Upper Missouri Reservoir Levels: Sakakawea & Ft. Peck

Lake Sakakawea and Ft Peck Reservoirs combined with flows from the Yellowstone River are the areas of most concern to Bismarck/Mandan residents.  The Corp of Engineers releases daily updates on Reservoir levels through their website which is linked below.

Understanding the Data:

The website update is given in rough data and looks like the screen shot posted below.  The Important columns have been highlighted in the screen shot  and explained so you know what to watch for.

Missouri River Reservoir Report

Current Lake Level: (Yellow Highlight) This is the current elevation of the two reservoirs above Bismarck/Mandan

Water Coming In: (Blue Highlight) This is the amount of water flowing into the lake from all its tributary rivers.

Water Coming Out: (Green Highlight) This is the amount of water being discharged or flowing through the dam.

This Army Corp of Engineers page is typically updated at 11am each day.

Spillway Depth:

This is the height of the top of the dams.  When the lake level reaches spillway depth these reservoirs will spill into the river which will eliminate all flood control besides localized diking.  The amount flowing into the rivers will be equal to the amounts flowing into the reservoir.

Ft Peck Spillway Elevation: Approximately 2250 ft or a bit higher.

Lake Sakakawea Spillway Elevation:  Approximately 1854 ft  or a bit higher.

If anyone has clarification on EXACT spillway elevations we’d love to have it.  Get in Touch.

How Quickly do the Reservoirs Fill?

It depends on how much water is coming in and how much water is going out.  For the past couple days (May 23,24,25) Lake Sakakawea has been filling at approximately 60,000 CFS (Inflow: 120,000 CFS minus Outflow: 60,000 CFS equals the fill rate) and has been rising approximately 3-4 inches per day.

Bottom line:  With record high flows like we’re seeing right now, it can fill relatively fast.

These are approximations based on watching the data closely for the last few days.  We hope to be in touch with the Corp of Engineers today (May 26) to get some hard numbers related to fill rates.

What is Cubic Feet per Second (CFS & KCFS)?

Cubic Feet per Second is the way we measure the volume of water flowing in a river.  1 cubic foot is the volume of water that would fill a box 1 foot tall by 1 foot wide by 1 foot deep.  In many of the measurements volume is abbreviated to KCFS which is short hand for thousands of cubic feet per second.

A gauge reading of 6.5 KCFS would equal 6,500 Cubic Feet per Second (6.5 x 1000)

The Yellowstone River:

The Yellowstone river is not a friend to the Bismarck/Mandan area right now.  The Yellowstone flows directly out of the Montana Mountains near Yellowstone park and Bozeman, MT. and contributes significant water to the Missouri River watershed when it joins the Missouri just west of Williston and Lake Sakakawea.  There is no flood control in place along the Yellowstone river, and flows are typically the result of Mountain snow melt.  Recent high flows in the Yellowstone have been attributed more to heavy rain than snow pack, which has yet to start flowing significantly due to the cool spring in Montana.  Here’s hoping for a slow melt!

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