Listed below are examples of case studies including best practices and/or innovative tools/approaches. This section will grow as entries are submitted or links to other sites with useful examples are provided. If you believe your agency has utilized a best practice/approach that others could learn from, please submit a short description to AASHTO (including any pertinent links) on the Share Info with AASHTO form. Please note that currently submissions are only being accepted from governmental entities.
Transportation officials in Minnesota will be better able to assess vulnerability of transportation assets to flooding and select appropriate adaptation options for damaged and at-risk infrastructure following a pilot study conducted by the Minnesota Department of Transportation. “The potential for more frequent extreme precipitation is a major risk facing our state’s aging transportation system,” said Philip Schaffner, Director of Minnesota DOT’s (MnDOT) Flash Flood Vulnerability and Adaptation Assessment Pilot Project.
The project is one of 19 Federal Highway Administration (FHWA)-funded climate vulnerability pilot studies that were carried out between 2013 and 2015. Each of the studies drew from guidance contained in FHWA's Climate Change and Extreme Weather Vulnerability Assessment Framework (FHWA Framework).
|Minnesota DOT's climate vulnerability assessment is helping the agency address threats such as this flooded culvert in District 6. Photo: Minnesota DOT|
The timing for the project could not have been better, Schaffner said.
In 2012, he explained, MnDOT had just identified climate-related flooding as a major risk to the system in the state transportation plan when Duluth experienced the worst flooding it had seen in centuries. It resulted in more than $100 million in damage to roads and other infrastructure. Other parts of the state also had recently experienced significant flooding. The state’s transportation system assets had not been originally designed to handle such extremely high levels of precipitation.
As it happened, Schaffner continued, at that same point in time, FHWA issued its second-round call for proposals to carry out pilot projects examining the effects of climate hazards on transportation systems. Unlike the broader first round of 2010-2011 pilots that primarily involved coastal locations, projects located inland were especially welcome.
MnDOT’s study had four goals:
One of the first steps taken was to create two technical committees to support the core project team. The first was composed of hydrologists, hydraulic engineers and planners. The other was staffed with climatologists and other state agencies that helped the core team understand and appropriately use climate model outputs. Much of the funding went to hire an external expert who worked closely with the in-house team.
For Phase 1 of the study, the team carried out a system-wide flash flood vulnerability assessment of the truck highway system in two of its eight districts: District 1 in the northeastern part of the state, and District 6 in the southeastern part of the state. Both districts had experienced high levels of flooding in recent years.
The assessment focused on the vulnerability of four types of assets: bridges, large culverts, pipes, and roads parallel to streams. A total of 1,819 assets were given vulnerability scores. Dozens of metrics were developed to quantify each asset’s vulnerability. Assessment scoring was based on the FHWA Framework’s definition of vulnerability, which includes three elements: exposure to a climate stressor; sensitivity to climate stressors; and to what extent the transportation system as a whole can adapt if a particular asset is taken out of service. Findings provided a detailed snapshot of the two Districts’ assets’ vulnerability.
For Phase 2 of the study, one high-risk culvert in each district was selected to examine in more detail in order to identify robust, cost-effective adaptation measures.
In District 1, the culvert was located along a stretch of the highway system that borders Lake Superior and already was on a list of assets to be improved. In District 6, the culvert lay beneath a road over a creek in a small town, and no improvements had been scheduled. The study teams examined vulnerability for both culverts under low, medium, and high climate change scenarios.
Adaptation options differed somewhat for each culvert. They included actions such as increasing the size of the culvert, replacing the culvert with a simple span bridge to improve fish passage, and enhancing the floodplain upstream of the culvert.
Next, a cost-effectiveness analysis for each option was carried out. The analysis considered both direct costs to MnDOT as well as social costs such as travel time costs to motorists taking detours. For one of the culverts, a clear adaptation choice emerged -- add cells to the existing culvert design. For the other culvert, the conclusion was more nuanced, depending upon whether or not the analysis included social costs.
