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Executive Summary BACKGROUND . . . . Cape Hatteras Lighthouse, the tallest brick lighthouse in the U.S., faces eventual destruction due to coastal erosion. The lighthouse was built in 1870, 1,500 feet (460 meters) from the shoreline, replacing a lighthouse built near the present site in 1803. It is 200 feet (61 meters) tall and weighs approximately 2,800 tons (2,540 metric tons). Protec- tive measures to reduce the rate of beach erosion in front of the lighthouse have provided a temporary respite, but by late 1987, the lighthouse stood only 160 feet (49 meters) from the sea. The motivation for protecting the lighthouse and its associated structures is to preserve a famous and historic landmark; modern navigational aids have outmoded its original t~unchon of protecting shipping in the stormy waters off the Outer Banks. Cape Hatteras Lighthouse is on one of the barrier islands that constitute North Carolina's Outer Banks. These islands are subject to powerful currents and storms that, in general, cause erosion of east-facing shorelines and accretion of south-facing shorelines. Thus, the east-facing shoreline in front of the lighthouse is expected to continue to recede until storm-driven waves undermine the tower's foundation and topple the lighthouse. The lighthouse now stands close enough to the water's edge to be vulnerable to damage by a severe hurricane. At the request of the National Park Service (NPS), the Board on Environmental Studies and Toxicology of the
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2 Saving Cape Hatteras Lighthouse National Research Council's (NRC) Commission on Physical Sciences, Mathematics, and Resources formed the Committee on Options for Preserving Cape Hatteras Lighthouse in July 1987. The committee's task was to evaluate and develop several options for preserving Cape Hatteras Lighthouse from the encroaching Atlantic Ocean. It is important to note that the committee's charge was how best to preserve the light- house, not whether to preserve it. Political feasibility of the various options or the nature and extent of public sentiment associated with them were not within the scope of the charge, and the committee did not critically assess them. NPS's decision on how to preserve the lighthouse will have to be made in the context of its mission to provide historic preservation, the various public policies relating to U.S. coastlines, and scientific and engineering constraints. In an interim report to NPS on October 14, 1987 (NRC, 1 987a), the committee tentatively concluded that relocation was the best option for preserving the lighthouse. This final report reaffirms and expands on that evaluation. Rate of Shoreline Retreat . The rate of beach erosion (and hence shoreline retreat) is affected by changes in sea level, among other factors. Sea level has been rising for at least the past 10,000 years, dur- ing which the barrier islands of the Outer Banks have been migrating westward. _ _ The committee concludes that a conservative estimate of sea-level rise for the next few decades would be a continua- tion of the rate of the past century--a relative rise of about .08 inch (2 mm) yearly at Cape Hatteras. Recently, another NRC committee also considered three possible scenarios of sea-level rise, accelerating at different rates from the present to the year 2100 (NRC, 1987b). If present trends continued, sea-level rise would be 2.4 inches (60 mm) by the year 2018; the high NRC ( 1 97Sb) scenario would yield 6.1 inches ( 155 mm) by 2018. Based on this range of values, the committee estimates that the shore- line in front of the lighthouse would retreat 157-407 feet (48- 124 meters) by the year 2018. By the year 208S, the retreat might reach 525-3,280 feet (160-1,000 meters).
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Executive Summary 3 Relevant Public Policies Numerous national, state, and local policies bear upon decisions concerning the preservation of historic structures and the management and protection of coastal areas. The committee considered these in evaluating the options for pre- serving the lighthouse. In particular, it identified potential conflicts between national and state policies concerning hardened structures on coasts and NPS policies concerning historic preservation and management of national parks. Historic Preservation . . ~ . - ~ . . ~.. . . Historic preservation has always been part of NPS's mis- sion. The NPS organic act of 1916 ( 16 U.S.C., Sec. 1 et seq.) stated that the purpose of the agency is "to conserve the scenery and the natural and historic objects and the wildlife therein and to provide for the enjoyment of the same in such manner and by such means as will leave them unimpaired for the en iovment of future generations." In 1935, the Historic Sites, Buildings, and Antiquities Act ( 16 U.S.C. Sec. 461 -467) broadened the NPS role in historic preservation. It author- ized the Historic American Buildings Survey, the Historic American Engineering Record, and the National Survey of Historic Sites. It also provided for establishment of national historic sites, preservation of properties "of national historic or archeological significance," and designation of national historic landmarks. The National Historic Preservation Act of 1966 ( 16 U.S.C. Sec. 470) involved NPS in the preservation of historic and arcneo~og~ca~ sites at the state and local levels. The act declared a national policy for historic preservation by provid- ing for the expansion of the National Register of Historic Places, matching grants to the states and the National Trust, and the Advisory Council on Historic Preservation. The act defined historic preservation as "the protection, rehabilita- tion, restoration, and reconstruction of districts, sites, build- ings, structures, and objects significant in American history, architecture, archeology, and culture." Congress amended the act in 1980 (94 Stat. 2987), expanding the roles of federal, ~. .. ... . . ..
