Table 2. USGS data sources.
Gaging station
number
Gaging station location
Period of wintertime record available
06793000
Loup River near Genoa
19301991
06792500
Loup River Power Canal near Genoa
19371990
06794500
Loup River at Columbus
19351979
06799100
North Fork Elkhorn River near Pierce
19611992
06798000
South Fork Elkhorn River at Ewing
19481953, 19611972, 19781992
06797500
Elkhorn River at Ewing
19481991
06798500
Elkhorn River at Neligh
19311958, 19611992
06799000
Elkhorn River at Norfolk
19461992
06799350
Elkhorn River at West Point
19731992
06800500
Elkhorn River at Waterloo
19291991
06770000
Platte River near Odessa
19391991
06770500
Platte River near Grand Island
19351992
06796000
Platte River at North Bend
19501992
06801000
Platte River near Ashland
19291960, 19891992
06805500
Platte River at Louisville
19541991
Natural Resources Districts, members of the Civil
records available. Important discharge parame-
Defense network, National Weather Service ob-
ters examined for each site include the maximum
servers, Corps of Engineers personnel and a rep-
average daily discharge Qmax and the date on
resentative from CRREL. A number of sources of
which it occurred. For ease in data handling, dates
information were identified in the meetings, and
were converted from a monthday format to a
several additional ice events were revealed.
Julian Day format, with Day 1 being 1 October,
the start of the water year. Thus, the date of Qmax
Hydrological data
would be termed JD Qmax.
In addition to the stage data and ice notes
discussed previously, USGS gaging station data
Meteorological records
also provided information about water dis-
The NWS operates a number of gages that col-
charge throughout the winter. Discharge is im-
lect meteorological data. Records obtained from
portant in characterizing ice jams for several
gages within the Lower Platte River basin (Table
reasons. First, discharge at freeze-up determines
3) included minimum and maximum air temper-
the stage at which the ice cover initially forms.
ature, snowfall and precipitation. From these
Second, as the discharge rises or falls through-
records we calculated average daily air tempera-
out the winter, the corresponding changes in
ture (ADAT), freezing degree-days (FDD), accu-
stage may result in ice conditions that are either
mulated freezing degree-days (AFDD) and accu-
more or less likely to break up and jam. Third,
mulated thawing degree-days (ATDD) for the
large increases in discharge and stage, such as
winter, all of which are described in detail below.
those due to rainfall, snowmelt or a combina-
Meteorological data, like discharge data, are
tion of both, may increase stages to the point
tracked by Julian Day (JD) starting with 1 Octo-
that the ice cover begins to break up. The dis-
ber, the start of the water year. Average daily air
charge at breakup can determine whether the
ice is transported downstream or whether it is
Table 3. National Weather Service
likely to jam at a particular location.
meteorological data sources.
Fortunately there are several gages within the
study area which have long-term discharge
NWS station
records. Many of these gages are located within
location
Period of record
jam areas or are affected by backwater from ice
Columbus
19491991
jams, depending on the jam length. Average daily
Genoa
19481991
discharge records were obtained for several USGS
North Platte
19481991
gaging stations, both within the study reach and
Grand Island
19001991
in the contributing drainage basins, for the
Omaha (Eppley)
19481991
months of January through April. Table 2 lists the
West Point
18921991
Ewing
19481991
gaging stations selected and the period of winter
4
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