UMRS Hydraulic Model Update - Questions & Answers

The Corps of Engineers has recently completed new, updated hydraulic models for the Upper Mississippi River System, including the Illinois Waterway. This collaborative effort involved review and coordination with a variety of state and federal agencies, and was facilitated by the Corps of Engineers Rock Island, St. Louis and St. Paul Districts, and uses the Hydrologic Engineering Center's River Analysis System (HEC-RAS).

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An experienced HEC-RAS hydraulic modeler will be able to run the model. It is important to have an experienced hydraulic modeler to assure appropriate use of the model inputs and modeling results. Most likely a scientist or manager would not have the training or experience to make modeling run in a workshop setting.

The updated HEC-RAS model parameters were reviewed and determined by the technical team using standard modeling practices, professional judgment, and by calibration of the model to observed data.

An electronic copy of the updated HEC-RAS model will be available to anyone wishing to obtain a copy.

Federal and state users of the model will periodically evaluate when the HEC-RAS model needs updating. The need for a model update would be identified by significant changes in system hydrology or topographic features.

The updated HEC-RAS model could provide the basis for future floodway computation, collaboration, and coordination, if desired.  A source of funding would need to be identified for such an effort.

HEC-RAS does not attempt to model the near-field, multi-dimensional effects of river training structures. The model incorporates the observed river geometry and bathometric data which reflects the impacts of these structures on the river morphology.

Updates required to support water management will be made through the Corps’ future Operation and Maintenance funding, if available. Other modifications to the model will require project funds related to the purpose of the changes.

The completed model will use HEC-RAS software which is available to the public at the following site:

If a community determines there may be an issue with the final model, the community should document the issue and contact the Corps to resolve it. During the HEC-RAS model implementation, a QA/QC and a technical review was performed by Corps modeling experts. State and federal agencies were also provided an opportunity to review the model and suggest edits during its development.

During implementation, outreach for updated bridge and levee elevation data was requested from federal, state and local partners. Only data certified by a licensed land surveyor was included in the updated model and incorporated where appropriate.

The updated HEC-RAS model can provide a variety of outputs related to ecological and economic analyses. Consultation with a trained and experienced hydrologic modeler should be conducted to determine whether the updated model is appropriate for the required analyses.

The updated HEC-RAS model can be broken down to pool reaches; however, the modeler would need to use the appropriate upstream and downstream boundary conditions for that specific pool reach. Additional downscaling may require the use of other modeling programs. Consult a trained and experienced hydraulic modeler to determine these requirements.

Alternatives can be modeled by modifying the updated HEC-RAS model. The alternative would need to be incorporated into a copy of the base condition (i.e., existing condition model) by a hydraulic modeler that has HEC-RAS modeling training and experience.

The updated HEC-RAS model will provide a base-condition hydraulic model that could be modified for various hydraulic modeling applications (i.e. sediment, water quality, etc.) by an experienced HEC-RAS hydraulic modeler with the appropriate HEC-RAS modeling training.

The updated HEC-RAS model was a coordinated effort involving the Corps of Engineers, Federal Emergency Management Agency, National Weather Service, U.S. Geological Survey; the states of Illinois, Iowa, Minnesota, Missouri, and Wisconsin; and interested private individuals as members of the public involvement group. In addition, technical advisory groups consisting of nationally renowned experts were formed to help address the complex issues of hydrology and hydraulics. The model update process also included comprehensive quality assurance, quality control, and independent technical reviews though several iterations and levels of review.