Coast and Beach

Observing erosion and deposition

Emergent coasts

Submergent coasts

The sand budget

Barrier islands

Society and the beach environment

Resources

The coast and beach, where the continents meet the sea, are dynamic environments where agents of erosion vie with processes of deposition to produce a set of features reflecting their complex interplay and the influences of changes in sea level, climate and sediment supply. “Coast” usually refers to the entire region of a continent or island that is significantly

affected by its proximity to the sea, whereas “beach” refers to a much smaller region, usually just the areas directly affected by wave action.

Observing erosion and deposition

Earth is constantly changing. Mountains are built up by tectonic forces, weathered, and eroded away. The erosional debris is deposited in the sea. In most places these changes occur so slowly they are barely noticeable, but at the beach, they are often observable.

Most features of the beach environment are temporary, steady-state features. This means that although features on beaches may appear to be permanent structures, they are constantly in a state of flux. For example, the size and shape of a spit, which is a body of sand stretching out from a point perpendicular to the shore, is similar to the level of the water in this example. To stay the same size, the rate at which sand is being added to the spit must be exactly balanced by the rate at which it is being removed. Failure to recognize this has often led to serious degradation of the coastal environment.

Sea level is the point from which elevation is measured. A minor change in elevation high on a mountain is undetectable without sophisticated surveying equipment. The environment at 4, 320 ft (1, 316.7 m) above sea level is not much different from that at 4, 310 ft (1, 313.6 m). The same 10-ft (3-m) change in the elevation of a beach would expose formerly submerged land, or inundate formerly exposed land, making it easy to notice. Not only is the environment different, but also the dominant geologic processes are different. Erosion occurs above sea level, deposition occurs below sea level. As a result, coasts where the land is rising relative to sea level (emergent

coasts) are usually very different from those where the land is sinking relative to sea level (submergent coasts).

Emergent coasts

If the coast rises, or sea level goes down, areas that were once covered by the sea will emerge and form part of the landscape. The erosive action of the waves will attack surfaces that previously lay safely below them. This wave attack occurs at sea level, but its effects extend beyond sea level. Waves may undercut a cliff, and eventually the cliff will fail and fall into the sea, removing material from higher elevations. In this manner, the cliff retreats, while the beach profile is extended at its base. The rate at which this process continues depends on the material of the cliff and the profile of the beach. As the process continues, the gradual slope of the bottom extends farther and farther until most waves break far from shore and the rate of cliff retreat slows, resulting in a stable profile that may persist for long periods of time. Eventually another episode of uplift is likely to occur, and the process repeats.

Emergent coasts, such as the coast along much of California, often exhibit a series of terraces, each consisting of a former beach and wave cut cliff. This provides evidence of both the total uplift of the coast, and its incremental nature.

Softer rocks erode more easily, leaving resistant rock that forms points of land called headlands jutting out into the sea. Subsurface depth contours mimic that of the shoreline, resulting in wave refraction when the change in depth causes the waves to change the direction of their approach. This refraction concentrates wave energy on the headlands, and spreads it out across the areas in between. The “pocket beaches” separated by jagged headlands, which characterize much of the scenic coastline of Oregon and northern California were formed in this way. Wave refraction explains the fact that waves on both sides of a headland may approach it from nearly opposite directions, producing some spectacular displays when they break.

Submergent coasts

If sea level rises, or the elevation of the coast falls, formerly exposed topography will be inundated. Valleys carved out by rivers will become estuaries like Chesapeake Bay. Hilly terrains will become collections of islands, such as those off the coast of Maine.

The ability of rivers to transport sediment depends on their velocities. When rivers flow into a deep body of water, they slow down and deposit their sediment in what will eventually become a delta. Thus, the flooding of estuaries causes deposition further inland. As the estuary fills in with sediment, the depth of the water will decrease, and the velocity of the water flowing across the top of the delta will increase. This permits further sediment transport. The delta builds out toward, and eventually into, the sea. The additional load of all the sediment may cause the crust of Earth to deform, submerging the coast further.

The sand budget

Wave action moves incredible amounts of sand. As waves approach shallow water, they slow down because of friction with the bottom, then get steeper, and finally break. It is during this slowing and breaking that sand is transported.

