Environment and development in coastal regions and in small islands

Coastal region and small island papers 19

Measuring beach profiles is an ideal activity for science-based assessments and science fair projects. Beach size often changes so quickly – in a matter of days – that interesting results can be guaranteed in a short time period. Furthermore, the information gathered may also be useful for environmental management and planning authorities who need such information when planning new development, but rarely have the resources themselves to collect the data.

Field methods

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 painted 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 are determined. Photographs should be taken of the reference points.

 
When to measure

The beach profile at each location should be measured every three months. This will give four data sets a year and will adequately cover seasonal changes. However, this is only a guide, and depending on the time available, the frequency of monitoring can be increased or decreased. If the profiles are set up in May 2001, subsequent measurements are due in August, November 2001, February and May 2002, and so on. In addition, the beach profiles should be re-measured as soon as possible after a major event such as a tropical storm or hurricane.
 

  Preparations for going into the field

• Prepare data sheets; a standard data form is shown in Figure A.
• Gather together the equipment: data sheets, clipboard, pencils, Abney level, tape measure, ranging poles, masking tape, camera loaded with film, spray paint.
• Prepare a plan for which beaches are to be measured on that day and in which order.
• Arrange transport for the field work.
   

  BEACH MONITORING PROGRAMME 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
  M-N
  N-O
  O-P
  P-Q
  Q-R
  R-S

  Figure A   Beach monitoring programme and profile data sheet
   

  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 (see Figure 1, page 14). 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. (If using a number system for the sites, it helps to add a location, e.g. ‘Grand Bay #1, southern site’.) This reduces the possibility of error when the data are entered on computer.

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.

6. 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. Check the profile alignment and reposition the pole if necessary. Always ensure the pole is vertical.

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

8. To read the Abney level, refer to Figure B. As can be seen from Figure B a), 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 – Figure B 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 -5and -6 degrees, it is likely that the minutes reading is about 30 minutes. To check the minutes, use the vernier scale – see Figure B c). 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 B   Reading the Abney level.

9. 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).

10. 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.

11. 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 – remember to check for profile alignment – and repeats steps g) through j). This is continued until the endpoint of the profile, see step b).

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

Figure C   Completed data form.
 

13. 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.

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

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

16. 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.

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

  On return from the field

• Check each data sheet, make sure it is complete, and place in binder or folder. It is advisable to set up a binder/folder for each site. Keep the binders/folders safely.
• Wash sand out of the tape measure in fresh water, leave to dry and rewind.
• Check on the Abney level; if it has any sand on it, wipe it carefully with a soft cloth.
• Store equipment carefully for future use.

Data analysis
This methodology and computer program was prepared by Gillian Cambers and David F. Gray, with the support of the University of Puerto Rico Sea Grant College Program (MRPD-11-75-1-98), November 1999, and is available free on request to UNESCO-CSI (csi@unesco.org).

This section describes the main routines of the computer program, Beach Profile Analysis (Profile). It draws the beach profile to scale and then determines the cross-sectional area and beach width. The program can display and print graphs of the profiles and superimpose up to eight profiles on top of each other. Tables showing changes in beach size over time can also be prepared and graphs plotted showing the resulting trends.

The computer program has been written for the Windows operating system and works on Windows 95 and newer versions. It contains fully compiled ‘Help’ files. This manual refers to Version 3.2, January 2000, and outlines the main routines. (For more detailed information use the ‘Help’ file.)

Getting started

Each site has its own data file: Each beach site has its data entered in a separate file. So the site at Grand Bay North will have its own data file and the site at Grand Bay Central will have a separate data file.

Furthermore, if the reference point is lost at Grand Bay North (file name Grand Bay North 1), possibly as the result of a hurricane, and a new reference point is selected, then a new file will have to be established; this will then have the file name Grand Bay North 2.

The main parameters – profile area and profile width: First of all, a note about what the parameters really measure. The program draws the beach profile to scale and then determines the area under the profile mathematically in m2. The program also determines the profile width in metres (m).

