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Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications (1988)

Chapter: Part I. Background Considerations

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Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
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Page 15
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 16
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 17
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 18
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 19
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 20
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 21
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 22
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 23
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 24
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 25
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 26
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 27
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 28
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 29
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 30
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 31
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 32
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 33
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 34
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 35
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 36
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 37
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 38
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 39
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 40
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 41
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 42
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 43
Suggested Citation:"Part I. Background Considerations." National Research Council. 1988. Saving Cape Hatteras Lighthouse from the Sea: Options and Policy Implications. Washington, DC: The National Academies Press. doi: 10.17226/9502.
×
Page 44

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Part ~ Background Consiclerations

The Physical Setting STRUCTURAL GEOLOGY OF THE HATTERAS SHORE The entire east coast of North America forms part of a trailing edge coast in the global plate-tectonic scheme Unman and Nordstrom, 1971~. Although such a trailing edge is seis- mically passive compared with the west coast of North Amer- ica, trailing edge coasts subside in response to gradual cooling of the underlying oceanic crust. The generally level appearance of the east coast of North America owes its topography to this passive accumulation of sediments eroded from the Appalachian mountains since the beginning of the Jurassic, more than 200 million years ago. Subsidence rates along the American east coast, however, have not been uni- form. ORIGIN OF THE OUTER BANKS The Outer Banks of North Carolina is one of the longest continuous barrier-island systems in the world. The Outer Banks includes all the barrier islands from Bogue Banks in the south to Currituck Banks in the north (Figure 3~. Strik- ing repetitive morphological patterns at all the Carolina capes and the location of all the Outer Banks islands on the Caro- lina Platform permit patterns identified in the Cape Lookout to Cape Fear region to be extrapolated northward to the Cape Hatteras region. 17

18 Background Considerations N.C. LGREENSBORO · DURHAM * RALEIGH FAYETTEVILLE ,~ TYRRELL COUNTY ~ FIGURE 3 not include Bogue Banks). The Outer Banks of North Carolina (figure does

The Physical Setting 19 The best Holocene (the past 10,000 years) sea-level curve on the Outer Banks is for Cape Lookout (Heron et al., 1984~. This curve--a function of sea level over time--is based on carbon- 1 4-dated peats in island cores (Figure 4) and demon A par ticularly sharp decline in the rate of sea-level rise occurred about 4,000 years ago. strafes that the rate of sea-level rise has declined. Before this, all barrier-island shorelines probably were moving landward. As a consequence of the sharp decline in rates of sea-level rise 4,000 years ago, some segments of the coast began moving seaward (prograding). Other coastal seg- ments, perhaps nearby, might have continued to erode. Along the North Carolina coast, this pattern meant that shorelines facing south--west of capes such as Cape Hatteras, Cape Lookout, and Cape Fear--began to accrete. Therefore, the most landward beach ridges at Bogue Banks are about 4,000 years old. The pattern of progradation at Buxton Woods on Hatteras Island (Figure 5) suggests that this area, too, is no more than 4,000 years old. This maximal age has coastline however, , , ~ been recorded for many barriers along the U.S. (Nummedal, 1983a). .. . . . The east-facing shorelines, continued retreating, so they are much younger. ISLAND MORPHODYNAMICS The capes evolved through a complex pattern of long- shore, offshore, and onshore sediment transport. This trans- port is controlled by longshore currents driven by some of the highest wave energies along the East Coast. The mean annual wave height at Cape Hatteras is 4.9 feet ( 1.5 meters), and deepwater waves in excess of 6.6 feet (2 meters) are present 25% of the time (Nummedal et al., 1977~. This high wave energy drives powerful and persistent longshore cur- rents along the Atlantic shore of the barriers. The resulting longshore transport rate along the east-facing barrier shore- line is calculated at 2.3 million cubic yards (1.7 million m3) of sand per year toward the south (Langfelder et al., 1968~. Tides are small at the Outer Banks because of the narrow ~~ ~ ~ The mean tide range and the adjoining continental shelf. Hatteras is only 3.6 feet ( 1.1 meters), currents are weak except at tidal inlets. at (:ape associated consequently, the

20 o 0' - ~6 re oh ~9 3 ° 12 - 8 15 Background Considerations ,~ _~ IRRENT SEA LEVEL ~_0O_ _* O ·/0*^ /0~ O . * . . · Shell MaterIal O Basal Peat O Peaty Clay and Sand · Wood Compacted Sample 1 1 1 1 1 1 1 ,1 1 1 9 8 7 6 5 4 3 2 1 0 Years Before Present (BP) x 103 FIGURE 4 Relative sea level at Cape Lookout during the past 9,000 years. Adapted from Heron et al., 1984. ~ i ~ <' -- : ~Pamlico Soun I; Buxton W1~ ~ ~'' ~., . . . ' , . .; ., : ~ , I--- F ~ ) Relics dunes jam :/' -~_- --~A\~ctd~neS H LighthOuse I| - _ ,- ,- ~ Active dunes .'~ v~,!~,,ie,i2i't,~'^~/~- ~ et\e\~_,C-~ I_. f:rlsco ~ / ', ~~~'~ ;',~ .J ~2 j',,~ 'C: r"·~" ,)/~l'anti~ ewe_- _ L._--- J FIGURE 5 Complex pattern of dune ridges at Cape Hatteras indicating pattern of progradation. From Dolan and Lins, 1986.

