Name_________________________________
Oceanography—Mr. Nelson
Analysis and Conclusions Questions
1. Based on your models, describe how the rate at which waves strike a shoreline affects the
erosion of a gradually sloping model beach.
2. How does the initial slope of the beach affect erosion?
3. Describe the distribution of the sand versus the distribution of the gravel in each of your
four trials. Why is there a difference?
4. Explain how the composition of a beach affects beach erosion. Give evidence for your
answer.
5. Describe any depositional features formed as a result of wave action on your model
beaches. In which trial was deposited material most noticeable?
6. Describe how a large storm could significantly change the features of Duxbury Beach.
7. Beach erosion is a significant problem for many seaside communities like Duxbury.
Suggest ways to stabilize shorelines in order to prevent erosion
Vanishing Beaches:
Homes built close to the ocean are in danger of being washed away. For example,
Summer cottages in Chatham have fallen into the water or have been demolished prior to.
Some places along the south shore of Long Island are being washed away at a rate of 2 meters a
year. Most of the North Carolina and Texas shorelines are disappearing even faster. Some
people suggest that over 80% of the beaches in the United States are being reclaimed by the
ocean.
One cause is that houses and other structures have been built on beaches. This has
disturbed than natural state of balance. The balance is between the processes that remove sand
from the beach and those that add to it. Sand can be removed from beaches by large waves. At
the same time, sand is also being added to beaches. Most of this sand comes from rivers. The
sand is carried to the sea where it can be deposited as deltas. In many locations, however, the
sand is carried along the shore by longshore currents and deposited on the beaches. Thus, over
a long period of time, the removal and addition of sand to a natural beach are nearly equal.
As the population of the U.S, has increased, more and more housed have been built on
beaches. At the same time, the sea level has been rising, due to the melting of part of the
icecaps. To protect houses from the rising sea level, seawalls have been built. See the figures
below.
1. What is the drawback of not building a sea wall to protect houses on the beach?
2. What is the drawback of building a sea wall?
3. A jetty is often built to cut down on beach erosion. Figure A below, shows a longshore
current along a beach. Using arrows in Figure B, show what effect a jetty would have on the
longshore current.
4. As we saw with turbidity in the Bluefish River, moving water can carry materials. The faster
the water is moving, the heavier the materials it can carry. When fast moving water slows
down, it deposits the materials. What effect would the jetty have on the sand carried by the
longshore current?
5. How does the presence of a jetty affect a beach? Include the effect on waves, currents, and
erosion in your answer