Figure 2. Details of the BufordTrenton Irrigation District. The cross sections are the locations used by the
Omaha District to monitor sediment aggradation. The locations where ice bridged across the river on 7 March
1992 are also shown.
or even the exact dates when ice cover breakup
Table 1. Missouri River discharge
and ice jamming have occurred in the past are
frequencies below the Yellow-
unknown. In the absence of more detailed histor-
stone River confluence.
ical information, spring breakup flows were tak-
en to be the first major peaks in flow occurring
during March or early April. These events may
not accurately represent the date of actual ice cov-
er breakup events and their discharge magni-
tudes, but they will provide a conservative esti-
mate for use in further analysis.
The estimated breakup discharge frequencies
presented in Table 2 were developed by ranking
these combined flows, plotting them on log-prob-
* After USACE (1978).
† Based on data provided by Roger L. Kay,
ability paper and fitting a curve by eye. The peri-
Omaha District, June 1992.
od of record ranged from 1966, after Lake Sakaka-
wea reached its maximum normal pool elevation,
through 1990. For comparison, dischargefre-
the month of March contained in the 1978 report
quency values for peak flows in March devel-
(USACE 1978) will be used later in the report.
oped by the Omaha District (USACE 1978) are
While these discharge values are appropriate
for determining open-water flood flows, the anal-
also included. The March values are somewhat
ysis of spring-breakup-related flooding requires
higher than the estimated breakup discharges
since they consider the maximum discharge in
breakup events. Unfortunately the actual flows
the calendar month rather than the first signifi-