ESTIMATED HYDROLOCilC CHARACTERISTICS 

>F SHALLOW AQUIFER SYSTEMS IN THE VALLEY AND RIDGE,

THE BLUE RIDGE, AND THE PIEDMONT PHYSIOGRAPHIC 

:OVINCES BASED ON ANALYSIS OF STREAMFLOW RECESSION

AND BASE FLOW

I

* ___r

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1422-B
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Estimated Hydrologic Characteristics of Shallow Aquifer 

Systems in the Valley and Ridge, the Blue Ridge, and 

the Piedmont Physiographic Provinces Based on Analysis 

of Streamflow Recession and Base Flow

By A.T. RUTLEDGE and T.O. MESKO

REGIONAL AQUIFER-SYSTEM ANALYSIS 

APPALACHIAN VALLEY AND PIEDMONT

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1422 B

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1996
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

The use of firm, trade, and brand names in this report is for 

identification purposes only and does not constitute 

endorsement by the U.S. Government.

Library of Congress Cataloging-in-Publication Data

Rutledge, A.T.

Estimated hydrologic characteristics of shallow aquifer systems in the Valley and Ridge, the Blue Ridge, and the Piedmont 

physiographic provinces based on analysis of streamflow recession and base flow / by A.T. Rutledge and T.O. Mesko.

p. cm. (Regional aquifer-system analysis Appalachian Valley and Piedmont) (U.S. Geological Survey professional paper; 1422-B)

Includes bibliographical references.

Supt.ofDocs.no.: 119.16:1422-8

1. Stream measurements Appalachian Region. 2. Aquifers Appalachian Region. I. Mesko, Thomas O. II. Title. 

HI. Series. IV. Series: U.S. Geological Survey professional paper; 1422-B. 

GB1216.5.R87 1996

551.49'0974 dc20 96-23309

CIP

For sale by U.S. Geological Survey, Information Services 

Box 25286, Federal Center, Denver, CO 80225
FOREWORD

THE REGIONAL AQUIFER-SYSTEM ANALYSIS PROGRAM

The Regional Aquifer-System Analysis (RASA) Program represents a 

systematic effort to study a number of the Nation's most important aquifer 

systems, which, in aggregate, underlie much of the country and which represent an important component of the Nation's total water supply. In general, 

the boundaries of these studies are identified by the hydrologic extent of each 

system and, accordingly, transcend the political subdivisions to which investigations have often arbitrarily been limited in the past. The broad objective for 

each study is to assemble geologic, hydrologic, and geochemical information; 

to analyze and develop an understanding of the system; and to develop predictive capabilities that will contribute to the effective management of the 

system. The use of computer simulation is an important element of the RASA 

studies to develop an understanding of the natural, undisturbed hydrologic 

system and the changes brought about in it by human activities and to provide a means of predicting the regional effects of future pumping or other 

stresses.

The final interpretive results of the RASA Program are presented in a 

series of U.S. Geological Survey Professional Papers that describe the geology, 

hydrology, and geochemistry of each regional aquifer system. Each study 

within the RASA Program is assigned a single Professional Paper number 

beginning with Professional Paper 1400.

Gordon P. Eaton 

Director

CONTENTS

Page Page

Foreword................................................................................................... iii Analysis of Streamflow Recession Continued

Abstract...................................................................................................... B 1 Relations Among the Recession Index and Low-Flow

Introduction.............................................................................................. 2 Variables...................................................................................... B18

Background........................................................................................ 2 Analysis of Base Flow and Hydrologic Budgets ................................ 19

Purpose and Scope............................................................................ 2 Hydrologic Budget Equations......................................................... 20

Study Methods.................................................................................. 2 Estimates of Ground-Water Recharge and Discharge and

Applicability of Methods................................................................. 4 Riparian-Zone Evapotranspiration......................................... 20

Previous Investigations.................................................................... 4 Variation in Recharge in the Study Area....................................... 22

Geologic Framework............................................................................... 4 Base-Flow Index................................................................................ 26

Analysis of Streamflow Recession......................................................... 5 Duration-Curve Surrogates for Mean Ground-Water Discharge... 28

Mathematical Basis for and Method of Determining the Components of Hydrologic Budgets of Basins............................. 28

Master Recession Curve of Ground-Water Discharge.......... 5 Effects of Drainage Area on Basin Hydrologic Characteristics......... 29

Definition of the Master Recession Curve in the Study Area..... 7 Summary................................................................................................... 33

Variation in Recession Characteristics in the Study Area........... 10 References.................................................................................................. 34

Estimates of Diffusivity, Specific Yield, and Transmissivity....... 15 Appendix Sources of Information on Basin Properties................... 55

ILLUSTRATIONS

Page

FIGURE 1. Map showing locations of the Regional Aquifer-System Analysis study area and the streamflow-gaging stations........................ 3

2-7. Graphs showing:

2. Schematic representation of the method used to determine the master recession curve of ground-water discharge...................... 6

3. Schematic representation of the master recession curve and the variables that define it...................................................................... 7

4. Typical master recession curves of ground-water discharge for streams in the Valley and Ridge Physiographic Province............ 8

5. Typical master recession curves of ground-water discharge for streams in the Piedmont Physiographic Province........................ 8

6. Typical master recession curves of ground-water discharge for streams in the Blue Ridge Physiographic Province shown for

	stations north and south of latitude 37..................................................................................................................................................... 9

7. Distribution of median basin recession index and second derivative of the master recession curve for basins in the three

	physiographic provinces............................................................................................................................................................................. 11

8. Map showing location of gaging stations for which master recession curves are concave and convex.............................................. 12

9-33. Graphs showing:

9. Distribution of basin relief in the three physiographic provinces............................................................................................................. 13

master recession curve for the three physiographic provinces............................................................................................................ 13

11. Relation between precipitation and the median basin recession index and between precipitation and the second derivative

of the master recession curve for the three physiographic provinces....................................................................................................... 14

12. Relation between latitude and precipitation for the Blue Ridge Physiographic Province..................................................................... 15

13. Relation between hydrologic characteristics of rocks in basins and the median basin recession index for the Valley and Ridge

Physiographic Province............................................................................................................................................................................ 16

14. Relations between hydrologic characteristics of rocks in basins and the median basin recession index for the Piedmont

Physiographic Province........................................................................................................................................................^ 17

15. The 7-day 2-year low flow shown as a function of the median basin recession index and the mean recharge for streamflowgaging stations in the Appalachian Piedmont Aquifer study area ...................................................................................................... 19

16. The 7-day 2-year low flow shown as a function of an estimator of the low flow that is a linear function of the median basin

recession index and the mean recharge for streamflow-gaging stations in the study area ............................................................ 19

17. Relation between mean ground-water recharge and ground-water discharge....................................................................................... 21

18. Mean ground-water recharge minus mean ground-water discharge shown as a function of the mean ground-water recharge

and as a box plot............................................................................................................................................................................^ 21

19. Relation between precipitation and the rate of recharge for the study area............................................................................................ 22

20. Relation between precipitation and the rate of recharge for the three physiographic provinces......................................................... 22
vi CONTENTS

FIGURE 21. Relation between basin relief and the rate of recharge for the three physiographic provinces ............................................................ 23

22. Relation between mean recharge and an estimator of mean recharge that is a linear function of precipitation and relief for

55 streamflow-gaging stations in the Blue Ridge and the Piedmont Physiographic Provinces....................................................... 23

23. Relation between hydrologic characteristics of rocks in basins and the mean recharge for the Valley and Ridge

Physiographic Province............................................................................................................................................................................. 24

24. Relation between hydrologic characteristics of rocks in basins and the mean recharge for the Piedmont Physiographic

Province......................................................................................................................................................................................................... 25

25. Distributions of the ratio of the 30-year estimate to the 10-year estimate for streamflow, ground-water recharge and

discharge, and the base-flow index.......................................................................................................................................................... 26

26. Distributions of base-flow index for basins in various parts of the study area....................................................................................... 27

27. Relation between precipitation and the base-flow index for the three physiographic provinces......................................................... 27

28. Ratio of six flow-frequency statistics to the mean ground-water discharge for the Valley and Ridge, the Blue Ridge, and the

Piedmont Physiographic Provinces .......................................................................................................................................................... 28

29. Relation between the 42-percent flow-frequency statistic and the mean ground-water discharge for the Valley and Ridge

Physiographic Province.............................................................................................................................................................................. 29

30. Relation between the 46-percent flow-frequency statistic and the mean ground-water discharge for he Blue Ridge and the

Piedmont Physiographic Provinces .......................................................................................................................................................... 29

31. Distribution of components of hydrologic budgets for basins in various parts of the study area....................................................... 30

32. Relation between the basin drainage area and various hydrologic variables for basins in the study area......................................... 31

33. Relations among physical and hydrologic variables for basins smaller than or equal to 50 square miles and basins larger

than 50 square miles.................................................................................................................................................................................. 32

TABLES

TABLE 1. Physical properties of drainage basins in the Appalachian Valley and Ridge, Blue Ridge, and Piedmont Physiographico

Provinces Regional Aquifer-System Analysis Program study area .................................................................................................... B 41

2. Characteristics of recession analysis and master recession curves in the Appalachian Valley and Ridge, Blue Ridge, and

Piedmont Physiographic Provinces Regional Aquifer-System Analysis Program study area......................................................... 45

3. Components of hydrologic budgets of basins in the Appalachian Valley and Ridge, Blue Ridge, and Piedmont

Physiographic Provinces Regional Aquifer-System Analysis Program study area, 1961-90........................................................... 49

4. Streamflow, recharge, and base flow in basins in the Appalachian Valley and Ridge, Blue Ridge, and Piedmont

Physiographic Provinces Regional Aquifer-System Analysis Program study area, 1981-90........................................................... 51

5. Estimates of the apparent specific yield in the study area.......................................................................................................................... 18

6. Statistical distribution of recharge and discharge for basins in the study area....................................................................................... 21

7. Statistical distribution of hydrologic budget components.......................................................................................................................... 31

CONVERSION FACTORS

Multiply By To obtain

inch per year (in/yr) 25.4 millimeter per year

foot (ft) 0.3048 meter

square mile (mi") 2.590 square kilometer

gallon per day (gal/d) 0.003785 cubic meter per day
REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

ESTIMATED HYDROLOGIC CHARACTERISTICS OF

SHALLOW AQUIFER SYSTEMS IN THE VALLEY AND RIDGE, THE BLUE

RIDGE, AND THE PIEDMONT PHYSIOGRAPHIC PROVINCES BASED ON

ANALYSIS OF STREAMFLOW RECESSION AND BASE FLOW

BY A.T. RUTLEDGE AND T.O. MESKO

ABSTRACT

Hydrologic properties of aquifer systems are estimated from the 

interpretation of streamflow records in the Appalachian Valley and 

Ridge, the Piedmont, and the Blue Ridge Physiographic Provinces. 

The analysis is divided into two parts streamflow recession and base 

flow.

The master recession curve (MRC) represents the recession of 

streamflow during times when all flow is from ground-water discharge, when no ground-water recharge is occurring, and when the 

configuration of the ground-water-head profile is nearly stable. The 

method used to describe the MRC shows flow on a logarithmic scale as 

a function of time on a linear scale and allows for the possibility that 

the MRC is nonlinear. The variation in the slope of one particular MRC 

and the variations among recession characteristics of different basins 

can be related to variation of transmissivity, specific yield, and the 

average distance from stream to hydrologic divide. The recession 

index is slightly lower in the Valley and Ridge Physiographic Province 

as compared with that in the other physiographic provinces possibly 

because of the high transmissivities of limestones and dolomites that 

underlie the Valley and Ridge Physiographic Province. The shape of 

the MRC can be related to variations in aquifer properties with changes 

in ground-water levels. Low parts of the MRC correspond to low 

ground-water levels in the basin. Upward concavity of the MRC may 

be caused by an increase in specific yield as the water table moves 

downward through zones of differing lithology Convexity may result 

from the reduction of specific yield with depth in the crystalline rocks 

of the Piedmont Physiographic Province. The MRC can be concave 

upward for basins of large relief, such as those of the Valley and Ridge 

and the Blue Ridge Physiographic Provinces. As ground-water levels 

decline, some streams may go dry, which results in an increase in the 

average distance from the stream to the hydrologic divide. Upward 

concavity of the MRC can result when the stream is fed by more than 

one aquifer. The concavity that results from multiple aquifers may be 

particularly evident in the Valley and Ridge Physiographic Province 

because of differences between the lithologies of the low-lying valleys 

and the adjacent ridges.

Variations in recession characteristics related to variation in precipitation and basin relief are, for the most part, obscured by scatter, 

which is possibly caused by variations in other unmeasured physical 

properties. The relation between the water-yielding capacity of rocks 

and the basin recession index is noticeably positive. From the analysis 

of streamflow recession, most values of hydraulic diffusivity are from 

8,000 to 60,000 feet squared per day, and most values of transmissivity

are from 80 to 5,000 feet squared per day. The annual minimum average 7-consecutive-day low-flow discharge with a 2-year occurrence 

interval is a variable that is related to the recession index, but a considerable amount of the scatter in the relation may be caused by variations 

in mean recharge.

Among the 89 basins for which the streamflow record from 1961 to 

1990 is continuous, the distribution of mean ground-water recharge, in 

inches per year, is minimum, 6; median, 13; and maximum, 50. The 

distribution of mean ground-water discharge, in inches per year, is 

minimum, 5; median, 12; and maximum, 46. Riparian-zone evapotranspiration, which is the loss of water to the atmosphere from ground 

water and from the stream channel, is generally 1 to 2 inches per year. 

The relation between precipitation and recharge for the study area 

shows a considerable amount of scatter; the best-fit linear equation has 

roughly unit gradient and an X-intercept that is about 24 inches per 

year. Plots of recharge as a function of basin relief show a slight negative relation for the Valley and Ridge Physiographic Province and a 

clear positive relation in the other physiographic provinces. In the Blue 

Ridge and the Piedmont Physiographic Provinces (combined), a good 

estimator of recharge can be derived from precipitation and basin 

relief. The relation between the capacity of rocks to yield water to 

wells and recharge in the Valley and Ridge Physiographic Province is 

generally not clear, but a positive relation is noted between the wateryielding capacity of rocks and the rate of recharge in the Piedmont 

Physiographic Province.

The base-flow index, which is the ratio of mean ground-water discharge to mean streamflow, ranges from 32 to 94 percent; the median is 

67 percent. The base-flow index is largest in the southern part of the 

Blue Ridge Physiographic Province. The best surrogate for mean 

ground-water discharge from the flow-duration curve is flow that is 

equalled or exceeded 42 percent of the time for the Valley and Ridge 

Physiographic Province and 46 percent for the Blue Ridge and Piedmont Physiographic Provinces.

On the basis of 72 basins, the median values for components of the 

hydrologic budgets in the study area (excluding the southern part of 

the Blue Ridge Physiographic Province) are, in inches per year, precipitation, 43; evapotranspiration, 26; streamflow, 16; ground-water 

recharge, 12; ground-water discharge, 11; and storm runoff, 6. On the 

basis of 17 basins, the median values for the components of the hydrologic budgets in the southern part of the Blue Ridge Physiographic 

Province are, in inches per year, precipitation, 58; streamflow, 38; 

ground-water recharge, 33; ground-water discharge, 29; evapotranspiration, 25; and storm runoff, 8.

Bl
B2 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

INTRODUCTION

The rates of surface- and ground-water use are 37 

trillion and 1.7 trillion gal/d, respectively, in the Appalachian Valley and Ridge, the Piedmont, and the Blue 

Ridge Physiographic Provinces (Swain and others, 

1991). Although large amounts of water are currently 

(1995) being withdrawn, processes of recharge, discharge, ground-water flow, and stream-aquifer interactions are poorly understood. This lack of 

understanding is related primarily to the diverse and 

complex nature of the hydrologic system.

BACKGROUND

This study is one of several regional investigations 

to assess the Nation's principal aquifer systems (Sun, 

1986). In 1978, the U.S. Geological Survey (USGS) 

began the Regional Aquifer-System Analysis (RASA) 

Program, as mandated by Congress, and was given the 

task of "initiating a program to identify the water 

resources of the major aquifer systems within the 

United States***and***establish the aquifer boundaries, 

the quantity and quality of the water within the aquifer, 

and the recharge characteristics of the aquifer" (Sun, 

1986, p. 2). This report is part of a RASA study of the 

area that includes the Appalachian Valley and Ridge, 

Blue Ridge, and Piedmont Physiographic Provinces 

(APRASA) (Swain and others, 1991). The RASA study 

was designed to provide a basis for more efficient use 

and management of water resources within the study 

area than is now possible by supplying data bases, a 

regional hydrogeologic framework, and interpretive 

analyses of ground-water flow systems.

PURPOSE AND SCOPE

This report describes how streamflow records were 

used to enhance the understanding of shallow groundwater-flow systems in the APRASA area. Of particular 

interest was the definition of streamflow recession during periods of base flow and the quantification of mean 

ground-water recharge and discharge. The nature of 

shallow ground-water-flow systems in the APRASA 

area, which generally are distinct in each basin, leads to 

the potential for analyzing properties of shallow aquifers by means of streamflow records. Also, the presence 

of fractured-rock flow systems in the study area adds to 

the benefit of streamflow analysis for determining aquifer properties over traditional aquifer-test methods, 

which can be unreliable in these systems because well 

diameter and length can be small relative to the scale of

fractures. Because the scale of streams is large relative 

to the scale of most fractures, ground-water flow can be 

conceptualized by means of continuum mathematics. 

Hydraulic properties obtained from stream-flow analysis are likely to be "average" values for the aquifer system. The principal problem with traditional aquifer-test 

methods in fractured rocks is the variance between the 

hydrogeologic conditions at the well site and the idealized conditions in the equations used for analyzing test 

results.

This report also (1) describes relations among properties of shallow ground-water flow systems, such as 

recession index and mean recharge rate, and the physical properties of the basins, such a relief, rock characteristics, and precipitation, (2) demonstrates relations 

among properties of shallow ground-water flow systems and streamflow statistics that have been widely 

used as indexes of stream-aquifer interactions, such as 

low-flow and flow-duration-curve variables, and (3) 

demonstrates the application of computerized methods 

that were developed as part of this study to interpret 

streamflow records [although these methods are 

described briefly in this report, the reader is referred to 

Rutledge (1993) for a thorough discussion]. Although 

the geology of the APRASA area is briefly described in 

this report, the reader is referred to Swain and others 

(1991) for a complete discussion.

STUDY METHODS

For the most part, this report describes the results of 

two types of analysis streamflow recession and base 

flow. The rate of streamflow recession is related to 

hydraulic diffusivity, which is transmissivity (T) 

divided by specific yield (Sy), and the configuration of 

the master recession curve (MRC), which is a graph of 

flow on a logarithmic scale as a function of time on a 

linear scale, is related in a general way to the capacity of 

the aquifer to yield water for supply during a time of 

sparse precipitation. Base-flow analysis consists mainly 

of the estimation of the mean rates of ground-water 

recharge and discharge over a long period of time (usually years). Computer programs were developed for 

describing the recession of ground-water discharge during periods of no recharge and for estimating the mean 

rates of ground-water recharge and discharge from 

streamflow records (Rutledge, 1993).