The Physical Setting 21 morphology of the Outer Banks barrier-island chain is that of a wave-dominated barrier characterized by long, thin barrier islands, frequently overwashed in their natural state, and subject to rapid landward migration. . . . .. .. . These islands are sepa- ra~ea oy migrating, weedy spaced tidal inlets (Nummedal et al., 1977~. The morphology at dramatic differences in Cape Hatteras is controlled by physical processes along the two flanks of this cuspate foreland. Due to the dominance of northeasters, the directional distribution in wave power is such that 75% of the total onshore power strikes the east- facing flank, but only 25% strikes the south-facing shore (Nummedal et al., 1977~. As a consequence, the east-facing shore generally is exposed to erosional waves; waves approaching the south shore cause accretion. Therefore, the history of Cape Hatteras has been one of shoreline retreat at the eastern shore and accretion to the south (see, e.g., Dolan and Hayden, 1983; Dolan and Lins, 1986~. The average rate of erosion at the northern part of Hat- teras Island, which faces east, is 6.4 feet ( 1.94 meters) per year. The accretion of the southern part of the island, which faces south, has progressed at 1.2 feet (37 cm) per year (Dolan and Lins, 1986~. If sea level continues to rise at its current rate, this pattern will be maintained. If sea level rise accelerates, as has been suggested recently (NRC. 1 987bi. the southern shore could become facing shore could erode more rapidly. Not all the sand that converges on Cape Hatteras accretes along the southern shore. Most of it is carried offshore onto the extensive Diamond Shoals (Figure 6~. These and related shoals along the Atlantic seaboard define zones of long-term sediment convergence during the Holocene retreat of the East Coast barrier islands. Much of the sand once contained in the barriers probably has been lost to these extensive shoals and the associated smaller, linear shelf sand ridges (Swift, 1976~. , ~ .,, ~ , ,, erosional, and the east

22 Background Considerations - 1 to ~ _ 1 o _ '^ ~ e~ = ~ --: :~ :-:-:-:-:- ~ ~ ~ C ~ )~ %~` ~ ~ ~ :~ ~0 . ~ ~60~ , W~ ~ ' ~ ~' =~ ~ ~ aid_ 40~N,\ ~ ~ ,~,~k,;~o ~ 4°: rem v' f o u 0 o - cd oo - c~ so o 0 t- so :, ~ · cot LL o V:2 · 0 .= cd LO lo - ~ 0 cot

The Physical Setting 23 STORMS Cape Hatteras Lighthouse is on a coast subject to numerous storms. The most powerful are hurricanes; how- ever, the most frequent are extratropical storms (north- easters), which sometimes have winds of hurricane force. The Outer Banks region has an annual hurricane landfall probability of about 20% (Simpson and Lawrence, 1971), the highest along the East Coast north of southern Florida. Yet, northeasters dominate the annual wave-energy distribution (Nummedal et al., 1977~. The mean annual wave power at Cape Hatteras is 23 x 103 watts/m, among the highest along the East and Gulf coasts (Nummedal, unpublished). Although an individual hurricane track is difficult to predict, docu- mented hurricanes historically follow a well-defined path across the Cape Hatteras region from south to north (Neumann et al., 1978~. Northeasters at Cape Hatteras are most frequent during November through March (Dolan and Lins, 1986~. Storms threaten the lighthouse in two major ways. First, erosion is accelerated. Storms generate powerful longshore currents that transport large quantities of sand. Such trans- port results in erosion of the east-facing shoreline at Cape Hatteras, while the south-facing shoreline accretes. Second, waves and storm surges caused by severe storms can wash over the barrier island, break open new inlets, and threaten land structures. Storm centers are areas of low barometric pressure and are associated with a local rise in sea level known as a storm surge. A storm surge of S.S feet (2.7 meters) above normal high tide has approximately a 1% probability of occurrence per year (MTMA Associates, 1980~. The cumulative effects of storm surge, storm waves, and spring tide during the Ash Wednesday storm of March 5-S, 1962, produced waves more than 30 feet (9 meters) high along the mid-Atlantic coast (Dolan and Lins, 1986~. Hur- ricane Diana produced sustained winds of 75 knots (138 kilo- meters per hour) and a modest storm surge of 5.5 feet ( 1.7 meters) at Carolina Beach in September 1984. Yet it proba- bly was responsible for shoreline retreat of as much as 50 feet (15 meters) (NRC, 1986~. The primary danger of a severe storm to the lighthouse is that the foundation would be undermined, and the structure

