Table 2. Major discharge-regulated tributaries of the Upper Mississippi River.
Winter average discharge
Tributary
(Dec.Jan.Feb.)
Q trib/
Total
Portion of
near confluence (m3/s)
Q mainstem area (Da) at
Flood-control
controlled Da
total Da
(percent) at mouth (km2)
(km2)
Tributary
Tributary
Mainstem
reservoirs
(percent)
Des Moines River
82
1086
7.5
38,900
Saylorville Lake
15,140
39
Red Rock Lake
Iowa River
32
1086
2.9
10,370
Coralville Lake
8480
80
The potential for reducing Illinois River dis-
A study by Jain et al. (1993) examined the pos-
charge by storing water during freezeup is even
sibility of controlling flow at tributary reservoirs
more limited. Even if tributary flow reductions
in the upper Ohio basin to promote rapid forma-
were deemed beneficial for forming ice covers on
tion of juxtaposed ice covers and minimize frazil
the main stem, it is unlikely that such reductions
production. Numerical models simulated ice
would significantly affect ice processes because
cover formation downstream of Pittsburgh on the
the tributary flow amounts to but a small fraction
Montgomery and Hannibal pools, predicting
of the main stem flow.* On these waterways,
water cooling, frazil growth, ice transport, and ice
tributary flood control reservoirs are typically
cover progression, under a variety of air tempera-
drawn down in the fall and maintained at low
ture and river discharge scenarios. The progres-
levels during the winter in anticipation of spring
sion model assumed that juxtaposition of floes
runoff events. To maintain storage capacity, res-
would occur only if the Froude number at the
ervoir inflow during winter typically equals out-
upstream edge of the ice cover did not exceed
flow. Even if discharge-controlled tributary inflow
0.05. The study found that optimal discharges
did represent a significant portion of the main
existed for minimizing the time required to form
stem river flow, it would probably be difficult to
ice covers on the two pools. A generalized case
convince water controllers that the ice-control
was developed to determine the minimum time
benefits of retaining water would justify the lost
to form an ice cover for a range of downstream
flood storage capacity.
depths, pool lengths, river bed slopes, and aver-
age air temperatures.
Ohio River
In spite of the potential for severe ice events, a
Early winter discharge and water velocity can
general lack of serious ice on the Ohio River from
be much higher and more variable on the Ohio
1980 to the present has dampened any interest in
River than on the Illinois and upper Mississippi,
flow control to manage ice on that river system.*
even though 30% of the total discharge from the
If an interest did arise for basin-wide flow con-
Ohio basin upstream of Pittsburgh is controlled.
trol to manage Ohio River ice, Corps water con-
The Ohio River has experienced a number of
trollers at the Ohio River Regional Office in Cin-
severe ice years, including 1918, 1940, 1948, 1963,
cinnati could use their FLOWSED unsteady flow
1971, 1977, 1978, and 1979. The worst recent win-
model to schedule reservoir releases to create
ter was 197778, when a combination of extreme
optimal hydraulic conditions for ice cover forma-
cold and high early December discharge pro-
tion. Similarly, the St. Louis and Rock Island Dis-
duced heavy ice on the river. At many locations,
tricts are set up with the UNET model (U.S. Army
water velocity was high enough to form shoved
1997), which has the added advantages of an ice
ice covers and jams, impeding navigation. A mas-
cover option and an ice cover progression routine.
sive thaw with rain in late January resulted in
breakup ice jams throughout the river system and
MIDWINTER PERIOD
caused what later became known as the "Mark-
land Dam Disaster," described in a later section
During the midwinter period, flow-control
of this report.
methods can alleviate ice problems faced by the
* Personal communication with William Koellner, Chief of
* Personal communication with Ronald Yates and George
McKee, Water Control Center, Ohio River Division, U.S. Army
Water Control, Rock Island District, U.S. Army Corps of Engi-
Corps of Engineers, Cincinnati, Ohio, April 1998.
neers, Rock Island, Illinois, April 1998.
8
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