|Environment and development
in coastal regions and in small islands
COAST AND BEACH STABILITY IN THE CARIBBEAN ISLANDS COSALC
UNITED STATES VIRGIN ISLANDS
BEACH MONITORING FIELD MANUAL
|3||Beach monitoring field techniques|
|3.3||Field measurement of the beach profiles|
|3.3.1||Preparations for going into the field|
|3.3.3||On return from the field|
|Appendix I. Description of the beach profile reference marks|
|List of Figures|
|1||Location of the monitored beaches in St. John|
|2||Standard data form|
|3||Reading the Abney level|
|4||Completed data form|
|5||To establish a new reference mark when the old one is lost|
University of Puerto Rico Sea Grant College Program
Dr. GILLIAN CAMBERS
1. EXECUTIVE SUMMARY
This manual describes a beach monitoring program that was started in St. John in the United States Virgin Islands in January, 1998. This program was established within the "Coast and Beach Stability in the Caribbean Islands" (COSALC) project. This regional program is jointly sponsored by UNESCO within their Environment and Development in Coastal Regions and Small Islands program and the University of Puerto Rico Sea Grant College Program (UPR-SGCP) within their Multi-Program and Regional Development facility. During January, 1998, people from the Virgin Islands National Park were trained in field techniques. This manual describes the criteria used for site selection, the locations and photographs of the monitoring sites, and the field methodology. It is hoped that this monitoring program will provide basic data for the effective management of the beaches in St. John and will compliment the ongoing monitoring of other parts of St. Johns coastal system.
The beach monitoring program in St. John was established within the "Coast and Beach Stability in the Caribbean Islands" (COSALC) project. COSALC is a regional project which covers the smaller English-speaking islands of the eastern Caribbean, including: Anguilla, Antigua & Barbuda, British Virgin Islands, Dominica, Grenada, Montserrat, St. Kitts-Nevis, St. Lucia, St. Vincent & the Grenadines, Turks and Caicos Islands, and has now been extended to the United States Virgin Islands.
The goal of the COSALC project is to develop in-country capabilities so that island states can measure, assess and manage their own beach resources within an overall framework of integrated coastal zone management. The program is jointly sponsored by UNESCO within their Environment and Development in Coastal Regions and Small Islands program and the University of Puerto Rico Sea Grant College Program (UPR-SGCP) within their Multi-Program and Regional Development facility. The coordinating center for the project is based at the UPR-SGCP.
Beach monitoring programs have been established in all the COSALC countries/territories, in some of the islands beach change databases now cover more than ten years. The monitoring programs have had several positive results:
3. BEACH MONITORING FIELD TECHNIQUES
A visit was made to St. John from the 12th-15th January, 1998. During this period people from the Virgin Islands National Park were trained in field techniques. Equipment was provided for field measurement. The beach sites were selected and the first set of field data were collected at each site.
The following people were trained in the beach monitoring
Mr. R. Collier,
Mr. T. Kelly,
Ms. E. Link,
Mr. J. Miller.
3.1 Site Selection
The Virgin Islands (British and U.S.) lie on a submerged platform over which water depths are less than 180 m. They consist of numerous islands, islets, rocks and cays. Many of the smaller rocks and cays are uninhabited. In the U.S. Virgin Islands, there are three main islands: St. Croix, St. John and St. Thomas. St. John is the most northeasterly of the U.S. Virgin Islands.
More than half of St. John is national park land, see Figure 1. The beaches within the Virgin Islands National Park are managed by the Park Service. Those beaches lying outside the boundaries of the National Park are managed by the Department of Natural Resources.
Figure 1. Location of the monitored beaches in St. John
Beaches along the north coast of St. John were selected for monitoring in the first instance. Trunk Bay was selected as a measurement site since it is one of the most heavily used beaches in the National Park and some recently erected lifeguard stations have caused serious localized erosion problems. A second beach, Cinnamon Bay, was selected because it had a history of beach erosion, and in addition only limited recovery had taken place since Hurricane Marilyn in 1995. A third beach, Honeymoon Beach, was selected for measurement as a control site. There are no known problems at this site. The location of the monitored beaches is shown in Figure 1.
Sites were established as follows:
Cinnamon Bay: 4 sites were established:
Cinnamon Bay East,
Cinnamon Bay Tombolo,
Cinnamon Bay Mahoe Swamp,
Cinnamon Bay West (Beach Cottages).
Trunk Bay: 4 sites were established:
Trunk Bay East,
Trunk Bay East Lifeguard Stand,
Trunk Bay West Lifeguard Stand,
Trunk Bay West.
