RIVER ICE INFLUENCES ON FORT PECK REACH, MISSOURI RIVER
11
occurred during the winter months. The average peak winter flows increased
from about 5,000 cfs to about 14,000 cfs. Figure 6 compares the pre-dam and
post-dam mean daily flows at the Wolf Point gage (RM 1700) for the water years
1930 and 1987. However, in the past two years, flow releases have varied sub-
stantially from the discharge for water year 1987 shown in Figure 6. Figure 7
20
15
)
0
0
0
1
Water year 1987
x
s
f
c
(
E 10
G
R
A
H
C
S
D
5
Water year 1930
0
Oct
Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Month
Figure 6. Hydrographs for water years 1930 and 1987,
before and after construction of the Fort Peck Dam.
shows the continuous records of discharge for water years 19701993, 1994
1996, and 19971999. Though the records differ for these periods, for all periods
the reach conveyed the largest flow rates during open water conditions.
Flow releases from Fort Peck Dam generally conform to a water manage-
ment schedule for the main stem dams on the Missouri River. The schedule,
called the Current Water Control Plan (CWCP), is under reconsideration by
USACE-Omaha. An alternate schedule, called the Preferred Alternative (PA), is
favored. The PA schedule would move the peak discharges into the spring, rather
than having them occur later in the year (Pokrefke et al. 1998). The variations in
flow rates between the PA and CWCP schedules are small compared to actual
variations in annual river flows; Figure 8 compares the annual flowfrequency
curves for the two schedules. It is thought that implementation of the PA sched-
ule would not substantially alter the behavior of the Fort Peck reach (Pokrefke et
al. 1998). The consequences for river ice formation, however, are unclear, as
river ice seems not to have been included in the evaluation of the possible effects
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