24 Background Considerations would collapse. An extremely severe storm could produce waves large enough to damage the lighthouse directly by their battering. The probability of such a severe storm, however, is very low. The most likely combination of events that would damage the lighthouse is a series of two or three moderately severe storms within a few weeks. In this case, the effects of the first storm would render the lighthouse more vulnerable to the effects of later storms. If the shore- line continues to retreat and protective measures are not taken, the lighthouse will become increasingly vulnerable to the effects of storms during the next few decades. Individual storms cannot be predicted reliably more than a few days in advance, much too late for any major protective measures. In addition, many years might pass with no major storms; in other years, several major storms might occur. The frequency and severity of storms also affects the rate of shoreline retreat, which has not been uniform. Therefore, it is impossible to make precise predictions concerning the sur- vival of the lighthouse. · ~ CHANGES IN SEA LEVEL The rate of change in sea level (the first derivative of sea level with respect to time), and changes in the rate of sea-level change (the second derivative of sea level with respect to time) have profound influences on the formation and behavior of barrier islands. - ~ estimating the risk to l hey are also critical In Cane Hatteras Lighthouse and effec- tiveness of options for protecting the lighthouse. - ~. Even if the second derivative is () (ye. sea-level rise IS not accelera- ting), the lighthouse is at risk because the barrier island will continue to migrate westward. There is no reason to believe that the first derivative will become O; an overwhelming body of evidence indicates that sea level will continue to rise for at least the next several hundred years (NRC, 1987b). Historical Trends Global (eustatic) sea level has fluctuated throughout geo- logic history in many cycles of different frequencies and

The Physical Setting 25 amplitudes (Nummedal, 1 983b; Haq et al., 1987~. Processes such as varying rates of sea-floor spreading, waxing and waning of ice-sheets, and changes in global ocean tempera- ture all cause sea-level changes. Of greatest concern is a continuing eustatic sea-level rise caused by melting of mid- latitude glaciers and thermal expansion of ocean waters (Gornitz et al., 1982~. Increasing concentrations of so-called "greenhouse gases" in the atmosphere are likely to cause global warming (NRC, 1983), which probably will increase the rate of rise in eustatic sea level (NRC, 1987b). Observed sea-level rise along a coastline equals the sum of land subsidence and eustatic sea-level rise. This relative sea level controls the actual position of the shoreline; the rate of change in relative sea level affects the rate of shoreline erosion. Tide gauges located at most major harbors of the world are the principal source of data for changes in local relative sea level. For the east coast of North Ameri- ca, local rates of change vary greatly (Braatz and Aubrey, 1987~. Because Wilmington and Cape Hatteras are located on the Carolina Platform, the value for Wilmington is represen- tative of the whole North Carolina coast. From 1920 to 1983, the rise in relative sea level at Wilmington averaged about .08 inch (2.0 mm) per year. Of this, .04 inch ( 1.0 mm) per year (Braatz and Aubrey, 1987) or .05 inch (1.2 mm) per year (Gornitz and Lebedeff, 1987) is probably the eustatic component. The North Carolina coast, therefore, appears to be subsiding at a rate of .03-.04 inch (0.S to 1.0 mm) per year. The rates used in calculations that follow are .05 inch ( 1.2 mm) per year for eustatic rise and .03 inch (0.8 mm) per year for local subsidence. Estimated Future Trends Eustatic sea-level change and subsidence are influenced by anthropogenic factors. Subsidence rates increase in response to withdrawal of fluids, such as groundwater and shallow oil and gas (Allen and Mayuga, 1970~; eustatic sea level increases in response to global warming (NRC, 1983~. With continued residential development along the Outer Banks, rates of subsidence are likely to increase due to groundwater use. However, in the absence of solid data to the contrary,

