PROJECT ALERT NOTICE (MN) Flooding in Minnesota, day 18

Date: Sun, 31 Mar 2019 15:10:14 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, 22 gages are above minor flood stage, including 5 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 flow into an interbasin diversion and provisional peak stages of record at two streamgages. 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 2 teams (3 staff) Saturday and 1 team (3 staff) Sunday to make flood measurements. Today staff measured (provisionally) 119,000 cfs at the Mississippi River at St Paul, which would be the 5th highest annual peak since record began in 1893. Since flooding began, 87 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, two bank-operated cableways, two DCPs and a gage battery. An ADCP was lost during a discharge measurement March 27.

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 conducted with Minnesota Public Radio concerning USGS flood preparations, monitoring and ice jams.

Flooding and staff response have begun working north into the Red River of the North and other basins in Minnesota.