The Charleston Peninsula Coastal Storm Risk Management Study is a federal feasibility study that investigated coastal storm impacts on the Charleston peninsula and, in partnership with the City of Charleston and its stakeholders, explored 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 investigated the feasibility of measures to reduce the risk of coastal storm surge inundation, taking into account tidal fluctuations and sea level rise in its analysis.  The study authority and funding did not include the investigation of measures to address flooding from tides or rainfall.

The ultimate purpose of this 3x3x3 feasibility study was 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 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 10.8:1,
• 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 included 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 45-day public comment period on the draft Feasibility Report/Environmental Impact Statement (draft FR/EIS) is now closed. 

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

The total estimated cost of the proposed project is currently $1.1 billion. Cost details are 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.

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.

No. First, the tentatively-selected plan has a number of low-income or minority community neighborhoods on the peninsula that are inside the plan’s primary structural measure, the perimeter storm surge wall. Among these are the public housing communities of Cooper River Court, Meeting Street Manor, Gadsden Green, and Robert Mills Manor. In addition, entire peninsula neighborhoods which are more than 50% minority or low income are encompassed within the storm surge wall.

Second, the recommendation of nonstructural measures rather than construction of a storm surge wall in the Rosemont and Bridgeview Village communities is primarily driven by topography and other constraints, not economic value.

In the case of Rosemont, construction of the wall in tidal areas would result in large and permanent wetland impacts that would also require costly mitigation. This is an environmental impact that USACE has sought to minimize to the extent practicable throughout the study area. Upland construction of the wall to avoid wetlands would require involuntary buyouts and removal of homes in order to accommodate the footprint of the wall —  something USACE has sought to avoid throughout the study area, including Rosemont. Elsewhere on the peninsula where a barrier is otherwise appropriate, the wall will be constructed on city-owned lands so as to avoid involuntary removal of citizens from their homes. This option is not available in Rosemont. Topographically, the natural tie-in for the storm surge wall is located on the eastward side of I-26 which would essentially encapsulate this community inside the wall. Given the lack of subsurface drainage throughout Rosemount, the wall would create a significant bathtub effect that would need to be mitigated by large pump stations at the end of most streets, which would in turn require significant real estate acquisition. For these reasons, the USACE currently believes non-structural solutions, such as elevating homes, are a better approach to reduce the coastal storm surge risk up to 12 ft NAVD88 faced by the residents of Rosemont.

Regarding Bridgeview Village, ground elevation and the surrounding wetland and cemetery are the overriding factors for the selection of non-structural alternatives for this community. The ground elevation in this area is already at an elevation of 9 ft NAVD88 or above, so the wall would only be around three feet above the surface to reach the 12 ft NAVD88 project elevation. In the Bridgeview Village area, construction would have to be on both uplands and wetlands, which would require buyouts and involuntary removal of citizens from their homes and impacts to surrounding wetlands. In addition, the historic Magnolia cemetery borders Bridgeview Village on one side, further complicating the constructability of a storm surge wall. Rather than impact these resources, the USACE currently believes non-structural solutions, such as flood-proofing, are a better approach to reduce the coastal storm surge risk faced by the residents of Bridgeview Village.

Finally, the Rosemont and Bridgeview Village communities (all structures) are part of the overall plan to address coastal storm surge on the peninsula. All non-structural costs are part of the overall cost estimate and will be cost-shared 65% (Federal) and 35% (City of Charleston). No funding will be needed by the residents of these communities to be part of the overall plan. Final details of the process and timeline will be identified in the pre-construction, engineering and design (PED) phase.

Nonstructural measures are applied to structures to prevent or provide resistance to flooding damages. This includes the raising of homes and utility equipment, as well as dry and wet flood-proofing.

Dry floodproofing consists of sealing all areas of a structure up to a maximum of approximately 3 feet above ground level to reduce damage caused by coastal storm surge inundation by making walls, doors, windows and other openings resistant to penetration by water. Walls are coated with sealants, waterproofing compounds, or plastic sheeting. Back-flow from water and sewer lines is prevented by installing mechanisms such as drain plugs, standpipes, grinder pumps, and back-up valves. Openings, such as doors, windows, sewer lines, and vents, may also be closed temporarily with sandbags or removable closures, or permanently sealed. Some common floodproofing measures include:

• Backflow valves;
• Closures on doors, windows, stairwells, and vents--they may be temporary or permanent;
• Rearranging or protecting damageable property--e.g. relocate or raise utilities;
• Sump pumps and sub-drains; and
• Water resistant material; metal windows, doors and jambs; waterproof adhesives; sealants and floor drains

Wet floodproofing is for allowing floodwaters to enter a portion of a structure through use of vents or break-away wall panels. The floodwaters equalize internal and external hydrostatic pressure on the structure foundation. The portion of the structure that will be flooded is typically constructed or retrofitted with materials (such as concrete) that will not be damaged by floodwaters.  Potential examples would be to retrofit a critical public facility such as a fire station garage, subject to limited and low-velocity flooding. Reduces flood risk to structure; may be less costly than other retrofitting methods; does not require additional lot space. Can be applied to a variety of foundation/structure types. Inundation of designated portions of structure reduces the dangers of buoyancy from hydrostatic uplift forces.

Learn more about nonstructural measures and flood proofing at Learn more at www.usace.army.mil/Missions/Civil-Works/Project-Planning/nnc.

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 storm 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. 

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.

The feasibility phase concludes with either the finding of no federal interest or the recommendation for the authorization of a specific water resources project. The analyses that support the recommendation are documented in the final FR/EIS, which serves as the decision document. The recommendation to Congress for authorization of a water resources project will be made by the Chief of Engineers in the form of a “Chief’s Report.” After the Chief’s Report is signed, the ASA(CW) will officially transmit the Chief’s Report to Congress along with the views of the Administration.

The recommended project and the technical and engineering appendices in the decision document will lay the groundwork for the next phase of the project, known as Preconstruction, Engineering and Design (PED). PED activities continue under the original study authorization and may begin before congressional project authorization and construction funding of the project are received, provided PED funds have been appropriated by Congress and a Design Agreement is executed with the non-Federal sponsor. During PED, USACE and the non-federal sponsor complete the detailed engineering, technical studies, and design needed to begin construction of the project as recommended in the decision document, including engineering design documentation and the plans and specifications of the first significant project construction contract.

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.