A total of 157 streamflow-gaging stations were 

selected in the APRASA area for analysis (fig. 1). The 

criteria for selection of these stations included a complete record of daily streamflow from 1981 to 1990, negligible regulation or diversion of flow, a record that was
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B3

PENNSYLVANIA^^

WEST 

VIRGINIA

TENNESSEE

SOUTH 

CAROLINA Valley and Ridge 

Physiographic Province

Blue Ridge Physiographic 

 Province

Piedmont Physiographic 

Province

Modified from Fenneman, 1946

A50 Streamflow-gaging station 

and number

Base from U.S.Geological Survey 

National Atlas, 1970,1:7,500,000

50 100 150 200 KILOMETERS

FIGURE 1. Locations of the Regional Aquifer-System Analysis study area, which consists of the three physiographic provinces, and 

the streamflow-gaging stations. (Gaging-station numbers are in sequence generally from southwest to northeast for cross reference 

with tables 1 to 4, which follow "References.")
B4 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

classified as "good" in USGS data books, and at least 75 

percent of the drainage area being within the APRASA 

study area. The drainage areas of all stations were 

larger than 2 mi2 and with the exception of three stations, all were less than 400 mi2. In the selection of stations, larger basins were avoided for the purpose of 

minimizing errors owing to bank storage and nonuniformity of storm systems. Although some calculations 

were performed by using the period from 1981 to 1990, 

the analysis of streamflow recession used the entire 

period of available record, and basin hydrologic budgets were calculated by using the period from 1961 to 

1990, for which 89 of the stations have complete 

records. Results of calculations of the components of 

hydrologic budgets of basins were based on the calendar year (January 1 through December 31).

A considerable part of the effort for this report consisted of compiling or determining the physical characteristics of the 157 basins. Discussion of the sources of 

basin characteristics is in the "Appendix" which 

includes precipitation, relief, and type of hydrogeologic 

terrane, and a listing of variables for all 157 basins is in 

table 1, which follows the "References." Basins are 

assigned numbers in figure 1 generally from southwest 

to northeast, from one State to another. These numbers 

are also listed in tables 2 through 4, which also follows 

the "References." Physical characteristics and analysis 

results listed in these tables (especially tables 3, 4) are 

only estimates. The accuracy of these results is considerably less than that implied by the number of decimal 

places.

APPLICABILITY OF METHODS

The methods developed and used in this study are 

intended for the analysis of the shallow ground-waterflow system of a basin with a streamflow-gaging station 

at the downstream end of the major draining stream. 

Regulation and diversion of flow should be negligible. 

The methods of base-flow analysis are appropriate only 

if the stream channel is the sink (discharge boundary) of 

the ground-water-flow system and if the flow system is 

driven by areally diffuse recharge events that can be 

considered to be roughly concurrent with peaks in 

streamflow. The methods are appropriate only if all or 

nearly all water is assumed to discharge to the stream, 

except for that water which is lost by riparian-zone 

evapotranspiration. The area of contribution in the 

ground-water system is assumed to be equal to the area 

of surface drainage area for the purpose of expressing 

flow in units of specific discharge, such as inches per 

year. Results are most accurate if the computerized

methods are used with data that covers a period of at 

least 1 year, as they are for this study.

PREVIOUS INVESTIGATIONS

Regional descriptions of the hydrology of the 

APRASA study area include works by Cederstrom, 

Boswell, and Tarver (1979), Heath (1984), Miller (1990), 

Schneider (1965a), Sinnott and Gushing (1978), Swain 

and others (1991), Wyrick (1968), Wyrick and Lloyd 

(1968), and Zurawski (1978).

Previous studies that include the analysis of streamflow records for the purpose of understanding properties of shallow ground-water systems in the APRASA 

area include Barksdale and others (1943), Becher and 

Root (1981), Becher and Taylor (1982), Biesecker, Liscensky, and Wood (1968), Bingham (1982, 1986), Carswell 

and Lloyd (1979), Daniel and Sharpless (1983), Dingman and Meyer (1954), Dingman and Ferguson (1956), 

Dine (1990), Duigon and Dine (1987, 1991), Evaldi and 

Lewis (1983), Gerhart and Lazorchick (1988), Harkins 

(1982), Hely and Olmsted (1963), Hewlett and Hibbert 

(1967), Hobba, Friel, and Chisholm (1972), Hoos (1990), 

Laczniak and Zenone (1985), Lichtler and Wait (1974), 

Lloyd and Growitz (1977), McGreevy and Sloto (1977), 

Nutter (1973, 1974), Nutter and Otton (1969), Olmsted 

and Hely (1962), Richardson (1982), Schneider (1965b), 

Stewart and others (1964), Stuart, Schneider, and 

Crooks (1967), Taylor, and others (1982), Taylor, 

Werkheiser, and Kriz (1983), Trainer and Watkins (1974, 

1975), Waller (1976), White (1977), Wood (1980), and 

Wood and others (1972). Some of these studies simply 

involve estimation of mean ground-water discharge, 

whereas others include additional subjects, such as 

characteristics of the recession of ground-water discharge or the effects of hydrogeologic variables on the 

rate of ground-water recharge.

GEOLOGIC FRAMEWORK

As described by Swain and others (1991), the 

APRASA study area is considered to be two distinct 

subareas on the basis of differences in geology and 

hydrologic characteristics. The first subarea consists of 

carbonate rock, sandstone, and shale of the Valley and 

Ridge Physiographic Province. The second subarea 

includes metamorphic and igneous crystalline rocks in 

the Piedmont and the Blue Ridge Physiographic Provinces. In addition, large rift basins, which extend from 

New Jersey to South Carolina within the Piedmont crystalline rocks, have been filled with sedimentary deposits of early Mesozoic age. Glaciation covered only a
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B5

small part (about 3,000 mi2) of the study area in eastern 

Pennsylvania and New Jersey. Locally, glacial deposits 

can provide significant quantities of water, but these 

deposits are not regionally significant.

Regolith, which consists of soil, alluvium, and 

weathered rock material, overlies most of the geologic 

units throughout both subareas. In some locations, it 

includes material that has been transported and deposited as glacial drift, colluvium, or alluvium, and in others, it consists only of weathered material called 

residuum, or saprolite, which remains atop the parent 

rock from which it has been derived. Thickness of the 

regolith throughout the study area is extremely variable 

and ranges from 0 to more than 150 ft. In some areas, 

the rate of weathering is about equal to the rate at 

which weathered material is removed by erosion; thus, 

thickness of regolith remains fairly constant in time.

The Valley and Ridge Physiographic Province is 

characterized by a sequence of parallel ridges and valleys that formed, in part, as a result of thrust faulting 

and folding. Ridge development is controlled by geologic structure and weathering characteristics of the different rock types. Generally, ridges are underlain by 

resistant conglomerate, sandstone, or cherty dolomite, 

whereas valleys are underlain by less-resistant siltstone, 

shale, limestone, or dolomite.

The Piedmont and the Blue Ridge Physiographic 

Provinces are underlain by Precambrian to Mesozoic 

igneous, metamorphic, and sedimentary rocks, which 

include massive granites and gneisses, foliated phyllites 

and schists, and consolidated sandstones. Sedimentary 

rocks of early Mesozoic age fill basins within the Piedmont Physiographic Province. Igneous and volcanic 

activity, which accompanied sedimentation, is manifested by basaltic and diabase dikes that were intruded 

into the Mesozoic sedimentary rocks. Rocks that crop 

out in the Piedmont underlie parts of the Atlantic 

Coastal Plain at depth.

ANALYSIS OF STREAMFLOW RECESSION

The mathematical description of the recession of 

ground-water discharge can be useful for estimating 

aquifer diffusivity and for discerning qualitative similarities or dissimilarities between ground-water-flow 

systems of various basins. Possible additional applications are the comparison of ground-water-supply 

potential of various basins and the assessment of loss of 

ground water to evapotranspiration or from the shallow 

local ground-water-flow system to deeper regional 

ground-water-flow systems.

MATHEMATICAL BASIS FOR AND METHOD OF

DETERMINING THE MASTER RECESSION CURVE

OF GROUND-WATER DISCHARGE

For the purpose of this report, the MRC represents 

the recession of streamflow during times when all flow 

is from ground-water discharge, no ground-water 

recharge is occurring, and the configuration of the 

ground-water-head profile is nearly stable. The MRC is 

usually assembled from numerous intervals of continuous recession; thus, it illustrates the recession that 

would occur for a period without recharge that is 

greater than any such time period that could be 

observed in nature. The matching strip method has 

been used for assembly of the MRC by Snyder (1939), 

Toebes and Strang (1964), and Nathan and McMahon 

(1990). The MRC is often constructed from nonsummer 

data so that the result will be minimally affected by 

evapotranspiration.

The log-linear model of base-flow recession may be 

sufficient in many applications (Barnes, 1939; Ineson 

and Downing, 1964; Rorabaugh, 1964; Bevans, 1986). 

When a period of time has elapsed since the last 

recharge event, the rate of base-flow recession for a 

basin is expressed as the recession index K (days per log 

cycle), which also is known as the storage delay factor 

(Singh and Stall, 1971). Rorabaugh's mathematical 

model is based on assumptions that the aquifer has uniform thickness, hydraulic conductivity, and storage 

coefficient, that it is fully penetrated by the stream, and 

that the distance from the stream to the hydrologic 

divide is equal at all places in the basin. It can be used 

to express recession by using the following equation 

(from Rorabaugh and Simmons, 1966, p. 12):

0.933 

K

(1)

Equation 1 can be rearranged to give the following 

base-flow recession index:

0.933Sv fl 2

K = y (2)

The above linear model of recession of ground-water 

discharge applies only after an amount of time has transpired since the last recharge event that is equal to critical time 0.2a2Sy/T (Rorabaugh, 1964, p. 434). Before 

critical time, the configuration of the ground-waterhead profile is unstable, and recession is nonlinear. 

After critical time, the configuration of the groundwater-head profile is stable, and recession is linear.
B6 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

Many factors can cause MRC nonlinearity in nature, 

even if the MRC represents times when the groundwater-head profile is stable, which is the case for this 

report. Most of these factors cause continuous variation 

in recession slope as streamflow recedes. Physical and 

mathematical models have shown that the presence of 

the declining free surface (water table) can cause nonlinearity of base-flow recession for a stream that is fed 

by an unconfined aquifer (Ibrahim and Brutsaert, 1965; 

Hornberger, Ebert, and Remson, 1970), and this nonlinearity can be enhanced by variable head at the groundwater-outflow boundary (the stream) (Werner and Sundquist, 1951; Singh, 1969; Singh and Stall, 1971). Nonlinearity can result from evapotranspiration or the gain 

or loss from shallow flow systems owing to interactions 

with underlying aquifers (Singh, 1969; Daniel, 1976) or 

from geologic heterogeneities in the basin (Horton, 

1933; Riggs, 1964; Ineson and Downing, 1964; Trainer 

and Watkins, 1974, 1975; Petras, 1986). Wood and others (1972) developed nonlinear MRC's for several 

streams in eastern Pennsylvania. Nutbrown and Downing (1976) indicated that nonlinearity can be common 

for even the simplest of ground-water systems in 

England.

For the purpose of constructing the MRC, its nonlinearity is assumed to be slight compared with that of 

streamflow recession during times when either storm 

runoff is significant or when the shape of the groundwater-head profile is not yet stable. Therefore, it is possible to extract segments of continuous recession from 

the record and to select "near-linear" parts of each segment that are indicative of the MRC. The recession segments are analogous to recession that occurs after

Rorabaugh's critical time, except that the mathematical 

model used here allows for the possibility of nonlinearity.

The basic steps for determining the MRC of groundwater discharge, as executed by a computer program 

(Rutledge, 1993), are illustrated in figure 2. First, the 

program locates periods of streamflow recession and 

allows the user to select nearly linear segments (fig. 2A). 

These segments represent periods during which all flow 

is from ground-water discharge, when there is no 

ground-water recharge, and when the configuration of 

the ground-water-head profile is nearly stable. Then, 

the best linear equation for time as a function of the logarithm of flow (LogQ) for each segment is determined 

by the program, which extracts a coefficient that is K of 

the segment (data points, fig. 2B). By using the assumption that K varies linearly with LogQ, the program then 

determines the best linear equation for K as a function 

of LogQ, which is the line in figure 2B. Coefficients of 

this equation are used to obtain the MRC (fig. 2C), 

which is a second-order polynomial expression for time 

as a function of LogQ in the following form:

(3)

where t is time, and A, B, and C are coefficients.

In the application of this recession model, considerable variation in the rate of recession can be assumed 

about the central tendency represented by the MRC. 

Nutbrown and Downing (1976) indicated that the precise shape of the recession curve may vary from time to 

time because of variations in the original distribution of 

hydraulic head. Another assumption is that the central

\

Master recession 

^curve

TIME AFTER LAST PEAK 

IN STREAMFLOW

RECESSION INDEX K TIME

FIGURE 2. Schematic representation of the method used to determine the master recession curve (MRC) of groundwater discharge. A, Selected recession segments, B, Recession index K (time per log cycle of streamflow recession) and 

best-fit line; C, The MRC, which is obtained from coefficients of function in B.
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B7

tendency shows a continuous relation between the 

recession rate and the flow; in other words, the MRC 

can be curved but does not show abrupt changes in 

slope. An abrupt change in slope may be attributed to 

processes at work during a specific recession segment; 

these processes are dependent on, for example, the areal 

distribution of recharge before that particular event. 

Anderson and Burt (1980) stated that such breaks in 

slope may prove to be apparent rather than real and 

may not indicate a change in flow process. Trainer and 

Watkins (1975, p. 37) identified compound MRC's with 

abrupt slope changes but stated that the discharge at 

which inflection occurs differs from year to year in a 

given basin. Detailed output files that are generated by 

the computer program yielded evidence that continuity 

is reasonable for basins in this study area.

DEFINITION OF THE MASTER RECESSION 

CURVE IN THE STUDY AREA

The computerized method of Rutledge (1993) was 

used to determine the MRC of ground-water discharge 

for all 157 streamflow-gaging stations. The entire 

period of record was used, but recession segments that 

began from June through August were eliminated from 

consideration to reduce the effects of evapotranspiration. Table 2 (follows "References") shows the years of 

record and the number of recession segments that were 

utilized for each station. The MRC is defined with the 

greatest accuracy for stations that have the longest 

period of record. The variables that describe the MRC, 

which are listed in table 2, are illustrated in figure 3. 

These include the coefficients A, B, and C, of equation 3, 

in addition to the variables MinLogQ and MaxLogQ, 

which are the smallest and the largest values of the 

LogQ respectively, among all the recession segments 

that are selected. MinLogQ and MaxLogQ define the 

lower and upper limits for the applicability of the equation.

When the values of the variables above have been 

computed for each basin (table 2), the MRC's can be 

plotted for the purpose of defining similarities or dissimilarities among the various parts of the study area. 

Figures 4 through 6 show MRC's that are typical for the 

three physiographic provinces. All graphs are shown at 

the same scale. From the perspective of ground-water 

hydrology, the important features of an MRC are its 

inclination and shape. Vertical differences in positions 

of MRC's are due mainly to differences in drainage area 

above the streamflow-gaging stations. Because of the 

notable variation between the northern and southern

in 

mLL

o

OQ ,-. 

=) O

O 2>

o

2 111

I Q-

-MaxLogQ

f = A(Log Q)+B (Log Q) + C

MinLogQ

TIME, IN DAYS (t)

EXPLANATION

A, B, C Coefficients of the equation defining the 

Master Recession Curve (eq 3)

MaxLogQ The maximum value of the logrithm of flow 

among all recession segments selected

MinLogQ The minimum value of the logarithm of flow 

among all recession segments selected

FIGURE 3. Schematic representation of the master recession 

curve and the variables that define it.

parts of the Blue Ridge Physiographic Province, two 

graphs are shown (fig. 6). Figures 4 through 6 will be 

discussed further.

Although the variables described above precisely 

identify the MRC, two variables inclination and 

shape need to be added. These two variables represent the basic characteristics of the MRC for the purpose 

of testing relations between hydrogeologic variables 

and MRC characteristics. The inclination is represented 

by the median value of the recession index among all 

recession segments that are selected (table 2). For the 

157 basins, this variable ranges from 22 to 168 days, and 

the 25th, 50th, and 75th percentiles of its distribution 

are 58, 72, and 100 days, respectively. The shape is represented by the second derivative of the MRC (eq 3), 

which is equal to 2 X A. This variable is positive if the 

MRC is concave (as viewed from above), negative if the 

MRC is convex, or 0 (or nearly 0) if the MRC is linear (or 

nearly linear). This variable ranges from -180 to 310, 

and the 25th, 50th, and 75th percentiles of its distribution are -2, 40, and 90, respectively.
B8 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

1,000

O

O

HI

W 100

CC

HI

0_

HI 

HI 

LL

O 

CD

D 

O

- 10

1

116

- 140

-67

-25

0 20 40 60 80 100 120

TIME, IN DAYS

FIGURE 4. Typical master recession curves of ground-water discharge for streams in the Valley and Ridge Physiographic 

Province. [Each curve is assigned a number that corresponds to map numbers in fig. 1 and table 2 (follows "References").]

1,000

Q

Z 

O 

O

S 100

CC 

HI 

Q_

HI 

HI 

H.

O 

CD

O

^ 10

1

-51

"13

87

0 20 40 60 80 100 120

TIME, IN DAYS

FIGURE 5. Typical master recession curves of ground-water discharge for streams in the Piedmont Physiographic Province. 

[Each curve is assigned a number that corresponds to map numbers in fig. 1 and table 2 (follows "References").]
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B9

1,000

100

10

O 

O LU 

CO

CC 

LU 

Q_

ti 1

LL 10,000 

O

CD

=5 

O

g

LL

1,000

North

100

10

South

-29

 37

20 40 60 

TIME, IN DAYS

80 100 120

FIGURE 6. Typical master recession curves of ground-water discharge for streams in the Blue Ridge Physiographic 

Province shown for stations north and south of latitude 37. [Each curve is assigned a number that corresponds to map 

numbers in fig. 1 and table 2 (follows "References").]
BIO REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

VARIATION IN RECESSION CHARACTERISTICS 

IN THE STUDY AREA

Although no strict generalizations can be made 

about the factors that determine base-flow-recession 

characteristics throughout the study area, some attempt 

is made here to show graphically the ways in which 

characteristics vary. The variation in the slope of one 

MRC and the variations in base-flow-recession characteristics among basins can be related to variation of 

transmissivity, specific yield, and the average distance 

from a stream to the hydrologic divide (eq 2).

As transmissivity becomes larger, the recession 

index becomes smaller (more rapid recession), but as 

the specific yield becomes larger, the recession index 

becomes larger (slower recession of flow). This direct 

opposition of the effects of transmissivity and specific 

yield can complicate the interpretation of ground-water 

recession as it relates to water-supply potential because 

it is usually considered to be favorable for water-supply 

purposes if T and Sy are large. A large recession index 

is often equated with the best conditions for water supply. This may often be reasonable because the aquifer 

may have a large specific yield, which may reflect reliability of water supply during periods of drought. 

However, a large recession index also may result from 

small transmissivity, which generally indicates small 

well yields.