Starting the program: Go to ‘My Computer’ and select the drive where the program (Profile) has been installed. Select Profile and you will see an opening screen and at the top left hand corner, a main menu with four selections as follows:

The sub-menu: As you work through the routines in the main menu, you will see a sub-menu appear about a third of the way down the screen on the left hand side. (To see this sub-menu, select ‘Site file’ from the main menu, select ‘New’, then select ‘Profile’ from the main menu, and select ‘New’.) This sub-menu has four options:

• Profile sub-menu: this is where the data is entered and quality control functions are performed.
• Profile graphs sub-menu: this is where the graphs for each profile are displayed and can be printed or transferred to other programs.
• Table sub-menu: this is where the values for profile area and profile width are listed in a table and annual mean values calculated.
• Table graphs sub-menu: this is where the values for profile area and width are shown graphically over time, either as actual values (in line graphs) or mean values (in bar graphs).

Profile
sub-menu
- entering data and quality control

Establishing a new site: At the opening screen, select ‘Site File’ from the main menu and then select ‘New’. In the box by ‘Description’, type the name of the beach site, e.g. Grand Bay South 1. Then select ‘Profile’ from the main menu, and select ‘New’. The screen will show a blank spreadsheet where the data for the first profile for a new site, e.g. Grand Bay South 1, can be entered.

Entering the data for the first profile: Start by entering the date when the first profile at the site was measured. The box by ‘Profile date’ shows today’s date. To enter the date the profile was measured, click on the figures in the box by ‘Profile date’ and enter the appropriate date (month/day/year). Alternatively, select the arrow by the side of the ‘Profile date’ box, a calendar will then be displayed. The month and year can be changed by selecting the arrows at the top left or right on the calendar; the day can be selected by just
clicking on the correct day.

Enter the distance down from the top of the reference point to the ground surface: Next, go the box below ‘Profile date’ labelled ‘Distance – reference point to surface.’ Enter the distance down from the top of the reference point to the surface that was recorded on the field sheet.

Enter the distance and slope measurements: Now, enter the profile data – the distance and slope measurements for each segment. To move around the spreadsheet use the arrow or Tab keys. For the first segment, a–b, enter the distance measurement in the column with the heading ‘Distance metres’, enter the degrees in the column with the heading ‘Angle degrees’ and enter the minutes in the column with the heading ‘Angle minutes.’ The program assumes the numbers are positive, so if a negative slope was recorded, e.g. -7° 30’, enter -7 in the ‘degrees’ column and 30 in the ‘minutes’ column. If the slope measurement is -0° 30’, mathematically minus zero does not exist, so enter 0 in the degrees column and -30 in the minutes column. Enter all the data for that profile.

Computation of the area and width values: As you enter the data, the program will calculate the cumulative horizontal and vertical values, so you will notice the figures in the columns labelled ‘Cumulative Horizontal’ and ‘Cumulative Drop’ change. You do not have to enter any values in these columns. The spreadsheet shows the profile area and profile width in two boxes at the bottom left of the screen labelled ‘Area’ and ‘Width.’

Fixing the standard total vertical drop: The ‘standard total vertical drop’ finalizes the end point of the profile. A particular profile always has the same starting point – the reference point or paint square. However, profiles end in the sea by the ‘offshore step’, this is a variable point which changes with the wave conditions. Reference to Figure D shows a hypothetical first profile measurement (green line) with a total vertical drop of 3.5 m. However, during the second measurement of the profile (red line) three months later, the offshore step had moved and the total vertical drop was 3.7 m. To compare the two profiles mathematically, the starting point and the end point of the profile have to be the same. In order to do this, the total vertical drop of the first profile at a site becomes the standard and the program will adjust all subsequent measurements at the site to the standard either by adding or deleting a section to the final slope segment.
 

The first profile (green line) had a total drop of 3.5 m. This value of 3.5 m becomes the standard total vertical drop for this site. The second profile at this site (red line) had a total drop of 3.7 m. So when ‘Fix Drop’ is selected, the program will cut off a small portion of the bottom of the second graph (red line), so that the total drop remains 3.5 m.

Setting the standard vertical drop: Once the data for the first profile at a site have been entered, it is necessary to set the standard total vertical drop. If the final segment of the first profile is f–g, move the cursor down to the next line, g–h, and note the value in the column with the heading ‘Cumulative Drop’. Enter this value in the box labelled ‘Standard total vertical drop’. (This box is located near the top of the screen below the box labelled ‘Description’).

