SO422 Assateague Field Trip
Requirements for Each Group
Directions to Assateague Island National Seashore:
Cross the Bay Bridge.
Take US 50 south, thru Cambridge and Salisbury.
Before arriving at Ocean City, follow signs south for the Seashore. This involves routes 113 and 376 from Berlin, or route 611.
Before crossing the small bridge across the lagoon onto the barrier island, there is a visitor's center on the right (last chance for running water).
Once on the barrier island, go right past the state park.
Just inside the Seashore entrance (guard shack and $ collected) there is a large parking lot on the left where we will meet.
Total distance is 126 miles; it takes about 2.5 hours driving the speed limit; lots of state police.
There is normally a fee of ($1 per person) to get into the Seashore, but we have a fee waiver when we go as a group.
Meet at 0630 in the Mid Store Parking Lot for inspection. We will be back by 1800 and you are expected to make evening formation.
Come prepared for: sun, wind, cold, wet, and heat. I repeat: have ready sun screen and lots of warm clothes. If you have a wet suit, you can bring it; some people may get wet.
We will have one box lunch per person. You can bring your own coolers, and may want to bring hot drinks. We cannot stop at a fast food restaurant on the way back unless you are in a reputable uniform (i.e. SDBs).
We will be model citizens on the beach, and obey all Park Service regulations. In particular you will not collect or measure anything behind the fences on the dunes.
Sequence of events:
Measure waves and longshore current
Measure first assigned profile
Measure waves and longshore current
Dig holes and collect sediment
Measure second assigned profile
Measure waves and longshore current
You will safeguard all government equipment and not leave it unsupervised on the beach. The surveying equipment is worth about $750 per set.
Measure as soon as we arrive, between your two profiles, and after the second profile
Longshore current—time to travel 30, 60, and 90 m
Height of every wave in 5 minute period (surf beat; this is about 50 waves) From this you can get average height and period. You will record your estimate of every wave’s height.
Angle of attack of waves
Calculate at home
Longshore current velocity as measured
Longshore Drift by Longuet-Higgins Equation
Wave distribution by time: height and period
Bar graph showing surf beat
|Graph showing surf beat|
Four samples of sand (locations below). You need about 500 g for each sample (a pound).
Four trenches one meter deep with description of the sand layering
Sample of the densest (blackest) sand and the largest sand available from your trenches. You need about 500 g for each sample (a pound).
Measure at home
Size distribution all collected samples (mean, std dev, and skewness)
Discussion of the size and sorting patterns visible on the beach among your samples.
Density of a normal sand, and the blackest sand found
Description and correlation of the four trenches, with graphical depiction of sand, and how the layering varies on the beach.
Measure two profiles, from behind dune into the water.
Calculate at home:
Plot profile with spreadsheet; turn in plot and table with the data, and clearly locate your profile location; compare your profile with others provided by instructor at same location
Data emailed to instructor: a file with distance and elevation for both profiles. This can be Quattro Pro You will have the distance starting from zero in the parking lot in the left column, and the elevation from the assumed 3 m point in the right column.
Compare your two profiles, and your data with previous results.
Compare your profiles with the LIDAR data
Two Person Groups
Groups with two persons will do the following requirements:
Take wave measurements upon arrival and before departure.
Dig two beach trenches.
Measure one profile, the “C” profile at the south end of the parking lot.
WAVE Height & period
Estimate the height of the breakers as best you can. Use the inner line of breakers, recognizing that there might be another line farther offshore that will be very difficult to estimate. It the weather is warm, you can have a member of your group in the water to provide a scale. Get the period by recording the height of every wave is a 5 minute time interval, and then dividing the time by the number of waves.
The purpose of the experiment is to measure the longshore current. The best way to do this is through the use of a neutrally buoyant piece of driftwood, styrofoam, tennis ball, etc. Place two rows of five stakes each 30 m apart along a line parallel to the shoreline. By sighting over the two stakes, the shore party can determine when the object has reached the appropriate point on the shore. A volunteer tosses the neutrally buoyant object into the surf zone. The time it takes for the object to travel each 100' interval is obtained and recorded. In this manner, an average time can be obtained. Variable wave action will cause differences in interval times. An alternative method uses dye, but getting the dye out into the current presents a major problem. Keeping dye off mids is a related problem.
Depending on the tide stage, either start at the parking lot or the water line. For designated Bench Mark, see instructor for corner of parking lot. Insure that you record the orientation of the profile, and describe where it is with relation to landmarks. You will measure elevations every 5 meters from the parking lot to the base of the dune, and then every 1 m to the water line. Insure that your profile proceeds in a straight line perpendicular to the shore along the boardwalk. Set the Philadelphia rod on the sand adjacent to the boardwalk. While this is not perfect, you will have no problems once you cross the dune and the boardwalk ends; that is the most important part of the profile. You will not estimate horizontal distances, but measure them with the tape. You will be assigned two specific locations, with assumed elevations, from:
A (N end parking lot; assume 3 m for corner of curb)
B (middle parking lot by bath house; assume 3 m at corner of bath house)
C (S end parking lot by ranger station; assume 3 m at brass pin in corner of curb)
D (N end of group camping area; assume 3 m at edge of parking lot)
E (S end of group camping area; assume 3 m at edge of parking lot)
F (N end of main camping area; assume 3 m at edge of parking lot)
Select representative sites along one of your profiles. The specific sites are: (1) beach face where the waves are breaking; (2) top of the beach face; (3) middle of the berm, and (4) the base of the dune
Scrape off top 1" of sand in a one foot by one foot area.
Obtain a 500g sample (= 1 pound) from the one square foot area.
Place the sand in a sample bag and clearly label the bag. Be sure that labels are secure so that they are not lost in transportation back to the lab. Also insure that damp sand will not destroy the labels.
On return to the Academy, we will wash the sand to remove vegetation debris and salt, and leave it to dry so we can sieve it later.
You will dig 4 trenches 1 meter deep to describe, and try to correlate the layering. Digging a 1 m hole takes about 5 minutes, and is not an onerous requirement. When describing the layers, look for thickness (measure with a meter stick), sand size, color, and nature of the layering. Dig the holes in moist sand away from the water line so they will not fill with water, about 3 m apart normal to the water line and with the second pair about 10 m away parallel to the water line. Insure every member of your group sees all 4 holes, and that the instructor checks you off before you fill the holes back in. You will be graded on the quality of you logs.
While your holes are open, insure that all members of the group see them, and that you collect a sand sample of the largest and the blackest sand.