Specific assessments for Module 7:

Formative assessments

Part 1

Longshore Transport at Ocean City Inlet, MD. Look at the aerial photo of the inlet and read the short article at the following link:

Questions:

Based on what you know about longshore sediment transport, what do you think is the most frequently occurring wave direction approaching the inlet?Why is the north end of Assateague Island (south of Ocean City Inlet) eroding?

Rubrics:

Points / Dominant Wave Direction (azimuth in degrees) / Cause for erosion of north end of Assateague Island (south of Ocean City Inlet)
4 / 0 – 90 / Due to insufficient sediment supply from the updrift side of the inlet
3 / 80 – 170 / Due to insufficient sediment supply
2 / 170 – 270 / Due to more frequent storms
1 / 270 – 360 / Due to the rising sea levels
0 / No answer: / No answer:

Part 2.

Using the provided Excel spreadsheet (groin_updrift_model.xlsx), compare the performance of a 50-m breakwater and a 15-m breakwater.

1)Approximately how long does it take from the shoreline directly updrift of the groin to accrete at least 10 m seaward? Evaluate two groin lengths (15 m and 50 m).Using the corresponding time from the previous questions, report the shoreline accretion at a location that is 500 m updrift of the groin for each groin length (select your time from the available solutions in the spreadsheet, corresponding to 5,10,25,100 and 365 days).

2)What has a greater effect on the shoreline and produces more accretion, a doubling of the incident wave angle or a doubling of the wave height? Evaluate this using a groin that is 50 m long.

3)With Hb of 1 m, αb of 10°, and groin length of 15 m, how does reducing the beach grain size by 0.05 mm affect the shoreline evolution? Does it erode or accrete? (Note: it may help if you focus at one location updrift of the groin to evaluate this)

Rubrics for

Module7
Assessment 2
q1 / groin length - 15 m (10 m accretion) / groin length - 50 m (10 m accretion) / accretion at 500 m updrift position (15 m groin length) / accretion at 500 m updrift position (50 m groin length)
points / Time to accrete / Time to accrete / Distance (m) / Distance (m)
4 / 365 / 100 / 0.43 / 0.001068
3 / 100 / 25 / 0 / 0
2 / 25 / 365 / 0 / 0
1 / 10 / 10 / 0 / 0
0 / 5 or no answer / 5 or no answer / no answer / no answer
q2 / no partial credit
points
4 / doubling of the wave height / correct answer
0 / doubling of the incident angle / incorrect answer
q3 / no partial credit
points
4 / the shoreline accretes / correct answer
0 / the shoreline erodes / incorrect answer

Part 3.

For this exercise you will calculate the erosion rate along the beach by Bay Champagne. The image dates you will use are provided below. Use the GPS pin location to find where each measurement will begin. Do this in Google Earth. Kmz file is provided with the three sites.

Dates: use the following image dates for your calculation. November 1989, October 2007, January 2004, and November 2012

Pin Locations: Start in 1989

  1. 29°6’52.6N , 90°9’58.52W
  2. 29°7’48.30N , 90°8’26.88W
  3. 29°8’35.06N , 90°7’11.16W

Questions:

  1. What is the average erosion at each site?
  2. Which period has the highest erosion for each site?
  3. Which site has the highest average erosion?
  4. Using the average erosion rate for site 2, how many years would it take to erode the headland by 1 kilometer?

Rubrics

Module 7
Assessment 3
q1 / negative implies erosion, positive implies accretion
points / site 1 - m/year / site 2 - m/year / site 3 - m/year
4 / -4.5 / -10.7 / -6.2
2 / -2 / -5 / -3
1 / 2–100 / 2–100 / 2–100
0 / no answer / no answer / no answer
q2
points / site 1 / site 2 / site 3
4 / Oct 2007–Nov 2012 / Oct 2007–Nov 2012 / Oct 2007–Nov 2012
2 / any other period selected / any other period selected / any other period selected
0 / no answer / no answer / no answer
q3
points
4 / site 2
3 / site 3
2 / site 1
0 / no answer
q4
points / 1 kilometer erosion using the average rate for site 2
4 / 90 – 100 years
3 / 100 – 500 years
2 / 10 – 50 years
1 / 1 year
0 / no answer

Summative Assessment:

We are revisiting the Ocean Beach article and erosion study. In your opinion:

  1. What is an alternative erosion mitigation method that could be used for this section of Ocean Beach instead of “hard” structures?

Points / Answer
4 / Beach nourishment, Dune restoration
2 / Geotubes, Geosynthetics
0 / No answer, seawall, rock revetment
  1. What could the city have done to reduce coastal vulnerability so that the risk from coastal erosion would not require “hard” coastal protection?

Points / Answer
4 / Locate Great Highway and Sewage Treatment Infrastructure away from the coastal zone
2 / Mentions locating Great Highway or Sewage Treatment Infrastructure away from the coastal zone, but not both.
0 / No answer