PROJECT ALERT NOTICE (MN) Flooding in southern Minnesota, day 15

Date: Thu, 28 Mar 2019 15:56:38 EDT

Summary: Flooding from snowmelt continues in Minnesota as the mainstem Minnesota and Mississippi rivers in the southern third of Minnesota begin to crest, while streams farther north begin to rise.

Flooding continues in southern Minnesota in the Minnesota River basin and tributaries to the Mississippi River. One or more gages have been at or above NWS flood stage each day since March 14. Currently, 20 gages are above minor flood stage, including 6 at major flood stage. Ice jams have been more frequent, widespread, and more 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). Mainstem Minnesota and Mississippi River gages are forecast to peak near the end of the 5-day forecast period, whereas flood forecasts are beginning to be issued for gages in the northern half of Minnesota as snowmelt ramps up further north.

USGS deployed 7 teams (12 staff) to make flood measurements, raise or repair gages, and collect suspended-sediment samples today. Since flooding began, 62 discharge measurements have been made in flooding parts of the state, and 4 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 an inundated DCP and gage battery. An ADCP was lost during a discharge measurement at the Pomme de Terre River. The gage on the Mississippi River above Red Wing (05355235) is being elevated to lessen the risk of inundation.

USGS has been participating on 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 preparations, monitoring and ice jams.