The storm generating the waves is far offshore.Water in the wave does not move forward with the wave; it moves in a circular motion.Longshore drift. Waves push sand up the beach at an angle. The water, with the sand, drains straight back down slope towards the water’s edge.The uprush (swash) and backwash of water from each breaking wave moves the sediment in a zigzag pattern along the beach. This movement can transport sand hundreds or even thousands of meters each day.With sea level rise, the beach and barrier island must maintain its water depth and slope of the bottom to stay in equilibrium with wave height.Evidence that a barrier island has migrated landward with time include:A lighthouse that was built on shore is now well offshore (island moved)oyster shells and tidal flat mud from the bay side of the barrier island are now found on the front beachstumps of trees that grew along the lagoon are now found on the front beach.Riprap boulders or a seawall reflect the waves back, causing more-rapiderosion of the sand and deeper water in front of the structure. Eventually the boulders or seawall topples into the deeper water in front of the structure. That deeper water permits still more-rapid erosion.Some solutions include:Learn to live with actively evolving beaches. Move buildings and roads back from the beach after storms.Remove old dams and prevent mining of sand from streams.It is finer-grained than beach sand and washed away more easily.U.S. Congress/the general public/national taxpayersName: _______________________Learning Unit 8: Coast Review QuestionsThis assignment is designed to assess your understanding of Unit 4 and includes some of the Questions forReview at the end of Chapters 3 and 4 from your text plus a few additional questions. Each question can be answered in one to two sentences. Please limit yourself to a maximum of three sentences. Access the assignment, complete it with ANSWERS IN A DIFFERENT COLOR FONT as a separate file, and send it back for evaluation and grading through the assignment tab by or before the due date. 1. How can there often be big waves at the coast when there is little or no wind?The storm generating the waves is far offshore.2. What force creates most waves? What factors influence the size of most waves?Waves are a result of wind energy transferred to water. Winds blowing across the sea push the water surface into waves because of friction between the air and the water. The three factors that influence the height, wavelength, and period of a wave are wind speed, length of time the wind has blown, and fetch (the distance the wind has traveled across the open ocean).3. Why do waves not break in the open ocean?Water in the wave does not move forward with the wave; it moves in a circular motion.4. Describe what happens to waves as they enter shallow water.When waves enter shallow water the orbits become elliptical and the particle paths atdepth are slowed down by friction from the sea bottom, while the particles near the sea surface retain their original velocity. Thus, the wave becomes oversteepened andeventually breaks.5. Where does beach sand originate?Streams and rivers, erosion of sea cliffs, ± longshore drift6. Why does sand gradually migrate along the beach? Briefly explain.Longshore drift. Waves push sand up the beach at an angle. The water, with the sand,drains straight back down slope towards the water’s edge.The uprush (swash) and backwash of water from each breaking wave moves the sediment in a zigzag pattern along the beach. This movement can transport sand hundreds or even thousands of meters each day. 7. Why do barrier islands gradually migrate landward with time? What evidence is there that a barrier island has migrated landward with time?With sea level rise, the beach and barrier island must maintain its water depth and slope of the bottom to stay in equilibrium with wave height. Evidence that a barrier island has migrated landward with time include:- A lighthouse that was built on shore is now well offshore (island moved)- oyster shells and tidal flat mud from the bay side of the barrier island are now found on the front beach- stumps of trees that grew along the lagoon are now found on the front beach.8. Which side of a beach groin collects sand?The upcurrent side (the direction from which the water is coming).9. List the purpose and effects of seawalls, groins, breakwaters and artificial reefs, an jetties?- Seawalls are structures built on land parallel to the coastline to protect building from damage and hold the shoreline in place.- Grains are linear structures placed perpendicular to the shore usually in groups (groin field). Each groin is designed to trap a portion of the sand from the longshoure drift.- Breakwaters are linear structures built parallel to the shoreline that protect limited stretches of shoreline from the force of large breaking waves. - Jetties are built in pairs perpendicular to the shore at the mouth of a river to or inlet to prevent it from being blocked or moved by sediment transport vial longshore drift..10. Why is piling riprap boulders or building a seawall to protect a sea cliff or beach houses not a good solution to erosion? Explain what happens.Riprap boulders or a seawall reflect the waves back, causing more-rapid erosion of the sand and deeper water in front of the structure. Eventually the bouldersor seawall topples into the deeper water in front of the structure. That deeper water permits still more-rapid erosion.11. Where does the sand go that is eroded from a beach during a storm?The sand eroded from a beach during a storm is stored offshore as linear strips of sediment that parallel the beach called longshore (or offshore) bars.12. Where would a sand spit form on a barrier bar island relative to the direction of longshore drift?At the down-drift end of the barrier island.13. What is a better solution than the variety of erosion-prevention efforts used on most coasts?Some solutions include:- Learn to live with actively evolving beaches. Move buildings and roads back from the beach after storms.- Remove old dams and prevent mining of sand from streams.14. Why is sand from dunes or lagoons not very good to replenish beaches?It is finer-grained than beach sand and washed away more easily.15. With large-scale replenishment of sand on beaches by the Corps of Engineers, who generally pays most of the tens of millions of dollars it costs? U.S. Congress/the
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