Charleston, South Carolina

The City of Charleston sits along inside Charleston Harbor at the confluence of three rivers. Established in 1670 by English settlers, Charleston quickly grew as one of the largest cities in North America during colonial times. Today, Charleston is a popular tourist destination and drew nearly 5 million visitors in 2012. The city has long focused on managing its historic resources and tourism sector in tandem; it was the first in the country to adopt a historic district zoning ordinance and a tourist management plan in 1931 and 1978, respectively. Local officials recognize that "a flourishing residential life in the historic neighborhoods is the backbone of the tourism industry and thus an important engine of economic development for the city as a whole." Rapidly changing environmental conditions are making management efforts more difficult as sea level rise and increasingly common tidal flooding threaten the future of Charleston's historic resources. Once a "walled city" surrounded by fortifications to protect it against attack during colonial times, the city is contemplating a massive infrastructure project to wall itself off once again, this time against the threat of rising waters.

The NOAA tide gauge in the Charleston Harbor indicates that local sea level has risen over one foot since 1921. Environmental conditions are also changing quickly in Charleston. The city's 2015 Sea Level Strategy, a guiding framework for municipal resiliency action, called for new facilities and infrastructure to include a 1.5-2.5 foot elevation to accommodate sea level rise over 50 years. Four years later, the 2019 Sea Level Rise Strategy increased the recommended elevation to 2-3 feet. Current sea level rise projections for Charleston are tracking along an an intermediate scenario.

Nuisance flooding and coastal storms are also having increasingly serious effects in Charleston. NOAA projects that high tide flooding events will occur at least 10-20 times annually by 2030 and 35-90 times annually by 2050. These are tides that crest seven feet above mean lower low water. The city is already breaking records though: 89 high tide flooding events were recorded in 2019. Compare this to the 1970s when Charleston experienced only two days of tidal flooding annually. Tides cresting eight feet or higher relative to mean lower low water are considered major events; over half of Charleston's highest recorded tides have occurred since 2015 (all of which were major events). Some of these highest recorded tides are associated with coastal storms. Hurricane Irma in 2017, for example, coincided with high tide and also brought seven inches of precipitation. The resulting tide crested at 9.9 feet above mean lower low water and closed 111 roads throughout the city.

Adapting historic resources in the face of environmental hazards has involved a mixture of planning initiatives, policy changes, public engagement, and infrastructure interventions. While a number of the responses explicitly address or consider historic resources, others are focused more on general adaptation.

Charleston's 2008 Preservation Plan is a comprehensive evaluation of the challenges that the city's historic resources face. The plan recognizes that the preservation and sustainability fields have evolved over time and must be responsive to changing environmental factors in order to continue to successfully preserve local heritage. A number of recommendations in response to flooding and sea level rise are in the plan; these include calls to implement and increase investments in stormwater drainage improvements, create elevation design guidelines, and improve public understanding of flood risks and adaptations.

The Charleston Board of Architectural Review issued its Design Guidelines for Elevating Historic Buildings (a recommendation from the 2008 Preservation Plan) in 2019. The city had previously concluded that "the best policy for the long-term preservation of historic structures was to support their need to elevate to the necessary FEMA requirement." The design guidelines provides a set of considerations, best practices, and successful examples for property owners pursuing elevation of their historic structures. Four key areas of consideration are covered: streetscape and context; site; foundation design; and preservation and architecture.

Charleston's "Living with Water" ethos is a data-driven approach to manage and accommodate environmental change. The city's 2019 Flooding and Sea Level Strategy is the key framing document for municipal action. Sea level rise initiatives are occurring across five critical components: infrastructure, governance, resources, land use, and outreach. The city has so far completed or started 41 of its 76 sea level rise initiatives. See Charleston's progress on the initiatives below:

Central to the "Living with Water" ethos is the Dutch Dialogues process Charleston participated in recently. This methodology is stakeholder-focused planning "modeled on the Dutch approach of developing actionable solutions through integrated water management and flood infrastructure planning with a preference for multi-benefit investments." The Dutch Dialogues team arrived in Charleston in 2018-2019 at the behest of the city and the Historic Charleston Foundation. The focus was to identify ways to reduce flood risk and better integrate flood management throughout different municipal entities and other organizations. Ultimately, the Dutch Dialogues team produced a series of recommendations--largely policy and programmatic--that could guide future action. Site-specific interventions at four focus areas are also included in the final report.