One of the unique features of their pilot project, Schaffner said, is their use of proxy variables. For example, the team used an estimate of the percentage of the drainage area that was forested as a proxy for potential woody debris that could clog a pipe, culvert or bridge opening in the event of a flood.
As is the case for any pilot project, he said, there were challenges along the way. For instance, it was difficult to compile consistent and accurate data for more than 1,800 assets. And upon reflection, there were several factors that would receive greater attention and refinement should MnDOT decide to carry out a new group of assessments.
First, more time would be devoted to discussing how to most accurately weigh each variable. Second, adaptive capacity would be extended beyond traffic volume and detours, which were the primary considerations in the pilot study. In addition, the team would look to more advanced techniques of downscaling data from global climate models.
Schaffner said the FHWA Framework was valuable in providing a “high level” foundation for the project. However, although the team was able to turn to earlier projects for some guidance, it was left to them to develop a detailed methodology. In feedback to FHWA on its Framework, he and his team highlighted the need for greater detail and specificity in terms of metrics.
For other DOTs interested in carrying out a similar assessment, Schaffner advised that they start small geographically and to take their time to calibrate their vulnerability metrics. It also is important to involve your maintenance team and other regional staff, he said. So far as the ability to carry out the project without external consultancy/funding goes, it would depend upon the agency’s in-house skill level and access to data.
Findings from the study are being used to inform MnDOT’s long-range transportation planning and asset management efforts. At this point, though no decisions have been made, the agency is exploring carrying out similar assessments in several of its other districts as well as evaluating other types of vulnerabilities such as slope failure.
Schaffner’s view is that additional assessments likely could be done at much less cost given that the basic methodology already is in place.
”One of the important findings of our pilot project was that adaptation doesn’t always require large, complex projects. In fact, small changes over time can make a big difference in the resilience of the system,” he said.
The Tennessee Department of Transportation is responsible for building and maintaining much of the state’s transportation infrastructure. Following a number of extreme weather events, the Tennessee Department of Transportation (TDOT) recognized that the agency’s management of those assets required methodological approach to assess the vulnerability of the state's transportation network.
In May 2010, Nashville, Tennessee experienced a 1,000-year flood event, causing 21 deaths in Tennessee and widespread property damage. In 2013, there were severe weather-related problems on the Cumberland Plateau, in the eastern part of the state. Rockslides blocked traffic in areas lacking alternative transportation routes. In other regions, sinkholes opened on interstate highways.
|Tennessee DOT faces extreme weather impacts such as this 2013 rockslide on State Route 25. Photo: Tennessee DOT|
These types of extreme events prompted TDOT officials to conduct a statewide vulnerability assessment for its transportation infrastructure as a first step in identifying cost-effective approaches to increasing the resilience of the system. The assessment took advantage of a pilot program offered by the Federal Highway Administration (FHWA).
FHWA has funded a series of studies across the country to begin increasing the resiliency of the country's transportation infrastructure in the face of increasingly frequent and severe weather events. The first round of FHWA pilot projects validated a general approach to conducting an extreme weather vulnerability assessment. They focused primarily on coastal locations where many of the risks were related to storm surge and sea level rise. FHWA’s second round of pilots, although also primarily focused on coastal states, included inland states, and Tennessee became the first inland state to perform a statewide vulnerability assessment.
TDOT is now trying to integrate the results of the screening-level, statewide vulnerability assessment into TDOT’s planning, management and operational policies, according to Alan Jones, Policy Manager, Long Range Planning Division at TDOT. The agency’s assessment has been an important screening tool to identify critical transportation assets, better understand extreme weather risks, and identify specific assets that warrant a more detailed analysis.
The Tennessee project developed an approach to the vulnerability assessment that was based on FHWA's Vulnerability Assessment Framework, while also taking into account the unique characteristics of Tennessee and its transportation system. The approach involved identifying critical transportation assets, defining the types of extreme weather events that could occur while taking into consideration expected changes in certain climate variables, assessing the damage potential and resilience of the transportation assets when impacted by the extreme weather event, and combining this information to reach conclusions about the vulnerability of the asset.