Honeymoon Beach: 2 sites were established:
Honeymoon Beach East,
Honeymoon Beach West.
These sites represent the foundation of the beach monitoring program. It is anticipated that additional beaches and sites will be added in the future.
3.2 Site Description
Appendix I contains detailed descriptions of each site. The monitoring consists of surveying the beach profile from a fixed point set up behind the beach. The fixed point is called the reference mark and is the starting point for the measurement. The reference mark is usually a red paint square on a wall or tree. (Ultimately permanent surveying monuments may be constructed which should withstand hurricanes better than the trees or buildings). It is essential to always start the beach profile measurement at the reference mark. The profiles run at right angles across the beach and in most cases specific orientations for the beach profiles have been determined. Appendix I shows photographs of the reference marks together with a written description of the sites and the profile orientations.
3.3 Field Measurement of the Beach Profiles
The beach profile at each location should be measured at three monthly intervals. The profiles were set up in January 1998, so subsequent measurements are due in April, July and October 1998, and so on in the following years. In addition, the beach profiles should be re-measured as soon as possible after a major event such as a tropical storm or hurricane.
3.3.1 Preparations For Going Into The Field
- Prepare data sheets, a standard data sheet is shown in Figure 2.
- Gather together the equipment: data sheets, clipboard, pencils, Abney level, tape measure, ranging poles, masking tape, camera loaded with film.
- Prepare a plan for which beaches are to be measured on that day and in which order.
- Arrange transport for the field work.
Figure 2. Standard Data Form
ST JOHN BEACH MONITORING PROGRAM
BEACH PROFILE DATA SHEET
Measurement down from the top of the reference mark: metres
Beach segment Length of segment (metres) Slope angle (degrees & minutes) A - B B - C C - D D - E E - F F - G G - H H - I I - J J - K K - L L - M
3.3.2 Field Measurements
- On arrival at the beach site locate the reference mark.
- Lay out the profile in segments, place a ranging pole at each break of slope, ensure the line of the profile follows the fixed orientation. The end point of the profile is the offshore step. This is near where the waves break and there is usually a marked downward step. If no offshore step exists at that time and date, and/or the wave conditions are too rough, just continue the profile as far into the sea as safety permits.
- Write the beach name on the data form, also the date and the names of the field personnel.
- Measure the vertical distance from the top of the reference mark to the ground level with the tape measure. Measure to the nearest cm. Record all measurements in metric units. Write the measurement down on the form.
- Measure the observer's eye level on both ranging poles, making sure that the surface of the sand just covers the black tip of the pole.
- Place the ranging pole at the first break of slope always making sure the surface of the sand just covers the black metal tip of the pole.
- The observer stands by the reference mark and uses the Abney level to sight onto his/her eye level on the ranging pole.
- To read the Abney level refer to Figure 3. As can be seen from the first drawing, the Abney level is divided into degrees, every 10 degrees is numbered. Readings to the left of the zero are negative or downhill, readings to the right of the zero are positive or uphill. To read the angle, determine where the arrow intersects the degrees scale. In the example, drawing b), the arrow falls midway between -5 and -6 degrees. So this angle would be recorded as -5 degrees 30 minutes. To check the minutes, use the vernier scale. For a downhill slope use the vernier lines to the left of the arrow. They are at 10 minute intervals and the 30 and 60 minute lines are numbered. Determine which of the vernier lines most closely intersects one of the degree lines below. In this case the 30 minute vernier line almost exactly lines up with the degree line below, so the vernier reading will be 30 minutes.
Figure 3. Reading the Abney level
a) The degrees scale
|b. Reading degrees and minutes||c. Checking the minutes with the vernier scale|
|The arrow is midway between the 5th and 6th degrees, so the reading is 5 degrees 30 minutes.||The 30 minutes line almost exactly lines up with one of the degree marks, this verifies the minutes reading is 30 minutes.|
Figure 4. Completed Data Form
ST JOHN BEACH MONITORING PROGRAM
BEACH PROFILE DATA SHEET
Site Name: Cinnamon Bay East
Date: 01.13.98 Surveyors: RC, GM, MK
Observations: High swells today
Measurement down from the top of the reference mark: 0.43 metres
Beach segment Length of segment (metres) Slope angle (degrees & minutes) A - B 2.09 + 14º 30' B - C 3.61 - 6º 00' C - D 5.09 -5º 00' D - E 8.13 -8º 80' E - F 0.46 -20º 50' F - G 4.49 -3º 30' G - H 15.28 -5º 00' H - I I - J J - K K - L L - M