Beach Profiling, Observing and Documenting a Changing Environment, Point Lookout, NY
Beach profiling and sediment analysis is a method used in sedimentology and coastal geomorphology to study dynamic beach processes and the effect of wave, current and anthropogenic structures on a beach. Sediment analysis for mean grain size, shape, sorting and skewness provide information on provenance and textural maturity. By combining these two methods students can put together a snapshot of the beach at the time of study. By comparing data taken over several seasons students can see a total picture of beach dynamics over time.
Context for Use
The lecture hours are part of the course content and would have been presented anyway. Visual analysis, although interesting for the student, is not a necessary part of the project and there have been some terms where we weren't able to do this. Team meetings can be done outside of the classroom.
Description and Teaching Materials
- In the field: 2-2m meter sticks, string and a bubble level for the profiling; handheld GPS units to mark locations of transects; 2- 1m meter sticks as markers on each end of the transect (dune and shore) to insure a straight line; geologic picks for hammering the meter sticks (and so we don't lose any meter sticks in the surf); 1-100 m measuring tape to mark off distances between transects; data sheets for recording of profile data and other field notes; plastic 50ml beakers for collecting sediment; labeled zip lock bags (the number of bags depends on the number of samples you collect); 1 sharpie per team.
- In the lab: RoTap machines with the following sieves: #10, 18, 35, 60, 120, 230 and pan; one medium plastic "boat" per team for weighing the total sample; 7 small plastic "boat" per team for weighing each fraction; manila folders for emptying the sediments from the sieves and pouring into the individual boats; a paint brush to insure all sediments go into the boats.
- Computer work: a specialized computer program for statistical analysis (this is not necessary because the students can calculate the statistics by hand); Microsoft Excel or any other spreadsheet program.
Beach Profile Data Sheet (Microsoft Word 33kB Jun19 10)
Teaching Notes and Tips
- While working in the field it's important that students set up properly and follow the transect line. Groups have a tendency to not follow the line from the landward marker stick to the seaward marker stick which will give inaccurate readings of beach length.
- Be sure they get accurate GPS coordinates of both ends of the transects
- If they are collecting one sample, have them measure the mid-point of the berm from their profile (distance) data and take the sample there.
- If they are collecting multiple samples have them take them from mid-berm as well as both landward and seaward ends of their transects.
- Be sure the sediments are dry before mechanically processing
- Stress the importance of neatness in doing the mechanical processing. Students think "it's just sand" or "a few grains of sand don't weigh very much so what difference does it make?" Show them that, in fact, the loss of a few grains of sand from each fraction (sieve) actually has a large affect on the total weight of the final sample. Show them what a gram of sand looks like.
- In the lab students don't always empty the sieves properly before putting their sediment sample in. They must also be very neat when emptying the sieves to insure they don't lose any sediment. Another place where students have difficulty is in tallying the total fraction weights within less than 0.5 grams of the original total weight. Sometimes this is simply a mathematical error in adding, sometimes it's because they lost sediment when emptying the sieves.
- The #10 sieve is the gravel portion and, depending on your beach, can contain pebbles, pieces of wood, seaweed or shells (whole or broken). Have the students take measurements and descriptions of the contents and note if the shells are whole or broken.
- Field work and laboratory work are done in teams of 3-4 students but students are graded based on their individual work and on how well they worked as members of the team; they are given individual grades for their computer work and final report. The final written report and presentation points count towards their lecture grade.
- Exam: students are given fraction weight data collected by students in previous years and are required to calculate weight percent and cumulative weight percent; they are then required to graph cumulative weight percent against phi sizes; from this graph they must determine the mean size, median size and approximate sorting values. This grade is part of their final lab exam.