SO422

Nearshore Oceanography

Fall 2005 Exam 1

 

 

 

Attachment:

Wave equations table

 

This is an open book exam.  You may use your text book and any notes you have permanently written in it.  You may not attach any papers to the book, but you can tab the book.

 

You will be issued a calculator for the exam, and cannot use your programmable calculator.

 

Read all questions carefully.  Full credit on the problems require that your method be clearly identifiable.  For the short answer questions insure that your answer is complete and concise, and covers the key points.  You will be graded by how well you show an understanding of the key concepts of the course.

 

5 definitions @4               20  ________

 

Problem                        30  ________

 

short answers @5, 10 and 20     50  ________

 

TOTAL                          100  ________

 

 

Budget your time.  This exam can be done if you know what you are doing, but do not waste time on a question you do not understand.  On the short answers note that you have some choices on which questions to answer.  Note also that the last short answer is worth 20 points, so you take more care in that answer.


 

(20) Definitions.  Briefly define 5 of the following terms with no more than a single sentence showing that you clearly understand its importance.  If you use a mathematical relationship, also explain its importance or significance:

 

·        Reflective profile:

·        Heavy mineral:

·        Orthogonals:

·        Snell’s Law:

·        Shoaling:

·        Sorting:

·        SPM or CEM:



(30) A wave has a period T=10 sec, and passes a wave gauge in water d=15 m deep. At the gauge H15=4.0 m, and the angle of attack a15=28°.   All calculations on this page use these values, and unless specifically stated you are not to provide answers for deep water.  The bottom slopes uniformly and smoothly offshore. For full credit you must show your method on all questions.  If you cannot solve for something you need, assume a reasonable value and proceed.

 

(5) What will be the wavelength of the wave at this depth (the wave gauge, not in deep water)?

 

(2) What will be the speed of the wave at this depth (the wave gauge, not in deep water)?

 

(5) What will be the orientation a0 of the wave in deep water.

 

(6) What will be the height H0 of the wave in deep water?

 

(3) Will the wave break before or after reaching this depth (the wave gauge)?

 

(4) At what depths will this wave transition from deep to intermediate depth, and from intermediate to shallow?

 

(5) Answer one of the following questions, for which you can neglect refraction.

·        At what depth would this wave have a speed of 7 m/sec?

·        At what depth will this wave have its minimum height?

·        Is there any way the wave could have the same height at two different depths?  You must defend your answer.

 

Lo 1.56*T*T 156
d/Lo 15/156 0.096154
Table
d/L 0.14
tanh 0.706
Ks=H/Ho 0.934
L Lo * tanh 110.1
L d/ (d/L) 107.1
c L/T 11.0 10.7
sin(alpha0) Co/C15 * sin(alpha15)
sin(alpha15)/tanh
sin(28)/tanh 0.664974 0.683551
alpha0 41.68032 43.12173
KR 0.919717 0.909212
Ho = H15/Kr/Ks 4.66 4.71

 

 

 



Short Answer.  Answer the following questions as directed with concise, complete answers.  You should use appropriate terminology and concepts.

 

Answer either the question on this page or the one on the next page. It is worth 10 points.

 

1.  These two graphs show the variation in a single parameter as two waves come ashore.  Suggest what parameter is depicted, what variable(s) in the wave climate is (are) different for the two waves, and why each graph has the shape it does.

 

 

2.  These diagrams show beach profiles measured at Duck, NC, Jan and Aug 1984.  Identify which profile is which, how you could tell, and what causes the difference between the two profiles.

 

 



Answer two of the next three questions.  Each is worth 10 points.

 

3.  What determines the mineral composition of the sand on a beach?  Discuss the general factors, and then list three minerals commonly found on beaches and the specific conditions that favor each.

 

 

4.  What kinds of features might you expect to find on the Peruvian coast of South America, in the vicinity of the Peru trench?  Why would you make these predictions?

 

5.  How does wave shape change as the wave approaches the shoreline, and how does this affect sediment motion and sorting?



6.  Answer this question, which is worth 20 points.  Insure that you provide a thoughtful answer that summarizes what we have learned in the first five weeks of the course.

 

 

Use the diagram above to show how a barrier island responds to changes in sea level and hurricanes.  Concentrate on the general case, and then briefly indicate any special conditions affecting what Hurricanes Katrina and Rita have done to the barrier islands on the Louisiana coastline.