SO422 Nearshore Oceanography

Fall 2001 Exam 2

 

 

Read all questions carefully.  The definitions should be a complete sentence that fully explains the term.   For the short answer questions insure that your answer is complete and concise, uses appropriate terminology, shows that you understand any terms used, and covers the key points.  The quality of your answer is critical, and not just a general understanding of concepts.

 

Problems                    30  ________

 

6 definitions @5            30  ________

 

4 short answers @10         40  ________

 

 

TOTAL                      100  ________

 

Note that you must answer 5 of the definitions and 5 of the short answer questions.  Insure that you do not waste time answering more than the required number in each section.

 

 

1. Problems:

 

The following sand (sample 6217301, p.B91) was collected at Duck, North Carolina:

Phi Size

Weight Percent

 

 

-2

0.000

 

 

-1

0.000

 

 

0

3.819

 

 

1

30.273

 

 

2

52.857

 

 

3

12.921

 

 

4

0.130

 

 

Pan

0.000

 

 

 

(2) What parameters define the best fitting log-normal distribution for this sand.

 

(2) Calculate the parameters that define the best fitting log-normal distribution for this sand.

 

(4) How would changing each of these parameters affect your graph on the next page?

 

(4) Calculate the parameter that determines how well this sand fits the log-normal distribution, and compare that result with a graphical measure.

 

(4) What is the size in mm of the median sand size?

 

(4) The sand we will use in the wave tank today has a median size of 0.32 mm.  What is this size in phi units, and what percentage of the sand from Duck is larger than this size?

 

Phi    Weight  % Retained  Cum % Retained  

-2.00    0.00        0.00      0.00        

-1.00    0.00        0.00      0.00       

 0.00    3.82        3.82      3.82       

 1.00   30.27       30.27     34.09       

 2.00   52.86       52.86     86.95       

 3.00   12.92       12.92     99.87       

 4.00    0.13        0.13    100.00       

 5.00    0.00        0.00    100.00       

 

Total weight      100.00

 

 

Phi16= 0.57   Phi50= 1.27   Phi84= 1.92

Mean= 1.25    Sigma (Std dev)= 0.67    Alpha (skewness)=-0.02

  

 

 

Median is Phi50 = 1.27

 

Phi50 = -log(2) dia mm

-Phi50 = log(2) dia mm

2^(-Phi50) = 2^( log(2) dia mm)

2^(-1.27) = dia mm

0.41 mm = diameter

 

 

0.32 mm is 1.64 Phi (-log10(0.32)/log10(2)), which is Phi71, making 71% of the sand larger than this.

 

 

(10). Complete the survey notes for a group at Assateague

 

The survey team starts with the rod at BM02 in the parking lot (elev 3.00) and the level halfway to the dune; the reading on the rod 1.63. They then take 3 readings at stations 5 m (reading 2.14), 10 m (reading 2.37), and 15 m (reading 2.98) away from the BM. They then move the level to the top of the dune and take a reading (0.87) with the rod still on the 15 m station.

 

Station

B.S.

H.I.

F.S.

Elev

Dist

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Station

BS

HI

FS

Elev

Dist

BM

1.63

4.63

 

3

0

 

 

 

2.14

2.49

5

 

 

 

2.37

2.26

10

 

0.87

2.52

2.98

1.65

15

 

 

2.  Definitions: with a single complete sentence, define 6 of the following terms.  Show that you clearly understand the concept involved.

 

·        Longuet-Higgins equation:

·        Bruun rule:

·        Rip current:

·        Cusp:

·        Closure depth:

·        Critical basal shear stress:

·        Regression:

·        Sink:


There are 6 short answer questions in part 3.  You must answer 4 of them.  Each is worth 10 points.  For full credit you must cover the important topics and use the correct terminology.

 

 

 

3a. This image is part of the "Duck Movie" we saw in lab.

·        Why do scientists take two different types of images for these movies?

·        What interesting feature is shown in this image?

 

3b.  What is the difference between the black minerals in the beach at Assateague and those of a black sand beach in Hawaii, and why are the black minerals important?

 

3c.  How does sediment movement vary in the marsh and under waves on the front side of a barrier island?  Why does this happened and why is it important?

 

3d.  How will a barrier island respond to sea level rise, and what will be the vertical pattern of sedimentary facies that you would see as a result?

 

3e.  How would you go about creating a budget for a typical coastal cell, and what would you expect to be the major contributors in the main categories?

 

3f.  Describe the process depicted in this diagram.