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Charleston Peninsula Coastal Flood Risk Management Study

About the Study

The Charleston Peninsula Coastal Flood Risk Management Study is a federal study that is investigating coastal storm impacts on the Charleston peninsula and, in partnership with the City of Charleston and its stakeholders, is exploring effective, economically-viable and environmentally-sound solutions to mitigate risks and build enduring coastal storm resiliency.

This four-year feasibility study began in 2018 and will conclude with submission of a final detailed report to Congress in the summer of 2022. The study is 100 percent federally-funded through the Emergency Supplemental funds appropriated by Congress.

In April 2020, USACE published the draft Feasibility Report and Environmental Assessment (FR/EA). This report outlined initial findings and identified several potential storm risk reduction measures, including a perimeter storm surge wall, pump stations and nonstructural measures. In March 2021, the study transitioned from an Environmental Assessment (EA) to an Environmental Impact Statement (EIS), enabling USACE to do more analysis on project impacts, more clearly define mitigation measures, and offer expanded public engagement through additional public meetings and the release of an updated draft report for public review.

Throughout the entire feasibility study, the objective has remained at the forefront: reducing coastal storm surge risks to human health, public safety, emergency access and the economic viability of the Charleston peninsula, while enhancing overall coastal resiliency. Public engagement and a continued close partnership with the study’s non-federal sponsor, the City of Charleston, also remain vital to the study’s success and its development of a potential federal project.

Over the last several months, the study has used public and agency feedback and results from detailed modeling to optimize the tentatively-selected plan. Among some of the plan’s most significant changes since the draft FR/EA are: a decrease in the estimated project cost from $1.75 billion to $1.1 billion, an increased benefit-cost-ratio from 2.2:1 to 10.2:1, the addition of living shorelines, a reduction of wetland impacts, the modeling of impacts to surrounding areas and a refined interior drainage analysis.

This feasibility study is one piece of the City of Charleston’s long-range flooding strategy. In the last several years, the City has initiated several flood reduction strategies, including its Flooding and Sea Level Rise Strategy, continued vulnerability assessments, rehabilitation of Low Battery Wall, the Dutch Dialogues and major drainage projects. This study primarily addresses coastal storm surge and, in conjunction with other flood mitigation efforts, also takes tidal flooding and sea level rise into account in its analysis.

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Frequently Asked Questions (FAQs)

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The Charleston Peninsula Coastal Flood Risk Management Study is a federal feasibility study that investigates coastal storm impacts on the Charleston peninsula and, in partnership with the City of Charleston and its stakeholders, explores effective, economically-viable and environmentally-sound ways  to mitigate  risks and build enduring coastal storm resiliency. Working in tandem with other flood mitigation efforts, the study primarily addresses the risks of coastal storm surges and considers tidal flooding and sea level rise in its analysis.

The study is currently in the initial (feasibility) phase of the USACE project delivery process. The ultimate purpose of this 3x3x3 feasibility study is to determine whether or not there is a federal interest in a storm surge solution on the peninsula, and if so, outline a project recommendation. If authorized and funded by Congress, subsequent phases of the project would include the Pre-Construction Engineering and Design (PED), construction, and operation and maintenance.

Coastal storm surge poses a grave threat to: human health, life and safety; emergency access to critical infrastructure; historic and cultural resources; and the economic sustainability of the Charleston peninsula. Coastal storm events can also limit or completely eliminate access to critical facilities, emergency services and evacuation routes. More than half (6,670 of 12,095) of the structures on the Charleston peninsula, including critical infrastructure and medical facilities, are in the 100-year floodplain.

Since release of the draft Feasibility Report/Environmental Assessment (FR/EA), USACE has used public and agency feedback and additional analysis to optimize the tentatively-selected plan. Among the most significant changes include:

  • Transitioned from environmental assessment to environmental impact statement,
  • A decrease in the total estimated project cost from $1.75 billion to $1.1 billion,
  • An increase in the benefit-cost-ratio from 2.2:1 to 10.2:1,
  • Inclusion of living shorelines,
  • Removal of the wave attenuator (breakwater),
  • Optimized alignment of the storm surge wall, reducing the number of impacted wetlands from 111 to 35 acres,
  • More defined non-structural analysis,
  • Expanded environmental justice review,
  • Refined interior drainage analysis, and
  • Detailed modeling on impacts to surrounding areas.

