A Living Shoreline Approach to Protect Historic Structures on Ocracoke Island

Jason. C. Doll1 and Johnny D. Martin, P.E.2

1Project Scientist, Moffatt & Nichol,1616 E. Millbrook Rd. Suite 160, Raleigh, NC 27609; PH (919) 781-4626; FAX (919) 781-4869; email: jdoll@moffattnichol.com 2Project Engineer, Moffatt & Nichol,1616 E. Millbrook Rd. Suite 160, Raleigh, NC 27609; PH (919) 781-4626; FAX (919) 781-4869; email: jmartin@moffattnichol.com

ABSTRACT

When the U.S. Coast Guard gave the historic Ocracoke Island Lifesaving Station to the State of North Carolina, and it became the North Carolina Center for the Advancement of Teaching (NCCAT), the change represented real opportunity for improvement to the historic site. One particular improvement was the recovery of the eroding section of Pamlico Sound shoreline behind the facility where years of wind and wave action were chewing their way landward toward the buildings. In a collaborative effort with NCCAT, the North Carolina Coastal Federation, and the North Carolina State Construction Office, Moffatt & Nichol engaged in the complex task of permitting, designing, and constructing a natural estuarine shoreline and tidal marsh complex to replace the eroding shoreline, which had been unsuccessfully armored against the advancing sound. The restoration project involved the design and construction of breakwater sills just off shore to dissipate wave energy, regrading of the gradual slope of a natural shore profile, and re-establishment of native shoreline marsh vegetation. The design also involved additional green amenities. An interpretive boardwalk and pier were constructed and future construction phases will include stormwater Best Management Practices (BMPs) on upland areas, such as bioretention cells and pervious parking areas. In addition, oyster habitat restoration and seeding are planned for the site. Execution of the project also involved substantive opportunities for outreach and education by using teacher volunteers to implement the marsh vegetation plantings. Construction thus far has resulted in restoration of approximately 300 feet of natural shoreline and two acres of coastal salt marsh aquatic habitat. This case study presentation will review the complex permitting, design and construction issues involved in this highly public project built in a sensitive marine environment.

BACKGROUND

The U.S. Government established the Life Saving Service (which became the U.S. Coast Guard) in 1874, and soon thereafter, the oldest lifeboat stations in the nation were built on the North Carolina coast. The Ocracoke Lifesaving Station, originally constructed in 1904, and replaced by a larger, more modern building in the early 1940s, is no exception. After almost 90 years of service, the facility was abandoned as the U.S. Coast Guard consolidated operations into a few larger stations. In 1996, the facility was granted to the North Carolina State Government, and in 2006 it found

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new life as it was renovated into the eastern branch of the North Carolina Center for the Advancement of Teaching (NCCAT). NCCAT was established as a place where teachers could re-energize through the experience of becoming students again themselves by engaging in training workshops and team building exercises.

One of the most immediate problems faced by NCCAT in the renovation and redevelopment of the campus was that storm events, as well as ongoing wind and wave action, had resulted in substantial losses of shoreline on the Pamlico Sound. The advancing sound was threatening the main buildings of the campus, which are on the National Registry of Historic Sites. Figures 1 and 2 illustrate the loss of shoreline (relative to yellow benchmark lines) over just three years from 2003 to 2006.

Figure 1. 2003 Aerial Photo of NCCAT Showing Pamlico Sound Shoreline.

The objective of this paper is present a case study illustrating the permitting, design, and implementation of a living shoreline to alleviate the erosion problems at NCCAT, while creating and enhancing natural coastal marsh habitat. As opposed to bulkheads and other shoreline hardening structures that reflect the wave energy back along the shoreline exacerbating erosion, living shorelines act as a more natural buffer that absorbs wave energy, thus minimizing shoreline erosion and protecting the marsh.

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Figure 2. 2006 Aerial Photo of NCCAT Showing Shoreline Loss.

PLANNING AND PERMITTING

Given that the project involved public land and received public funding, a portion of which was federal funding, it was subject to the requirements of the National Environmental Policy Act (NEPA). In order to satisfy NEPA requirements, an Environmental Assessment (EA) document was prepared in 2007, which set forth the need and purpose of the project, and demonstrated that multiple alternatives, in addition to the project approach finally chosen, were taken into consideration.

Establishing the need for the project was the easiest task. Through benchmark analysis of historical aerial photos, such as illustrated in Figures 1 and 2, Moffatt & Nichol was able to document a shoreline retreat of as much as 80 to 100 feet over the period analyzed. While the vast majority of such shoreline erosion is event based, due to tropical storms and nor’easters hitting North Carolina’s Outer Banks, the annualized rate of erosion was calculated at nine feet a year over the study period. At that rate of loss, the encroaching Pamlico Sound was only a few years (or one or two more storm events) from taking over the historic buildings and other valuable public infrastructure on the site. Additional elements of need set forth in the EA included restoration of natural shoreline ecology and establishment of educational opportunities.

