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Charleston Peninsula Coastal Flood Risk Management Study Overview

In 2018, the U.S. Army Corps of Engineers, Charleston District received $3 million in federal Emergency Supplemental Funding to study coastal storm impacts on the Charleston Peninsula and, in partnership with the City of Charleston and its stakeholders, develop an economically-viable, environmentally-sound solution that effectively mitigates long-term storm risks. The plan is preliminary and still requires several months of refinement. The plan also requires authorization and funding from Congress prior to possible implementation.

  • The workshop presentation with the City of Charleston below provides a detailed overview of the project.
  • All project documents and frequently asked questions can be found below the workshop presentation.
  • You can contact the project manager on the right hand side of the page with any questions.
  • The Interactive Module at the bottom can be used to see detailed aspects of the selected plan, alternatives, history of peninsula flooding and more. For a full-screen experience, click here.

City Council Workshop: Charleston Peninsula Coastal Flood Risk Management Study



On May 21, 2020, the U.S. Army Corps of Engineers participated in a virtual workshop hosted by the City of Charleston to present initial findings highlighted in the draft report and address council members’ questions. The workshop, which was also open to the general public, describes the Army Corps’ feasibility study process, identifies key dates in the study timeline and covers some of the analysis and modeling behind the Corps’ tentatively selected measures and overall conceptual plan. The workshop was also an opportunity for the Corps team to answer questions on a wide variety of topics, including storm wall alignment, project funding and how the study incorporates findings from the Dutch Dialogues into a comprehensive coastal storm damage reduction project. The full meeting and question-and-answer session were recorded and are available to watch at the above video.

Frequently Asked Questions

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The Charleston Peninsula Coastal Flood Risk Management study investigates solutions to address coastal storm risk to people, property and infrastructure on the peninsula.

Coastal storms on the Charleston Peninsula place people at risk, including the potential for loss of life and declines in public health. The Charleston Peninsula experiences coastal storm surges that adversely affect the economic sustainability of Charleston, including impacts to businesses, organizations and industry; critical facilities and infrastructure; and residents. Coastal storm events also limit access to critical facilities, emergency services and evacuation routes. Historic and cultural resources are at risk of damage due to storm surge flooding.

Currently estimated at $1.75 billion, the National Economic Development (NED) Plan includes a perimeter storm surge wall (also built to withstand earthquakes), an offshore wave attenuation structure and nonstructural measures, such as home raising. If the project is authorized and funds are appropriated by Congress as a result of the study, the City of Charleston would be responsible for — based on current estimates — approximately $600 million.

The draft report is available above in the "Project Documents" section. Hard copies of the draft report are also available for those with limited internet access at Charleston District office in a locker outside 69A Hagood Avenue, Charleston, SC, Monday-Friday from 7 a.m.-4:30 p.m. until July 19.

The public is encouraged to provide feedback on the report on our website or by sending written comments to our district office (Environmental & Planning Office, 69A Hagood Ave, Charleston, SC 29412) through June 19, 2020.  Comments on the contents of the current draft feasibility report and environmental assessment should be provided in this initial comment period.  All feedback will be addressed in the final report.

Following a series of hurricanes and severe storms, the Army Corps of Engineers received $3 million of federal Emergency Supplemental Funding to study the impact and potential solutions of coastal storm events on the Charleston Peninsula. The study does not involve a cost-share requirement from the City until the next phase of preliminary engineering designs is approved and funded by Congress, which would be in 2022-2023 at the earliest.

The City of Charleston, Army Corps of Engineers and many stakeholders worked together to develop seven alternatives to alleviate coastal storm flooding on the peninsula. Only two of the alternatives met the objectives to reduce loss of life, increase safety and minimize economic damages in a coastal storm event. Alternative 3, the National Economic Development (NED) Plan, best meets the study objective of effectively reducing the risk of damages on the peninsula from coastal storm events and provides the best return for the federal investment.

It is important to remember that these communities, including the Bridgeview Village apartments and the Rosemont community, are at a higher elevation already — between 8 and 11-ft NAVD88 — compared to the lower peninsula. Due to higher elevation, the plan recommends more minimal measures, such as ring dikes and temporary barriers, to mitigate storm surge risks in these areas. In general, developed areas and structures outside the conceptual wall alignment rest on higher elevation so there was not the need for storm surge wall in these areas. The Army Corps of Engineers study was inclusive of all of the lower-income residents of the Neck Area and other sites. The natural topography of these area has made it more cost effective to use nonstructural measures.

Additional modeling and analysis over the next 12 months will include the investigation of adverse impacts to surrounding communities.  If the analysis determines that adverse impacts to adjacent communities are likely, the Army Corps of Engineers will assess the need for and appropriate mitigation to address those impacts.  Formal recommendations by the Army Corps of Engineers cannot move forward without weighing the potential for adverse impacts to adjacent communities.

Coastal storm events are hurricanes, tropical storms or tropical depressions that approach and pass through the Charleston vicinity or move on shore at or near the Charleston vicinity. The low elevations and tidal connections to the Ashley and Cooper Rivers and Charleston Harbor place a significant percentage of the city at risk of flooding from these coastal storm events, even if the storms do not make landfall.

