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debate stems from the fact that the relations between emissions, acid deposition, and environmental effects are poorly understood. The Geological Survey has been investigating the chemistry of precipitation and the affected streams and lakes for the past three decades and has published a number of significant findings related to acid rain. One recent study, however, deserves special mention. An analysis of sulfur dioxide emissions and Geological Survey water-quality data collected over the past 10 to 1 5 years at 47 small headwater streams having little or no development indicates that sulfur dioxide emissions in the Northeast have decreased over the past 1 5 years and that trends in the water-quality characteristics of these headwater streams are consistent with decreased acid deposition. Throughout much of the remainder of the country, sulfur dioxide emissions have increased over the past 1 5 years, and trends in the water-quality characteristics of streams are consistent with increased acid deposition. The Geological Survey is accelerating its research, areal studies, and monitoring activities to further define the critical relation between acid deposition and consequent changes in stream and lake chemistry.

Resource assessments were a major endeavor of the Geological Survey in 1983. Under the provisions of the Wilderness Act and subsequent related legislation, we and the U.S. Bureau of Mines completed a 20-year effort to assess the mineral resource potential of about 45 million acres of Forest Service wilderness areas. The summary of these mineral surveys, which was released in December 1983, indicates that there is evidence of mineralization in about 65 percent of the areas examined. The percentage of individual wilderness areas having mineral resource potential ranges from 0.1 of 1 to 100 percent and averages about 20 percent. Assessments of oil and gas resources of wilderness lands in 11 Western States also were completed this year. Results of the assessments indicate that about two-thirds of the wilderness lands have some petroleum potential. The study also marked the first systematic resource assessment to integrate the available geologic information on designated Federal lands through a computer-based digital cartography system. During the next several years, we plan to complete a

similar program to assess the petroleum resources of wilderness lands in Alaska and other major Federal lands in Alaska and the Western United States.

On March 10, 1983, President Reagan proclaimed the "Exclusive Economic Zone," which extends jurisdiction of the United States for a distance of 200 nautical miles seaward of our shorelines. This new national boundary gives our Nation jurisdiction over the vast living and nonliving resources within those 3.9 billion acres. The importance of the Exclusive Economic Zone is emphasized when its size is compared to the total onshore area of the United States and its territories which is only 2.3 billion acres. Reconnaissance studies, in conjunction with the Federal Republic of Germany in 1982, suggested that mineral-rich crusts occurring on seamounts (underwater volcanoes) in the central Pacific contain significant quantities of cobalt, nickel, and manganese. There are more than 200 islands and seamounts within the boundaries of the Exclusive Economic Zone in the Pacific.

Recognizing the importance of the President's proclamation to the Nation's energy and mineral self-sufficiency, we have moved aggressively to coordinate our own marine geology activities with those of other Federal agencies, academia, and industry to identify and assess the resources of this vast area.

In August, we began an intensive 1 5-month program of marine geologic and geophysical investigations in the Pacific Ocean that will extend from the Arctic to Antarctica. Planned activities for scientists on board the Research Vessel Samuel P. Lee include sea-floor photography of sulfide deposits on the Juan de Fuca Ridge, seismic surveys in the Bering Sea and in the south Pacific, additional sampling in the central and south Pacific for cobalt-manganese crusts, and seismic profiling in offshore Antarctica.

The eruption of Kilauea Volcano in Hawaii, catastrophic landslides in Utah and California, and the earthquake at Coalinga, California, attracted considerable public attention in 1983 and emphasized the need for Geological Survey programs aimed at mitigating losses from these hazards. Volcanologists and seismologists from the Survey accurately predicted the reawakening of Kilauea Volcano and successfully forecast the continuing dome-building

eruptions of Mount St. Helens. Survey landslide experts responded to an emergency request from the State of Utah to help identify potentially damaging landslides triggered by the rapid melting of a record mountain snowpack and locally heavy spring rains.

Mapping needs of Federal, State, and local agencies have caused the Geological Survey to accelerate completion of the standard large-scale map coverage of the United States to 1989. To reach our goal, we began publishing provisional edition maps in 1982. These interim products have the same level of information as the standard topographic maps but are prepared more rapidly and at lower cost by making some minor modifications to field and compilation procedures and by reducing some of the map-finishing operationsactivities that can be performed in conjunction with the revision of the maps. This year, we published about 700 new topographic quadrangle maps and have completed about 82 percent of the largescale map coverage of the conterminous United States and Alaska.

Recognizing the wide range of applications for digital cartographic data, we are in the process of building a National Digital Caitographic Data Base and of developing the necessary data standards, computer techniques, and equipment capabilities for its support. Production to date has primarily focused on providing the basic data categories shown on 7.5-minute published topographic quadrangle maps to meet the needs of other Federal and State agencies.