Adjusting the drop for subsequent profile measurements: For subsequent profile measurements at this site, the program will standardize the total vertical drop (profile end point) when the ‘Fix Drop’ box is selected. For example, when entering the data for the second profile measurement at a site, after the data are all entered, click on the ‘Fix Drop’ box (located below the ‘Distance – reference point to surface’ box). The program will adjust the distance measurement of the final segment accordingly, and also make the necessary adjustments to the profile area and profile width values.

Saving the file for the first time: From the main menu, select ‘Site File’, select ‘Save As’. In the box by ‘File Name’, type the name of the file (e.g. Grand Bay South 1 in our example) and select ‘Save’. Before doing this, you may wish to set up a separate folder to store all your beach data files.

Closing the site file: From the main menu, select ‘Site File’, select ‘Close File’, the program returns to the opening screen. If you have not saved your data or changes, the program will ask you whether you want to save them, select ‘Yes’ or ‘No’ accordingly.

Exit the program: From the main menu, select ‘Site File’, select ‘Exit’. If you select ‘Exit’ without saving your changes, the program will ask you if you want to change your changes, select ‘Yes’ or ‘No’ accordingly.

Entering the data for the second profile: From the main menu ‘Site File’, select ‘Open’. Select the folder where the beach data is stored. The program will list the files; select the appropriate file and select ‘Open’. The screen will show the spreadsheet for the most recent measurement at this site. From the main menu, select ‘Profile’, and then select ‘New’. The screen will show a blank spreadsheet. Enter the data for the second profile as described earlier. Once all the data have been entered, select ‘Fix Drop’, this will standardize the
profile endpoint.

Select ‘Site File’ from the main menu and ‘Save’ to save the second set of measurements. However, if you try to close the file or exit the program without saving the data, a check box will automatically appear asking if you want to save the changes.

When you have finished entering the data for second profile measurements, a box may appear on screen telling you to check the data.

Displaying spreadsheet data for different dates: From the main menu ‘Site File’, select ‘Open’. Select the folder where the beach data is stored. The program will list the files; select the appropriate file and select ‘Open’. Go to the box at the top right-hand side of the screen showing the dates of the profile measurements. Click on the date you wish to display (use the up/down arrows to see further dates) and the screen will display the spreadsheet for that date.

Deleting a profile spreadsheet: To delete a profile spreadsheet, first of all display the spreadsheet you wish to delete on the screen. Once it is displayed on the screen, select ‘Profile’ from the main menu, then select ‘Delete’.

Printing the spreadsheet: To print a spreadsheet, select ‘Site File’ from the main menu, select ‘Print’. Click on the box by ‘Include profiles’ a tick mark will appear, then select ‘All’ (to print all the profile spreadsheets in the file), ‘Current’ (to print the profile spreadsheet displayed) or ‘Selected’ (to print the profile spreadsheets you have selected by ticking the boxes to the left of the dates – displayed at the top right of the screen), click on ‘OK’ and the spreadsheet(s) will be printed.

Data quality control: After the data for a new profile at a particular site have been entered, then as you select ‘Fix Drop’, a box may come on the screen warning you that the new data set is significantly different to the average for the previous twelve months. Select ‘OK’ and then check your data entries making sure the data are entered accurately, correct any mistakes. Especially check whether you have entered negative slopes correctly.

The quality control has been set at 20%, i.e. if the profile measurement varies by more than 20% from the average of the measurements for the previous twelve months, the quality control check box will appear. At most sites there are only small changes from profile to profile, so 20% is reasonable. However, at some high energy beaches, changes may be of considerable magnitude from one measurement date to the next, so it may be advisable to change the quality control percentage setting for the data files for these sites.

To change the quality control percentage setting, select ‘Site File’ from the main menu, select ‘Options’ and change the percentage value accordingly in the box by ‘Check percent for area and width’.

