Saving Cape Hatteras Lighthouse from the Sea Options and Policy Implications (1988) / Chapter Skim
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Part II. The Criteria, Options, and Evaluation
Part II. The Criteria, Options, and Evaluation
Pages 45-100
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From page 45... ...
rag I' The Criteria Options' and [valuation
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From page 47... ...
Other options, such as beach nourishment or breakwater construction, could be used in combination. The committee did not evaluate every possible option, but selected the following as worthy of consideration: Incremental relocation of the lighthouse intact Rehabilitation of the groinfield without revetment Rehabilitation of the groinfield with revetment Seawall/revetment Artificial- reefs · Offshore breakwaters and groinfield rehabilitation Deployment of artificial seagrass Continuing beach nourishment No action New lighthouse CRITERIA TO EVALUATE PRESERVATION OPTIONS To evaluate the options, the committee developed a set of criteria or tests against which to judge the options.
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From page 48... ...
Protection of natural resources. What are the potential effects on ecological, hydrological, geomorphological, and related natural systems and processes in the vicinity of Cape Hatteras Lighthouse?
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NPS shoreline-management policies. Is the option consistent with NPS policy not to obstruct natural processes on coastal barriers?
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_ resources, aesthetic impact, public access and preservation of other options in the short and construction time, and NPS shoreline-management policies and North Carolina's coastal policies. The third category consisted of criteria that overlapped with one or more in category 2: Coastal Barrier Resources Acts flood-hazard mitigation, and wetlands effects.
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From page 51... ...
also might arise in other NPS decisions regarding historic preservation and conservation. The committee suggests that an approach similar to one it used -- developing a set of relevant criteria and studying options against those criteria -- would prove useful for other decisions that involve conflicting considerations.
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For example, if OMB's current discount rate of 10°h per year is applied, a cost of $5 million 30 years in the future is minor compared with a similar cost next year. Except in the case of beach nourishment, the committee did not attempt to account for inflation in future costs, and all estimates of future costs are in present dollars.
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From page 54... ...
Navy facility north of the lighthouse, although the south groin was installed south of its originally planned location to extend protection to the lighthouse (U.S. Army Corps of Engineers, 1985~.
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From page 55... ...
The lighthouse would be lowered onto rollers that rest on multiple horizontal steel-rail beams supported by precast concrete piles. The entire lighthouse structure would be moved on the tracks with hydraulic jacks and pulled to its new site , where it would be placed on a newly constructed foundation, such as a pile-supported concrete mat (Figure 9~.
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From page 56... ...
,~ ,. ~ c 1 ~ rig q ~ ·, Concrete piles under / girder Heavy steel rail-beam Girders - pile supported for full length Note: End beams are either very deep prestressed concrete beams or steel trusses FIGURE 9 Schematic drawing of proposed tion.
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prestressed concrete piles at 100T capacity FIGURE 10 Schematic drawing of proposed lighthouse relocation, showing some external reinforcing of the structure. Cross section of A - A from Figure 9.
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From page 58... ...
. The committee's cost estimates were based on the follow ~ng: · Current site Sheet piling around excavation; dewatering and excavation; piling; concrete reaction/support beams; concrete ring reinforcement; prestressing rods; main support beams; end-support trusses; prestressing; installation of beams, including.
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From page 59... ...
Uncovering the needle beams, rejacking the lighthouse Railbeams, piles, etc.; construction of 500-foot move track New foundation, and site preparation (e.g., landscaping) E· nglneerlng Insurance · Contractor9s profit $150,000 105,000 500,000 1 1 5,000 100,000 1 50,000 280,000
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From page 60... ...
However, many large, heavy structures -- some larger and older than Cape Hatteras Lighthouse-have been moved successfully (Appendix C)
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As the force of static friction decreases suddenly to the force of moving friction, the lighthouse will begin to accelerate rapidly. The rate of change in acceleration from O to an increasing rate is a "jerk," a dynamic action that tends to change the stability of the mass.
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. ,, ~ ,, The committee suggests temporarily placing a new, heavily reinforced concrete tension ring around the base of the lighthouse.
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. The move track must not encounter any substantial topographic relief, such as the relict dune ridge and swale system along the Buxton Woods nature trail.
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Adapted from aerial photographs and United States Geological Survey map. (Stippled areas represent marshy areas.
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threat from shoreline retreat for The only sites that meet these criteria lie within a narrow band extending approximately southwest from the lighthouse's present location and running approximately parallel to the paved road leading from the lighthouse to the parking lot near the nature trail. The committee considered three general areas along this path.
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From page 66... ...
A location near the road would facilitate access during preparation of the move track and probably maximize distance from the eroding east-facing shoreline. A protective fringe of vegetation between the road and the new site of the lighthouse could help preserve the tradition of isolation of the lighthouse and its associated structures from the violation of historic values implicit in the close presence of roads, cars, and parking lots.
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From page 67... ...
site for the repositioned lighthouse and associated structures. Habitat Damage Along the Move Track Ecological damage along the move track depends on the precise location and design of the new site for the lighthouse complex and the path taken to reach it.
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Topsoil would need to be handled carefully during preparation and restoration of the move track, because soil organics accumulate very slowly on coastal barriers. Their absence would greatly retard vegetation recovery (Au, 1974~.
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This is one reason that much of Buxton Woods has been proposed as an "area of environmental concern" by the North Carolina Coastal Resources Commission to restrict the types and density of development that would create more demand on the limited freshwater resource. Even if all the water needs for concrete used in the move track and the new foundation were met by water-table extractions, the amount -- about 242,000 gallons (916,000 liters)
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From page 70... ...
