PROJECT ALERT NOTICE (MN) Flooding in southern Minnesota, day 14

Date: Wed, 27 Mar 2019 18:29:26 EDT

Summary: Flooding from snowmelt continues in southern Minnesota as tributaries are beginning to peak and drive rises on the main-stem Minnesota and Mississippi Rivers.

Flooding continues in southern Minnesota in the Minnesota River basin and southern tributaries to the Mississippi River basin. One or more gages have been at or above NWS flood stage each day since March 14. Currently, 17 gages are above minor flood stage, including 5 at major flood stage. Ice jams have been more frequent, widespread, and severe than recent snowmelt events, causing unpredictable backwater flooding. Ice jams caused the Redwood River at Marshall (05315000) to flow into an interbasin diversion into the Cottonwood River basin, and have caused provisional peak stages of record at Root River near Houston (05385000) and Chippewa River near Watson (05030000). Without additional rain, Mississippi main-stem gages from the Twin Cities to Iowa are forecast to continue rising beyond the forecast period at the end of March.

USGS deployed 4 teams (7 staff) today to make measurements , repair gages, and collect suspended-sediment samples. To date, 5 secondary stage sensors have been installed at gages to improve data during ice-out or in-case ice and debris destroy orifice lines. Damages and losses due to ice-heave, ice flows, and ice jams, include crest-stage gages for peak confirmation, possibly an index-velocity meter at Minnesota River at Ft Snelling (05330920), two bank-operated cableways, and a DCP and gage battery (inundated). Today an ADCP was lost while making a discharge measurement at the Pomme de Terre at Appleton. Tomorrow a gage on the Mississippi River above Red Wing (05355235) will be elevated to lessen risk of inundation.

USGS has been participating in NWSChat, communicating with the USACE-St Paul District, MNDOT and local emergency managers and public works directors, especially in communities where gages have been relocated since previous floods of this magnitude (including Marshall, New Ulm, Mankato, Houston, and Jackson, MN). The Corps of Engineers has asked USGS to make discharge measurements at the outlet of a Minnesota River flood structure that is under renovation. Two interviews have been performed with Minnesota Public Radio concerning USGS flood monitoring and ice jams.

Flooding will continue to work north into the Red River of the North Basin and other basins in the northern two-thirds of Minnesota over the next several weeks.