Worked answers to the wave problems appear at the end of this file.


SO422 Nearshore Oceanography

Spring 2001 Exam 1a

 

Attachment:   Wave equations table

 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 and 10    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.

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

·        Bruun rule:

·        Heavy mineral:

·        Sink:

·        Eustatic sea level rise:

·        Sorting:

·        SPM:


(30) A wave has a period T=12.5 sec, a height H18=4.5 m, and an angle of attack a18=28°.   The wave moves into water that is d=18 m deep.  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.

(3) For this wave, how deep does the water have to be for it to be considered deep and the wave a deep water wave?

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

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

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

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

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

(2) Is the wave deep, shallow, or intermediate at this depth?

(5) At what depth would this wave a height of 6 m?  You may neglect refraction for this answer.

 

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.  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.

 


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

 2.  These diagrams show wave and beach profiles measured at Duck, NC, in Dec 1989.  Discuss what each diagram shows, and why each is important.  What happened during this time?

Fig. 1.  Surveyed profiles lines.  Thick line surveyed 12/21/89, and thin line 12/28/89.

 

Fig. 2. Wave periods at Duck, December 1989.  

Fig. 3. Wave height, measured in 18 m of water,  at Duck, December 1989.

 

Fig. 4. Storm surge (difference between measured and predicted tide levels) at Duck, December 1989.



Answer both questions on this page.  Each is worth 5 points.

 3.  What has been the effect of the jetties at Ocean City on the sediment budget there? 

 4.  Discuss two differences between Airy and Stokes wave theories, and how they apply to the nearshore.

 


Answer one question on this page.  It is worth 5 points.

 5a.  What conditions today lead to sea level dropping, and where is this happening?

 5b.  This is a tide gauge record from a station in Ecuador.  Does it show sea level rise or drop?  Is this record easy or hard to interpret, and what does this say about discovering the global rate of sea level change?

 

 



Answer three of the next five questions.  Each is worth 5 points.

 6a.  Fig. 2-5A.  This diagram below shows a portion of the coastline of England.  Discuss what factor or factors control the creation of the Stair Hole, Lulworth Cove, and Mupe-Warbarrow Bay.

 6b.  Fig. 2-13.  What is the feature seen below, on what kind of coast is it most likely to develop, and what did this feature do in the century depicted by the diagram?

6c.  Fig. 2-24.  This diagram shows a region on the coast of Mexico.  What feature does it represent, and it responding to a transgression or regression?  Defend your answer.

6d.  (Figure 4-29)  This graph shows the change in elevation (“sea level”) north along the Hudson River in New York.  This region was affected by the Pleistocene continental glaciation.  Explain how parts of New York State can be subsiding while other parts are being uplifted.

6e. (Fig.2-16)  What is the feature depicted by  this diagram, and how does it form.


 SO422 Nearshore Oceanography

Spring 2001 Exam 1b

Exam 1b differed from 1a as follows:

(30) A wave has a period T=12.5 sec, a height H18=4.5 m, and an angle of attack a18=18°.   The wave moves into water that is d=18 m deep.  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.

(3) For this wave, how deep does the water have to be for it to be considered deep and the wave a deep water wave?

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

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

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

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

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

(2) Is the wave deep, shallow, or intermediate at this depth?

(5) At what depth would this wave a height of 6 m?  You may neglect refraction for this answer.

 

 

 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.

 


SO422 Nearshore Oceanography

Spring 2001 Exam 1c

Attachment:

Wave equations table

 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 and 10    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.

(20) Definitions.  Briefly define 5 of the following terms as they relate to the nearshore with no more than a single sentence.  If you use a mathematical relationship, also explain its importance or significance:

  • Bruun rule:  

  • Heavy mineral:

  •   Source:

  • Isostatic sea level rise:

  • Sorting:

  • Corps of Engineers:

 

(30) A wave has a period T=12.5 sec, a height H18=4.5 m, and an angle of attack a18=23°.   The wave moves into water that is d=18 m deep.  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.

(3) For this wave, how deep does the water have to be for it to be considered deep and the wave a deep water wave?

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

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

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

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

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

(2) Is the wave deep, shallow, or intermediate at this depth?

(5) At what depth would this wave a wavelength of 56 m?  You may neglect refraction for this answer.

 


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.  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.

 


 

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

 2.  These diagrams show wave and beach profiles measured at Duck, NC, in Dec 1989.  Discuss what each diagram shows, and why each is important.  What happened during this time?

Fig. 1.  Surveyed profiles lines.  Thick line surveyed 12/21/89, and thin line 12/28/89.

 

Fig. 2. Wave periods at Duck, December 1989.  

Fig. 3. Wave height, measured in 18 m of water,  at Duck, December 1989.

 

Fig. 4. Storm surge (difference between measured and  predicted tide levels) at Duck, December 1989.



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

   

3.  Discuss three differences between Airy and Stokes wave theories, and how they apply to the nearshore.

 


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

 

4. These two graphs show the tidal gauge records from two stations.   What do they show, and how might the two stations differ?

 

 


 

Answer two of the next three questions.  Each is worth 5 points.

5a.  (Fig. 4-41).  What model does this diagram illustrate, and what process does it describe?

 5b.  (Fig. 3-13).  What does this diagram depict, and what is the difference between the white and the black arrows?

6e. (Fig.2-16)  What is the feature depicted by  this diagram, and how does it form.



Answers to the wave problem:


A version B version C version units
T 12.5 12.5 12.5 sec
H18 4.5 4.5 4.5 m
alpha-18 28 18 23 deg
Lo=1.56T*T 243.75 243.75 243.75 m
Deep if D > 0.5Lo 121.9 121.9 121.9 m
D/Lo=18/Lo 0.0738 0.0738 0.0738  
D/L  (intermediate if between 0.05 to 0.5) 0.1150 0.1150 0.1150  
tanh(2PiD/L) 0.618 0.618 0.618  
Ks18 0.969 0.969 0.969  
L at 18=tanh*Lo 150.6 150.6 150.6 m
C at 18=L/T 12.1 12.1 12.1 m/sec
alpha-0=asin(sin(alpha-18)/tanh)) 49.4 30.0 39.2 deg
Kr=sqrt(cos(alpha-0)/cos(alpha-18)) 0.858 0.954 0.917  
Ho = H18/Kr/Ks 5.41 4.87 5.06 m
H/D (broken if > 0.78) 0.25 0.25 0.25  
       
For H=6 m, Ks must be 6/Ho 1.1088 1.2329    
That Ks is at D/Lo 0.0329 0.0199    
Then D = D/Lo * Lo 8.02 4.85   m
       
For L=56, then tanh = 56/Lo     0.229744  
That tanh is at D/Lo     0.0087  
Then D = D/Lo * Lo     2.120625 m