Recommendations for flood mitigation efforts on the Peninsula largely focus on improving the effectiveness of the city's water management system to ensure there is adequate capacity to capture stormwater, manage groundwater, and store water on public and private spaces. As it relates specifically to historic structures, flood adaptations do not go beyond endorsing the city's Board of Architectural Review's guidelines for historic structure elevation. Perimeter protection for the entire Peninsula is lightly discussed and focuses on what environmental factors to consider and how proposals may be evaluated; the USACE was evaluating options for perimeter protection as the Dutch Dialogues process was occurring.

In January 2020, the Charleston City Council adopted recommendations from the Dutch Dialogues into the city's comprehensive plan and stormwater design standards manual. The adopted recommendations "will direct new growth away from flood-prone areas, improve how drainage is managed during development, set aside funds for capital improvements, and tackle other sea level rise vulnerabilities in the build environment.

The USACE released the preliminary results of the Charleston Peninsula Coastal Flood Risk Management Study in April 2020, roughly a year after the Dutch Dialogues process. The USACE results were three years and $3 million in the making to determine the most appropriate pathways to mitigate the effects of coastal storms on the Peninsula. In contrast to the Dutch Dialogues approach to living with and adapting to change, the USACE proposal calls for massive infrastructural investment to protect the Peninsula.

Seven alternatives with varying levels of investment, scope, and hard versus soft protections were evaluated. Ultimately, the USACE study determined that a combination of perimeter protection, nonstructural interventions, and a wave attenuator would be the most "economically-viable, environmental-sound and provides the peninsula with the most robust and comprehensive reduction of coastal storm risks." There are six key components to the tentatively selected alternative:

1. Storm surge wall: involves two types of storm surge walls built to 12 feet above mean sea level; would encircle roughly eight square miles of the Peninsula
2. Storm surge gates: a number of gates built into the storm surge wall that can be closed prior to expected major flooding
3. Wave attenuator: currently conceived as a riprap breakwater at the point of the Peninsula
4. Non-structural measures: potentially involves relocations, buyouts, structural elevations, and floodproofing
5. Pump stations: five permanent and five mobile pump stations are proposed to handle stormwater that may be "stuck" inside the Peninsula once a storm surge wall is built
6. Other measures: proposes amenity additions built into storm surge wall

Following the release of the USACE proposal and its endorsement from city officials, public outcry over the lack of concrete details and short comment period has led to a significant revamping of Charleston's public engagement process. An additional six months have been added to the timetable for outreach and public engagement before a second round of public comments is solicited in early 2021. As the tentatively selected alternative is estimated to cost between $1.75-2.2 billion and Charleston would be on the hook for roughly half of the bill, the plan is drawing intense concerns over the equity implications of funding interventions that will protect on a quarter of Charleston's population. The USACE will also complete additional modeling and analysis to identify any adverse environmental effects the proposal on surrounding areas of Charleston that may raise other equity and engineering concerns.

The USACE notes that 119 of historic structures in the Peninsula would be exposed to coastal storm flooding without a project, and all but five would be protected with a project. The Historic Charleston Foundation, one of organizations that brought the Dutch Dialogues to the city, notes that it is "generally supportive of the concept of perimeter protection if our concerns about the design, aesthetics and impacts to historic resources can be alleviated." Others are more critical of the USACE plan contending that a massive seawall will not stop flooding and would lull property owners into "a false sense of security." There are also concerns that the USACE proposal is being treated like a silver bullet when the city should be doing more to prevent poor planning and development in hazardous areas.

With sea level expected to rise four feet in the Charleston area (assuming trends do not accelerate), it is hard to imagine a future where Charleston does not pursue hard structural interventions. Many of the drainage improvement projects and small-scale interventions are primarily aimed at decreasing the extent of tidal and pluvial flooding rather than mitigating future sea level rise. With much of the Peninsula exposed to sea level rise and already experiencing flooding, protection of its historic resources can be achieved at the asset-scale in the short-term; however, conversations about long-term adaptations have been firmly grounded at the district-scale. Whether Charleston becomes a "walled city" yet again remains to be seen.