PROJECT ALERT NOTICE (MN) Flooding in MN, day 19

Date: Mon, 01 Apr 2019 15:34:25 EDT

Summary: Flooding from snowmelt continues in Minnesota as the mainstem Minnesota and Mississippi rivers in the southern third of Minnesota are cresting, 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, 21 gages are above minor flood stage, including 4 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. Provisional peak discharges have commonly had Annual Exceedance Probabilities (AEPs) of 0.2 to 0.1, but a few gages have had AEPs as low as 0.01. Mainstem Minnesota and Mississippi River gages are forecast to peak in the next 2-3 days, while flood forecasts are just beginning to be issued for gages in the northern half of Minnesota.

Today 6 teams (10 staff) are making flood measurements and repairing gages. Since flooding began, 90 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 and a field laptop have been lost during discharge measurements.

USGS has been participating on NWSChat, communicating with the USACE-St Paul District, MNDOT and local emergency managers and public works directors including communities of Marshall, Granite Falls, New Ulm, Mankato, Houston, and Jackson. 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.

Flooding and staff response have begun working north into the Red River of the North and the Mississippi and St Croix headwaters tributaries.