Our Nation's coastal lands are dynamic environments. The natural appeal of coasts has attracted people for centuries by providing a pleasant living environment, access to natural resources, and ease of transportation. Presently, more than half of the population of the United States lives within 50 miles of a coast. By the year 2010, it is estimated that 75 percent of the U.S. population will live within an hour's drive of a coast. Of the 10 largest metropolitan areas of the United States, 9 are located in coastal regions.
Coastal environments, whether adjacent to an ocean or a large lake, are constantly changing shape and location in response to natural processes and human activities. Waves, currents, and wind are natural forces that combine to continually reshape the beaches, dunes, and shoreline. The Nation's beaches, especially its national seashores and lakeshores, are among the Nation's most important natural assets. Storms, whether frequent winter events that last for days or single intense events, such as hurricanes, can greatly modify the shape of the coastal area and can damage or destroy structures such as roads, buildings, homes, and piers.
Coastal erosion is a national problem because it affects all 30 coastal States and all of the U.S. island territories. Beaches are categorized into three types: (1) mainland beaches that stretch for miles along the edge of major land masses (such as along the coast of Washington, Oregon, and California), (2) pocket beaches formed between rocky cliffs (such as along the coast of Maine), and (3) barrier island beaches, which are part of a complex system that includes marshes, bays, tidal flats, and inlets (such as along the Gulf of Mexico and the east coast). Louisiana's barrier islands are eroding the fastest of any coast in the Nation, at a rate that in places reaches 60 feet per year. Understanding the processes that shape and change coastal regions is critical if we wish to live in harmony with the natural coastal environment.
By the year 2010, it is estimated that 75 percent of the U.S. population will live within an hour's drive of a coast.
The coastal system extends from the offshore lake bottom or sea floor and overlying water (tens of miles from the land) to the onshore beaches, dunes, lagoons, estuaries, and wetlands. Sediment (sand and mud) is derived from rivers and the coastal area itself. Where sediment accumulates, it can build land; where it is removed, dry land can be converted to sea floor or lake bottom. The beach environment is dynamic, changing through the seasons of the year. Beach width and slope change with the seasons as wave energy changes. High-energy waves and strong winds in winter form a narrow, steep beach covered with coarse sand and gravel. In the summer, smaller waves and gentler winds produce a broad, gently sloping beach covered with fine sand.
Dunes are an integral part of the beach environment. They form behind the beach as the wind picks up the fine beach sand and deposits it in ridges. Dunes, ranging in height from several feet to hundreds of feet, help protect the beach by preventing storm waves from washing inland and transporting sand out of the beach environment. Dunes are nature's protection for the wetlands and lagoons behind a beach. They also protect structures people have built. Dunes are complex but fragile and can be destroyed easily by trampling, off-road vehicles, construction, or mining. Coastal erosion is a significant natural process in the Great Lakes, occurring at an average rate of 28 inches per year; land is gained in some places, lost in others. This gain and loss of land is of great concern to population centers built at lake's edge, such as Chicago.
In Indiana Dunes, the 18-mile shoreline retains much of its natural character. Adjacent to the park's beaches, however, the shoreline has been altered by the construction of harbors and industrial complexes and the use of rip rap (large boulders) to protect the shore. Of the 41 miles of shoreline between Michigan City, Ind., and the Illinois border, more than half have been altered to protect private residential or industrial properties. Structures, such as the jetties at Michigan City, Burns Harbor, and U.S. Steel, interrupt the normal longshore (parallel to the beach) transport of sand. The beach is built up as sand accumulates on the updrift side of structures; the beach erodes as sand is then removed on the downdrift side.
Shoreline erosion in the park results especially from storms in the early spring and late fall and during mild winters, when ice on Lake Michigan does not freeze to the shore. In March 1964, Lake Michigan began rising until it reached a record high for the century in 1986. When lake levels are high, the beaches become narrow. The waves break at the base of the dunes and erode them. Narrow beaches provide less space for the 2 million visitors who use the beaches during the summer. People are forced onto the foredune, where they interfere with the plants and animals present and cause trail erosion. High lake levels and their resultant narrow beaches also reduce the sand supply available to replenish and build the dunes.
In order to prevent Mount Baldy from eroding, the U.S. Army Corps of Engineers placed 120,000 tons of sand in front of it in 1981. This placement of sand, called beach nourishment, must be continued to provide protection. By spring 1984, all the sand that had been placed on the beach was gone, and the waves were again breaking on the base of the dune.
Just as people can delay, but not reverse, natural processes, people can also accelerate such processes. A case in point is the use of breakwaters in the vicinity of Burns Ditch and Michigan City. When the transport of sand is interrupted along a coast, erosion can increase, such as occurs to the west of the breakwaters at Burns Ditch, and sediment deposition can increase, such as occurs on the east side of Bethlehem Steel on Cowles Bog Beach. The Michigan City breakwaters cause deposition on the city's Washington Park beach while causing erosion of the beach in front of Mount Baldy.
Plants, such as marram grass, help stabilize the dunes. As people create footpaths in the dunes and the grass dies, the wind picks up the sand and moves it farther inland, where it buries woodlands. Blowouts and depressions in the dunes occur where large volumes of sand have been removed. Thus, a seemingly harmless action, such as the passage of feet alone, can change the face of the dunes.
Last Updated: 27-Apr-2009