Fellow Highlight: Assessing Vulnerability through Storm Transposition

Monday, July 20, 2015

In June of 2008, the village of Lake Delton, Wisconsin, along with other areas of the Midwest, was devastated by a massive precipitation event, known infamously throughout the state as the “Lake Delton storm”. Extensive flooding resulted as over a foot of rainfall drowned the area, collapsing a dam, breeching levees and causing serious damage to local infrastructure. Thankfully the Lake Delton area has a relatively small population; however, this storm left the rest of the state concerned about their own vulnerability. Nearby Dane County, which contains the state capital of Madison, is especially concerned due to high population and levels of infrastructure situated within a watershed with a multi-lake system. In 2012, U.W. Professor Ken Potter and his colleague David Liebl began research on the development and application of new methods for addressing a variety of flooding issues in Dane County, WI.  This research was initially funded by NOAA, and subsequently by the Northeast Climate Science Center.  From the beginning the research involved stakeholders from local and state water managers.  The Water Resources Engineering Division of Dane County Land & Water Resources Department were major stakeholders in this collaboration.

To determine the county’s vulnerability to lake flooding, the team has been using a method based on “storm transposition and Lake Mendota extreme event modeling”, explains student and NE CSC Fellow Pearl May. Pearl is a graduate student specializing in Water Resource Engineering at the University of Wisconsin Madison. Although usually found behind-the-scenes, she is a primary component of the current research headed by Potter and Liebl. The storm transposition approach, which was developed by Ken Potter, “is taking an event that happened in one area…and seeing what would happen if it hit another place,” defines Pearl. They are currently assessing Dane County’s vulnerability by transposing the Lake Delton storm. The benefit of this tactic is two-fold: first, taking data from an actual event evades the uncertainties in statistical modeling; second, the public will be more likely to embrace vulnerability assessments based on a storm whose occurrence and effects are still vivid in memory.

Assessing vulnerability in the region

Led by Division Manager Jeremy Balousek, the Dane County Water Resources Engineering (WRE) Division is responsible for the “county-wide storm water management program, lake-level management…and [management of] the lock and dam systems on the lake system,” explains Balousek. Understanding the characteristics of the region’s vulnerability is invaluable for the “design and construct of our storm water infrastructure [and] in our regulatory practices to ensure that [where] development is occurring we’re mitigating the effects of the impervious cover and improv[ing] drainage systems”, continues Balousek. Determining how the Division manages and operates the lake and river system depends on the vulnerability of infrastructure and development in the county.

Pearl’s storm transposition and extreme event modeling research has maintained relevance to the WRE’s needs through mutual contact through Potter. Pearl shares the evolution of her models with Potter, who offers direction based on his understanding of the stakeholders’ concerns, which he has gained through regular meetings with WRE staff. A memorable shift happened when WRE “wanted more [model] accuracy day to day,” rather than on 15-day cycles as previously used, “because that’s the scale they make decisions on,” reflects Pearl. To test the county’s current infrastructure against extreme events, “we want to [transpose] a short-duration, high-intensity storm because those are the ones that usually hit us hard and cause us a lot of damage,” affirms Balousek. Widening the understanding of their vulnerability against a diversified spectrum of storm characteristics will better prepare their management and design responses.

A storm in recent memory

Beyond the innovative role that storm transposition modeling has brought to management and design, Balousek values the credibility that comes with vulnerability assessments based on actual, and memorable, occurrences. “The biggest thing for us is that when [we’re talking to the public] about how we’re designing a certain piece of storm water infrastructure...when we start talking about a storm that’s in their recent memory,…everyone still remembers because it was such a huge storm and the damage that occurred. It gives a lot of credibility to the design [and] that carries a lot of weight with the public.”

As Balousek acknowledges an increasing frequency of storms, the importance of effective citizen engagement will only grow with time. “[Storm transposition] will be a tool that we use going into the future,” remarks Balousek, who recognizes the importance of both identifying his county’s vulnerability and maintaining public support for infrastructural and management revisions needed to mitigate such vulnerabilities. With this tool, Balousek and Dane County will be able to effectively adapt their management and infrastructure to mitigate the effects of an impending increase in storm frequency.   Pearl is excited to contribute, "There is a large population that lives in Dane County and we are definitely vulnerable to flooding with these large precipitation events.  Helping Dane County, the City of Madison, and the University of Wisconsin-Madison with this project has been particularly important to me because I was born in Madison, and much of my immediate family lives here.   Modeling the resulting stream and lake responses with the storm transposition method gives local municipalities and stakeholders another tool to protect this community from floods."

By Colton Ellison, NE CSC Communications Intern, UMass Amherst

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Top image: Pearl May stands in front of Lake Mendota in Madison, Wisconsin (Photo: Dana O'Shea)