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4 Saving Cape Hatteras Lighthouse state, local, and private sectors and providing new mandates for federal land managers. Management and Protection of the Coast The U.S. has 80,560 miles ( 129,621 kilometers) of coast (excluding the Great Lakes), of which 19,240 miles (30,957 kilometers) is erosional (U.S. Army Corps of Engineers, 1971~. Marine shorelines generally are retreating level rise (May et al., 1983~. This natural process of shore- line migration clashes with demographic growth and develop- ment pressure in the coastal zone. Coastal development has increased dramatically in recent decades (Dolan and Lins, 1986; Nordstrom, 1987~. Population pressure on the coast is a severe test of environmental and land-use planning capaci- ties (Platt et al., 1987~. An array of federal statutes and regulations govern devel 1n response to sea opment and protection ot the coast as well as contiguous marine areas. North Carolina's Coastal Area Management Act ( 1974) discourages efforts to harden or artificially stabilize retreating shorelines. Notwithstanding these measures and historic concern for the American coast, the nation and its coastal states have yet to formulate an adequate response to the increasing problems of a shoreline moving landward and a population moving seaward. Resolving the Conflicts In selecting an option or combination of options to pre- serve the lighthouse, NPS will need to comply with public policies concerning historic preservation as well as those concerning coastal management and protection. The main conflict in the present case--between policies that would preserve the historic lighthouse and policies that would allow natural processes to occur unimpeded--is representative of a large class of conflicts between historic preservation and natural conservation. With its dual mandates of historic preservation and conservation of natural areas, NPS must deal with such conflicts frequently. The committee was mindful of this conflict and its general nature, and is confident that the favored option--relocation
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Executive Summary s of the lighthouse--is consistent with preservation and conser- vation policies. Further, the committee hopes that a solution that resolves the conflict in the present case will serve as an example for other similar decisions. THE PRESERVATION OPTIONS AND EVALUATIONS The committee evaluated 10 options for preserving the lighthouse and associated buildings. Three were considered in depth and the rest more briefly. Incremental Relocation of the Lighthouse Intact This option--the committee's preferred option--involves moving the lighthouse complex 400-600 feet ( 122- 183 meters) southwest of its present position to a new site near the far side of the existing parking lot and landscaped area. The committee estimates that this relocation would cost approxi- mately $4.6 million and take approximately 1 year, including planning and site preparation. The committee estimates that a future move of an additional 500 feet in the same direction as the first would cost approximately $1,600,000 in 1988 dollars. Despite the apparent difficulty of moving a large brick structure, the operation entails minimal risk. Many structures larger and older than Cape Hatteras Lighthouse have been moved successfully, and the technology for such operations is well established. The committee envisions that subsequent moves eventually will be required and, therefore, suggests that the steel lifting beams that would be inserted through the lighthouse founda- tion be left in place for use in future moves. Incremental relocation would provide the most reliable, cost-effective, and prudent long-term protection for the lighthouse by allowing it to be moved away from the approaching sea as the need arises. This option best satisfies public policies regarding historic preservation, conservation, and coastal management; minimizes ecological damage; and involves little risk to the lighthouse. The committee also believes that moving the
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6 Saving Cape Hatteras Lighthouse lighthouse would attract much attention and, therefore, would provide an opportunity to educate the general public con- cerning problems of coastal erosion and the value of historic preservation. Seawall/Revetment The design for a seawall and revetment considered by the committee was prepared for NPS by the U.S. Army Corps of Engineers in 1985. The proposed design involves four ele- ments: a concrete seawall encircling the lighthouse, a sheet- pile cutoff wall below the seawall, an underground stone revetment fronting the seawall, and a compacted earth fill behind the seawall (U.S. Army Corps of Engineers, 1985~. The crest of the wall would be 23 feet (7 meters) above mean sea level and 15 feet (4.6 meters) above grade at the base of the lighthouse. The underground revetment would reach 208.5 feet (63.6 meters) seaward of the lighthouse. The U.S. Army Corps