Managing Coastal Erosion (1990) / Chapter Skim
Currently Skimming:
2. Coastal Erosion: Its Causes, Effects, and Distribution
2. Coastal Erosion: Its Causes, Effects, and Distribution
Pages 20-43
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 20... ...
coastline characteristics, which serves to emphasize the diversity of shore types that must be considered in erosion management policies. Historical shoreline changes along the coasts of the United States range from highly erosional to accretional.
|
From page 21... ...
Beaches are composed of loose sediment particles, ranging in grain size from fine sand to large cow blest Pocket beaches form between erosion-resistant headlands and are usually quite small. Pocket beaches are common along the rocky coast of New England and the cliffed coasts of California and Oregon.
|
From page 23... ...
inlets. Physically separated barrier islands often are linked by the longshore sediment transport system, so that an engineering action taken in any one beach area can have major impacts on adjacent downdrift beaches.
|
From page 24... ...
Pacific coast were major contributors of sand, but dam bui23ing has greatly reduced the sediment that reaches the beaches. In contrast, most rivers along the Atlantic and Gulf coastal plains have Tow gradients and limited capacities to transport coarse sediment.
|
From page 25... ...
In contrast to sediment sources, littoral sinks function to reduce the volume of sand along the coast. The most common sinks to beaches are landward transport of sand through tidal inlets to form flood-tide shoals, storm-generated overwash deposits, landwardmigrating sand dunes, losses down submarine canyons that extend close to shore (Pacific coast only)
|
From page 26... ...
In some areas submerged sand on the inner shelf still is being transported shoreward and thus contributes to overall shoreline stability or accretion (Williams and Meisburger, 1987~. In other areas there are no offshore sources of sand, and the slowly rising sea level induces beach erosion.
|
From page 27... ...
Subsidence usually results in a similar impact on the shore: beach erosion. When nearshore elevations drop, it is equivalent to a sea level rise of the same magnitude; the beach profile is thrown out of equilibrium by the creation of a sand sink offshore, and this induces offshore sediment transport and shore recession.
|
From page 28... ...
28 MANAGING COASTAL EROSION FIGURE 2-1 Several homes in jeopardy and vertical scarp, western end of Seadrift, Stinson Beach, California, January 27, 1983. SOURCE: Photo provided by Robert E
|
From page 29... ...
The following three examples illustrate how human-induced changes affect beaches. O C EAN C ITY INLET, MARYLAND The barrier island breach that later became Ocean City Inlet was caused by a major hurricane in September 1933.
|
From page 30... ...
P ORT CANAVERAL, F LORIDA This inlet was cut in 1951, the jetties were constructed in 1953 and 1954, and a beach nourishment project was carried out in 1974. The net longshore sediment transport has been estimated by the U.S.
|
From page 31... ...
1 N:.. A,: Upward Growth of Assateague Island due to Sea Level Rise over a Distance of 10,000 m ( + 0.6 x 1 06m3)
|
From page 32... ...
40 Sebastian Inlet Entrance ~ I ~ -1 0 i~ 1955-1974 (Postentrance, Prenourishment) -15 ~ l / o 10 20 30 DISTANCE SOUTH FROM PORT CANAVERAL ENTRANCE (miles)
|
From page 33... ...
This 56 million cubic yards would be sufficient to advance the sandy beach about 25 feet seaward along the entire 375-m~le east coast of Florida. Sand Mining The loss of sand from beaches because of mining for construction and other purposes can be considerable.
|
From page 34... ...
Quantities in Millions of Cubic Yards (2) Total in Excess of 56 Million Cubic Yards FIGURE 2-5 Estimated quantities of maintenance dredging disposed of in the deep water off the east coast of Florida.
|
From page 35... ...
Thus, water resource planners and national decision makers should consider carefully the effects of dams on the supply of sand to beaches. Increased research and development of economical means to transport sand to beaches and alternative operations of dams would provide the information needed to make future decisions wisely.
|
From page 36... ...
Scattered small pocket beaches can be found at shoreline reentrants along the erosion-resistant crystalline rock of northern New England. In contrast, the cliffs along southern New England and New York are erodible glacial deposits, with some notable exceptions such as the rocky headlands at Point Judith, Rhode Island, and Cape Anne, Massachusetts.
|
From page 37... ...
Recreational beaches are a major source of revenue for Florida, and state officials are considering spending tens of millions of dollars each year for beach nourishment. The Miami Beach project, completed in 1980 at a cost of $65 million for 10 miles of beach, represents the scale and magnitude of potential future projects along this rapidly urbanizing coast, which is becoming dominated by highdensity, high-rise-type developments.
|
From page 38... ...
Because of extensive and widespread nourishment projects, many beaches reportedly are wider today than they were a century ago. The long-term trend of shore recession has been reversed successfully through coastal engineering projects (largely beach nourishment)
|
From page 39... ...
The fault continues northwest, forms Tomales Bay, and then moves out to sea and back across land, forrn~ng Bodega Bay. The region is tectonically active, which affects the relative change in mean sea level.
|
From page 40... ...
Natural events sometimes occur that have a major anp act on the sources of sand in a littoral cell; for example, the Los Angeles River flowed through Ballona Gap until 1825, when it was diverted to the south during a severe flood, joining the San Gabriel River discharging into San Pedro Bay. During severe floods in 1862 and 1884, some of the Los Angeles River waters again flowed to the sea via Ballona Creek, but since then it has discharged only into San Pedro Bay (Kenyon, 1951~.
|
From page 41... ...
Lake Michigan's 1,362 miles of shorelands has every shore type characteristic of the Great Lakes. Most impressive is the expanse of sand dunes that extend almost continuously from the Indiana Dunes National Lakeshore on southern Lake Michigan northward along Michigan's western shore to the Leelanau Peninsula.
|
From page 42... ...
Pp. 520-542 in Proceedings of ASCE Specialty Conference on Coastal Sediments '77.
|
From page 43... ...
Proceedings, ASCE Specialty Conference on Coastal Sediments '87, New Orleans, Louisiana.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.