When a breaking wave washes up onto the beach at a slight angle it moves sand on the beach with it. This movement is mostly towards shore, but also slightly down the beach. When the water sloshes back, it goes directly down the slope, without any oblique component. As a result, sand moves in a zigzag path with a net motion parallel to the beach. This is called “longshore drift.” Although most easily observed and understood in the swash zone, the area of the beach that gets alternately wet and dry with each passing wave, longshore drift is active in any water shallow enough to slow waves down.

Many features of sandy coasts are the result of longshore drift. Spits build out from projecting land-masses, sometimes becoming hooked at their end, as sand moves parallel to the shore. At Cape Cod, Massachusetts, glacial debris deposited thousands of years ago is still being eroded and redistributed by wave action.

An artificial jetty or “groin” can trap sand on one side of it, broadening the beach there. On the other side, however, wave action will transport sand away. Because of the jetty it will not be replenished, and erosion of the beach will result.

The magnitude and direction of transport of long-shore drift depends on the strength and direction of approach of waves, and these may vary with the season. A beach with a very gentle slope, covered with fine sand every July may be a steep pebble beach in February.

Barrier islands

Long, linear islands parallel to the shore are common along the Atlantic coast. Attractive sites for resorts and real estate developments, these barrier islands are in constant flux. A hurricane can drive storm waves over low spots, cutting islands in two. Conversely, migration of sand can extend a spit across the channel between two islands, merging them into one.

Interruptions in sand supply can result in erosion. This has happened off the coast of Maryland, where Assateague Island has become thinner and moved shoreward since jetties were installed at Ocean City, just to the north.

Society and the beach environment

Coastal areas of the continental United States comprise only 17% of the land area of the country, but house over one-half of the population. In 2003, the population of this zone was 153 million, an increase of 33 million since 1980. The coast is attractive for a wide variety of reasons, and economic growth of the zone typically follows the growth of the population. The impacts on the coastal environment can result in environmental degradation, particularly within environmentally sensitive areas.

Often, the dynamic nature of the beach environment is not properly assessed when beach areas are developed. In places away from the coasts, where rates of erosion and deposition are much slower, development projects can change the topology of the land and the results will persist for centuries. In a beach environment, however, modifications are ephemeral. Maintaining a parking lot where winds would produce a dune requires removal of tons of sand every year. Even more significantly, because the flow of sediment is so great, modifications intended to have only a local, beneficial effect may influence erosion and deposition far down the beach.

Coastal retreat is a significant issue along many areas of coastline. Efforts are ongoing to quantify the rate of retreat along the coast, to designate areas of

KEY TERMS

Emergent coast— A coast rising relative to sea level, characterized by exposed terraces consisting of older wave cut cliffs and formerly submerged beaches.

Longshore drift— Movement of sand parallel to the shore, caused by waves approaching the shore obliquely, slowing and breaking.

Refraction— The bending of light that occurs when traveling from one medium to another, such as air to glass or air to water.

Submergent coast— A coast sinking relative to sea level, characterized by drowned river valleys.

particular risk, and to match appropriate uses with the location. Even in areas with minimal retreat, the movement of sediment along the shore can impact the property owner significantly. Utilization of engineered shoreline protection can affect nearby properties. Sediment budgets for a shoreline can be impacted by the damming of rivers upstream. Even artificial means of beach nourishment can have unintended environmental impacts. One might be able to protect the beach in front of a beach house by installing a concrete barrier, but this might result in eroding the supports to the highway giving access to the beach house.

The costs of shoreline protection are high and may not be factored in during development. Furthermore, these costs may be borne by the taxpayer rather than the property owner. The long-range outlook for all such costs is that they may in some cases exceed the value of the property and may be exacerbated by rising sea levels associated with global climate alteration. Many scientists and engineers are concerned with the migratory nature of the coast, and caution that structures built upon a moving coastline are subject to the same fluctuating forces that control the beaches themselves.

See also Beach nourishment; Ocean; Shoreline protection;Tides.

Resources

BOOKS

Bird, Eric. Coastal Geomorphology: An Introduction. West Sussex, England: John Wiley & Sons Ltd. 2000.

U.S. Army Corps of Engineers. Coastal Geology. Honolulu, Hawaii: University Press of the Pacific, 2004.

