GROUND-WATER FLOW AND

SIMULATED EFFECTS OF DEVELOPMENT IN

STAGECOACH VALLEY, A SMALL, PARTLY

DRAINED BASIN IN LYON AND STOREY

COUNTIES, WESTERN NEVADA

OREGON I IDAHO

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1409-H
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Ground-Water Flow and Simulated Effects 

of Development in Stagecoach Valley, 

a Small, Partly Drained Basin in 

Lyon and Storey Counties, Western Nevada

By JAMES R. HARRILL and ALAN M. PREISSLER

REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1409-H

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1994
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

Any use of trade, product, or firm names in this publication is for

descriptive purposes only and does not imply endorsement by the

U.S. Government

Library of Congress Cataloging-in-Publication Data

Harrill, James R.

Ground-water flow and simulated effects of development in Stagecoach Valley, a small, partly drained basin in 

Lyon and Storey Counties, western Nevada / by James R. Harrill and Alan M. Preissler.

p. cm. (U.S. Geological Survey professional paper ; 1409-H) (Regional aquifer system analysis Great 

Basin, Nevada-Utah) 

Supt. of Docs, no.: I 29.16:1409

1. Groundwater flow Nevada Lyon County. 2. Groundwater flow Nevada Storey County. 3. Economic 

development Environmental aspects Nevada. I. Preissler, Alan M. II. Title. III. Series. IV. Series: Regional 

aquifer system analysis Great Basin, Nevada-Utah. 

GB1197.7.H365 1993

553.7'9'0979356 dc20 93-7514

CIP

For sale by Book and Open-File Report Sales, U.S. Geological Survey 

Federal Center, Box 25286, Denver, CO 80225
FOREWORD

THE REGIONAL AQUIFER-SYSTEM ANALYSIS PROGRAM

The Regional Aquifer-System Analysis (RASA) Program was started in 

1978 following a congressional mandate to develop quantitative appraisals of 

the major ground-water systems of the United States. The 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, both 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, 

and where the volume of interpretive material warrants, separate topical 

chapters that consider the principal elements of the investigation may be 

published. The series of RASA interpretive reports begins with Professional 

Paper 1400 and thereafter will continue in numerical sequence as the interpretive products of subsequent studies become available.

Gordon P. Eaton 

Director

CONTENTS

Abstract 

Introduction 

Location and general features of the study area 

Approach and methods 

Acknowledgments 

GrGolo£?ic settin? » -»««»-« -«-»»» » «« 

units « « ««»« --- - -» -»«« 

li I HO i ei*/\i*v wwl jr _ - - «»«» » « « . -« « . -. _ . _._ _ _ _ _. . .--

Hydrologic setting

Climate and precipitation

Page

HI 

i

9^

2

2

4

Source, occurrence, and movement of ground water 8

Basin-fill aquifer 11

ArGal Gxt&nt --« -«« « - « - « « «« 11

Thickness ___________________________ 11

xivdraulic oroofirtifis -»» ««»»««» «« w«» « 12

Hydraulic conductivity 12

Storage properties 16

Ground water in storage 16

Recharge from precipitation 18

Maxey-Eakin method 18

Chloride-balance method 18

Discharge by evapotranspiration 18

Ground-water development 19

Simulation of ground-water flow __________ H19

Conceptualization of ground-water flow in basin-fill

Digital computer model 

Boundary conditions 

Initial conditions 

Transmissivity 

jjea.ixa.ncG - « «".»-«««» -- - --- - 

Storage coefficient 

Evapotranspiration of ground water 

Method of analysis of simulation results 

Results of simulation 

Predevelopment conditions 

Response to development 

Water-level declines 

Reductions in evapotranspiration 

Changes in inflow and outflow 

Ground-water budgets 

Sensitivity analysis 

Limitations of the model 

Simulated response to hypothetical development scenarios -

CtiTvi O11J.A 111 Uld. Q 4*1 VJ.UJJ. nn V*OQH X CO til 1 i~G wO ................................... «.««.»» - ........... ................. ...............

uiscussion ox res \iits ~~~»»» . .. ....................................

Summary and conclusions 

19

20

26

26

26

27

27

27

33

33

33

35

35

35

35

41

41

42

44

45

46

47

49

ILLUSTRATIONS

Page

FIGURE 1. Map showing location and general features of Stagecoach Valley H3 

2-11. Maps showing:

2. Generalized geology of Stagecoach Valley area 6

3. Generalized depth to ground water, predevelopment (pre-1971) conditions 9

4. Generalized water-level contours in basin-fill deposits, predevelopment (pre-1971) conditions 10

6. Distribution of horizontal hydraulic-conductivity values, upper 150 feet of saturated basin fill 14

7. Estimated vertical hydraulic conductivity, upper 150 feet of saturated basin fill 15

8. Distribution of estimated specific-yield values, upper 150 feet of saturated basin fill 17

9. Ground-water use areas in Stagecoach Valley, 1982 21

10. Ground-water-level contours, spring 1982 22

11. Ground-water-level declines, spring 1971 to spring 1982 23 

12. Block diagrams illustrating inflow-outflow relations, hydrogeologic section, and model-derived representation

13-19. Maps showing:

13. Finite-difference grid used to model ground-water flow system in Stagecoach Valley 25

14. Model-derived transmissivity of layer 1 of model 28

15. Model-derived transmissivity of layer 2 of model 29

16. Model-derived transmissivity of layer 3 of model 30

17. Model-derived leakance between layers 1 and 2 31

18. Model-derived leakance between layers 2 and 3 32

19. Simulated steady-state potentiometric surface for layer 2 34
VI CONTENTS

	Page 

FIGURE 20. Graph showing closeness of fit between observed or estimated and model-derived heads H35

21. Map showing observed and simulated areas of evapotranspiration 36

22. Map showing simulated water-table decline (layer 1), spring 1971 to spring 1982 37

23. Simulated and observed hydrographs of three wells completed in geologic equivalant of layer 1 38

24. Map showing simulated water-level decline in layer 2, spring 1971 to spring 1982 39

25. Simulated and observed hydrographs of five wells completed in geologic equivalent of layer 2 40 

26-34. Maps and graphs showing simulated responses to hypothetical development scenarios:

AO* ocenario x\ «. -. . - . - « «« -. «- "~ -. ". .-.-.--.«....--.... ...-. ... .~ . ~«--~....«-.... 0*

27 Scenario B __________ _______ _-____ _--------_____________ ___ __-____________ 54

98 £*U. Srpnnrin kJWClldX i\J \J P - "- ...-.-.--" - ... -..........-- --- ----- .--..-..-.... - - - - _ ... - __ _ ________________________________________________ WSfi

29 Scenario D ________-_- _____-_ __________._. ._____________________......._._.__ 58

U\Jt ^fl S/>a«avir> hJl*CXim LU 12J Tf ~ ~ ..... - ..-... .~.........-- . ~ .-. ....... ......................................... ....... ...............................-.. .-..-.-........ ...... ........ \j\J fifl

*J&, QO S/>onai'ir> kJljCXlttl Iw VJ d .. .. - - - -.- .- - -~ "..... . .~ «~ - - ........... .................__ _................ ................ ....-........_........._..___.___....... . ... _... fi4. \/f

UU3^ , fJ^dLdl Sr>pnnrin L\J J.J. TT- «....«-.. «.- ..... __- _._..........__................_. __ ___ __ ... __-..-..... ..... - -.-.................._.... ... .. ..... _..___._._....... ... fifi W

34 Scenario I _______________________________________________________________ 68

TABLES

	Page 

TABLE 1. Geologic units, their general hydrologic properties, and representative parts of ground-water flow model H5

2. Hydraulic conductivities of basin-fill deposits 12

3. Estimates of water stored in basin-fill aquifer of Stagecoach Valley, predevelopment (pre-1971) conditions 18

4. Estimated average annual recharge to basin-fill aquifer from precipitation, Stagecoach Valley 19

5. Estimated irrigated acreage, population, and ground-water pumpage, Stagecoach Valley, 1971-82 20

6. Simulated net changes in inflow and outflow from spring 1971 to spring 1982 41

7. Predevelopment (pre-1971) and 1981-82 ground-water budgets based on field observations and empirical analysis

3.H.Q OH St63.Qy~St3.t6 £HiQ tI*3nS16Iit SlXllUJ.3 tlOnS »«---------- " ------- - *- -' «*«»«»» «»« »«««» » -«--» -«» *r-5

o Su.iUTH3.rv of modGl~SGnsitivitv i*uns -~ ----------------------------------------------------------------------------^ 43

9. Simulated development scenarios 45

10. Ground-water budgets for scenario A 70

11. Ground-water budgets for scenario B 70

12. Ground-water budgets for scenario C 71

13. Ground-water budgets for scenario D 71

14. Ground-water budgets for scenario E 72

15. Ground-water budgets for scenario F 72

16. Ground-water budgets for scenario G 73

17. Ground-water budgets for scenario H 73

18. Ground-water budgets for scenario I 74

19. Comparison of aquifer responses under nine different development scenarios 46

CONVERSION FACTORS AND VERTICAL DATUM

Multiply By To obtain

acre

acre-foot (acre-ft)

acre-foot per year (acre-ft/Vr) 

cubic foot per second (fWs)

foot (ft)

foot per second (ft/s)

square foot per day (ft2/d)

gallon (gal)

inch (in.)

mile (mi)

square mile (mi2)

4,047

1,233

1,233 

28.32

0.3048

0.3048

0.0929

3.785

25.4

1.609

2.59

square meter

cubic meter

cubic meter per year 

liter per second

meter

meter per second

square meter per day

liter

millimeter

kilometer

square kilometer

For temperature, degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) by using the formula °C=0.5556(°F-32).

Sea Level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929, formerly 

called "Sea-Level Datum of 1929"), which is derived from a general adjustment of the first-order leveling networks of both 

the United States and Canada.
REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT

IN STAGECOACH VALLEY, A SMALL, PARTLY DRAINED BASIN IN LYON

AND STOREY COUNTIES, WESTERN NEVADA

By JAMES R. HARRILL and ALAN M. PREISSLER

ABSTRACT

Stagecoach Valley is a small, topographically closed basin in 

western Nevada with a total area of about 70 square miles. 

Local hydraulic continuity exists between Stagecoach Valley and 

the adjacent Carson River to the south and beneath parts of the 

northeastern area adjacent to Churchill Valley. Most of the 

locally derived runoff and recharge is generated in the Flowery 

Range on the north side of Stagecoach Valley. The basin fill is at 

least 500 feet thick throughout most of Stagecoach Valley and 

has a maximum thickness of about 3,000 feet.

A ground-water flow model was used to simulate the hydrology of Stagecoach Valley. It is estimated that about 1 million 

acre-feet of water is stored in the basin-fill aquifer of the Stagecoach Valley and that under predevelopment conditions the annual flow through the basin-fill aquifer underlying the valley 

was about 920 acre-feet. On the basis of the simulation, the flow 

components are (1) total inflow that included about 550 acre-feet 

per year of recharge from local precipitation, about 280 acre-feet 

per year of subsurface inflow from the upstream reach of the 

Carson River, and about 90 acre-feet per year of subsurface inflow from the downstream reach of the Carson River and (2) 

total outflow that included about 630 acre-feet per year by 

evapotranspiration, about 170 acre-feet per year by subsurface 

flow to Churchill Valley, and about 120 acre-feet per year by subsurface outflow to the downstream reach of the Carson River.

During the 11 pumping seasons 1971 through 1981, slightly 

more than 11,000 acre-feet of water was pumped from the basinfill aquifer. Of this, slightly less than 1,000 acre-feet of the water 

pumped for irrigation was recirculated back to the aquifer, 

resulting in a net pumping draft of about 10,000 acre-feet. About 

3,000 acre-feet was supplied by reductions in evapotranspiration 

and by changes in subsurface inflow and outflow; the remaining 

7,000 acre-feet of the pumpage was derived from ground-water 

storage. Water-level declines throughout the basin-fill aquifer 

ranged from 1 foot or less near the Carson River to more than 15 

feet in the developed area. Changes in subsurface inflow and 

outflow primarily involved inducing additional inflow from the 

Carson River.

The probable response to long-term pumping stress was evaluated by simulating nine hypothetical development scenarios. The 

results suggest that the sustained-yield concept of managing 

basin development is viable for Stagecoach Valley. This concept 

involves regulating pumpage so that over a long term withdrawals do not exceed the amount of natural discharge plus the

additional induced recharge. In all scenarios, considerable additional subsurface inflow was induced from the Carson River. 