The concrete slabs needed for the move track could be prefabricated or made with salt water, which is satisfactory when concrete is not expected to be permanent. Water needed for construction of a new foundation (approximately 12,000 gallons (45,000 liters)
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From page 71... ...
The cost of preparing and relocating the lighthouse, all the associated buildings, the parking lot, and the access trails, estimated by this committee to be $4.6 million, is comparable to the cost of other options and lower than some. Furthermore, long-term costs (other than routine maintenance)
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Some beach nourishment would be required at least initially to start accretion between the old and new groin or groins. Subsequent beach nourishment would be determined by the incidence of major storms.
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From page 73... ...
The committee estimates the initial cost of this option to be $3.7-$4.7 million. This includes $ 1 million for one new groin, $1.9 million to repair the existing groins, and $800,000 for 300,000 cubic yards (230,000 cubic meters)
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From page 74... ...
The groins and beach could be overwhelmed by such an event. The committee does not favor this option because it would not protect the lighthouse against severe storms, recurrent maintenance costs probably would be needed, and it would not ensure long-term protection for the lighthouse.
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From page 75... ...
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REINFORCED CONCRETE WALL CONSTRUCTED IN SLURRY TRENCH - CONTINUOUS AROUND PERIM ETER OF FOUNDATION. Schematic diagram of proposed -35 caisson revet
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From page 77... ...
Army Corps of Engineers, because it does not protect the lighthouse from battering by large storm waves that would occur after the shoreline retreated to the lighthouse. Therefore, the caisson revetment would have to be accompanied by rehabilitation of the groin field to maintain the protective beach in front of the lighthouse.
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From page 78... ...
Maintenance' repair, and renourishment costs were estimated at $31 million over 100 years. The committee estimates the initial construction costs to be $4.7-6.7 million, including initial beach nourishment of 300,000 cubic yards of sand.
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From page 79... ...
would be encircled by an octagonal reinforced concrete seawall constructed symmetrically with the base of the lighthouse. The design has four major structural components: a gravity-mass concrete seawall, a prestressed concrete sheetpile cutoff wall extending from the toe of the seawall to 16 feet (4.9 meters)
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80 Criteria, Options, and Evaluation ~ 0 ~= ~ ~ ~ O ~ ~ ~ .
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below MSL -- anoroximatelv 11.5 feet Cost MTMA Associates ( 1980) estimated a cost of $4.5 million initially, $1.1 million in maintenance cost over 100 years, and a total cost of $5.6 million.
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Evaluation of the Options FIGURE 16 Artist's impression of Cape Hatteras Lighthouse surrounded by seawall 10-20 years after construction.
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This committee estimates approximately $6 million in construction costs to construct the seawall/revetment proposed by the Army Corps of Engineers, with substantial but unquantifiable maintenance and repair costs. Evaluation The seawall/revetment option would require a long construction phase -- 19 to 20 months -- during which the lighthouse would be exposed to potentially serious risks.
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The initial construction cost estimated by the U.S. Army Corps of Engineers (1985~ -- $5.6 million -- is high but not out of line with other options for a permanent solution.
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The Hatteras offshore is strewn with more than 100 submerged wrecks; these probably have contributed to the longevity of this protruding section of coastline. Deliberate sinking of ships would require some costly preparation and cleaning to rid them of oil and other contaminants, a disadvantage that could be avoided by constructing artificial reefs from other materials.
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From page 87... ...
Therefore, large but unquantifiable maintenance costs are associated with this option. The committee is unable to cite an example of artificial reefs in areas with wave energy as high as that at Cape Hatteras.
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The committee estimated this option would cost $5 million, with unknown maintenance costs. Evaluation This option would interfere with natural processes, which would violate NPS policy and alter the beach contrary to the regulations of the North Carolina Coastal Resources Commission.
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In southern California, a carefully controlled and monitored experimental installation of artificial seagrass did not effectively alter beach dynamics (Jenkins and Skelly, 1987~. None of the applications of Seascape at Cape Hatteras promoted beach accretion.
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Cost MTMA Associates ~ 1980) estimated an initial cost of $2.9 million to pump 500,000 cubic yards (380,000 cubic meters)
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From page 91... ...
The decisive criterion that this option fails is cost. The costs of beach nourishment are prohibitive, as described above, and, as the shoreline continues to retreat, the costs of maintaining an increasingly large artificial promontory at the lighthouse would grow disproportionately.
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However, NPS's purpose is to preserve Cape Hatteras Lighthouse as required by its mandate to preserve historic Historical precedent would be fol ~.
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Reconstruction merely suggests the form and materials of the old structure. To replicate the lighthouse in all its detail, using original construction methods and materials, would be prohibitively expensive and might not be possible.
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CONTRACTING CONSIDERATIONS Because of the unusual nature of lighthouse relocation and the intricacies of federal procurement regulations, the committee believes it prudent to comment on the potential NPS contracting process. NPS must comply with the Federal Acquisition Regulations System ( 1987)
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This would include the following: Prepare detailed plans to strengthen the lighthouse to give it full structural integrity. Prepare detailed plans for the permanent foundation of the relocated lighthouse.
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From page 97... ...
Rather, performance criteria, such as the desired lighthouse site location, structural and architectural rehabilitation and strengthening, measurable damage limitations, allowable displacement of structural components, and other criteria suggested above are preferable for this type of project. INSURANCE Builder's risk insurance is available to cover any physical damage to a structure that results from external events, such as tornadoes and hurricanes during the contract period.
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From page 98... ...
wide, totalling 120,000 cubic yards (92,000 cubic meters)
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From page 99... ...
The present visitor parking and picnic areas impinge on the historical setting of the lighthouse. The committee suggests that additional parking and other visitor facilities should be separated from the lighthouse complex and screened by natural vegetation.
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