In the aftermath of the 2019 flood in the Lower Missouri River Basin, the U.S. Army Corps of Engineers (USACE) was tasked by the four governors of Iowa, Nebraska, Kansas and Missouri to “do something different” in terms of flood resiliency in the region. As part of this effort, we have coordinated with many of you in Planning Assistance to States efforts in 2020 and 2021, the Lower Missouri River Flood Risk and Resiliency Study, or System Plan, and ongoing “spin-off” studies in the State of Missouri with more studies to come in the future. In support of this historic effort to look at flood risk, USACE is also conducting updates to the Flow and Stage Frequencies on the lower river. This effort is an important step in USACE’s mission to provide accurate tools for flood risk management, and we’d like to invite you to attend a webinar to hear final results of the Flow Frequency analysis. Responses to frequently asked questions will also be covered. Please submit questions prior to the presentation if possible.

Description: The Flow Frequency Analysis Data is a critical update and will inform future study, action and planning for flood risk management in the Lower Missouri Basin. USACE and our partners will be able to use this updated data and information. ​​

Status: The study team has completed the final report. Links to the report and appendices are below. USACE expects to publish a revision 1.1 of the main report in October 2023 to address a few minor format and graphics issues and be fully 508 compliant. No changes will be made to any analysis or results.

Way Ahead: The Flow Frequency Report has been uploaded below. Stage Frequency analysis has begun. Stage frequency analysis and reviews will take approximately two years.​

What is Flow Frequency? Flow frequency analysis calculates the annual probability that a flow will be met or exceeded at a specific location.  

Flow frequency paired with stage frequency is a critical update needed to formulate localized solutions such as the current and future spin-off studies, as well as action and planning for flood risk management in the Lower Missouri Basin. Flow frequency was calculated at 10 mainstem gages.

What is Stage Frequency? Annual chance of exceeding a given stage (feet) in any year, incorporating hydraulic impacts on stage-flow, e.g., inflow timing, tributary backwater effect, bridges, levees and accounts for timing and shifts in the river to determine stage frequency between gages. 

Why is it important? Updated flow and stage frequency provides accurate information for planning and future design purposes. These updated values help to formulate solutions for increased flood risk on today's river. Using 20-year-old data isn't reflective of today's river. Flooding will occur again and want stakeholders to be prepared and understand the risk that exists today.

Flow Frequency Study results are now available. Click the links below to view the results:

Flow Frequency Study Results

Flow Frequency Study Results - Appendix A

Flow Frequency Study Results - Appendix B

Flow Frequency Study Results - Appendix C

Flow Frequency Study Results - Appendix D

Flow Frequency Study Results - Appendix E

Flow Frequency Study Results - Appendix F

Flow Frequency Study Results - Appendix G

Flow Frequency Study Results - Appendix H

Flow Frequency Study Results - Appendix I

Flow Frequency Study Results - Appendix J

Flow Frequency Study Results - Appendix K

Flow Frequency Study Results - Appendix L




Want to watch previously recorded webinars and meetings about the Flow Frequency and Stage Analysis studies? Click on the videos below. 

July 19, 2023 Flow Frequency Study Results Webinar Slides 



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