This induced flow in turn suggests that the basin-fill aquifer of 

the valley is capable of attaining a new equilibrium in response 

to pumping rates far in excess of the natural (predevelopment) 

inflow rate of 920 acre-feet per year. Consequently, the 

predevelopment or natural flow through the aquifer is not considered the best criterion to be used in determining a sustained 

pumping rate in Stagecoach Valley. The limiting factor probably 

is the degree to which decreases of Carson River flows can be 

tolerated. The ground-water flow system is sensitive to variations in pumping rates and to the location of pumping; pumping 

the central and northern parts of the valley has the least effect 

on Carson River flows. Water-level changes alone are not 

adequate criteria for evaluating the aquifer's response; changes 

in subsurface inflow and outflow must also be considered. Because of the area's small size, the proximity of the aquifer 

boundaries strongly affects the response to any pumping stress.

INTRODUCTION

The hydrologic study of Stagecoach Valley was a 

part of the Great Basin Regional Aquifer-System 

Analysis (RASA) conducted by the U.S. Geological 

Survey. As discussed in the "Foreword," the RASA 

program is a study of ground-water systems at a 

large scale and is designed to systematically evaluate the major aquifer systems in the United States. 

The Great Basin area of Nevada, Utah, and adjacent States is considered to contain a regional aquifer system because the numerous individual basins 

within the area share many common characteristics 

and can be studied collectively. Currently about 240 

hydrographic areas (valleys that contain one or 

more structural basins) have been recognized 

within the study area of the Great Basin RASA 

(Harrill and others, 1983, p. 5). Detailed studies of 

all 240 areas were precluded because of limitations 

in time and resources. Consequently, a major 

problem in planning the study was allocating the

Hi
H2 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

available resources in a manner most likely to 

produce information with significant transfer value. 

The approach taken was to study areas that have 

conditions typical of other areas that would not be 

studied. Eight basins, which collectively represent 

most hydrologic conditions present in the Great 

Basin, were selected for study by use of groundwater flow modeling techniques.

Stagecoach Valley was selected because it is a 

small arid basin that is topographically closed to 

surface drainage yet at the same time is partly 

drained by subsurface flow. The boundary conditions are complex and appear to have a strong influence on the hydrologic regime of the area. 

Knowledge developed about the influence of the 

boundary conditions on the hydrologic regime and 

on the general response to pumping stresses should 

be applicable to other small arid basins. Also, detailed information about the boundary conditions of 

the basin-fill aquifer may have significant transfer 

value for parts of larger basins.

PURPOSE

The primary purpose of this study was to gain insight into processes affecting ground-water flow in 

small, arid alluvial basins. The specific objectives of 

the study were to describe the basin-fill aquifers in 

Stagecoach Valley quantitatively, configure and calibrate a ground-water flow model to simulate nine 

pumping scenarios, and present the results of the 

model simulations in general terms that may be 

compared with other areas modeled as a part of the 

Great Basin RASA study. This report presents the 

results of the study and also evaluates the applicability of the sustained-yield concept of management 

to this type of area. This concept involves regulating pumpage so that, over a long term, pumping 

rates do not exceed the amount of natural discharge 

that can be captured by pumping plus any additional 

recharge that is induced as a result of pumping.

LOCATION AND GENERAL FEATURES OF THE STUDY AREA

Stagecoach Valley is in western Nevada about 20 

mi east of Carson City (fig. 1). The general study 

area is bounded on the north by the Flowery Range, 

on the east by Churchill Valley and Churchill 

Butte, on the west by the Carson Plains part of 

Dayton Valley, and on the south by the Carson 

River. Stagecoach Valley is topographically closed 

and has a drainage area of about 70 mi2 , about 33

mi2 of which is underlain by basin-fill deposits. The 

study area includes Stagecoach Valley and adjacent 

parts of both Churchill Valley and the Carson River, 

which have some degree of hydrologic continuity 

with Stagecoach Valley. The highest mountains in 

the study area are in the Flowery Range and have 

a maximum altitude of 7,095 ft above sea level. 

Mountains bordering the east side of the area have 

altitudes of 5,812 ft or less, and those bordering the 

southwest margin of the valley have altitudes of 

5,221 ft or less. Most surficial drainage is to a 

playa, Misfits Flat (altitude about 4,260 ft), in the 

southeastern part of the valley (fig. 1). Sand dunes 

west of Misfits Flat cause intermittent ponding to 

occur where a few minor streams drain to a small 

area of alkali soil and sparse vegetation on the 

southwestern part of the valley floor. Vegetation in 

the remainder of the valley is sparse, especially on 

the valley floor where sage and shadscale predominate; pinon pine and juniper are present at higher 

altitudes at the north end of the area. Stagecoach 

Valley was virtually undeveloped before 1971.

APPROACH AND METHODS

Fieldwork began in the spring of 1982 and was 

completed by fall 1983. It consisted primarily of 

cataloging and measuring water levels in about 60 

wells; surveying altitudes of most of these wells; assembling and interpreting existing hydrologic and 

geologic information; mapping the geology and hydrologic features of selected areas; inventorying 

pumpage based on house counts and areas of lawns 

and irrigated cropland; collecting 24 water samples 

for chemical analysis; and performing geophysical 

surveys, including gravity readings at 100 stations 

and two seismic profiles. Quantitative estimates of 

aquifer geometry were based on the analysis of geophysical information and data reported by Schaefer 

and others (1986) and Schaefer (1988). Estimates of 

other aquifer properties were based on analysis of 

geologic and hydrologic information reported in well 

logs and on field observations. Harrill and others 

(1984) did a preliminary analysis of the geologic 

controls on ground-water flow and later analyzed 

water samples to obtain geochemical information to 

verify patterns of ground-water flow (Harrill and 

others, 1993).

A multilayered ground-water flow model was 

formulated on the basis of available information 

and an analysis of the hydraulic properties of aquifer materials. One pumping test and 11 specificcapacity values from drillers' logs were used to
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H3

119°25' 119°20'

39°20'

R. 22 E.

Base from U.S. Geological Survey 

Churchill Butte. 1:62.500.1957

VALLEY AREA

1 2 3 4 KILOMETERS

EXPLANATION

.._.._ TOPOGRAPHIC DIVIDE 

A GAGING STATION

MOUNTAINOUS AREA Includes 

some areas of older alluvium 

underlain by shallow bedrock

FIGURE 1. Location and general features of Stagecoach Valley. Base contour interval 200 feet.
H4 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

estimate the hydraulic properties of the aquifer 

materials. The model was calibrated against 

predevelopment heads and observed changes in 

head during the 11 pumping seasons from 1971 to 

1981. The calibrated model was used to simulate 

the generalized long-term response to nine selected 

development scenarios.

The water-level data and well information are from 

the data base of the ground-water site-inventory files 

of the U.S. Geological Survey' s National Water Data 

Storage and Retrieval System (WATSTORE). This information may be obtained through the U.S. Geological Survey office in Carson City, Nev, or through any 

designated National Water Data Exchange 

(NAWDEX) assistance center (Edwards, 1987).

ACKNOWLEDGMENTS

We thank the residents of Stagecoach Valley for 

their cooperation in supplying data and permitting 

access to their wells. Information on the Stagecoach 

public water-supply system was furnished by Oley 

Lawson of Stagecoach Utilities, Inc. The Utah Mining 

and Construction Company provided detailed information pertaining to the drilling and testing of 

several exploratory wells. Drillers' logs were obtained 

from the Nevada Division of Water Resources.

GEOLOGIC SETTING 

GEOLOGIC UNITS

The 11 principal geologic units in Stagecoach 

Valley are grouped into two general types: (1) unconsolidated and partly consolidated basin-fill clastic deposits and (2) consolidated rock that composes 

the mountains and underlies the basin fill. The first 

group consists of mostly highly porous materials 

such as sand and gravel, which in general readily 

transmit water, whereas the consolidated rock commonly has low porosity and permeability and does 

not readily transmit water except where highly 

fractured. The 11 units are described in terms of 

their geologic characteristics and water-bearing 

properties in table 1, and the generalized geology of 

the study area is shown in figure 2.

STRUCTURAL FEATURES

The structural features that appear to have most 

strongly influenced the geometry of the basin-fill 

aquifer in Stagecoach Valley are the Carson lineament and basin-and-range-type extensional faulting.

The Carson lineament is one of several northeasttrending structural zones with left-lateral strikeslip movement that are present in the western 

Basin and Range province. They were described by 

Slemmons and others (1979) as occurring in that 

part of the Basin and Range province between the 

eastern fault escarpment of the Sierra Nevada, 

about 25 mi to the west of the study area, and the 

Walker Lane, about 20 mi to the east. The Carson 

lineament extends northeastward from Carson City 

for about 94 mi (Rogers, 1975) and passes through 

Stagecoach Valley (fig. 2). Shawe (1965) described 

this feature as a left-lateral complement to the 

Walker Lane, which is a northwest-trending structural feature with a right-lateral component of 

movement. The low, broad divides separating Stagecoach Valley from the adjacent basins to the east 

and west are geomorphic expressions of the Carson 

lineament in the study area. No evidence of recent 

movement has been observed in Stagecoach Valley, 

but near Carson City, about 20 mi to the southwest, 

Rogers (1975) showed Holocene left-lateral, obliqueslip movement on faults cutting the Quaternary 

basin fill. The structural basin that underlies 

Stagecoach Valley appears to be elongate parallel to 

the Carson lineament, and fracturing possibly 

resulting from movement along the lineament 

might provide conduits for leakage of water from 

within the topographic boundaries of the area.

Basin-and-range faulting oriented generally 

north-south also has had a significant influence on 

the geometry of the basin underlying Stagecoach 

Valley. Churchill Butte, which is on the east side of 

the area, was described by Moore (1969, p. 22) as 

the exposed part of a westward-tilted fault block. 

The western part of this tilted block appears to extend beneath Stagecoach Valley and to form a 

north-south-trending structural trough beneath 

Misfits Flat and that part of the area northeast of 

Table Mountain. Basin-fill deposits in this trough 

allow for hydraulic continuity between the floodplain deposits of the Carson River and Stagecoach 

Valley. Relatively intensive normal faulting along 

the southwest boundary of Stagecoach Valley may 

have also provided for hydraulic continuity between 

flood-plain deposits of the Carson River and Stagecoach Valley by producing fractures in andesitic 

rocks and by tilting parts of a relatively permeable 

basalt flow to a position below the water table (fig. 

2, cross section).

GEOLOGIC HISTORY

The pre-Tertiary event that most significantly 

influenced the present hydrologic regime was the
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H5

TABLE 1. Geologic units, their general hydrologic properties, and representative parts of ground-water flow model

[Composite descriptions are based on Thompson (1956), Bonham (1969), Moore (1969), and Rose (1969) and on drillers' logs and field observations.

 , locally unknown]

Geologic unit Age Thickness 

(feet)

Geologic description Occurrence, general hydrologic properties, and 

representative parts of ground-water flow model

Cenozoic basin-fill deposits

Playa deposits.

Flood-plain 

deposits.

Younger 

alluvium.

Lacustrine (Lake 

Lahontan) 

deposits.

Holocene and 0-40 

Pleistocene.

.do. 0-30

,.do. 0-250

.do. 0-50

Unconsolidated clay, silt, and 

fine sand.

Unconsolidated sand, gravel, 

and some silt.

Unconsolidated sand, gravel, 

silt, and clay. Alluvial-fan 

and colluvial basin-fill 

deposits. Sand and gravel 

deposits interfingered with 

silt and clay toward center 

of basin.

Unconsolidated silt, clay, sand, 

and some gravel.

Older alluvium...... Pleistocene or 0-3,000

Pliocene.

Unconsolidated and partly 

consolidated sand, gravel, 

silt, and clay.

Occurs on and adjacent to Misfits Flat. Deposits have high 

porosity and low hydraulic conductivity; generally function 

as confining beds and do not readily yield water to wells. 

Represented in ground-water flow model as active cells in 

top layer (layer 1) with low hydraulic conductivity.

Occurs as terrace and channel deposits along Carson River 

flood plain. Contains highly permeable sand and gravel 

deposits that are aquifers and readily yield water to wells. 

