Advanced Hydrologic Prediction Service: Mississippi River at St. Paul

Graphical representation of flood inundation for NWS flood categories are based on steady state hydraulic modeling of water surface elevations for incremented discharges. Map shows approximate inundation areas for given water surface elevations and should not be used for navigation or permitting or other legal purposes, but strictly as a planning reference tool.

Site-specific information:
The flooding conditions depicted in this map reflect the ground elevation from topographic data collected in November 2011. Any changes in ground elevation post November 2011 will change the depicted flood conditions.

Levee embankments and flood walls are present in the City of St. Paul. Levees/floodwalls are depicted as red lines on the map, and the leveed areas protected by the levee/floodwalls are depicted as yellow polygons. The structures included in the model within the mapping reach are the St. Paul/USACE Levee, Xcel Levee, St. Paul Holman Field Airport Floodwall, and Pig’s Eye Waste Water Treatment Facility Levee. These protection systems include both permanent structures as well as temporary structures implemented with each flood event. These inundation maps were developed with the assumption that these temporary structures were constructed. Additional protection in other areas is also typically constructed by the state and/or individual businesses in preparation for a flood. This additional protection is not included in the hydraulic modeling or display of the flood-inundation maps.

These maps also assumed that areas behind the levees/floodwalls remained dry until these flood control structures were overtopped. These maps did not account for seepage or potential structural problems that may occur prior to or after water levels rise above the top of the levee or floodwall.

In addition, the maps do not account for ground water seepage, ponding of water due to movement through the soil layers, or flooding due to localized heavy rainfall and snow melt. The intent of these maps is to show flooding as a result of rises on the Mississippi River.

The maps will show bridges as inundated once the water hits the lowest point of the bridge deck. However, the bridge owner will determine when the bridges will be closed. Due to other safety concerns, they may close the bridges prior to the maps showing the bridges being impacted.

The stream gage at this location has been recently relocated from Smith Ave to Roberts St. When the gage was re-installed at the Roberts St location, due diligence was performed to ensure the stage level continuity. The impact stages & gage record are valid and consistent for both the Smith Ave and Roberts St locations.

Any building flooding and associated depth of flooding shown is representative of flooding at the adjacent grade elevation of the structure. Depths should be carefully evaluated on a case-by-case basis, relative to the adjacent grade elevation. It should not be assumed that flooding overtops the roof of the structure, however, the ground around the building and lower levels of the building may be inundated.

For further information about this study, see the USGS report at: http://pubs.usgs.gov/sir/2014/5079/

Extended rating:
The USGS has developed a rating curve, or relationship between stage and streamflow, for stages and streamflows up to the 1965 flood of record. Above the level of the 1965 flood of record, the rating curve was extrapolated based on hydraulic computations by the USACE. There is additional uncertainty in the flood forecasts and flood-inundation maps at these unprecedented streamflows.

Map Overlays