Beach Nourishment for Hurricane Protection: North Carolina Project Performance In Hurricanes Dennis and Floyd

By Spencer M. Rogers Jr. North Carolina Sea Grant 5600 Marvin K. Moss Lane, Wilmington, NC 28409 (910) 962-2491 [email protected]

ABSTRACT ADDITIONAL KEYWORDS: In 1999, Hurricanes Dennis and Floyd combined to cause erosion that threatened or Beach fill, building damage, ero- destroyed buildings along the entire ocean shoreline of North Carolina. The threat- sion. ened and destroyed buildings were surveyed following the two hurricanes. Although almost 1,000 buildings were affected, beach nourishment projects constructed for hurricane protection in three communities protected all of the buildings within their bels, such as “condemned,” “uninhabit- project limits. Smaller beach nourishment projects in several communities designed able,” or “power disconnects.” With few to provide long-term erosion protection were not effective in preventing the storm- exceptions, the common condition induced erosion threat. among the buildings was that at least part of the foundation had been undermined ince 1996, the coast of southeast exceeded 40 feet (U.S. Army Corps of by erosion during one of the storms. ern North Carolina has been af Engineers 1999). The degree of damage to buildings fected by many hurricanes and S On 16 September 1999, less than two classified as threatened varied consider- tropical storms. In four hurricane sea- weeks later, Hurricane Floyd made land- sons, four storms made landfall at Cape ably. Most of the buildings were single- fall at Cape Fear as a Category 2 hurri- Fear near Wilmington, NC, and a fifth family houses constructed on piling foun- cane (Figure 1). The peak storm surge dations with elevated living floors over passed nearby (Figure 1). In 1996, there exceeded +10 feet NGVD. Based on under-house parking and storage. In were Hurricane Bertha and Hurricane National Flood Insurance Program pre- some cases, only a single piling or row Fran that made landfall within one month dictions, the storm surge return frequency of pilings experienced erosion, with ero- of each other. After a relatively quiet year was 75 years (FEMA 1985). The combi- in 1997, Hurricane Bonnie made land- sion depths as shallow as one foot. Re- nation of storms closely spaced in time fall in 1998. This paper reports on the pair could be as simple as replacing a set caused coastal flooding, shoreline ero- of steps to meet the building code re- erosion threats to oceanfront buildings sion and wave damage along the entire quirement of two means of access. In the during Hurricanes Dennis and Floyd in North Carolina coast. Approximately 300 other extreme, a significant share of the 1999 and on the relative performance of miles of shoreline were affected. threatened houses experienced wave-in- five beach nourishment projects during duced erosion landward of the building. those storms. DESCRIPTION OF DAMAGE Vertical erosion losses around the sea- TO COASTAL INFRASTRUCTURE SUMMARY OF ward side of the foundation were as much The severity of the earlier hurricanes LANDFALL EVENTS as eight feet. Most of the buildings were unfortunately made tallies of building Beginning on 31 August 1999, Hurri- found to lie somewhere between those damage a low priority immediately after cane Dennis became stationary for five extremes. Those classified as threatened the storms of the 1990s. However, by the days 150 miles offshore of Cape generally were expected to be repaired time Dennis and Floyd hit, local govern- Hatteras, soon after, it passed offshore by the following spring. The state’s ments were well practiced in storm Cape Fear. It caused moderate shoreline oceanfront setback line for new buildings preparation and recovery. For the first erosion statewide during its passage. is based on the long-term erosion rate time, local governments documented Conditions were significantly worse rather than an individual storm’s erosion, major structural damage to buildings. north of Cape Hatteras due to the dura- but the requirement uses the seaward line Destroyed buildings were identified us- tion of the storm. Because the highest of stable dune vegetation as a reference ing FEMA’s substantially damaged defi- winds remained offshore, the shoreline line to measure landward for the setback. nition (greater than 50 percent damaged) conditions were similar to an unusually The erosion-relocated vegetation line and were considered irreparable. Com- severe northeast storm. Storm surge lev- was a significant repair incentive because munities identified structurally damaged els were generally less than five feet the setback line had been moved far but repairable buildings by various la- above normal but offshore wave heights enough landward to make many of the

