Flood Mitigation, Choose Your Own Adventure Style

By Ashley Wilson posted 01-24-2018 11:57


Owners of buildings that are susceptible to flooding are currently evaluating what they can do to protect their properties. Here at the National Trust for Historic Preservation, we have been going through that process with our site that frequently floods, the Farnsworth House in Plano, Illinois.

Farnsworth House after flooding in 2017. | Credit: National Trust for Historic Preservation

Farnsworth is a tricky case study because it was designed to handle some amount of flood waters—that is why it’s elevated on stilted legs. Farnsworth also isn’t your typical property: It’s a National Historic Landmark and arguably one of the most recognized modern buildings in the world. As a result, a lot of people are invested in what we, its owners, decide to do. Furthermore, we were not willing to abandon the site by relocating the building. Although the site had been altered, it is the location that Ludwig Mies van der Rohe selected, and we consider that relevancy worth saving. As a national preservation organization, we needed a sensitive preservation solution. Flood mitigation, we realized, is very similar to other interventions that are necessary for the safe continued use of historic buildings—like seismic retrofitting, ADA compliance, or building code compliance. We ultimately selected a lift system to elevate the Farnsworth building during floods. We are basically adding a basement that will hold the lift equipment below ground, out of view of the visiting public. When the site floods by more than four feet, we will be able to activate the lift and lock the building in place until the waters recede.

Before we settled on this solution, we spent five years working with engineers to consider many other options. In the process, we realized both that we had learned an awful lot about flood protection and that we had not seen other sources that compared the different options. Realizing that the information we had gathered could help other property owners, we applied for a National Center for Preservation Technology and Training grant to help us present the information to the public through an interactive website. These are some of the questions we are most frequently asked about our project. 

How did you come up with a quiz format? And how does it work?

We set out to objectively compare flood mitigation approaches with the goal of prescribing the best solutions for different circumstances. While we started with a matrix, we quickly realized that many of the options had similar strengths and weaknesses, which made an interactive and graphically pleasing quiz more useful.

The quiz presents about the expected flood level, the amount of land, and the budget, and then directs users toward different mitigation options based on their answers. Users can also visit pages that describe these various options, providing a definition, advantages and disadvantages, important considerations, helpful links, and images of the solution in use.

What systems did you compare?

We analyzed wet floodproofing, dry floodproofing, permanent floodwalls, temporary barrier systems, relocation, elevation by raising the grade, elevation on columns/piers, elevation by hydraulic lift, and elevation by buoyancy.

What are the major flood mitigation issues related to preservation?

One question that preservationists always ask themselves is, how much of the intervention should be visible? At many properties, adding visible safety or protection features, such as smoke detectors, is considered perfectly acceptable. For flood protection, such options include retractable flood gates or barrier walls, which can easily be incorporated into the landscape.

Potential environmental ramifications are another important consideration. We don’t want to recommend solutions that save one property by diverting water toward neighboring resources. Adding fill can also be environmentally tricky because flooding typically first occurs on low land that was filled before there were environmental regulations against it.

Other considerations include getting neighborhood buy-in—especially in urban environments—as well as mobilization time and staff capacity.

What did you learn while doing this research?

The amount and flow of the floodwater determines the solution—minor flooding is much easier to deal with through inexpensive solutions. If the water rises more than around six feet, some of the barriers don’t work. If the water rises more than 15 feet, relocation is the only permanent option.

How did this study change your views about sea-level rise and sustainability?

Flood protection is expensive, and while we know that the need for it is growing, specifics are difficult to predict. I expect that the country won’t fully deal with this issue until it becomes an economic imperative. For preservationists, it’s important to reorient the conversation away from the precious and toward the realistic.

Ashley Wilson, AIA, is the Graham Gund Architect in the Historic Sites department of the National Trust for Historic Preservation.


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