Bogue Banks Restoration Project Phase I (2001-02)
The Pine Knoll Shores/Indian Beach (PKS/IB) Joint Restoration effort represents "Phase I" of the larger-scale Bogue Banks Restoration Project. The entire project consists of an ~16.8-mile stretch of Bogue Banks extending from the Atlantic Beach/Pine Knoll Shores town boundary westward, to approximately one mile east of the present location of Bogue Inlet. The Bogue Banks Restoration Project is one of the three supplemental projects that have been aimed to nourish the beach within the 6 to 8 year interim before the construction phase of the U.S. Army Corps of Engineers Shore Protection Project is initiated. The project is sponsored by Carteret County in conjunction with the Towns of PKS, IB, and Emerald Isle (EI). "Phase I" as stated above represents the PKS/IB Joint Restoration Project (2001-02), "Phase II" represents the Eastern EI Restoration Project (2003), and "Phase III" represents the Western EI Restoration Project (2004-05) that entails the realignment of Bogue Inlet and the use of the shoal material dredged during this realignment event for beach restoration purposes.
View Graphic: Bogue Banks Restoration Project
Both PKS and IB passed bond referendums with special oceanfront and non-oceanfront tax districts in 2001 to create a fair and equitable method for funding the project. IB is incurring project costs for IB, the unincorporated town of Salter Path, and the State-owned portion of the Roosevelt State Park. The tax rate for the oceanfront and non-oceanfront tax districts in IB are 0.45 and 0.03 cents per $100 valuation, respectively. IB also levied a similar tax for Salter Path at 0.43 and 0.03 cents per $100 valuation for oceanfront and non-oceanfront districts, respectively. PKS levied a tax of 0.40 and 0.04 cents per $100 valuation, respectively. The entire cost of the project is $12,585,000.36 with PKS, IB, and the State contributing $7,549,999.38, $4,135,000.98, and $900,000 respectively. The State has appropriated $900,000 to defray the cost of nourishment at the Roosevelt State Park, located within the unincorporated town of Salter Path. Coastal Science & Engineering (CSE) prepared the Environmental Impact Statement, Environmental Assessment, Biological Assessment, and construction documents for the project (CSE 2001 & 2002). The dredging contract was awarded to Great Lakes Dredge and Dock Company (GLDD).
(B) Project Background
The PKS/IB Joint Restoration Project can be conceptualized as a 39,202 foot long project that tapers at the "0" foot mark at the AB/PKS boundary and the "39,202" footmark at the IB/EI boundary. Sand sources for the project were delineated in three borrow sites denoted as A, B1, and B2 on the figure provided below. The project construction and post-project activities were conducted in accordance with protocols and stipulations provided in N.C. State Permit Number 124-01 issued by the N.C. Division of Coastal Management, and Permit Number 200000362 issued by the U.S. Army Corps of Engineers.
View Graphic: PKS/IB Joint Restoration Project
Specifications for the engineered beach were developed using a volumetric analysis (profile volume method) that was supplemented with historical erosion rate data. 111 transects at ~1,000-foot intervals were established along the entire length of Bogue Banks in 1999 to assess pre-project beach conditions. At each transect, the profile geometry was determined by surveying the grade of the beach from the toe of the dune to the depth of closure estimated at -12 feet NGVD. The depth of closure in this case was considered as the depth beyond which there is active motion of the seafloor for only 12 hours per year (CERC, 1984). Precise volumes were calculated by interpolating elevation boundaries for each cell and converting the distances and elevational differences to volumetric quantities. The profile volume method establishes site-specific criteria whereby volume deficits can be determined against a designed profile volume that accounts for the overall deficit and incorporates an additional beachfill volume to increase project longevity (Kana, 1993; Kana and Mohan, 1998).
