The flood stage at the gage (9 ft) was exceeded
The effects of these fluctuations in Loup River
by ice events occurring in 1962, 1965, 1969, 1971,
Power Canal diversions on discharge, ice forma-
1972, 1974, 19771983, 1985, 1986 and 1989. The
tion and ice transport in the Loup River below the
1988 ice event may have exceeded flood stage; the
diversion structure have not been quantified. Some
precision of ice-jam stage measurement is larger
local residents have expressed the opinion that
than 0.01 ft. The maximum open-water stage at
the resulting fluctuations in water level cause or
the Genoa gage was 13.93 ft during the storm of
exacerbate ice jams in the Loup River downstream
August 1966. In comparison, the peak ice-related
from the canal diversion. However, it would only
stage of 12.35 ft at the gage on 21 February 1982
be possible to evaluate the situation after a de-
was caused by an ice jam. According to Nebraska
tailed study. A quantitative analysis would be dif-
Civil Defense records, this jam was about one mile
ficult given the lack of good ice records. A quali-
long and resulted in lowland flooding. The next-
tative analysis might address such issues as the
highest ice-related stage was 12.12 ft on 18 March
potential effects of raising and lowering water
1978. Civil Defense records indicate that ice jams
levels on the formation of border ice, frazil pro-
causing flooding in 1978 were located both east
duction, frazil ice transport and the effects of sud-
and west of the bridge.
den decreases in river flow on ice movement (e.g.
Two ice jams at Genoa were reported by other
stranding ice blocks, increased frazil deposition).
sources. On Thursday, 20 March 1969, the Colum-
Changes in the sediment regime of the river re-
bus Daily Telegram reported that the ice jam at
sulting from canal operations may also have im-
Genoa was still in place and water was 1 ft lower
pacted ice formation and transport processes. The
than Wednesday, 19 March, but still "slightly" out
difficulties involved in evaluating Loup River
of bank. According to Nebraska Civil Defense
Power Canal operations are illustrated in Figure
records (1971), a 5-mile-long ice jam formed at
4, which presents measured flows at the Loup
Genoa during the storm of February 1971. No
River Power Canal gage, the Loup River gage
information about water stages, or the exact loca-
near Genoa, the combined flow in the canal and
tion in reference to the gage, was provided. Al-
the river, and air temperatures at Columbus dur-
though the date of jam formation was not speci-
ing the period 15 November through 9 December
fied, the jam was in place and causing flooding at
1993. The canal operated at fairly steady flows
least between 24 February and 6 March 1971, and
between 15 and 23 November, while the river
perhaps for a longer period.
flows were slowly decreasing. Canal flow de-
The Loup River Power Canal diversion struc-
creased sharply on 23 November and remained
ture, consisting of a gated dam and gated canal
very low until 28 November, when flows were
headworks, is located on the Loup River about
increased. The increased canal flow fluctuated
six miles upstream from the USGS gage on the
roughly diurnally. In most cases, increases in
Loup River near Genoa. Outflow from the canal
canal flows are associated with decreases in river
enters the Platte River below Columbus. The
flows (see, for example, 6 December 1993).
canal system, which began diversions in Decem-
The rather marked decrease in river flow mea-
ber 1936, includes a settling basin, two hydro-
sured at the Loup River gage on 26, 27 and 28
power plants and Lake Babcock.
November may actually reflect water going into
A USGS gage is located at the settling basin
storage when the frazil ice produced during the
weir two miles downstream from the headworks.
low temperatures experienced during this period
No ice jams were reported at the Loup River Pow-
increased flow resistance due to shore ice and
er Canal gage. Canal operations, however, are sus-
anchor ice buildup and the formation of freeze-
pended in early winter when heavy frazil ice dis-
up jams. A transient peak flow of the magnitude
charge might adversely impact power production.
and duration experienced on 1 December is un-
Regular canal operations resume when frazil ice
usual. This high flow might be attributable either
concentrations are low or a sheet ice cover forms
to the release of water from storage as a result of
on the canal. The average flow for the period 1938
rising temperatures, or it could be an artifact of
1989 at this gage was 1600 cfs, in contrast to the
increased stage due to backwater from ice accu-
average daily flow at the Loup River gage near
mulations downstream from the gage.
Genoa, which is about 680 cfs for the period 1944
Ice jams and associated flooding have been re-
1989. Instantaneous Loup River Power Canal flows
ported in the vicinity of the Monroe Bridge, south
during the period January through March have
of Monroe. One jam was reported at this location
varied from essentially zero to 3160 cfs.
on 19 March 1969 in the Columbus Daily Telegram.
7
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