Represented in ground-water flow model as active cells in 

top layer (layer 1) that have high hydraulic conductivity 

and high specific yield. Flow to and from Carson River is 

simulated from flood-plain deposits in model.

Occurs on valley floor and as alluvial fans at margins of 

valley. Lenses of sand and gravel and reworked shoreline 

lacustrine deposits yield water readily to wells and are 

most productive aquifers in valley. Saturated deposits 

represented as active cells in top and sometimes underlying layers of ground-water flow model; cells have high 

hydraulic conductivity and high specific yield.

Occurs below altitudes of 4,400 feet as prominent levee delta 

between Misfits Flat and Carson River. Deposits on much 

of valley floor covered by younger alluvium. Generally 

fine-grained materials with high porosity and low hydraulic conductivity; however, beach deposits, beds of sand, and 

some gravel lenses may yield water readily to wells. Simulated in ground-water flow model as active cells in either 

top or underlying layer of model. Hydraulic conductivity 

may range from low to high depending on deposit type.

Exposed in limited areas along north margin of valley. Also 

occurs at depth. Lenses of sand or gravel may yield 

moderate to large volumes of water to wells. Hydraulic 

conductivity thought to decrease with depth. Simulated as 

active cell in lower and middle layers of ground-water flow 

model; hydraulic conductivity of cells in middle layer is 

moderate to high and in lower layer is generally low.

Cenozoic and Mesozoic rocks

Basaltic rocks...

Andesitic rocks.

Pleistocene or 

Pliocene.

Pliocene and 

Miocene.

Sedimentary .do.

rocks.

Rhyolite tuff.......... .....do..........

Granitic rocks........ Cretaceous

Metasedimentary Jurassic or 

rocks. Triassic.

Predominantly thin lava flows 

with interbeds of scoriaceous basalt breccia and 

diatomaceous sedimentary 

rocks.

Flow breccias, lava flows, and 

agglomerates with interbedded sedimentary rocks. 

Locally includes basaltic 

and rhyolitic rocks.

Tuffaceous sandstone, siltstone, 

diatomaceous shale, and 

rhyolitic tuff.

Devitrified, slightly to strongly

welded, crystal-rich ash-flow

tuff. 

Nonporphyritic quartz monzonite,

granodiorite, and mafic rocks,

undivided.

Mainly shale, slate, tuffaceous 

siltstone, sandstone, and graywacke; largely derived from 

volcanic rocks. Minor interbeds 

of conglomerate, limy shale, 

limestone, dolomite, and gypsum.

Comprises most of Churchill Butte and occurs as scattered 

outcrops along south border of basin. Hydraulic 

conductivity may be high to moderate in scoriaceous 

zones and along numerous cooling joints and fractures. 

These generally saturated and fractured rocks are 

simulated as active cells in top or middle layer of groundwater flow model.

Crops out extensively around valley margins. Includes the 

Alta and Kate Peak Formations and the Chloropagus 

Formation of Axelrod (1956). Has virtually no interstitial 

permeability but locally may have zones of moderate to 

high permeability due to cooling fractures and joints. Flow 

breccias may have localized zones of moderate to high hydraulic conductivity. Generally simulated in ground-water 

flow model as inactive cells except in localized areas that 

are characterized by highly fractured rock.

Crops out along northeast boundary of area. Includes the 

Coal Valley Formation of Axelrod (1956). Generally low 

permeability; simulated in ground-water flow model by 

inactive cells.

Crops out in some minor exposures in northwestern part of 

basin. Includes the Hartford Hill Rhyolite Tuff of former usage. 

Simulated in ground-water flow model by inactive cells.

Represents two intrusive bodies whose outcrops total

several square miles in surface exposure in western part 

of area. Has very low hydraulic conductivity; locally may 

transmit some water if highly fractured. Simulated in 

ground-water flow model by inactive cells.

Minor exposures in western part and at northeast margin of 

valley. Low hydraulic conductivity; transmits water only 

where fractured. Simulated in ground-water flow model 

by inactive cells.
H6 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

emplacement of poorly permeable granitic rocks 

during Late Cretaceous to early Tertiary time (96 to 

63 Ma). This event formed the mass of poorly 

permeable granitic rocks on the west border of the 

area and altered existing rocks of Triassic or Jurassic age to form the metamorphic rocks exposed on 

the east flank of the Flowery Range.

A major tectonic change occurred during Miocene 

time (24 to 5 Ma) with the onset of extensional

faulting at about 17 Ma. This faulting formed the 

major basins and ranges that characterize the 

present-day physiography. The initial extension was 

accompanied by volcanic activity that continued 

into late Tertiary time and produced widespread 

sequences of andesitic rocks throughout the area. In 

late Tertiary time, a structural basin began to form, 

and the sediments mapped by Rose (1969) as the 

Coal Valley Formation were deposited in the north39°20'

Base from U.S. Geological Survey 

Churchill Butte, 1:62,500, 1957

Geology modified in 1983 by A.M. 

Preissler from Thompson (1956), 

Bonham (1969), Moore (1969), 

and Rose (1969)

FEET 

5500-

5000- 

4500- 

4000-

3500

3 5

1

1 

3 5

1 

10

10

I

I 

15

15 MILES

I

I 

20 KILOMETERS

FIGURE 2. Generalized geology of Stagecoach Valley area. See table 1 for description of lithologic units. "WATER TABLE" in section

refers to projection of water table from beneath flood plain of Carson River.
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H7

ern part of the area. The boundaries of the structural basin associated with these deposits probably 

did not coincide well with the present-day boundaries of Stagecoach Valley. High-angle extensional 

faulting probably was occurring contemporaneously, 

and during this same general time a structural 

block that underlies Churchill Butte and extends 

about 2 mi west beneath Stagecoach Valley began 

tilting to the west. This tilting initiated the deformation that accounts for the main structural 

depression underlying Stagecoach Valley.

During Pliocene or early Pleistocene time, 

renewed volcanic activity covered a significant part 

of the area with basalt flows. Structural deformation, primarily high-angle normal faulting and possibly some left-lateral movement along the Carson 

lineament, continued during this time, completing

EXPLANATION

QUATERNARY Holocene and Pleistocene 

PLAYA DEPOSITS

FLOOD-PLAIN DEPOSITS

YOUNGER ALLUVIUM

LACUSTRINE (LAKE LAHONTAN)

QUATERNARY OR TERTIARY Pleistocene 

or Pliocene

OLDER ALLUVIUM

BASALTIC ROCKS 

TERTIARY Pliocene and Miocene 

ANDESITIC ROCKS

SEDIMENTARY ROCKS

RHYOLITE TUFF Includes Hartford Hill 

Rhyolite Tuff of former usage

CRETACEOUS

GRANITIC ROCKS 

JURASSIC OR TRIASSIC

METASEDIMENTARY ROCKS

CONTACT

FAULT Dashed where approximately located, dotted where 

concealed

TOPOGRAPHIC DIVIDE 

FIGURE 2. Continued.

the structural depression that now underlies Stagecoach Valley.

In Pleistocene time, before the development of 

ancient Lake Lahontan (which, during part of the 

Pleistocene, covered much of western Nevada), the 

major topographic features of the study area were 

similar to those of today, except that the area was 

not a topographically closed basin. Runoff from the 

Flowery Range flowed southeastward across Stagecoach Valley and contributed to the pre-Lahontan 

flow of the Carson River. When Lake Lahontan 

formed and reached its highest levels (altitude of 

about 4,366 ft in the vicinity of Stagecoach Valley), 

most of the valley floor was submerged to a depth 

of at least 100 ft. During interlake stages, sediment 

carried by the Carson River was deposited across 

the mouth of the pre-Lahontan drainage from 

Stagecoach Valley, forming a pronounced natural 

levee that blocked surface discharge from Stagecoach Valley and caused the playa, Misfits Flat, to 

form. Hydrologic processes, such as subsurface outflow and ground-water evapotranspiration, also 

were affected. The exact time (or times) at which 

blockage occurred is not known; however, radiocarbon dating indicates that Lake Lahontan rose 

high enough to flood the basin and then receded at 

least three times during the Lake Lahontan pluvial 

period: at least once before 40,000 yr B.P. (radiocarbon years before 1950), from 25,000 to 21,500 yr 

B.P, and from 13,600 to 11,100 yr B.P. (Benson, 

1978, p. 312-315). For the past 11,000 yr the area 

has been a topographically closed basin, and a relatively thin sequence of playa deposits has accumulated behind the topographic divide formed by the 

levee. Lacustrine beaches and nearshore deposits 

associated with the rise and recession of Lake 

Lahontan form relatively permeable units in the 

upper basin fill.

HYDROLOGIC SETTING 

CLIMATE AND PRECIPITATION

The climate in Stagecoach Valley and the surrounding mountains varies from arid to semiarid, 

depending principally on altitude. There are no precipitation stations in the area, but average annual 

precipitation at three stations within 10 to 15 mi of 

Stagecoach Valley is 9 in. at Virginia City, altitude 

6,002 ft; 4.4 in. at Lahontan Dam, altitude 4,158 ft; 

and 6.6 in. at Fernley, altitude 4,160 ft (Glancy and 

Katzer, 1975, p. 18). Precipitation for most of the 

valley is within this range except for those areas 

above 6,000 ft altitude, which generally receive
H8 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

more precipitation. Most of the precipitation falls as 

rain and snow in the winter months; minor 

amounts of rain fall during thunderstorms in the 

summer. Summers are hot and dry, with daytime 

temperatures occasionally exceeding 100°F, and 

winters are cool, with temperatures sometimes falling below 0°F. The average growing season is about 

120 days.

SURFACE WATER

The streams in Stagecoach Valley flow only during periods of rapid snowmelt or intense precipitation. Their channels are poorly defined downstream 

from the mountains because flow usually spreads 

out over the porous Quaternary basin-fill sediments 

and infiltrates rapidly. Consequently, significant 

flow reaches Misfits Flat only during exceptionally 

wet seasons or after periods of intense rainfall. 

Flow that reaches Misfits Flat ponds and evaporates. There is no surface outflow to the Carson 

River. Because of the intermittent flow and the 

small size of the drainage areas, the streams probably contribute relatively small amounts of recharge to the ground-water system after leaving the 

mountains.

The Carson River is one of the major rivers 

draining the east flank of the Sierra Nevada. Its 

headwaters are in the Sierra Nevada, about 60 mi 

southwest of Stagecoach Valley, and the river terminates in the Carson Sink, about 60 mi northeast of 

Stagecoach Valley. Based on 71 yr of record, the average annual flow at a gaging station on the Carson 

River near Fort Churchill, about 2 mi downstream 

from Stagecoach Valley, was 264,000 acre-ft as of 

1982 (Frisbie and others, 1983, p. 141). An additional 16,000 acre-ft/yr of water is diverted upstream of the gaging station through the Buckland 

ditch (Glancy and Katzer, 1975, p. 66), so the total 

flow averages about 280,000 acre-ft/yr.

Much of the annual flow occurs during snowmelt 

periods in May or June. Lowest flows generally occur during August, September, or October. There 

have been some periods of no flow at the gaging 

station each year since 1923 (Frisbie and others, 

1983, p. 141); however, low-flow conditions in the 

Buckland ditch (fig. 1) are not well documented, so 

firm flow-duration estimates of periods of low flow 

cannot be made. Schroer and Moosburner (1978, p. 

211) indicated that flow at the gaging station 

equaled or exceeded 1 ft3/s 85 percent of the time 

and that flow equaled or exceeded 10 ft3/s about 70 

percent of the time.

Reaches of the Carson River are in hydraulic 

continuity with the aquifers in Stagecoach Valley. 

The river may be either a source of subsurface 

inflow or a drain for subsurface outflow, depending 

on the local hydraulic gradients. The annual flow of 

the river is much greater than the annual groundwater flow through Stagecoach Valley; consequently, 

changes in inflow to or outflow from Stagecoach 

Valley aquifers would probably not be significant in 

relation to overall annual volume of river flow. 

However, the changes may be significant during 

periods of very low flow.

SOURCE, OCCURRENCE, AND MOVEMENT OF GROUND 

WATER

Virtually all the ground water in Stagecoach 

Valley is derived from two sources: precipitation 

that falls within the drainage basin and subsurface 

inflow from beneath the flood plain of the Carson 

River. Most recharge occurs in or adjacent to the 

mountain fronts (where precipitation infiltrates a 

thin mantle of unconsolidated deposits), through 

weathered or fractured consolidated rock, or where 

intermittent runoff infiltrates channel deposits and 

percolates down to the zone of saturation.

