The House of Seven Gables: Managed Retreat to Protect a National Historic Landmark

Abstract: “Sea level rise” and “coastal resiliency” are quickly becoming widespread buzzwords that most engineers, scientists, and consultants working on any waterfront project are familiar with. When it comes to determining which resiliency adaptation strategy is best suited for a specific site, the most effective solution may not be as obvious as it might seem. The House of Seven Gables (HOSG) in Salem, MA recognized that they were in a race against time and nature to protect six valuable historic landmarks against the threats of sea level rise, as storm flooding commonly inundated the waterfront property and threatened the historic structures. The campus constitutes its own district on the National Register for Historic Places, and the HOSG organization needed to take action to protect the 17th century structures to continue welcoming and engaging people of all backgrounds in an inclusive American story.
Funded through a Massachusetts Office of Coastal Zone Management (CZM) Coastal Resiliency Grant, the HOSG in conjunction with Collins Engineers, Inc. (Collins), Union Studios (Union), and Horsley-Whitten Group (HW) has been developing an adaptation solution to combat the future projected inundation of the site while still preserving the important and diverse history of the campus. The original preferred design solution involved raising the elevation of the property’s existing stone masonry seawall along the shoreline of Salem Harbor to provide edge protection from current and future projected storm scenarios. Led by HW, current and future flood and storm scenarios were modeled using the Massachusetts Coast Flood Risk Model (MC-FRM) developed by Woods Hole Group to analyze future anticipated coastal flooding extents for storm scenarios forecasted for 2030, 2050, and 2070. The modeling results indicated that the foundations of five of the six historic structures at the HOSG campus fall within the floodplain of a 50-year storm in 2070.
One of the major challenges associated with raising the elevation of the HOSG’s seawall is the potential for flood waters to flank the ends of the seawall and enter the site through lower-lying areas of neighboring properties. The abutting properties to the east and west of the campus currently have no intentions of raising the elevations of their waterfront infrastructure, so adapting the HOSG seawall alone would still leave the campus susceptible to inundation. The proposed solutions were analyzed and reviewed, but most of the structural improvements would drastically change the historical aesthetic of the site and risk unintentionally divert water to neighboring properties.
This paper summarizes the structural improvements that could be implemented but also discusses the somewhat unique approach to floodproofing, whereby the HOSG is able to leverage the surrounding topography of the campus and strategically relocate all six historic buildings to upland areas of the site in a phased approach. The “retreat” must be planned in a meticulous and historically accurate manner to allow nature to take its course and reclaim this historic property over time.

How does this project / topic contribute to the advancement of the industry and profession?: Resiliency designs to combat coastal flood protection often encompass robust designs to withstand intense wave forces and several feet of storm surge in defensive approaches to managing sea level rise and improving the coastal resiliency of a site. With a non-water-dependent site, our resiliency project with the HOSG encourages outside-the-box thinking of using topography to our advantage as we plan for the inevitable sea level rise. Our goal is to showcase that a passive approach to resilient design can sometimes be the most effective option to preserve historic assets.

Does the project / topic implement new and innovative techniques, materials, technologies, and delivery methods?: What is unique about our project is that we are opting to implement one of the most basic approaches to sea level rise and coastal resiliency adaptation that is often overlooked given the developments in waterfront infrastructure design and construction in recent years. Managed retreat is not a commonly implemented adaptation strategy as many project goals are to maintain the existing waterfront, instead of allowing nature to run its course and reclaim some of the shoreline through rising tides in coming years.

What was the most challenging aspect of your project / topic and how did you handle it to ensure success?: With such a high-profile historic property, developing coastal resiliency solutions that not only met the site-specific sea level rise forecasts, but also maintained the historic character and aesthetic of the structures, as well as the functionality of the HOSG organization as a museum and event center was no small undertaking. We worked in close collaboration with the HOSG and our consultant team to ensure that the needs of the HOSG operations were met as this design was developed and that interim adaptation strategies are implemented to maintain the property until the larger managed retreat relocation plan can be executed.

Who is the target audience for this paper?: Waterfront engineers, landscape architects, coastal and environmental scientists, and owners of non-water dependent waterfront properties will benefit from reading our approach to developing an unconventional resiliency design to protect the HOSG property. In addition, historic architecture enthusiasts and the local Salem community will enjoy reading about how our project preserves one of the most prominent historic properties along the northern Massachusetts shoreline in an increasingly vulnerable environment.