To manage the number and range of transportation assets statewide, TDOT's first step was to group its transportation assets into generic asset categories. The categories included roads, rail lines and rail yards, navigable waterways, ports, bridges, airport runways, pipelines, transit systems, and more. It was not possible in this initial screening study to differentiate the unique characteristics of specific facilities, such as pavement binder or age of asset.
Criteria for determining the criticality of an asset included the volume of activity, the asset's strategic importance, the existence of redundant capability, the asset's use for emergency response, and local knowledge of the importance of the asset.
The range of extreme weather events and climate change to be expected in Tennessee was based on analysis of information from the National Weather Service and well-tested global climate models. The types of weather events included were extreme temperatures (both high and low), heavy rain, drought, strong winds and tornados, ice storms, and major snowfalls. Trends in the data identified which counties were most likely to see increased severity and frequency of extreme events. The climate data also identified counties that can expect the most significant changes with respect to projected temperature and precipitation.
The process of assessing damage potential and asset resilience was performed through a statewide survey conducted of transportation stakeholders, such as government agencies, freight carriers, transit service providers, airport authorities, and shippers.
The survey results painted a picture of tremendous variation in vulnerabilities across Tennessee. Key findings included:
TDOT plans to take a number of steps to implement the results of its vulnerability assessment.
The agency plans to follow-up with TDOT's four regions to communicate the results of the study. This will include developing regional "briefing books" to condense the study and communicate specific vulnerabilities so they can be easily understood and quickly referenced. These briefing books will be tailored to each of the four TDOT regions to account for differences across the State and to make the information more useful to local and regional planners. The agency also will select up to 20 of the state's most vulnerable assets for more refined, targeted analyses, including development of potential adaptation strategies.
In addition, TDOT will incorporate information from the screening-level vulnerability assessment as it develops its risk-based transportation asset management plan (TAMP) required under the Moving Ahead for Progress in the 21st Century Act (MAP-21).
TDOT will also consider additional tasks in following up on the vulnerability assessment.
A statewide vulnerability assessment is an ambitious project and required a significant commitment of time and resources; however, the project results served as a vital screening tool that can be used to determine where best to focus a more detailed study to determine what, if any, adaptation measures might be warranted. For example, the statewide study required grouping assets into classes, such as “roads,” but this approach has substantially limited the number of roads in the state that warrant a further review, a review which will allow more unique characteristics of the asset to be evaluated to determine vulnerability, such as pavement binder, age of the road, and more.
Another lesson learned is the importance of local stakeholder knowledge and input. The project conducted regional meetings across the state and were able to get a much better understanding of what assets and routes are considered critical, or not, from a local perspective. Local knowledge of how assets perform during extreme weather events was also vital to the study. TDOT field staff already have a great deal of knowledge of regional vulnerabilities that were relevant to the study.
For more information, contact Alan Jones, Tennessee Department of Transportation at Alan.Jones@tn.gov.
In the wake of the devastating floods wrought by Tropical Storm Irene in 2011, the Vermont Agency of Transportation is working to expand training and awareness on how to properly manage highway infrastructure in concert with the natural ebb and flow patterns of the state's river systems.
Irene's torrential rains and flooding washed out or damaged hundreds of miles of roads and hundreds of bridges and left entire communities stranded. In its wake, Irene also taught an important lesson: the need to manage the state's road infrastructure to be more compatible with its streams and rivers.
Irene's devastating floods "changed the way we do business in Vermont,” according to VTrans Deputy Secretary Rich Tetreault, who served as the agency’s Director of Program Development and Chief Engineer.
|In-stream restoration work following Tropical Storm Irene. Photo: VTrans|
Tetreault said VTrans employees are being sent back to the classroom for coursework on the science of rivers. Also known as "fluvial geomorphology," this science stresses how natural cycles of periodic flooding and deposition allow river systems to reach a balanced state known as "equilibrium." Both online and classroom training is available. The contents, which are grouped into three tiers ranging from basic to advanced, have been developed by engineers at the Vermont Agency of Natural Resources.
