Presentation on theme: "1 The Grain Drain Boston New York Washington, DC Miami Dune areas on the continental shelf caused by breaking waves are called sand bars. Waves pile up."— Presentation transcript:
1 The Grain Drain Boston New York Washington, DC Miami Dune areas on the continental shelf caused by breaking waves are called sand bars. Waves pile up large deposits of ocean sand and sediment from rivers on to these sand bars until they become barrier islands like those present off shore from Maine to Florida. ME FL Barrier islands typically have low elevation with grasses and scrub vegetation. Maritime forest with pine and oak trees may occur in sheltered areas on larger islands.
2 Storms washing over barrier islands, carry sand to the landward side of the island. As sand is moved, the island moves closer to the land. East Coast - Currents erode the south end of barrier islands and deposit the sand at the north end, so the islands move in the same direction as the currents. (West Coast is opposite)
3 The Indians, who lived all over Florida, never built any permanent structures or mounds on barrier islands. Perhaps, they understood the temporary nature of shifting sand much better than the developers and real estate buyers of today. EPA
4 Coastlines are eroded by two types of currents: NOAA 2. Long shore currents develop when waves hit the beach at angles other than 90 degrees. The currents carry sand along the shore and deposit it in slow moving areas.
5 Jetties are armored structures that extends out into the water intended to protect a navigation channels or marinas.
6 NOAA On the East coast, sand builds up on the south side of the jetty but is removed from the north side.
7 GROIN – perpendicular to shore to prevent movement of sand
8 Fences constructed perpendicular to the shoreline help prevent beach erosion. But measures to increase the sand on one beach or to divert sand from shipping lanes, robs another beach down the coast of the supply of sand it needs.
9 Seawalls and bulkheads are common structures used to armor much of the developed shoreline. While they do deflect the wave energy that destroys buildings and real estate, they are only temporary measures. They also prevent the natural flow of sand. Without the beach, a cliff develops and eventually the ocean tears out the wall.