The recession index is slightly smaller in the Valley 

and Ridge Physiographic Province, and its distribution 

shows less scatter than the other provinces (fig. 7). A 

possible explanation for small recession indexes in the 

Valley and Ridge Physiographic Province is that larger 

transmissivities are associated with limestone and dolomite aquifers in the area. The second derivative of the 

MRC is considerably smaller in the Piedmont as compared with the other provinces negative values are 

observed for a large number of streams in the Piedmont, for only a small number of Blue Ridge streams, 

and for no Valley and Ridge streams (fig. 7). This tendency also is evident from figures 4 through 6, which 

show MRC's that are "typical" for each of the provinces all MRC's for the Valley and Ridge Physiographic Province are concave (fig. 4), and most MRC's 

for the Blue Ridge Physiographic Province are concave 

(fig. 6), while several MRC's in the Piedmont Physiographic Province are convex (fig. 5). More than one-half 

of the streams in the Piedmont show convexity (fig. 7), 

and the tendency is spatially correlated (fig. 8).

The shape of an MRC can be related to variations in 

T/Sy with ground-water levels because lower parts of 

the MRC correspond to lower ground-water levels in 

the basin. Concavity of the MRC could theoretically be 

caused by the decrease in aquifer transmissivity that

occurs as the zone of saturation becomes thinner, but 

the amount by which the thickness of the saturated 

zone actually decreases is probably not enough to 

explain observed concavity. The effect also could be 

caused by an increase in specific yield that may occur as 

the water table declines through zones of varying lithology If the specific yield becomes smaller as the water 

table declines, then the MRC may be convex. This may 

be one reason for the convexity of MRC's in the Piedmont Physiographic Province crystalline rocks may 

exhibit reduction of specific yield with depth. Olmsted 

and Hely (1962, p. 20) stated that the gravity yield in the 

basin of Brandywine Creek basin in the Piedmont of 

Pennsylvania decreases rapidly with depth. Barksdale 

and others (1943, p. 143) stated that the specific yield of 

rocks of the Triassic system in New Jersey decrease with 

depth. Stewart (1962) showed graphically that as depth 

increases, specific yield continuously decreases at a site 

north-northeast of Atlanta, Georgia, in the Blue Ridge 

Physiographic Province.

Concavity of the MRC can occur for basins with 

large relief for the following reasons. As ground-water 

levels decline, some stream segments may go dry. This, 

in turn, causes an increase in the distance from some 

points on the hydrologic divide to the nearest active 

stream segment, which results in an increase in the 

average distance from the stream to the hydrologic 

divide (a) (J.F. Daniel, U.S. Geological Survey, oral commun., 1993). The positive relation between a and the 

recession index is shown in equation 2. Concavity may 

be more prevalent in the Blue Ridge Physiographic 

Province than in the lithologically similar Piedmont 

because of the greater relief in the former (fig. 9). The 

tendency of concavity of the MRC in the Blue Ridge 

Physiographic Province caused by variation in the average distance from the stream to the divide may outweigh the tendency for convexity as a result of the 

reduction of specific yield as the water table recedes. 

Amounts of scatter in the relations between basin relief 

and median basin recession characteristics are considerable (fig. 10). The slight positive relation between relief 

and the second derivative of the MRC in the Blue Ridge 

Physiographic Province indicates that concavity tends 

to increase with relief.

Concavity of the MRC can result when the stream is 

fed by more than one aquifer. Riggs (1964, p. 353-354, 

fig. 1) explained and showed graphically that when a 

stream is fed by two aquifers, the various combinations 

of two straight-line recession curves (each of which represents one of the aquifers) result in a family of concave 

recessions that blend into a flatter curve at the lower 

end. The analyses of stream-flow records for this 

project do not indicate a flatter curve at the lower end 

but instead demonstrate a continuous nonlinear ten-
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B11

IOU

CO

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go

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T n

T

VALLEY BLUE 

AND RIDGE 

RIDGE

PIEDMONT

PHYSIOGRAPHIC PROVINCE

VALLEY BLUE PIEDMONT 

AND RIDGE 

RIDGE

PHYSIOGRAPHIC PROVINCE

EXPLANATION

Percentile-Percentage of 

values equal to or less 

than indicated values

-r 90th

T

75th

50th (Median) 

25th 

10th

FIGURE 7. Distribution of the median basin recession index and the second derivative of the master recession curve 

for basins in the three physiographic provinces. (N is the number of gaging stations in the sample.)
B12 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

PENNSYLVANIA

KENTUCKY

TENNESSEE

NORTH 

CAROLINA

Valley and Ridge

oeraphic Province

Blue Ridge Physiographic 

Province

Piedmont Physiographic 

Province

Modified from Fenneman, 1946

Concave master 

recession curve

(A) Convex master 

recession curve

Base from U.S.Geological Survey 

National Atlas, 1970,1:7,500.000 50 100 150 200 MILES

I I I I I

0 50 100 150 200 KILOMETERS

FIGURE 8. Locations of gaging stations for which master recession curves are concave and convex.
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B13

20

15

- 10

I I T 

/V=44

= 54

T

VALLEY AND 

RIDGE

BLUE RIDGE PIEDMONT

EXPLANATION

Percentile-Percentage of 

values equal to or less 

than indicated values

-r 90th

75th

50th (Median) 

25th 

10th

PHYSIOGRAPHIC PROVINCES

FIGURE 9. Distribution of basin relief in the three physiographic provinces. (The quantity 

N is the number of basins in the sample.)

Q° 

co UJ Q-1

O DC

UJ UJ

DC (X

Z M

SI

zi

UJ

100

§

0

300

200

-i

Oo

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§8 

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Si o

Q DC 

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VALLEY AND RIDGE 

PHYSIOGRAPHIC PROVINCE

BLUE RIDGE 

PHYSIOGRAPHIC PROVINCE

PIEDMONT 

PHYSIOGRAPHIC PROVINCE

,+ +

* +H 

^

10 20 0 10 20 30 0 

BASIN RELIEF, IN PERCENT

10

FIGURE 10. Relations between basin relief and the median basin recession index and between basin relief and the second 

derivative of the master recession curve for the three physiographic provinces.
BH REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

dency. This may indicate the effects of more than two 

aquifers. The concavity that results from this multipleaquifer effect may be particularly evident in the Valley 

and Ridge Physiographic Province because of differences between the lithologies of the low-lying valleys 

and those of the surrounding ridges. This may explain 

why all streams in the Valley and Ridge Physiographic 

Province exhibit concavity.

The median basin recession index is notably small 

for basins that have extremely small relief (close to 

zero) in the Piedmont Physiographic Province (fig. 

10). If the relief gradually increases above zero, then 

the increase in the recession index is marked. However, 

when relief exceeds some small value, the recession 

index exhibits no further increase. This effect may exist 

only for basins that have extremely small relief, such as 

those of the Piedmont Physiographic Province. The 

effect may not manifest itself in other areas of similar 

geology, such as the Blue Ridge Physiographic Province, because extremely small values of basin relief have 

not been sampled (fig. 9).

Convexity also may be caused by downward leakage to deeper ground-water-flow systems (Singh, 1969; 

Daniel, 1976). Chlorofluorocarbons were used to age 

date ground water in Prince William County, Virginia, 

by Nelms and Ahlin (1993), who found that young 

waters (post-1945) are present at depths of greater than 

200 ft and that the median age of water from fracturedrock aquifers in the Piedmont is generally younger than 

that of water from the Coastal Plain aquifers. Swain 

(1993) identified zones of high well yield in the Piedmont between depths of 350 and 650 ft, which indicates 

the potential for deep ground-water flow.

The characteristics of the MRC vary with precipitation differently in the three physiographic provinces 

(fig. 11). Variations with precipitation are slight and 

only evident for the Blue Ridge Physiographic Province, where the tendency is slight for the recession 

index and the second derivative of the MRC to increase 

with precipitation. The increase in the recession index 

with precipitation may be evident from figure 6, which 

shows that MRC's have a larger recession index in the

VALLEY AND RIDGE 

PHYSIOGRAPHIC PROVINCE

BLUE RIDGE 

PHYSIOGRAPHIC PROVINCE

PIEDMONT 

PHYSIOGRAPHIC PROVINCE

o cc

LJJ LJJ

CC 0.

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Q CC

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100

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200

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1

+ + +

Y, - \£+ ++

-&M*++; * -

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30 40 50 60 40 50 60 70 80 90 40 

PRECIPITATION, IN INCHES PER YEAR

50 60

FIGURE 11. Relations between precipitation and the median basin recession index and between precipitation and the second derivative of the 

master recession curve for the three physiographic provinces. (The rate of precipitation is the mean for the period from 1961 to 1990.)
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B15

southern part of the Blue Ridge Physiographic Province 

than in the northern part. The rate of precipitation is 

considerably higher in the southern part of that province than in the northern part (fig. 12).

a: 80

LU

70

60

50

40

30

34 35 36 37 38 39 

LATITUDE, IN DEGREES NORTH

40

FIGURE 12. Relation between latitude and precipitation for the 

Blue Ridge Physiographic Province. (The rate of precipitation is the 

mean for the period from 1961 to 1990.)

Relations between the capacity of rocks to yield 

water to wells and the recession characteristic of basins 

are slight and can be obscured somewhat by scatter, as 

shown in figures 13 and 14. Because there are no rocks 

with high well yields in the Blue Ridge Physiographic 

Province, these illustrations are presented for the Valley 

and Ridge and the Piedmont Physiographic Provinces 

only. In both physiographic provinces, the relation 

between the water-transmitting capacity of rocks as 

measured by well yield and specific capacity and the 

recession index is notably positive. Figures 13 and 14 

may indicate that the capacity of aquifers to transmit 

water to wells is dependent on the specific yield of 

aquifers. If transmissivity were the only variable that 

determined well yield, then rocks with high well yields 

would coincide with small recession indexes (eq 2). 

However, because these rocks coincide with large recession indexes, the specific yield may be significantly 

larger for rocks with high well-yielding properties than 

for rocks with low well-yielding properties.

ESTIMATES OF DIFFUSIVITY, SPECIFIC YIELD, 

AND TRANSMISSIVITY

The hydraulic diffusivity of the aquifer can be determined by the following rearrangement of equation 1:

0.933a 2 

K

(4)

Although estimates could be made for specific 

basins, the intent here is to give estimates of the range 

of most diffusivities in the APRASA area. For this estimate, it is reasonable to begin with lower and upper 

limits between which most values would fall. In figure 

7, most values of K fall between 60 and 110 days; the 

median is about 70 days. Initial estimates for the range 

of a, which are obtained by scanning the literature (Hely 

and Olmsted, 1963; Horton, 1945; Langbein, 1947; 

Trainer, 1969; Trainer and Watkins, 1975), include lower 

and upper limits of 1,000 ft and 2,000 ft, respectively; an 

initial estimate of the median is about 1,300 ft. By solving equation 4 for various combinations, it is estimated 

that most diffusivities will range from 8,000 to 60,000 

ft2 /d. The central tendency for the distribution of diffusivity, which is calculated from the median values of K 

and a, is about 20,000 ft2 /d.

Transmissivity can be estimated by rearranging 

equation 4 as follows:

T -

0.933Sya 2 

K

The solution of this equation requires an estimate of 

the apparent specific yield of the aquifer, which is considered to be the "gravity yield" of the zone of watertable fluctuation. Because the estimation of the apparent specific yield requires considerable ground-waterlevel monitoring in a basin in combination with an estimate of the volume of outflow from ground water, only 

a few estimates are available (table 5). To estimate the 

range within which most values of transmissivity in the 

APRASA area will occur, a method is used that is similar to that described above for estimating a range for 

diffusivities. A simplistic approach is used, wherein all 

the numbers for specific yield in table 5 are considered 

to be a sample, and the 25th, 50th, and 75th percentiles 

are determined. The resulting numbers, which are 0.01, 

0.04, and 0.08 after conversion to decimals, are then 

combined with the corresponding ranges for K and a; it 

is estimated that most transmissivities will range from 

80 to 5,000 ft2 /d and that the central tendency is about 

900 ft2 /d in the APRASA area.
B16 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

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BASINS BASINS 0 5 10 1!

URYDRn<^N URYD!nrAlq AREALLY WEIGHTED AVERAGE SPECIFIC CAPACITY 

WITH WITH OF ROCK TYPES IN THE BASIN, IN GALLONS

PREDOMINANTLY PREDOMINANTLY PER MINUTE PER FOOT OF DRAWDOWN

SMALL WELL LARGE WELL

YIELDS YIELDS

EXPLANATION 

Percentile-Percentage of

values equal to or less 

than indicated values

90th

75th

50th (Median) 

25th

-L- 10th

FIGURE 13. Relation between hydrologic characteristics of rocks in basins and the median basin recession index 

for the Valley and Ridge Physiographic Province. (Hydrologic characteristics of rocks in basins are explained in 

the Appendix. N is the number of basins in the sample.)
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B17

200

UJ _j 

O

O 150

cc

UJQ_

03

100

X

UJ 

Q

z

z 

o

50

UJ

o

UJ 

DC

0

A/=2T

A/=11

T

T

150

100

50

0

BASINS 

UNDERLAIN 

BY ROCKS

WITH

PREDOMINANTLY

SMALL WELL

YIELDS

BASINS 

UNDERLAIN 

BY ROCKS

WITH

PREDOMINANTLY

LARGE WELL

YIELDS

0 1 2

AREALLY WEIGHTED AVERAGE SPECIFIC CAPACITY

OF ROCK TYPES IN THE BASIN, IN GALLONS

PER MINUTE PER FOOT OF DRAWDOWN

EXPLANATION

Percentile-Percentage of 

values equal to or less 

than indicated values

90th

75th

50th (Median)

25th

-L- 10th

FIGURE 14. Relation between hydrologic characteristics of rocks in basins and the median basin recession 

index for the Piedmont Physiographic Province. (Hydrologic characteristics of rocks in basins are explained in 

the Appendix. The variable Nis the number of basins in the sample.)
B18 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

TABLE 5. Estimates of the apparent specific yield in the study area

Source citation Location of basin

Specific

yield, in

percent

Becher and Root (1981, p. 12) 

Becher and Taylor (1982, p. 32) 

Duigon and Dine (1987, table 3).

Hoos, (1990, table 4).

Lloyd and Growitz (1977, p. 29) 

Meisler (1963, p. 32) 

Nutter and Otton (1969, p. 28) 

Olmsted and Hely (1962, p. 18) 

Trainer and Watkins (1975, p. 40)

Wood and others (1972, p. Ill)

Conodoguinet River Basin in the Valley and Ridge 5.0 

Physiographic Province in Pennsylvania (Great Valley).

Shales of the Martinsburg Formation in the Valley and Ridge .5 

Physiographic Province in Pennsylvania.

Frederick County Maryland:

Blue Ridge Physiographic Province:

Catoctin Creek Basin 8.0 

Hunting Creek Basin 1.2 

Fishing Creek Basin 21.0

Piedmont Physiographic Province:

Monocacy River Basin 1.6 

Bennett Creek Basin 6.3

Tennessee:

Valley and Ridge Physiographic Province:

Lick Creek Basin 1.0 

South Chestuee Creek Basin 1.1

Blue Ridge Physiographic Province:

Doe River Basin 1.0 

Little River Basin 14.0

Muddy Creek Basin in the crystalline rocks of the Piedmont 8.0 

Physiographic Province in Pennsylvania.

Lebanon Valley carbonates, in the Valley and Ridge Physio- 5.0 

graphic Province of Pennsylvania (Great Valley).

Quartz-mica schist of the Wissahickon Formation in the Pied- 8.0 

mont of Maryland.

Brandywine Creek Basin in the crystalline rocks of the Piedmont 7.5-10 

Physiographic Province in Pennsylvania.

Potomac River Basin:

Fractured rock with thin regolith .5 

Fractured rock with thick regolith 1.0 

Carbonate rocks 3-4

Schantz Spring Basin in the Valley and Ridge Physiographic 4.1 

Province in Pennsylvania (Great Valley).

RELATIONS AMONG THE RECESSION INDEX 

AND LOW-FLOW VARIABLES

Because low-flow variables are measurements of 

flow after periods of sparse recharge, their magnitudes 

can be related to the rate of recession. Variables such as 

the annual minimum average 7-consecutive-day lowflow discharge with a 2-year recurrence interval (7Q2) 

and a 10-year recurrence interval (7Q10), have been 

related to the recession index (Harkins, 1982; Bingham, 

1982, 1986; Vogel and Kroll, 1992). Johnston (1971) 

showed that in the Coastal Plain, another low-flow variable, the flow at 90-percent duration, is related to the 

hydraulic diffusivity of the aquifer, T/S which is as

shown related to the recession index, equation 4. How 

the recession index is related to low-flow variables 

needs to be demonstrated because of the abundance of 

past work that relates low-flow variables to the hydrogeologic framework (Hely and Olmsted, 1963; 

Schneider, 1965b; Trainer and Watkins, 1975; White, 

1977; Armbruster, 1976; Hayes, 1991).

The 7Q2 is positively related to the median basin 

recession index (fig. 15A) and the mean ground-water 

recharge (fig. 15B). The former relation (fig. 15A) indicates that to some extent, the recession index can determine the 7Q2. For example, a large recession index will 

mean that the rate of recession of flow is small and that 

the residual flow after the period of recession is, there-
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B19

1.2

1.0

0.8

UJ

i 0.6

SQUARE PER 

0 ho *.

Q

SECOh FEET PER1x3 M°

m 1.0

ID 

O

I 0.8

g

g 0.6

g

0.4

0.2

0

<

i i 

A

-

-

+

++> I

"trtKrH" +a+

 if= JHf^ JLi 

5 50 75 

RECESSION INDEX,

I I

B

-

'

A +

+ + + , ^+ £ ++4

Jpf^ + :

) 10 20

+ ' +

+

+

+ +

+

iC++: + ;

"*"

i i

100 125 150 

IN DAYS PER LOG CYCLE

I i

+ -*

+

+

+ +

+

i i

30 40 50

MEAN RECHARGE, IN INCHES PER YEAR

FIGURE 15. The 7-day, 2-year low flow (7 Q2) shown as a 

function of ( A) the median basin recession index and ( B) the 

mean recharge for streamf low-gaging stations in the study area. 

(The period of calculation is from 1961 to 1990.)

fore, large. Conversely, a small recession index will 

result in rapid attrition of flow and, therefore, a smaller 

residual flow. The latter relation (fig. 15B) indicates that 

after some period of sparse recharge, the residual flow 

(7Q2) may be dependent on the long-term rate of 

recharge. This could be conceptualized as a relation 

that is separate from the one that involves the recession 

index. If two basins have the same recession index, yet 

one exhibits larger recharge over time, then the recession curves may have the same slope, but one will be 

displaced upward relative to the other, which will result 

in a larger residual flow after prolonged periods of 

sparse recharge. The 7Q2 is determined by using methods described by Hayes (1991), and recharge is determined by using the Rorabaugh Method, which is 

computerized (Rutledge, 1993).

If the two x-axis variables in figure 15 are considered 

to be the variables that determine the value of the 7Q2, 

then it may be proposed that the considerable scatter in 

each plot is due to variations in the determining variable in the other plot. A new determining variable,

which accounts for the recession index and the 

recharge, is introduced. This new variable is considered 

to be an estimator of the 7Q2 and is the best-fit linear 

equation of 7Q2 as a function of the median basin recession index and the mean basin recharge:

E = (0.00445 Km ) + (0.022258 GWR) - 0.401682, 

where

E is the estimator of the 7Q2, in cubic feet per 

second per square mile,

Km is the median basin recession index, in days 

per log cycle, and

GWR is the mean rate of ground-water recharge 

for the basin, in inches per year.