26 Background Considerations the committee assumes that this factor will remain insignifi- cant for the next few decades. Consequently, future changes in the rate of relative sea-level rise are assumed to be strictly a function of changes in the rate of eustatic rise. The current best estimate is that eustatic sea-level rise will follow a power-function law (NRC, 1987b) of the form: E(t) = 0.0012t + bt2 (Equation 1), in which E(t) is the additional eustatic component (in meters) above present sea level, t is the time in years from the present, and b is a coefficient of the change in the rate of sea-level rise. The first term in this equation represents a simple linear extrapolation of the average rate of rise for the past century, and the second term represents an increasing rate of rise (quadratic) in response to greenhouse warming. Subsidence must be added to E(t) to obtain the relative or observed rise in sea level, as described below. The NRC ~ 1987b) recognized the uncertainties in projec- ting rates of rise and evaluated the engineering implications of sea-level rise in terms of three scenarios involving eustatic rises by year 2100 of a low rate, L, of 1.6 feet (0.5 meter); a medium rate, M, of 3.3 feet ~ 1.0 meter); and a high rate, H. of 4.9 feet ~ 1.5 meters). The associated b factors are summarized in Table 1. The choice of three scenarios for future sea-level rise is based on a series of analyses published during the past 5 years (Revelle, 1983; Hoffman et al., 1983, 1986; Robin, 1986; and NRC, 1983~. These studies were summarized by the NRC ~ 1987b), but the original studies should be consulted for an appropriate understanding of the complex array of assump- t~ons that their models involve The data are too scant and the models too uncertain to justify assigning probabilities to the three sea-level rise scenarios. I T.sin~ the NR(: estimates for rates of eustatic rise com O ~ _ ~ ~ e ~ a, ~ , .~ ~ , ~ ~ e ~ ,~ T _ . olneu with the assumed steady sunslaence tor the Cape nat- teras area of .03 inches (0.8 mm) per year, the local relative sea-level rise can be calculated for any desired future date, T(t), as: T(t) = E(t) + S(t) (Equation 2),

The Physical Setting 27 where S(t) is the change due to ground subsidence. Using the numbers above anti combining equations 1 and 2 yields: T(t) = 0.002t + bt2 (Equation 3~. Calculated magnitudes of sea-level rise are summarized in Table 1. SHORELINE RETREAT Estimates of the rate of shoreline retreat in response to rising sea level can be obtained by different methods that apply varying levels of sophistication. The committee emphasizes, however, that so many unpredictable factors affect shoreline retreat (e.g., frequency and magnitude of storms and measures taken to protect the shoreline) that no method can provide a precise estimate. Common approaches for such estimates include extrapolation of historical trends and use of the Bruun rule (NRC, 1987b). Several factors complicate any predictions of shoreline retreat. First, there are the tour estimates of rates of sea- level rise: a continuation of historic trends and the three NRC scenarios. Second, various methods can be used to estimate the rate of shoreline retreat for any estimated rate of sea-level rise. Third, the rate of shoreline retreat would be much greater for an unprotected coast than for a pro- tected one; the coast in front of the lighthouse is partially protected. The committee did not choose between the four rates of sea-level rise. However, the most reliable estimates for shoreline retreat were believed to be those provided by trend analysis (Leatherman, 1984) assuming some shoreline protec- tion. Analyses of estimated shoreline retreat by Bruun's rule and trend analysis in the absence of shoreline protection are provided in Appendix B for comparative purposes. They pre- dict greater shoreline retreat than trend analysis assuming protective structures for all rates of sea-level rise.

28 - Background Considerations o cry cd m cry ce cd _ a' ~ Q I) Cal C: I Cal an ~O V] _) C4- C* m ~ 0 cry ._ - ,, ;> as _ _ ~ ~w ._ ~0 :' cd ._ 4- cry u' ~ ~ . 4 - cd S:L ~ ~ ~ cry - - ~ ~ u, ~ _ ~ cd in, cry ~ u, ~ to ·_ ~ O ~ o.= ~ 00 00 lo ~7 ._ ~ .= u' 00 - ~ O v, ~ ~ ° O ce ~ - u, c,_ ~ .m :, ~ ce 0 ~ ;. 63 cd ~ E A__ _ ooooo O~ OON ~J.=- ~OX ~ _- _c~ _~ _ __<~\_ O~ u~ __ ~ _~ _~t _~ _ __ C~ ~_ oO O _~ _ - __ ~O OOO~ _~ ~ ~ _ __ · -]~ ~ _ _- _ - _ ___ ~ ~ _ _ ~ _~ _~ _ _ _ _~ __ ~ ~ oo~ ~ O O _ O _O _~ _ O O _ _ _ oo O 0 0 0 _ O O O O O 3 ~O4 O O ~ O_ Z Z Z oO _ c~ O ce ~ Z C> ~ co ~ 0 - P~ - '7 a~ q,) _ ce _ - . 4_ _ ~ ~ .~0 CL- O C) ce ~ _ o ~V ~ c,, _ ·_ . - i_ ~ ~V c: ao O _ C) cd cd c~ _ . ~ L, o ce ;^ J: _ C) ce c: ~ ._ ~ u~ O <) _ ce q) C) ~ (V ._ c~ c~ c~ - ~L C/7 ._ a' ~~ ce co c' ._ ct c~ c~ ._ c~ ._ :> ~> 1 ce ~ ~ ce C/7 o a' cd C/7 a~ cd > L. cO o - oo - .= ~ o