Ground water occurs in saturated basin fill under both water-table and confined conditions. The 

general depth to ground water in 1971, prior to development, is shown in figure 3. The general configuration of the water table in Stagecoach Valley 

prior to development in 1971 is shown in figure 4. 

The water-level contours were constructed using 

the earliest data available, mostly measurements 

in the early 1970's. Contours along the flood plain 

of the Carson River are based on controls from a 

few wells and on controls at points where contours 

on topographic maps cross the river. In the north 

and central parts of the valley, flow is generally 

from areas adjacent to the Flowery Range toward 

Misfits Flat and the flood plain of the Carson 

River southeast of Misfits Flat. The water table 

between Misfits Flat and the Carson River is 

nearly flat. However, the flood plain of the Carson 

River has an eastward gradient of about 7 ft/mi. 

Consequently, along the downstream reach of the 

river some water may flow northward into Stagecoach Valley in the vicinity of Table Mountain, 

whereas a short distance downstream water flows 

southeastward from Stagecoach Valley toward the 

flood plains of the river. There is probably a small 

net outflow from Stagecoach Valley to the Carson 

River.
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H9

119°30' 119025' 119°20'

39°25'

39°20'

Base from U.S. Geological Survey 

Churchill Butte, 1:62,500,1957 3 MILES

0

BASIN FILL 

CONSOLIDATED ROCK

4 KILOMETERS

EXPLANATION

 30 LINE OF EQUAL DEPTH TO WATER, 

PREDEVELOPMENT (PRE-1971) 

CONDITIONS Dashed where approximately located. Interval, in feet, is 

variable

-- -- TOPOGRAPHIC DIVIDE 

 WELL Used as control point

FIGURE 3. Generalized depth to ground water, predevelopment (pre-1971) conditions.
H10

119 

39°25'

'SOREGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

119°25' 119°20'

39°20'

Base from U.S. Geological Survey 

Churchill Butte. 1:62.500.1957 3 MILES

1 I

2 3

EXPLANATION

4 KILOMETERS

BASIN FILL Cross hachures indicate area of playa

CONSOLIDATED ROCK Stipple indicates rock 

permeable enough to allow subsurface inflow 

to Stagecoach Valley

AREA OF NATURAL GROUND-WATER DISCHARGE 

Vegetated primarily by greasewood (P.A. Glancy, 

U.S. Geological Survey, written commun., 1982)

-4240 WATER-LEVEL CONTOUR, PREDEVELOPMENT 

(PRE-1971) CONDITIONS Dashed where 

approximately located. Contour interval, in 

feet, is variable. Datum is sea level

GROUND-WATER DIVIDE

TOPOGRAPHIC DIVIDE

WELL Used as primary control point

WELL Where data were extrapolated back to estimate predevelopment (pre-1971) conditions. Used 

as supplemental control point

FIGURE 4. Generalized water-level contours in basin-fill deposits, predevelopment (pre-1971) conditions.
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA Hll

In sec. 1, T. 17 N., R. 23 E. (fig. 4) the groundwater divide between Stagecoach Valley and 

Churchill Valley is located about 1/4 mi west of the 

topographic divide. The steep hydraulic gradient between Stagecoach Valley and Churchill Valley could 

indicate either low permeability or a narrowing of 

the flow section.

In the western part of the valley, the water-level 

contours indicate that water moves northeastward 

toward Misfits Flat (fig. 4). Harrill and others 

(1993) use an average hydraulic gradient of about 5 

ft/mi, a width of section of about 1 mi, and an estimated transmissivity of about 4,000 ft2/d to estimate an annual flow of 130 to 170 acre-ft/yr moving 

northeastward from the area of postulated subsurface inflow (fig. 4).

Because most local recharge is generated in 

areas of higher altitude in the Flowery Range, the 

expected direction of flow is generally eastward or 

southeastward toward the playa. The 4,250-ft contour (fig. 4) was based on data from three wells 

that all had measurements in the early 1970's, 

were completed in the same interval of saturated 

basin fill, and had altitudes determined by leveling; consequently, the northeast flow direction indicated by this contour is considered valid. This 

suggests that inflow occurs in the southwestern 

part of the valley. The most probable explanation 

is that ground water beneath the flood plain of the 

Carson River, with a head about 25 ft higher than 

ground water in adjacent Stagecoach Valley, flows 

northeastward into Stagecoach Valley through fractured consolidated rock. Harrill and others (1993) 

conclude that this hypothesis is valid by evaluating the geologic feasibility of flow through the 

andesitic and basaltic rocks at the south end of the 

valley and by showing that the stable isotopic composition of water downgradient from the area of 

inferred inflow is similar to that of water in the 

Carson River.

BASIN-PILL AQUIFER

Stagecoach Valley occupies a structural depression that is bounded and underlain by consolidated 

rock. The depression is filled in part by deposits of 

gravel, sand, silt, and clay derived primarily from 

the adjacent mountains. These deposits form the 

basin-fill aquifer in Stagecoach Valley; the sand and 

gravel in particular yield a large amount of water 

to wells.

AREAL EXTENT

The approximate areal extent of the basin-fill 

aquifer of Stagecoach Valley is shown by the extent 

of younger alluvium in figure 2. Total surface area 

is about 33 mi2, or almost 50 percent of the total 

drainage area of Stagecoach Valley (fig. 1). The 

basin-fill aquifer is bounded on the north and east 

by consolidated rock of the Flowery Range and 

Churchill Butte, respectively. On the west an 

alluvium-covered topographic divide exists between 

Stagecoach Valley and the Carson Plains part of 

Dayton Valley and is underlain by consolidated rock 

at relatively shallow depth. The southwestern part 

of the basin-fill aquifer is bounded by exposures of 

volcanic rock, but in the southeastern part the 

aquifer is continuous with the flood-plain deposits 

of the Carson River.

THICKNESS

Wells drilled in Stagecoach Valley range in depth 

from several tens of feet to 820 ft, and most are 

completed in basin fill. Gravity surveys were used 

to obtain estimates of the thickness of basin-fill 

deposits. The vertical acceleration of gravity is affected, in part, by the density of underlying materials. Unconsolidated basin-fill deposits typically 

have substantially lower densities than adjacent 

and underlying consolidated rock, therefore gravity 

anomalies in the valley are roughly proportional to 

the thickness of basin fill.

Schaefer (1988) constructed a detailed Bouguer 

gravity anomaly map on the basis of about 100 

measurements made in the Stagecoach Valley area. 

These data were processed using techniques similar 

to those used in producing maps of gravity anomalies in several valleys in west-central Nevada 

(Schaefer, 1983, p. 6-9). Thickness of basin fill was 

estimated semiquantitatively using a computer program that makes a three-dimensional analysis of 

gravity anomalies based on a specified density contrast between basin-fill deposits and consolidated 

rock (Cordell and Henderson, 1968). A density contrast of 0.5 g/cm3 was used in this analysis. Two 

seismic profiles were made to verify the thicknesses 

computed from the gravity data.

The structural depression that underlies the valley is complex. The thickest deposits of basin fill 

occur along a zone that extends from the northcentral part of the valley beneath Misfits Flat to
H12 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

the area northeast of Table Mountain (fig. 5). Moore 

(1969, p. 22) stated that Churchill Butte was the 

exposed part of a westward-tilted fault block. The 

north-south-trending area of thickest fill shown on 

figure 5 may indicate the downdropped west edge of 

this fault block. There also are indications of a 

shallow structural depression oriented along the 

general trend of the Carson lineament. The thickest 

fill (3,000 ft) occurs slightly southwest of Misfits 

Flat. However, most of the fill is between 500 and 

2,000 ft thick. In the southeastern part of the valley, the basin fill appears to be continuous with 

flood-plain deposits of the Carson River, and the 

depth to consolidated rock northeast of Table Mountain is estimated to range from 500 to more than 

1,000 ft (see the area of downstream reach shown 

in fig. 5). Data from a seismic profile at Misfits Flat 

show an increase in density at a depth of about 530 

ft. The denser material may be partly consolidated 

fill and probably does not transmit water as readily 

as the overlying deposits.

HYDRAULIC PROPERTIES

HYDRAULIC CONDUCTIVITY

Most alluvial deposits in Stagecoach Valley are 

nearly flat lying; thus, horizontal hydraulic conductivity is usually much greater than vertical hydraulic conductivity. Approximate values of the 

horizontal hydraulic conductivity of deposits typical 

of those in the basin-fill aquifers are listed in table 2;

these values agree closely with those shown for 

similar materials by Chow (1964, fig. 13-8).

The general distribution of horizontal hydraulicconductivity values in Stagecoach Valley was 

mapped using lithologic descriptions from drillers' 

logs, the results of one pumping test, and 11 specific capacities. The estimated average horizontal 

hydraulic-conductivity values of the upper 150 ft of 

saturated basin fill are shown in figure 6.

The average vertical hydraulic conductivity of a 

sequence of deposits is estimated as a geometric 

mean that is influenced strongly by low values typical of intervals of silt and clay. The ratio between 

the average vertical and average horizontal hydraulic conductivities varies according to the types of 

material in the interval evaluated. Sequences of 

well-sorted sand and gravel commonly have higher 

vertical hydraulic conductivities than sequences 

that contain significant amounts of clay, silt, or 

cemented materials, for which the average vertical 

hydraulic-conductivity values can be as small as 0.1 

to 1 percent of the horizontal hydraulic conductivity. The distribution of estimated vertical hydraulicconductivity values in the upper 150 ft of saturated 

basin fill (fig. 7) was based on the distribution of 

geologic materials and estimated ratios between the 

average vertical and horizontal conductivity. The 

range of values for average vertical hydraulic conductivity shown in figure 7 is less than the range of 

values shown in figure 6 for horizontal hydraulic 

conductivity because the average values of vertical 

hydraulic conductivity are weighted toward values 

typical of silt and clay.

TABLE 2. Hyraulic conductivities of basin-fill deposits 

[Geologic units are described more fully in table 1]

Geologic unit Typical materials

Estimated range of 

horizontal hydraulic

conductivity 

(feet per second)

Playa deposits........................... Clay and silt......................................

Very fine sand....................................

Flood-plain deposits ................. Sand....................................................

Gravel.................................................

Younger alluvium ..................... Mostly silt, some sand and gravel..

Sand and gravel1 ...............................

Lacustrine (Lake Lahontan) Silt and clay.......................................

deposits. Fine sand............................................

Older alluvium2 ........................ Mostly silt, some sand and gravel1 .

Sand and gravel................................

l.OxKT6 

l.OxKT6

4.6xl(T5 2.3xlO~4

l.OxKT6 

4.6xl(T5

l.OxKT6 

l.OxKT5

l.OxKT6 

4.6xlO~5

to 3.0xl(T6 

to 1.8xl(T5

to 3.0xl(T4 

to 1.7xl(T3

to 4.6xl(T5 

to 1.7xl(T3

to 6.0xlO~5 

to 4.6xl(T5

to 4.6xl(T5 

to 1.7xlO~3

'Poorly sorted mixtures that occur primarily in fanglomerate deposits in younger and older alluvium.

2Same typical materials as younger alluvium, but materials are more likely to be semiconsolidated. 

