SCOPE OF WORK - June 2000
HYDROGRAPHIC SURVEYING AND WAVE & CURRENT
MEASUREMENTS IN SUPPORT OF THE
WILMINGTON HARBOR MONITORING PLAN

Background.

Navigational improvements are proposed for the Wilmington Harbor Project extending from the ocean entrance of the Cape Fear River to Wilmington, NC. The ocean bar channel will be both deepened and realigned. Littoral material dredged from the channel during initial construction and periodic maintenance will be placed on the adjacent beaches. The material will be placed within designated areas which include approximately 16,000 feet along Bald Head Island to the east (including 14,000 feet of South Beach and 2,000 feet of West Beach) plus about 25,000 feet of Oak Island to the west. The maintenance of the channel will be such that every third beach disposal will be placed along Oak Island based on the present understanding of sediment transport patterns for the area. The response of the beaches and nearshore waters to the operation of the new channel project will be observed through a routine monitoring program. This program, as described in the Wilmington Harbor Monitoring Plan, dated June 2000, consists of seven basic tasks including: (1) offshore beach profile surveys along Bald Head and Oak Islands, (2) surveys of the channel and ebb tide delta, (3) operation of a directional wave gauge, (4) current measurements along the entrance channel, (5) onshore beach profile surveys along Bald Head and Oak Islands, (6) color aerial photography, and (7) report preparation. Tasks 1 through 4 are to be accomplished by or through the Field Research Facility (FRF), tasks 5 & 6 will be obtained under separate service contracts through the Wilmington District (SAW) and task 7 will be the responsibility of SAW.

Services Provided by the FRF.

Task 1 Offshore Beach Profile Surveys.

Coverage.
Beach profile locations have been established along Oak Island and Bald Head Island as shown on Figures 1 & 2, respectively. For Oak Island, profiles follow an existing Corps of Engineers baseline and are spaced about every 500 feet for a total of 62 lines. For Bald Head Island, the beach profile locations duplicate those currently being monitored by the Village under its own program. In this case the profiles have an approximate 400-foot spacing for a total of 58 lines. Offshore surveys obtained by the FRF will be along every other line as indicated in the Figures as longer profile lines. A total of 61 offshore profiles are required with 32 lines located along Oak Island and 29 located along Bald Head Island. Surveys shall be accomplished using the accurate LARC survey system developed by the FRF. Coverage for each profile shall begin from the beach berm extending offshore to the 25-foot depth contour or 15,000 feet, which ever is encountered first. Coordinate listings as well as standard HYPACK software files establishing each profile track will be provided by SAW.
Survey Datum.
All survey data shall be in reference to the North American Datum of 1983 (NAD83) horizontally and the National Geodetic Vertical Datum of 1929 (NGVD29) vertically.
Schedule of Work.
An initial survey will be accomplished as soon as practicable following the receipt of funds with the intent on completing the offshore survey prior to the start of the ocean bar dredging scheduled to commence in September 2000. A second survey will be accomplished one (1) year thereafter in September 2001, duplicating the initial coverage.
Submittals.
Profile survey data shall be submitted within 3 months following completion of the fieldwork. Data files shall be submitted in standard ISRP 2-D format as well as in tabular xyz ASCII format. All data shall be in reference to the above survey datum and submitted in feet.

Task 2 Channel and Ebb Tide Delta Surveys.

Coverage.
The proposed aerial extent of the ebb tide delta survey coverage is indicated on Figure 3. The FRF shall provide a high-resolution bathymetric and side scan sonar survey of this area. This survey shall be supplemented by the LARC/system to provide coverage over shoal areas not safely accessible by the survey vessel. The high-resolution survey will be conducted using an interferometric system (ISIS 100), or equivalent, capable of a 2-meter grid resolution or better.
Survey Datum.
All survey data shall be in reference to the North American Datum of 1983 (NAD83) horizontally and the National Geodetic Vertical Datum of 1929 (NGVD29) vertically.
Schedule of Work.
An initial survey will be accomplished as soon as practicable following the receipt of funds with the intent on completing the offshore survey prior to the start of the ocean bar dredging scheduled to commence in September 2000. A second survey will be accomplished one (1) year thereafter in September 2001, duplicating the initial coverage.
Submittals.
A bathymetric chart and ASCII text file in tabular xyz format of the survey data shall be submitted within 3 months following completion of the fieldwork. All data shall be in reference to the above survey datum and submitted in feet.

Task 3 Shipboard Current Profiles.


Description.
Currents will be measured across the mouth of the Cape Fear River, along the east bank near Bald Head Island, and in the vicinity of the channel re-alignment. The current measurements will be recorded using a shipboard-mounted acoustic Doppler current profiler (ADCP) operated along the proposed tracks as shown in Figure 4. Currents will be measured continuously throughout the water column along these tracks for a complete semi-diurnal tidal cycle (>12.4 hrs).
Schedule of Work.
Current measurements shall be accomplished as soon as practicable following the receipt of funds with the intent on completing the work prior to the start of the ocean bar dredging scheduled to commence in September 2000. A second set of measurements will be accomplished one (1) year thereafter in September 2001, duplicating the initial coverage.
Submittals.
The results of the current measurements shall be submitted within 3 months following completion of the fieldwork. The submittals shall include a 3-D graphical representation showing current magnitude and direction throughout the water column at discrete points and times selected by the FRF and SAW. Supporting data files shall be submitted as ASCII text files. All reported measurements shall be presented in English units.

Task 4 Directional Wave Gauge.


Description.
The FRF will supply, install, operate and maintain a directional wave gauge in support of the monitoring plan. The gauge will be located just offshore of Bald Head Island in about 20 feet of water, eastward of the new channel as shown in Figure 4. The final location will be coordinated between the FRF and SAW. The bottom-mounted gauge will consist of a combination of an Acoustic Doppler Current Profile (ADCP) meter and pressure gauge or equivalent capable of producing measurements of wave height, period and direction as well as currents over the water column. These measurements will in turn be used to compute potential sediment transport rates necessary for the proper placement of maintenance material along the beaches. The gauge is to be hardwired to shore provided that an adequate phone and power lines can be found within 6,000 feet of the gauge site. Data will be posted on the Internet near real time on the FRF’s web site.
Length of Operation.
The directional wave gauge will be installed as soon as practicable following the receipt of funds with the intent on having the gauge operational prior to the start of the ocean bar dredging scheduled to commence in September 2000. The gauge is to be maintained for a period of approximately two (2) years thereafter until 30 September 2002. Additional yearly extensions for operation of the gauge are possible, subject to the availability of funds.
Submittals.
Data shall be submitted monthly in tabular and/or graphical form showing average daily wave height, wave period, wave direction, bottom current magnitude & direction, surface current magnitude & direction along with computed potential sediment transport rates. All data shall be in English units (feet, feet/sec, cubic yards/day). Directional data shall be referenced to grid north. Sediment transport direction shall follow the convention of westerly transport being positive and easterly transport being negative.