PROJECT ALERT NOTICE (MN) Flooding in Minnesota, day 20

Date: Tue, 02 Apr 2019 18:25:43 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 and is beginning in western Minnesota in the Red River of the North Basin. 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 Mississippi River gages are forecast to peak in the next two days, while flood forecasts are just beginning to be issued for gages in the northern half of Minnesota.

Today 6 teams (8 staff) are making flood measurements and repairing one gage. Since flooding began approximately 92 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 were lost during discharge measurements.

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