PROJECT ALERT NOTICE (MN) Flooding in southern Minnesota

Date: Mon, 25 Mar 2019 18:09:48 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 especially in the Minnesota River basin and southern tributaries to the Mississippi River basin. Currently, 14 NWS river forecast gages are above minor flood stage; 4 of which are greater than major flood stage. Ice jams have been more frequent, widespread, and severe than recent snowmelt events, causing unpredictable backwater flooding. At 05315000 Minnesota River at Marshall, MN (05315000), an ice jam caused the Redwood River to flow into an interbasin diversion into the Cottonwood River basin. Another ice jam resulted in a provisional peak (stage) of record at 05385000 Root River near Houston, MN, and nearly flooded the town of Houston. 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 has 3 teams (4 staff) deployed today to make measurements and repair gages. To date, 5 secondary stage senors have been installed at gages to improve data during ice-out or in-case ice and debris destroy orifice lines. Damages to date include crest-stage gages for peak confirmation, possibly an index-velocity meter at 05330920 Minnesota River at Ft Snelling, MN, and a bank-operated cableway; all destroyed by ice-out or ice flows.

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, and a third is possible.

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