DARE CO CAPE HATTERAS 2006 GROIN REHAB FEASIBILITY STUDY, INTRO TO RECOMMENDATIONS

Prepared For: REcEyrVk
RECEIVED NOV--31006
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ELIZABETH CITY
COUNTY OF DARE
NORTH CAROLINA
EXISTING GROIN REHABILITATION
FEASIBILITY STUDY
CAPE HATTERAS, NORTH CAROLINA
5 JULY 2006
TABLE OF CONTENTS
EXISTING GROIN REHABILITATION FEASIBILITY STUDY
APPENDIX A
— FIGURES
APPENDIX B
— PHOTOGRAPHS
APPENDIX C
— OPINION OF PROBABLE COST(S)
APPENDIX D
— CALCULATIONS
APPENDIX E —
EXISTING GROIN REFERENCE DRAWINGS
APPENDIX F —
CAMA MANUAL FOR COASTAL DEVELOPMENT
APPENDIX G
— SYNOPSIS OF THE CAPE HATTERAS LIGHTHOUSE
Submitted by:
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Moffatt & Nichol
1616 East Millbrook Road, Suite 160
Raleigh, North Carolina 27609

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County of Dare, North Carolina
Existing Groin Rehabilitation Feasibility Study
COUNTY OF DARE, NORTH CAROLINA
EXISTING GROIN REHABILITATION
FEASIBILITY STUDY
CAPE HATTERAS, NORTH CAROLINA
TABLE OF CONTENTS
Page No.
1.0
INTRODUCTION
1
2.0
HISTORY OF EXISTING GROINS
1
3.0
CONDITION OF EXISTING GROINS
2
4.0
REHABILITATION ALTERNATIVES
3
4.1 PRECAST CONCRETE SHEET PILE ALTERNATIVE
4
4.2 STEEL SHEET PILE ALTERNATIVE
4
4.3 RECOMMENDED ALTERNATIVES
4
5.0
OPINION OF PROBABLE COST AND PERMITTING ISSUES
5
6.0
RECOMMENDATIONS
7
APPENDIX A — FIGURES
FIGURE 2.1 — Groins 1, 2 & 3 Construction (1969)
A
— 1
FIGURE 2.2 — Original Construction
A
— 2
FIGURE 2.3 — Groins 1, 2 & 3 Repairs (1975)
A
— 3
FIGURE 2.4 — Groin Repairs (1975)
A
— 4
FIGURE 2.5 — Groins 1, 2 & 3 Repairs (1980 to 1982)
A
— 5
FIGURE 2.6 — Groin Repairs (1980 to 1982)
A
— 6
FIGURE 2.7 — Groins 1, 2 & 3 Repairs (1994)
A
— 7
FIGURE 2.8 — Groin Repairs (1994)
A —
8
FIGURE 2.9 — Groins 1, 2 & 3 Proposed Repairs
A —
9
APPENDIX B — PHOTOGRAPHS
PHOTOGRAPH 1 — Northeast View of Groin 1 B - 1
PHOTOGRAPH 2 — East View of Groin I B - 1
PHOTOGRAPH 3 — North View of Groin I B - 2
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County of Dare, North Carolina
Existing Groin Rehabilitation Feasibility Study
PHOTOGRAPH 4 — North View of Landside Portion of Groin 2 B - 2
PHOTOGRAPH 5 — East View of Groin 2
t
PHOTOGRAPH 6 — Northeast View of Steel Sheet Piles at Groin 2 B - 3
PHOTOGRAPH 7 — Southwest View of 1980 to 1982 Construction of
PZ 27 Sheet Piles at Groin 3 B - 4
PHOTOGRAPH 8 — North View of Groin 3 of 1980 to 1982 Sheet (Left)
and 1994 Sheets (Right) B - 4
PHOTOGRAPH 9 — North View of 1994 Sheet Piles at Groin 3 B - 5
PHOTOGRAPH 10 — East View of Groin 3
I:
PHOTOGRAPH 11 — East View of Groin 3 Showing Failed Concrete Sheet Piles B — 6
PHOTOGRAPH 12 — South View of Groin 3 Showing Gaps in Sheets B — 6
PHOTOGRAPH 13 — View of Sacrificial Anodes on Sheet at Groin 3 B — 7
APPENDIX C — OPINION OF PROBABLE COST(S)
APPENDIX D — CALCULATIONS
APPENDIX E — EXISTING GROINS REFERNCE DRAWINGS
APPENDIX F— CAMA MANUAL FOR COASTAL DEVELOPMENT
APPENDIX G — SYNOPSIS OF THE CAPE HATTERAS LIGHTHOUSE
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County of Dare, North Carolina
Existing Groin Rehabilitation Feasibility Study
1.0 INTRODUCTION
This Existing Groin Rehabilitation Feasibility Study was prepared under the direction of the County of
Dare, North Carolina. The purpose behind the project was the recent need of the County to investigate
the possible repair or replacement of three existing groin structures located in the Atlantic Ocean adjacent
to the USCG Station property which housed the original Cape Hatteras Lighthouse. Each of these
existing groin structures has exhibited some form of failure or repair since the original construction.
