Page images
PDF
EPUB
[graphic]

Locations of the seven pilot projects of the National Water-Quality Assessment Program.

[ocr errors]

consistent description of current waterquality conditions for a large part of the Nation's water resources; define longterm trends (or lack of trends) in water quality; and identify, describe, and explain the major factors that affect water-quality conditions and trends.

be linked together through a prescribed set of study approaches and protocols for sample collection, sample handling, laboratory analysis, and quality assurance. Data for the study units will be collected and interpreted on a nationally consistent set of water-quality constituents. Consistent records will be recorded on streamflow and basin characteristics, well and aquifer characteristics, and land use and other measures of human activity. In addition, written reports will contain similar information for each study unit; and finally, data will be stored in national data files, where they will be available to the user community upon request.

Assessment activities in each of the study units will be done on a rotational rather than continuous basis, and only a portion of the study units will be studied

in detail at a given time. For each study unit, 3- to 5-year periods of intensive data collection and analysis will be alternated with longer, less intensive periods of study.

Even a very effective National Water-Quality Assessment Program will not and should not eliminate the need for other water-quality data-collection activities. For some issues and questions, the sampling requirements and procedures may be different from those which this program is designed to address. By providing a strong, high-quality National Water-Quality Assessment Program, the USGS will help underpin and unify the Nation's water-quality activities. Such an assessment program should satisfy a significant share of the water-quality information needs of the country.

[graphic][ocr errors][subsumed][subsumed][ocr errors][subsumed][subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed][subsumed][ocr errors]

Geologic Investigations

Mission

Nhe basic mission of the Geologic Division is to

evaluate the Nation's geologic structure and the

geologic processes that have shaped it, to assess the Nation's mineral and energy resources, and to identify and investigate geologic hazards. • Investigations of geologic hazards provide information for predicting and delineating hazards from earthquakes and volcanoes and for identifying engineering problems related to ground failure hazards. • Regional geologic studies provide geologic maps and regional syntheses of detailed geologic data essential to mineral, energy, and hazard assessments. • Offshore geologic studies identify and describe the mineral and petroleum resources of the offshore areas of the United States, including the Exclusive Economic Zone, an area one-third larger than the land area of the United States. • Mineral resource investigations assess the distribution, quantity, and quality of the Nation's mineral resources, with particular emphasis on strategic and critical minerals. • Surveys of energy resources provide assessments of the Nation's coal, petroleum, uranium, and geothermal resources and enhance capabilities to explore for and develop new sources of energy.

[graphic][merged small]
[graphic]

Highlights

Erosion of Louisiana's Coastal Barriers

By Asbury H. Sallenger, Jr.,
Bruce E. Jaffe, and
S. Jeffress Williams

loss exceed 80 square miles per year. Louisiana's barrier islands, which serve to protect wetlands, are eroding, in some places as much as 65 feet per year. The islands are decreasing in area as they migrate landward. For example, between 1890 and 1979, Louisiana barrier islands decreased in area by 37 percent. If this rate of land loss continues, the barrier islands will disappear, which in turn will accelerate the destruction of valuable wetlands. Louisiana contains 41 percent of the Nation's wetlands, which support a $1 billion annual fishery industry.

Many of the processes contributing to barrier island erosion are poorly understood and are not quantifiable with any degree of confidence. These processes must be better understood in order to predict the future shoreline response and, thus, allow better management of our coastal resources. In 1986, the U.S. Geological Survey and the Louisiana Geological Survey began a planned 5-; year study focused on the processes causing barrier island erosion.

Nearly three-quarters of the U.S. population lives within an hour of the Nation's coasts. Coastal erosion and wetland loss, therefore, are serious problems with long-term economic and social consequences. Developed areas face billions of dollars in property damage and potential loss of life as a result of long-term erosion and storm impacts, and valuable wetlands are being altered at rapid rates. Of the 30 States bordering the oceans, the Gulf of Mexico, or the Great Lakes, all are undergoing some erosion and 26 are presently experiencing an overall net erosion of their shorelines. The National Academy of Sciences has forecast increasing rates of sea-level rise, which means that erosion is likely to accelerate in the future.

Because of natural and manmade causes, Louisiana has the highest rates of coastal erosion and wetland loss of any region in the United States. In the Mississippi River delta plain, rates of wetland

Valuable wetlands are being altered at rapid rates.

[ocr errors][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

Long-term erosion of Louisiana's barrier islands is due both to sea-level rise, relative to the land, and to diminishing sand supply. The primary objectives of the study are to better quantify processes related to sea-level rise and sand supply and to present the results in a form that can be applied to such practical problems as predicting future changes.

The study is divided into three main parts: • Investigating the geologic framework within which the barriers have formed and migrated landward. This work uses cores and geophysical information to provide a broad regional understanding of the historical development of the barrier islands and a conceptual understanding of the processes of barrier island erosion. • Developing a better quantitative understanding of the various processes responsible for erosion. We have focused on only a few of the many processes, including relative sea-level rise, overwash,

[merged small][ocr errors][merged small][merged small][ocr errors][merged small][merged small]
[ocr errors]

50 100 KILOMETERS

Figure 1. Location of the Isles Dernieres barrier islands.

« PreviousContinue »