OTHER

Geological Society of America (GSA). Beach Nourishment: The Wave of the Future for Erosion Control (Part A). Southeast Section Annual Meeting Abstracts. 2001 (accessed October 19, 2002). <gsa.confex.com/gsa/2001SE/finalprogram/session_77.htm>. National Oceanic and Atmospheric Administration

(NOAA). Managing Coastal Resources. NOAA’s State of the Coast Report, 1998. <http://state-of-coast.-noaa.gov/bulletins/html/crm_13/crm.html> (accessed October 19, 2002).

National Oceanic and Atmospheric Administration (NOAA). Monitoring the Coastal Environment. NOAA’s State of the Coast Report. 1998. <http://state-of-coast.noaa.gov/bulletins/html/mcwq_12/mcwq.html> (accessed October 18, 2002).

National Oceanic and Atmospheric Administration (NOAA). Population at Risk from Natural Hazards. NOAA’s State of the Coast Report. 1998. <http://state-of-coast.noaa.gov/bulletins/html/par_02/par.html> (accessed October 19, 2002).

National Oceanic and Atmospheric Administration (NOAA). “Population Trends Along the Coastal United States: 1980-2008.” September 2004. <http://marineeconomics.noaa.gov/socioeconomics/assessment/population.html> (accessed October 11, 2006).

Otto H. Muller

Coast and beach

The coast and beach, where the continents meet the sea, are dynamic environments where agents of erosion vie with processes of deposition to produce a set of features reflecting their complex interplay and the influences of changes in sea level , climate, sediment supply, etc. "Coast" usually refers to the larger region of a continent or island that is significantly affected by its proximity to the sea, whereas "beach" refers to a much smaller region, usually just the areas directly affected by wave action.

Observing erosion and deposition

Earth is constantly changing. Mountains are built up by tectonic forces, weathered, and eroded away. The erosional debris is deposited in the sea. In most places these changes occur so slowly they are barely noticeable, but at the beach, they are often observable.

Most features of the beach environment are temporary, steady state features. To illustrate this, consider an excavation in soil , where groundwater is flowing in, and being pumped out by mechanical pumps. The level of the water in the hole is maintained because it is being pumped out just as fast as it is coming in. It is in a steady state, but changing either rate will promptly change the level of the water. A casual observer may fail to notice the pumps, and erroneously conclude that the water in the hole is stationary. Similarly, a casual observer may think that the sand on the beach is stationary, instead of in a steady state. The size and shape of a spit, which is a body of sand stretching out from a point, parallel to the shore, is similar to the level of the water in this example. To stay the same, the rate at which sand is being added to the spit must be exactly balanced by the rate at which it is being removed. Failure to recognize this has often led to serious degradation of the coastal environment.

Sea level is the point from which elevation is measured. A minor change in elevation high on a mountain is undetectable without sophisticated surveying equipment. The environment at 4,320 ft (1,316.7 m) above sea level is not much different from that at 4,310 ft (1,313.6 m). The same 10-ft (3-m) change in the elevation of a beach would expose formerly submerged land, or inundate formerly exposed land, making it easy to notice. Not only is the environment different, but also the dominant geologic processes are different: Erosion occurs above sea level, deposition occurs below sea level. As a result, coasts where the land is rising relative to sea level (emergent coasts) are usually very different from those where the land is sinking relative to sea level (submergent coasts).

Emergent coasts

If the coast rises, or sea level goes down, areas that were once covered by the sea will emerge and form part of the landscape. The erosive action of the waves will attack surfaces that previously lay safely below them. This wave attack occurs at sea level, but its effects extend beyond sea level. Waves may undercut a cliff, and eventually the cliff will fail and fall into the sea, removing material from higher elevations. In this manner, the cliff retreats, while the beach profile is extended at its base. The rate at which this process continues depends on the material of the cliff and the profile of the beach. As the process continues, the gradual slope of the bottom extends farther and farther until most waves break far from shore and the rate of cliff retreat slows, resulting in a stable profile that may persist for long periods of time. Eventually another episode of uplift is likely to occur, and the process repeats.