Same range of estimated horizontal hydraulic conductivity is shown for both younger and older alluvium, 

but materials in older alluvium are more likely to have values near lower end of range because of greater 

consolidation and cementation.
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H13

119°30' 

39°25'

119°25' 119°20'

39°20'

££--V>-; ' -«-^lb

Z~J* :-' ^H.\< ^y^-^s 1"^ -*s "'O

k « ,f%_-\ r

.vOrV;^ ^

Base from U.S. Geological Survey 

Churchill Butte. 1:62.500.1957 1 3 MILES 

J

I I I 

234 KILOMETERS

EXPLANATION

BASIN FILL

CONSOLIDATED ROCK

30 ---- LINE OF EQUAL ESTIMATED THICKNESS OF 

BASIN FILL Dashed where line based on 

gravity data was modified on basis of welllog, seismic, or geologic information. Interval, 

500 feet 

970

LOCATION OF SEISMIC PROFILE Number is 

calculated thickness of basin fill, in feet

 TOPOGRAPHIC DIVIDE

FIGURE 5. Estimated thickness of basin-fill deposits. Adapted from Schaefer (1988).
H14

119°30'

REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

119°25' 119°20'

39°25'

39°20'

Base from U.S. Geological Survey 

Churchill Butte. 1:62.600,1957

CONSOLIDATED ROCK

1 2 3 4 KILOMETERS 

EXPLANATION

ESTIMATED HORIZONTAL HYDRAULIC .._.._ TOPOGRAPHIC DIVIDE

CONDUCTIVITY OF BASIN FILL , IN FEET 

PER SECOND

Less than l.OxlO'5 

I.OXIO-5 to 7.5X10-5 

7.5X10-5 to 12.5X10-5 

Greater than 12.5X10"5 

Not estimated

20 WELL Where hydraulic conductivity 

was estimated on basis of specific 

capacity or aquifer test. Estimated 

hydraulic conductivity is given in 

1X10-5 feet per second. "A" 

following value signifies value 

based on aquifer test

FIGURE 6. Distribution of horizontal hydraulic-conductivity values, upper 150 feet of saturated basin fill.
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H15

119°30' 119°251 119°201

39°25'

39°20-

Base from U.S. Geological Survey 

Churchill Butte. V62.500.1957 3 MILES

1 1 1

1

D 1

I 

2

I 

3

I 

4 KILOMETERS

EXPLANATION

CONSOLIDATED ROCK

ESTIMATED VERTICAL HYDRAULIC 

CONDUCTIVITY IN BASIN FILL, IN 

FEET PER SECOND

Less than l.OXlO'7 

1.0X10-7 to 1.5X10-7 

1.5X10-7 to 2.0X10-7 

2.0XlO-7 to2.5XlO-7 

Greater than 2.5X10'7 

Not estimated

 TOPOGRAPHIC DIVIDE

FIGURE 7. Estimated vertical hydraulic conductivity, upper 150 feet of saturated basin fill.
H16 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

STORAGE PROPERTIES

Specific yield of alluvial deposits ranges from less 

than 5 percent in compacted clay or deposits with 

extensive cementation or caliche development to 

about 30 percent in well-sorted sand or gravel (fig. 

8). Estimates of specific yield were developed by 

evaluating lithologic descriptions in drillers' logs 

and assigning values based on specific-yield data 

listed by Morris and Johnson (1967) for similar 

deposits. An area of predominantly playa deposits 

beneath Misfits Flat was assigned an average 

specific yield of less than 5 percent. Areas on the 

valley floor underlain predominantly by finegrained lacustrine and other deposits were assigned 

average specific-yield values of 5 to 10 percent. The 

alluvial-fan and associated coarse-gravel deposits 

around the margins of Stagecoach Valley were 

assigned specific yields of greater than 10 percent. 

Assigned values for individual deposits ranged from 

10 to 30 percent, with the higher values representing well-sorted sand and gravel (primarily reworked 

beach and nearshore lacustrine deposits) and the 

lower values representing poorly sorted deposits 

such as mudflows. Average specific yield for these 

deposits was estimated to be about 13 percent.

Coarse-grained deposits, such as sand and gravel, 

are characterized by a relatively rigid framework 

that is supported by grain-to-grain contact; aquifer 

compression in these deposits is typically elastic. 

Fine-grained deposits, such as clay or silt, generally do not possess a rigid framework. In a confined 

aquifer, if the head is high enough to keep framework stresses below the level of preconsolidation 

stress of the sediments, then water yielded would 

be from elastic expansion of water. However, if the 

head falls to the level where framework stresses 

exceed the preconsolidation stress of the sediments 

but is still above the altitude of the confining bed, 

then water yielded would be from inelastic compression of the sediments as well as from expansion 

of water. Studies in other areas (Holzer, 1981) have 

shown that water levels had to be lowered about 50 

ft, to as much as 200 ft below prepumping levels, 

before the preconsolidation stress of the sediments 

was exceeded and inelastic depletion of storage 

began. Consequently, for this study, the groundwater system is considered to be an elastic system. 

In several model scenarios developed in a later 

section of this report, localized drawdowns exceed 

100 ft; however, errors induced by not including 

inelastic storage are considered relatively small 

and probably do not significantly affect the overall 

results.

For elastic conditions, Lohman (1972, p. 53) 

stated that the rule-of-thumb relation to roughly 

estimate a storage coefficient of a confined aquifer 

is to multiply the thickness of the aquifer by IxlO"6. 

In Stagecoach Valley, saturated basin fill ranges 

from 0 to 3,000 ft in thickness. If no fine-grained 

deposits were present and yielded water was entirely from the expansion of stored water in the 

confined part of the aquifer, the storage coefficient 

of confined deposits for thicknesses of 100 to 3,000 

ft would be IxlO"4 to 3xlO~3.

GROUND WATER IN STORAGE

The potentially recoverable water stored in the 

basin-fill aquifer can be estimated as the product of 

an area, a thickness, and a specific yield. The following procedures were used to compile estimates 

of water stored in the basin-fill aquifer of Stagecoach Valley: (1) The area underlain by basin fill 

was divided into 176 rectangular cells identical to 

those used in the ground-water model discussed 

later in this report. (2) For each cell the thickness 

of saturated basin fill was determined using total 

thickness of fill shown in figure 5 and depths to 

water shown in figure 3; the specific yield was 

determined from figure 8. (3) Two intervals were 

used, the upper 200 ft of saturation and the underlying remainder of the saturated basin fill. The 

water stored in the interval below 200 ft was further reduced by 5 to 15 percent of the estimated 

amount to account for the expectation of lower specific yields in the older, more deeply buried deposits. (4) Values for cells were summed to give 

estimates of total stored ground water (table 3). 

Computations were made for pre-1971 conditions 

for two general areas, the area that was developed 

as of 1982 and the remainder of the basin-fill 

aquifer (fig. 8).

The total amount of water stored in the basin-fill 

aquifer of Stagecoach Valley prior to development 

(before 1971), estimated to be about 1 million acreft (table 3), illustrates the large volume of water 

that has accumulated over many centuries in a 

comparatively small basin. Much of this water cannot be pumped because of economic factors (such as 

high pumping lifts, which mean high costs using 

existing technology), legal issues (such as probable 

depletion of flow in the Carson River), and environmental factors (such as land subsidence and drying 

of habitat along the flood plain of the Carson 

River). The quality of the deeper water is not 

known; however, in the upper 200 ft of saturated
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H17

119°25' 119°20'

Base from U.S. Geological Survey 

Churchill Butte. 1:62.500.1957

39020'

4 KILOMETERS

ESTIMATED SPECIFIC YIELD OF BASIN 

FILL, IN PERCENT

Less than 5 

5 to 10 

More than 10 

Not estimated

 BOUNDARY OF AREA WHERE STORAGE

OF WATER IN AQUIFER WAS COMPUTED

 - - - BOUNDARY OF GENERAL AREA OF 

DEVELOPMENT, AS OF 1982

 - - TOPOGRAPHIC DIVIDE

FIGURE 8. Distribution of estimated specific-yield values, upper 150 feet of saturated basin fill.
H18 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

TABLE 3. Estimates of water stored in basin-fill aquifer of 

Stagecoach Valley, predevelopment (pre-1971) conditions

[ , not applicable. All values are rounded to two significant figures]

Ground water in storage 

(acre-feet)

saturated 

basin fill 

(feet)

Inside area 

developed 

as of 1982

Outside area 

developed 

as of 1982

Total

Stagecoach Valley

0-200..................

>200 ....................

.............. 89,000

.............. 220,000

180,000 

470,000

270,000 

690,000

Subtotal ..................... 310,000 650,000 960,000

Area between Carson River and topographic divide 

of Stagecoach Valley1

0-200. 

>200...

26,000

45,000

26,000

45,000

Subtotal 71,000 71,000

Combined areas

Total ........................... 310,000 720,000 1,000,000

'Area that is expected to be affected under simulated development scenarios.

basin fill, the estimated 89,000 acre-ft of water inside the 1982 area of development and some of the 

180,000 acre-ft outside that area probably can be 

pumped with economic pumping lifts, using the 

1982 distribution of pumping. Even so, depletion of 

this amount of storage might reduce heads significantly in places and would probably induce significant inflow from the Carson River.

RECHARGE FROM PRECIPITATION

MAXEY-EAKIN METHOD

Ground-water recharge from precipitation was estimated using the method outlined by Eakin and 

others (1951, p. 79-81). The average precipitation 

for altitude zones within the basin (fig. 1) was estimated using data from local stations and values 

from a map of Nevada showing annual precipitation 

(Hardman and Mason, 1949, p. 10). Then for each 

altitude zone the percentage of the total precipitation that would potentially become ground-water 

recharge was estimated using coefficients developed 

by Maxey and Eakin (1949, p. 40-41). The highest 

estimated percentages. of recharge occur in the 

mountain areas, where most of the annual precipitation occurs. Over most of the valley floor, the 

estimated percentage of recharge is negligible, 

although some recharge may be generated in the

valley floor area during extremely localized storms. 

The estimated average annual recharge to the 

basin-fill aquifer of Stagecoach Valley from precipitation falling within the drainage area is about 580 

acre-ft/yr (table 4).

CHLORIDE-BALANCE METHOD

A technique to estimate recharge on the basis of 

chloride balance between precipitation and ground 

water was developed and applied to selected areas 

in the Great Basin by Dettinger (1989). This technique assumes that chloride is conserved, that 

areas of recharge are known, that chloride concentrations in precipitation (C ) and in ground water 

(C ) in and near recharge areas are known, and 

that the volume of precipitation that falls on the 

recharge areas (V ) can be estimated. When these 

assumptions are valid, the volume of recharge (Vr) 

can be approximated as follows:

Using 0.4 mg/L as the average concentration of 

chloride in precipitation, 12,200 acre-ft/yr as the 

average volume of precipitation at altitudes of 5,000 

ft or higher (see table 4), and 11.0 mg/L as the 

average concentration of chloride in ground water 

in the recharge area based on 10 samples from 4 

springs and wells in or near recharge areas in 

Stagecoach Valley (Dettinger, 1989, p. 69), the recharge to the basin-fill aquifer from precipitation is 

estimated to be about 440 acre-ft/yr. Although this 

estimate is somewhat less than the 580 acre-ft/yr 

estimate (table 4), both indicate relatively low volumes of annual recharge and are considered to be 

reasonable.

DISCHARGE BY EVAPOTRANSPIRATION

Of about 4,000 acres of phreatophyte vegetation 

mapped in the valley (fig. 4), about 3,000 acres consists primarily of low- to moderate-density greasewood (generally less than 10 percent areal cover) 

and about 1,000 acres (Misfits Flat) consists primarily of bare soil and low-density greasewood 

mounds. Average annual ground-water consumption 

in these areas was estimated to be 0.2 and 0.1 ft/yr, 

respectively, on the basis of rates used by Glancy 

and Katzer (1975, p. 62-64). Using these rates and 

areas, the total estimated evapotranspiration of 

ground water in Stagecoach Valley is about 700 

acre-ft/yr.
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H19

TABLE 4. Estimated average annual recharge to basin-fill aquifer from precipitation,

Stagecoach Valley

[Average annual precipitation for altitude zones and percentage recharge are same as those used for 

Dayton Valley by Glancy and Katzer (1975, p. 48). , negligible or not applicable. Totals are 

rounded to two significant figures]

Altitude zone 

(feet above 

sea level)

7,000-8,000 

6,000-7,000 

5,000-6,000 

<5,000

Area 

(acres)

30 

4,630 

8,890 

31,600

Average annual 

precipitation

(feet, 

rounded)

1.5 

1.1 

.8 

.5

(acre-feet, 

rounded)

45 

5,090 

7,110 

15,800

Average annual 

recharge

(percent)

15

7 

3

(acre-feet, 

rounded)

7 

360 

210

Total ........... 45,000 28,000 '580

'Additional 30 acre-feet per year recharge, mostly generated from precipitation that falls on 

southwest flank of Churchill Butte, is estimated to occur in area between topographic divide of 

Stagecoach Valley and Carson River.

GROUND-WATER DEVELOPMENT

Ground-water withdrawals for crop irrigation and 

for public water supply began in 1971, and about 

320 acre-ft of water was pumped that year. 

Pumpage increased steadily until 1977, when the 

total annual pumpage was about 1,600 acre-ft. 

