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Protecting Roads From Flood Damage

MnDOT knows what kind of damage flooding can do to our transportation system and the efforts required to repair that damage. With the impacts of climate change increasing, new approaches are needed to understand vulnerabilities across the transportation system and what actions can be taken to minimize expanding risks.

MnDOT has multiple research projects and initiatives addressing this topic.

Slope Stabilization Guide for Minnesota Local Government Engineers

Slope Stabilzation Guide CoverSlope failures must be repaired to prevent damage to roadways and embankments. When slope damage is severe, a geotechnical engineering firm must step in at some expense. But when damage is less severe, a county can often stabilize the slope using local materials and simple techniques.

A new guidebook provides eight cost‐effective stabilization techniques that local government engineers can undertake to stabilize slopes using local materials and equipment. It includes a simple, three-step flowchart that helps engineers quickly select the most appropriate repair technique.

The methods are the result of a research effort that analyzed recent slope failures in Minnesota. Researchers examined 14 destabilized sites, analyzing soil samples from each; identified 12 potential stabilization techniques from a literature search; and used computer modeling to examine the viability of various techniques at sites where soil was sandy, fine-grained or rocky. They also interviewed local engineers about what practices have worked well.

Project Materials

This project dovetails with two ongoing MnDOT research efforts, Slope Failure Risk Analysis and MnDOT Slope Vulnerability Assessments.

Highway 210 Reconstruction Project

Section of Highway 210 destroyed by 2012 flood Up to 11 inches of rain fell in areas of Carlton County in June 2012 and caused widespread flooding and significant damage to both public and private infrastructure. A two-mile section of Hwy 210, which serves as the east entrance to Jay Cooke State Park, was closed due to significant damage from severe flooding.

The highway was severely impacted not only by the rainfall and associated hillside slumping along several stretches of the highway within the park, but also by the failure of an earthen embankment along the south shore of Forbay Lake just east of the state park headquarters.

MnDOT repaired slopes, restored damage, reestablished vegetation and resurfaced the highway in areas that washed out during the 2012 flood. Work began in late May 2015 and is scheduled to be completed in October 2017.

MnDOT Flash Flood Vulnerability and Adaptation Assessment Pilot Project

Flood waters washing out road and bridge in District 1
Minnesota’s climate is changing. Temperatures are on the rise and extreme precipitation events and asso-ciated flooding are becoming more frequent and severe. As the Earth continues to warm, these events are projected to become even more common since a warmer atmosphere is capable of holding more water vapor.

Recognizing this, MnDOT planners and engineers have long considered minimizing the risk of flash flooding in the siting and design of the state’s roadway network. However, as has been the standard practice worldwide, they have traditionally assumed that future climate conditions will be similar to those recorded in the past. Climate change challenges this assumption and calls for new approaches to understanding vulnerabilities across the highway system and at specific transportation facilities so that appropriate actions, adaptations, can be taken to minimize expanding risks.

This project, one of 19 Federal Highway Administration (FHWA) climate vulnerability pilot studies nationwide looking at the effects of climate hazards on the transportation system, represents a starting point for developing these new approaches. The focus of this pilot study is on flash flooding risks to the highway system. While flooding is not the only threat to the state’s highway system posed by climate change, it is likely to be one of the most significant and has already caused extensive disruptions to the transportation system in many areas.

A final report for the MnDOT Flash Flood Vulnerability and Adaptation Assessment Pilot Project was published in November 2014.

Design Considerations for Embankment Protection During Road Overtopping Events

Spring flooding in Red River ValleyRoadway overtopping is a major safety concern for Minnesota transportation managers because of the potential for rapid soil erosion and mass wasting resulting in partial or complete failure of the roadway embankment. This multi-year research study focused on various aspects of the roadway embankment overtopping.

A robust literature survey was performed to identify research, reports and other published knowledge that would inform the project. A fieldbased research campaign was developed with the goal of collecting data on the hydraulics associated with full-scale overtopping events.

Finally, a series of laboratory experiments were conducted at the St. Anthony Falls Laboratory, University of Minnesota to study the hydraulic and erosional processes associated with embankment overtopping and in particular study of three slope protection techniques under overtopping flow. The largest component of the research project was the laboratory hydraulic testing, which focused on bare soil (base case) and three slope protection technologies. A fullscale laboratory facility was constructed to carry out the testing.

Three erosion protection techniques were examined including armored sod, turf reinforcement mat and flexible concrete geogrid mat.

Overtopping depths of up to one foot were used to determine the failure point of the protection technique and soil on both the 4h:1V and 6V:1H slopes.

The full project report, published in June 2017, details the testing of each protection technique as well as observations and findings made during the testing.

Slope Failure Risk Analysis

This project involves the development of a GIS-based slope failure risk model to identify areas of low, medium, and high susceptibility to slope failure in a region. The model was applied to two counties in Minnesota, and the results are presented in map format showing areas where slope failure is likely and the expected level of risk.

Project Materials

The Slope Failure Risk Analysis project is scheduled to be completed in November 2017.

MnDOT Slope Vulnerability Assessments

Slope failures can damage or obstruct roads and rail lines as well as inflict significant damage to properties. The disruptions can sometimes last years (see the Minneapolis River Road as a current example). The MnDOT Flash Flood Vulnerability and Adaptation Assessment Pilot Project identified an assessment of slope vulnerability as a key next step. Several districts have also expressed interest in identifying and measure risks of future slope failures.

Several LRRB-funded research projects are studying slope failures and developing GIS-based vulnerability tools. In addition, University of Minnesota Geology Department, the DNR and Hennepin County are currently researching slope failures and identifying risk factors for future slides. Other efforts have been undertaken in states like Colorado and Washington.

This effort would build on the LRRB and Hennepin County work, other national research, and the flood vulnerability assessment to identify vulnerable slopes near trunk highways (and potentially CSAH or MSAS routes) in three or four MnDOT districts. High-priority districts for inclusion in this effort are districts 6, 7 and Metro.

The MnDOT Slope Vulnerability Assessments project is just getting underway and a project completion date is yet to be set.