The subject property is currently owned by the United States Government and once housed a United
States Coast Guard (USCG) station. The USCG station has recently become inactive and the Department
of Homeland Security has determined that the site is no longer required for operational purposes.
Therefore, the County of Dare is considering the opportunity to take over the long term lease on the
waterfront property. This study will be utilized by the County of Dare to aide in the decision to lease the
site and will assist in determining if additional beach erosion preventive measures will be required for this
area. However, this study does not address the actual coastal engineering solutions for beach erosion
prevention in the vicinity.
Authorization for the completion of the study was provided to Moffatt & Nichol (M&N) on November
29, 2005. The services associated with the performance of this project included: a detailed inspection of
the three existing groin structures; review of the existing groins construction history; a wave loading
analysis; and schematic design developments, including opinions of probable costs for the most practical
repair or replacement alternative. As part of this work, M&N also determined the value of the existing
groin structures to meet the requirements of the "North Carolina Administrative Code" Section 15A
NCAC 07J.0210. This task provides preliminary research into North Carolina Division of Coastal
Management (DCM) permitting issues that could possibly arise with regards to this proposed project.
2.0 HISTORY OF EXISTING GROINS
The main reason for constructing the three original groins was to stop or slow down beach erosion near
the original location of the Cape Hatteras Lighthouse. The 1969 construction of the three precast concrete
sheet pile groins are shown in plan on Figure 2.1 in Appendix A. Figure 2.2 shows the original
conceptual construction details. Groin 1, the northern most groin, was approximately 530 feet long.
Groin 2, the middle groin, was also approximately 530 feet long. Groin 3, the southern most groin, was
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County of Dare, North Carolina
Existing Groin Rehabilitation Feasibility Study
closet to the original lighthouse location. Groin 3 was originally constructed to be 610 feet long. Storms
occurring between 1969 and 1975 destroyed portions of these original groins.
In 1975, steel sheet piles were installed, which appeared to be a PZ-27 size based on the field dimensions
that were taken during this inspection. At Groin 1, steel sheet piles replaced approximately 250 feet of
the original concrete sheet piles. At Groin 3, steel sheet piles replaced approximately 140 feet of the
original concrete sheet piles. No repairs were performed on Groin 2 at this time. Figures 2.3 and 2.4 in
Appendix A show conceptually the construction that was performed in 1975.
Between 1980 and 1982, Groin 3 had approximately 300 feet of steel sheet piles installed mostly near the
landside end of the original construction. These sheets ran approximately at a 30 degree angle to the
south of the existing bulkhead line. The steel sheets were PZ-27 sheet piles and appeared to have
sacrificial anodes installed near the top of each sheet. Figure 2.5 and 2.6 in Appendix A show
conceptually the construction of this improvement.
In 1994, additional improvements were made at Groin 3. Approximately 180 feet of PZ-40 steel sheet
piles were installed near the landside end. Additionally, drawings and records indicate some scour
protection was installed at Groin 3 in 1984 and 1994. Figures 2.7 and 2.8 in Appendix A show
conceptually the construction that was performed for these improvements. There appeared to be
sacrificial anodes installed toward the top of each sheet.
In 1999, the Cape Hatteras Lighthouse was relocated approximately 2,900 feet to its current location. No
additional groin improvements were considered. Appendix G provides a more detailed history of the
lighthouse and the groins.
3.0 CONDITION OF EXISTING GROINS
M&N performed a top side an underwater inspection of Groins 1, 2, and 3 on February 21, 2006. Groin 1
is in very poor condition with the only usable portion of the groin being buried inland. We estimate the
buried portion of the groin that extends towards the shore to be approximately 146 feet. The original
precast concrete sheet piles are leaning significantly to the north. There are only small portions of the
steel sheet piles remaining. The remaining 18 steel sheets total have approximately 75% to 100% loss of
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County of Dare, North Carolina
Existing Groin Rehabilitation Feasibility Study
section due to corrosion. Photographs 1 through 3 in Appendix B show the conditions of Groin 1. All
report photographs are found in Appendix B
Groin 2 was found to have twenty five, four feet wide, precast concrete sheet piles still remaining near the
shoreline and in fair condition. Additionally, we estimate there is 146 feet of concrete sheet pile wall that
is buried and extends inland. Except for the twenty five sheets mentioned above, the remaining concrete
and steel sheets have failed or have corroded to the point that they are no longer capable of resisting storm
wave forces. Photographs 4 through 6 show the conditions of Groin 2.
