Page images
[merged small][ocr errors]

the 2 water years. Water discharge to the tidal river near Washington, D.C., during 1980 averaged 16,280 cubic feet per second, 43 percent above normal (51-year average is 11,400 cubic feet per second), while during 1981 the average discharge was 6,905 cubic feet per second, 39 percent below normal. The percentages of sediments and nutrients trapped in the various zones of the tidal river and estuary are shown in the table. For the 2 water years, 98 percent of supplied sediment was trapped in the tidal river and estuary. Corresponding figures for phosphorous, nitrogen, and dissolved silica were 68 percent, 57 percent and 46 percent.


Flow Modeling

The tidal Potomac River from the head-oftide in the northwestern quadrant of Washington, D.C., to Indian Head, Maryland, was modeled mathematically using a general one-dimensional network-type flow-simulation model. Water-surface elevations and discharge can be computed at any desired location throughout the network of channels using the model. The flow model was calibrated using recorded water-surface elevations as well as measured discharges from throughout the network. The general model is a proven viable and economical flow-assessment tool that is applicable to a wide range of hydrologic conditions and varying field situations. Through the use of such techniques, water managers and scientists involved in similar comprehensive assessments can better understand the interrelationship of predominant riverine and estuarine processes.

Shoreline Erosion

Field studies, comparisons of historical maps, and photogrammetric measurements were carried out to identify erosion processes along the shores of the tidal Potomac River and Esturary, to measure rates of shoreline recession, and to estimate the mass of sediment contributed to the system by shore erosion. Results indicate that the average recession rate in the estuary (1.2 feet per year) is more than twice as high as the average recession rate in the tidal river and transition zone (0.5 foot per year). Of the total mass of sediment derived from shore erosion annually (670,000 tons), 35 percent originates in the tidal river and transition zone, and 17 percent and 48 percent are derived from the Maryland shore and from the Virginia shore of the estuary, respectively. About 40 percent of the sediment derived from shore erosion (262,000 tons) is in the silt- and clay-sized fraction. This is the same size of material as the suspended sediment in this area from other sources and represents 12 to 13 percent of the total mass of suspended sediment contributed to the tidal Potomac River.

Submersed Aquatic Vegetation From 1978 through 1982, distribution and

abundance of submersed aquatic vegetation in the tidal Potomac River and Estuary were

[ocr errors][ocr errors][ocr errors]

studied with the assistance of the U.S. Fish and Wildlife Service. Of 16 identified species of submersed aquatic plants, 14 were vascular plants, and 2 were species of the algae Chara. The majority of the plants are located in the Potomac River transition zone and Wicomico River tributary, with a few isolated populations in the tidal river and lower estuary. Wild celery, horned pondweed, widgeon grass, and redhead-grass were the most abundant and widespread species. The present distribution and abundance are very different from those of the early 1900's, when flats in the tidal river were covered with lush vegetation including wild celery and pondweeds and the lower estuary had an abundance of eelgrass.

[ocr errors]

It is exceedingly difficult to isolate the factors responsible for the decline of submersed aquatic vegetation in the tidal Potomac River and Estuary. The most likely reasons for their almost complete disappearance from the tidal river include extensive storm damage in the 1930's, increasing nutrient enrichment with a shift in the relation or balance between submersed aquatic plants and phytoplankton, a change in availability of light, and grazing by predators before adequate rhyzome mats or minimum bed size is established. The wide variation of salinity concentrations in the transition zone may account for the relative abundance of vegetation and the diversity of species within this reach as compared to other reaches.

[ocr errors]
[ocr errors][ocr errors][graphic][subsumed][merged small][merged small][merged small][graphic][ocr errors]
[ocr errors]
[ocr errors]

Pt. . Roosevelt Island ‘P / ; River National Airport // /// Wilson Bridge

Piscataway Creek

Nanjemoy Tra sition Zone . Port Tobacco River 1 Mathias Point Morgantown ower Cedar Point Wicomico River

Nomini Bay

Lower Estuary

5 l0 15
l l l



[ocr errors]

Figure 4. —Potomac River study area map showing transport stations at Chain Bridge, Wilson Bridge, Quantico, Route 301 bridge, and Piney Point.

High Plains Regional Aquifer-System Analysis

In 1978, the High Plains study was initiated in response to concern about the impact of declining water supplies on agriculture. This study is part of the Regional Aquifer-System Analysis Program of the U.S. Geological Survey, which was implemented to provide hydrologic information needed for effective management of the Nation's ground-water resources.

The High Plains aquifer underlies 174,000 square miles in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming. The region has abundant sunshine, moderate precipitation (16-18 inches annually), and high rates of evaporation (60-100 inches annually). The soils of the High Plains are highly productive when adequate water is available.

About 3.25 billion acre-feet of drainable water is stored in the aquifer. Approximately 66 percent of the water in storage is in Nebraska, and 12 percent is in Texas. New Mexico, the State with the smallest water resource in the High Plains, has only 1.5 percent of the volume of water in storage.

The quality of water in the High Plains aquifer generally is suitable for irrigation. However, the water does not satisfy Environmental Protection Agency drinkingwater standards in many places. Excessive concentrations of dissolved solids, fluoride, chloride, and sulfate occur in parts of the aquifer in all States.