Emergent coasts, such as the coast along much of California, often exhibit a series of terraces, each consisting of a former beach and wave cut cliff. This provides evidence of both the total uplift of the coast, and its incremental nature.

Softer rocks erode more easily, leaving resistant rock that forms points of land called headlands jutting out into the sea. Subsurface depth contours mimic that of the shoreline, resulting in wave refraction when the change in depth causes the waves to change the direction of their approach. This refraction concentrates wave energy on the headlands, and spreads it out across the areas in between. The "pocket beaches" separated by jagged headlands, which characterize much of the scenic coastline of Oregon and northern California were formed in this way. Wave refraction explains the fact that waves on both sides of a headland may approach it from nearly opposite directions, producing some spectacular displays when they break.

Submergent coasts

If sea level rises, or the elevation of the coast falls, formerly exposed topography will be inundated. Valleys carved out by rivers will become estuaries like Chesapeake Bay. Hilly terrains will become collections of islands, such as those off the coast of Maine.

The ability of rivers to transport sediment depends on their velocities. When rivers flow into a deep body of water, they slow down and deposit their sediment in what will eventually become a delta . Thus, the flooding of estuaries causes deposition further inland. As the estuary fills in with sediment, the depth of the water will decrease, and the velocity of the water flowing across the top of the delta will increase. This permits further sediment transport. The delta builds out toward, and eventually into, the sea. The additional load of all the sediment may cause the crust of the earth to deform, submerging the coast further.

The sand budget

Wave action moves incredible amounts of sand. As waves approach shallow water, they slow down because of friction with the bottom, then get steeper, and finally break. It is during this slowing and breaking that sand is transported. When waves reach the shore, the approach is almost straight on, so that the wave front is nearly parallel to the shore as it breaks.

When a breaking wave washes up onto the beach at a slight angle it moves sand on the beach with it. This movement is mostly towards shore, but also slightly down the beach. When the water sloshes back, it goes directly down the slope, without any oblique component. As a result, sand moves in a zigzag path with a net motion parallel to the beach. This is called "longshore drift." Although most easily observed and understood in the swash zone, the area of the beach that gets alternately wet and dry with each passing wave, longshore drift is active in any water shallow enough to slow waves down.

Many features of sandy coasts are the result of long-shore drift. Spits build out from projecting land masses, sometimes becoming hooked at their end, as sand moves parallel to the shore. At Cape Cod, Massachusetts, glacial debris deposited thousands of years ago is still being eroded and redistributed by wave action.

An artificial jetty or "groin" can trap sand on one side of it, broadening the beach there. On the other side, however, wave action will transport sand away. Because of the jetty it will not be replenished, and erosion of the beach will result.

The magnitude and direction of transport of long-shore drift depends on the strength and direction of approach of waves, and these may vary with the season. A beach with a very gentle slope, covered with fine sand every July may be a steep pebble beach in February.

Barrier islands

Long, linear islands parallel to the shore are common along the Atlantic coast. Attractive sites for resorts and real estate developments, these barrier islands are in flux. A hurricane can drive storm waves over low spots, cutting islands in two. Conversely, migration of sand can extend a spit across the channel between two islands, merging them into one.

Interruptions in sand supply can result in erosion. This has happened off the coast of Maryland, where Assateague Island has become thinner and moved shoreward since jetties were installed at Ocean City, just to the north.

Society and the beach environment

Coastal areas of the continental United States comprise only 17% of the land area of the country, but house over one-half of the population. Currently, the population of this zone is above 139 million and expected to rise to 165 million by the year 2015, a rate of growth greater than that of the country as a whole. The coast is attractive for a wide variety of reasons and economic growth of the zone typically follows the growth of the population. Unfortunately, the impacts on the coastal environment are not so positive. Environmental degradation accompanies shoreline development in a variety of forms. Furthermore, development within the coastal zone is increasingly located within high-risk areas of natural or man-made shore degradation.

In many cases, the public or property developer in the coastal region has an incomplete understanding of the coastal environment. Often, the dynamic nature of the beach environment is not properly respected. At higher elevations, where rates of erosion and deposition are much slower, man can construct huge hills to support interstate highways, level other hills to make parking lots, etc., expecting the results to persist for centuries, or at least decades. In a beach environment, however, modifications are ephemeral. Maintaining a parking lot where winds would produce a dune requires removal of tons of sand every year. Even more significantly, because the flow of sediment is so great, modifications intended to have only a local, beneficial effect may influence erosion and deposition far down the beach, in ways which are not beneficial.