Groin 3 was found to have most of the 1969 precast concrete sheet to be in very poor condition and not
able to resist the storm wave forces. The improvements performed between 1980 and 1982 are still
present. The sacrificial anode cathodic protection appears to be past its useful life. These PZ-27 sheets
have sustained approximately 16% loss of section, and still have enough section to perform their function.
Photographs 7 through 13 show the conditions of Groin 3.
The Groin 3 PZ-40 steel sheet pile improvements performed in 1994 appear to have lost approximately 16
feet of the original 180 feet due to storm damage. The remaining 164 feet has sustained approximately
18% loss of section due to corrosion. The sacrificial anode cathodic protection system appears to be past
its useful life. Due to the more shallow depth, the existing sheets can still function with some normal
overstresses during storm conditions.
4.0 REHABILITATION ALTERNATIVES
Upon consulting with DCM staff it became apparent that the most likely way to be able to strengthen the
groins (from a permitting standpoint) was to repair them in kind. The two kinds of existing construction
were precast concrete sheet piles and steel sheet piles. Therefore, these were the two alternatives that
M&N considered.
In order to review the feasibility of these two alternatives, M&N performed a wave study for this area.
The wave loads study provided pressures so that a structural analyses could be performed of two
alternatives. For shallower areas of the groins closer to land, the wave loads produced lateral pressures on
the order of 420 pounds per square foot (psf). The deeper areas further away from shore produced lateral
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County of Dare, North Carolina
Existing Groin Rehabilitation Feasibility Study
pressures ranging from 590 psf to 710 psf. The wave load and sheet pile calculations are found in
Appendix D.
4.1 PRECAST CONCRETE SHEET PILE ALTERNATIVE
The first alternative evaluated was precast sheet piles similar to the original construction performed in
1969. Groins 1 and 2 would need to increase the thickness to at least I8 inches and be 29 feet deep.
Groin 1 has approximately 146 linear feet of usable groin which was buried from sight. Groin 2 has
approximately 246 linear feet of usable groin. At Groin 2, approximately 146 linear feet of the 246 linear
feet is buried from sight.
It was found at Groin 3, for it to resist the wave forces, the precast sheets would need to be greater than
over 24 inches in thickness which is not a typical precast concrete sheet pile section. Therefore, for Groin
3 the precast sheet pile alternative was not considered feasible from a practical construction aspect. M&N
could not locate a precaster, who has fabricated this thick of a concrete sheet pile, or a contractor that has
installed this thick of a sheet, and therefore a quantitative cost estimate on this alternative was not
provided for Groin 3.
4.2 STEEL SHEET PILE ALTERNATIVE
The other alternative consisted of installing steel sheet piles groin similar in kind to the 1994
improvements at Groin 3. It was found that for Groins 1 and 2, a 29 foot long PZ-27 A690 grade would
be able to resist the wave loads. For Groin 3, a 38 foot, PZ-40 Grade A690 sheet would be sufficient to
resist the wave loads. Since it is extremely difficult to maintain coatings or a sacrificial anode cathodic
protection system, we recommend a more durable A690 grade which provides a better corrosion resistive
composition than A328 carbon steel.
4.3 RECOMMENDED ALTERNATIVES
Groins 1 and 2 could be repaired with either precast concrete sheet pile or steel sheet pile sheets since the
estimated costs are comparable. If the county desires to pursue rehabilitating Groins 1 and 2, the
decision for which alternative to use can be made during the final design phase. For Groin 3, we
recommend using the steel sheet pile alternative since it is the only feasible alternative.
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County of Dare, North Carolina
Existing Groin Rehabilitation Feasibility Study
5.0 OPINION OF PROBABLE COSTS AND PERMITTING ISSUES
In discussions with the North Carolina Division of Coastal Management (DCM) staff, the existing groins
are classified as hardened structures, and therefore are considered "non -conforming" structures along the
oceanfront. In determining whether work on a structure is repair or replacement of the structure, the
current physical value of the structure is used as the baseline for the 50% repair and/or replacement rule.
The repair and/or replacement issue for non -conforming structures in the ocean hazard Area of
Environmental Concern (AEC) is critical because replacement of non -conforming structures is
inconsistent with current rules. The estimated cost to repair the entire structure "in -kind" (similar
conditions to what it was when first constructed but up to current codes) and within the same footprint
must be computed and then compared to the current existing value. If the estimated repair cost is more
than 50% of the current existing value, the project will be considered replacement and a permit will be
required. If the estimated repair cost is less than 50% of the current existing value, the structure may be
repaired with no permit required. These repairs may be phased over time, but again, it is important to
note that the repair cost must be computed for the entire structure.