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In light of the documented needs, the EA set forth the purposes for the project as follows:

• Restore and protect the shoreline from further erosion • Reclaim eroded upland area to the maximum extent possible • Restore natural shoreline ecology and habitat • Create shoreline and marsh educational opportunities for NCCAT

In the interest of achieving the stated objectives, the EA offered a series of alternatives including a no action alternative, armoring of the existing shoreline in place, habitat construction with protection by sandbags, and construction of breakwater sills with several material options such as geotubes, timber, marl, and stone. Restoration of shoreline vegetation and habitat without construction of sills was also considered, but the alternative was rejected due to projections that the restored shoreline could not withstand the ongoing erosive force of wave action from the sound, particularly during storm events. By the same token, sill construction materials other than stone were rejected due to projections of limited wave resistance and longevity. As a result of the stresses that would be exerted on the shoreline over time, the chosen alternative consisted of construction of a series of breakwater sills comprised of stone, with regrading of the shoreline and establishment of marsh vegetation behind the sills. The approach has come to be known as a living shoreline. Based on the stated need and purpose, and the strength of the project approach chosen relative to the alternatives considered, the project was granted a Finding of No Significant Impact (FONSI) in October 2008 after a year-long multi-agency review.

In addition to construction of the living shoreline, numerous improvements to the upland area were planned for the project, which included expanded parking areas with a bioretention cell to capture and treat runoff, a boardwalk to connect the educational dock in the shoreline marsh to the rest of the facilities and installation of rainwater harvesting systems throughout the facility (details to follow in Design section). Collectively, over and above the FONSI, numerous permits were required before the project could be built, partly due to project’s impact on the shoreline of a major estuary (Tar River-Pamlico Sound system), which is deemed Nutrient Sensitive Waters by the North Carolina Department of Environment and Natural Resources (NCDENR) and subject to a nutrient management strategy. The permits which had to be obtained included:

• 404 Permit – US Army Corps of Engineers • 401 Water Quality Certification – North Carolina Division of Water Quality • Coastal Area Management Act (CAMA) Major Permit – North Carolina

Division of Coastal Management • Variance from Tar-Pamlico Riparian Buffer Rules – North Carolina Division

of Water Quality • Stormwater Permit (including Sediment & Erosion Control) – North Carolina

Division of Water Quality

The entire permitting process took approximately two years and numerous hurdles were experienced during that period. The most difficult permitting issue stemmed

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from the project requiring a significant amount of fill beyond the existing normal high water mark of Pamlico Sound to reclaim the lost upland area and establish the gradual slope necessary for the survival of a coastal marsh ecosystem. Permitters were reluctant to grant permission for such extensive “fill,” but in the interest of promoting the use of the bio-engineered living shoreline approach, (which collectively offered a much better approach to water quality and ecology than any other realistic alternative) they relented and signed off on the project.

DESIGN

The most critical and complex element of the project design, after selecting and permitting the living shoreline approach, was that of designing the breakwater sills. The sills were critical to protecting the shoreline from erosion and maintaining the success of the marsh vegetation. However, the permitting agencies and the project owner all expressed stern objection to having sills that were overly large, due to adverse impacts to the site aesthetics.

In order to determine appropriate design elevations for the sills (which in turn governed their base width, overall size and visual impact) the project team surveyed the near-field bathymetry for the project area. FEMA flood surge elevation and NOAA tidal records were then utilized in conjunction with the bathymetry to develop still water flood-exceedance return intervals for a range of design storms including 2-year, 5-year, and 10-year storm events. For each design storm, depth-limited wave heights were calculated on the basis of the projected depth from the flood surge and high tide combined. The storm surge elevations and coincident wave heights were used to determine the required rock size (D50) and sill dimensions (top elevation, width and side slopes) that would attenuate the wave energy to a condition that would allow the wetlands behind to become established and also remain in place. The wave height tolerance threshold was set conservatively at 1.7 feet to protect the living shoreline during the early growth period before the marsh vegetation was fully established (USACE-ERDC, 2000). The sill design height for each storm event was calculated to be the height above projected water surface elevations necessary to dampen incoming waves down to the tolerance threshold, accounting for the permeability of the sill through which a portion of each wave would be allowed to transmit.

After determining the sill heights necessary to dampen the waves for each of the storm events, the results were vetted with project owners and permitting agencies to determine the appropriate balance between protection from storm-driven wave erosion and aesthetic impacts. Based on costs, aesthetics and stakeholder preferences, the structural design projected for a 2-year storm surge event was selected. The client deemed that the rock size and the elevation and profile of the structure required for larger return events would overwhelm the natural character of the site and overwhelm the existing landscape. The selection resulted in a sill height of approximately three feet above mean high tide elevation for the final design. The end result in terms of the visual impact of the sill can be seen in the aerial view of the completed project in Figure 3, which shows the project during a low tide condition when the portion of the sill protruding from the water surface is largest.

