WSP05631

• File Number: 8407.500
• Description: Platte River Basin - River Basin General Publications - Missouri River
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 1/14/1988
• Author: MBSA
• Title: A Review of the Missouri River Main Stem System Operation
• Water Supply Pro - Doc Type: Report/Study

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good sized reservoir and it's really the last point on
the river where we have a significant control. Gavins
Point almost doesn't show up on the chart because of
its small size. It tends to reregulate the fluctuating
releases from Fort Randall. It has a small amount of
flood control storage as does Big Bend, but for all
practical purposes, the upper three and Fort Randall
contain the flood control storage in the system.

The bar chart on the upper right shows Garrison to
be the largest at 24 million acre-feet, Oahe 23, and
Fort Peck 19. I point that out because these are the
third, the fourth, and the fifth largest storage reser-
voirs in the United States. I have said that a number
of times. The only projects that are built to store more
water than these are on the Colorado River.

If we were to add all these reservoirs together and
put them in one lump project, we would present it like
the picture on your right. System storage in the entire
six reservoirs is 74 million acre feet. These are allo-
cated into four separate storage zoneS. The lower most
is ina.ctive, that inactive zone is to provide an adequate
head to generate hydroelectric power and to support
a minimum fishery. The next zone, multipurpose car-
ryover, is water that's designed to support hydropower,
navigation, and other functions during extended
drought periods. The annual flood control and mul-
tiple use zone, 1&% of the total system storage, is in-
tended for use annually. We purposely store water in
that zone during the flood runoff period March
through July and evacuate that water during the bal-
ance of the year. That's what we commonly refer to
as the desired operating range. The exclusive flood
control zone, the top 6%, is reserved for only remote
floods.

Much of the runoff that we get into the reservoir
system comes to us as snow melt. This is a picture
taken up in the mountains. The drawing on the right
shows the drainage area above Sioux City. The dif-
ferent colors reflect the different amounts of run off
under average conditions. We normally get very low
runoffs through much of the plains part of the basin.
lt increases as we move on down to the south and the
east because of the increased rainfall, but by far and
away the bulk of our runoff comes to us from the
mountainous areas of the basin. The Yellowstone
Basin, you will note_, is shown in red as is the upper
end of the Missouri. So much of our water comes to
us into Fort Peck and also into Garrison. This is shown
on this chart and has a signiflcant influence on the
wav the system is operated. About a third of our water
no~mallY comes into Fort Peck. That is, of the total
runoff above Gavins Point, almost half of it comes in
that reach, mostly from the Yellowstone River between

Fort Peck and Garrison. A smaller amount from Gar-
rison to Oahe and smaller amounts then on the down-
stream reaches. 1987 was different than this. Actually
these were much smaller than their average share and
these down here were much bigger. That has been true
in both 1987 and 198&,

Because much of our runoff comes to us as snow
melt, it forms a general shape like we see on this chart
right here. This calendar year shown is January
through December. We have low runoffs in the winter
time, higher runoffs in the March/April period during
the plains snow melt and the spring rains, but the bulk
of the ru,noff, about half,occurs within the three
months of May, June, and July. Mountain snow melt
causes this very large rise. That's when we get the
bulk of our water into Fort Peck and into Garrison.

As you can imagine, the runoff that we experience
is much above normal to much below normal. This is
a graph (Figure 2) that shows the annual runoff above
Sioux City in millions of acre-feet. That's not partic-
ularly important except to note that the average i~
right here, 25 million acre-feet. We've had runoffs as
low as ten million and as high as 40 million acre feet.
Somehow our plans have to allow for the variations
in runoff. This is only above Sioux City. We get similar
variations in runoff in the tributaries downstream. If
you are living at Bismarck, North Dakota, you would
like the system to take care of the vagaries of nature
at Bismarck. If you are living at Sioux City, you would
like it to take care of the vagaries of nature at Sioux
City. Likewise at Nebraska City, Kansas City, or
Booneville or wherever you might live. This helps to
demonstrate that there. are some wide variations in
the runoff that we expect. Actually a ratio of four to
one between the largest year and the lowest year.

The system is designed to serve these authorized
purposes. These have aII been mentioned before. I did
not list on this chart endangered species. I consider
that to he part of fLsh and wildlife. I will talk about
endangered species when we discuss fish and wildlife
in just a few moments.

How do we do this? Some of the things Dr. Sheer
mentioned this morning were making plans and run-
ning studies and that sort of thing, and I am going to
demonstrate now what we have done in the Missouri
River Basin to decide how these reservoirs ought to
be operated.

First of all we publish an annual operating plan,
which you may obtain by contacting me. We discuss
this at our fall meeting in October. That has just been
printed. We got it back from the printer yesterday and

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