Establishing an actual datum height for the reference point: If an absolute height is established for the reference point (using surveying techniques to tie in the reference point to a known datum), this can be displayed on the profile graph. Select ‘Site File’, ‘Options’, ‘Have datum height for reference point’, ‘OK’. A box will appear under ‘Standard total vertical drop’ named ‘Datum height for reference point’. Enter the actual height in this box. The spreadsheet will then show another column under ‘Cumulative’ named ‘Height’. When the ‘Profile Graphs’ sub-menu is selected, the profile will be displayed with the absolute height of the reference point.
 

Profile graphs
sub-menu –
display and print
the graphs

‘Max. horizontal for the graph’: This box is located in the top mid-section of the screen below and to the right of the box for ‘Standard total vertical drop’. This sets the maximum distance for the ‘X’ axis on the graph. To change the setting, delete the figures displayed in the box and substitute a new value.

‘Current’: This is the box at the bottom left of the screen and allows you to display the graph for the current spreadsheet.

‘Selected’: This box is to the right of ‘Current’ and allows you to select up to a maximum of eight profiles to show on one graph. To select the profiles you want, go to the box at the top right-hand corner of the screen where the dates of the profile measurements are listed. Check the profile dates you wish to display on the screen by clicking on the box next to the desired date; a tick mark will appear in the box. (To uncheck a date, click on the tick mark. To uncheck all the profiles, select ‘Profile’ from the main menu and select ‘Uncheck all
profiles’.)

‘Top’: This box is to the right of ‘Selected’ and next to it is a box with a number and an up/down arrow. This allows you to select the top (up to a maximum of eight) profiles to show on the graph. By changing the number in the box you can select the top 2, 3, 4, etc. profiles to display on the graph.

‘Print’: The program will print the graph displayed on the screen.

‘Copy’: This copies the displayed graph to the clipboard; you can then paste it into a word processing program such as Microsoft Word.

‘Save’: This saves the graph as a BITMAP (BMP) file. A box appears on the screen asking you to confirm the file name. This file can then be inserted as a picture in a word processing program, e.g. Microsoft Word.

‘Markers’: This box to the right of ‘Save’ inserts markers onto the displayed profiles.

‘B & W’: This box, below ‘Markers’ allows you to display the graph in colour or in black and white.

‘Adjust scale’: This box to the right of ‘B & W’ has two boxes to the right, ‘Vert’ and ‘Hor’. These allow you to adjust the vertical exaggeration of the graph and the size of the graph.
 

Table
sub-menu
– list values and
annual means
for profile area
and width

To print the table, select ‘Site File’ from the main menu, select ‘Print’. Click on the box by ‘Include table’, a tick mark will appear, then click on ‘OK’ and the table will be printed. (Make sure to uncheck the ‘Include profiles’ box.)


 

Table graphs
sub-menu –
graphs showing
changes over
time

‘Profiles’: This shows a line graph of the values for profile area and/or width over time. To select profile area only, put a tick in the ‘Areas’ box, to select profile width only, take out the tick marks in the ‘Areas’ box and tick the ‘Widths’ box. To display both profile area and profile width values on the same graph, place a tick in the ‘Areas’ box and in the ‘Widths’ box.

‘Means’: This shows a bar graph of the mean annual values for profile area and/or profile width over time. To display profile area or profile width mean values separately, tick the ‘Areas’ or ‘Widths’ box accordingly.

‘Show only selected years’: This allows you to show a line graph or a bar graph for selected years only. Go to ‘Selection’ on the main menu, select ‘By year’, enter the first and last years of your selection in the boxes by ‘Show’, click on ‘Select profiles’ and ‘OK’, then click on the box below the graph by ‘Show only selected years’. The graph will then display the values for the time period you have selected.

‘Print’: The program will print the graph displayed on the screen.

‘Copy’: This copies the displayed graph to the clipboard, you can then paste it into a word processing program.

‘Save’: This saves the graph as a BITMAP (BMP) file. A box appears on the screen asking you to confirm the file name. This file can then be inserted as a picture in a word processing program, e.g. Microsoft Word.

‘Markers’: This box to the right of ‘Save’ inserts markers onto the displayed profiles.

‘B & W’: This box, below ‘Markers’, allows you to display the graph in colour or in black and white.

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