Shore & Beach • Vol. 75, No. 1 ■ Winter 2006 Page 37 an elevation of +13.5 feet NGVD (U.S. Army Corps of Engineers 1993a; 1993b). The nourishment plans consisted of add- ing sand to the lower beach width every two to four years to offset the pre-exist- ing long-term erosion and other project losses. The dune and part of the beach width were designed to provide the build- ing protection during hurricanes. Main- tenance of the projects was expected to always take place before the minimum protection cross-section is eroded. Funding coordination problems for both towns halted maintenance in the 1970s, allowing a reversion to severe, pre-project erosion conditions along Wrightsville Beach some sections of the shoreline (Figure 3). Both projects were substantially rebuilt about 1980 and maintenance has been conducted on a regularly scheduled ba- sis since that time (Figures 4 and 5). The USACE designed a similar cross-section for 3 miles of shoreline in Kure Beach and the south end of Carolina Beach. The project was advertised for bids when Hurricane Fran hit; by that time approxi- mately 20 houses were lost at Kure Beach, with many more threatened due to storm erosion impacts. The nourish- Figure 1. Hurricane Floyd’s wind speeds (mph) at landfall over Cape Fear. ment project was redesigned for the post- most eroded lots at least temporarily eral different purposes and practiced on Fran shoreline conditions and completed unbuildable for new construction. several different scales. There are three before Hurricane Bonnie in 1998. hurricane protection projects designed by The survey results are summarized in HURRICANE-INDUCED IMPACTS the U.S. Army Corps of Engineers; two Figure 2; communities are listed from The previously described projects somewhat smaller-scale — but regularly north to south. Hurricanes Dennis and were designed to provide sufficient pro- maintained — public/private projects; Floyd combined to cause damage along tection for a coastal storm with the re- one very large port-dredging beach-dis- the entire North Carolina oceanfront, turn frequency on the order of 50 years. posal site; and several hundred small, from Virginia to the South Carolina bor- Hurricanes Fran and Floyd, in compari- unmaintained beach-disposal fills from der. Statewide, local governments deter- son, had associated return frequencies of nearby navigation projects. The building mined that 65 buildings were destroyed 120 and 75 years respectively. damage inventory conducted following or substantially damaged. The survey Hurricanes Dennis and Floyd provides a Because design levels were exceeded identified 903 additional oceanfront unique opportunity to evaluate the per- by the two storms, some degree of dam- buildings as erosion-threatened. Al- formance of the larger nourishment age to the nourishment project and to the though the buildings affected by Dennis projects and compare the damage ob- protected buildings is expected. The dune and Floyd are scattered down the coast, served at the nourished areas with dam- and beach portions of these projects are they generally cluster near historical ages at non-nourished beaches nearby. commonly designed as sacrificial fea- problem areas for long-term erosion. The tures that may be consumed during the storms significantly broadened the pre- SUMMARIZED PROJECT duration of a major storm. In fact some vious problem areas and damaged many DESCRIPTIONS sections of the manmade dunes were buildings that previously had been only With local sponsorship, the U.S. Army completely eroded after the passage of close to the edge. Corps of Engineers (USACE) built 2.6 Hurricanes Fran and Floyd (Figures 6 to miles of beach nourishment project at COMPARISON OF 9). The dunes were rebuilt to the design Wrightsville Beach and Carolina Beach INFRASTRUCTURE DAMAGES cross-section during the regularly sched- in 1965. Initial construction and mainte- AT NOURISHED AND uled maintenance in 1998, about 18 nance costs, as well as the benefit/cost NON-NOURISHED BEACHES months after Hurricane Fran. The new ratios were based primarily on hurricane Several North Carolina coastal com- Kure Beach project was constructed at protection for buildings rather than any munities have used beach nourishment about the same time. All three Corps recreational beach benefits. Both projects over the past 35 years (Finkl et al. 2006). projects were tested again by Hurricane have construction cross sections 250 feet Nourishment has been conducted for sev- Bonnie and its associated storm surge wide, with a dune crest 25 feet wide, and