A plot of the 7Q2 as a function of the estimator 

shows a clear positive relation with relatively small 

scatter (fig. 16). This and the previous figure demon1 0

0.8

O ^ 0.6 MO

o ^ 

? uj 0.4

_ Q0.2

A

-0.5 0 0.5 1

ESTIMATOR OF LOW FLOW, IN CUBIC FEET PER 

SECOND PER SQUARE MILE

1.5

FIGURE 16. The 7-day, 2-year low flow (7Q2) plotted against an 

estimator of the low flow that is a linear function of the median 

basin recession index and the mean recharge for streamflow-gaging 

stations in the study area.

strate that the 7Q2 is related to the recession index, but 

the considerable scatter in the relation is due to variations in recharge. Conversely, the 7Q2 is related to the 

rate of recharge, and a considerable amount of the scatter in the relation is due to variations in the recession 

index.

ANALYSIS OF BASE FLOW AND 

HYDROLOGIC BUDGETS

The main purpose of base-flow analysis is to estimate the mean rates of ground-water recharge and discharge, which are important components of the 

hydrologic budgets of basins. The methods are applied 

over a long period of record (several years), so that the
B20 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

effects of changes in storage can be considered to be negligible. The mean ground-water discharge (base flow), 

therefore, may be considered to be equal to effective 

recharge. The mean ground-water recharge should 

exceed the mean effective recharge by an amount equal 

to riparian evapotranspiration, which is the loss of water 

to the atmosphere from ground water and from the 

stream channel.

Estimates of components of the hydrologic budgets of 

basins are presented for two periods 1981 to 1990 and 

1961 to 1990. The 157 basins that are used in this report 

(fig. 1) have complete records for 1981 to 1990, and 89 of 

these have complete records for 1961 to 1990. This 30- 

year period is used for construction of the "best" estimates of hydrologic budgets because this period should 

be representative of long-term conditions and corresponds to that of "normal" precipitation data available 

from the National Climatic Data Center (Appendix).

HYDROLOGIC BUDGET EQUATIONS

The various components of the hydrologic budgets 

of basins in the APRASA are estimated by using three 

equations, which are presented here. These equations 

begin with the most basic and continue with those that 

include ground-water terms. Ground-water withdrawals and leakage to or from deeper ground-water-flow 

systems are assumed to be negligible. In the simplest 

form, the hydrologic budget of a basin in the APRASA 

can be expressed as follows:

PR = ET+SF, (5)

where

PR is the mean precipitation, in inches per year,

ET is the mean evapotranspiration, in inches per

year, and 

SF is the mean streamflow, in inches per year.

The variable PR is obtained as described in the 

appendix, the variable SF is obtained from USGS 

streamflow records; and the variable ET, which represents total evapotranspiration, is estimated simply as 

the difference.

The streamflow can be expressed as the sum of a 

surface and a subsurface term:

SF = DR + GWD (6)

where DR is the mean direct runoff in inches per year, 

and GWD is the mean ground-water discharge (base 

flow), in inches per year.

The following equation is used to account for 

ground-water recharge:

GWR = GWD + RET, (7)

where RET is the mean riparian evapotranspiration, in 

inches per year.

ESTIMATES OF GROUND-WATER RECHARGE

AND DISCHARGE AND RIPARIAN-ZONE

EVAPOTRANSPIRATION

Two computerized methods are used in base-flow 

analysis recession-curve displacement, which estimates 

ground-water recharge, and base-flow-record estimation, 

which estimates ground-water discharge. The documentation of the computerized methods used here (Rutledge, 

1993) includes detailed discussion of the mathematical 

development of the methods, instructions for execution 

of the programs, and comparisons between results of the 

programs and those of the corresponding manual methods. Results of the computerized recession-curve-displacement method are tested by comparison with results 

of the corresponding manual method (Rutledge and 

Daniel, 1994).

The recession-curve-displacement method, or the 

Rorabaugh Method (Rorabaugh, 1964; Daniel, 1976), is 

based on the estimation of the total potential groundwater discharge of the aquifer at a critical time after the 

peak. Two estimates of the total potential ground-water 

discharge are obtained for each streamflow peak one 

extrapolated from the period of recession that precedes 

the peak and the other from the period that follows the 

peak. The recharge is determined from the difference. 

The method, which can be applied to a long period of 

record to give an estimate of the GWR, was applied in 

earlier studies by using manual methods (Wilder and 

Simmons, 1978, 1982; Daniel and Sharpless, 1983; Bevans, 1986; Gerhart and Lazorchick, 1988; Faye and Mayer, 

1990; Hoos, 1990).

The computerized method of base-flow-record estimation, which was adapted from earlier methods called 

streamflow partitioning (Knisel and Sheridan, 1983; Shirmohammadi, Knisel, and Sheridan, 1984; Shirmohammadi, Sheridan, and Knisel, 1987), consists of the 

estimation of a daily record of ground-water discharge as 

part of the total stream-discharge record. The algorithm 

scans the record for days that fit a requirement of antecedent recession, designates ground-water discharge to 

be equal to streamflow on these days, and then linearly 

interpolates the daily record of ground-water discharge 

for days that do not fit the requirement of antecedent 

recession. The practice of base-flow-record estimation, 

which is usually applied to a long period of record to 

give an estimate of the GWD, has been applied earlier by 

manual methods (Horton, 1933; Barnes, 1939; Snyder, 

1939; Olmsted and Hely 1962; Chow, 1964).
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B21

Correlation is good between ground-water recharge 

and discharge (fig. 17). The distributions of recharge 

and discharge are shown in table 6 for 1981 to 1990, during which complete records were available for 157 

basins, and for 1961 to 1990, during which complete 

records were available for 89 basins.

50

40

til 30 

O CC <

O

LLJ

cr 

£ 20 I

Q

Z

o 10 

o

Line of zero

riparian-zone

evapotranspiration

0 10 20 30 40 50 

MEAN GROUND-WATER DISCHARGE, IN INCHES PER YEAR

FIGURE 17. Relation between mean ground-water recharge and 

discharge. (Data points represent the mean rates from 1981 to 

1990 for 157 streamflow-gaging stations in the study area.)

10

Q

^o: 

z <

1> 6

UJ CC

O tu 

CC Q- 

< CO g£

B!§ 4

£i ^

Q 9 

Z ^

o

CC

o

+ +

10 20 30

MEAN GROUND-WATER RECHARGE, 

IN INCHES PER YEAR

40

TABLE 6. Statistical distribution of recharge and discharge, in inches per 

year, for basins in the study area

1981 to 1990 

(sample size, 157)

1961 to 1990 

(sample size, 89)

Mean Mean Mean Mean 

recharge discharge recharge discharge

Maximum

75th percentile

Median

25th percentile

Minimum

46

18

13

10

5

42

16

12

9

4

50

19

13

10

6

46

17

12

9

5

Theoretically, riparian evapotranspiration is the difference between mean ground-water recharge and discharge (eq 7). This difference, which shows a positive 

relation to ground-water recharge (fig. 18), has the potential for considerable error in its representation of riparian 

evapotranspiration because it is calculated as the difference between two other variables that are about an order 

of magnitude larger. However, the range of RET in the 

APRASA area can be assumed to be as depicted in figure 

18B. After elimination of the apparent outlier at 8.4 in/ 

yr, RET ranges from 0.4 to 3.8 in/yr, and the 25th, 50th, 

and 75th percentiles of the distribution are 1.0, 1.4, and 

2.1 in/yr, respectively. Ground-water evapotranspiration was estimated to be about 3 in/yr for three Coastal 

Plain basins in the Delmarva Peninsula (Johnston, 1976) 

and 2.4 in/yr for a stream in Alabama (Daniel, 1976).

B EXPLANATION

Percentile-Percentage of 

values equal to or less 

than indicated values

90th

75th

50th (Median) 

25th 

10th

50

FIGURE 18. Mean ground-water recharge minus mean ground-water discharge. A, As a function of the mean ground-water recharge; B, 

As a box plot. (The sample represents mean rates for 157 streamflow-gaging stations in the study area from 1981 to 1990.)
B22 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

VARIATION IN RECHARGE IN THE STUDY AREA

A plot of recharge as a function of precipitation for 

the APRASA area shows a positive correlation with a 

considerable amount of scatter (fig. 19). The best-fit lin50

£ 40

CL

CO

LU

O 30

LU 

020

<

O

LU

cc 10

y=0.862X- 24.04 _

30 40 50 60 70 80 

PRECIPITATION, IN INCHES PER YEAR

90

FIGURE 19. Relation between precipitation and the rate of recharge 

for the study area. (Rates shown are the mean from 1961 to 1990.)

ear equation has roughly unit gradient (0.86) and an Xintercept that is close to 28 in/yr. The X-intercept may 

be dependent, for the most part, on evapotranspiration 

and may represent a threshold that must be exceeded 

by precipitation before recharge is significant. The 

median evapotranspiration for the study area, which 

was calculated from equation 5, is 26 in/yr. Similar 

plots generated for each physiographic province show 

that the widest range of precipitation (and thus 

recharge) occurs in the Blue Ridge Physiographic Province (fig. 20); the highest rates of precipitation tend to be 

in the southern parts of that province (fig. 12).

Plots of recharge as a function of basin relief differ 

among the three physiographic provinces. A slight negative relation between recharge and relief is suggested in 

the Valley and the Ridge Physiographic Province; however, the relation is clearly positive in the Blue Ridge and 

Piedmont Physiographic Provinces (fig. 21). The reason 

for the positive correlation is not known a negative correlation is more easily reconciled because as relief 

increases, the direct runoff would seem to increase, thus 

reducing the amount of infiltration. The positive correlation may be related to a slight increase in precipitation as 

relief increases. This, in turn, is related to orographic 

effects because areas of high elevation tend to be areas of 

greater relief.

In the Blue Ridge and the Piedmont Physiographic 

Provinces (combined), a reasonably good estimator of 

recharge can be derived from precipitation and basin 

relief (fig. 22). The estimator is obtained from the best-fit 

linear equation of recharge, which is a function of precipitation and relief,

Er = (0.70963 PR) + (0.88927 REL] - 22.996,

where Er is the estimator of recharge, in inches per year, 

and jREL is the median basin relief, in percent. Other 

such attempts were made to relate physical properties to 

recharge in other parts of the APRASA study area, with 

little success.

For the most part, the relations are not clear between 

the water-yielding capacity of rocks and recharge in the 

Valley and Ridge Physiographic Province (fig. 23), but 

the tendency is slightly positive in the Piedmont Physiographic Province (fig. 24).

VALLEY AND RIDGE

PHYSIOGRAPHIC

PROVINCE

BLUE RIDGE

PHYSIOGRAPHIC

PROVINCE

PIEDMONT

PHYSIOGRAPHIC

PROVINCE

QC " 

S

£ 20 

a.

CO

UJ

I 15

UJ

O 10

O

UJ

CC 5

50

40

30

20

10

++ +

-H-

+ + 

+ 

++

25

20

15

10

30 40 50 60 30 40 50 60 70 80 90 

PRECIPITATION, IN INCHES PER YEAR

30 40 50 60

FIGURE 20. Relation between precipitation and the rate of recharge for the three physiographic provinces. (Rates represent the 

mean 1961 to 1990.)
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B23

VALLEY AND RIDGE

PHYSIOGRAPHIC

PROVINCE

o: 25

LU

85 20

0.

CO 

LU

z

LU 

| 1 °

O

LU

DC 5

Z

LU

0

+ + -f- '+ '

++ +

£ + +

+++++++++ + + T + +-

.+

I I

10 15

50

40

30

20

10

BLUE RIDGE

PHYSIOGRAPHIC

PROVINCE

5 10 15 20 

BASIN RELIEF, IN PERCENT

25

25

20

15

10

 h

PIEDMONT

PHYSIOGRAPHIC

PROVINCE

10

FIGURE 21. Relation between basin relief and the rate of recharge for the three physiographic provinces. (Recharge shown is the mean 

for 1981 to 1990.)

50

40

LU 20

CD

OC

10

+ . + +

10 20 30 40 

ESTIMATOR OF RECHARGE, IN INCHES PER YEAR

50

FIGURE 22. Relation between mean recharge and an 

estimator of mean recharge that is a linear function of 

precipitation and relief for 55 streamflow-gaging stations in 

the Blue Ridge and the Piedmont Physiographic Provinces. 

(The period of calculation is from 1961 to 1990).
B24 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

30

DC

<

111 >-

DC

111

Q- 20

CO

HI I 

o

HI

I

uj 10

DC

<

HI

0

A/=17 A/=11

30

20

10

0

+ ++ +

+ +

f -b. +

+

BASINS 

UNDERLAIN 

BY ROCKS

WITH

PREDOMINANTLY

SMALL WELL

YIELDS

BASINS 

UNDERLAIN 

BY ROCKS

WITH

PREDOMINANTLY

LARGE WELL

YIELDS

0 5 10 15

AREALLY WEIGHTED AVERAGE SPECIFIC CAPACITY

OF ROCK TYPES IN THE BASIN, IN GALLONS

PER MINUTE PER FOOT OF DRAWDOWN

EXPLANATION 

Percent! le-Percentage of

values equal to or less 

than indicated values

-r 90th

75th

50th (Median)

25th

-1- 10th

FIGURE 23. Relation between hydrologic characteristics of the rocks in basins and the mean recharge for the Valley and 

Ridge Physiographic Province. (Hydrologic characteristics of rocks in basins are explained in the Appendix. Recharge is 

calculated for 1981 to 1990. N is the number of basins or sample size.)
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B25

20

DCa 15 >

DC 

LLJ 

Q_

CO 

LU

I 

O

i 10

LlT

O 

DC 

<

a

DC

0

N = 21

1

A/= 11

T

20

15

10

BASINS 

UNDERLAIN 

BY ROCKS

WITH

PREDOMINANTLY

SMALL WELL

YIELDS

BASINS 

UNDERLAIN 

BY ROCKS

WITH

PREDOMINANTLY

LARGE WELL

YIELDS

0

+

+++4+

0 1 2

AREALLY WEIGHTED AVERAGE SPECIFIC CAPACITY

OF ROCK TYPES IN THE BASIN, IN GALLONS

PER MINUTE PER FOOT OF DRAWDOWN

EXPLANATION

Percentile-Percentage of 

values equal to or less 

than indicated values

-r 90th

75th

50th (Median)

25th

-L- 10th

FIGURE 24. Relation between hydrologic characteristics of rocks in basins and the mean recharge for the Piedmont 

Physiographic Province. (Hydrologic characteristics of rocks in basins are explained in the Appendix. Recharge is 

calculated for 1981 to 1990. N is the number of basins or sample size.)
B26 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

BASE-FLOW INDEX

The base-flow index (BFI) (Nathan and McMahon, 

1990), which is calculated as the ratio of mean groundwater discharge (base flow) to mean streamflow, provides a way of normalizing ground-water discharge to 

climatic conditions. The stability of the BFI relative to 

various components of the hydrologic budget can be 

demonstrated by calculating the ratio of BFI for one 

time period to that for another time period and comparing this ratio with the corresponding ratios for various 

components of the water balance. Stability of the BFI is 

demonstrated by the proximity of the ratio to unity (fig. 

25). The stability of the BFI may make it ideal for basin

comparisons when the various basins have differing 

periods of streamflow record or the available period of 

record is short.

The BFI ranges from 32 to 94 percent, and the 25th, 

50th, and 75th percentiles are 59, 67, and 75 percent, 

respectively, for the APRASA area (sample size is 157). 

The BFI is largest in the southern part of the Blue Ridge 

Physiographic Province (fig. 26).

The BFI exhibits a clear increase with precipitation 

for the Blue Ridge Physiographic Province, but not for 

the other provinces (fig. 27). A slightly negative relation is evident for the Valley and Ridge Physiographic 

Province, although the relation shows considerable 

scatter.

1.2

HI hi

C/) 

HI

DC 

HI

6 

O 

HI

C/) 

HI

HI

6 

CO 

LL

O

o

1.0

O.i

1

T- T

i

EXPLANATION 

Percent! le-Percentage of 

values equal to or less 

than indicated values

90th

75th

50th (Median) 

25th

J- 10th

S 1

CD

DC

HUJ 

< CD

DC 

CD

LU

3

FIGURE 25. Distributions of the ratio of the 30-year estimate to the 10-year estimate for the streamflow, 

ground-water recharge and discharge, and the base-flow index. (The 30-year period is from 1961 to 

1990, and the 10-year period is from 1981 to 1990. Sample size is 89.)
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B27

IUU

Z 

LU

O

CC 

LU 

Q_

z

x"

g 50

Z

1LL.

LU

C/3

m 25

0

i i i 

North

A/=38

1 A/=16 A/=27

-x- T 

1 -

i i i

VALLEY BLUE 

AND RIDGE 

RIDGE

PIEDMONT

PHYSIOGRAPHIC PROVINCE

100

75

50

25

South

A/=16

A/=28

A/=26

I

EXPLANATION

Percentile-Percentage of 

values equal to or less 

than indicated values

-r 90th

75th

50th (Median)

25th

-L- 10th

VALLEY BLUE 

AND RIDGE 

RIDGE

PIEDMONT

PHYSIOGRAPHIC PROVINCE

FIGURE 26. Distributions of the base-flow index for basins in various parts of the study area. (The time period of calculation is from 1981 to 1990. 

For each physiographic province, the base-flow index is shown for streamflow-gaging stations north and south of latitude 37. N is the number of 

gaging stations in the sample.)

VALLEY AND RIDGE BLUE RIDGE PIEDMONT

PHYSIOGRAPHIC PHYSIOGRAPHIC PHYSIOGRAPHIC

PROVINCE PROVINCE PROVINCE

-1 f\f\ 4 nn -t rtrt

1 \J\J

z" 90

LU

O

QCLU 80

Q. 

Z 

X 70

LU 

Q

I"

3LL 50

LU

CO

CQ 40

30

.

+++

~ ~f~

++ + t + +* + +

t ~*i ^++ + + + +

+ +J +-^ -H1 _^H +

i

+ + -

i ~r

-

i i i i i

IUU

90

80

70

60

50

40

30

+ + -JJ" ~H" +

, -|--j-j_ "-p

?#} +<+ +

*" 

1- +

.

-

IUU

90

80

70

60

50

40

30

"+ ++ + ++ f + +

+ + + + +

" + +++ + ++ + + '

I ~*~ i

*~-& ~"~ + ++

I | + _j_

- + ++

+ , i

30 35 40 45 50 55 60 40 50 60 70 80 90 40 45 50 55 6

PRECIPITATION, IN INCHES PER YEAR

FIGURE 27. Relation between precipitation and the base-flow index for the three physiographic provinces. (The period of calculation is from 

1981 to 1990 for the base-flow index and from 1961 to 1990 for precipitation.)
B28 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

DURATION-CURVE SURROGATES FOR MEAN 

GROUND-WATER DISCHARGE

Many studies have used a statistic from the flowduration curve as a substitute for direct estimates of 

mean ground-water discharge (base flow). The flowduration curve, which is simply a cumulative frequency curve (Searcy, 1959), shows the percentage of 

time that specified rates of flow are equaled or 

exceeded. Some workers select a variable, such as the 

Q90 (the flow that is equaled or exceeded by 90 percent 

of the flow on record), as a conservative estimator for 

ground-water discharge (Wyrick, 1968; Lichtler and 

Wait, 1974). Others have run tests to determine the best 

surrogate for mean ground-water discharge. Gushing, 

Kantrowitz, and Taylor (1973) found that the Q50 

(median flow) was a reasonable estimate on the basis of 

comparisons of duration-curve statistics and results of 

hydrograph separation for Coastal Plain streams in the 

Delmarva Peninsula. Trainer and Watkins (1975, p. 42- 

43) stated that in the upper Potomac River Basin, "the 

estimated base-runoff discharges correspond to discharge values on the flow-duration curve that range 

from 39 to 61 percent and average 52 percent." The correct duration-curve statistic may depend on the hydrogeologic setting (Lichtler and Wait, 1974, p. 19; Wyrick 

and Lloyd, 1968, p. H-19).