View Graphic: Monitoring Map Insert
AB was determined as the healthiest portion of beach along Bogue Banks with the most sand volume along its profiles. AB was most recently nourished in 1994 as part of the Brandt Island beach disposal event that occurs every 8 to 10 years. Approximately 4.6 million cubic yards (mcy) were pumped onto the shores of Fort Macon and AB during this event. Development in AB sustained almost no damage as a result of the tropical storms/hurricanes that impacted Bogue Banks from 1996-1999. In contrast, approximately $10 million of damage was reported for oceanfront structures in PKS, IB, and EI (Kana et. al, 2002). Based on this information and additional profile analysis, CSE determined that 175 cubic yards (cy) per linear feet was a threshold minimum profile volume. Once this minimum profile volume was established, volume deficits were established for PKS and IB. The minimum deficit was augmented by an additional sand volume to increase project longevity based on erosion rates and final costs for cy of sand. The additional sand volume was estimated to account for ten years of historical erosion rates. Thus, the volume of sand placed on the beach for the project was engineered to provide adequate protection for ~10-year return period events. This analytical process is detailed in the Executive Summary - Shoreline Assessment and Preliminary Beach Restoration Plan and the Environmental Assessment (CSE, 1999 and 2001)
Based on the profile analysis and bid prices, 770,233 cy of sand were to placed along the 13,727 foot (ft) stretch of shoreline encompassing IB, Salter Path, and the Roosevelt State Park, for an average of 65 cy/linear ft in the non-tapered portions of the project beach. 1,402,983 cy were to be placed along the shorelines of PKS (an average of approximately 55 cy/linear foot). Precise volumes per construction transects (design templates) are included in the construction details and were measured separately by GLDD and CSE for payment verification. Sand was dredged from the borrow sites areas using two ocean-certified, self-contained hopper dredges (Manhattan Island and Sugar Island). Subsequent to completing a cut, each dredge traveled and discharged sand to a buoyed pipeline with a floating booster that extended to the pre-construction dry beach. A secondary "Y-valve" discharge pipe was used to transport sand eastward, then westward to complete each ~1-2 mile section. Dredged sand was bulldozed into general construction specifications for subsequent grading into final contours and opened for recreational use. In general, the project was to be constructed from east to west.
View Graphic: Discharge
(C) Construction History
During the initial phases of the project, GLDD were encountering up to 100 tires a day during sand intaking activities (8,582 total). These tires were derived from a broken artificial reef complex constructed by the N.C. Division of Marine Fisheries (AR-342) comprised of 42,000 to 85,000 tires lashed together with chains. The tires and chains were impeding the flow of sediment into the dredges, causing a significant amount of downtime. The N.C. Division of Marine Fisheries collected the tires from the dredges, and a scallop trawler was subcontracted to sweep the borrow areas for remaining tires to the most practical extent possible. Because the tires were buried beneath a thin veneer of sand and are intermittently disbursed in the borrow sites, there were no indication of tires during coring, magnetometer, or side-scan sonar study phases of the project. The original dredging construction volumes were altered to compensate for the tire takings and different areas of the borrow sites were avoided.
Four turtles (2 Kemp's Ridley and 2 Loggerheads) were taken during the uploading of cuts 52 and 53 on December 15, 2001. Per conditions of the operating permit, dredging operations were discontinued until a Biological Assessment modification was submitted by CSE and reviewed by U.S. Army Corps of Engineers and National Marine Fisheries Service. It was apparent that no dredging operation protocols were breached, nor were there indications that the takings could have been avoided by the methodology specified in the original Biological Assessment. Higher than normal water temperatures in the area were considered the primary cause of turtle occurrences. The project was permitted to continue with the approved Biological Assessment modifications on December 21, 2001.
The unexpected delays combined with mechanical breakdowns near the beginning of the year (2002) resulted in a few project modifications. A request to extend the dredging window to April 30, 2002 was granted to permit more time for beachfill construction activities. Also, permission was granted to dredge material unconditionally from borrow areas B1 and B2. If borrow area "A" was to be used, then the 2 to 1 "B" to "A" ratio should have been applied in accordance with the Environmental Impact Statement. In terms of construction modifications, a 16% reduction in the total volume of sand for the entire project was scheduled to compensate for delays and the overall decrease in production rates resulting from continued tire takings. The total reduction was 350,000 cy, or a reduction from 2.17 to 1.82 mcy for the entire project (1.18 mcy for PKS, 645,871 cy for IB).