Pumpage has declined slightly since then and in 

1982 was about 1,200 acre-ft. Changes in irrigated 

land, population, and estimated pumpage during 

the period 1971-82 are shown in table 5. The distribution of irrigated land and areas of domestic and 

public supply by ground water in 1982 are shown in 

figure 9. Similar maps prepared for the 11 pumping 

seasons 1971 to 1982 were used to help estimate 

the distribution of pumpage values for the groundwater flow model.

During the 11 yr from spring 1971 to spring 1982 

(excluding most of 1982 pumpage shown in table 5), 

a total of about 11,000 acre-ft of water was pumped 

from the basin-fill aquifer, mostly for irrigation. 

Most of the water was consumed by evapotranspiration; however, some of the water pumped for irrigation infiltrated deep enough to escape consumption. 

Initially, part of this infiltrated water was retained 

as soil moisture, and the remainder returned to the 

water table. Generalized contours of water levels in 

the aquifer as of spring 1982 are shown in figure 

10. The net decline in ground-water levels during 

the period spring 1971 to spring 1982, determined 

on the basis of the difference between pre-1971 

water levels (fig. 4) and the spring 1982 water 

levels (fig. 10), is shown in figure 11. Additional 

control was provided by nine wells with measured 

changes between 1972 (or earlier) and 1982.

Declines of 5 to 15 ft occurred throughout most of 

the area of ground-water withdrawals, and the 

maximum measured decline was about 19.5 ft.

SIMULATION OF GROUND-WATER FLOW

The preceding sections of this report have presented information that describes ground-water 

flow in the basin-fill aquifer of Stagecoach Valley. 

The remainder of this report describes a digital 

computer model of the ground-water flow in the 

aquifer. The model was calibrated using (1) 

predevelopment conditions and (2) estimated 

pumpage from 1971 to 1982 and the resultant 

water-level declines. The calibrated model was used 

to simulate long-term trends that describe the 

probable future response to selected developmental 

scenarios.

CONCEPTUALIZATION OF GROUND-WATER FLOW 

IN BASIN-FILL AQUIFER

Ground-water flow in the basin-fill aquifer of 

Stagecoach Valley was conceptualized as a threelayer flow system (fig. 12). The top layer (layer 1, 

fig. 12C) represents the water table and 50 ft of underlying saturated material. The zone represented 

by layer 1 is where the processes of recharge from 

precipitation, irrigation-return flow, evapotranspiration, interaction with the Carson River, and depletion of water by draining of aquifer materials occur. 

The middle layer (layer 2, fig. 12C) represents the 

zone from 50 to 300 ft below the water table. The
H20 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

TABLE 5. Estimated irrigated acreage, population, and ground-water pumpage, Stagecoach Valley, 1971-82

[Totals are rounded to two significant figures]

Calendar 

year

1971........

1972........

1973........

1974 ....... .

1975 ........

1976........

1977........

1978 ....... .

1979 ........

1980........

1981 ........

1982 ........

Irrigated land3

(acres)

.... 100

.... 110

.... 140

.... 315

.... 315

.... 390

.... 520

.... 420

.... 440

.... 280

.... 310

.... 330

Served by 

domestic wells

20 

20 

30 

40 

50 

60 

70 

80 

90 

100 

110 

110

Population

Served by 

public systems

30 

60 

110 

140 

170 

150 

150 

370 

460 

510 

560 

570

Pumpage 

(acre-feet per year)

Total

50 

80 

140 

180 

220 

210 

220 

450 

550 

610 

670 

680

Irrigation

300 

330 

420 

940 

940 

1,170 

1,560 

1,260 

1,320 

840 

930 

990

Domestic 

and stock

>10 

10 

10 

10 

10 

10 

10 

20 

20 

20 

30 

30

Public 

supply

>10 

10 

20 

30 

40 

30 

30 

80 

100 

110 

130 

130

Total

>320 

350 

450 

980 

990 

1,200 

1,600 

1,400 

1,400 

970 

1,100 

1,200

Total.......................................................................................................... 11,000 190 720 12,000

Estimates based on field inventory of houses and lots in 1982, house count from photographs taken in 1974, dates when domestic wells 

reportedly were drilled, number of hookups on Stagecoach Utilities water system, and supplemental information from photographs taken in 

1980. Population was estimated using average occupancy of 2.75 persons per household (U.S. Department of Commerce, 1983, p. 61, 63).

2 Irrigation use based on estimated water use of 3 feet per acre. Alfalfa is principal crop, although some garlic was grown in early 1980's. 

Domestic and public-supply water use based on estimated use per household. Each household was assumed to contain, on average, 2.75 persons 

who use 100 gallons per day (gpd) each for household purposes. Overall use was estimated as sum of household use plus water used for lawn 

and garden irrigation. Estimates beyond field inventory of lawn and garden irrigation ranged from 0 to as much as 3 acre-feet per household in 

1982. Thus, overall estimates based on 1982 inventory ranged from about 0.3 to about 3.3 acre-feet per household; average use was estimated to 

be about 0.65 acre-feet per household or about 210 gpd per person.

'Estimates based on field inventories, aerial photographs, orthophoto maps, and Landsat images.

zone represented by layer 2 is where virtually all 

pumpage occurs and is the conduit for much of the 

subsurface inflow and outflow. The bottom layer 

(layer 3, fig. 12C) represents the zone that extends 

from 300 ft below the water table to consolidated 

rock. This zone is the conduit for deep flow in the 

basin fill and a source of stored water. Vertical flow 

between the layers is restricted by the combined 

effect of numerous discontinuous, fine-grained 

deposits at various depths within the basin fill that 

collectively act as confining beds.

DIGITAL COMPUTER MODEL

A three-layer digital computer model was used to 

simulate the predevelopment conditions and the 

response to development of the basin-fill aquifer of 

Stagecoach Valley. The model is based on a partial 

differential equation that describes the threedimensional movement of ground water of constant 

density through porous earth material. This equation and its approximation as a finite-difference 

expression were described by McDonald and 

Harbaugh (1988, p. 2-1 to 2-20). They also described a modular computer program that uses the 

finite-difference approximation of the differential 

equation of ground-water flow. This approximation 

is capable of simulating ground-water flow in a 

multilayer heterogeneous aquifer system with 

irregular borders and a variety of stresses such as 

pumping wells, evapotranspiration, and headdependent flow to and from a river. Flow between 

layers is treated as vertical flow through confining 

beds; horizontal movement and storage of water in 

the confining beds is assumed to be insignificant. 

The basin-fill aquifer of Stagecoach Valley is represented by a three-layered finite-difference network 

composed of 25 columns and 22 rows with nodes 

spaced 2,000 ft apart at the center of each cell. The 

network has 210 active cells in the top layer (layer 

1), 209 active cells in the middle layer (layer 2), 

and 170 active cells in the bottom layer (layer 3), as 

shown in figure 13. The perimeter of the model, 

outside the model cells, is surrounded by no-flow 

boundaries as required by the computer code. The 

strongly implicit procedure was used to solve the 

finite-difference equations simultaneously for flow 

between cells. (For detailed information about the 

model, see McDonald and Harbaugh, 1988.)
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H21

119°30' 119°25' 119°20'

39°25'

39°20' -

Base from U.S. Geological Survey 

Churchill Butte. 1:62.500.1957 3 MILES

BASIN FILL

CONSOLIDATED ROCK

234 KILOMETERS

EXPLANATION

GROUND-WATER USE AREAS

Land irrigated in 1982

Area supplied by domestic wells Water for 

household, lawn, garden, and stock use

Area served by public water supply Service 

area of Stagecoach Utilities

 - - TOPOGRAPHIC DIVIDE

FIGURE 9. Ground-water use areas in Stagecoach Valley, 1982.
H22

119°30'

REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

119°25' 119°20'

Base from U.S Geological Survey 

Churchill Butte. 1:62.500,1957 3 MILES 

J

4 KILOMETERS

EXPLANATION

BASIN FILL

CONSOLIDATED ROCK Stipple indicates rock 

permeable enough to transmit subsurface flow 

to Stagecoach Valley

-4230 WATER-LEVEL CONTOUR, SPRING 1982 Shows altitude of 

water level for wells that penetrate most heavily pumped 

zone of basin fill. Dashed where approximately located. 

Contour interval, in feet, is variable. Datum is sea level

 - - TOPOGRAPHIC DIVIDE 

 WELL Used as control point

FIGURE 10. Ground-water-level contours, spring 1982.
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H23

119°30' 119°25' 119°20'

39°25'

39°20

Base from U.S. Geological Survey 

Churchill Butte, 1:62,500.1957 3 MILES

3 1

1 

2

1 1 

3 4 KILOI

BASIN FILL

CONSOLIDATED ROCK

EXPLANATION

 5 -

 LINE OF EQUAL WATER-LEVEL 

DECLINE In wells that penetrate 

most heavily pumped zone of basin 

fill. Dashed where approximately 

located. Interval, 5 feet

 TOPOGRAPHIC DIVIDE

2.56

 WELL Value is measured decline, in feet, 

between 1972 and 1982

FIGURE 11. Ground-water-level declines, spring 1971 to spring 1982. Most wells were completed in depth interval corresponding to

model layer 2.
to

Most local recharge from precipitation and 

surface runoff is generated in this area

CVO WT

EXPLANATION

BASIN FILLFLOOD-PLAIN DEPOSITS OF CARSON RIVER 

CONSOLIDATED ROCK

CONTACT FAULT Dashed where approximately located

ACTIVE CELL IN FINITE-DIFFERENCE GRID Model 

calculations are for node in center of cell

INACTIVE CELL IN FINITE-DIFFERENCE GRIDLABELS USED ON SKETCHES

CRF Carson River flood plain

CRI Subsurface inflow from Carson River

CRO Subsurface outflow to Carson RiverCVO Subsurface outflow to Churchill Valley

R Recharge from infiltration of precipitation and surface runoff

ET Evapotranspiration of ground water by phreatophytes

P Pumpage (from layer 2)

WT Water table

FIGURE 12. Schematic block diagrams. A, Selected inflow-outflow relations. B, Generalized hydrogeologic section. C, Representation of basin-fill aquifer derived using

three-dimensional finite-difference grid of ground-water flow model.

Layer 1

Oi io2

1 i

H

IS1I
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H25

'30' 119°25' 119°20'

>^7/.'--.'^r?

, n \/: EK5TTE>

"y \S\ ) \ N> V/^x I

t*~"^* f ^x. H Xv 2 5 KklK

39°20

i r

1 2 3 4 KILOMETERS 

EXPLANATION

BASIN FILL

CONSOLIDATED 

ROCK

TOPOGRAPHIC 

DIVIDE

GRID CELL Where only layer 1 is active

GRID CELL Where layers 1 and 2 are active

GRID CELL Where layers 1, 2, and 3 are active

C3 GRID CELL Where constant-head conditions 

in layer 3 are used to simulate outflow to 

Churchill Valley

R GRID CELL Where "river leakage package" 

is used to simulate inflow from or outflow 

to Carson River in downstream part of 

Stagecoach Valley

C1 GRID CELL Where constant-head conditions in W GRID CELL Where constant flux of 

layer 1 are used to simulate inflow from Carson recharge is introduced into layer 1 

River in upstream part of Stagecoach Valley

FIGURE 13. Finite-difference grid used to model ground-water flow system in Stagecoach Valley. Row number is shown at left end of

row; column number is shown at bottom of column.
H26 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

BOUNDARY CONDITIONS

The model solution is strongly influenced by the 

boundary conditions specified; consequently, evaluating and specifying the boundary conditions constituted an important part of this study. Cells in the 

finite-difference grid were designated either active 

or inactive depending on whether ground-water 

flow through the aquifer sediments could be represented by that cell (fig. 13). Generally, basin-fill 

deposits were considered permeable, whereas most 

areas of consolidated rock were considered to have 

very low hydraulic conductivity except for localized 

zones of fractured and weathered rock. Thus, basinfill sediments were represented as active cells, and 

consolidated rock as inactive cells. Local areas of 

basalt and fractured andesite in the southwestern 

part of Stagecoach Valley (fig. 2) were considered 

permeable and were represented by active cells. 

Various flux conditions at the model boundaries 

were treated by assigning appropriate flow conditions to active cells adjacent to the no-flow boundary outside the model cells.

