Idaho Falls. Freezeup ice jam floods
on the Snake River affected Bear Island homeowners during the winters of 1982-83 and 1984-85. Ice jam floods also
threatened two houses on the west bank of the river. The homeowners associated their flooding problems with the rebuilt
dams located 9.6 km (6 miles) downstream. As a result, they requested help from the city of Idaho Falls, the Federal
Energy Regulatory Commission, and elected officials. Field data collection and hydraulic analyses indicated that ice jams
were caused by frazil produced in turbulent open water sections of the Snake River. The results showed that the changes
in reservoir levels and the dams had no direct effect on ice jam flood levels in one area, although two properties were
affected by changes in reservoir levels. Based on CRREL's recommendations, the City of Idaho Falls decided to pur-
chase the two properties affected by the Upper Power Project (Zufelt, Earickson, and Cunningham 1990).
5-6. Platte River, NE - Dusting
a. In February 1978, disastrous ice jam flooding took place on the Platte River in Nebraska, causing millions of dol-
lars in damages. Record cold temperatures in January 1979 produced both extremely thick ice on the Platte River and its
tributaries and a consequent threat of similar ice jams during spring breakup. Ice dusting, approximately 3 weeks before
breakup, was recommended for alleviating ice jam floods.
b. The Nebraska Civil Defense agency decided to try dusting selected areas with technical assistance from the Corps.
The Corps assisted with advance preparation for the ice dusting operation during the actual dusting procedures to ensure a
5-4
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