The ratio of flow-frequency statistic to mean 

ground-water discharge is plotted for a range of flow1.5

1.0

1.5

1.0

O CM <fr CD 00 O

333338

0.5

B

frequency statistics to determine the best surrogate for 

the APR AS A area. As a result of experimentation, these 

statistics were found to be similar for the Blue Ridge 

and the Piedmont Physiographic Provinces and, therefore, are plotted together (fig. 28). The best surrogate 

will result in a ratio that is closest to 1.0. The surrogates 

are, therefore, determined to be Q42 for the Valley and 

Ridge Physiographic Province and Q46 for the other 

two provinces. They can be confirmed by plotting 

ground-water discharge as functions of Q42 for the Valley and Ridge Physiographic Province (fig. 29) and Q46 

for the Blue Ridge and Piedmont Physiographic Provinces (fig. 30).

COMPONENTS OF HYDROLOGIC 

BUDGETS OF BASINS

The results of equations 5 through 7 and the computer programs for estimating ground-water recharge 

and discharge, which are listed for 89 basins in table 3, 

are illustrated for various subareas of the APRASA in 

figure 31. Notable differences between the southern 

part of the Blue Ridge Physiographic Province and the 

rest of the study area are shown in table 7. Numbers 

that represent the distribution of each hydrologic budget component were determined separately. Therefore, 

the numbers in any given row in table 7 may not represent the same basin.

EXPLANATION

Percentile-Percentage of 

values equal to or less 

than indicated values

-r- 90th

O CM <* CD

3333

o

8

75th

50th (Median)

25th

__ 10th

FlGUEE 28. Ratio of six flow frequency statistics to the mean ground-water discharge. A, Valley and Ridge Physiographic Province; B, Blue 

Ridge and the Piedmont Physiographic Provinces. (The Qxx is the streamflow that is equal to or exceeded by xx percent of streamflow on record. 

The time period is from 1981 to 1990. Sample sizes are 54 for A and 97 for B.)
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B29

25

20

15

Line of equal value

5 10 15 20 

O42, IN INCHES PER YEAR

25

FIGURE 29. Relation between the Q42 flow-frequency statistic and 

the mean ground-water discharge for the Valley and Ridge 

Physiographic Province. (The Q42 is the streamflow that is equal to or 

exceeded by 42 percent of the streamflow on record. The time period is 

from 1981 to 1990. The number of data points is 54.)

50

w 30

O

QC

O 

CO 

Q

£ 20

<

Q

10

Line of equal value10 20 30 

O46, IN INCHES PER YEAR

40 50

FIGURE 30. Relation between the Q46 flow-frequency statistic and 

the mean ground-water discharge for the Blue Ridge and the Piedmont 

Physiographic Provinces. (The Q46 is the streamflow that is equal to or 

exceeded by 46 percent of the streamflow on record. The time period is 

from 1981 to 1990. The number of data points is 97.)

EFFECTS OF DRAINAGE AREA ON BASIN 

HYDROLOGIC CHARACTERISTICS

In general, basin hydrologic characteristics indicate 

diminishing variability from one basin to another as 

basin drainage area increases (fig. 32). Although part of 

this effect may be related to the reduction in sample 

number as the drainage area increases, part also may be 

attributed to an averaging of physical properties within 

the basins. This averaging effect can be demonstrated 

by using an idealized hypothetical model in which a 

number of physical variables precisely determine a 

hydrologic variable. For this simple example, the 

hydrologic variable is mean recharge, and the three 

physical variables each represent a particular geology A, B, or C. Any particular map location in the 

hypothetical model is characterized as having one of 

these geologic types. The mean rate of ground-water 

recharge at that location is determined by the geologic 

type; that is, locations with geologic type A have a rate 

of 5 in/yr; geologic type B, 10 in/yr; and geologic type 

C, 15 in/yr. The hypothetical world is mapped by polygons of various sizes and shapes that represent geologic 

types. If basins also are conceptualized as polygons of 

various sizes, then the rate of mean recharge for the 

entire basin (averaged over time and over the basin 

area) can be determined by the following

5Ga

100

15G

100 100 (8)

where Ga, G^, and Gc are the percentages of the basin 

area that is covered by geology A, B, or C, respectively.

The small basins are considerably more likely than 

the large basins to be underlain by only one geologic 

type. This characteristic causes a larger spread among 

values of mean recharge for the small basins than for 

the larger basins. This apparent effect of drainage area 

manifests itself on a graph of mean basin recharge as a 

function of basin area, and similar effects should be evident for other basin hydrologic variables (fig. 32). The 

effect of drainage area is referred to as "apparent" 

because the model shows the effect without explicitly 

using the variable "drainage area."

Other models could be constructed for determining 

the other hydrologic characteristics. Some of these 

models might have a mathematical structure that is similar to equation 8 but with different variables. In the 

case of variables such as the recession index, the mathematical model would be considerably more complex if 

it could be formulated at all but the tendency for variables to exhibit greater variations among basins of small 

drainage area would probably be similar.
B30 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

VALLEY AND RIDGE 

PHYSIOGRAPHIC PROVINCE

BLUE RIDGE 

PHYSIOGRAPHIC PROVINCE

PIEDMONT 

PHYSIOGRAPHIC PROVINCE

ou

40

30

20

10

0

or 80

55>-

cc

UJ Q. 70

O>

UJ

I

O

z 

~ 60

50

40

30

20

10

0

1 1 1 1

J

r-h " 9

-

- 8ii y E

i i i i

i i

North

N =26

-

T -

Q -

1 1

i i i i

-

- $

-

- *

- i +

_

:: +

^

i i i i

2 o ^ m g 

f 

1 

EC 

M"5 X

1 1 1 1 

s I i 1

> p 1 uj K z

-J D

£ g o o

1 1

South

N =6

-

-

-

-

-

_

$

$ + -

I i

UJ U. O u. 

cc o

< z

X D

DISC GROUND-WATER 

DIRECT R

1 I 

North

I I 

South 

A/=17

T

I I 

North 

W=13

I i 

South 

A/=15

EXPLANATION

Percentile-Percentage of 

values equal to or less 

than indicated values

-p 90th 

i " 175th

T

50th (Median) 

25th

10th

>

+ Single sample (no box)

PRECIPI TRANSP

O

Q.

* *

TOTAL E\

STREAI . 

<

u

UJ 

CC

cc

UJ

<

/-*

GROUNC

u 

v> 

o 

cc

UJ

<

GROUND

u.

t

UJ 

CC

O

FIGURE 31. Distribution of components of hydrologic budgets for basins in various parts of the study area. (All rates represent the mean from 

1961 to 1990. For each physiographic province, the estimates are shown for streamflow-gaging stations north and south of latitude 37. N is the 

number of gaging stations in the sample.)
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B31

TABLE 7. Statistical distribution of hydrologic budget components, in inches per year

Precipitation

Evapotranspiration

Ground- GroundStream- water water _. 

_ , , . , Direct runoff flow recharge discharge

Study area, except the southern part of the Blue Ridge Physiographic Province1

Maximum ... 58

75th percentile 46 

Median............ 43

25th percentile 40 

Minimum. ....... 34

35 

30 

26 

24 

16

29 24 21 

20 15 14 

16 12 11 

14 9 8 

11 6 5

12 

7 

6

5 

3

Southern part of the Blue Ridge Physiographic Province2

Maximum ... 80

75th percentile 66 

Median............ 58

25th percentile 55 

Minimum........ 44

STREAMFLOW, MEAN INNCHES PERYEAR

** rocoui-» _o o 0,0

</T£>

-|RECESSION INDEX,N DAYS PERLOG CYCLE

B"ro -L 

8 z._o .

-\- \

feRrt|id-+f"

ft.d|FlBPl.-H^|- JpQ5i$r+ j* +

1 400

is is 72. 2Sample size is 17.

i

^^ + +tt+

400

+ +

1

OUND-WATER RECHARGE, 

NCHES PERYEAR

i ro*>. coco, 

O Z 

Z 10

UJ

33 

31 

25 

18 

7

+

55 50 46 

45 38 34 

38 33 29 

26 21 19 

19 16 14

oc 

i , UJ UJ + ~

I>

oo f -tj, +

l| ^[^^$40- + + Q cc lllg^i^r- +^"

8 ~^+ + LLJ 

CO

_ann ' 1 800 0 400 

DRAINAGE AREA OF BASIN, IN SQUARE MILES

+=M^t+ 

feA +

H-mriJSlF i4t_i_ yagmfT -^-pr

800 °o

1

UJ 4- 

- | 40-

- ii».V tr cr J0 ^

f ll +4^-i ++ " ir°"f^

N-+ § -rfifc ?f+++ + + - i io »

+ 2 -Ipfilnr1 0

400 800 0

14 

9 

8 

6

5

-

800

1

HK+ + + -

1

400 80

DRAINAGE AREA OF BASIN, IN SQUARE MILES

FIGURE 32. Relation between the basin drainage area and various hydrologic variables for basins in the study area.
B32 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

Although the simple conceptual model would show a 

greater spread of mean recharge rates among basins of 

small area, all basins would exhibit mean recharge that 

agrees with the result of equation 8, regardless of the 

drainage area of the basin. A verification that no other 

effects of drainage area are taking place could be 

obtained simply by comparing the result of equation 8 

with the estimate of recharge obtained from analysis of 

the stream-flow record. In the real case of the APRASA 

project, no such simple model was obtained for the 

hydrologic variables of interest. However, some tests 

were performed to determine whether effects that cannot 

be explained simply by averaging the physical properties 

explained above were due to drainage area. Results of 

these tests indicate no readily apparent change in relation 

between large and small basins (fig. 33). A change in relation would manifest itself as a significant difference in 

graphical location between the small and large basins. If 

such a difference occurred, then it would be analogous in 

the hypothetical model to unreliability of equation 8. For 

example, it might be valid for small basins but invalid for 

large basins. Other tests not illustrated yielded results 

similar to those in figure 33.

The above discussion of variability with drainage 

area may highlight the importance of central tendencies 

of distributions of hydrologic variables relative to the 

extreme values. Drainage area may be only one of many 

physical variables that can cause extreme values of the 

hydrologic variables for various basins. For this reason, 

many of the descriptions in this report of variable distributions include statistics, such as the 25th, 50th, and 

75th percentiles.

PIEDMONT 

PHYSIOGRAPHIC PROVINCE

PIEDMONT 

PHYSIOGRAPHIC PROVINCE

VALLEY AND RIDGE 

PHYSIOGRAPHIC PROVINCE

150 200

150

100

50

n

*

n

2 4 

BASIN RELIEF, IN PERCENT

1 2 0 5 10 

AREALLY WEIGHTED AVERAGE SPECIFIC CAPACITY OF ROCK 

TYPES IN THE BASIN, IN GALLONS PER MINUTE PER FOOT

15

20

15

10

30

25

20

15

10

n n

t

246 

BASIN RELIEF, IN PERCENT

1 2 0 5 10 

AREALLY WEIGHTED AVERAGE SPECIFIC CAPACITY OF ROCK 

TYPES IN THE BASIN, IN GALLONS PER MINUTE PER FOOT

15

EXPLANATION

+ Basins smaller than or equal to 50 square miles 

D Basins larger than 50 square miles

FIGURE 33. Relation among physical and hydrologic variables for basins that are smaller than or equal to 50 square miles and larger than 

50 square miles.
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B33

SUMMARY

Interpretations of streamflow records in the Appalachian Valley and Ridge, the Piedmont, and the Blue 

Ridge Physiographic Provinces have provided estimates of hydraulic properties of shallow aquifers and 

quantified the rates of ground-water recharge and discharge. The analysis is divided into two parts streamflow recession and base flow. Streamflow recession can 

relate to the hydraulic diffusivity of the aquifers and 

their capacity to yield water during times of sparse 

recharge. Base-flow analysis consists mainly of the estimation of the mean rates of ground-water recharge and 

discharge over a long period of time (usually years).

The study area is considered to be two distinct subareas on the basis of differences in geologic and hydrologic characteristics. One subarea consists of carbonate 

rock, sandstone, and shale of the Valley and Ridge 

Physiographic Province. Generally, ridges are underlain by resistant conglomerate, sandstone, or cherty 

dolomite, whereas valleys are underlain by less-resistant siltstone, shale, limestone, or dolomite. The other 

subarea consists of metamorphic and igneous crystalline rocks in the Blue Ridge and the Piedmont Physiographic Provinces. Types of rocks include massive 

granites and gneisses, foliated phyllites and schists, and 

consolidated sandstones. Sedimentary rocks of early 

Mesozoic age fill basins within the Piedmont Physiographic Province. Regolith, which consists of soil, alluvium, and weathered rock material, overlies most of the 

bedrock units throughout both subareas.

For the purpose of this report, the base-flow MRC 

represents the recession of streamflow during times 

when all flow is from ground-water discharge, no 

ground-water recharge is occurring, and the shape of 

the ground-water-head profile is nearly stable. The 

MRC, which is a graph of flow on a logarithmic scale as 

a function of time on a linear scale, is assembled from 

numerous intervals of continuous recession. Two variables are introduced for defining recession characteristics of a basin. The first variable, which represents the 

inclination of the MRC, is the median basin recession 

index among all recession segments that are selected in 

the computerized method. The second variable, which 

represents the shape of the MRC, is the second derivative of the MRC, which is positive for concave (as 

viewed from above) curves and negative for convex 

curves.

As transmissivity increases, the median basin recession index decreases (more rapid recession of flow), but 

as the specific yield increases, the recession index 

increases (slower recession). The opposite effects of T 

and Sy can complicate the interpretation of groundwater recession as it relates to water-supply potential 

because T and Sy should be large for the most favorable 

water-supply potential. A large recession index is commonly related to good potential for water supply 

because the aquifer likely has a large specific yield, 

which may reflect reliability of water supply during 

periods of drought. However, a large recession index 

also may reflect a small transmissivity and, consequently, small well yields.

The median basin, recession index is slightly lower 

in the Valley and Ridge Physiographic Province compared with the other physiographic provinces possibly 

because of the comparatively high transmissivities of 

limestones and dolomites in this area. In the Piedmont 

Physiographic Province, the tendency is much greater 

for MRC convexity than in the other provinces; all 

MRC's for the Valley and Ridge Physiographic Province 

and most MRC's for the Blue Ridge Physiographic 

Province are concave.

The shape of the MRC can be related hypothetically 

to a variation in aquifer diffusivity with changes in 

ground-water levels. Low parts of the MRC correspond 

to low ground-water levels in the basin; thus, MRC concavity may be caused by an increase in specific yield 

that may occur as the water table declines through 

zones of variable lithology If the specific yield becomes 

smaller as the water table declines, then the MRC may 

be convex. This may be one reason for convexity of 

MRC's in the Piedmont Physiographic Province namely, specific yield of crystalline rocks may 

decrease with depth.

The MRC can be concave for basins with high relief 

because as ground-water levels decline, some streams 

may go dry, which can result in an increase in the average distance from the stream to the hydrologic divide. 

Concavity may be considerably more prevalent in the 

Blue Ridge Physiographic Province than in the lithologically similar Piedmont Physiographic Province because 

of the greater relief in the former.

Concavity of the MRC can result when the stream is 

fed by more than one aquifer. The concavity that results 

from this multiple-aquifer effect may be particularly 

evident in the Valley and Ridge Physiographic Province 

because of differences between lithologies of the lowlying valleys and adjacent ridges.

Variations in recession characteristics with variations in basin relief and precipitation are, for the most 

part, obscured by scatter. A noticeably positive relation 

between the water-yielding capacity of rocks and the 

median basin recession index may indicate that the 

capacity of aquifers in the APRASA area to supply 

water to wells depends on the specific yield of the aquifers.
B34 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

Most values of diffusivity range from 8,000 to 60,000 

ft2 /d; the central tendency is about 20,000 ft2 /d. Most 

values of transmissivity range from 80 to 5,000 ft2 /d; 

the central tendency is about 900 ft2 /d.

The 7Q2 is related to mean recharge, but a considerable amount of the scatter in the relation may reflect 

variations in the recession index. Conversely, the 7Q2 is 

related to the recession index, whereas a considerable 

amount of the scatter in the relation may be related to 

variations in recharge.

Two variables are obtained from the base-flow analysis mean ground-water recharge, which is obtained 

from the recession-curve-displacement method, and 

mean ground-water discharge, which is obtained from 

base-flow-record estimation. Among the 89 basins for 

which the 1961 to 1990 record is continuous, recharge 

ranges from 6 to 50 in/yr, and the median is 13 in/yr. 

The discharge ranges from 5 to 46 in/yr, and the 

median is 12 in/yr. Riparian-zone evapotranspiration 

is generally from 1 to 2 in/yr.

The relation between precipitation and recharge for 

the study area shows a considerable amount of scatter. 

The best-fit linear equation has roughly unit gradient 

(0.86) and an X-intercept of about 28 in/yr. The intercept may, for the most part, depend on evapotranspiration and may represent a threshold that must be 

exceeded by precipitation before recharge is significant.

Plots of recharge as a function of basin relief show a 

slight negative relation for the Valley and Ridge Physiographic Province and a clear positive relation in the 

other physiographic provinces. In the Blue Ridge and 

the Piedmont Physiographic Provinces (combined), a 

reasonably good estimator of recharge can be derived 

from precipitation and basin relief.

No clear relation between recharge and the wateryielding potential of rocks in the Valley and Ridge 

Physiographic Province was found, but a slightly positive relation is noted between recharge and the wateryielding capacity of rocks in the Piedmont Physiographic Province.

The stability of the BFI makes it ideal for basin comparisons when the various basins have differing periods 

of streamflow record or the available period of record is 

short. Among the 157 basins, the BFI ranges from 32 to 

94 percent; the median is 67 percent. The BFI is largest 

in the southern part of the Blue Ridge Physiographic 

Province.

A statistic from the flow-duration curve can be used 

as a surrogate for direct estimates of mean groundwater discharge (base flow). The best surrogates are the 

Q42 in the Valley and Ridge Physiographic Province 

and the Q46 in the Blue Ridge and Piedmont Physiographic Provinces.

Basic water-balance equations are combined with 

the results of base-flow analysis to obtain hydrologic 

budgets of basins in the study area. Except for the 

southern part of the Blue Ridge Physiographic Province, the median values for components of the budgets 

for the study area (sample size, 72) are, in inches per 

year, precipitation, 43; evapotranspiration, 26; streamflow, 16; ground-water recharge, 12; ground-water discharge, 11; and storm runoff, 6. For the southern part of 

the Blue Ridge Physiographic Province (sample size, 

17), the median values are, in inches per year, precipitation, 58; evapotranspiration, 25; streamflow, 38; groundwater recharge, 33; ground-water discharge, 29; and 

storm runoff, 8.

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 1945, Erosional development of streams and their drainage 

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 1976, Relation of ground water to surface water in four small 

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B36 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

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 1964, Estimating changes in bank storage and ground-water 

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ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B37

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TABLES 1 THROUGH 4

ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B41

TABLE 1. Physical properties of drainage basins in the Valley and Ridge, Blue Ridge, and Piedmont Physiographic Provinces Regional Aquifer-System 

Analysis Program study area

and Ridge; Province 2, Blue 

igh B2 and PI through P6,

Map 

number 

(% 1)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

U.S. Geological 

Survey 

station 

number

02408540

02462000

02401370

02401390

02400100

02399200

02213050

02212600

02221525

02220900

02338660

02337500

02337000

02395120

02398000

03568933

02381600

02380500

02333500

03558000

02178400

02177000

02185200

03567500

03543500

03497300

03466228

03491000

03550000

03504000

03500000

03500240

03512000

03439000

03455500

03456500

03460000

02149000

03463300

02137727

Latitude

32.92

33.45

33.81

33.84

34.06

34.29

32.97

33.10

33.25

33.31

33.24

33.53

33.77

34.24

34.47

34.90

34.57

34.67

34.53

34.79

34.89

34.81

34.84

35.01

35.58

35.66

36.20

36.43

35.14

35.13

35.15

35.16

35.46

35.14

35.40

35.46

35.67

35.42

35.83

35.69

Longitude

86.27

87.12

86.38

86.26

85.61

85.68

83.62

83.72

83.48

83.44

84.99

84.93

84.61

84.89

85.34

85.46

84.47

84.51

83.94

84.24

83.53

83.31

82.98

85.21

84.75

83.71

82.74

82.95

83.98

83.62

83.38

83.39

83.35

82.82

82.94

82.87

83.07

82.11

82.18

82.06

Drainage 

area

(mi2)

263.0

148.0

45.0

141.0

252.0

199.0

29.0

72.2

190.0

262.0

127.0

37.0

246.0

33.1

192.0

149.0

10.0

236.0

153.0

177.0

56.5

207.0

72.0

428.0

117.0

106.0

13.7

47.3

104.0

51.9

140.0

57.1

184.0

67.9

27.6

51.5

49.2

79.0

43.3

126.0

Percentage of basin covered by the geohydrologic terranes indicated

Relief 

(percent)

2.71

2.06

5.22

3.38

3.42

3.19

1.32

1.57

1.53

1.58

1.59

2.48

1.71

1.72

3.12

5.19

5.59

7.06

4.26

9.25

14.18

9.76

4.15

2.52

3.28

18.99

2.62

6.62

13.35

15.28

12.49

14.57

21.22

10.69

23.25

19.70

17.95

8.68

17.67

11.89

Province

3

1

1

1

1

1

3

3

3

3

3

3

3

1

1

1

2

2

2

2

2

2

2

1

1

2

1

1

2

2

2

2

2

2

2

2

2

3

2

2

VI

0.0

34.5

54.0

20.8

35.5

99.9

.0

.0

.0

.0

.0

.0

.0

17.8

25.8

54.1

.0

.0

.0

.0

.0

.0

.0

19.9

30.7

.0

19.1

75.5

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

V2

0.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.1

1.5

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

V3

0.0

31.1

45.0

57.8

13.0

.1

.0

.0

.0

.0

.0

.0

.0

80.0

74.2

39.8

.0

.0

.0

.0

.0

.0

.0

77.0

26.9

.0

.0

20.4

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

V4

0.0

34.4

1.1

20.4

27.1

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

6.1

.0

.0

.0

.0

.0

.0

.0

3.1

40.9

.0

80.9

4.2

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

V5

0.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

Bl

(0-25)

0.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

4.1

77.2

34.4

66.8

24.5

65.5

.0

.0

.2

.0

.0

.0

85.4

78.6

91.2

19.9

66.3

100.0

100.0

.9

.0

17.9

81.4

B2

(>25)

0.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

100.0

81.0

8.8

65.1

18.3

24.0

16.6

.0

.0

18.1

.0

.0

70.8

12.6

2.8

8.7

5.5

8.7

.0

.0

37.7

.0

.0

8.1

PI 

(0-10)

35.7

.0

.0

.0

20.8

.0

.0

9.8

.0

.4

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

0

.0

.0

.0

P2 

(10-20)

4.7

.0

.0

.0

.0

.0

6.1

.0

.0

.0

6.4

17.2

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

P3 P4 

(20-30) (30-50)

54.2

.0

.0

.0

.0

.0

90.1

86.0

99.9

98.6

92.1

82.8

87.4

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

100.0

.0

.0

0.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

P5 s « 

0.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

0.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0
B42 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

TABLE 1. Physical properties of drainage basins in the Valley and Ridge, Blue Ridge, and Piedmont Physiographic Provinces Regional Aquifer-System 

Analysis Program study area Continued

Map 

number 

(fig. 1)

41

42

43

44

45

46

47

48

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

U.S. Geological 

Survey 

station 

number

02138500

02152100

02143040

02111000

03479000

02143500

02142000

02111500

02112120

02120780

02118500

02114450

02113850

02128000

02088000

02085500

02077200

02082770

02082950

03475000

03471500

03488000

03165000

03167000

03167500

03170000

03173000

02069700

02070000

02053800

02056900

02056650

02055000

02055100

02017500

02018000

02014000

02011400

02011460

02015700

02022500

02059500

02061500

02058400

02065500

Latitude

35.79

35.49

35.59

35.99

36.24

35.42

35.95

36.17

36.25

35.72

36.00

36.30

36.40

35.39

35.57

36.18

36.40

36.11

36.19

36.71

36.76

36.90

36.65

36.94

36.89

37.04

37.27

36.57

36.57

37.14

37.04

37.23

37.26

37.42

37.51

37.67

37.73

38.04

38.25

38.20

37.83

37.17

37.21

36.95

37.08

Longitude

81.89

81.68

81.57

81.56

81.82

81.26

81.24

81.17

81.04

80.60

80.75

80.43

80.56

79.83

78.59

78.88

79.20

77.92

77.88

81.82

81.63

81.75

80.92

80.89

80.73

80.56

80.71

80.13

79.99

80.27

79.84

79.87

79.94

79.94

80.11

79.91

80.04

79.88

79.77

79.57

79.44

79.52

79.30

79.53

78.76

Drainage 

area 

(mi2)

66.7

60.5

25.7

28.8

92.1

69.2

28.2

89.2

128.0

118.0

155.0

42.8

231.0

106.0

83.5

149.0

45.9

166.0

177.0

211.0

76.1

222.0

39.4

247.0

278.0

300.0

305.0

84.6

108.0

110.0

115.0

56.8

395.0

11.7

104.0

329.0

153.0

158.0

60.1

110.0

35.0

188.0

320.0

350.0

98.0

Percentage of basin covered by the geohydrologic terranes indicated

Relief 

(percent)

10.73

7.46

7.95

11.21

11.81

2.07

6.08

10.65

7.68

1.04

3.29

2.75

3.83

1.04

.79

1.31

1.77

1.31

1.05

5.82

10.44

12.32

4.14

5.04

5.27

4.60

8.97

4.28

2.75

8.34

5.00

7.87

7.76

2.12

11.36

11.27

13.43

12.59

16.07

9.52

9.83

4.18

3.15

3.28

1.54

Province

2

3

3

2

2

3

3

2

2

3

3

3

2

3

3

3

3

3

3

1

1

1

2

1

2

2

1

2

3

0

2

2

1

1

1

1

1

1

1

1

1

2

2

0

3

VI

0.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

47.6

63.6

74.2

.0

57.7

.0

5.0

77.4

.0

.0

34.5

.0

17.0

56.4

.0

97.5

91.5

95.6

90.6

94.4

84.8

85.9

15.1

.0

.0

.0

V2

0.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

6.4

.0

.0

.0

22.8

.0

.0

.0

.0

.0

2.1

.0

.0

30.5

65.9

.0

.3

.2

.0

.0

.3

.0

.4

.0

.0

.0

V3

0.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.7

.0

.3

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

2.5

4.5

4.1

6.7

2.9

15.0

.0

.0

.0

.0

.0

V4

0.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

45.3

36.4

25.5

.0

19.5

.0

.0

22.6

.0

.0

1.4

.0

7.2

12.3

34.1

.0

3.7

.2

2.5

2.6

.0

14.1

.0

.0

.0

.0

V5

0.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

Bl

(0-25)

30.5

.0

.0

69.9

53.0

.0

.0

88.2

58.4

.0

.0

.0

74.9

.0

.0

.0

.0

.0

.0

.0

.0

.0

80.3

.0

94.5

73.2

.0

7.0

.6

44.2

98.4

75.8

.7

.0

.0

.0

.0

.0

.0

.0

.0

82.4

82.6

40.8

.0

B2

(>25)

3.2

.0

.0

0.9

6.6

.0

.0

11.8

17.9

.0

.0

.0

15.8

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

4.4

21.2

.0

60.8

.0

15.4

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

2.0

.0

.0

.0

PI

(0-10)

0.0

.0

.0

.0

.0

.0

.0

.0

.0

8.4

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

0.0

4.1

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

14.9

.0

1.3

P2 

(10-20)

0.0

1.5

25.2

.0

.0

15.1

4.1

.0

.0

80.2

47.3

3.0

.0

9.3

3.5

80.7

97.2

72.0

52.7

.0

.0

.0

.0

.0

.0

.0

.0

21.8

23.7

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

3.7

29.3

P3 

(20-30)

0.0

98.5

74.8

.0

.0

84.8

95.9

.0

.0

11.4

51.4

97.0

.0

90.7

57.9

19.3

.0

26.8

45.9

.0

.0

.0

.0

.0

.0

.0

.0

1.1

71.7

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

2.4

54.1

69.4

P4 

(30-50)

0.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

29.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

£ <>-

0.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.1

.0

.0

0.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B43

TABLE 1. Physical properties of drainage basins in the Valley and Ridge, Blue Ridge, and Piedmont Physiographic Provinces Regional Aquifer-System 

Analysis Program study area Continued

Map 

number 

(fig-D

86

87

88

89

90

91

92

93

94

95

96

97

98

99

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

U.S. Geological 

Survey 

station 

number

02079640

02039000

02038850

02027800

02027000

02028500

01626850

01627500

01632000

01632900

02031000

02032400

02052500

02044500

02046000

02041000

02036500

01673800

01666500

01663500

01662800

01660400

01658500

01643700

01634500

01654000

01646000

01638480

03180500

01605500

01606500

01616500

01617800

01637500

01643500

01591700

01591000

01591400

01583500

01584050

01581700

01580000

01496200

01560000

01613050

Latitude

36.68

37.26

37.42

37.61

37.72

37.87

38.09

38.22

38.64

38.69

38.10

38.15

36.62

36.98

37.07

37.28

37.60

38.17

38.33

38.59

38.66

38.49

38.59

38.99

39.08

38.81

38.98

39.26

38.54

38.64

38.99

39.42

39.51

39.43

39.29

39.17

39.24

39.26

39.51

39.45

39.52

39.63

39.63

40.07

39.90

Longitude

78.33

78.49

78.64

78.92

78.98

78.82

78.88

78.84

78.85

78.64

78.59

78.54

77.70

77.80

77.60

77.87

77.82

77.60

78.10

77.97

78.07

77.43

77.43

77.80

78.33

77.23

77.25

77.58

79.83

79.34

79.18

77.94

77.78

77.56

77.41

77.02

77.06

77.05

76.68

76.48

76.37

76.40

76.04

78.49

78.13

Drainage 

area 

(mi2)

53.4

69.7

8.5

147.0

92.8

94.6

149.0

212.0

210.0

93.2

95.4

37.0

65.2

309.0

112.0

158.0

22.1

77.4

179.0

287.0

27.6

34.9

7.6

123.0

103.0

23.5

57.9

89.6

133.0

182.0

642.0

272.0

18.9

66.9

62.8

27.0

34.8

22.9

59.8

9.4

34.8

94.4

9.0

172.0

10.7

Percentage of basin covered by the geohydrologic terranes indicated

Relief 

(percent)

1.64

1.54

1.19

4.12

12.90

9.10

4.11

3.92

11.43

4.20

4.13

5.26

.83

.83

.00

.09

.00

1.07

2.75

4.28

2.80

1.31

1.29

3.67

7.59

1.69

1.71

2.13

9.21

12.52

14.64

0.86

0.89

5.71

2.76

1.72

2.12

1.84

3.24

2.58

2.60

2.64

1.72

6.24

4.33

Province

3

3

3

2

2

2

0

0

1

1

2

2

3

3

3

3

3

3

2

2

2

3

3

2

1

3

3

2

1

1

1

1

1

2

3

3

3

3

3

3

3

3

3

1

1

VI

0.0

.0

.0

.0

.0

.0

19.5

17.6

96.8

62.4

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

90.4

.0

.0

.0

97.8

78.0

80.4

43.1

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

79.0

100.0

V2

0.0

.0

.0

.0

.0

.0

15.7

21.9

1.1

.6

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.8

.0

.0

.0

.0

10.0

9.1

4.8

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

3.8

.0

V3

0.0

.0

.0

.0

.0

.0

.0

.0

2.1

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

8.7

.0

.0

.0

2.2

9.3

10.4

13.3

100.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

17.2

.0

V4

0.0

.0

.0

.0

.0

.0

22.8

20.0

0.1

37.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

2.6

.0

38.7

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

V5

0.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

Bl

(0-25)

0.0

.0

.0

78.5

91.2

97.9

9.8

1.6

.0

.0

93.6

80.0

.0

.0

.0

.0

.0

.0

93.1

98.1

100.0

.0

.0

100.0

.0

.0

.0

94.4

.0

.0

.0

.0

.0

99.3

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

62

(>25)

0.0

.0

.0

0.2

.0

1.9

15.4

36.2

.0

.0

6.4

20.0

.0

.0

.0

.0

.0

.0

2.0

1.8

.0

.0

.0

.0

.0

.0

.0

2.3

.0

.0

.0

.0

.0

0.7

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

PI 

(0-10)

0.0

1.1

1.9

19.3

.0

.0

.0

.0

.0

.0

.0

.0

.0

.3

30.1

.0

.0

.0

.7

.0

.0

41.7

.0

.0

.0

.0

3.0

.0

.0

.0

.0

.0

.0

.0

84.5

.0

46.0

1.1

1.9

.0

10.8

1.1

.0

.0

.0

P2 

(10-20)

100.0

71.1

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

68.5

61.7

39.0

12.1

.0

55.9

1.7

.0

.0

48.6

26.9

.0

.0

19.1

30.5

.0

.0

.0

.0

.0

.0

.0

.0

8.9

.0

.0

.0

6.7

.0

.0

6.8

.0

.0

P3 

(20-30)

0.0

27.9

98.1

1.1

.0

.0

.0

.0

.0

.0

.0

.0

20.3

38.0

25.8

87.8

100.0

44.1

2.5

.0

.0

9.7

73.1

.0

.0

80.9

64.8

.0

.0

.0

.0

.0

.0

.0

9.2

91.1

54.0

98.9

80.5

61.1

88.6

92.9

93.2

.0

.0

P4

(30-50)

0.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

11.2

.0

5.2

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

0.4

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

£ <>»

0.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

1.3

.0

.0

.0

.0

.0

.0

.0

6.3

.0

.0

.0

17.6

32.2

.6

.5

.0

.0

.0

0.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0
B44 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

TABLE 1. Physical properties of drainage basins in the Valley and Ridge, Blue Ridge, and Piedmont Physiographic Provinces Regional Aquifer-System 

Analysis Program study area Continued

Map 

number 

(fig. 1)

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

U.S. Geological 

Survey 

station 

number

01564500

01558000

01547200

01567500

01569800

01568000

01571500

01574000

01555500

01555000

01470779

01468500

01470756

01480675

01472157

01471980

01475300

01474000

01451800

01452000

01449360

01448500

01447500

01442500

01401000

01398107

01445500

Latitude

40.21

40.61

40.94

40.37

40.23

40.32

40.22

40.08

40.61

40.87

40.41

40.63

40.51

40.10

40.15

40.27

40.02

40.01

40.66

40.62

40.90

41.04

41.13

41.00

40.33

40.56

40.83

Longitude

77.93

78.14

77.79

77.40

77.14

77.17

76.90

76.72

76.91

77.05

76.17

76.13

75.88

75.74

75.60

75.68

75.42

75.21

75.63

75.48

75.50

75.54

75.63

75.14

74.68

74.73

74.98

Drainage 

area 

(mi2)

205.0

220.0

265.0

15.0

21.6

200.0

216.0

510.0

162.0

301.0

66.5

133.0

159.0

8.6

59.1

85.5

5.2

64.0

53.0

75.8

49.9

2.4

91.7

259.0

44.5

9.0

106.0

Percentage of basin covered by the geohydrologic terranes indicated

Relief 

(percent)

5.44

7.24

6.24

5.43

0.00

6.61

3.59

1.97

5.29

7.87

1.09

5.47

3.68

1.45

3.71

4.36

0.33

1.08

3.14

2.90

4.01

3.58

2.19

4.16

1.31

0.00

2.95

Province

1

1

1

1

1

1

0

3

1

1

1

1

1

3

3

0

3

3

1

1

1

1

1

1

3

3

1

VI

92.3

69.9

53.3

49.1

3.3

71.4

8.0

.0

100.0

72.0

15.1

99.2

92.8

.0

.0

13.4

.0

.0

100.0

59.3

85.0

100.0

100.0

88.7

.0

.0

7.4

V2

2.3

1.5

1.5

6.5

4.2

13.4

.3

.0

.0

18.6

21.1

.8

2.7

.0

.0

1.1

.0

.0

.0

2.1

.0

.0

.0

1.3

.0

.0

.0

V3

5.4

15.4

16.5

44.4

90.2

15.1

18.5

.0

.0

7.8

18.4

.0

1.5

.0

.0

.2

.0

.0

.0

24.6

.0

.0

.0

.0

.0

.0

44.9

V4

0.0

13.2

23.7

.0

2.3

.0

16.0

.0

.0

1.6

40.2

.0

3.0

.0

.0

24.1

.0

.0

.0

14.0

.0

.0

.0

.0

.0

.0

.0

V5

0.0

.0

5.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

15.0

.0

.0

10.0

.0

.0

5.0

Bl 

(0-25)

0.0

.0

.0

.0

.0

.0

26.4

10.1

.0

.0

.0

.0

.0

 0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

B2

(>25)

0.0

.0

.0

.0

.0

.0

3.1

7.8

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

PI

(0-10)

0.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.4

4.0

.0

.4

.2

.0

.0

.0

.0

.0

.0

.0

.0

.0

P2 

(10-20)

0.0

.0

.0

.0

.0

.0

5.4

11.0

.0

.0

.2

.0

.0

.6

8.2

1.2

.0

.0

.0

.0

.0

.0

.0

.0

15.1

6.1

.0

P3 

(20-30)

0.0

.0

.0

.0

.0

.0

12.3

12.7

.0

.0

4.2

.0

.0

98.6

62.8

59.7

99.6

40.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

P4 

(30-50)