The Physical Setting 29 TREND ANALYSIS The following discussion uses the observed retreat rates at Cape Hatteras during the past 50 years, over which time var- ious engineering interventions were implemented (see Appen- dix A). It is assumed that the existing groins will continue to have some effect in maintaining the present rate of retreat during the next few decades, although their effect for the next 100 years will be minimal without major reconstruc- tion. It is difficult to determine a typical shoreline retreat rate since the 1 930s, because various shoreline engineering meas- ures were implemented at different times. The rate of retreat at Cape Hatteras has decreased steadily since the 1 930s (Everts et al., 1983; Figure 7~. To determine a rela- tionship between shoreline retreat and sea-level rise for this period, therefore, becomes somewhat arbitrary. The average retreat rate at the lighthouse from 1945 to 1983 reported by the U.S. Army Corps of Engineers ( 1985) was 5.2 feet per year ( 1.6 meters per year; Figure 8~; during this time, short periods of accretion occurred. Assuming a past local rate of sea-level rise at Wilmington of .08 inch (2.0 mm) per year, .39 inch ( 1 cm) of sea-level rise corresponds to 26 feet (8 meters) of shoreline retreat, a ratio of 1:800. Table 2 sum- marizes future shoreline retreat based on the four estimates for sea-level rise and assuming a ratio of sea-level rise to shoreline retreat of 1:800. It is clear that even with intervention, the shoreline at Cape Hatteras will continue to recede. SUMMARY OF SHORELINE RETREAT ESTIMATES 1. The local relative sea level at Cape Hatteras 30 years from now will be 2.4 inches (6.0 cm) higher than it is now, if the trends of the past century continue unchanged; in 100 years it will have risen 7.9 inches (20 cm). With the high NRC ( 1 987b) scenario, the corresponding values are 6.1 inches (15.5 cm) in 30 years and 49 inches (125 cm) in 100 years. 2. Predictions of shoreline retreat are rough estimates because of uncertainties in future rates of sea-level rise and

30 Background Considerations PAMLICO SOUND my. BUXTON LEGEND (Mean High Water Line) 1 980 1975 1 963 1 94647 1917 1 872 1 860 1852 W_ql 11j LIGHTHOUSE 1~. ,1 ~ SKI A I ~ _ I x 1 _ il l . t 1 .s ~ CAP E HAT TERAS 0 1 MILE 1000 1 1000 3000 5000 7000 FEET FIGURE 7 Position of the shoreline at Cape Hatteras 1852- 1980. SOURCE U.S. Army Corps of Engineers, 1985.

The Physical Setting u' _ 0 ._ ~ - c, 0 C: ~ c, ·= 4_ _ 0 0 ~ ~ ~_] (D cot, ~ cot cot I 0 ~C: A c<, ~ cat ~ Em .~ ~ ~ 4 - An._ =-_ 0 . _ 4_ i= _ _ 4D V ~ · _ C_I 0 ~ ,4 ._ 0 _ ~4 ~ 2 ~ cad cut:- ._ ~ ._ t1) be:, 0 ~ 31 00 00 of - set a_ _' _ 4_ O 4_ ~ ~ ·= .- cd - a) ~0 * u, · _ _ (V ~ ~ _ U] c~, C) ._ cd c~ _4 ~i .O O ~ _ ~ ~ _ - oo oo - c ~O O O . ~c ~ ' _ _ ~ _ O ~oo O - - o _3 ~0 ·_ C: z e~ c~ o ._ c' c~ ~ _ - - · ~ .O - v 4_ a, ~ ~ u, CL ~ ~L o u, e~ :O ._ ~o ~._ ~ '~ Z Z .o c ._ c - - c~ cd ~ O .3 U) - C~ ~o . 4 - s~ - o ~ . C.) *

32 inadequately quantified storm frequency. Background Considerations models of shoreline response and 3. The committee believes that the most realistic projec- tions of shoreline retreat are those based on trend analysis of the past 40 years because existing structures will continue to have some effect for the next few decades. Accordingly, continuation of the present erosion rate will move the shore- line l 57 feet (48 meters) landward in the next 30 years. With NRC's ~ l 987b) high scenario, the retreat would be 407 feet ~ l 24 meters). -300 a) ~a) - 250 at a: 200 llJ 7 Lll -1 50 ct o I On Lu -100 - FIGURE ~Cumulative Lighthouse, l 945- l 983. Engineers, 1985. Average Erosion Rate 1945- 1983 _ - 5,'~t 'i: \ 1 1 1 / c`: 00 0 ~ _ z ~ O ~ l ~, . , 1 1 1945 1955 1965 1975 1985 YEAR shoreline change SOURCE U.S. at Cape Hatteras Army Corps of