With the exception of the initial fill areas of PKS, there were project-wide reductions. To achieve the 1.18-mcy apportionment of sand dedicated to PKS, the remaining beach fill for PKS was to be 40.5 cy/foot. This accounted for the volume of sand in the initial "full" cy/foot profile dimensions that were constructed toward the eastern shoreline of PKS that is subtracted from the volume of sand required for the remaining stretch of PKS shoreline. Conversely, the equation for IB was less complex as construction for this reach did not begin at this point. To achieve the 645,871-cy apportionment of sand dedicated to IB, the remaining beach fill was to be 54.4 cy/foot, or a straight 16% reduction from the initial volume. The town boundary lines were also altered for payment purposes from the 25,875 ft mark to the 25,475 ft mark. From mid-January to early March, dredging productivity was it its highest for the project, averaging almost 19,000 cy/day. Permission was also granted to use Borrow Site A, unconditionally. However, mechanical problems ensued causing the mobilization of a third dredge (Dodge Island) to the site in order to complete the project by the April 30th deadline. The third dredge was on site for a total of 14 production days.
View Graphic: Dredge Project
The construction phase of the project was terminated abruptly per permit conditions and the National Marine Fisheries' Regional Biological Opinion for sea turtles on April 11th when the fifth turtle (7th Kemp Ridley turtle for the southeastern seaboard) was taken for the project aboard the Sugar Island. This left a series of "gaps" in the project, extending from the foot marks 37,600 to 39,202 (IB), 36,100 to 37,500 (IB), and 31,600 to 33,900 (Salter Path). The Salter Path region that was not completed lies entirely within the State-owned area of the Roosevelt State Park.
(D) Final Construction Summary
Work stoppages associated with turtle takings, tire takings, and mechanical difficulties resulted in less beachfill than prescribed in the original contract. For IB, this resulted in a 41% reduction from 770,233 cy (contract) to 456,994 cy (actual). For PKS, this resulted in a 9% reduction from 1,402,983 cy (contract) to 1,276,586 cy (actual). In terms of linear feet, 3,502 ft were not constructed in IB. Precise beachfill volumes have been documented by CSE's final post-project surveying activities. The "gaps" in the project, most notably in the Roosevelt State Park and easternmost IB area, have equilibrated significantly to the position of the expanded, project beach berm. Baseline and subsequent high-resolution beach surveying has provided precise measurements to this effect. Per conditions of the working permits, tilling was completed for the entire project beach. Subsequent compaction analysis indicates that the beaches of IB and PKS were -23% and +11% compacted than pre-project beach conditions, respectively (CSE, 2002).
CERC, 1984. Shore Protection Manual. 4th Edition, U.S. Army Corps of Engineers, Coastal Engineering Research Center, Ft. Belvoir, Virginia, U.S. Governmental Printing Office, Washington, D.C., 2 vols.
Coastal Science & Engineering, 1999. Executive Summary - Shoreline Assessment and Preliminary Beach Restoration Plan, Bogue Banks, North Carolina. Columbia, S.C.
Coastal Science & Engineering, 2000. Technical Proposal, Coastal
Engineering Services for a Beach Nourishment Project, Town of Indian Beach, North Carolina. Columbia, S.C.
Coastal Science & Engineering, 2001. Environmental Impact Statement - Bogue Banks Beach Restoration Plan. Columbia, S.C.
Coastal Science & Engineering, 2001. Environmental Assessment - Bogue Banks Beach Restoration Plan. Columbia, S.C.
Coastal Science & Engineering, 2001. Supplement to Bogue Banks Beach Restoration Plan Final Environmental Impact Statement. Columbia, S.C.
Coastal Science & Engineering, 2001. Biological Assessment - Bogue Banks Beach Nourishment Project, Carteret County, North Carolina. Columbia, S.C.
Coastal Science & Engineering, 2002. Beach Fill Compaction, Spring 2002 - Bogue Banks Beach Nourishment Project. Columbia, S.C.
Kana, T.W., 1993. The Profile Volume Approach to Beach Renourishment. In Stauble, D.K. and Kraus (eds.), Beach Nourishment Engineering and Management Considerations, Association of Civil Engineers, New York, NY, p. 176-190.
Kana, T.W. and Mohan, R.K., 1998. Analysis of Nourished Profile Stability Following the Fifth Hunting Island (SC) Beach Nourishment Project. Coastal Engineering, v. 33, p. 117-136.
Kana, T.W., White, T.E., Forman, J.W., and McKee, P.A., 2002. Shoreline Erosion Along Bogue Banks, North Carolina. Proceedings from Solutions to Coastal Disasters Conference, Association of Civil Engineers, San Diego, CA., Feb. 25-27, 2002.