The northwest boundary of the study area is 

recharged by inflow from the Flowery Range and 

was treated as a constant-recharge boundary in the 

model. Cells along this boundary in layer 1 of the 

model were characterized by recharge at a constant 

rate (fig. 13). The west, north, east, and parts of the 

south boundaries of the area were modeled in a 

similar way, except that not all cells receive 

recharge (or rates of recharge to the cells were 

negligible).

Ground water in the northeastern part of the 

area flows into Churchill Valley in the subsurface. 

This outflow condition was simulated in the model 

by extending the area of active cells the equivalent 

of about 1 mi east into Churchill Valley and then 

representing the lowest water level in that area as 

a constant-head cell in layer 3 (cell C3 in fig. 13). 

This approximation is adequate to represent steadystate conditions. However, the assumption of 

constant-head cells may have introduced error in 

the simulation results because pumping changes 

flow rates to or from the constant-head cell but does 

not remove water from storage and does not change 

water levels in the constant-head cells. However, if 

the distance of the constant-head boundary is far 

away from the pumping centers, then the approximation probably is adequate for the intended uses 

of the model.

Two reaches of the Carson River are in hydraulic 

continuity with the basin-fill aquifer of Stagecoach 

Valley. Boundary conditions at the upstream reach

were simulated by a constant-head cell in the top 

layer of the model, representing the Carson River 

(cell Cl in fig. 13). The head was set at the altitude 

of the average river stage. The constant-head cell 

provides a source of water to adjacent cells representing permeable basaltic and andesitic rocks that 

transmit flow into the basin-fill aquifer of Stagecoach Valley. Boundary conditions along the downstream reach of the Carson River were simulated 

by using the model's river package, whereby areas 

traversed by the river are represented by five active 

cells that are characterized by head-dependent 

fluxes to and from the river (McDonald and 

Harbaugh, 1988, p. 6-1 to 6-30). Average altitudes 

estimated from topographic maps were used to represent the average river stage. A riverbed conductance value of 0.10 ft2/s was used to simulate 

continuity between the river and layer 1 of the 

model. This riverbed conductance was estimated using a river length of 2,000 ft in each cell, an average river width of 50 ft, a thickness of streambed 

material of 50 ft, and a vertical hydraulic conductivity of 5x10~5 ft/s. The high value of vertical 

hydraulic conductivity was used because the sand 

and gravel deposits that underlie the Carson River 

contain hardly any silt and clay and are highly 

permeable. Fluctuations in stage due to variations 

in river flow were ignored. The river was treated 

primarily as either a source of or sink for water.

INITIAL CONDITIONS

Prior to development (before 1971), the hydrologic 

system was in a state of dynamic equilibrium 

where, over the long term, the average recharge 

equaled the average discharge and there was no 

appreciable change in storage or decline in water 

level. Pumping of water from wells produces a 

nonequilibrium condition where some of the water 

is removed from aquifer storage and ground-water 

levels decline with time.

The pre-1971 ground-water levels shown in figure 

4 were assumed to represent equilibrium conditions 

and are considered to be best represented by conditions in layer 2 of the model. Similar maps were 

prepared for layers 1 and 3 and were used as the 

initial head conditions to represent the undeveloped 

flow system in the model.

TRANSMISSIVITY

The transmissivity of each of the three layers in 

the model was initially estimated as the product of
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H27

the thickness of that layer and a hydraulicconductivity value. The values used for thickness of 

saturated material in layers 1 and 2 were the average thickness values assigned to these layers in the 

model (50 and 250 ft, respectively); the thickness 

value used for layer 3 was assumed to be the difference between the estimated total thickness of saturated basin-fill material (fig. 5) and the 300 ft 

already assigned to layers 1 and 2.

The horizontal hydraulic-conductivity values used 

for layers 1 and 2 were estimated from specific 

capacity or from aquifer tests (fig. 6). Horizontalconductivity values used for layer 3 were derived by 

reducing these values 5 to 15 percent to account for 

the anticipated decrease in conductivity with depth. 

All these adjustments to initial estimates were 

made during the calibration process in model simulations. The distribution of transmissivity values 

used for the three layers of the model is shown in 

figures 14, 15, and 16, respectively. The adjustments made during the calibration process imply 

that values of hydraulic conductivity in layers 2 

and 3 should be lower than the values shown in figure 6. These lower values worked best in the model 

and might be attributed to pre-Lake Lahontan 

deposits having lower values of hydraulic conductivity. The transmissivity of layer 1 (fig. 14) was derived from the calibrated model of steady-state 

conditions. For transient pumping simulation, the 

altitude of the bottom of layer 1 was entered into 

the model so that when simulated pumping removed water from storage and the water table was 

drawn down, the transmissivity would be adjusted 

to represent the newly reduced thickness of saturated material in layer 1. Transmissivities of layers 

2 and 3 were considered to be constant because no 

water-table changes below layer 1 would occur under 

the pumping conditions used to calibrate the model 

for transient conditions for the period 1971-82.

LEAKANCE

Flow between the three layers of the model was 

simulated as vertical flow through two confining 

units, representing the cumulative effect of numerous discontinuous, lenticular, fine-grained deposits 

at various depths within the basin fill. The ability 

of a confining unit to transmit vertical flow is expressed as leakance, which is the ratio K7b', in 

which K' and b' are the vertical hydraulic conductivity and thickness, respectively, of the confining 

unit (Lohman, 1972, p. 30). For the purposes of this 

model, the thickness of the confining unit was

represented as the distance between the midpoints 

of two adjacent layers, and the vertical hydraulic 

conductivity used was the average vertical hydraulic conductivity of the basin-fill materials in the 

interval of interest.

The distribution of leakance values between 

layers 1 and 2 (fig. 17) and between layers 2 and 3 

(fig. 18) was simulated using the vertical hydraulic 

conductivities shown in figure 7. Values of vertical 

hydraulic conductivity for layer 3 were reduced by 5 

to 15 percent to reflect the anticipated lower values 

of vertical hydraulic conductivity at depth. Distance 

between the midpoints of layers 1 and 2 was 150 ft, 

whereas distance between midpoints of layers 2 and 

3 varied according to the thickness of layer 3. For 

two localized areas adjacent to Churchill Valley 

(figs. 17, 18), unrealistically high values of leakance 

were used to allow the outflow from a single constant-head cell to be integrated over a larger area.

STORAGE COEFFICIENT

The specific-yield values shown in figure 8 were 

used as the storage coefficients for layer 1. A uniform storage coefficient of 0.0003 was used for layer 

2; rounded to one significant figure, it was estimated using the approximate relation given by 

Lohman (1972, p. 53) and a thickness for layer 2 of 

250 ft. A uniform storage coefficient of 0.0007 was 

used for layer 3; it was estimated from the compressibility of water and an assumed average thickness of layer 3 of 700 ft. (The thickness of layer 3 

varies from 0 to 3,000 ft; however, 700 ft probably 

is an acceptable average.)

EVAPOTRANSPIRATION OF GROUND WATER

Evapotranspiration of shallow ground water is 

approximated assuming a linear decrease from a 

maximum value, when the water table is at the 

land surface, to 0, when the water table is at the 

extinction depth (the depth at which significant 

evapotranspiration ceases). The value used for 

maximum evapotranspiration, 3.5 ft/yr, is about 

equal to the average annual lake evaporation in the 

area (Kohler and others, 1959, pi. 2). The extinction 

depth was set at 12 ft beneath areas of bare soil 

(such as most of Misfits Flat) and at 35 ft beneath 

stands of phreatophytes (on the basis of observed 

depth to water at the outer edges of such stands). A 

transition zone with extinction depths between 12 

and 35 ft was used to represent a band of sparse 

phreatophytes around the margins of Misfits Flat.
H28

°30'

REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

119°25' 119°20'

39°20'

Base from U.S. Geological Survey 

Churchill Butte. 1:62.500.1957

4 KILOMETERS

EXPLANATION

BASIN FILL

CONSOLIDATED ROCK

 0.02 LINE OF EQUAL TRANSMISSIVITY 

OF LAYER 1 Interval, 0.01 feet 

squared per second

_.._.._ TOPOGRAPHIC DIVIDE

FIGURE 14. Model-derived transmissivity of model layer 1 (corresponding to upper 50 feet of saturated basin fill).
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H29

119°25' 119°20'

- ~"> f ^-s * f£f- *" ;i-JX~ I"""' JZ£'--'*s ,-f '* 55BRW- y \-X> \ I U

^^i^'^/'^CS

39°20'

Base from U.S. Geological Survey 

Churchill Butte. 1:62,500.1957

4 KILOMETERS

EXPLANATION

BASIN FILL

CONSOLIDATED ROCK

 0.01 LINE OF EQUAL TRANSMISSIVITY 

OF LAYER 2 Interval, 0.01 feet 

squared per second

_.._.._ TOPOGRAPHIC DIVIDE

FIGURE 15. Model-derived transmissivity of model layer 2 (corresponding to interval 50-300 feet below steady-state water table)
H30

39°25'

REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

119°25' 119°20'

39°20'

\ »--/ r-HV.." a J ~ 11 s-s/ r* r <^r/ * ~' v i -. . S^.^^- :yv^ _Jr'

Base from U.S. Geological Survey 

Churchill Butte. 1:62.500,1957

I I I I

1 2 3 4 KILOMETERS

EXPLANATION

BASIN FILL

CONSOLIDATED ROCK

 0.01 LINE OF EQUAL TRANSMISSIVITY 

OF LAYER 3 Interval, 0.01 feet 

squared per second

_.._.._ TOPOGRAPHIC DIVIDE

FIGURE 16. Model-derived transmissivity of model layer 3 (corresponding to saturated deposits 300 feet below steady-state water

table to bottom of basin fill).
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H31

119°30' 119°25' 119°20'

39°25' R

39°20'

Base from U.S. Geological Survey 

Churchill Butte. 1:62.500.1957

4 KILOMETERS

EXPLANATION

BASIN FILL

CONSOLIDATED ROCK

AREA WHERE UNREALISTICALLY HIGH 

LEAKANCE VALUES WERE USED To 

allow subsurface inflow or outflow to be 

represented by single constant-head node

 5 LINE OF EQUAL LEAKANCE BETWEEN 

LAYERS 1 AND 2 Unit is IXlO'10 feet 

per second. Interval, 5X10'10 feet per 

second

 TOPOGRAPHIC DIVIDE

FIGURE 17. Model-derived leakance between model layers 1 and 2.
H32

119°30' 

39°25'

REGIONALAQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

119°25' 119°20'

39°20'

Base from U.S. Geological Survey 

Churchill Butte, 1:62,500,1957

1 I

3 4 KILOMETERS

EXPLANATION

BASIN FILL

CONSOLIDATED ROCK

 2 LINE OF EQUAL LEAKANCE BETWEEN 

LAYERS 2 AND 3 Unit is IXlO'10 feet 

per second. Interval, IXIO"10 feet per 

second

 - - TOPOGRAPHIC DIVIDE

AREA WHERE UNREALISTICALLY HIGH 

LEAKANCE VALUES WERE USED To 

allow subsurface outflow to be represented 

by single constant-head cell

FIGURE 18. Model-derived leakance between model layers 2 and 3.
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H33

METHOD OF ANALYSIS OF SIMULATION RESULTS

If a reasonable match between observed and 

simulated conditions can be obtained, then within 

the limitations inherent in the simulation (Harrill, 

1986, p. 26-28) the flow model is expected to provide information on the availability of ground water 

and probable hydrologic responses to future development. The basin-fill aquifer and its response to 

development were simulated in three phases: (1) 

the undeveloped condition, before 1971 (steady 

state), (2) the response to conditions from 1971 

through 1981 (transient), and (3) probable longterm responses to selected future-development 

scenarios (transient). Analysis of the first phase 

provided insight about predevelopment basin-fill 

aquifer characteristics and was a means of evaluating parameters used in the model. The steady-state 

and transient simulations were calibrated so that 

computed heads, water-level changes, and distribution of evapotranspiration values agreed reasonably 

well with observed values. Transmissivity, vertical 

hydraulic conductivity, recharge, and subsurface inflow and outflow from the valley were adjusted to 

be within ranges compatible with field measurements or other available data mostly during the 

first-phase calibration. Storage coefficients and rate 

of recirculation from irrigation-return flow were 

adjusted mostly during the second-phase calibration. Once the fit between observed and simulated 

values was reasonable, we ran a series of simulations varying selected parameters to evaluate how 

sensitive the model was to errors in the values of 

the parameters.

Finally, during the third phase, a series of simulations were made to evaluate the probable longterm response to hypothetical pumping stresses 

associated with various development scenarios. The 

purpose was not to make specific predictions but 

rather to develop insight regarding the general 

response of the basin-fill aquifer to sustained (longterm) stresses.

RESULTS OF SIMULATION

PREDEVELOPMENT CONDITIONS

Simulation of predevelopment conditions provides 

a means of analyzing the system under conditions 

of natural steady-state equilibrium. The simulated 

steady-state potentiometric surface for layer 2 of 

the model (fig. 19) is in reasonable agreement with 

the pre-1971 potentiometric surface based on field 

data (fig. 4). The potentiometric surfaces simulated

for layers 1 and 3 are similar to the surface simulated for layer 2. The simulation allowed for downward flow in recharge areas and upward flow in 

discharge areas by incorporating small head differences between layers.

The closeness of fit between observed and simulated water levels was evaluated using two methods. 

The first method was to compare heads measured 

at 16 wells (in 1972 or earlier and in 1982) with 

model-derived heads computed for the cells that 

correspond to the areas in which the 16 wells are 

located (fig. 20). About half of the model-computed 

heads were within 5 ft of the measured heads. Part 

of this error probably is due to the fact that measured heads for wells located anywhere within a 

2,000-ft by 2,000-ft cell were compared to the 

model-computed head at the center of the cell. In 

most cases this could cause a difference of 1 to 2 ft 

given the prevailing head gradient of the basin-fill 

aquifer. The second method was to select those 

model cells where there was adequate water-level 

information to make a reasonable estimate of the 

predevelopment head. In addition to the 16 wells 

that had measurements in 1972 or earlier, wells 

that had measurements in the mid-1970's provided 

supplemental control based on extrapolations of water-level trends back to 1971. In the model grid, a 

group of 120 contiguous cells was selected for comparison. About 70 percent of the 120 cells in layer 1 

and about 60 percent of the 120 cells in layer 2 had 

differences between estimated (predevelopment) 

and simulated heads of 5 ft or less (fig. 20). Differences of this magnitude were considered reasonable, especially since land-surface altitudes at some 

wells were determined from topographic maps. The 

areas of poorest fit were along the northeast boundary of the model, where measurements indicated a 

steep hydraulic gradient toward Churchill Valley.

Values of recharge and discharge computed by the 

model are in good agreement with those estimated 

using empirical techniques. However, the model 

results indicate significant additional subsurface 

inflow and outflow.

Comparison of the modeled distribution of evapotranspiration values with the mapped extent of 

phreatophytes in Stagecoach Valley (excluding 

riparian areas shown in fig. 4) provides an additional check on the ability of the model to simulate 

the basin-fill aquifer of Stagecoach Valley (fig. 21). 

Areas where phreatophyte vegetation was mapped 

but where no evapotranspiration was calculated by 

the model occur where the depth to water calculated by the model exceeds 35 ft. Adjustments for a 

closer fit were not attempted because the error is
H34 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

119°25' 119°20'

39°20'

Base from U S Geological Survey 

Churchill Butte. 1:62,500.1957

BASIN FILL 

CONSOLIDATED ROCK

1 I 

1 2 3 4 KILOMETERS

EXPLANATION

 4240 SIMULATED STEADY-STATE WATER-LEVEL 

CONTOUR IN LAYER 2 OF MODEL Dashed 

where approximately located. Contour interval, 

in feet, is variable. Datum is sea level

 BOUNDARY OF 120-CELL AREA Area used to 

compare simulated heads to observed heads. 

Results of comparison are shown in figure 20

_.. .. TOPOGRAPHIC DIVIDE

FIGURE 19. Simulated steady-state potentiometric surface for model layer 2.
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H35

probably a combined effect of land-surface altitudes 

determined at the centers of the cells, assigned extinction depths for evapotranspiration, and aquifer 

properties assigned to layer 1.

RESPONSE TO DEVELOPMENT

From spring 1971 to spring 1982, more than 

11,000 acre-ft of water was pumped from the basinfill aquifer of Stagecoach Valley. Simulation of this 

11-yr period of pumping has indicated a response 

that includes water-level declines, reductions in 

natural evapotranspiration, changes in subsurface 

inflow and outflow, and depletion of ground water 

in storage.

WATER-LEVEL DECLINES

Water-level data from shallow wells are not adequate for a detailed comparison of measured and 

simulated water-table fluctuations in layer 1; however, short-term records available at several wells 

indicate net declines of the same general magnitude 

as the simulated declines shown in figure 22. 

Hydrographs of three shallow wells for the period 

1977 82 are plotted in figure 23 for comparison

100

90

80

70

60

50

40

30

20

10

0

120 selected cells

in layer 2 /

120 selected cells 

in layer 1

16 wells measured

in or before 1972

and in 1982

1 23456789 10

DIFFERENCE BETWEEN OBSERVED OR ESTIMATED 

AND MODEL-DERIVED HEAD, IN FEET

FIGURE 20. Cumulative-frequency distributions showing closeness of fit between observed or estimated heads and 

model-derived heads.

with simulated water-level altitudes in the model 

cell that contains each well. The fluctuations in the 

observed data reflect seasonal variation in pumping 

rates that were not simulated in the model; consequently, only the trends are comparable.

For the period spring 1971 to spring 1982, the 

simulated water-level declines for layer 2 of the 

model (fig. 24) are in general agreement with the 

observed declines (fig. 11). Any differences probably 

are due to the observed declines being measured at 

individual wells, whereas the simulated declines 

represent values averaged over a 2,000-ft by 2,000- 

ft finite-difference cell. Hydrographs of five wells 

that penetrated more than 50 ft of saturated basin 

fill (into the equivalent of layer 2), based on periodic measurements during 197182, are plotted in 

figure 25; also shown are simulated water-level 

changes in the cells that contain each well so that 

trends can be compared.

Simulated water-level declines in layer 3 for the 

same period were less than those in layer 2 and 

generally were distributed over larger areas. There 

are no observation wells that penetrate the basin 

fill to depths represented by layer 3 of the model.

REDUCTIONS IN EVAPOTRANSPIRATION

The simulated annual evapotranspiration of 

ground water decreased from about 640 to about 

180 acre-ft/yr from 1971 to 1982. This reflects the 

decline of the water table by pumping. Field observations in 1982 and 1983 indicated that the areal 

extent of phreatophytes was about the same as had 

been mapped in the early 1970's. However, the general vigor and areal density of the plants appeared 

slightly less than before 1971. The simulated 

change could not be precisely verified because decreased consumption of ground water may have 

been partly offset by increased consumption of soil 

moisture as the plants responded to stresses caused 

by declining water tables.

CHANGES IN INFLOW AND OUTFLOW

The 11 pumping seasons provided sufficient time 

to affect all head-dependent fluxes at the margins 

of the area simulated, in the ground-water flow 

model. The simulated changes are listed in table 6. 

As with evapotranspiration, these changes in subsurface flow represent water captured by pumping 

in Stagecoach Valley. They could not be verified by 

field observations, but they are comparable to the 

general magnitude of observed water-level declines
H36

119°30'

REGIONALAQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

119°25' 119°20'

39°25'

39°20'

Base from U.S. Geological Survey 

Churchill Butte. 1:62,500,1957

EXPLANATION

BASIN FILL 

CONSOLIDATED ROCK

AREA OF PHREATOPHYTE VEGETATION 

Primarily greasewood (P.A. Glancy, U.S. 

Geological Survey, written commun., 1982). 

Predevelopment (pre-1971) conditions

CELL IN LAYER 1 WHERE EVAPOTRANSPIRATION 

WAS CALCULATED BY MODEL Value is rate, in 

feet per year

 TOPOGRAPHIC DIVIDE

FIGURE 21. Observed and simulated areas of evapotranspiration.
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H37

119°25' 119°20'

39°25'

39°20'

Base from U.S. Geological Survey 

Churchill Butte. 1:62.500.1957

BASIN FILL

CONSOLIDATED ROCK

EXPLANATION

 5 LINE OF EQUAL SIMULATED DRAWDOWN IN LAYER 1 For 

period spring 1971 to spring 1982. Interval, 2.5 feet

_.._.._ TOPOGRAPHIC DIVIDE

/ 

 ^ WELL Letter corresponds to hydrograph shown in figure 23

FIGURE 22. Simulated water-table decline in model layer 1, spring 1971 to spring 1982.
H38

4245

4240

4235

4230

REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

I I I I I I I I I I I I

G . G---. ©...._ A

4245

4240

- 4235

LU 

Q

K

ti 

<

^ 4230

i r

B

'" > . >---_

I I I I

4240

4235

4230

4225

4220

" ©-... ©--.. ©-..

 O-----G-...

c

 0-----0----0

I I J__I

1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982

YEAR

EXPLANATION

 MEASURED HEAD FOR WELL WITHIN CELL AREA

---O--- SIMULATED HEAD FOR CELL IN LAYER 1

FIGURE 23. Comparison of simulated 

and observed hydrographs for three 

wells (fig. 22) completed at depths 

corresponding to model layer 1. (See 

fig. 13 for layer 1 cell locations.) A, 

Well in SW% sec. 9, T. 17 N., R. 23 

E.; well depth 82 feet and top of open 

interval at 52 feet; cell (11,11) in 

layer 1 used for simulation. B, Well 

in SEX sec. 9, T. 17 N., R. 23 E.; well 

depth 84 feet and top of open interval 

at 82 feet; cell (10,13) in layer 1 used 

for simulation. C, Well in NEK sec. 

10, T. 17 N., R. 23 E.; well depth 88 

feet and top of open interval at 86. 

feet; cell (10,15) in layer 1 used for 

simulation.
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H39

°30' 119°25' 119°20'

39°20'

Base from U.S. Geological Survey 

Churchill Butte. 1:62,500,1957

\ \

3 4 KILOMETERS

BASIN FILL

CONSOLIDATED ROCK

EXPLANATION

- 5 LINE OF EQUAL SIMULATED DRAWDOWN IN LAYER 2 For 

period spring 1971 to spring 1982. Interval, 5 feet

 TOPOGRAPHIC DIVIDE 

 " WELL Letter corresponds to hydrograph shown in figure 25

FIGURE 24. Simulated water-level decline in layer 2, spring 1971 to spring 1982.
H40 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

4255

4245

4240

4235

4230

4225

4220

4215

4245

4240

4235

4230

4225

4220

A

I i i I I I I 3 I I

4215

I \ 

o

B

i i

1970 1972 1974 1976 1978 

YEAR

1980 1982

 0---Q

b---

c

I I I I I I I I

 e <y*

4250

4245

4240

4235

4230

4255

4250

4245

4240

4235

4230

4235

4230

4225

4220 . I I I I I I I I I I I I 

1970 1972 1974 1976 1978 1980 1982

 er 

D

I i i

YEAR

EXPLANATION

 MEASURED HEAD FOR WELL WITHIN CELL AREA 

... o - - - SIMULATED HEAD FOR CELL IN LAYER 2
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H41

TABLE 6. Simulated net changes in inflow and outflow from 

spring 1971 to spring 1982

[Values that are in acre-feet per year are rounded]

Rate Change in rate, 

(acre-feet per year) 1971-82

Pre-1971 Spring (acre-feet [percent]) 

__________________________1982______________

Inflow

From upstream reach,

Carson River.

From downstream reach,

Carson River.

To Churchill Valley ..........

To downstream reach,

Carson River.

280

90

Outflow

170

120

300

100

160

110

20

10

-10

-10

[7]

[11]

[-6]

[-8]

in observation wells along the margins of the area, 

as modeled. These changes are small in relation to 

the flow of the Carson River, whose mean annual 

flow is about 380 ft3/s and mean flow in September, 

the month with the lowest mean discharge, about 

10 ft3/s (Schroer and Moosburner, 1978, p. 212). 

The total capture of water from the river (increase 

in inflow plus decrease in outflow, as indicated in 

table 6) is equivalent to a flow in the river of only 

about 0.05 ft3/s.

GROUND-WATER BUDGETS

Ground-water budgets listed in table 7 summarize the inflow to and outflow from the basin-fill 

aquifer of Stagecoach Valley for predevelopment

FIGURE 25. Comparison of simulated and observed hydrographs 

for five wells (fig. 24) completed at depths corresponding to 

model layer 2. (See fig. 13 for layer 2 cell locations.) A, