Search USGS⌕ Search
Home/Archive/USGS

USGS · wsp2284

Evaluation of the ground-water resources of the lower Susquehanna River basin, Pennsylvania and Maryland

James M. Gerhart·George J. Lazorchick
View original source ↗Read source document ↗Export metadata ↓

Abstract

Ground water in the 3,458-square-mile lower Susquehanna River basin occupies secondary openings in bedrock. The distribution of openings is a function of lithology, depth, and topography. Local flow systems account for most of the total ground-water flow. Average annual recharge for the lower basin is 1,857 million gallons per day, most of which discharges to streams. The water table is a subdued replica of land surface; its depth varies with topography but is generally 20 to 70 feet below land surface. Ground water circulates to depths of 500 to 600 feet below the water table. A digital model of regional, unconfined groundwater flow was developed and used to evaluate the ground-water resources of the lower basin. On the basis of lithologic and hydrologic differences, the area was subdivided into 21 hydrogeologic units, each with different hydrologic characteristics. Each unit was divided into two layers to take into account decreasing secondary permeability with depth. A finite-difference grid with square blocks approximately 1 mile on a side was used. The model was calibrated under steady-state and transient conditions. In the steady-state calibration, the model-generated results were compared with estimated water-table altitudes and estimated base flows. In the transient calibration, the model-generated results were compared with observed changes in water-table altitude from November 1, 1980, through April 22, 1981. Hydraulic conductivity increases from hilltops to Valley bottoms. The average hydraulic conductivity for carbonate units is about 21 feet per day, which is an order of magnitude greater than the corresponding averages for Paleozoic sedimentary, Triassic sedimentary, and crystalline units. The Cumberland Valley carbonate rocks have the greatest average hydraulic conductivity-about 174 feet per day in valley bottoms. The average gaining-stream leakage coefficient for all carbonate units is about 16 feet per day, which is two orders of magnitude greater than the corresponding averages for the other lithologies. The Cumberland Valley carbonate rocks have the greatest gaining-stream leakage coefficient--about 43 feet per day. The specific yields are 0.035, 0.020, 0.020, and 0.007 for the carbonate, Paleozoic sedimentary, crystalline, and Triassic sedimentary units, respectively. The calibrated model was used to simulate the effects of a ground-water withdrawal of 1 inch per year on water-table altitudes and average annual base flows in the modeled area. The overall effect is least for the carbonate units and greatest for the Triassic sedimentary units. The model also was used to simulate a standardized potential yield for each unit by assuming that the maximum acceptable consequence of a hypothetical withdrawal scheme is an ultimate 50-percent reduction in average annual base flow. Based on this, the potential yield for the modeled area is 891 million gallons per day. The Cumberland Valley carbonate rocks have the greatest potential yield--0.47 million gallons per day per square mile. The carbonate units have the greatest average potential yield, followed by the Paleozoic sedimentary, crystalline, and Triassic sedimentary units. About 90 percent of the eventual decline in water-table altitudes and the eventual reduction in average annual base flows occurs within 5 years of the implementation of the hypothetical withdrawal scheme. Nearly all of the ground water withdrawn is derived from reduced discharge to streams. The calibrated model can be used to estimate the impacts of ground-water development schemes on regional ground-water levels and base flows of streams, it cannot be used to simulate local cones of depression or local base-flow changes. The reliability of the model is a function of its approximation of the physical characteristics of the ground-water flow system, the two calibrations, various simplifying assumptions, and the lack of calibration under ground-water withdrawal conditions, it ca

Explore related subjects

Water Supply PaperReport

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

James M. Gerhart, George J. Lazorchick. 1988. Evaluation of the ground-water resources of the lower Susquehanna River basin, Pennsylvania and Maryland. https://doi.org/10.3133/wsp2284

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2004

Basic ground-water hydrology

Ground water is one of the Nation's most valuable natural resources. It is the source of about 40 percent of the water used for all purposes exclusive of hydropower generation and electric powerplant cooling. Surprisingly, for a resource that is so widely used and so important to the health and to the economy of the country, the occurrence of ground water is not only poorly understood but is also, in fact, the subject of many widespread misconceptions. Common misconceptions include the belief that ground water occurs in underground rivers resembling surface streams whose presence can be detected by certain individuals. These misconceptions and others have hampered the development and conservation of ground water and have adversely affected the protection of its quality. In order for the Nation to receive maximum benefit from its ground-water resource, it is essential that everyone, from the rural homeowner to managers of industrial and municipal water supplies to heads of Federal and State water-regulatory agencies, become more knowledgeable about the occurrence, development, and protection of ground water. This report has been prepared to help meet the needs of these groups, as well as the needs of hydrologists, well drillers, and others engaged in the study and development of ground-water supplies. It consists of 45 sections on the basic elements of ground-water hydrology, arranged in order from the most basic aspects of the subject through a discussion of the methods used to determine the yield of aquifers to a discussion of common problems encountered in the operation of ground-water supplies. Each section consists of a brief text and one or more drawings or maps that illustrate the main points covered in the text. Because the text is, in effect, an expanded discussion of the illustrations, most of the illustrations are not captioned. However, where more than one drawing is included in a section, each drawing is assigned a number, given in parentheses, and these numbers are inserted at places in the text where the reader should refer to the drawing. In accordance with U.S. Geological Survey policy to encourage the use of metric units, these units are used in most sections. In the sections dealing with the analysis of aquifer (pumping) test data, equations are given in both consistent units and in the inconsistent inch-pound units still in relatively common use among ground-water hydrologists and well drillers. As an aid to those who are not familiar with metric units and with the conversion of ground-water hydraulic units from inch-pound units to metric units, conversion tables are given on the inside back cover. Definitions of ground-water terms are given where the terms are first introduced. Because some of these terms will be new to many readers, abbreviated definitions are also given on the inside front cover for convenient reference by those who wish to review the definitions from time to time as they read the text. Finally, for those who need to review some of the simple mathematical operations that are used in ground-water hydrology, a section on numbers, equations, and conversions is included at the end of the text.

Water Supply Paper↗
USGS2002

Use of stable isotopes of carbon, nitrogen, and sulfur to identify sources of nitrogen in surface waters in the lower Susquehanna River basin, Pennsylvania

With the exception of sewage and septic effluents, most nitrogen sources and soils contain larger proportions of organic and reduced forms of carbon, nitrogen, and sulfur than inorganic, oxidized forms. In contrast, most surface water and ground water contains larger proportions of dissolved inorganic carbon, nitrogen, and sulfur forms than organic forms. Data indicate that carbon, nitrogen, and sulfur are extensively processed in soils and streams.

Water Supply Paper↗
USGS2001

Validation of a numerical modeling method for simulating rainfall-runoff relations for headwater basins in western King and Snohomish Counties, Washington

The validity of a previously determined numerical modeling method was assessed. Numerical models for 11 drainage basins were constructed with the Hydrologic Simulation Program-FORTRAN (HSPF) with parameter values that were generalized for the physiographic region. Large and recurrent simulation errors were initially identified, but three systematic modifications of the models corrected those errors for 10 out of the 11 basins. The validity of the numerical modeling method for simulating rainfall-runoff relations in the study area, as modified during this investigation, was not rejected, but observed streamflow data were needed to apply the method.

Water Supply Paper↗