The optimized tentatively-selected plan includes three key features: perimeter storm surge wall with pumps and gates, nonstructural features, and natural and nature-based features (NNBF), such as living shorelines. Specific details, such as aesthetics and exact placement, will continue to be refined throughout this study and are finalized in subsequent phases, if the project moves forward. 

  1. Perimeter Storm Surge Wall: The proposed project includes construction of a 12-foot NAVD88 storm surge wall along the perimeter of the peninsula. It would be strategically aligned to minimize impacts to existing wetland habitat, cultural and aesthetic resources, and private property while allowing continued operation of all ports, marinas, and the Coast Guard Station.  The wall would tie into high ground as appropriate, including the shoreline at the Citadel and the existing Battery Wall.

    The storm surge wall would include multiple pedestrian, vehicle, railroad, and storm (tidal flow) gates.  Typically, the gates would remain open, and gate closure procedures would be initiated based on storm surge predictions from the National Weather Service. To mitigate interior flooding related to the storm surge wall, preliminary interior hydrology analyses indicate the need for five temporary and permanent small-to-medium hydraulic pump stations.
     
  2. Nonstructural Measures: In residential areas where construction of the storm surge wall is impractical due to topography and other constraints, the proposed project would also include nonstructural measures, such as home-raising and flood-proofing. These neighborhoods include Bridgeview Village and the Rosemont community.
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  3. Natural and Nature-Based Features (NNFB): In association with the storm surge wall, oyster reef-based living shoreline sills would be constructed in some locations to reduce coastal storm impacts to natural shorelines and other resources seaward of the wall. The living shoreline sills would reduce erosion of existing wetland marsh, while reducing scour at the proposed storm surge wall. The design and method of the reef-based living shoreline would be determined during the Pre-Construction, Engineering and Design phase, should the project move forward.

The study encourages  public comments on the draft Feasibility Report and Environmental Impact Statement (FR/EIS) during a 45-day public comment period through Oct. 25, 2021. To submit comments:

  • Complete the online comment form.
  • Mail comments to the Charleston District, Planning and Environmental Branch, 69A Hagood Ave, Charleston SC, 29403.
  • Call the voicemail line at (843) 329-8017.
  • Attend the Virtual Public Meeting Oct. 5 from 5:30-7:30 p.m.

The study will also host a virtual public meeting Oct. 5, 2021 from 5:30-7:30 p.m. to present the optimized federal plan and receive additional public feedback. Stay tuned for more on how to access the virtual meeting. For those unable to attend, USACE will share the recorded meeting on this webpage following the event.

Comments submitted during this period will inform the study’s continued analysis and will be addressed in the final report.

For more information on commenting during the NEPA process, see the Council on Environmental Quality Citizens Guide to NEPA.

Public comments submitted on the draft April 2020 FR/EA will not be further considered as comments on this draft FR/EIS.  The study team considered all substantive public comments received on the draft April 2020 FR/EA. These comments informed USACE’s decision to transition from an EA to an EIS and were used as part of the scoping process for the EIS.  Those desiring to provide public comment on this FR/EIS should submit comments within the 45-day comment period and should not rely on, or reference, previous input on the draft April 2020 FR/EA. Only public comments submitted and received within the 45-day comment period on the current draft report will be considered in the agency’s NEPA analysis and development of the final FR/EIS.

The total estimated cost of the proposed project is currently $1.1 billion. Cost estimates will continue to undergo refinement throughout the duration of the study. Details will be published in the final Feasibility Report/Environmental Impact Statement (FR/EIS).

Federal civil works projects require a cost-share with the non-federal sponsor. Based on the current estimate, the federal cost share would be $715 million (65 percent), and the City’s would be $385 million (35 percent). USACE and the City will work together to determine future funding requirements on an annual basis.  Cost-share amounts are not required upfront and are broken-up based on annual requirements over each fiscal year. USACE will not seek federal funding from Congress during the design and construction phases unless the City has identified funding for the cost-share match. 

As the non-federal sponsor, the City of Charleston must comply with all applicable federal laws, policies and other requirements, including but not limited to committing to a cost-share of 35 percent of project construction, provision of all easements and rights-of-way, and identification and removal of hazardous substances. For a complete description of a non-federal sponsor’s responsibilities, see the Non-Federal Sponsor Requirements.

Yes. Over the last several months, the study has optimized the tentatively-selected plan (TSP) using public and agency input. The TSP now incorporates natural and nature-based features (NNBF), including oyster living shoreline sills, at various locations along the peninsula perimeter. These NNBF would complement combination walls in the marsh and help reduce erosion of the storm surge wall and maintain existing wetlands. Preliminary locations for the combo wall and NNBF currently include Wagener Terrace and along the Coast Guard Station. The location, design and methods used for the reef-based living shoreline would be determined during the Pre-Construction, Engineering and Design phase.

