SO422 Nearshore Oceanography
Spring 2009
Duck Lab
Once
you start on this exercise and during the writeup of the exercise, you may consult and work only
with other midshipmen assigned to the same group.
You will turn in one assignment for the entire group.
You may not consult other
midshipmen.
The program (located in c:\guthprog\duck.exe, or downloadable here) we will use this week has an extensive help file, with a detailed discussion of the theory behind wave breaking and bar development. While it will help a great deal, the discussion there was written with the intention of forcing you to think about the answers to the questions below. Before starting, look up the following topics in the program’s help file: CRAB, and multiple bars. You could also visit the Duck web site.
In addition to the program help file, these directions will help you get started.
· Wave climate is the statistical variation of waves over time in terms of period, height, and angle of attack.
· A Rayleigh distribution, applicable to waves approaching a shoreline, is a skewed distribution with the mean greater than the mode.
For your assigned profile line, with the wave and tide data and the surveyed profiles available, prepare a 2-3 page typed (double spaced, maximum length, exclusive of graphics) discussion of the annual pattern of waves and beach profiles at Duck. You can include figures if you label them and clearly refer to them in your text; the instructor will not try to figure out unlabeled figures not mentioned in the text. For full credit you must write a coherent discussion that addresses these questions, and not a repetition of the question followed by the answer. This is a writing requirement.
When do the most storms hit the
How does the wave climate vary through the year? When are the highest average waves and longest periods found? The smallest? How great is the annual variation? Which variable shows the pattern better, wave height or period?
How does the position of the shoreline (horizontal position of mean sea level) vary with the seasons? How great is this seasonal movement? Has the shoreline position changed during the 10 year period for which you have survey data, and if so, is erosion or deposition occurring?
As a generalization, when are the offshore bar(s) best and most poorly developed? Why? The answer to this question may be more complex than a simple, single response.
You have the storm surge for one year’s (1989) data. How large is storm surge compared to the waves, and when do the largest values occur?
Duck, NC experienced a major storm on Christmas Eve, 1989. You should be able to get profiles surveyed on 21 and 28 December, before and after the storm. The storm waves had T=12.5 sec and H18=4.5 m. You may assume that a=0. You may not assume that H18= Ho. Calculate where this wave should have broken, and how that depth corresponds to the profiles surveyed by the CRAB.