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Missouri River Water Management


Frequently Asked Questions about the Missouri River System

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 What caused flooding in Sioux City, IA and areas to the south on the Missouri River in 2024?

The flooding in late June/early July 2024 was due to heavy rain that fell in the unregulated areas of the basin downstream of Gavins Point Dam.

Those tributaries include: Rock River River, Vermillion River, Big Sioux River, Little Sioux River and the Floyd River which all had record high levels. In an effort to offset some of the high flows, releases were reduced from 29,000 cfs to 24,000 cfs on June 21.

In order to provide addition flexibility the Gavins Point spillway was operated in conjunction with flows through the powerhouse with approximately 15,000 cfs through the spillway and 9,000 cfs through the powerhouse.  Total releases were not increased.

Flows have been further reduced as inflows into Gavins Point reservoir have tapered off. Releases from Fort Randall Dam averaged less than 12,000 cfs beginning June 21 and was further lowered to an average of 2,000 cfs on June 22 with several periods of zero release.


 Why do you store more water for Recreation or Fish and Wildlife?

We do not hold more water for recreation or fish and wildlife! 

Because water exists behind a dam, there is naturally an opportunity for recreation. By having Recreation and Fish and Wildlife n authorized as a purpose means we can receive federal funds to have and maintain campsites, boat ramps, park rangers, equipment to provide water rescues, etc.

The purpose for Fish and Wildlife allows us to plant food plots for the wildlife that call the land surrounding the dams home, it also allows agencies like state Game, Fish and Parks to stock the lakes and the Department of Fish and Wildlife to have Fish Hatcheries such as the ones at Fort Peck, Garrison and Gavins Point Dams.

 Can you add river stations to the bulletins on your website?

Yes. We’ve recently modified our Daily River Bulletin to include additional river stations.

We also link to hourly data for several stations. 

 Which technical reports are updated to reflect annual runoff?

Technical studies are periodically updated to include the most recent information. The report “Runoff Volumes for AOP Studies” was last updated in August 2013 to include runoff data from 1898 to 2011. 

A variety of studies and reports on the operation of the Missouri River Mainstem System are prepared and published regularly.

Statistical information on the operation of the Missouri River Mainstem System is recorded and evaluated by the Missouri River Water Management Division.

 Which agency is responsible for making runoff inflow projections?

The U.S. Army Corps of Engineers (Corps) Missouri River Basin Water Management (MRBWM) office develops runoff volume forecasts for the purpose of meeting downstream flow targets to serve system purposes such as navigation, water supply and flood control.

Runoff forecasts for Mainstem System operations use data from the National Weather Service’s Missouri Basin River Forecast Center and Climate Prediction Center, the U.S. Geological Survey, the Natural Resources Conservation Service, State climate offices, and others.

Short-Range Runoff (Inflow) Projections: Day-to-day scheduling of releases is necessary to regulate the System on an integrated basis and requires the Corps to develop daily flow forecasts at key streamgaging locations throughout the basin. These forecasts are based on observed and anticipated precipitation, temperature, temperature-snowmelt relationships, rainfall-runoff relationships, observed streamflow in the main stem of the Missouri River and tributaries, previous precipitation and other factors that often may be subject to only qualitative analysis.

Lower Missouri River Streamflow Forecasting: Scheduling releases from Gavins Point during the open-water season (generally late March through mid-December) is based on downstream navigation target locations on the Missouri River at: Sioux City, IA; Omaha, NE; Nebraska City, NE; and Kansas City, MO. Of these four locations, Omaha, Nebraska City and Kansas City also serve as downstream flood control target locations. The Corps’ Missouri River Basin Water Management office schedules the mainstem project releases, including Gavins Point. Scheduling Gavins Point releases requires developing accurate forecasts of lower Missouri River reach inflows between Gavins Point, the lowermost System dam, and flow forecasts of at the four downstream target locations. These forecasts are developed daily and project 14 days in the future. They are compared to daily forecasts developed by the NWS's Missouri Basin River Forecast Center.

Monthly Reach Inflow (Runoff) Forecasts: The first week of each month, the MRBWM office prepares a monthly incremental inflow forecast for the six System reservoir reaches. These forecasts are based on, but not limited to: monthly average reach runoff, historical reach runoff, existing and previous soil moisture conditions, reach precipitation and/or river gage readings during March-April and May-July, observed reach temperature, accumulated snow over the incremental drainage area, long-term precipitation and temperature outlooks, and accumulated mountain snow water equivalent. Projected runoff calculations includes water in the system, in the soil, in mountain snow, and plains snow estimates and precipitation outlooks from the National Weather Service's Climate Prediction Center.

 Why does the runoff forecast change so much in some years?

Short-term forecast precipitation is not included in runoff volume forecasts. When and where precipitation occurs and how it appears in tributaries is imprecise. Forecasting runoff volume without including forecast precipitation is why runoff volume estimates can change significantly.

 What is current stage and flow in my location?

The National Weather Service Missouri River Basin Forecast Center provides forecasts for rivers and tributaries in the Missouri River Basin.

The Daily River Bulletin is a daily product from the U.S. Army Corps of Engineers Missouri River Basin Water Management office, which includes current stages and flows for various locations throughout the basin.

 What are you going to be releasing in the next few months?

Each month we update our upper basin runoff forecast and reservoir studies. The Missouri River Mainstem System of dams is operated as a system and release decisions are evaluated system-wide.

 Are there flood forecasts, similar to Hurricane Season predictions?

Yes, the National Weather Service regularly issues Hydrologic Outlooks. They also share considerable information regarding Flood Safety on their website.

There are two types:
Short-term (1 to 7 days) Hydrologic Outlooks can be issued to alert the public of the potential for flooding in the near-term such as when heavy rainfall is forecast that could result in flooding or aggravate an existing flood if it occurs.

Long-term (weeks to months) Hydrologic Outlooks may also provide river or reservoir level and/or flow information. This information could be used for water supply concerns or projection of snowmelt flooding. In the Missouri Basin, the Spring Hydrologic Outlook is issued in February and March.

A long-range river flood outlook is available on the NWS website and shows locations with a greater than 50% chance of exceeding river flood levels in the next 3 months. The website is interactive and can show flood chance percentages from 5 to 95%.

Hazardous Weather Outlooks and Alerts may also be indicators of potential for flash flooding.

Similarly, drought information is also available for Weekly, Monthly or Seasonal Outlooks.

 Why don't you release more water in the winter months?

The Missouri River freezes completely over in the upper basin during the winter, which greatly restricts the amount of water we can release from the Fort Peck, Garrison and Oahe reservoirs. While it appears it would be beneficial to make higher releases during the winter, it is not that simple. During the winter an ice cover forms over the river channel making the river a “pipe”. If we push too much water down the “pipe”, it will burst. When the ice cover forms, the river stage dramatically increases. Once the ice cover forms, we slowly increase releases and smooth out the underside of the “pipe”; thus releasing more water. However, the maximum winter releases are never going to be as high as the releases we can make during open water (non-ice cover) conditions.

 Wouldn’t higher releases prevent river ice from forming?

Increasing flows on the river does not prevent ice from forming. Reasons for this include sustained outside temperatures below freezing, high wind chills, and water temperatures that will drop below freezing at the water’s surface.

Increasing flows also increases the river stage. The river will still freeze but at a higher stage, which would increase flood risk.

A warmer winter, even in Montana and North Dakota, still means below-freezing temperatures and frozen tributaries and rivers.

 What does flood storage capacity mean and why can’t it be bigger?

Space is reserved in each reservoir to capture and manage runoff during the high runoff months (March-July) which is then emptied during the lower runoff months (August-November). That reserved space is the designated flood storage volume. A volume of 16.3 million acre-feet (MAF) was established based on more than 100 years of hydrometeorogical data and the engineering capacity of the System projects.

The Missouri River Basin Water Management office makes regulation decisions so all 16.3 MAF of the reserved flood control space is available at the start of each runoff season, which is around March 1. The combined flood control space of the six projects totals 16.3 MAF. When we have 16.3 MAF of flood control space available to capture runoff, we are also storing 56.1 MAF of water in the six reservoirs.

If the 16.3 MAF of flood control space were larger, then the releases would be even lower when runoff is lower and releases would be even higher when runoff is higher. This is because the System would still be operated to return to the set amount of available flood control space by March 1.

 Who do we contact when the river is flooding?

There are different resources available to you when the river is flooding dependent upon your location.

Local levee sponsors should be contacted regarding interior drainage issues, or water on the "dry side" of the levee. The National Levee Database is the best resource for locating your local levee sponsor.

If you want to take measures to prevent stream bank erosion during a high water event, work with local Regulatory offices to ensure you are in compliance with state and federal laws.

If you represent a Federal, Tribal, State or Local agency you can contact either the Kansas City District Emergency Management Office (for Missouri Basin locations south of Rulo, NE) or the Omaha District Emergency Management Office (for Missouri Basin locations north of Rulo, NE).

 What locations are above flood stage today?

The National Weather Service Missouri River Basin Forecast Center shows locations that are currently in minor flood stage or higher.

This NWS MRBFC chart shows river stage observations for locations throughout the Missouri River Basin.

 What do we need to know about El Nino and La Nina?

The National Oceanic and Atmospheric Administration monitors the status of El Nino and La Nina providing outlooks each quarter.

Quarterly climate outlooks are published through the National Integrated Drought Information System.

The National Weather Service Climate Prediction Service has compiled several frequently asked questions about El Nino and La Nina.

 How do Spillway Gates hold back water without leaking?

Each gate has rubber seals around them. There will still typically be some leakage. There are stoplogs that can be placed on the upstream side of the gate that will allow work, such as inspecting or replacing the rubber seal, on a dewatered gate to take place when water is above the spillway elevation.

 What are the navigation service levels?

Service levels are established flow rates at 4 target locations on the Missouri River which when combined with the Missouri River Streambank Stabilization and Navigation Project (BSNP) provide for reliable commercial navigation.  The target locations are Sioux City, Omaha, Nebraska City and Kansas City.  The Corps manages system releases to be either full service flows, minimum service flows, or intermediate service flows.  Minimum service flows, combined with the BSNP should provide for an 8-foot deep by 200-foot wide channel, while full service flows should provide a 9-foot deep by 300-foot wide channel.  Intermediate service flows would provide channel dimensions some where between full and minimum service.  

 How do you meet navigation service levels?

The U.S. Army Corps of Engineers makes system releases that when combined with tributary inflow below Gavins Point Dam meet the desired flow targets.  If the tributaries are producing a relatively higher amount of water, then releases will be decreased.  If the tributaries are producing a relatively lower amount of water then releases will be increased.

(However, during a drought, if there is no barge traffic in a given reach, water managers may choose to not meet one or more of the targets as a means to conserve water in the upper basin reservoirs.).


 Where are the pinch points in lower Missouri River -- what is the non-damaging conveyance at each Missouri River streamgaging location from Gavins Point Dam to Hermann, Missouri?
Missouri River Location Flood Stage (in feet) Flow at Flood Stage (in cfs)
Sioux City 30.0 125,000
Decatur 35.0 121,000
Omaha 29.0 116,000
Nebraska City 18.0 92,000
Rulo 17.0 90,000
St. Joseph 17.0 100,000
Kansas City 32.0 241,000
Waverly 20.0 117,000
Boonville 21.0 162,000
Hermann 21.0 195,000
 What volume can the upstream dams hold before releases from Gavins Point become mandatory?

It is unclear what is meant by mandatory releases as we are required to release water from all the projects every day to meet the Congressionally authorized purposes. However, with respect to flood control operations, there are two separate zones -- the annual flood control and multiple use zone and the exclusive flood control zone. Ideally we would operate in the annual flood control and multiple use zone year-round. While in this zone, we could capture the spring and early summer runoff that could cause or contribute to flooding and meter that water out at the lowest possible rate over the longest period of time. This provides the greatest amount of flood risk reduction.

The top of the annual flood control and multiple use zone is set at 67.7 million acre feet (MAF).  Once System storage exceeds this mark we are in the exclusive flood control zone, which we attempt to empty as quickly as practicable. It is important to keep in mind that any water stored in these flood control zones must be evacuated before the next runoff season.

 What is the design level recurrence interval for Pick/Sloan and/or Federal levees?

Only the federal levees that protect cities (e.g. Omaha or New Haven) were designed for recurrence interval and that level is generally 500-year.The remainder of the levees are referred to as agricultural levees and were designed to a certain discharge (flow rate); they were not designed for a certain level of protection. The design discharge varied depending on location.

 If flood control is not a large factor in the Gavins Point reservoir, what is it's role or how are it's operations considered?

Gavins Point is a re-regulation reservoir with a very small amount of flood control storage, which is to be used only for small, local events.  Gavins Point smooths out releases from upstream Fort Randall, which has large release fluctuations based on hydropower demands.

 Does the sediment affect the re-regulation aspect of Gavins Point Dam?

The sediment doesn’t currently affect the re-regulation, but it does affect access in the Gavins Point headwaters and the water levels in the Niobrara area.

  1. Sedimentation in the reservoirs continues to be a big concern for the League and many other groups. How is the Corps working with federal, state, and tribal agencies and landowners to implement practices that will reduce erosion from entering the system?
  2. Can you provide any updates on exploring methods to reduce the amount of accumulated sediment currently in the reservoirs?
  1. In general, sediment management in the watershed is not the responsibility of USACE. The Corps lacks authority to implement projects in the watershed. However, the Corps has done some studies in the Niobrara river basin through our regional sediment management program where we identified a number of possible sources and identified at the conceptual level some possible solutions that could be implemented if authority and funding was provided.
  2. There are multiple reservoir flushing events across the US being monitored by the Corps. We are currently developing better tools to develop sediment yield from the reservoirs where data is sparse. USACE is updating the regulatory guidance on permitting discharging sediments from reservoirs and incorporating this into lessons learned. We are looking at efforts in reservoir sediment research to develop tools that can be used.

    Multiple districts including the Omaha District have begun working on Sediment management plans for reservoirs to examine ways to reduce sediment load from the watershed as well as ways to regain equilibrium of sediment transport in the channel below the dams. These efforts are in their infancy, and in these two efforts in particular, action is still quite a ways into the future.