of Engineers estimated a construc- tion time of 20 months from award of the contract at a total' cost of $5,575,000 in 1985 dollars. The committee accepts the U.S. Army Corps of Engineers' estimates of construction time and cost. Although the committee judges that the seawall/revetment probably would protect the lighthouse for 20-30 years or more, it does not favor this option. The seawall would obstruct the view of the lower portion ' of the lighthouse, and thus would change the appearance of the historic landmark. The associated lighthouse keepers' dwellings and other struc- tures would be separated from the lighthouse, which would degrade the historical integrity of the site. Constructing a large, hard, defensive structure around the lighthouse would conflict with several national, state, and NPS policies. In addition, the beach in front of the seawall would be lost when the shoreline eroded to 'the seawall, impeding movement along the beach. Eventually, the encircled lighthouse' would become a tombola or an island, which would further degrade the historical integrity of the site and make it difficult for the public to visit the lighthouse. During construction, the lighthouse's vulnerability to storms would be increased; thus, this option presents the greatest construction-related risk of
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Executive Summary 7 all the options considered. Finally, the seawall/revetment effectively would foreclose future relocation of the light- house. Rehabilitation of Groinfield with Revetment . This option involves repairing and shortening the existing three groins, constructing one or two new groins south of the lighthouse, and building a below-grade, reinforced con- crete revetment around the lighthouse. The revetment would protect the lighthouse from the undermining effects of storms, but not from the battering of waves. The rehabili- tated groinfield would stabilize the beach in front of the lighthouse, and the beach would prevent storm waves from ~ , _ ~ . . _ . ~ directly battering the lighthouse, except during the most severe storms. The committee estimated that this option would cost $4.7- 6.7 million and would require less than 1 year to construct. This option would protect the lighthouse for 20-30 years, barring a disastrous storm. · ~.. . I. . . . Eventually, as the shoreline out slae one groins 1ela continued to retreat, it would become increasingly expensive, and perhaps impossible, to maintain a beach in front of the lighthouse, ~ ~ ~ · · ~. .& . . - W~lCh WOU1d become increasingly vulnerable to wave damage in severe storms. The groinfield/revetment option would make future relocation of the lighthouse more difficult and expensive. ~· ~· ~ In addition, placing hardened defensive structures on the beach even below ground, is not in accord with state and national coastal policies. committee did not favor this option. However, of the options that would pre serve the lighthouse in situ by defensive means, this offers some protection to the lighthouse at relatively low cost. Because of these disadvantages, the Other Options Other options considered by the committee were rejected for a variety of reasons. The primary reasons included excessive cost (continuing beach renourishment), uncertain
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8 Saving Cape Hatteras Lighthouse effectiveness and cost (artificial reefs), failure to protect the lighthouse for any period (artificial seagrass and no action), failure to provide either long-term protection or reliable short-term protection (rehabilitation of the groinfield without a revetments, violation of various coastal policies (offshore breakwaters and rehabilitation of the groinfield), and failure to preserve the historic lighthouse (new lighthouse). BROADER ISSUES In addition to evaluating options to preserve Cape Hat- teras Lighthouse, the committee was asked to address the broader context of national policy concerning historic preser- vation versus conservation and coastal issues. Indeed, as sea level continues to rise, additional decisions will need to be made concerning whether and how to protect coastal struc- tures. Moreover, NPS faces decisions concerning historic preservation versus ecological far from the coast. The committee believes that the present study offers guid- ance for future decisions on historic preservation and con- servation. Although the conclusion itself--to relocate the lighthouse--may not be applicable directly to other cases, the decision process could be emulated. The essence of this process is that options are identified and evaluated against the criteria of natural and engineering constraints, public policy, cost, and effectiveness. Full review of those factors will allow sound public policy to be developed regarding his- toric preservation and conservation. The committee com- mends NPS for its willingness to reconsider its initial deci- sion to build a seawall. conservation t~or its properties
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