About 62 percent of the area of the High Plains aquifer contains water with 250 to 500 milligrams per liter dissolved solids; only 3 percent of the area of the aquifer (mostly in Texas) contains water exceeding 1,000 milligrams per liter dissolved solids. Generally, dissolved-solids concentrations are lowest where the aquifer is covered by dune sand because recharge is relatively high and the sand contains few highly soluble minerals. in most areas where the concentration of dissolved solids in the aquifer exceeds 1,000 milligrams per liter, the chemical composition of the water is affected by the underlying bedrock.

Irrigation development began in the southern High Plains in the 1930's and 1940's. In 1949, nearly 4 million acre-feet of ground water was pumped to irrigate about 2 million acres in the High Plains. In 1978, an estimated 170,000 wells pumped 23

million acre-feet of water to irrigate 13 million acres.

The rapid increase in pumpage since 1949 has resulted in extensive water-level declines in the High Plains aquifer. Since irrigation began, water levels have declined more than 10 feet in 50,000 square miles of the aquifer and more than 50 feet in 12,000 square miles of the aquifer. Water-level declines of as much as 200 feet have been reported in Texas since irrigation pumpage started. The volume of water in storage in the aquifer has decreased about 5 percent or 166 million acre-feet since ground-water development began. About 70 percent of the depletion has occurred in Texas; about 16 percent of the depletion has occurred in Kansas.

To forecast future water-level changes, the High Plains Regional Aquifer-System Analysis will develop a geohydrologic data base and computer model of the aquifer. The data base will provide water managers with regional information needed for effective ground-water resource management. The computer model will provide managers with a tool for evaluating water-management alternatives.

Because of a plentiful supply of ground water, irrigation has developed the High Plains into one of the Nation's major agricultural areas. Of the total United States crop production in 1977, the High Plains produced 16 percent of the wheat, 13 percent of the com, 40 percent of the sorghum, and 25 percent of the cotton. The total value of crops produced in the High Plains in 1977 was about $4.6 billion ($2 billion from irrigated crops). in addition, the High Plains produced about 40 percent of the feedlot beef (valued at over $10 billion) raised in the United States.

Over 20 percent of the irrigated land in the United States is in the High Plains, and about 35 percent of the ground water used in the United States is pumped from the High Plains aquifer. Pumpage has caused a really extensive water-level declines in the aquifer. Consequently, many irrigators have experienced increased pumping costs and decreased well yields.

Regionally, the High Plains aquifer is a water-table aquifer consisting mainly of hydraulically connected near-surface sand and gravel deposits of Tertiary and Quater

[merged small][ocr errors][merged small][ocr errors][ocr errors][subsumed][graphic][merged small][ocr errors][subsumed][subsumed]



NEW l MEXICO TEXAS \ EXPLANATION \ . 34D _ Water-level changes, in feet - Rise more than 10

10 to — 10

— 10 to — 50

Decline more than v 50 32,, _______ __ __A 0 50 100 150 MILES

[ocr errors]

Predevelopment to 1980 water-level changes in the High Plains aquifer.

Office of Earth Sciences



The Office of Earth Sciences Applications of the U.S. Geological Survey was established to demonstrate and increase the use of earth science information in land use and resource planning processes. The public and its elected officials, planners, policymakers, resource managers, and decision makers increasingly must cope with many issues, such as zoning, permitting, geologic hazard warnings and contingency plans, buildingsite selections, and so forth, that entail technical information at varying levels of complexity and from a diverse range of scientific disciplines. Many times, important geologic or hydrologic considerations are not included in the planning process because the information is not available, not known to be available, or not compatible to the needs of the user.

The major functions of the Office include the following:

' Enhancing the usefulness of earth science information in the planning-decisionmaking process.

' Reviewing environmental impact statements prepared by other Federal agencies.

' Applying remote-sensing technology and data in land resource and environmental analyses.

Return of the Office Functions to the Divisions

A decision was made to disband the Office of Earth Sciences Applications during fiscal year 1982 and to place all the functions and personnel in appropriate operating Divisions. This decision signified that the innovative layman-oriented information and

technology transfer techniques developed by this special Office since 1975 have become more or less routine and accepted functions of the Geological Survey and that these functions could now be housed in the Survey’s traditional organization. The Earth Resources Observation Systems Office was transferred intact to the National Mapping Division, the Visual Information Services Office went intact to the Geological Division's Office of Scientific Publications, and most of the Environmental Affairs Office was transferred to the Water Resources Division, except for the Oil Spill Trajectory Analysis function and personnel, who were reassigned to the newly formed Minerals Management Service of the Department of the Interior. The personnel of the Earth Sciences Assistance Office and the Resource Planning Analysis Office were divided among the Geologic, Water Resources, and National Mapping Divisions according to function.

During fiscal year 1982, however, the units of the Office of Earth Sciences Applications continued to operate. A brief summary of their activities and major research projects follows.

Significant Activities Environmental Affairs Office

During ~fiscal year 1982, the Environmental Affairs Office served as the primary focal point for coordination of environmental matters within the U.S. Geological Survey and for assurance of overall compliance with the National Environmental Policy Act and other environmental laws.

« PreviousContinue »