0.0

.0

.0

.0

.0

.0

10.0

52.3

.0

.0

.0

.0

.0

.0

2.3

.2

.0

22.5

.0

.0

.0

.0

.0

.0

34.6

.0

.0

P5

(50- 

100)

0.0

.0

.0

.0

.0

.0

.0

.0

.0

.0

.9

.0

.0

.4

22.6

.0

.0

33.6

.0

.0

.0

.0

.0

.0

5.0

.0

.0

P6

0.0

.0

.0

.0

.0

.0

.0

6.1

.0

.0

.0

.0

.0

.0

.1

.0

.0

2.8

.0

.0

.0

.0

.0

.0

45.3

93.9

.0
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B45

TAI5LE 2. Characteristics of recession analysis and master recession curves in the Appalachian Valley and Ridge, Blue Ridge, and Piedmont 

Physiographic Provinces Regional Aquifer-System Analysis study program

[MR< I, master recession curve]

Map 

number 

(fg-1)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

Period of 

analysis

1980-91

1953-91

1978-91

1965-91

1962-91

1958-90

1961-91

1964-91

1977-91

1977-91

1978-91

1954-91

1937-91

1980-91

1937-91

1979-91

1974-91

1938-91

1929-91

1913-91

1964-91

1939-91

1967-91

1928-91

1934-91

1963-91

1977-91

1941-91

1914-91

1940-91

1944-91

1961-91

1945-91

1935-91

1954-91

1954-91

1934-91

1951-91

1957-91

1980-91

1922-91

1959-91

1961-91

1939-91

1940-91

Number 

of 

recession 

segments 

used

10

6

26

39

19

44

24

31

11

10

25

35

26

12

47

22

19

24

42

44

17

46

14

46

43

19

46

42

37

36

35

15

25

39

22

37

26

35

28

21

33

24

23

31

30

Median 

recession 

index 

(d/log cycle)

89.3

69.6

47.3

52.3

100.2

22.1

62.4

50.8

72.6

68.4

58.4

118.5

76.7

71.9

78.4

42.3

106.1

127.8

118.8

128.6

105.9

112.2

101.6

77.2

63.6

62.5

86.3

47.0

79.0

95.1

99.6

100.7

71.9

103.9

66.1

70.6

80.7

145.9

78.9

99.4

76.1

122.7

110.7

102.2

65.9

Range of MRC 

(fig- 3)

MinLogQ

1.892

1.776

.963

1.324

1.861

-.109

.062 

-.625

1.540

1.369

0.708

0.995

1.561

1.202

1.885

1.237

.472

2.156

1.833

2.152

1.630

2.068

1.512

2.063

1.156

1.418

.411

.450

1.667

1.604

2.010

1.682

1.927

1.792

1.386

1.358

1.449

1.581

1.242

1.803

1.502

1.491

1.077

1.040

1.448

MaxLogQ

2.445

2.416

1.903

2.217

2.407

2.531

1.353

1.626

2.151

2.282

2.245

1.952

2.522

1.639

2.543

2.294

1.387

2.906

2.787

3.041

2.357

3.148

2.443

2.686

2.124

2.396

1.328

1.688

2.460

2.320

2.811

2.276

2.803

2.507

2.049

2.183

2.136

2.333

2.079

2.483

2.160

2.186

1.653

1.879

2.217

Coefficients of MRC 

(fig. 3)

A

24.817

34.135

25.272

30.001

102.765

3.449

4.422

-13.169

-24.451

5.782

-4.252

-2.917

-6.948

14.615

50.538

32.495

27.712

19.647

16.786

82.675

61.230

50.277

-14.506

59.504

51.717

39.867

.954

26.630

57.228

124.202

59.136

69.259

73.188

85.922

47.984

46.857

69.641

10.644

21.804

44.186

8.139

55.902

64.853

-1.219

45.771

B

-203.888

-217.011

-123.898

-165.256

-560.863

-38.952

-75.758

-24.195

13.484

-92.423

-42.930

-108.322

-48.259

-116.134

-307.926

-173.075

-166.135

-231.227

-209.503

-568.914

-365.005

-390.431

-45.623

-368.754

-251.319

-224.954

-88.708

-121.617

-330.128

-628.039

-397.346

-383.806

-450.495

-497.270

-239.244

-256.209

-342.661

-200.738

-157.682

-298.212

-108.764

-327.645

-304.887

-88.302

-251.472

C

350.125

325.059

144.247

218.904

754.595

76.489

94.422

74.149

84.093

180.783

117.793

222.619

165.893

151.063

456.252

226.039

177.160

505.997

453.457

965.512

520.185

730.810

198.020

561.187

300.474

310.115

116.083

129.414

465.799

788.550

649.688

514.777

687.701

706.609

288.763

336.001

414.203

410.456

233.558

468.034

196.978

449.069

326.774

180.813

332.524
B46 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

TABLE 2. Characteristics of recession analysis and master recession curves in the Appalachian Valley and Ridge, Blue Ridge, and Piedmont 

Physiographic Provinces Regional Aquifer-System Analysis study program Continued

Map 

number 

(fig- 1)

46

47

48

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

88

89

90

Period of 

analysis

1951-91

1953-91

1939-91

1964-91

1979-91

1951-91

1960-91

1964-91

1954-91

1939-91

1925-91

1964-91

1963-91

1959-91

1931-91

1920-91

1920-91

1944-91

1911-91

1911-91

1928-91

1938-91

1962-91

1928-91

1960-91

1976-91

1974-91

1917-91

1956-91

1926-91

1925-91

1928-91

1974-91

1974-91

1960-91

1927-91

1930-91

1937-91

1963-91

1946-91

1961-91

1946-91

1966-91

1960-91

1938-91

Number 

of 

recession 

segments 

used

45

40

35

12

15

20

18

26

46

29

41

28

19

35

16

38

28

27

38

40

47

48

14

49

17

17

21

43

25

49

44

36

18

16

28

48

28

19

20

34

25

40

23

36

46

Median 

recession 

index 

(d/log cycle)

89.5

102.8

140.9

117.6

85.1

110.8

103.4

98.0

70.5

45.2

57.7

37.5

66.2

53.9

80.1

88.9

53.9

128.0

78.7

113.3

91.7

69.0

113.0

138.7

99.3

104.3

61.9

80.3

68.4

50.5

57.0

58.5

59.1

68.7

67.9

62.0

93.1

78.4

113.9

92.7

58.9

108.7

79.0

87.7

60.6

Range of MRC 

(fig- 3)

MinLogQ

.854

.975

1.623

1.720

1.409

1.842

1.056

2.163

.558

-.366

.063

-1.511

.696

.121

1.902

1.349

1.443

1.307

1.767

2.024

1.905

1.484

1.779

1.683

1.382

1.329

.413

1.737

.356

.939

1.524

1.241

1.528

.466

1.519

.837

1.672

1.337

1.793

1.257

-.352

1.087

-.006

1.570

.968

MaxLogQ

2.071

1.815

2.434

2.323

1.990

2.588

1.674

2.720

2.066

1.960

2.086

1.598

2.227

2.228

2.439

1.984

2.446

2.040

2.517

2.832

2.759

2.414

2.212

2.299

2.226

2.200

2.019

2.679

1.223

1.986

2.417

2.117

2.181

1.595

2.060

1.527

2.369

2.552

2.734

2.145

1.557

2.015

1.213

2.429

2.215

Coefficients of MRC 

(fig- 3)

A

-13.106

37.201

43.803

73.033

-1.620

1.400

15.871

-4.316

-15.324

-2.414

-5.844

-8.941

-14.509

-8.743

73.325

68.685

36.333

68.909

62.207

36.073

12.939

45.944

80.140

-16.756

47.573

15.489

-.604

26.294

11.736

26.751

21.451

35.998

31.814

34.823

65.641

35.912

30.308

18.070

-12.004

14.101

-1.117

11.311

-11.241

8.957

25.922

B

-56.436

-209.000

-322.924

^27.932

-83.158

-126.346

-150.037

-78.783

-20.833

-39.454

-43.838

-22.503

-21.272

-33.553

^08.782

-329.373

-206.629

-363.999

-357.891

-300.123

-158.854

-263.120

^54.012

-76.850

-264.537

-166.514

-66.104

-196.146

-95.949

-143.387

-152.110

-191.788

-180.850

-152.019

-313.772

-157.351

-221.848

-165.208

-50.204

-149.585

-62.328

-148.904

-73.908

-123.687

-168.102

C

173.040

256.798

526.509

600.006

171.933

317.560

206.713

246.173

108.454

86.589

116.873

58.773

119.293

118.123

560.843

383.107

288.041

455.759

506.694

560.629

339.795

367.426

612.155

265.247

353.150

291.380

135.901

336.736

99.785

179.259

242.350

244.663

243.114

153.892

367.805

156.545

355.481

303.950

226.936

256.006

99.754

254.099

106.173

247.625

245.162
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B47

TABLE 2. Characteristics of recession analysis and master recession curves in the Appalachian Valley and Ridge, Blue Ridge, and Piedmont 

Physiographic Provinces Regional Aquifer-System Analysis study program Continued

Map 

number 

(fig. 1)

91

92

93

94

95

96

97

98

99

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

Period of 

analysis

1943-91

1974-91

1925-91

1925-91

1960-91

1942-91

1979-91

1953-91

1950-91

1946-91

1946-91

1944-91

1962-91

1943-91

1942-91

1958-91

1971-91

1951-91

1965-91

1937-91

1947-91

1935-91

1970-91

1943-91

1940-91

1928-91

1947-91

1963-91

1947-91

1948-91

1978-91

1944-91

1978-91

1944-91

1975-91

1967-91

1926-91

1967-91

1939-91

1965-91

1938-91

1938-91

1955-91

1954-91

1976-91

Number 

of 

recession 

segments 

used

46

27

39

45

36

18

15

27

43

29

23

15

14

34

28

31

36

47

15

48

29

23

14

25

33

35

25

29

47

32

17

49

18

28

27

14

48

14

31

36

25

26

10

29

25

Median 

recession 

index 

(d/log cycle)

67.4

81.0

84.7

52.5

81.6

68.3

49.3

47.5

69.2

51.6

58.1

56.6

45.5

63.3

59.5

59.6

47.6

37.0

43.2

52.4

65.7

106.0

61.9

49.6

62.7

71.7

92.3

108.2

48.3

85.4

108.1

89.9

103.6

126.2

113.3

132.1

127.7

97.0

54.0

40.3

56.7

58.3

76.1

64.5

167.5

Range of MRC 

(fig. 3)

MinLogQ

.860

1.720

1.937

.565

1.059

1.550

1.093

-.306

.487

.274

.402

.400

.850

1.659

1.636

.002

.593

-.385

.599

.957

.291

.645

1.020

.289

1.271

1.910

1.545

.281

.467

1.049

.357

.731

.415

1.120

.356

1.196

1.525

-.016

1.055

-.089

.952

1.911

2.317

.488

1.345

MaxLogQ

2.190

2.321

2.493

1.992

2.015

2.054

1.576

1.846

2.578

2.099

2.197

1.436

1.909

2.416

2.646

1.508

1.537

.863

2.077

1.936

1.372

1.820

1.922

2.093

2.236

2.884

2.415

1.405

2.045

1.936

1.480

1.847

1.645

1.922

1.188

1.684

2.271

1.159

2.163

1.186

2.168

2.593

2.575

1.341

1.893

Coefficients of MRC 

(fig. 3)

A

20.210

64.472

63.552

10.311

32.055

15.970

7.826

-6.708

-6.334

-3.896

-.395

-20.515

-15.658

6.074

17.102

-3.838

-16.774

-10.748

-5.604

12.394

-19.609

-5.716

-7.230

5.669

36.845

39.521

17.756

1.508

14.502

6.003

-3.037

18.953

29.334

-28.740

19.761

-89.675

51.961

-3.720

25.500

.073

25.750

61.676

71.288

84.671

156.935

B

-148.855

-358.496

-368.531

-84.737

-195.330

-130.656

-71.300

-34.115

-45.535

-42.419

-57.096

-22.928

.805

-97.057

-143.360

-58.832

-14.244

-35.623

-29.788

-97.890

-33.797

-80.236

-34.158

-66.057

-204.048

-262.420

-171.330

-111.681

-98.414

-109.788

-102.069

-147.325

-176.008

-36.621

-149.486

123.786

-336.176

-92.538

-144.692

-41.737

-163.037

-347.531

-428.883

-256.946

-677.004

C

229.042

484.726

523.789

127.868

263.464

201.025

92.933

85.859

159.518

106.229

127.330

75.193

55.502

199.010

259.598

97.421

61.524

38.765

86.053

143.086

83.290

164.937

92.339

113.431

272.030

428.090

310.187

153.918

140.631

190.034

157.669

207.463

210.143

176.607

149.715

45.889

495.470

112.223

193.680

49.399

232.461

486.452

631.716

192.290

719.184
B48 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

TABLE 2. Characteristics of recession analysis and master recession curves in the Appalachian Valley and Ridge, Blue Ridge, and Piedmont 

Physiographic Provinces Regional Aquifer-System Analysis study program Continued

Map 

number 

(fig- 1)

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

Period of 

analysis

1929-91

1911-91

1928-91

1929-91

1929-91

1974-91

1947-91

1973-91

1966-91

1968-91

1974-91

1972-91

1965-91

1966-91

1944-91

1966-91

1948-91

1943-91

1950-91

1953-91

1978-91

1921-91

Number 

of 

recession 

segments 

used

34

18

35

18

45

16

18

15

26

16

14

14

19

22

27

39

27

31

47

23

22

20

Median 

recession 

index 

(d/log cycle)

55.9

85.5

50.8

49.3

65.3

129.1

59.4

57.9

65.5

118.3

90.8

149.0

64.9

43.4

44.9

80.2

99.0

66.8

61.0

36.1

35.4

70.8

Range of MRC 

(fig. 3)

MinLogQ

1.522

2.049

1.444

1.081

1.588

1.604

1.924

1.433

-.163

1.070

1.539

.251

1.209

1.106

.584

1.254

-.367

.898

1.747

-.151

.031

1.370

MaxLogQ

2.438

2.513

2.674

2.354

2.650

2.173

2.480

2.341

1.134

1.920

2.110

1.169

2.059

1.851

1.980

2.080

.618

2.262

2.740

1.442

1.436

2.323

Coefficients of MRC 

(fig- 3)

A

27.254

130.353

25.442

18.776

36.403

103.719

18.718

25.849

-3.825

26.804

19.310

23.828

-3.390

39.218

17.799

58.190

41.042

35.865

53.709

-2.328

10.370

41.301

B

-181.717

-727.613

-174.266

-125.837

-242.557

-524.080

-150.158

-178.765

-63.508

-206.544

-162.946

-176.854

-57.450

-171.918

-106.291

-293.749

-122.830

-220.176

-335.582

-30.771

-53.556

-239.790

C

281.045

1005.326

284.089

192.175

387.153

649.038

257.270

276.845

76.927

297.754

257.841

174.206

132.662

183.843

140.675

359.244

60.221

314.557

516.273

49.202

55.527

334.165
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B49

TABLE 3. Components ofhydrologic budgets of basins in the Appalachian Valley and Ridge, Blue Ridge, and 

Piedmont Physiographic Provinces Regional Aquifer-System Analysis study area, 1961-90

[in/yr, inches per year]

Map 

number

12

13

15

19

20

22

25

28

29

'30

31

33

34

J 35

36

38

J 39

41

42

44

45

46

47

48

51

52

54

55

56

59

61

62

63

64

65

66

67

69

70

73

74

75

76

80

81

Precipitation 

(in/yr)

53.40

55.30

57.60

65.50

62.90

73.60

56.20

45.20

59.30

66.90

65.90

56.80

80.20

57.90

55.60

49.90

55.10

56.60

52.30

57.60

59.40

48.50

49.50

53.50

47.50

46.80

46.90

46.20

44.90

44.60

45.60

44.20

45.20

40.10

44.20

40.20

40.20

48.90

41.00

40.20

39.90

35.70

35.70

41.40

43.50

Evapotranspiration

(in/yr)

31.77

34.95

30.98

31.78

23.90

28.64

33.96

28.42

25.21

12.06

27.68

18.25

31.46

7.33

17.91

25.04

9.60

24.00

32.07

32.89

32.02

31.03

30.42

30.87

28.76

31.86

32.70

32.69

31.89

31.83

25.04

25.32

21.80

24.73

24.81

24.23

25.60

31.78

27.15

28.09

25.86

18.45

19.24

22.93

29.80

Streamflow

(in/yr)

21.63

20.35

26.62

33.72

39.00

44.96

22.24

16.78

34.09

54.84

38.22

38.55

48.74

50.57

37.69

24.86

45.50

32.60

20.23

24.71

27.38

17.47

19.08

22.63

18.74

14.94

14.20

13.51

13.01

12.77

20.56

18.88

23.40

15.37

19.39

15.97

14.60

17.12

13.85

12.11

14.04

17.25

16.46

18.47

13.70

Recharge

(in/yr)

17.20

12.67

18.93

28.44

36.24

40.97

14.12

10.85

28.40

49.70

34.48

33.11

43.72

40.54

32.63

20.94

35.72

24.95

16.01

21.23

20.77

12.35

15.32

19.47

14.66

9.10

7.29

8.41

6.23

7.39

16.40

13.22

19.01

11.57

15.48

12.70

10.29

13.24

10.69

8.70

11.36

14.05

11.90

13.66

9.79

Base flow

(in/yr)

16.03

11.87

16.76

26.01

33.00

36.98

12.51

9.46

25.74

45.97

31.22

29.53

40.11

36.57

29.41

19.49

32.89

22.69

14.91

19.50

18.66

11.37

14.06

17.99

13.30

8.42

6.52

7.46

5.31

6.47

15.23

11.14

17.76

10.64

14.10

11 .44

9.27

12.29

9.80

7.84

10.32

12.05

10.58

12.20

8.81

Direct 

runoff

(in/yr)

5.60

8.48

9.86

7.70

6.00

7.98

9.73

7.32

8.35

8.87

7.00

9.02

8.63

14.00

8.29

5.37

12.61

9.91

5.32

5.21

8.73

6.10

5.03

4.64

5.43

6.52

7.68

6.05

7.70

6.30

5.33

7.74

5.64

4.74

5.30

4.53

5.33

4.83

4.05

4.27

3.72

5.20

5.88

6.27

4.89

Base-flow 

index 

(percent)

74.1

58.3

63.0

77.2

84.6

82.3

56.3

56.4

75.5

83.8

81.7

76.6

82.3

72.3

78.0

78.4

72.3

69.6

73.7

78.9

68.1

65.1

73.6

79.5

71.0

56.3

45.9

55.2

40.8

50.6

74.1

59.0

75.9

69.2

72.7

71.6

63.5

71.8

70.8

64.7

73.5

69.9

64.3

66.0

64.3
B50 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

TABLE 3. Components ofhydrologic budgets of basins in the Appalachian Valley and Ridge, Blue Ridge, and 

Piedmont Physiographic Provinces Regional Aquifer-System Analysis study area, 1961-90 Continued

Map 

number 

(fig- 1)

82

83

85

87

89

90

91

94

95

98

99

100

101

102

104

105

106

108

110

111

112

114

116

117

119

122

124

127

129

131

132

133

134

136

137

138

139

140

150

152

153

154

155

157

Precipitation 

(in/yr)

