The Charleston Peninsula Coastal Flood Risk Management Study is currently in the initial (feasibility) phase of the Army Corps’ 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.

In the last several years, the City has initiated 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. This study primarily addresses the risks of coastal storm surges, while working in tandem with other flood mitigation efforts. It is one piece of the City’s overall comprehensive flooding strategy.

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.

The draft report, released April 2020, tentatively recommends the following features:

1. A storm surge wall (also built to withstand earthquakes),
2. An offshore wave attenuation structure, and
3. Nonstructural measures, such as home raising.

These are conceptual only and are currently undergoing additional analysis.

The study is currently in the initial (feasibility) phase of the Army Corps’ 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 the project moves to the design phase (the next phase in the project delivery process), the Corps will work with the City of Charleston and local stakeholders to closely look at design details, including height, placement and material selection, and prepare renderings. The Corps will request design funds to begin closely examining the look and feel of the surge wall around the Charleston Peninsula, as well as refining other aspects of the plan. The design phase is a collaborative effort. Within Federal parameters, the Corps will work with the City of Charleston and local stakeholders (such as Historic Charleston, Preservation Society and many others) on determining design features. The City may propose some additional features to aesthetics and the alignment that would be entirely funded by the City.

Regardless of the final design features of a perimeter storm surge wall, the perceived elevation of the wall will vary depending on the location’s topography (i.e., the above-ground wall height will vary according to whether an area is lower-lying or higher ground).

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.

Army Corps feasibility studies does not guarantee construction. In the draft feasibility report, the Army Corps of Engineers has identified three generalized measures to reduce coastal storm surge risks on the peninsula: a perimeter surge wall, an offshore wave attenuator and nonstructural measures. The Army Corps’ project delivery process has several steps before a surge wall could be constructed, including finalization of the current draft report (Spring 2021) after ongoing refinements, incorporation of comments, and any necessary modifications to the plan; the City of Charleston must agree with the recommendation and be willing to accept the local cooperation requirements of a non-federal sponsor; the Army Corps 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 make the decision whether to authorize the project; and, finally, Congress would need to appropriate and the City would have to provide the necessary funds to commence the design phase and later the construction phase of a cost-shared project.

This initial (feasibility) phase of the study is 100 percent federally funded. Future phases, including the design phase and construction phase, require a 35 percent cost-share from the City. This means, the City must fund 35 percent of the total cost of that phase. The cost-share amount is not required upfront and is broken up based on annual requirements over each fiscal year. If Congress authorizes the next phase of the study and provides appropriation, the Army Corps estimates a total design phase cost of roughly 7 percent of the total project. This is a standard calculation and will likely change.

The tentative alignment of the storm surge wall is conceptual only. Based on public and agency comments, the Army Corps will continue to evaluate the alignment of the storm surge wall, including those areas outside of the alignment which are proposed for non-structural and other measures. More information on non-structural areas will be presented at the 2nd public review in early 2021.

At this stage of the Army Corps’ project delivery process, the storm surge wall’s alignment is a conceptual layout only. The actual location of the perimeter surge wall is not finalized until the design phase, a later project delivery phase that requires additional authorization and appropriation.

The 12-foot NAVD88 surge wall is ultimately designed to mitigate storm surge damages to meet FEMA standards. In general, areas and structures outside the tentative surge wall are on higher elevation or were designed within FEMA’s standards. For these areas and structures, the study recommends nonstructural and other measures to reduce the risks of storm surge.

Hurricane Hugo was a Category 4 hurricane when it made landfall just north of Charleston in 1989. In the Charleston harbor, peak storm tides reached 9.4-foot NAVD88, or 10-12 feet above mean sea level. Those tidal heights would not have overtopped a 12-foot NAVD88 storm surge wall.

Additional modeling and analysis over the next 6 months will include the investigation of adverse impacts to surrounding communities. These results will be presented to the public during the second review period in early 2021. 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.

Natural and nature-based features (NNBF), or green solutions, can be effective for other sources of flooding (tidal, SLR), but alone are not sufficient for storm surge flooding. You can save, restore or enhance the wetlands, and they are very helpful for absorbing wave action and storing water when it gets here, but they will not stop the storm surge. Wetlands do not reduce the height of the surge (the water on top of the tide level). The same is true for living shorelines. While not suitable for coastal storm surge risk reduction, the study recommends a number of green infrastructure practices that the City of Charleston could implement to help with localized flooding.

To date, there have been no official requests for an Environmental Impact Statement (EIS) from state or federal agencies. In accordance with the National Environmental Policy Act (NEPA), an Environmental Assessment (EA) is conducted to determine whether significant adverse effects will result from a federal action, the extent to which those impacts can be mitigated, and whether an EIS is warranted. The Corps has incorporated feedback from other agencies in its ongoing optimization of the tentatively selected plan to further avoid and minimize impacts to the environment, and which provides for appropriate compensatory mitigation for remaining impacts. As part of its NEPA compliance, the Corps continues to review updated project impacts and public input in periodic reassessment of its conclusion that a mitigated Finding of No Significant Impact (FONSI) is the appropriate NEPA document.

At the outset, we expanded the initial public review period from 30 to 60 days. Due to the ongoing refinements to the tentative plan, including storm surge wall alignment, salt marsh impacts, and other important aspects of the plan, the Army Corps will offer a second comment period in early 2021. Second or additional public review periods are not required for feasibility studies and are generally not common practice. However, we know how important this study is to Charleston and want to provide the community an opportunity to provide input on updated aspects of the plan.

To reduce the impact on taxpayers and hold agencies accountable, Congress directed the Corps to expedite feasibility studies in 2014 as a law. To do this, the Corps follows the 3x3x3 policy for feasibility studies like this one: no more than $3M cost, completion within 3 years, and 3 concurrent levels of review. Exceeding the cost or completion limits requires an exemption. Public input is integral to our process. In addition to the initial extended public review and the second review early next year, the public will be invited to review and weigh-in during the design phase, if Congress/City of Charleston elect to move forward to that phase with the Army Corps’ recommendation.

All comments will be evaluated and taken into consideration as the Corps continues to refine the current plan and proceeds to the final report. Comments will be addressed in the final feasibility report.

To view our complete list of FAQs, open the Charleston Peninsula Study FAQs.