It should also be noted that the Coastal Resources Commission (CRC) is considering revisions to the
above rule. The draft revision also provides a separate method for determining if water -dependent
structures like piers, bulkheads and groins need repair/replacement determinations. Under this latest
proposal, work would be considered replacement if it exceeds more than 50% of the linear footage of the
structure, as determined by DCM staff. We have provided a copy of the Coastal Area Management Act
(LAMA) Handbook for Development in Coastal Carolina as Appendix F to this report.
M&N estimates that at Groin 1, approximately 146 linear feet of the original 530 linear feet, is usable.
The 146 feet consist of the buried portion of the original concrete sheet pile bulkhead. M&N could not
confirm this length since it was buried. The remaining 384 feet of the original 530 feet of groin was
almost completely gone or deemed unusable to resist the design wave forces. The estimated value of the
146 ft of usable groin is approximately $223,000. The estimated cost to repair in kind with an 18 inch
thick precast concrete sheet pile repair or PZ-27 A690 steel sheet pile repair each being 29 feet in height
of the remaining 384 It in plan of groin would be approximately $496,000. For the new construction, we
assumed that mobilization and demobilization will occur twice in case of severe weather. Since the cost
of repairs of $496,000 is greater than 50% of the existing value of $223,000, the project would be
considered a replacement, and a CAMA permit would be required. Figure 2.9 in Appendix A illustrates
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County of Dare, North Carolina
Existing Groin Rehabilitation Feasibility Study
the length of usable groin, and the amount of groin that would require replacement for Groins 1, 2, and 3.
All opinions of probably costs can be found in Appendix C
M&N estimates that at Groin 2, approximately 246 linear feet of the original 530 linear feet, is usable.
The 146 feet consist of the buried portion of the original concrete sheet pile bulkhead. M&N could not
confirm this length since it was buried. The additional 100 feet of bulkhead has such a shallow depth that
is should be able to resist reasonable wave forces. The remaining 284 feet of the original 530 feet of
groin was almost completely gone or deemed unusable to resist the design wave forces. The estimated
value of the 246 It of usable groin is approximately $341,000. The estimated cost to repair in kind with
an 18 inch thick precast concrete sheet pile repair or PZ-21 A690 steel sheet pile repair each being 29 feet
in height of the remaining 284 ft in plan of groin would be approximately $393,000. For the new
construction, we assumed that mobilization and demobilization will occur twice in case of severe weather.
Since the cost of repairs of $393,000 is greater than 50% of the existing value of $341,000, the project
would be considered a replacement, and a CAMA permit would be required.
M&N estimates that at Groin 3, approximately 466 linear feet of the 910 linear feet of groin, is usable.
The landside PZ-27 sheets and the newer PZ-40 sheets installed in 1994 still have adequate section to
resist the storm wave forces. The remaining 444 feet of the original 910 feet of groin was almost
completely gone or deemed unusable to resist the design wave forces. The estimated value of the 466 ft
of usable groin is approximately $1,136,000. The estimated cost to repair in kind with a PZ-40 A690
sheet pile repair of the remaining 444 ft of groin would be approximately $1,281,000. For the new
construction, we assumed that mobilization and demobilization will occur twice in case of severe weather.
Since the cost of repairs of $1,281,000 is greater than 50% of the existing value of $1,136,000, the project
would be considered a replacement and a CAMA permit would be required.
If all three groins were repaired, the approximate cost would be $2,170,000. If extremely poor weather
occurs during construction the costs could be higher.
As can be seen from above, each one of the groins would be considered a replacement and as such, a
CAMA permit will be required, and these historically have been found difficult to obtain. The fact that
this structure is "non -conforming" to existing CAMA rules, a replacement of this type would be
inconsistent with existing rules. Additionally, hardened structures are not currently allowed in North
Carolina, a permit for replacement, even in -kind, is very unlikely.
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6.0 RECOMMENDATIONS
Our recommendation for the next step is to present this information to the DCM staff and verify the work
completed to date, that a permit for replacement is not likely to be granted, and to determine what other
types of shoreline protection alternatives may be allowed.
Another option to present to DCM staff is to rebuild the groins so that the value of the repairs is not over
50% of the present value of the existing usable groins remaining. M&N cannot determine at this time if
this strategy will help the beach erosion at this area, or if it is currently allowed. Initial discussions with
DCM staff have not been promising, as they have indicated that the structures must be replaced in -kind
from a length and section standpoint. However, it appears if this strategy is allowed by DCM, that
permits may not be required.
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