Coastal retreat is a significant issue along many areas of coastline. Efforts are ongoing to quantify the rate of retreat along the coast, to designate areas of particular risk, and to match appropriate uses with the location. Even in areas with minimal retreat, the movement of sediment along the shore can impact the property owner significantly. Utilization of engineered shoreline protection can affect nearby properties. Sediment budgets for a shoreline can be impacted by the damming of rivers upstream. Even artificial means of beach nourishment can have unintended environmental impacts. One might be able to protect the beach in front of a beach house by installing a concrete barrier, but this might result in eroding the supports to the highway giving access to the beach house.

The costs of shoreline protection are high, yet they are rarely considered when the development of a coastal property is contemplated. Furthermore, these costs are often borne by the taxpayer rather than the property owner. The long-range outlook for all such costs is that they will ultimately exceed the value of the property and are likely to be exacerbated by rising sea levels associated with global climate alterations.

Many scientists encourage that the migratory nature of the coast should be recognized, and claim it is unwise to assume that structures built upon a moving coastline are immovable.

See also Beach nourishment; Ocean; Shoreline protection; Tides.

Resources

books

Bird, E. C. F. Submerging Coasts: The Effects of a Rising Sea Level on Coastal Environments. Chichester, New York: John Wiley & Sons, 1993.

Carter, R. W. G. Coastal Environments: An Introduction to the Physical, Ecological, and Cultural Systems of Coastlines. London; San Diego: Academic Press, 1988.

Carter, R. W. G., and C. D. Woodroffe. Coastal Evolution. Cambridge: Cambridge University Press, 1994.

Griggs, Gary, and Lauret Savoy, eds. Living with the California Coast. Durham, NC: Duke University Press, 1985.

other

Geological Society of America (GSA). Beach Nourishment: The Wave of the Future for Erosion Control (Part A). Southeast Section Annual Meeting Abstracts. 2001 [cited October 19, 2002]. <gsa.confex.com/gsa/2001SE/finalprogram/session_ 77.htm>.

National Oceanic and Atmospheric Administration (NOAA). Managing Coastal Resources. NOAA's State of the Coast Report, 1998 [cited October 19, 2002]. <http://state-ofcoast.noaa.gov/bulletins/html/crm_13/crm.html>.

National Oceanic and Atmospheric Administration (NOAA). Monitoring the Coastal Environment. NOAA's State of the Coast Report. 1998 [cited October 19, 2002]. <http://state-of-coast.noaa.gov/bulletins/html/mcwq_ 12/mcwq.html> (October 18, 2002).

National Oceanic and Atmospheric Administration (NOAA). Population at Risk from Natural Hazards. NOAA's State of the Coast Report. 1998 [cited October 19, 2002]. <http://state-of-coast.noaa.gov/bulletins/html/par_02/par.html>.

Otto H. Muller

KEY TERMS

Emergent coast

—A coast rising relative to sea level, characterized by exposed terraces consisting of older wave cut cliffs and formerly submerged beaches.

Longshore drift

—Movement of sand parallel to the shore, caused by waves approaching the shore obliquely, slowing and breaking.

Refraction

—The bending of light that occurs when traveling from one medium to another, such as air to glass or air to water.

Submergent coast

—A coast sinking relative to sea level, characterized by drowned river valleys.

COAST AND GEODETIC SURVEY

COAST AND GEODETIC SURVEY. The Coast and Geodetic Survey was born in 1807 when Congress, on the initiative of President Thomas Jefferson, passed a law authorizing "a survey to be taken of the coasts of the United States." The Survey, originally called the Coast Survey, was—for the first time in the history of the new nation—"to designate the islands and shoals, with the roads and places of anchorage, within twenty leagues of any part of the shores of the United States.…" The Survey, using new scientific methods, would be responsible for producing accurate charts of these features and would also identify other key characteristics of what can roughly be defined as the coastal zones of the United States. As the nation grew, new areas such as Florida, Texas, the Pacific Coast, and Alaska were added to the Survey's growing mission.

