SO422 Nearshore Oceanography

Fall 2009 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     60  ________

 

TOTAL                          110  ________

 

 

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.

 

All work on this exam is individual.  You may not any materials (books, notes, computers), and you may not use IM, texting, talking, or any other means to communicate with other individuals.

 

Red comments are key points, not complete answers.

 

 

 

(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:

 

·        Dissipative beach profile:

·        Heavy mineral: ρ> 3.0 gm/cm³

·        Plunging breakers:

·        Tombolo: refraction

·        Active continental margin:

·        Sediment sorting: size segregation

·        Phi scale:

(30) A wave has a period T=8 sec, and passes a wave gauge in water d=75 m deep. At the gauge H75=4.0 m, and the angle of attack a75=28°.   All calculations on this page use this depth of a depth of 10 m, and 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.

 

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

 

(5) What will be the wavelength of the wave at this depth (the wave gauge)?

 

(2) What will be the speed of the wave at this depth (the wave gauge)?

 

(5) What will be the orientation a0 of the wave in 10 m of water.

 

(6) What will be the height H0 of the wave in 10 m of  water?

 

(3) Will the wave break before or after reaching 10 m depth?

 

(5) Answer one of the following questions, for which you may neglect refraction:

·        At what depth would this wave have a speed of 5 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?

 

 

 

Lo "1.56*T*T   99.84 m    
C0 1.56*T or Lo/T   12.48 m/sec    
           
Deep when D/Lo > 0.4981 D= 49.7303   So 75 m is deep
Shallow when D/Lo < 0.0152 D= 1.517568      
           
At D= 10          
d/Lo     0.10016      
           
Table            
d/L     0.145      
tanh     0.722      
Ks=H/Ho     0.929      
           
L Lo * tanh   72.1      
L d/ (d/L)   69.0      
c L/T   7.2 6.9    
           
sin(alpha10) C10/C0 * sin(alpha0)        
sin(alpha0)*tanh          
sin(28)*tanh   0.338958 0.324292    
alpha0     19.81343 18.92271    
           
KR     0.968765 0.966122    
           
H10=KR * KS * H75   3.60 3.59    
           
           
5m/s 5/Co   0.400641 "=tanh"    
Table, d/Lo 0.027        
d=0.035*Lo 2.69568        
           
Min Height Ks = 0.913          
D/Lo= 0.161        
D=  16.07        
           

 

 

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

 

Answer the question on this page. It is worth 10 points.

 

1.  Which of these graphs could you use to discuss the changes that take place in the wave for which you did computations on the last page?  Which wave parameters follow this pattern of change as the wave comes ashore?

 

 


 

Answer the question on this page. It is worth 10 points.

 

2.  This graph shows a size distribution analysis for three sand samples.  Describe what each axis represents, and  discuss three parameters that we use to quantify the relationships shown in the graph.  Use two samples to show how each of the three parameters varies and what that means for the sand sample.

 


 

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.

 

Local abundance, chemical stability, and physical durability.  Have to mention quartz (SiO2)

 

 4.  What kinds of features might you expect to find on beach in the Aleutian islands, in the vicinity of the 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 (fig 2-24 of Komar) above to show how a barrier island responds to changes in sea level and hurricanes. 

 

Transgression/regression, and shift of environments (sediment size)