souri River into four areas: East, Middle, West
as the base for the ice analysis. Since the field data
and Zero Bottoms (Fig. 1). The following project
collection program indicated that significant ice
description was taken from Design Memoran-
events were driven by ice breakup on the Yellow-
dum No. MGR-146 "BufordTrenton Irrigation
stone River and that the ice on the Missouri River
District: Backwater and Drainage Problems"
above the confluence typically ran several weeks
(USACE 1978):
later, the Yellowstone River HEC-2 data file was
merged with the Missouri River data file at the
The project consists of a pumping plant, the main
canal and lateral system and all other features
confluence. The Missouri River above the conflu-
needed to deliver water to each farm unit. This
ence was not included in the model, except as a
also includes the drainage system carrying the
tributary source of water inflow.
return flows from the irrigated land back to the
Figure 2 shows the locations of cross sections
Missouri River and Lake Trenton. When fully de-
used by the Omaha District to monitor sediment
veloped the project consisted of about 16,800
aggradation. These cross sections also correspond
acres of which 10,000 were irrigable. In 1958 the
to some of the cross sections used to evaluate
Corps acquired the East Bottom for the Garrison
water surface profiles along the rivers using the
Dam-Lake Sakakawea project... This reduced the
HEC-2 computer program (USACE 1990). How-
total acreage of the District to about 10,100 acres
ever, the HEC-2 data file contained several cross
and the irrigated acreage to about 7100 acres.
sections intermediate to those ranges, as well as
cross sections farther downstream on the Missouri
BACKGROUND
and upstream on the Yellowstone. The HEC-2 cross
section numbers correspond to 1960 Missouri
The Missouri River above Williston has a
River mileage.
drainage area of approximately 164,500 square
The modeled area ranged from cross section
miles, with roughly 70,000 square miles contrib-
number 1497.11, which is roughly 50 miles below
uted by the Yellowstone River and 90,000 square
Williston and well into Lake Sakakawea, to
miles by the Missouri above the confluence with
1594.38, about 10 river miles upstream of Fairview,
the Yellowstone. The Missouri River discharge
Montana, a distance of about 100 miles. Points of
below the confluence, based on daily mean val-
interest include the Route 85 bridge at 1552.70,
ues, ranges from about 3,000 to 22,000 cfs during
Hurley Bend at approximately 1570, Ryder Bend
the fall freezeup and mid-winter periods. Mean
near 1578 and the Yellowstone River confluence at
flows for the months of December through Febru-
roughly 1582.
ary range from about 10,000 to 11,000 cfs. At a
flow of 10,000 cfs, the Missouri River has a water
Hydrology
surface width on the order of 5001000 ft, a thal-
An analysis of open-water conditions along the
weg depth of 1020 ft and water velocities of 13
Missouri River from Fort Peck Dam to Garrison
ft/s. Water surface slopes are relatively flat
Dam was conducted by the Omaha District
(0.00002 or less) below the Route 85 bridge (cross
(USACE 1978). USGS discharge records are avail-
section 1552.7). Above the Route 85 bridge the
able for the Missouri River at Williston for the peri-
water surface slope is on the order of 0.00011,
od from 1929 to 1965, when it was discontinued.
while on the lower Yellowstone River it is about
The flow record was extended through 1975 by
0.00018.
transposing the combined flow records for the
Missouri River at Culbertson, Montana, and the
Yellowstone River at Sidney, Montana. The results
The hydraulic analysis portion of this investi-
of an annual peak dischargefrequency analysis
gation relied heavily on the HEC-2 Water Surface
based on those records are summarized in Table 1.
Profiles computer program (USACE 1990) with
The results of the 1978 dischargefrequency analy-
the ice cover analysis option. This option pro-
sis have since been extended through 1984, again
vides the user with the capability to determine
using the Culbertson and Sidney gage data. These
water surface profiles for streams with stationary
values, also presented in Table 1, show that extend-
floating ice covers. In addition, a utility program
ing the record has resulted in a lowering of predict-
called ICETHK (Wuebben and Gagnon, in prep.)
ed discharge values, ranging from about 5% at a
was employed to facilitate the use and interpreta-
two-year event to 9% at the 500-year event. Both
tion of the HEC-2 ice option.
sets of values are presented for comparison, since
Verified, open-water HEC-2 data sets, ob-
an analysis of peak discharges occurring during
tained from the Omaha District, were employed
2
Previous Page
