Environment and development
in coastal regions and in small islands
colbartn.gif (4535 octets)

COAST AND BEACH STABILITY IN THE CARIBBEAN ISLANDS COSALC

ST THOMAS,
UNITED STATES VIRGIN ISLANDS
BEACH MONITORING FIELD MANUAL

1 Executive summary
2 Introduction
3 Beach monitoring field techniques
    3.1 Site selection
    3.2 Site description
    3.3 Field measurement of the beach profiles
      3.3.1 Preparations for going into the field
      3.3.2 Field measurements
      3.3.3 On return from the field
4 Concluding remarks
    Appendix I. Description of the beach profile reference marks
  List of Figures
  1 Location of the monitored beaches in St. Thomas
  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
                By
Dr. GILLIAN CAMBERS
February, 1998.

1. EXECUTIVE SUMMARY

This manual describes a beach monitoring program that was started in St. Thomas in the United States Virgin Islands in June, 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 June, 1998, persons from the Division of Fish and Wildlife of the Department of Planning and Natural Resources were trained in the 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. Thomas and will compliment the ongoing monitoring of other parts of St. Thomas’ coastal system.

2. INTRODUCTION

The beach monitoring program in St.Thomas 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 and Barbuda, British Virgin Islands, Dominica, Grenada, Montserrat, St. Kitts and Nevis, St. Lucia, St. Vincent and 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. Thomas from 15-17th June, 1998. During this period persons from the Division of Fish and Wildlife (DFW) of the Department of Planning and Natural Resources were trained in the field techniques. Equipment was provided for the field measurement. The beach sites were selected and the first set of field data was collected at some sites.

The following persons from the DFW were trained in the beach monitoring techniques:

Ms. R. Gomez,
Ms. S. LaToya,
Ms. S. Maidment-Caseau.

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. Thomas is the most westerly of the U.S. Virgin Islands.

Several easily accessible beaches along the central and eastern sections of the north coast of St. Thomas were selected for monitoring at three monthly intervals. These include popular beaches which are heavily used for recreation such as Magen’s Bay and Coki Bay. Other sites selected included Lindquist Bay, Vessup Bay and Bluebeard’s Beach. Bluebeard’s Beach is the site of the Ritz-Carlton Hotel. The location of the monitored beaches is shown in Figure 1.

Figure 1. Location of the monitored beaches in St. Thomas

It was also decided to monitor several less accessible beaches on the western side of St. Thomas on a twice yearly basis, so as to be able to provide more extensive post-storm assessments in the event of a hurricane. These sites will most likely include: Hull Bay Beach, Neltjeberg Bay, Botany Bay and Brewers Bay Beach, see also Figure 1.

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 blue 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.

It is anticipated that as additional beaches and sites are added in the future, specific descriptions of each site can be added to this manual.

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 June 1998, so subsequent measurements are due in September and December 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

  1. Prepare data sheets, a standard data sheet is shown in Figure 2.

  2. Gather together the equipment: data sheets, clipboard, pencils, Abney level, tape measure, ranging poles, masking tape, camera loaded with film.

  3. Prepare a plan for which beaches are to be measured on that day and in which order.

  4. Arrange transport for the field work.

Figure 2. Standard data form


ST THOMAS BEACH MONITORING PROGRAM
BEACH PROFILE DATA SHEET
_____________________________________________________________________________

Site Name:

______________________________________________________________________________

Date:                   Surveyors:

______________________________________________________________________________

Observations:

______________________________________________________________________________

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

  1. On arrival at the beach site locate the reference mark.

  2. 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 location or time, and/or the wave conditions are too rough, just continue the profile as far into the sea as safety permits.

  3. Write the beach name and date on the data form, also the names of the field personnel.

  4. 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.

  5. 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.
  1. 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.

  2. The observer stands by the reference mark and uses the Abney level to sight onto his/her eye level on the ranging pole.

  3. 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 the degrees would be recorded as -5 degrees. Since the arrow falls approximately midway between -5 and -6 degrees, it is likely that the minutes reading is about 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. So this reading will be recorded as -5 degrees 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 5 and 6 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.
  1. Record the segment slope in degrees and minutes, to the nearest ten minutes on the data sheet. Always remember to record whether it is a plus or a minus slope (plus is an uphill slope, minus is a downhill slope).

  2. Measure the ground distance from the base of the reference point to the first ranging pole with the tape measure, to the nearest cm, record this measurement on the data form. Measure along the slope, not the horizontal distance.

  3. The observer then proceeds to the ranging pole at the first break of slope and sights onto the ranging pole which has been placed at the second break of slope and repeats steps g) through j). This is continued until the endpoint of the profile, see step b).

  4. Ensure all measurements are recorded clearly. Figure 4 shows a completed data form.

Figure 4. Completed data form


ST THOMAS BEACH MONITORING PROGRAM
BEACH PROFILE DATA SHEET
___________________________________________________________________________

Site Name: Magen's Bay North

______________________________________________________________________________

Date: 17.06.98     Surveyors: RG, SM-C, LS.

______________________________________________________________________________

Observations:

______________________________________________________________________________

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 + 14 30'
B - C 3.61 - 6 00'
C - D 5.09 -5 00'
D - E 8.13 -8 80'
E - F 0.46 -20 50'
F - G 4.49 -3 30'
G - H 15.28 -5 00'
H - I    
I - J    
J - K    
K - L    
L - M    
  1. Record on the data sheet under "Observations" anything else of interest e.g. recent sand mining pits, evidence of recent storms etc., take photographs if possible.

  2. As the paint squares (reference marks) begin to fade, touch them up with spray paint.

  3. Collect up all equipment and return to vehicle and proceed onto the next site.

  4. Should a reference mark be lost due to a particularly severe storm or due to man's action in cutting down a tree etc., establish a new reference mark as near as possible to the old one and try and determine the ground distance between the new point and the old one along the line of the profile, see Figure 5. (It may then be possible to compare the measurements from the original reference mark with those from the new reference mark).

Figure 5. To establish a new reference mark when the old one is lost.

  1. If there have been very significant changes at a beach, perhaps due to a heavy groundsea or human activity, then take photographs of the beach.

3.3.3 On Return From The Field

  1. Check each data sheet and place in binder or file, it is advisable to set up a binder/folder for each site.

  2. Wash sand out of the tape measure in fresh water, leave to dry and rewind.

  3. Check on the Abney level, if it has any sand on it, wipe it carefully with a soft cloth.

  4. Store equipment carefully for future use.

4. CONCLUDING REMARKS

The beach monitoring program described in this manual is based on simple methods. The schedule of measurements can be modified according to local priorities and concerns, e.g. more beaches can be added, the frequency of measurement at a particular beach can be changed.

Data analysis is a vital component of any monitoring program. Since the software for data analysis is at present being re-written from Lotus for DOS to MSExcel, it was decided to wait until the new software is available (end of 1998) before installing the beach analysis software in St. Thomas.


APPENDIX I

DESCRIPTION OF THE BEACH PROFILE REFERENCE MARKS

 
Magen’s Bay North   Magen’s Bay Middle
The reference mark and
starting point is a blue paint
square on a grape tree. The
profile runs in line with the
gap at Grass Cay.
Magen’s Bay South   Lindquist Bay Middle
     
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