SO422

Nearshore Oceanography

Spring 2000 Exam 1

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.  Your essay should be a logical and coherent discussion.

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:

·        Shoaling:

·        Undertow:

·        Refraction:

·        Source:

·        Eustatic sea level rise:

·        SPM:

(30) A wave has a period T=8.3 sec, a height H0=1.7 m, and an angle of attack a0=28°.   The wave moves into water that is d=2.9 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 a of the wave at this depth (not in deep water).

(5) What will be the height of the wave at this depth (not 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 have its minimum height?  You may neglect refraction for this answer.

Given:  T=  8.30 sec        Ho=  1.70 m    &   Alpha-o=  28.0

then at  d=  2.90 m

Lo= 1.56 * T^2=  107.47 m        Co= Lo/T = 1.56 * T =   12.95 m/sec

d / Lo =   0.0270

d/L       d/Lo      tanh    H/Ho(Ks)

Table values:  0.0675    0.0270    0.4000    1.1500

L=   42.96 m   &  C=    5.18 m/sec using L= d / (d/L) & C = L/T

L=   42.99 m   &  C=    5.18 m/sec using L = Lo * tanh & C=L/T

H= Ks * Ho =  1.95 m   (if no refraction)

alpha1=   10.82  using alpha = arcsin( C / Co * sin(alphao))

alpha1=   10.82  using alpha = arcsin(tanh * sin(alphao))

Kr=    0.95 using Kr=sqrt(cos(alphao)/cos(alpha))

H =    1.85 m    using Ho*Kr*Ks

H/d=    0.64

Breaks:  FALSE   (if H/D > 0.78)

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

1.  These two graphs show the variation in parameters as a wave comes ashore.  Suggest what parameter each graph could depict, what variable(s) in the wave climate affect the shape of the graph, and why each has the shape it does.

2a.  Discuss how building the jetties at Ocean City changed the local sediment budget.

2b.  Discuss what happens at a tidal pass, and what will determine its stability.

3.  What is the common characteristic of calcite beaches and black volcanic sand beaches?

4.  What is sediment sorting and why does it occur?

5a.  Discuss the effect of the different slopes seen on the East Coast, West Coast, and Guam, and how these affect waves coming ashore.

5b..  Why is it so hard to predict where a wave will break?

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. 2-11.  This diagram below shows a coastline.  This type of coast is classified as a ________________. Correctly place 4 of the following features on the diagram:

·        Arch

·        Barrier island

·        Bay

·        Cuspate foreland

·        Pass

·        Sea stack

·        Spit

·        Tombolo

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. 4-40)  Explain the importance of the model represented by  this diagram.