COASTAL OBSERVATIONS: Spatial and temporal variability in dune field: Pea Island, North Carolina By Elizabeth J. Sciaudone1, Liliana Velasquez-Montoya1, Elizabeth A. Smyre2, and Margery F. Overton1 1) North Carolina State University Department of Civil, Construction, and Environmental Engineering Campus Box 7908, Raleigh, NC 27695-7908 [email protected] 2) Dewberry 2610 Wycliff Road, Suite 410, Raleigh, NC 27607 ea Island is an approximately 13-mile stretch of primarily undeveloped barrier Pisland along the North Carolina Outer Banks, extending from Oregon Inlet south to the town of Rodanthe (Figure 1). While named as an “island,” this region now exists as the northern tip of Hatteras Island, with the shoreline adjacent to the inlet stabilized by a terminal groin built in 1989-1991. It is home to the Pea Island National Wildlife Refuge, es- tablished in 1938. The Cape Hatteras National Seashore, established in 1953, is co-located within the refuge boundaries on Pea Island and extends further north and south along the Outer Banks. There is limited infrastructure on Pea Island, consisting of a visitor’s center and other facilities associated with the wildlife refuge, as well as the coastal highway NC 12. NC 12 is the only north-south roadway connecting the Outer Banks with mainland North Carolina; it serves as the only terrestrial evacuation route for the 4,300 residents of Hat- teras Island and all visitors to the Cape Hatteras National Seashore and local communities. According to the Outer Banks Visitors Bureau (2016), the Seashore had a total of 2,266,579 visitors during the year 2014. As part of the long-range planning to main- tain a transportation corridor connecting the northern Outer Banks (including Nags Head, Kitty Hawk, and Duck) with Hatteras Island (including the communities of Rodanthe, Buxton, and Hatteras Village), the North Carolina Department of Transportation (NC- DOT) has been conducting a comprehensive monitoring study of Pea Island since 2011 (e.g. Overton 2015). This study is based on Figure 1. Location map of Pea Island. Reference transects are shown at 1-mile intervals along the coastal monitoring program study area. The intensive data collection and analysis, with location of the NOAA station ORIN7, Oregon Inlet Marina is shown for aerial photography taken six times a year, and reference. The Oregon Inlet waverider buoy is located approximately 10 digital photogrammetry processing to produce miles offshore east of Mile 1. The white line indicates the NC 12 highway digital terrain models four times a year. These location along Pea Island. data are examined to assess the condition of Shore & Beach Vol. 84, No. 2 Spring 2016 Page 49 the National Wildlife Refuge System Improvement Act was passed. This act amended the 1966 act to ensure that the NWRS is managed as a national system of related lands, waters, and interests for the protection and conservation of our nation’s wildlife resources. The 1997 act established a formal process to determine “compatible use” of a wildlife refuge, and whether or not a proposed use would be allowed. Essentially a “wildlife first” policy is maintained with specified pri- Figure 2. Construction of brush fencing., Photo courtesy National Park ority public uses for wildlife-dependent Service, Cape Hatteras National Seashore Collection (with permission). recreation (e.g. observation and pho- tography, environmental education and the barrier island’s dunes, back-barrier 1984; Dolan et al. 1973). Repair of bar- interpretation, etc.; see the Comprehen- channels, shoreline position, and other rier dunes by the National Park Service sive Conservation Plan for the Pea Island morphologic factors affecting the vulner- also occurred after the Ash Wednesday National Wildlife Refuge (U.S. Dept. ability of the coastal highway. storm of 1962, at locations on Bodie, of the Interior 2006)). Any proposed Pea, and Hatteras Islands (USACE 1965). use or activity such as road relocation, This coastal observation was prepared beach nourishment, or dune construction using data from the NCDOT NC 12 During the 1970s there was a shift in must undergo an evaluation known as a Coastal Monitoring Program, and illus- National Park Service policy, detailed in Compatibility Determination, which also trates the spatial and temporal variability Behn and Clark (1976). This coincided requires public notice and comment. Pas- in the dune field along Pea Island over the with the publication of works by Dolan sage of this act required that any NCDOT 2014 study year. (1972) and Dolan et al. (1973) positing activities outside of the existing NC 12 that the dunes created a barrier to sand HISTORICAL CONTEXT easement within the refuge would need transport and island migration and that Before the 1930s, Pea Island was a to obtain a Compatibility Determination the original state of the island did not wide, flat beach regularly overwashed by ensuring that those activities represented support such