A historic flood occurred in Northeastern Minnesota June 19 and 20, 2012. Some meteorologists have called it a "1,000-year-flood" suggesting another flood of this magnitude has only a one-in-one-thousand chance of occurring in any given year. The St. Louis River and its natural drainage areas reached record-breaking high levels. Flooded roads and damaged infrastructure immobilized many areas in Duluth and in areas south and north of Duluth. Within two-weeks most roadways were reopened after emergency, temporary or permanent repairs were made.
The most serious road-related flood damage occurred on Hwy 210. Hwy 210 winds through hilly terrain with steep slopes above and below the highway. These slopes are primarily composed of silty-clay with seams of sand and gravel. This type of soil is prone to slides during heavy rains. Heavy rain during a storm in early-June saturated the soil and caused minor slides. The June 19/20 storm dropped an additional 10 inches of rain on the already-unstable slopes and multiple mud slides occurred throughout the Hwy 210 corridor.
Damage on Hwy 210
There were six major areas of damage on Hwy 210. The damaged areas are listed below from the west to east. Hwy 210 photos are available.
- A 18-foot-diameter overflow pipe located next to the Thomson Bridge failed when St. Louis River flood waters overwhelmed the pipe’s capacity. MnDOT replaced this pipe with a new 110-foot-long bridge. The new bridge opened in December 2012.
Overflow water from the St. Louis River was confined in the overflow pipe to an area of 254-square-feet. The new bridge provides a 1360-square-feet area for overflow water to bypass the Thomson Bridge.
The new bridge and damage to the pavement approaching the Thomson bridge was completed as part of the existing contract that was in place for a scheduled bridge rehabilitation project that began in June. The Thomson Bridge reopened in December 2012.
- The west Jay Cooke State Park entrance had to close after a 6-foot-diameter culvert buried beneath Hwy 210 was overwhelmed and caused a 35-foot-deep, 100-foot-wide gap in the pavement. KGM Contractors was awarded a $793,000 contract for this repair.
A $310,000 custom-made box culvert was installed. The new culvert is 250-feet-long, 12-feet-wide and 8-feet-high, and consists of about 50-sections that were connected on-site. Hwy 210 to Jay Cooke State Park Headquarters and the campground reopened in October 2012.
- An earthen embankment along the south shore of Forbay Lake just east of Jay Cooke State Park headquarters gave-way on June 20. Within minutes of the collapse, all of the water in lake gushed through woods, carrying with it rocks, trees and anything else in its path. Jay Cooke State Park officials estimate that 750 million gallons of water was released when the embankment failed. When this water reached Hwy 210 its speed and velocity sliced a 50-foot-deep, 250-foot-wide gash in the highway.
MnDOT engineers and consultants have been collaborating to discuss repair options. This section of Hwy 210 will not reopen until Novemeber 2013. MnDOT hired the bridge and design consultants through an emergency contract.
- Another contractor was hired using an emergency contract; to make safety improvements for workers testing soils in the damaged area; to do any work necessary to prevent more damage to the highway until permanent repairs can be made; and to prevent erosion from occurring and potentially causing environmental damage.
- Between Jay Cooke Road and the Minnesota Power Generating Station, the storm caused a 7-foot-diameter culvert to become plugged with debris including a huge stump. Unable to properly drain through the culvert, the water eroded the soil beneath Hwy 210 and caused a section 25-feet-deep and 100-feet-wide to wash away. In this same area a 500-foot-long slope failure above and below the highway occurred. In some areas the highway slid into the ravine.
A new, 12-foot-diameter corrugated steel culvert was installed using an emergency contract to provide Minnesota Power employees access to the station. Slopes near the power station were stabilized with soil nails (see below). All soil nailing work on this section is complete. The highway is currently open to Minnesota Power Employees and contractors only.
- Numerous mud slides buried Hwy 210 and/or exposed the highway by washing away the earth below it between Jay Cooke Road and Snowball Landing. This section remains closed as damage assessments are being made and a long-term plan is developed.
- MnDOT hired Soil Nail Launcher, Inc. to stabilize areas along Hwy 210 that are prone to mud slides. The process they used is called soil nailing. Slopes west of the park and near the Minnesota Power Generating Station were stabilized under an emergency contract.