The Tier 1 training - which also is used by ANR for its own staff – is an online self-guided basic course that describes the value of rivers and hydrologic and sediment regimes; explains river behavior, including river morphology, river equilibrium, and channel evolution; discusses rivers and human development, including flood and erosion hazards and efforts to control rivers; and explains how best to manage rivers for equilibrium.
The course summarizes the following key points about river processes and management:
The training helps professionals learn how to better identify areas with severe erosion hazards, how best to mitigate areas where damage has occurred, and how to better design roads and features to avoid future damage. It is applicable to a range of transportation professionals including engineers, technicians, equipment operators, and highway foremen.
"This goes from the hydraulics engineer to the bridge and roadway designers, to the local road foreman and the excavator operator that's working in the river, so they all better understand the dynamics of the river when they are working on public infrastructure," Tetreault said. At the same time, the training is being provided to local agency partners and contractors.
The Tier Two training is a classroom and field-based training that delves more deeply into the topics of physical river processes, aquatic habitat and the interactions between rivers and adjacent infrastructure. It also explains the permitting process and standards that must be met. Emphasis is placed on accommodating stream equilibrium, avoiding practices that trigger further instability, and minimizing impacts to aquatic habitat during emergency flood response and recovery operations when technical support is not available. Contents are particularly geared toward design, construction, maintenance and planning professionals.
It includes “a lot of hands on work, both in the classroom with custom built flumes and in the field, knees deep in a local stream,” said Scott Rogers, VTrans Director of Operations. “We have mandated some of our folks from the maintenance garages attend Tier 2 to become more intimately familiar with the dynamics of the systems. They are the ones running the equipment (or making the decisions on repair work) in the field,” he added.
In 2015, the Tier 2 format was modified slightly to mix participants from VTrans with those from municipalities. In addition, a special training was held for regional planning commission transportation planners and another for private sector engineers. Mixing participants allowed for state-municipal dialogue that resulted in technical transfer and the development of greater appreciation for differing perspectives.
The Tier 3 training currently is under development, with completion scheduled for spring 2016 and training sessions to begin near the end of 2016. Tier 3 will focus on advanced engineering and construction oversight topics, specifically the design and construction oversight of the stream alteration practices outlined in the Vermont Standard River Management Principles and Practices document (2014).
In addition to offering the training courses, VTrans has updated its hydraulics manual to codify the "river science" approach. While the previous manual was based on the hydraulic capacity of infrastructure – focused strictly on water – the revised manual also considers sediment and debris.
The new manual allows for more risk-based design in terms of roadway safety and stream stability. It also corresponds to VTrans' latest stream alteration permit, codifying a process that currently is required under permit but not recognized as a standard by authorities such as the Federal Emergency Management Agency (FEMA).
"The new manual doesn’t change the hydrologists' methodology. It codifies it such that when FEMA comes to town we will have another documented standard to fulfill when they are replacing public infrastructure," Tetreault said.
For example, where slope repairs are needed adjacent to rivers, workers historically had dumped stone down the slope, further constricting the river channel. Such repairs now would start with defining the stable channel dimensions for the river and then building the slope to match - all with the help of fluvial geomorphologists. "Across the board, we are really making this part of our standard operating procedure," Tetreault added.
Tetreault said that the "river science"-based approach is important for all ongoing activities of maintaining existing infrastructure, up to and including reconstruction or new construction of highways. For example, such considerations are important when addressing a culvert replacement or a slope failure or a river channel that needs some adjustment to respond to the built environment around it.
"There is a dynamic going on continuously with the rivers, and there is maintenance going on with drainage systems or even the river itself. People need to be aware of the fact that the river is working and we need to work with it and understand the changes that occur over time," he said. "So the minute you get an excavator out and you're working near a river, stop and think: if I put this rock here or if I remove this tree trunk here, what is it doing to the dynamics of the river as it is now and will be in the future?"
Tetreault said other states with river systems could benefit from the self-administered training course, which is posted online and is free of charge. The Tier 1 training course can be accessed online.
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