Elicitation Questions for Waves and Energy Transfer
1. Sketch the shape of an ocean wave if viewed from a helicopter hovering close to the water surface.
2. Can you name the parts of the wave?
3. What happens to the path of waves as they approach the shoreline at an angle?
4. What effect do waves have on the motion of a piece of wood floating out in the ocean?
The Contextual Problem
The pressures of the modern workplace encourage an increasing number of people to spend some of their vacation time away from the city, perhaps in the countryside and often close to water. Because our province boasts numerous seaside destinations, coastal tourism represents a large fraction of the dollars spent by visitors. But, as the density of tourists in any area rises, previously unrecognized factors become important, e.g., landform stability.
The Situation: You are one member of a team hired by developers who wish to turn a section of coastline into a small tourist village especially for seniors. Your particular task is to determine if their plans are putting clients at risk from natural forces, e.g., wave action. This unit on waves and energy transfer will give you the background to help you with your response. Realize that you must be familiar with many aspects of waves. Be prepared to answer the knowledgeable developers who may question both your own theoretical understanding and your suggestions. They might favor this area of coast and be reluctant to attempt a development project elsewhere. Only a through grasp of wave behaviors will give you the credibility needed to convince the developers.
The Proposed Location: A point of land juts SE into the ocean. It is 4 m high. The land is weak sandstone full of loose cobble stones. A cavern starting on the W side of the neck extends halfway through it. Waves normally approach the point of land from the SW; the outer lengths of the wave crests travel past the end of the point. Ocean records show that waves normally seen in this area travel in three distinct height categories - 1 m, 1.5 m and 2 m tall waves. The average wavelength is 0.8.m and the average wave travels 2 m in 3 s.
The Analysis: You must use certain criteria to decide if the proposed location is safe or not. To help the developers understand your reasoning, you show them your answers to the following questions you think a person interested in questions of the long term safety of this exposed area should be asking. Note: each question has additional information to generate ideas to carry into the Conclusion.
1. What is the largest wave that could hit the shore?
Create a wave sum graph showing the result of constructive interference if all three wave groups arrived together. This could indicate the wave height in a Hundred Year storm.
2. Find the speed, frequency and period of the waves.
The speed indicates the preparation time based on the location of a storm. The frequency indicates how often waves impact the shore. The period tells one for how long a single wave grinds against the
shoreline.
3. a) Generally speaking, how much energy must the shore absorb in the run of a day?
Find the average wave height of the three wave groups. Lets say that each 0.5 units of wave height equals 70 units of wave energy. How much energy is in a wave of average height? From the frequency, how often does a wave hit the shore? How many waves will hit therefore hit the shore in 24 hrs? What is the total energy of the waves hitting the shore during a day?
b) How will the cavern affect the stability of the location?
Would the cavern lengthen or widen due to wave action? If it does, will the land above it be stable?
What effect will that have on safety?
4. a) Where would you place breakwaters?
What is their purpose?
b) Why?
How will they achieve their goal in their proposed location?
c) How will the point of land affect its own future?
Due to the overall shape of the point of land, a large natural breakwater, what will happen to the
water depth on the E side of the point of land? Why?
Conclusion: Based on your answers to the criteria above, what do you decide about the safety of this site? The developers will want to see an explanatory statement showing how you integrated your Analysis answers to arrive at your conclusion.