Currently, the study proposes a storm surge wall with a 12-foot NAVD88 elevation along the peninsula perimeter. The visible height of the wall would vary across the peninsula — both from land and water — depending on the area’s topography and elevation and would appear higher in areas with lower ground surface elevation.

The study team recognizes that aesthetic resources in and around the Charleston Peninsula are an integral part of the community and addressing these resources with care is in the public interest. The study team is committed to considering the mitigation of significant impacts to aesthetic resources in its design of the storm surge barrier and other project features during the Pre-Construction, Engineering and Design (PED) phase. The City may propose additional features to address aesthetics and the alignment that would be entirely funded through the City.

Although the tentatively-selected plan has the potential to cause significant impact to aesthetic resources, the new storm surge wall would also reduce the risk to the abundance of aesthetic and cultural resources within the Charleston Peninsula which would lack this protection if no storm surge wall or project are constructed.

Since release of the draft FR/EA in April 2020, the study team has conducted a thorough review into whether the tentatively-selected plan would deflect water or adversely impact communities directly adjacent to the peninsula, including James Island, West Ashley, North Charleston, Daniel Island and Mount Pleasant. Based on comprehensive modeling, the storm surge wall induced a marginal difference in water surface elevation — an increase or decrease of around an inch — during severe storm surge events of 9-17 feet. This marginal difference in water surface elevation would be in addition to what would have statistically occurred in that location during a coastal surge event. Structural damages as a result of the marginal differences in water surface elevations would be unlikely.

The objective of the tentatively-selected plan (TSP) is to reduce coastal storm surge risks to human life and the area’s economic vitality. This includes all residents and businesses within the study area. The combined features of the TSP, including the storm surge wall, nonstructural measures and living shorelines, would improve the resilience of the entire Charleston Peninsula and provide protection to a cross-section of socio-economic communities, without disproportionately burdening minority, low income or disadvantaged communities. To augment protection in areas where construction of the storm surge wall is impractical, the study recommends nonstructural measures, such as flood-proofing and home-raising to achieve the same level of risk reduction. Those neighborhoods include Bridgeview Village and the Rosemont community.

Upon further agency analysis of the refined plan, as well as consideration of public input in response to the draft FR/EA, the study team determined that some of the tentatively-selected plan’s potential adverse impacts are significant and might not be reduced below a level of significance through project mitigation. This uncertainty merited an Environmental Impact Statement.

Conducting an EIS allows USACE to perform an expanded analysis on project impacts and more clearly define measures to mitigate those impacts. The EIS includes the same categories of impact analyzed in the EA, including the effects on historical and cultural resources, visual resources, natural resources, and community resources. In addition, the EIS allows for expanded public engagement on the proposed plan through additional public meetings and release of the revised report for public review. The EIS process also gives USACE, the study sponsor and cooperating agencies additional time to assess and mitigate for adverse environmental impacts. As a result, the study’s completion date has been extended from Fall 2021 to Summer 2022.

The EIS process does not alter the study’s objectives, expand the authorized focus on coastal storm surge, or change the City’s role in the study. The study’s original objectives for the Charleston peninsula remain the same: reduce risk to human health, safety, and emergency access from coastal storm surge inundation on the Charleston Peninsula through the year 2082, and reduce economic damages resulting from and increase resilience to coastal storm surge inundation on the Charleston Peninsula through the year 2082, through an effective, economically-feasible and environmentally-sound solution.

Hurricane Hugo was a Category 4 hurricane when it made landfall just north of Charleston in 1989. Hugo generated the highest storm tides, or still water surge (a combination of tidal and storm surge elevations), ever recorded on the East Coast of the United States. In the Charleston harbor, peak still water surge reached 9.4-feet NAVD88, or 10-12 feet above mean sea level. That surge elevation would not have overtopped a 12-foot NAVD88 storm surge wall. However, the proposed storm surge wall would not have stopped the highest surge observation from that storm of around 20-feet near McClellanville.

The Dutch Dialogues Charleston Report provides a large-scale framework for addressing several sources of flooding across the region and contains multiple recommendations. The Corps proposal is one aspect of this framework and would, if implemented, require coordination with all other flood reduction efforts. To learn more about how the Corps proposal works with the Dutch recommendation, view the USACE-Dutch Integration.