Relevant Public Policies In selecting an option or combination of options to pre- serve the lighthouse, the NPS is guided by a complex series of public policies that address diverse public concerns. The policies are declared by different levels of government and, in some cases, these policies conflict. Conflicts also may arise among different programs and. agencies of the same level of government. Many laws affecting the coastal zone, such as the Nation- al Flood Insurance Program, are conceived in response to actual disasters or other events and trends perceived to be harmful. Public policies seldom anticipate and mitigate future harms whose time of occurrence is unknown. Similarly, public policies commonly focus on the short term. Deciding how to preserve Cape Hatteras Lighthouse is not easy, as it involves numerous and various public policies. And it is not possible to wait until the lighthouse is about to fall to a storm; by then it will be too late. The changes that will lead to that vulnerability are unpredictable and will occur over decades rather than months or years (aside from an unlikely storm of great severity, which could affect the lighthouse now). The decision requires a long-term view, as NPS recognizes. With these considerations in mind, the committee iden- tified the following public policies as being relevant to the lighthouse preservation decision. 33

34 Background Considerations PROTECTION OF NAVIGATION The original purpose of the lighthouse--to prevent ship- wrecks on Diamond Shoals--is of little significance to the question of how the lighthouse should be preserved. The present light is visible on a clear night for 24 nautical miles (44 kilometers) and is supplemented by a beacon on a "Texas tower" 13 nautical miles (24 kilometers) seaward at the outer edge of Diamond Shoals. Modern shipping relies chiefly upon LORAN and other electronic navigational systems; the light- house is chiefly of navigational value to small craft. NATIONAL PARK SERVICE MANDATE The National Park Service Organic Act of 1916 ( 16 U.S.C., Sec. 1 et seq.) charges NPS with a dual mandate to preserve and facilitate public enjoyment of NPS facilities, namely: "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 enjoyment of future generations." In the case of Cape Hatteras Lighthouse, this mandate applies equally to the lighthouse as a historical artifact of great importance and to the beach, dunes, wetlands, and other natural resources of the national seashore. Options that compromise natural resources in the interest of preserv- ing the lighthouse presumably are disfavored. PROTECTION OF HISTORIC STRUCTURES The National Historic Preservation Act of 1966 ( 16 U.S.C. Sec. 470) and Executive Order 1 1593 (U.S. President, 1971 ) declared a national policy favoring the preservation of his- toric structures. Cape Hatteras Lighthouse is on the national and state registers of historic landmarks. This public objec- tive of preservation is articulated further in NPS Management Policies (U.S. National Park Service, 1978~: "Historic struc- tures constitute a major component of the cultural resources entrusted to the National Park Service. The continued integrity of these resources, based upon their classification,

Relevant Public Policies 35 appropriate treatment, management, and use, is a primary concern of the Service.n Relocation of a historic structure that individually pos- sesses national significance in terms of criteria for evaluating proposed national historic landmarks is not permitted under NPS policies. Although a memorandum from the NPS asso- ciate director for cultural resources (J. L. Rogers, 1987) implies that relocation of Cape Hatteras Lighthouse is per- missible, relocation would require the NPS director to waive the guideline (R. I. Beallus, National Park Service, personal communication, 1988~. NPS management policies further indicate that "no historic structure shall be moved if its adversely affected thereby." In addition, "every effort shall be made to reestablish its historic orientation, immediate setting, and general relationship to its environment." structural integrity or preservation would be COASTAL BARRIER RECESSION The Coastal Barrier Resources Act (CBRA) of 1982 ( 16 U.S.C., Secs. 3501-3510) demonstrated congressional recogni- tion of the migratory and dynamic nature of coastal barriers. The CBRA prohibits federal subsidies for infrastructures and other actions that would encourage development of undevel- oped, nonpublic coastal barriers. The Cape Hatteras site is federally owned and is not within the direct purview of the CBRA. Nevertheless, the CBRA reflects a broader national policy. Public investment decisions should be consistent with that policy, rather than- contradict it. NPS generally favors letting nature take its collrs~ with respect to sites under its auspices. tin~uish between natural zones and h interim song However NPS does dis- __ . In the latter, NPS management policy (U.S. National Park Service, 1978) provides that "control measures, if necessary, will be predicated on thorough studies taking into account the nature and velocity of- the shoreline processes, the threat to the cultural resource, the significance of the cultural resource, and alternatives . . . and how control measurets] would impair resources and processes in natural zones." It is further provided that "where erosion control is required by law, or where present developments must be protected to achieve