Historians agree that the Coast Survey led American science away from the older descriptive methods to the modern methods of statistical analysis and the prediction of future states of natural phenomena based on mathematical modeling. Virtually all branches of science, including the social and biological sciences, have adapted similar methodologies and similar techniques in their quest for scientific truth. (National Oceanic and Atmospheric Administration, "Comments on the Archive of the Coast and Geodetic Survey," 1991).

The survey was placed under the jurisdiction of the Treasury Department but its gestation and evolution were complicated and politicized from the outset. A Swiss immigrant to the United States, the geodesist and mathematician Ferdin and Rudolph Hassler, was selected to head the Survey. He left for Europe in 1811 to secure the necessary scientific books, instruments, and knowledgeable expertise necessary for conducting a massive, complex, and accurate survey of the coastal areas of the United States. None of these necessities was available in America at that time. Hassler remained in Europe until 1815 and it was not until 1816 that Congress appropriated the funds for the survey. Hassler was officially made superintendent of the survey in 1816. However, in 1818 Congress changed the law and specified that only military and naval officers could be employed in the survey, neither of which Hassler was. The instruments and management of the project were turned over to the Navy Department.

In 1832 Congress reactivated the original 1807 legislation placing the Survey in the Treasury Department, and Hassler was again appointed superintendent. The tensions between military and civilian control of the Survey continued. In 1834 the Survey was again transferred to the Department of the Navy, but after repeated protests from Hassler it was once more returned to the jurisdiction of the Treasury Department in 1836. Further efforts to move the Survey to naval jurisdiction continued until 1882.

After the death of Hassler in 1843, Alexander Dallas Bache, a great-grandson of Benjamin Franklin, took over as superintendent of the Coast Survey. Bache built on the strong foundation that had been created, and is credited with developing the Survey into the first real scientific organization in the federal government. He became a leader in the American Association for the Advancement of Science and was a founding member of the National Academy of Sciences.

The scope and flair of the Survey is captured in the following description taken from an analysis of its annual reports:

The Survey was continental in scope, tying together east and west coasts by an invisible transcontinental network of triangles while leading American commerce by means of precise nautical charting surveys into the ports of our Atlantic, Gulf, and Pacific shores. Storms, mountains, dust, mud, deserts, wild beasts, heat and cold; all were the companions of the Coast Surveyors. They engaged in a great physical adventure that is little known and little understood. Beyond the romance of the Coast Surveyors, there was an enduring intellectual adventure as the field men and the office force of the Coast Survey engaged in a fascinating quest for the ultimate limits of accuracy of scientific measurement. They were seekers of scientific "truth." No effort was too great or hardship too onerous to overcome in this quest. The perseverance and fortitude of the field men was matched by the office force of mathematicians, physicists, geodesists, astronomers, instrument-makers, draftsmen, engravers, and pressmen. These men and women (the Coast Survey hired women professionals as early as 1845) helped push back the limits of astronomic measures, designed new and more accurate observational instruments for sea and land surveying, developed new techniques for the mathematical analysis of the mountains of data obtained by the field parties, and further refined techniques of error analysis and mitigation. (National Oceanic and Atmospheric Administration, "Comments on the Archive of the Coast and Geodetic Survey," 1991)

In 1878 the program was officially renamed the Coast and Geodetic Survey. In 1903 it was transferred to the Department of Commerce and Labor and it remained in Commerce after Labor became a separate cabinet department in 1913. In 1920 the title "superintendent" was changed to "director."

In 1965 the Coast and Geodetic Survey became part of the Environmental Science Services Administration (ESSA), which also incorporated the Weather Bureau and the National Bureau of Standards' Central Radio Propagation Laboratory. When the National Oceanic and Atmospheric Administration (NOAA) was created in 1970 as a new entity within the Department of Commerce, ESSA and thus the Survey became part of NOAA.

The Survey is considered to have been one of the major birthplaces of modern American science, including many disciplines not generally associated with geodesy and hydrology. Its creation is a cornerstone of the rapid growth of science and technology and of the development of natural resources for commercial use in the United States.

BIBLIOGRAPHY

Dracup, Joseph F. The United States Horizontal Control Network, 1816–1976. Rockville, Md.: National Oceanic and Atmospheric Administration, n.d.