No. Details of the proposed project will continue to undergo refinement through the remainder of the feasibility study and, if authorized and funded by Congress, through subsequent phases of the project. Changes to the alignment may occur during the Pre-Construction Engineering and Design (PED) phase as appropriate. Drivers of the potential minor changes include, but are not limited to, new developments in technology or construction methodologies, results of additional engineering analyses, unforeseen cultural and historic resources, the presence of buried utilities not discovered during feasibility, and real estate acquisition challenges. Also, changes related to detailed designs may occur during the PED phase for the purpose of aesthetic and cultural mitigation that could not be identified during the feasibility study.

No, USACE feasibility studies do not guarantee construction. The USACE project delivery process has several steps before construction. First, the study must produce a finalized feasibility report, and the City of Charleston must agree with the recommendation and be willing to accept the local cooperation requirements of a non-federal sponsor. Then, the USACE Chief of Engineers must approve the final feasibility report and submit a Chief’s Report to Congress with a favorable recommendation of the project. Congress must then authorize and appropriate funds for the project. The City would need to provide the necessary non-federal funds to commence the design phase, and later the construction phase, of the cost-shared project.

Buyouts and relocations may be a sound solution for coastal flood risk management in some coastal areas, but certainly not all. The Charleston Peninsula is the historic core and urban center of the City of Charleston and is home to approximately 40,000 people. It is unique in its combination of historical/cultural, natural, and aesthetic resources, the presence of critical medical infrastructure, and as an economic driver for the Lowcountry. Retreat does not offer a viable option to significantly reduce flood risk to these interests. The tentatively-selected plan would significantly reduce the risk of damage to resources, infrastructure, and economic values from coastal storm surge, and would benefit a cross-section of socio-economic groups, including minority and disadvantaged communities that call the Peninsula home. Expecting Charleston to retreat from the Peninsula might be like asking Venice, Italy to retreat from her historic location.

Following public review of the draft Feasibility Report/Environmental Impact Statement (FR/EIS), the study team will evaluate all public feedback and the effect on the study recommendation before moving forward with completion of a final report. The public will have one last opportunity to review how comments were incorporated in late Spring 2022. This will not be a comment period, only review of the final FR/EIS.

Upon approval by the U.S. Army Chief of Engineers, the recommended plan would be submitted to Congress for authorization and funding. If authorized and funded by Congress, subsequent phases of the project would include the Pre-Construction Engineering and Design (PED), construction and operations and maintenance.

City of Charleston 3 x 3 Advisory Committee | Sept. 10, 2021

The study team presented the optimized tentatively-selected plan to the City of Charleston 3x3 Advisory Committee on Sept. 10, 2021. 

45-Day Public Comment Period: Sept. 10-Oct. 25, 2021

USACE invites the public to review and comment on the draft Feasibility Report and Environmental Impact Statement (FR/EIS) and Programmatic Agreement (PA) during a 45-day public comment period from Sept. 10 - Oct. 25, 2021. To access the draft report and appendices, please see the report links below. Limited hard copies can be made available upon request by calling (843) 329-8017 for pick-up at 69A Hagood Ave, Charleston, SC 29403. 

During this time, the South Carolina Department of Health and Environmental Control, Division of Ocean and Coastal Resource Management (OCRM) will also be accepting comments on the Federal Consistency Determination that USACE has prepared for concurrence by OCRM.

How to Submit Comments on the Draft FR/EIS

  • Complete the online comment form
  • Mail comments to the Charleston District, Planning and Environmental Branch, 69A Hagood Ave, Charleston SC, 29403
  • Call the voicemail line at (843) 329-8017
  • Attend the Virtual Public Meeting Oct. 5 from 5:30-7:30 p.m.

USACE will also host a virtual public meeting Oct. 5 from 5:30-7:30 p.m. to present the optimized federal project and receive additional public feedback. Stay tuned for instructions on how to access and attend the virtual meeting. For those unable to attend, USACE will share the recorded meeting on this webpage following the event.

Draft Programmatic Agreement (PA)

How to submit comments on the PA:

Email Meredith.A.Moreno@usace.army.mil or send comments to Archeologist, U.S. Army Corps of Engineers Jacksonville District P.O. Box 4970 Jacksonville, FL 32232-0019 by Oct. 25, 2021.

Questions?

Have a question? Email the Charleston Peninsula Coastal Flood Risk Management Study at chs-peninsula-study@usace.army.mil

Interactive Study Overview