Page 38 Shore & Beach ■ Vol. 75, No. 1 • Winter 2007 with an estimated return period of 37 years. Hurricane Bonnie caused minor erosion of the lower beach but no sig- nificant erosion of the dunes (Figure 7). In some cases, overtopping and wind transport observed during H. Bonnie raised the elevation of the manmade dune. During Hurricane Floyd, some sec- tions of the manmade dunes were flat- tened again, but less extensively than during Hurricane Fran. The inventory of destroyed and threat- ened buildings can be used as a measure of the effectiveness of the beach nour- ishment projects. The nourished beaches of Wrightsville, Carolina, and Kure Beaches were impacted by the highest storm surges during Hurricane Floyd (USACE 2000), yet show marked reduc- tions in the number threatened and de- stroyed buildings compared to unnourished communities both north and south. The benefits of the nourishment projects are actually more evident than implied in Figure 2. All of the threatened buildings listed for the three nourished beaches were located outside the nour- ishment project limits or in transition ar- eas at the ends of the projects where the dunes were not constructed. Hurricanes Floyd and Dennis threatened or de- stroyed 968 buildings outside the three nourishment projects limits. Remarkably, not even one building behind the project dunes was threatened by erosion.

The actual dollar value of building Figure 2. Location of erosion destroyed and threatened buildings following damage would be a better measure of the Hurricane Dennis and Hurricane Floyd along the North Carolina coast. success of the hurricane-protection nour- ishment projects. This paper documents Figure 3. Wrightsville Beach erosion hot-spot in 1979 when maintenance was only the reduction in erosion threat to abandoned. The 1965 pre-project shoreline condition was similar. individual building foundations in hurri- cane conditions up to observed events with an approximate maximum return frequency of 75 years. However, previ- ous studies have shown that the highest building loss rates and most severe dam- age will occur in the storm-eroded areas closest to the ocean (Rogers 1990). The three nourishment projects provided storm-protection and prevented erosion and damage to coastal infrastructure on these beaches. Smaller, privately funded, nourish- ment projects at Figure “8” Island, and Bald Head Island (both in North Caro- lina) also provided some level of storm- protection. Figure “8” Island has con- ducted beach nourishment on irregular

Shore & Beach • Vol. 75, No. 1 ■ Winter 2006 Page 39 intervals since 1979, through private funding by local property owners. Beach nourishment also has been used for ero- sion control on Bald Head Island since 1991. Project widths vary but have typi- cally placed 100 to 150 feet of new berm without any dune. Sections of Figure “8” had been filled several months prior to Floyd. Following the storm, 63 houses were threatened by erosion. Bald Head has relatively few beachfront buildings but seven were threatened (Figure 10.) These smaller projects may have reduced the erosion and number of threatened buildings, but appear to offer relatively less storm protection than the larger cross-sections and higher dunes charac- teristic of the federally funded hurricane- protection projects. Figure 4. The 1980 reconstruction in progress. Atlantic Beach has been fortunate to receive beach nourishment as part of Figure 5. Shown in 1995 prior to the hurricanes of the 1990s. dredging from the nearby state port in Morehead City. Sand dredged for chan- nel maintenance is placed in an inland, diked disposal area. When the disposal area fills every 8-10 years, sand is moved to the shore of Atlantic Beach, allowing the disposal area to be reused for more frequent maintenance. Volumes have been as high as 4 million cubic yards, placed as a wide berm. Over time, the beach has widened on the order of 300 feet. Dunes have not been constructed but have naturally developed seaward of the existing buildings. Atlantic Beach was in the fringe of both Dennis and Floyd and was not as directly impacted as the other nourish- ment project mentioned here. Even though the area was not directly impacted by hurricane-force winds, above-average wave heights and storm surges impacted the area. No buildings were threatened or destroyed during the two hurricanes on Atlantic beach, similar to what was observed in Wrightsville, Carolina, and Kure beaches. CONCLUSIONS The federally funded beach nourish- ment projects in North Carolina that are designed for hurricane protection by the USACE performed well and provided significant storm-protection to coastal infrastructure during Hurricanes Floyd and Dennis. The building survey con- ducted following hurricanes Floyd and Figure 6. In 1996 after Hurricanes Bertha and Fran. The dune was eroded as Dennis found that no buildings were anticipated but erosion was kept seaward of the buildings (and birdhouse.) threatened by erosion inside the nourish- Sand piles on the beach were from overwash deposits removed from the ment project limits, while 903 buildings streets.