features. Behn and Clark waves, with inlets opening and closing a compatible use of the wildlife refuge. (1976) describe how, while the National with storms (Birkemeier et al. 1984). That Since passage of the act, all routine Park Service did not make a public an- changed during the early 1930s, when an road maintenance, including minor road nouncement that they were no longer extensive public works project was initi- relocations, have occurred within the maintaining the barrier dunes, this was ated in order to create a continuous line existing 100-ft easement. Major storm in fact the official policy. of vegetated, protective foredunes from repairs have been allowed outside of the the Virginia state line to Ocracoke Inlet as The coastal highway that is now NC easement through Special Use Permits. described in Weatherwax (1937), Dolan 12 along Pea Island was first paved in RECENT CONDITIONS et al. (1972), Birkemeier et al. (1984), the 1950s (FHWA, NCDOT 2010). (2011-2014) and others. This project was backed by Historically, as the NCDOT worked to In general, barrier dunes first con- the federal government through various maintain a transportation corridor along structed in the 1930s and sporadically agencies including the Works Progress Pea Island, when erosion threatened maintained thereafter have been degraded Administration, and by 1937 was under the road, the preferred alternative was over the intervening years by storms and charge of the National Park Service to relocate the road landward, away long-term erosion. In late August 2011, the (Weatherwax 1937). The effort included from the active shoreline. As a part of island was impacted by Hurricane Irene, construction of brush sand fencing and the cleanup of the prior location of the and two breaches formed, one just south planting of vegetation (Figure 2). Mul- road and easement, dune restoration and of Mile 6 and one in northern Rodanthe tiple levels of sand fencing were often planting of vegetation were often done to (approx. Mile 11.5), eliminating the dune placed to increase the dune height. The re-establish the beach-dune system. This field in those locations (Figure 1). constructed dune heights varied from 10 strategy continued through the mid-1990s to 26 feet, and the dune base widths were when road relocation projects allowed The breach near Mile 6 occurred approximately 80-330 feet (Birkemeier et for restoration of dunes along the former where multiple historic inlets known as al. 1984). Once the dunes were built to highway easement. New Inlet have opened and closed (see the desired height and width, the vegeta- Birkemeier et al. 1984; Clinch et al. However, in 1997 regulatory changes tion was planted, primarily beach grasses 2012). This breach existed as a tidal inlet caused a shift in the management strategy and shrubs (Weatherwax 1937). from 2011 until 2013 and was known for the coastal highway. The National as the Pea Island Breach (Velasquez- The initial construction was fortified Wildlife Refuge System (NWRS) was Montoya et al. 2015); the opening of by the National Park Service along the created in 1966 with passage of the Na- this ephemeral inlet destroyed part of the Cape Hatteras National Seashore later in tional Wildlife Refuge System Adminis- NC 12 highway, which was closed for a the 1950s using bulldozing, brush sand tration Act. The NWRS includes the Pea month — requiring residents and visitors fencing, and plantings (Birkemeier et al. Island National Wildlife Refuge. In 1997, to access Hatteras Island via ferry — until Page 50 Shore & Beach Vol. 84, No. 2 Spring 2016 Figure 3. Lines show a 0.5-mile running average of maximum elevation at each transect displayed from north to south along the study area for each topographic data set. Elevations at the centerline of NC 12 are plotted in with hollow triangles for comparison. Background colors correspond to the locations described in Table 1. Modified from Overton (2015). Table 1. Alongshore dune characteristics at Pea Island, North Carolina. Average dune Average horizontal crest elevation distance of dune in 2014 crest from edge of Location Local name Description (ft NAVD88) pavement in 2014 (ft) Miles 0-2 Canal Zone NC 12 is immediately adjacent to dunes; 20 194 dune sand is highly mobile via wind and water transport Miles 2-4 Northernmost NC 12 is immediately adjacent to dunes; 14 90 Freshwater overwash observed during Sandy; dunes Pond have minimal vegetation. Miles 4-6 Old NC 12 was relocated landward from 20 236 Sandbag original alignment in this area in 1996; Area some remnant dunes that were constructed at that time still exist. Mile 6 Pea Island Temporary metal bridge in place at breach; 12 322 Breach dunes removed over most of this section, frequent overwash and flow through breach during storms. Mile 7-10 Stable Zone Wider island, NC 12 located at substantial 28 741 distance from active beach; historical constructed dunes still in place over most of the area; dunes highly vegetated.