One major interagency effort getting underway is a program with the Bureau of Census to digitize all the hydrography and transportation data for the country at a scale of 1: 100,000. The data resulting from this effort will not only be used to support the 1990 census but should be very useful to State and other Federal agencies for many other applications as well.

Another interagency effort is the development of a Federal Mineral Land Digital Data System that will contain information on Federal land surface and subsurface ownership, mineral occurrence, mining restrictions, and other data essential for establishing mineral development policy. Combining information from various data bases in a geographic information system will allow persons involved with resource development issues to more easily integrate and analyze these data to answer questions related to the availability and development of mineral resources on Federal lands.

If spatial or cartographic data are to be used for computer analyses and computeraided decisionmaking, then such information must be organized into a data base that meets consistent and exacting standards for widespread public use. To address these issues and to avoid duplication and waste, the Department established the Interior Digital Cartography Coordinating Committee, which is chaired by the Geological Survey. The Committee addresses digital cartographic data standards, data production planning, applications development, and technological information exchange. Subsequently, in April 1983, we were designated by the Office of Management and Budget as lead agency for digital cartography data coordination in the Federal Government.

Nineteen eighty-three was a year of challenges, new beginnings, and accomplishments. Many ambitious tasks, however, remain on our agenda. Whatever the challenges, I have the utmost confidence that we shall meet them with the same dedication, ability, and success that has served the Nation so well for 104 years.

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Perspectives

Flooding: A Unique Year By A. L. Putnam

Background

Floods have been and continue to be one of the most destructive hazards facing the people of the United States. Of all the natural hazards, floods are the most widespread and the most ruinous to life and property. Today, floods are a greater menace to our welfare than ever before because we live in large numbers near water and have developed a complex reliance upon it. From large rivers to country creeks, from mountain rills to the trickles that occasionally dampen otherwise arid wastelands, every stream in the United States is subject to flooding at some time. Floods strike in myriad forms, including sea surges driven by wild winds or tsunamis churned into fury by seismic activity. By far the most frequent, however, standing in a class by themselves, are the inland, freshwater floods that are caused by rain, by melting snow and ice, or by the bursting of structures that man has erected to protect himself and his belongings from angry waters.

An inland, freshwater flood is any abnormally high streamf low that overtops the banks of a stream. Such flooding is a natural characteristic of rivers. Flood plains are normally dry-land areas that act as natural reservoirs and temporary channels for floodwaters. If more flow is generated than the stream banks can accommodate, the water will overtop the banks and spread over the flood plain causing social and economic disruption and damage to crops and structures.

Floods can take place in the United States in all seasons, but, in particular areas, they are more likely at certain times of the year. Winter floods due to rainfall and abnormal temperature patterns take place in the Eastern United States. The incidence of winter floods progresses northward from the Gulf States in January to the Ohio River valley in March. Winter floods, caused by eastward moving cold fronts, also occur along the western slopes of the Sierra Nevada and Cascade Range in California, Oregon, and Washington.

Early spring floods are common in the northwestern States, the Great Lakes area, the Missouri River basin, the Red River of the North basin, the eastern slopes of the Cascade Range in Washington and Oregon, the Sierra Nevada Range in California, and the mountains of Arizona. The floodwater results from melting snow that accumulated during the previous winter. Ice jams also frequently cause flooding in some northern States and in some of the mountainous areas. Early spring floods in the lower Mississippi River basin are caused by the seasonal rainfall pattern. Late spring floods in the mountains mainly result from melting snow at high altitudes.

Summer floods are likely to occur in any part of the United States, but they are rare along the west coast. Although some summer floods have been caused by general cyclonic storms, most are caused by thunderstorms that affect small areas. Some are severe enough to cause considerable property damage and loss of life. During late summer and in the autumn, hurricanes commonly cause floods along the coasts of the Gulf of Mexico and the Atlantic Ocean.

Finally, catastrophic dam failures have also caused major flooding resulting in property damage and loss of life. These can occur at any time of the year but are more likely during periods of heavy runoff.

To rate floods on a statistical basis, hydrologists use a rather simple system. Depending upon the records of the historical behavior of a given river, a particular inundation may be classified as a 10-year or a 100-year flood, meaning that a flood of that size or greater may be expected to occur, on the average, every 10 or every 100 years, respectively. This does not mean, of course, that floods are neatly spaced at regular 10- or 100-year intervals. What the system does do is assess the chances of, say, a specific flood occurring in any specific year; for example, a 100-year flood has, roughly, 1 chance in 100 of occurring.