41.90

42.20

42.90

42.90

42.00

47.40

45.40

34.20

34.60

43.30

43.40

43.50

43.50

42.10

45.90

43.70

41.20

41.30

35.70

40.80

40.80

45.10

41.90

37.80

42.30

40.90

44.80

44.00

38.60

37.60

39.80

38.20

39.00

39.00

39.10

40.40

42.80

42.40

45.70

50.90

45.50

48.40

45.60

44.60

Evapotranspiration 

(in/yr)

28.38

28.39

28.91

29.46

26.06

23.95

24.57

21.19

23.99

28.75

29.72

29.90

30.35

29.52

28.58

27.26

28.24

29.03

22.32

24.08

26.01

17.56

25.81

25.75

27.07

25.43

29.36

25.91

19.91

21.36

16.29

17.63

21.38

19.04

20.67

24.04

23.63

21.85

25.56

24.36

18.04

19.27

24.89

24.01

Streamflow 

(in/yr)

13.52

13.81

13.99

13.44

15.94

23.45

20.83

13.01

10.61

14.55

13.68

13.60

13.15

12.58

17.32

16.44

12.96

12.27

13.38

16.72

14.79

27.54

16.09

12.05

15.23

15.47

15.44

18.09

18.68

16.24

23.51

20.57

17.62

19.96

18.43

16.36

19.17

20.55

20.14

26.54

27.46

29.13

20.71

20.59

Recharge 

(in/yr)

9.74

10.23

9.51

9.76

12.86

19.91

17.02

7.51

8.57

7.56

8.55

8.00

7.66

8.42

13.24

12.32

10.38

6.81

9.24

7.13

8.99

18.42

11.08

8.96

12.08

11.93

12.94

15.04

12.93

10.80

20.09

16.83

13.48

14.53

16.65

9.42

14.42

17.40

14.97

21.41

22.88

24.12

10.28

18.75

Base flow 

(in/yr)

8.81

9.10

8.81

8.99

11.50

17.46

15.11

5.82

7.79

6.57

7.77

6.90

6.72

7.44

11.59

10.92

9.18

5.67

7.93

6.34

8.43

15.32

9.79

8.11

10.53

11.09

11.94

13.81

10.75

8.98

17.47

15.40

11.88

12.40

14.96

7.90

12.18

15.42

12.68

20.31

20.91

21.36

8.39

16.97

Direct 

runoff 

(in/yr)

4.71

4.70

5.18

4.44

4.45

5.99

5.72

7.19

2.82

7.98

5.91

6.69

6.43

5.14

5.73

5.52

3.78

6.60

5.45

10.38

6.36

12.22

6.30

3.94

4.70

4.38

3.51

4.28

7.93

7.26

6.05

5.17

5.74

7.56

3.47

8.47

6.99

5.13

7.46

6.23

6.55

7.76

12.32

3.62

Base -flow 

index 

(percent)

65.2

65.9

63.0

66.9

72.1

74.5

72.5

44.7

73.4

45.2

56.8

50.8

51.1

59.2

66.9

66.4

70.8

46.2

59.3

37.9

57.0

55.6

60.8

67.3

69.1

71.7

77.3

76.3

57.5

55.3

74.3

74.8

67.4

62.1

81.2

48.3

63.5

75.0

63.0

76.5

76.1

73.3

40.5

82.4

Estimates of precipitation and evapotranspiration for this station may be in error because of difficulty in estimating

precipitation.
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B51

TABLE 4. Streamflow, recharge, and base flow in basins in the Appalachian Valley and Ridge, Blue 

Ridge, and Piedmont Physiographic Provinces Regional Aquifer-System Analysis study areas, 

1981-90

Map number 

(fig- 1)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

Streamflow 

(in/yr

20.94

28.22

23.92

23.17

19.96

32.53

10.80

9.23

10.19

10.64

15.07

18.71

18.07

17.15

24.65

22.05

22.07

26.76

27.84

33.39

37.78

37.73

27.26

21.32

18.71

33.53

11.23

14.14

30.28

49.33

32.04

30.22

36.29

42.62

45.69

33.06

27.47

22.30

40.52

25.80

29.90

17.99

24.53

22.33

24.88

Recharge 

(in/yr)

13.47

18.41

16.03

13.40

14.21

23.94

6.18

4.57

6.76

6.52

10.44

15.06

11.09

12.65

17.61

15.52

18.17

23.71

23.54

30.95

33.75

34.88

23.65

11.47

12.10

26.39

9.74

9.71

25.51

45.53

29.19

26.02

31.58

38.81

37.60

29.18

24.67

18.64

32.41

21.93

23.93

14.42

19.11

19.17

19.63

Base flow 

(in/yr)

12.44

16.35

14.12

11.34

13.36

15.59

5.29

3.97

6.06

6.10

9.23

14.09

10.32

11.62

15.48

12.36

16.86

21.32

21.50

28.11

31.35

31.28

21.92

10.56

10.52

23.59

8.93

8.42

22.80

41.70

26.27

24.41

28.13

35.40

33.82

26.24

22.51

17.41

30.15

20.10

21.74

13.40

17.52

17.61

17.30

Base-flow index 

(percent)

59.4

57.9

59.0

48.9

66.9

47.9

48.9

43.0

59.5

57.4

61.2

75.3

57.1

67.7

62.8

56.1

76.4

79.7

77.2

84.2

83.0

82.9

80.4

49.5

56.2

70.3

79.5

59.5

75.3

84.5

82.0

80.8

77.5

83.1

74.0

79.4

81.9

78.1

74.4

77.9

72.7

74.5

71.4

78.9

69.5
B52 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

TABLE 4. Streamflow, recharge, and base flow in basins in the Appalachian Valley and Ridge, Blue 

Ridge, and Piedmont Physiographic Provinces Regional Aquifer-System Analysis study areas, 

1981-90 Continued

Map number 

(fig- 1)

46

47

48

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

88

89

90

Streamflow 

(in/yr

14.87

17.77

19.95

17.96

12.30

17.43

14.33

17.46

14.48

11.79

13.23

13.47

14.56

13.45

15.60

19.28

16.98

22.60

14.65

18.82

15.57

13.39

21.42

17.42

14.25

15.22

13.30

12.15

14.73

17.12

16.03

15.73

14.23

19.95

19.00

14.76

14.95

15.07

14.97

14.13

13.02

13.23

10.96

15.68

22.60

Recharge 

(in/yr)

10.75

14.58

17.40

15.27

8.24

13.52

8.73

14.57

7.25

6.97

6.28

6.88

9.79

7.69

12.72

15.41

12.60

18.19

11.30

15.19

12.80

9.61

18.08

13.15

11.09

11.74

9.99

8.49

11.69

14.15

11.27

11.84

11.16

13.44

13.58

9.94

10.45

10.76

10.16

9.55

5.89

9.88

7.86

13.00

19.65

Base flow 

(in/yr)

9.85

13.46

15.92

13.84

7.39

12.16

7.91

12.90

6.42

5.99

5.39

5.81

8.42

6.65

11.19

14.08

10.43

16.83

10.37

13.80

11.39

8.69

16.50

12.12

10.13

10.73

8.78

7.62

10.52

12.07

9.94

9.96

9.42

11.74

12.01

8.82

9.41

9.58

9.34

8.83

5.13

8.90

7.19

11.50

17.32

Base-flow index 

(percent)

66.2

75.7

79.8

77.1

60.1

69.8

55.2

73.9

44.3

50.8

40.8

43.1

57.8

49.4

71.8

73.1

61.4

74.5

70.8

73.3

73.1

64.9

77.0

69.6

71.1

70.5

66.0

62.7

71.5

70.5

62.0

63.3

66.2

58.8

63.2

59.8

62.9

63.6

62.4

62.5

39.4

67.2

65.6

73.4

76.6
ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B53

TABLE 4. Stream/low, recharge, and base flow in basins in the Appalachian Valley and Ridge, Blue 

Ridge, and Piedmont Physiographic Provinces Regional Aquifer-System Analysis study areas, 

1981-90 Continued

Map number 

(fig.D

91

92

93

94

95

96

97

98

99

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

Streamflow 

(in/yr

20.16

18.21

16.95

12.22

10.34

15.51

15.90

13.83

12.72

12.65

11.97

11.64

12.10

16.74

15.19

11.66

11.85

11.38

12.35

13.35

15.01

13.13

13.52

28.23

13.60

16.06

11.56

6.42

13.83

13.35

13.28

13.76

13.67

14.48

15.03

18.87

16.95

16.05

17.90

16.06

15.16

23.13

21.00

17.86

24.68

Recharge 

(in/yr)

16.75

14.74

13.83

7.15

8.29

11.56

10.78

6.93

8.13

7.47

7.06

7.71

6.97

12.64

11.35

9.27

7.01

6.68

10.11

8.98

5.56

7.94

8.95

18.73

9.94

10.99

8.68

6.23

11.39

10.12

9.31

10.99

10.23

12.59

12.19

14.31

14.48

10.62

12.41

12.26

10.59

20.37

17.34

13.69

25.40

Base flow 

(in/yr)

14.72

13.15

12.30

5.58

7.47

10.22

9.29

5.96

7.49

6.44

6.29

6.63

6.01

10.97

9.99

8.07

6.11

5.48

8.24

7.70

4.74

7.34

7.96

15.47

8.47

9.74

7.70

5.71

9.85

9.18

8.43

10.20

9.38

11.50

11.27

13.28

13.17

9.82

10.30

9.60

8.82

17.48

15.88

11.94

23.30

Base-flow index 

(percent)

73.0

72.2

72.6

45.7

72.3

65.9

58.4

43.1

58.9

50.9

52.5

56.9

49.7

65.5

65.8

69.2

51.6

48.1

66.8

57.7

31.6

55.9

58.9

54.8

62.3

60.6

66.6

89.0

71.2

68.7

63.5

74.1

68.6

79.4

75.0

70.4

77.7

61.2

57.6

59.7

58.2

75.6

75.6

66.9

94.4
B54 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

TABLE 4. Streamflow, recharge, and base flow in basins in the Appalachian Valley and Ridge, Blue 

Ridge, and Piedmont Physiographic Provinces Regional Aquifer-System Analysis study areas, 

1981-90 Continued

Map number 

(fig. 1)

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

Streamflow 

(in/yr

18.94

17.28

15.30

18.53

20.20

20.22

26.02

21.37

19.10

19.36

19.97

20.30

21.64

23.67

21.05

26.83

26.74

29.00

29.20

20.85

22.94

22.11

Recharge 

(in/yr)

13.90

15.74

9.13

14.16

17.28

18.53

24.42

16.11

12.42

14.10

14.79

14.01

13.71

17.24

14.90

24.22

21.18

24.15

24.32

10.32

15.48

20.24

Base flow 

(in/yr)

11.77

14.12

7.73

11.99

15.51

17.14

21.49

13.84

11.11

13.11

13.46

13.11

12.26

14.52

12.60

22.22

19.60

21.83

21.30

8.22

12.16

18.19

Base-flow index 

(percent)

62.2

81.7

50.6

64.7

76.7

84.7

82.6

64.8

58.1

67.8

67.4

64.6

56.7

61.3

59.8

82.8

73.3

75.3

72.9

39.4

53.0

82.3
APPENDIX

ESTIMATED HYDROLOGIC CHARACTERISTICS OF SHALLOW AQUIFER SYSTEMS B57

SOURCES OF INFORMATION ON BASIN 

PROPERTIES

This appendix describes the sources of information on physical properities of basins that are used in this report. The listing 

of properties for all basins is in table 1 (follows "References) and 

mean precipitation from 1961 to 1990 is listed in table 3 (follows 

"References) for basins that have complete streamflow records 

for this period.

Variables From U.S. Geological Survey Data Books

Data obtained directly from USGS data books include latitude, longitude, and drainage area. The latitude and longitude 

reported in USGS data books (published separately for each 

State) represent the location of the streamflow-gaging station.

Precipitation

The source of basin precipitation is a data tape obtained 

from the National Climatic Data Center (NCDC) in Ashville, 

North Carolina. The data tape includes the "normal" precipitation from 1961 to 1990, which represents the mean annual precipitation for this period for specific locations in the United 

States. The data were transferred to a point coverage in a geographic informaiton system (GIS) by using the latitude and longitude that are obtained from the NCDC. The point values of 

mean precipitation were then plotted with polygon coverages 

that represent the drainage boundaries of the 157 basins. A 

value for mean precipitation was then assigned to each basin by 

visual interpolation.

Physiographic Province

The physiographic province of a basin was assigned by 

intersecting the polygon coverage of basin boundaries with that 

of physiographic province. If more than 75 percent of a basin is 

located in a particular province, then the basin is assigned a 

number in table 1 according to the following:

Physiographic 

province

Number 

issued

Valley and Ridge. 

Blue Ridge............

Piedmont..............

If the largest fraction of a basin's area that is in one physiographic province is less than 75 percent, then the number 

assigned is 0.

Basin Relief

Elevation point data were digitized from 30-second point 

elevation data provided by the National Oceanic and Atmospheric Administration, National Geophysical Data Center, 

Boulder, Colorado (D.C. Schoolcraft, National Geophysical 

Data Center, written commun., 1989). For purposes of this 

study, data were reformatted with each point being assigned a

latitude, longitude, and elevation value. GIS point data coverages were created from the reformatted elevation data. A Triangulated Irregular Network was constructed to interpolate 

surface-elevation contours and surface-relief model. The variable basin relief that is used in this report is the median of all 

values for relief in that basin. The variable is listed for each 

basin in table 1.

Hydrogeologic Terrane

The first step in development of variables for testing the 

relations between hydrologic characteristics and geologic characteristics of basins is the introduction of 13 variables; each represents the percent of the basin that is characterized by a 

hydrogeologic terrane. The hydrogeologic terranes represent 

different ranges of well yield or specific capacity. State geologic 

maps were digitized into a GIS coverage. This included assigning a rock type to each geologic formation and aggregating all 

polygons that contain the same rock type into groups. The rock 

type was based on the lithologic term in the geologic formation 

name and may not reflect the bulk lithology of the formation in 

the study area. In the Valley and Ridge Physiographic Province, all units are placed in one of five hydrogeologic terranes 

that are based on Hollyday and others (1992) and Knopman 

and Hollyday (1993). For this report, the following five variables represent the percentage of the basin that is characterized 

by a hydrogeologic terrane:

Variable name 

included

VI

V2

V3

V4

Rock types

Siliciclastics.

Argillaceous carbonates.

Limestone.

Dolomite and mixtures of

V5

limestone and dolomite.

Alluvium.

Because the GIS data base does not include alluvium, values for the V5 were assigned manually for use in this report on 

the basis of map information from E.F. Hollyday and others 

(written commun., 1994). The only alluvium of any significance to regional hydrogeology in this study area is of glacial 

origin and is restricted to New Jersey and Pennsylvania (E.F. 

Hollyday, U.S. Geological Survey, written commun., 1994).

Two hydrogeologic terranes are designated for the Blue 

Ridge Physiographic Province, and six for the Piedmont Physiographic Province. The following eight variables represent the 

percentage of the basin that is covered by a hydrogeologic terrane. The prefix B stands for the Blue Ridge Physiographic 

Province and the prefix P stands for the Piedmont Physiographic Province. The numbers in parentheses represent the 

range of well yields in gallons per minute:
B58 REGIONAL AQUIFER-SYSTEM ANALYSIS APPALACHIAN VALLEY AND PIEDMONT

Variable name

Bl 

B2 

PI 

P2 

P3 

P4 

P5 

P6

Group BRM1 (0-25).

Group BRM2 (greater than 25).

Group PDM1 (0-10).

Group PDM2 (10-20).

Group PDM3 (20-30).

Group PDM4 (30-50).

Group PDM5 (50-100).

Group PDM6 (greater than 100).

Because some rock types are not areally extensive, there 

were not enough well-yield data to allow for a statistically significant assignment to a terrane. Because of this, the sum of all 

variables that quantify the amount of a basin covered by each 

terrane may not be equal to 100 percent for some basins. The 

variables pertain only to the part of the basin that is within the 

APRASA area.

As described in the following text, data are reduced further, 

before testing relations between rock characteristics of basins 

and hydrologic variables. The tests, which are illustrated in figures 13, 14, 23, 24, and 33, are performed in such a way that 

basins in the Valley and Ridge Physiographic Province are 

tested separately from those in the Blue Ridge and the Piedmont Physiographic Provinces because of the difference 

between these two subareas of the study area (Swain and others, 1991). In the latter subarea, tests are performed for the 

Piedmont Physiographic Province only because of the absence 

of rocks with high well yields in the Blue Ridge Physiographic 

Province. The elimination of the Blue Ridge Physiographic 

Province from these tests also reduces the interference caused 

by other variables, such as relief and precipitation, that vary 

much more in that province than in the Piedmont Physiographic Province.

Basins With Predominantly Small or Predominantly Large 

Well-Yield Rocks

This report designates some basins as being predominantly 

underlain by rocks with small or large well yields. The designations include various sets of hydrogeologic terranes and various thresholds that must be exceeded, which are established in 

such a way as to distinguish between the basins with small well 

yields and those with large well yields, without allowing the 

sample size of either to become excessively small.

 In the Valley and Ridge Physiographic Province, basins are 

considered to have predominantly small well-yield rocks 

if VI exceeds 90 percent.

 In the Valley and Ridge Physiographic Province, basins are 

considered to have predominantly large well-yield rocks 

if the sum of V2, V3, V4, and V5 exceeds 60 percent.

 In the Piedmont Physiographic Province, basins are considered to have predominantly small well-yield rocks if the 

sum of PI and P2 exceeds 60 percent.

 In the Piedmont Physiographic Province, basins are considered to have predominantly large well-yield rocks if the 

sum of P3, P4, P5, and P6 exceeds 90 percent.

Areally Weighted Average Basin Specific Capacity

This report uses a variable that represents the areally 

weighted average specific capacity of the rocks in a basin, the 

derivation of which is described below. The average basin specific capacity is a representation of the general water-transmitting capacity of the rock types in the basin and is simply a 

method for quantifying hydrogeologic properties.

First, a value for the median specific capacity for each 

hydrogeologic terrane is selected. To minimize bias, specific 

capacities are used instead of well yield, and the values used 

represent only the "most-productive" wells in the Valley and 

Ridge Physiographic Province (E.F. Hollyday, U.S. Geological 

Survey, written commun., 1994) and the "nondomestic" wells in 

the Blue Ridge and the Piedmont Physiographic Provinces.

Variable representing the

percentage of a

basin underlain by rocks

of a terrane

Specific capacity of rocks 

in this terrane 

[(gal/min)/ft]

VI

V2

V3

V4

V5

PI

P2

P3

P4

P5

P6

1.4

4.1

10.0

17.0

28.0

0.285

0.230

0.470

0.780

1.200

2.080

The areally weighted average specific capacity of rock 

types in a basin (SCB) is then determined by using one of the 

following equations:

Valley and Ridge Physiographic Province:

SCB =

1.4 x VI + 4.1 x V2 + 10 x V3 + 17 x V4 + 28 x V5 

100

Piedmont Physiographic Province:

0.285 x P1 + 0.23 x P2 + 0.47 x P3 + 0.78 x P4 + 1.2 x P5 + 2.08 x P6 SCB =

100

The only values of SCB that are used are for basins that have 

sufficient areal definition of rock characteristics the sum of VI 

through V5 or the sum of PI through P6 must be larger than 80 

percent.
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