Page 40 Shore & Beach ■ Vol. 75, No. 1 • Winter 2007 Figure 7. In 1998 following Hurricane Bonnie, the dune that had been rebuilt during regular maintenance operation was not eroded. Wind-blown sand buried recently planted dune vegetation.

Figure 8. In 1999 after Hurricanes Dennis and Floyd, the dune was again eroded but landscaping (and birdhouse) indicate erosion was kept seaward of the buildings.

Shore & Beach • Vol. 75, No. 1 ■ Winter 2006 Page 41 ate rates of long-term erosion but pro- vide less protection during major storms such as Hurricanes Floyd, Dennis, and Fran. REFERENCES FEMA, 1985. Flood Insurance Study, New Hanover County NC. Finkl, C.W.; Benedet, L., and T. Campbell 2006. “Beach nourishment experience in the United States: Status and trends in the 20th century.” Shore & Beach, 74(2), 8-16. Rogers, S.M., Jr. 1990. “Designing for storm surge and wave damage in coastal buildings.” Proc. 22nd Int. Conf. Coastal Eng., Delft, The Netherlands. ASCE, 2908-2921. USACE 2000. High Water Marks and Inundation Mapping: Hurricane Floyd, May 2000.” USACE 1999. August and September 1999 water level records, Field Research Facility, Duck, NC. USACE 1993a. Section 934 Reevaluation Report and Environmental Assessment, Carolina Figure 9. Wrightsville Beach in 2003 following five hurricanes in the 1990s. Beach and Vicinity — Carolina Beach Por- were threatened and 65 destroyed on ad- Damage analysis from Hurricane Fran tion, Carolina Beach, North Carolina, Wilmington District, South Atlantic Divi- jacent, non-nourished beaches. This ex- in 1996 would be expected to show even sion, revised February 1993. perience shows that properly designed greater benefits from the nourished USACE 1993b. Feasibility Report and Environ- and maintained beach nourishment projects than the examples shown here. mental Assessment on Shore and Hurricane projects are an effective tool for hurri- Preliminary reviews indicated that not Wave Protection, Wrightsville Beach, North one building behind the project limits Carolina, Wilmington District, South Atlan- cane protection. This paper showed a tic Division, September 1982, Revised Feb- comparison between nourished and non- was destroyed by hurricane-induced ruary 1983. nourished locations based on number of waves and storm surges. Outside the buildings impacted by storm waves and project limits, in similar wave and storm surge conditions, an estimated 500 Previously published at National Beach Preser- storm surges but dollar values were not vation Conference; 7-10 August 2000; Maui, HI. presented. The remaining question is how oceanfront buildings were destroyed. American Shore and Beach Preservation Asso- quantitatively beneficial the nourishment Smaller nourishment projects have his- ciation. projects were in dollar figures. torically been successful against moder-

Figure 10. Hurricanes Dennis and Floyd left 63 erosion-threatened buildings on Figure 8 Island, even with a small- scale beach nourishment project.

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