US Army Corps of Engineers
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District Projects

Upper Mississippi River and Illinois River Flow Frequency Study

Rock Island District
Published Sept. 15, 2020
2019 Record Flooding - Davenport, Iowa

2019 Record Flooding - Davenport, Iowa


Upper Mississippi River Basin


The current Upper Mississippi River and Illinois River flow frequency study, completed in 2004, was created using a period of record ending in 1998. Since then frequent and record setting major floods have occurred. The flood of 2019 was not only historic with regards to flood heights, but also in its duration. The Mississippi River was above flood stage at Cape Girardeau for 145 days. In addition, many communities between Dubuque, Iowa, and St. Louis, Missouri, have experienced the majority of their top ten flood crests in the past 20 years. Significant flooding on the UMR occurred in 2001, 2008, 2011, 2013, 2014, 2018, and 2019. The Illinois River has experienced the same unprecedented flooding. At Peoria, Illinois, (on the Illinois Waterway), 5 of the 10 highest flood crests have occurred since 1998; including the record crest in 2013.

This effort will update the flood flow frequency profiles on the Upper Mississippi River from Birds Point (Mile 0.0) to St. Paul, Minnesota (Mile 840.4), and the Illinois River from Grafton, Illinois (Mile 0.0), to Lockport Lock (Mile 285.0). Previous methodologies will be reviewed and modified as needed to confirm they meet the current state of the practice of flood frequency calculation. The study will utilize input data gathered during the previous flow frequency effort, augmented with new observed data to complete a 122 year period of record (1898 to 2020). Completion of the proposed study, utilizing the updated period of record and new federal guidelines for determining flood flow frequencies, Bulletin 17C, will improve confidence and reliability of flow frequencies on the UMR and IWW to support flood risk management planning and communication and the USACE Dam and Levee Safety Programs. This will provide an opportunity to incorporate available climate change into the analysis of a large river system using the latest USACE Guidance. Updated frequency profiles and associated documentation will be published at the completion of this effort.


The benefits of an updated flow frequency study on the Upper Mississippi and Illinois Rivers will be realized immediately, and ensuring water resource decisions are made using current and accurate data will provide a considerable value to the nation. The Corps continually engages with watershed stakeholders through its various programs and authorities. These stakeholders routinely ask what the effects these recent common and historic floods are on the previously calculated frequencies, and have demanded this data be included when making water resource decisions. In addition, Corps critics are quick to point out after every major flood event, how many 1% events we have seen in recent years at multiple locations throughout this region.

In FY18 to FY20 the Corps collaborated with the Upper Mississippi River Basin Association (UMRBA), on a Planning Assistance to States effort to capture Upper Mississippi River actions that were generally agreed to and could have an immediate benefit. The effort sought consensus on these actions through routine and continual engagement with potentially affected interest within the Upper Mississippi River Basin, including communities, levee and drainage districts, industry, and environmental groups. One of these high leverage actions identified in the current draft report included updating the flow frequencies. This information was viewed as fundamental to future planning and decision making. In addition, the Corps has been advancing the development of HEC-RAS hydraulic models on the Mississippi River and Illinois Rivers. The updated models on the Mississippi River will be completed in FY20 and can be immediately utilized for updating the flow frequencies, which will save time and money.


This project is a potential new start project.

If funded, major tasks in this effort include:

  • HEC-HMS models will be used to compute local inflow for the period of record.
  • Existing HEC-RAS models will be used to route the period of record flows and compute profiles for frequency analysis.
  • Existing CWMS models from regulated basins within the study area will be utilized as needed to route inflow and provide regulated vs unregulated flow information.
  • Development of an interagency team which will include USACE (MVS, MVP, and MVR), FEMA, USGS, NWS, NRCS, and state agencies from Missouri, Illinois, and Iowa.
  • Internal review and coordination will be conducted within the HH&C CoPs from MVD and HQ, and with HEC, the USACE Climate Change team, and the USACE hydrology committee, as required. Additional outside expert assistance may also be required.
  • Funding for this study will be pursued under General Investigations (GI) authorities Sec 216, Flood Control Act and the GI Flood Plan Management Services (FPMS)

Additional Information


Section 216, Flood Control Act of 1970 or General Investigations Floodplain Management Services (FPMS)

Summarized Project Costs

Estimated Federal Cost $ 2,600,000
Estimated Non-Federal Cost $ 0
Estimated Total Project Cost $ 2,600,000
Allocations Prior to FY 2020 $0
FY 2020 Allocation $0
FY 2020 Total Capability $0
FY 2021 President’s Budget $0


Major Work Item Current Year

FY 2020: None