Table 11. Ice events with normalized stage greater than 1.0.
Normalized
Location
Flood stage (ft)
Date(s)
stage
Loup River at Genoa
9
16 February 1962
1.11
Loup River at Genoa
9
1 April 1965
1.15
Loup River at Genoa
9
19 February 1971
1.15
Loup River at Genoa
9
28 February 1972
1.02
Loup River at Genoa
9
15 February 1984
1.01
Loup River at Genoa
9
23 February 1977
1.13
Loup River at Genoa
9
18 March 1978
1.35
Loup River at Genoa
9
15 March 1979
1.21
Loup River at Genoa
9
18 January 1980
1.20
Loup River at Genoa
9
30 December 1980
1.31
Loup River at Genoa
9
21 February 1982
1.37
Loup River at Genoa
9
17 February 1983
1.04
Loup River at Genoa
9
27 February 1985
1.05
Loup River at Genoa
9
27 January 1986
1.13
Loup River at Genoa
9
10 March 1989
1.04
Loup River at Columbus
11
21 March 1969
1.02
Platte River at North Bend
8
13 February 1952
1.02
Platte River at North Bend
8
29 March 1960
1.01
Platte River at North Bend
8
20 February 1971
1.53
Platte River at North Bend
8
29 February 1972
1.27
Platte River at North Bend
8
17 February 1974
1.07
Platte River at North Bend
8
19 March 1978
1.94
Platte River at North Bend
8
14 March 1979
1.25
Platte River at North Bend
8
18 January 1980
1.31
Platte River at North Bend
8
22 February 1982
1.16
Platte River at North Bend
8
18 February 1983
1.19
Platte River at North Bend
8
28 February 1985
1.32
Platte River at North Bend
8
24 February 1988
1.02
Platte River at North Bend
8
12 March 1989
1.02
Platte River at Louisville
9
28 March 1962
1.01
Platte River at Louisville
9
19 February 1971
1.17
Platte River at Louisville
9
3 March 1979
1.09
Platte River at Louisville
9
22 February 1982
1.11
Note: There were no normalized stages greater than 1.0 at Waterloo
isville. Stages greater than flood stage occurred
than of actual ice event occurrence. For example,
most frequently at Genoa (73%), followed by Lou-
ice jams occurred at ungaged sites in 1966 and
isville (50%) and North Bend (46%). Normalized
1969. They may also have occurred at gaged sites,
stages ranged between 0.34 and 1.94, with a mean
but stages associated with large flows during the
of 0.93 and standard deviation of 0.28. The fre-
summertime, particularly in 1966 (USAED,
quency distribution of the normalized stages is
Omaha 1966), may have obscured high ice-related
given in Figure 8a. The most frequently occurring
stages. A review of archived winter USGS stage
normalized stages fall between 1.0 and 1.1 (16.7%),
and discharge measurement records for the gaged
followed by 12.8% between 1.1 and 1.2. Assum-
sites could be useful in identifying and verifying
ing a log-normal distribution, the exceedance
ice event information. Large-scale climatic varia-
probability of a given normalized stage is given
tions, increased development, modification of land-
in Figure 8b. Flood stage is equaled or exceeded
use practices, and changes in the sediment regime
about 40% of the time at the gaged sites in the
of the rivers may also affect the apparent frequen-
study area; however, factors unique to each site
cy of flooding, in addition to data uncertainties.
may cause it to experience a significantly greater
In addition to characterizing the frequency and
or smaller probability of exceeding flood stage.
stage of ice events, it is also important to charac-
Although the ice events shown in Figure 7
terize the hydrological and meteorological condi-
which result in flooding appear to occur more
tions associated with ice events. The probability
frequently after 1970, this may actually be more a
distributions for the occurrence of discharge events
reflection of the quality and availability of data
or temperatures can be developed with greater
17
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