36 Background Considerations park management objectives, the Service will employ the most natural appearing and effective method feasible." State policy to similar effect is expressed in North Caro- lina's constitution, Article XIV, Section 5 ( 1973; conservation and protection of lands and waters); the Coastal Area Man- agement Act of 1974 (natural shoreline preservation); and the 1987 Guidelines of its Coastal Resources Commission (policy against permanent shoreline stabilization). FLOOD-HAZARD MITIGATION The National Flood Insurance Act (NFIP) of 1968 as amended (42 U.S.C., Secs. 4001-4128) reflects a national pol- icy that coastal and riverine flood losses should be reduced by discouraging activity in flood-hazard areas, in contrast with past reliance upon structural flood-control projects. The NFIP has mapped inland and coastal flood-hazard areas and set minimum standards for local management of new development in such areas. Executive Order 11988 (U.S. President, 1977) further provides that the federal government will avoid investing in identified flood-hazard areas when reasonable alternatives exist. Recent amendments to the NFIP are discussed with reference to relocating the light- house in Part II. ENHANCEMENT OF RECREATION AND TOURISM Cape Hatteras Lighthouse is a symbol of the Outer Banks and a focal point of the Cape Hatteras National Seashore. Although the lighthouse is not open to the public, approxi- mately 140,000 people visited the lighthouse site in FY 1986 ( 1 .6 million visited the entire national seashore in that year). Such tourism provides an important contribution to the econ- omy of the area. Maintenance of continuity of the beach along Hatteras Island in its unobstructed state is important to the recreational function of the national seashore.

Relevant Public Policies 37 PUBLIC EDUCATION Cape Hatteras Lighthouse and its site are resources for public education, an important component of the NPS mission. Topics that may be studied at the site include the maritime and settlement history of the Outer Banks, the physical and ecological nature of coastal barriers, the phenomena of hur- ricanes and coastal storm hazards, and the design and opera- tion of this lighthouse and of U.S. lighthouses generally. FEDERAL CONSISTENCY WITH STATE LAW The Federal Coastal Zone Management Act of 1972, as amended (16 U.S.C., Secs. 1451 et seq.) declared "a national interest in the effective management, beneficial use, protec- tion, and development of the coastal zone" (16 U.S.C., Sec. 1451 ) and further noted that "important ecological, cultural, historic, and aesthetic values in the coastal zone . . . are being irretrievably damaged or lost." To implement national coastal policy, the act facilitated development of state coastal zone management programs under federal guidelines and partial funding and provided that "each federal agency conducting or supporting activities directly affecting the coastal zone shall conduct or support those activities in a manner which is, to the maximum extent practicable, consis- tent with approved state management programs" ( 16 U.S.C., Sec. 1456 (c) ( 1~. In addition, state law predating the Coastal Zone Management Act may regulate activities on fed- eral coastal lands (California Coastal Commission et al., 1987~. WETLANDS PROTECTION Section 404 of the Clean Water Act (33 U.S.C., Sec. 1344) reflects a broad policy favoring the protection of tidal and freshwater wetlands and establishes a permit program to reg- ulate dredging or filling of wetlands under the joint adminis- tration of the U.S. Army Corps of Engineers and the U.S. Environmental Protection Agency. In general, disturbance of natural wetlands is discouraged if a suitable, nonwetland site

38 Background Considerations is available. Executive Order 11990 (U.S. President, 1 977) similarly prohibits federal actions that disturb wetlands if alternative sites are available. ECONOMIC EFFECTIVENESS Since the Flood Control Act of 1936 (33 U.S.C., Sec. 701 a et seq.), Congress has required that certain flood-control and other water-resource projects be justified by a cost/benefit analysis demonstrating that anticipated benefits would exceed costs "to whomsoever they may accrue." The requirement for a cost/benefit analysis applies chiefly to projects proposed by the U.S. Army Corps of Engineers and certain other federal construction agencies but not to NPS. Although a proposed seawall/revetment would be constructed by the U.S. Army Corps of Engineers, NPS is the deciding agency, and a cost/ benefit analysis is not required. Nevertheless, this long- standing provision indicates the importance of selecting an option whose anticipated short- and long-term benefits are optimal compared with short- and long-term costs. ENVIRONMENTAL PROTECTION Numerous statutes embody a federal policy of commitment to environmental protection. For example, Section 101 of the National Environmental Policy Act of 1969 recognized "the profound impact of man's activity on the interrelations of all components of the natural environment" and declared a fed- eral policy to "assure for all Americans safe, healthful, pro- ductive~ and aesthetically and culturally pleasing surround- ~ngs; preserve important n~stor~c, cultural, and natural aspects -` -I --' ~ -" The act requires an environmental impact statement be prepared concerning any "major federal action significantly affecting environment" (Section 102 Iced. The foregoing policies do not suggest the most favorable option for the preservation of the lighthouse. Indeed, poli- cies do conflict as applied to the problem. For instance, the need to preserve a historic structure may conflict with a laissez faire approach to coastal barrier erosion. In addition, .. ()I U ur Ila~luna1 north,. the quality of the human

