IntroductionOur coasts are reaching a crisis. Threats to coasts and to coastal communities are growing as development, recreation, and waste disposal activities increase, often in conflict with long-term natural processes. Other threats to our coasts, such as sea-level rise and reduction in sediment supply, result from global warming and the damming of rivers.
The impending crisis of our coasts stems from misconceptions about what coasts are-and from actions based on those misconceptions. Differences between our perceptions and the reality of coasts intensify the conflicts between people and nature. These conflicts will worsen as the coastal population expands and competing uses of the recreational, wildlife, shipping, and mineral resources of coasts increase.
Perception and RealityWe think of land as stable and treat it as a permanent asset. For most land, this premise is reasonable because land generally changes very slowly. Although tectonic and geologic processes, such as continental drift and erosion, are always at work, they usually result in very gradual changes that are barely noticeable during a human lifetime.
Coasts, however, are not static; they are dynamic. They quickly change shape and location in response to natural forces and human activities. These forces and activities continually push and pull at coasts -- sometimes in the same direction, but often in opposite directions. As a result, the shape of the coast-line changes. Sand and other materials are moved onto and off of beaches by currents and waves. Seasonal movement of coastal materials creates broad summer beaches followed by narrow winter beaches in an annual cycle. During major storms, huge waves and storm surges can move large amounts of coastal sediments and can flood vast areas in a matter of hours.
On a larger scale, the coast itself moves as it tries to achieve equilibrium with the forces acting on it. Barrier islands and offshore sand bars move landward and along the coast, driven by longshore currents. Headlands are eroded back, moving the coast inland. Sediment is deposited on river deltas, extending the coast out into the water. Coastlines also move in response to changes in sea level; even if the land remains stationary, a rise in sea level will move the coastline inland.
Coastal Focus: Prudhoe Bay, Alaska
People vs. NatureBecause we treat the coast just like all other land -- as a stable platform on which we can safely and easily build -- some of our actions directly conflict with the dynamic nature of coasts. Other human activities, such as the increasing release of greenhouse gases, may indirectly affect our coasts through global warming, causing worldwide sea-level rise as glaciers melt. Still other actions, such as the damming of rivers for flood control and water management, may affect the stability of coastlines by restricting the supply of new sediments being carried to the coasts.
Conflicts between people and nature have always existed along the coasts. The increasing desirability and accessibility of coasts as places to work and live have intensified these conflicts greatly over the past 50 years. The 1990 census shows that 25 of the 30 coastal States have had dramatic population increases since 1980; the largest increases were in Alaska (36 percent), Florida (31 percent), and California (24 percent). Coastal areas across the United States now have population densities five times the Nation's average. Currently, 50 percent of the Nation lives within 75 kilometers of a coast; this number is projected to increase to 75 percent by the year 2010. As the coastal population grows, so does the need for additional facilities for transportation, recreation, potable water, and waste disposal. Pollution is already severe near large coastal urban areas and has hurt recreation activites and the fishing industry.
Wetlands and marshes are now widely recognized as important but fragile parts of the coastal environment. Louisiana, which contains more than 40 percent of the tidal wetlands in the 48 conterminous States, is losing as much as 100 square kilometers of wetlands each year. These marshes are one of the world's most productive ecosystems. Their continued demise seriously affects migratory waterfowl, songbird populations, and fish and shellfish resources, as well as the coastal culture of Louisiana.
In the future, the mineral potential of coastal sand, including its potential for gold and other metals, may result in another competing use of our coastal resources as cheaper onshore mineral supplies are exhausted. Mining coastal sand for heavy minerals and construction materials without a carefully designed plan may further stress the fragile coastal environment.
The Key: Earth-Science InformationHow should we deal with these competing needs? How can we manage the coastal crisis? The first step is to understand our coasts better, to build a solid foundation of earth-science data on coastal processes and evolution, and to identify what factors are important in quantitatively determining the location and movement of coasts. Only after thorough research and interpretation can the critical scientific results be translated into practical terms and be incorporated into sound coastal management policies.
This report briefly explains coasts-the types of coasts, the natural processes that create and modify them, and the human activities that affect them. It gives specific examples of coasts that are dramatically changing as a result of, or in conflict with, human interests and actions. It documents the critical need for a better understanding of our coasts through earth-science investigations and the collection of scientific data-information that is essential to Federal, State, and local agencies as well as to the private sector, homeowners, and other decision-makers who wrestle with the growing crisis on our coasts.
|Maintained by J.M. Watson||http://pubs.usgs.gov/circ/c1075/intro.html||Last updated 9.16.97|