National Oceanic and Atmospheric Administration. "Comments on the Archive of the Coast and Geodetic Survey." Available at http://www.lib.noaa.gov.

National Oceanic and Atmospheric Administration. "Functions of the Coast Survey and the Coast and Geodetic Survey." Updated February 17, 2000. Available at http://www.lib.noaa.gov.

U.S. Department Commerce. U.S. Coast and Geodetic Survey: 150 Years of Service, 1807–1957. Washington, D.C., 1957.

Wright, A. Joseph, and Elliot B. Roberts. The Coast and Geodetic Survey, 1807–1957: 150 Years of History. Washington, D.C.: U.S. Department of Commerce, 1957.

Steffen W.Schmidt

See alsoGeological Survey, U.S.

Coast and beach

The coast and beach, where the continents meet the ocean, are everchanging environments where the conflicting processes of erosion (wearing away) and sedimentation (building up) take place. Coast is the land that borders an ocean or large body of water. Beach refers to a much smaller land region, usually just the area directly affected by wave action.

Coasts

Coasts are generally classified into two types: emergent and submergent. Emergent coasts are those that are formed when sea level declines. Areas that were once covered by the sea emerge and form part of the landscape. This new land area, which was once protected underwater, is now attacked by waves and eroded. If the new land is a cliff, waves may undercut it, eventually causing the top portions of the cliff to fall into the sea. When this happens, the beach is extended at its base. Along emergent coast shorelines the water level is quite shallow for some distance offshore. Much of the coast along California is emergent coast.

Submergent coasts are those that are formed when sea level rises, flooding formerly exposed land areas. Valleys near coastal areas that had been carved out by rivers become estuaries, or arms of the sea that extend inland to meet the mouth of a river, for example, Chesapeake Bay in Virginia and Maryland. Hilly terrains become collections of islands, such as those off the coast of Maine.

Beaches

Most of the sand and other sediments making up a beach are supplied by weathered and eroded rock from the mainland that is deposited by rivers at the coast. At the beach, wave action moves massive amounts of sand. As waves approach shallow water, they slow down because of friction with the bottom. They then become steeper and finally break. It is during this slowing and breaking that sand gets transported.

Words to Know

Emergent coast: A coast that is formed when sea level declines and is characterized by wave-cut cliffs and formerly underwater beaches.

Longshore drift: Movement of sand parallel to the shore, caused by slowing and breaking waves approaching the shore at an angle.

Submergent coast: A coast that is formed when sea level rises and is characterized by drowned river valleys.

When a breaking wave washes up onto the beach, it does so at a slight angle, moving sand both toward and slightly down the beach. When the water sloshes back, it does so directly, without any angle. As a result, the water moves the sand along the beach in a zigzag pattern. This is called longshore drift. The magnitude and direction of longshore drift depends on the strength of the waves and the angle at which they approach, and these may vary with the season.

Barrier islands

A barrier island is a long, thin, sandy stretch of land that lies parallel to a mainland coast. Between the barrier island and the mainland is a calm, protected water body such as a lagoon or bay. If the coastline has a broad, gentle slope, strong waves and other ocean currents carry sand offshore and then deposit it, creating these islands. In the United States, most barrier islands are found along the Gulf Coast and the Atlantic Coast as far north as Long Island, New York.

Sand being moved by longshore drift and being replenished on beaches by eroding highlands is a natural, constant cycle. Beaches erode, however, when humans intervene in the cycle, often by building on coastal land. Two methods used to remedy beach erosion include pumping sand onto beaches from offshore and building breakwaters away from shore to stop longshore drift.

[See also Erosion; Ocean; Tides ]

coast / kōst/ • n. 1. the part of the land near the sea; the edge of the land. ∎  (the Coast) the Pacific coast of North America.2. a run or movement in or on a vehicle without the use of power.• v. 1. [intr.] (of a person or vehicle) move easily without using power: the engines stopped, and the craft coasted along. ∎  act or make progress without making much effort: he coasted to victory. ∎  slide down a snowy hill on a sled.2. [intr.] sail along the coast, esp. in order to carry cargo.PHRASES: the coast is clear there is no danger of being observed or caught.