The Army Corps of Engineers’ coastal storm study is a piece of an overall comprehensive flooding strategy for the City of Charleston, and our team of engineers and technical experts are determined to do everything we can to help in this effort. In the last few years, the City has rolled out several flood mitigation actions, including its Flooding and Sea Level Rise Strategy, a vulnerability assessment, rehabilitation of Low Battery Wall, Dutch Dialogues and major drainage projects. In addition to reduced damages and risks from coastal storms, the federal project would also provide the City with opportunities to incorporate features that protect against other flood-related issues.

No. Pedestrian, vehicle, rail, storm and access gates along the perimeter storm surge wall would remain open until a storm surge event. These gates would be closed at low tide during storm events to ensure water storage is available in marsh areas, alleviating any flooding caused by storm runoff. Pump stations along the perimeter storm surge wall would mitigate flooding in areas with no marsh storage. The Army Corps of Engineers has done a detailed water surface modeling analysis to ensure there would be no bathtub impacts.

At this preliminary phase, the study discusses but hasn’t identified the need for eminent domain or buyouts as part of the tentatively selected plan. Army Corps of Engineers’ sponsors must have the ability to use eminent domain if required. Negotiation is required to acquire real estate. Fair market value as established by a real estate appraisal is the basis for the initial offers to the owner. If negotiation fails, eminent domain is an option that can be utilized. Waivers can be granted on a very limited basis to allow the Army Corps to initiate the eminent domain process in place of the sponsor. This does not replace the reasonable efforts to negotiate a purchase before initiating an eminent domain action. Again, while the non-federal sponsor must generally possess the capability to exercise eminent domain, use of this process assumes that particular relocations or buyouts are identified as necessary for the project.

Yes, the storm surge wall could be added to or made higher in the future. In the structural appendix, we state the T-Wall and Combo Wall have battered piles which are currently to be driven into the soil (Cooper Marl stratum) providing more lateral resistance. This will allow for easier retrofitting of the barrier to provide an increased level of protection without requiring structural or foundation upgrades.

The storm surge wall must tie into high ground or elevation 12-ft NAVD 88. Based on topography, the natural tie-in location is the I-26 location depicted in the alternative 3 map. Anything with an elevation greater than 12-ft NAVD 88 would require expensive modifications to I-26 and the Ashley River bridges.

Once the final elevation of the storm surge wall is determined, the view will depend on where you are on the Peninsula. Storm surge wall elevations are dictated by topographic requirements. Areas with the lowest topography elevation, for example, are more susceptible to severe coastal storm surge damages and, from a standing perspective, would have higher storm surge wall elevation. Areas with a higher topography elevation would require less storm surge wall elevation and maintain water views. Preserving the area’s historic and cultural character is an important part of the Corps objective. We will continue to work with the city, local stakeholders and agencies, and the community on ways to avoid, mitigate or minimize impacts. Betterments (i.e. aesthetics) and recreation features can also be added to avoid, mitigate or minimize impacts.

These structures, including the South Carolina Aquarium and African American Museum, have base elevation levels higher than the proposed storm surge wall elevation. A storm surge seawall with an elevation less than the structures base elevation will do nothing to reduce the risk of damages during a storm event.

The storm surge wall is modeled at elevation 12ft NAVD 88 (high battery wall is currently 9ft NAVD 88 for reference) and, if constructed, would tie into high ground around I-26 on the Ashley River side and along Morrison Drive on the Cooper River side. However, the storm surge wall is projected to vary at different visual heights based on existing topography. Please refer to the map in the final report for a broad conceptual alignment. Please note this conceptual alignment will likely change with additional public input and analysis.

The City is not responsible for any costs associated with the phase we are currently in, the feasibility phase, which ends in October 2021, with the submittal of a recommended plan to Congress. If Congress approves and funds the next phase, Pre-Construction Engineering and Design (PED), also known as the Design Phase, the city would be responsible for 35% of the design phase cost.Right now, the study estimates design costs at 7% of the total project cost, or $76 million, which is a standard calculation the Corps uses until a more refined cost can be developed.This estimate will more than likely change. The City's cost-share for the PED phase is not required up-front and occurs in phases. If Congress approves and funds the phase after PED, the Construction Phase, that is also cost-shared at 35% for the City.

Optimization is the next step in the study process and involves further refinement of the tentatively selected plan, also known as the National Economic Development (NED) Plan. The City of Charleston and Army Corps of Engineers — with input from stakeholders and the public — will assess different perimeter storm surge wall elevations and alignment throughout the study area. The Army Corps of Engineers will also do additional coastal and economic modeling to analyze various sea level rise scenarios during coastal storm events. The optimization stage begins April 2020 and ends early 2021.

After the feasibility study is complete, the City of Charleston and U.S. Army Corps of Engineers will enter the design phase of the National Economic Development (NED) Plan. This phase does not begin until Congress provides funding. At this time, we are unable to describe how the physical aspects of the NED plan will look in front of businesses and residences.

Over the next 12 months, we will continue to refine the plan with input from the public, additional modeling and analysis.  Refinements are expected to include optimization decisions regarding storm surge wall alignment and elevation, changes in environmental considerations, and further development of nonstructural measures.  Prior to release of the final report, we will hold a second public comment period in early 2021 limited to allowing the public to address these refinements.  All feedback will be addressed in the final report.

Contact

Please click here if you would like to address a question about the study to the Charleston Peninsula Study Project Manager.

If you would like to provide feedback on the study, please use the link in the module above.

Interactive Study Overview