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Figure 3. Aerial View of Completed NCCAT Living Shoreline Project

Another important aspect of the design involved the distribution of the planned marsh vegetation relative to the slope of the regraded shoreline. Based on shoreline marsh ecosystems in the U. S. Mid-Atlantic and Southeast, a transitional tidal marsh vegetation community was planned for the site with Smooth Cordgrass (Spartina alternaflora) at the lowest elevations, Saltmeadow Hay (Spartina patens) and Black Needlerush (Juncus roemerianus) at the intermediate elevations and Marsh Elder (Iva frutescens) and Wax Myrtle (Morella cerifera) at the back edge (USACE-ERDC, 2000). Live Oak (Quercus geminata) plantings were planned to provide habitat, aesthetic benefit and soil stabilization in the upland areas of the site. Achieving the correct distribution of plant species relative to the tidal elevation was important because the individual plants have specific tolerances for the frequency and duration of soil saturation. The cross sectional view in Figure 4 shows the elevation distribution of the marsh plant species planned for the NCCAT project. The plan view of the distribution of marsh vegetation species, and the other features of the final site design, are shown in Figure 4.

Beyond the living shoreline installation, the improvements designed for the upland areas of the site (Figure 5) included addition of new parking spaces, inclusion of a turn-around area behind the main buildings, a bioretention cell (rain garden) to capture and treat the runoff from these paved areas, and the boardwalk leading to the pedestrian pier that extends out into the shoreline marsh. The purpose of the boardwalk and pier is to serve as an outdoor classroom, offering education opportunities to NCCAT, so teachers and the public could be educated on shoreline marsh ecosystems. The boardwalk and pier have been upfit with educational signage describing the ecosystem and application of the Living Shoreline at the site. Note that Figure 5 also shows the areas planned for installation of oyster reefs for oyster reseeding. The oyster re-establishment portion of the project was conducted by a

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group of volunteers, including visiting teachers and NCCAT staff members, which were organized by the North Carolina Coastal Federation.

Figure 4. NCCAT Living Shoreline Project Planting Plan – Section View.

CONSTRUCTION

Upon completion of final plans and specifications, the project was let out to bid in spring 2009, and the construction project was awarded to Paul Howard Construction of Greensboro, North Carolina for $1,828,000. Construction began in October 2009 and was completed in August 2010. Construction was originally scheduled to be completed in April 2010, but significant delays were experience as a result of inclement weather and difficulties involved in obtaining construction materials. The greatest challenge to construction on Ocracoke Island was the delivery of construction to the island, which is far from the mainland, with no transportation connection to the outside world other than ferries. This challenge was compounded by the fact that the building materials, especially stone and lumber, had to come from far away. For instance, the nearest source for granite stones of the diameter required for the project was in Rocky Mount, North Carolina, more than 200 miles away, and the original bid specification called for more than 9,000 tons of stone.

Construction of the project was aided and the cost of materials reduced due to a concurrent North Carolina Department of Transportation (NCDOT) project that involved the removal of sand that had been deposited by recent storms from the only roadway that spans the island (N.C. Highway 12) and, because the NCCAT living shoreline project was also state-owned, NCDOT gave the sand to NCCAT.

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Figure 5. NCCAT Living Shoreline Project Planting Plan – Plan View.

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CONCLUSIONS

Now more than two years after the completion of construction, by any measure, the project can be judged to be a complete success thus far. As opposed to simply armoring the existing shoreline in place, the living shoreline has created almost two acres of natural shoreline marsh habitat, and has formed the basis for a rich outdoor classroom space at the NCCAT facility. Working on a small island with a year-round population of less than 1000 people makes for a great deal of contact with the local citizens, and by all accounts they highly approve, and are very appreciative, of the living shoreline installation.

In terms of providing protection from shoreline erosion, the system could not be performing better. Since completion of construction, Ocracoke has experienced major impacts from two separate hurricanes, Irene in August 2011, and Sandy in October 2012. It should be noted that Irene, in particular, scored a “direct hit” on the Outer Banks by coming up the North Carolina coast, with the center of the storm passing to the Pamlico Sound side of the barrier island, such that the most destructive front of the storm (the portion to the right of the eye) passed directly over Ocracoke Island. Between the two storms, the property immediately across the entrance to the Silver Lake harbor lost as much as 20 to 25 feet of shoreline from storm-induced erosion, while the Pamlico Sound shoreline at NCCAT showed no loss or damage whatsoever.

In terms of aesthetic improvement of the NCCAT shoreline, the results speak for themselves, as shown in Figures 6 and Figure 7 on the following page. Both photos were taken from the same distance and perspective while arriving on the incoming ferry.

REFERENCES

USACE-ERDC. (2000). “Wetlands Engineering Handbook”. Compiled by Donald F. Hayes, Trudy J. Olin, J. Craig Fischenich and Michael R. Palermo for the Wetland Research Program, U.S. Army Corps of Enhgineers – Engineering Research and Development Center (March 2000).

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Figure 6. NCCAT Living Shoreline Project – Before, 2006.

Figure 7. NCCAT Living Shoreline Project – After, 2012.

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