ature search, an examination of various State and
clear whether the reported value is the actual peak
Federal agency records, and a series of local pub-
or the average value that occurred on the peak
lic meetings. Weather records and river discharge
day. Also, it is possible that ice events that did not
and stage records were also collected from the
cause an annual peak gage height will not be re-
National Weather Service (NWS) and the U.S. Geo-
ported. In some cases a gage height is reported as
logical Survey (USGS). The Nebraska Civil De-
being caused by an ice jam. Generally, without
fense Agency also made available a number of
further information, we assume that an ice jam
documents which provided additional informa-
must have been observed at or very close down-
tion on ice events within the study reach.
stream from the gage when this form of reporting
is used. In other cases the gage height might be
reported as being affected by backwater from ice.
Ice records
The initial search for records of ice events in
We assume in these cases that an ice cover located
the study area utilized the Ice Jam Data Base*
at or downstream from the gage is causing back-
developed at the U.S. Army Cold Regions Re-
water effects to be felt at the gage. The ice cover
search and Engineering Laboratory (CRREL).
may range from smooth to rough or even a jam.
Some ice-jam events included in the database are
Ice thickness is measured by the USGS when-
well documented, while only sketchy informa-
ever possible during winter discharge measure-
tion exists for others. The database relies heavily
ments at gaging stations. Written ice thickness
on USGS sources (e.g. USGS 1989) and, in partic-
data that have been collected in Nebraska are lo-
ular, on data collected for the USGS report series
cated at the USGS office in Lincoln. Obtaining all
of the historical ice thickness measurements made
thai 1968). As a result the most frequently report-
by the USGS within the study area would be be-
ed ice events are those which occurred at the sites
yond the scope of this study; however, records for
of USGS water-stage gages between the mid-1930s
particular locations for particular years were ob-
(when many gage records were begun) and the
tained (Table 1).
early 1960s. Ice events that occur away from USGS
Once a number of ice events had been identi-
gages are not well represented as yet. While gage
fied through literature searches and agency con-
records often include such useful data as the local
tacts, the Corps contacted local residents and agen-
stage and discharge, they rarely provide informa-
cies to corroborate and expand on the information.
tion on the thickness, extent, likely causes or dam-
A series of meetings was held in October 1993
ages associated with a particular ice event.
with the objective of identifying additional sourc-
The ice events that can be identified through a
es of information and learning more about the ice
review of peak USGS records are most commonly
jams which occur at the seven sites identified in
associated with the peak annual gage height (or
Figure 1. The meetings were held at Columbus
discharge) at a particular location. It is not always
(26 October), Gretna (27 October) and Fremont
(28 October). For convenience these meetings were
held in two parts: first, a meeting with local, State
and Federal agencies; and second, a meeting with
* The CRREL Ice Jam Data Base (White 1992) is a data-
the general public. The agency portions of the
base of ice events in the United States. It is updated
meetings were attended by city and county offi-
periodically; the latest version can be found at
cials, representatives of irrigation districts and
www.usace.army.mil/crrel on the World Wide Web.
Table 1. Locations and water years of ice thickness measurements obtained
from USGS.
USGS gaging
station number
USGS gaging station location
Water years
06793000
Loup River near Genoa
1948, 1969, 1978, 1979, 1987, 1993
06794500
Loup River at Columbus
1948, 1969, 1978
06799000
Elkhorn River at Norfolk
1966, 1969, 1978, 1979, 1987, 1993
06800500
Elkhorn River at Waterloo
1966, 1969, 1978, 1979, 1987, 1993
06770500
Platte River near Grand Island
1971, 1978, 1979, 1987, 1993
06796000
Platte River at North Bend
1971,1978, 1979, 1987, 1993
06805500
Platte River at Louisville
1971, 1978, 1979, 1987, 1993
3
Previous Page
