Chapter 17 Flashcards
What factors control the size of waves?
The size of waves are determined by the wind velocity, the length of time the wind blows in the approximately the same direction, and the area of water over which it blows.
If the average wavelength of a series of waves is 100 m, at what depth of water will the waves start to feel the bottom, and how will that change their behaviour?
Waves will start to feel” the bottom at around 50% of the wavelength, so at a 50 metre depth in this case. This will slow the waves down and also cause their amplitude to increase.
What is the difference between a longshore current and longshore drift?
A longshore current is the movement of water parallel to the shore in the surface zone caused by waves approaching at an angle. Longshore drift is the movement of sediment parallel to the shoreline, caused partly by the longshore current and also by swash and backwash on the beach.
On Figure A the waves (dashed blue lines) are approaching an irregular coast. The red arrows represent the energy of those waves, and one has been extended to show where that energy would hit the shore. Extend the other “energy lines” in a similar way, and comment on how this relates to erosion of this coastline.
Wave energy is focused on the headland, with more wave energy vectors per length of coast than in the bays, and thus the headland is eroding faster than the bays on either side, leading to coastal straightening.
Explain the origins of a wave-cut platform.
Rocky coasts are eroded by waves and that erosion is greatest within the surface zone. As stacks and arches are eventually eroded away, a wave-cut platform is left.
How do we define the limits of the beach face, and what are some other terms used to describe this zone?
The beach face is the relatively steep area of the beach between the low and high tide levels. This is also known as the foreshore or swash zone.
A spit is really just a beach that is only attached to the shore at one end. What conditions are necessary for the formation of a spit?
A spit can form where there is longshore drift and the geometry of the shoreline is such that a sand bar extends away from the shore.
Barrier islands are common along the Atlantic coast of the U.S. as far north as Massachusetts. Why are there almost none in the northeastern U.S. or along the coasts of New Brunswick, Nova Scotia, and Newfoundland?
The area of the Atlantic coast north of Massachusetts (including New Hampshire, Maine, New Brunswick, Nova Scotia, and Newfoundland plus all of the area inland) was glaciated during the Pleistocene and has since rebounded isostatically. This is all now relatively young rocky coast that is being actively eroded.
If a dam were to be built on the Fraser River near Hope, what would be the long-term implications for beaches in the Vancouver area? Explain why.
Sediments would be trapped in the reservoir behind such a dam, and the water flowing through the dam would be sediment-free. Although there would be erosion of new sediments downstream from the dam, the water reaching the ocean at Richmond would have less sediment than it does now. This is likely to result in the beaches around Vancouver being starved of sediment, and they would gradually get smaller.
