OCEANOGRAPHY Beach Lab Part I

Transcription

1 OCEANOGRAPHY Beach Lab Part I Name Equipment # Description 6 compass (4) 12 two-m meter sticks 6 8-m plastic tubing filled with colored liquid (or string with levels) (4) 6 10m tape measure (or marked line) 6 stopwatches 1. Location 2. Direction waves are coming from 3. Direction wind is coming from 4. Determine the wave period. Measure the time between 10 consecutive wave crests, and calculate the wave period (T). Would you divide by 9 or 10? Why? Period (T) = sec 5. Calculate the speed (Celerity) of the waves. Celerity of deep water waves is C=L/T. However, we are in shallow water, and we also don t know the wavelength (L). One piece of information that helps is that the period (T) of a wave never changes once it is formed, but wavelength (L) and speed (C) do. In shallow water, C is determined by water depth (D), and can be expressed as C = (gd). Remember that g = 9.8 m/s 2. Assume that the water depth is 1.5 m for now. cm/s 6. The relationship between wind speed and waves is Average period (in sec.) = x wind speed (in knots) What would the generating wind speed have been? 7. Make notes about the beach shape. (flat, arc-shaped, headlands, rocks, etc., also how steep it is, are there berms, etc.)

2 8. Comment on and any natural features and hardscape structures on the beach. (dunes, riprap, walls, etc.) 9. Break into groups of 3 or 4. Measure the slope of the beach from the dunes to the water. Place the 2-meter sticks five meters apart. Then use the level to determine the difference between the up-beach one and the down-beach one. Do this twice, once in an area of dunes and once where there are houses. Location Location Beach type (Natural/Built) Beach type (Natural/Built) No. Upper Lower Difference 1 No. Upper Lower Difference Share your data with the rest of the class. ( the data to me tonight)

3 9. Draw the beach profiles at each of the locations done by the class. Use Excel to do this, or an ENTIRE piece of graph paper to do this. 10. Are there any differences in the slopes? Why? 11. Go to the site listed below and get the information for roughly the same time we collected data at the beach (this has to be done asap, within 24 hours!) Compare your data with the buoy data. Portland buoy Look at the Detailed Wave Summary, and click on it to see what it means a) Compare the average wave period to what you found. Then look at the Plot of wave energy versus frequency (and period) b) The plot shows which wave periods have the most energy. What is the period of peak energy? c) Does this peak match your measured period? d) Which is closer the average period in the table or the spectral peak? How do the measured waves at buoy differ from what you measured on the beach? Height Period If there are differences, how may they be explained? World buoy map use this to find the Portland buoy (44007) mentioned above

4 CALCULATING THE SPEED OF THE LONGSHORE OR LITTORAL CURRENT You can determine the speed of the longshore current by conducting the following simple group experiment. You will need a tape measure (or other measuring device) an orange or two, a watch with a second hand and a group of students. Use the other side of this worksheet to enter and calculate your data. Break into groups of 3 or 4. Procedure: 1. Measure off and draw a ten-meter line in the sand parallel to the ocean. 2. Position one student at each end of the line you have drawn. Position everyone else along the line. One student should assume the role of timekeeper and have a watch with a second hand. 3. Throw an orange into the water, just behind the line of breakers, approximately 2 meters. Note the trajectory. Note: The longshore current is closer to the shore than you might expect! 4. When the orange passes the beginning of the line the timekeeper should start timing. 5. When the orange passes the person stationed at the end of the line, he or she should tell the timekeeper to stop timing. Record the time on worksheet below. Repeat this process again so you can calculate the average of the 2-3 trials. Calculate the speed of the longshore current for each trial, and then calculate the average. 6. This procedure is NOT foolproof. If your orange does not move north after a few minutes, try again. Shorten the length of drift if it is real slow. If you cannot get this to work at all, it may be due to weather conditions or tidal stage. Make observations of the factors that might cause this experiment to not work and record them on the bottom of this worksheet. 7. Repeat but throw orange in front of breakers, again taking note of the trajectory. TODAY'S DATE: / / TIME OF DAY: WEATHER CONDITIONS: TIDAL STAGE: WIND DIRECTION: Behind Breakers Trial 1 Trial 2 Trial 3 Average Distance 10 Meters 10 Meters 10 Meters (Length of Transect Line) Time (in Seconds) Speed of Current Circle (m/s or cm/s) In Front of Breakers Trial 1 Trial 2 Trial 3 Average Distance 10 Meters 10 Meters 10 Meters (Length of Transect Line) Time (in Seconds) Speed of Current Circle (m/s or cm/s) Direction of Current: NOTES: For your report write a few of sentences about the. Was it consistent? Did behind or in front of the surf make a difference? Was it related to the waves at all? etc.

5 BEACH LAB - Part II Read through the following sites on beaches in Maine. STATE OF MAINE BEACH PROFILING PROJECT Laudholm and Drakes Island Beaches - Before and After Beach Nourishment Variety of Maine's Changing Shoreline an example of how beach profiling is done. shows some data from NJ 1) write a page or so about The importance of beach studies 2) go to a. examine the list of morphologic codes and keep it handy as you plot the data b. at the bottom of the page click on the MAUI INDEX c. examine the map find where VSPR Sprecklesville is, then go to the table and got to the VSPR data d. examine the site map to see where the data were taken e. then go to Data, retrieve the VSPR xls file, open it in Excel f. make a graph of each of the sets of X (on the X axis) vs Z (on the Y axis) g. Write an analysis of the data comparing i. What happens from winter to summer ii. What happens from year to year