To provide information for this floodfrequency rating system, collection of data about floods, whether large or small, is a continuing objective of the U.S. Geological Survey. A network of about 8,000 continuous-record streamflow gaging stations is maintained throughout the United States and the trust territories. Flood information is only one aspect of the data from that network, and it is supplemented by several thousand high-flow stations that provide annual maximum stage and discharge data. During major floods, data on discharge and peak elevation are collected on ungaged streams in addition to the gaged sites to help determine the areal distribution and magnitude of the floods.

From data collected by the Geological Survey, information is furnished to the public and private sectors. The information is widely used in the design of bridges, channel capacities, and roadbed elevations; for flood-plain zoning and for floodforecast, flood-alert and flood-warning systems; and in studies of the economics of flood-protection works, water supply, and flood-insurance programs. The most common use of flood information is by regulatory authorities who use it to establish design criteria that properly balance the hydrologic, economic, social, and political variables that might be considered in a comprehensive analysis. Afterwards, planners and designers use the information in analyses that ensure compliance with the minimum regulatory criteria which are usually stated as a frequency value.

In flood-warning activities, streamflow data are used by the National Weather Service, in combination with other data, to forecast the stage and time of an imminent flood. Telemetering and satellite data relay systems are used by the Survey to obtain current stage information that supports flood forecasting. Improvements in the capability to provide data for the prediction of timing and extent of floods is a continuing objective of the Survey.

1982-83 Conditions and Events

In most average years, one or more of the seasonal events generally produce some significant flooding in a few random locations throughout the United States. In some rare years, one particular seasonal event may produce a flood of such magnitude and widespread distribution that the

flood is classified among the greatest floods of the United States. Since December 1, 1 982, however, almost every State in the United States and the Virgin Islands has experienced significant flooding. This in itself may uniquely place the 1982-83 sequence of events among the great flood episodes in the United States. Highlights of some of the most outstanding events since December 1, I982, are described in the following paragraphs.

Mississippi River Basin

Winter rainfall and temperature patterns began prematurely in late autumn. Two main storms, December 2 to 7 and December 24 to 29, 1982, were both related to deep low-pressure troughs over Texas and the Southwest. The resulting flow pattern fed warm air over the lower Mississippi River basin and created atmospheric disturbances over the Gulf of Mexico and southeast Texas that encouraged development of the storm systems. Subsequent slow movement of these systems toward the northeast produced tornadoes, severe thunderstorms, and intense rainfall of long duration. Additional moderate, but spotty, rains in December served to maintain a high soil moisture content, thereby contributing to high runoff and extreme floods.

The floods of December 1982 and early January 1983 affected an area approximately 250 miles wide and 1,000 miles long through the central and southern part of the United States extending from the Great Lakes to the Gulf of Mexico. This area was roughly centered over the central and southern part of the Mississippi River basin.

Illinois, Missouri, and Arkansas were affected severely by the December 2 to 7 storm. The December 24 to 29 storm had the greatest affect in Lousiana and Mississippi. Western Tennessee, Kentucky, and other States on the fringe of the storms were not severely affected by either storm but had moderate to heavy rainfall from both events that caused moderate flooding on some streams.

Many of the outstanding peak flood flows during December were on large streams because of the generally widespread and long duration of the rainfall. Previous peaks of record were exceeded, and recurrence intervals were greater than 100 years at many sites.

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Illinois was affected most severely by the early December storm with several streams exceeding previously known maximum floods. Missouri, like Illinois, was affected most by the early December storm and also had many new peaks of record established.

Arkansas had severe flooding caused by the early December storm, and the southeastern part of the State received additional flooding from the late December storm. Peaks of record were exceeded at many locations. An outstanding example occurred near Poughkeepsie on the Strawberry River where the maximum peak since 1936 was exceeded by 6.6 feet and the December 3 peak discharge was more than 3 times the previous maximum. This flood was greater than a 100-year event.

Large flood peaks in Mississippi were mostly in the western part of the State. Only a few really unusual peaks occurred because Mississippi was on the eastern fringe of the storms.

Louisiana was affected by both December storms. The late December storm was

the most severe. The Little River near Rochelle exceeded the previous maximum since 1958 by 5.6 feet. The December 29 peak discharge was nearly twice as large as the previous maximum and had a frequency in excess of 100 years.

The mainstem of the Mississippi River, although not exceeding any previous maximum floods, had fairly high peaks from Illinois downstream to its mouth. Peak discharges in the lower reaches exceeded 1 million cubic feet per second at Tarbert Landing, Mississippi.

Ironically, as the passing of winter led into the seasonal rainfall patterns of spring, the storms brought abnormally intense rainfall of extended duration. From April 6 to 10, 1983, southeastern Louisiana and southern Mississippi were again deluged with intense rainfall for extended time periods. Several streams experienced record breaking floods, and frequencies exceeded 100 years. Most notable was the Pearl River where the maximum flood of record since I874 caused extensive flooding in the Slidell and Pearl River, Louisiana,

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