Relevant Public Policies 39 policy-oriented criteria to select a preferred option must be viewed in light of scientific, engineering, and other technical factors. USE AND PROTECTION OF THE COAST nears, 1971 ) The United States 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 Engi At present, the sea is rising, so the shoreline is moving landward (May et al., 1983~. This natural compres- sion from the sea clashes with outward demographic growth and development pressure in the coastal zone; the population of coastal areas has grown faster than that of the U.S. as a whole (West, 1987), and coastal development has increased dramatically in the past few decades (Dolan and Lins, 1986; Nordstrom, 1987~. Population pressure on the coast is a severe test of environmental and spatial planning capacities (Platt et al., 1987~. An array of federal statutes and regulations govern the development and protection of the coast as well as the con- tiguous marine areas. North Carolina has adopted a singular approach to its migratory coastline: its policy is to discour- age attempts at permanent stabilization of the shore. Not- withstanding these measures and historic concern for the American coast, the nation and the coastal states have yet to formulate an adequate response to the increasing problems of a shore moving landward and a population moving seaward. Cape Hatteras Lighthouse stands on the line of compres- sion. Resolution of its future might act as a signal to the country of the problems confronting the coast and illuminate approaches to solving the problems of living with a rising sea.

Concepts of Historic Preservation Sande ( 1984) describes the purposes of historic preserva- tion as continuity--the conservation of physical evidence of restoration and inter pretation; plausibility--the recreation of a true feeling of an earlier time; and meaning--the hopes, dreams, and satisfac- tions nurtured in those who visit the site. From the standpoints of continuity and historic integrity, Cape Hatteras Lighthouse ideally should be preserved at its original site. The tower first was constructed 1,500 feet (460 meters) from the ocean, but since 1919, it has been close to the water's edge; preservationists have the choice of which era to restore. Plausibility and meaning depend on nonscientific senti- ment. Yet, they are a force behind the decision to save the lighthouse. Cape Hatteras Lighthouse stands about 200 feet (61 meters) tall on a flat and narrow island, is painted with black and white stripes, and has a rotating beacon of 250,000 candlepower (U.S. Coast Guard, 1971~. It is a forceful pres- ence in the surrounding community and can be seen from great distance on land and at sea. the past; integrity--the accuracy of Citizens of Hatteras Island and many visitors want to save the lighthouse at its original site for as long as possible. However, this might not be a realistic, long-term solution to preservation. Historic preservation has been a mission of the National Park Service since its beginning. The National Park Service 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 41

42 Background Considerations provide for the enjoyment of the same in such manner and by such means as will leave them unimpaired for the The word "historic" was Horace Albright, second director of the Nob and a oratter of the legislation, explained that he and Stephen Mather, the first director, always envisioned the inclusion of historic parks and sites in the NPS domain (Albright, 197 1~. The election of Franklin D enjoyment ot tuture generations. included deliberately. ~ . . . . . . Roosevelt as president afforded an opportunity to realize this vision. Roosevelt issued a presidential order transferring to NPS more than 60 national battlefields, national monuments, and other historic sites then under the care of other government agencies. In 1935, the Historic Sites, Buildings, and Antiquities Act (16 U.S.C. Sees. 461-467) broadened the role of NPS in his- toric preservation. It authorized 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 archeological sites at the state and local level. The act stated a national policy for historic preservation by providing 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, state, local, and private sectors and providing new historic preservation mandates for federal land managers. Numerous other laws and executive orders affect the preservation of historic or archeological properties and apply to NPS. A 1987 list of all "water-related" properties on the National Register of Historic Places comprises 750 entries, approximately half of which are historic vessels. Of the . · . 42

Concepts of Historic Preservation 43 remaining half, most are lighthouses or lifesaving stations. It is reasonable to assume that no more than seven or eight individual historic coastal properties might be endangered by rising sea level and erosion during the coming years. A primary threat to all historic structures is lack of funds and associated neglect. A recent report (U.S. Department of Interior, 1987) estimates that $100 million is needed to repair historic structures in the national parks administered by the Southeast region alone. Because of past and recent develop- ment patterns along the barrier islands and ocean bluffs, historic structures probably are not considered the most pressing public policy issue posed by erosion and rising sea levels. Rather, beach houses and roads are pressing con- cerns, followed by concern for coastal cities. 43

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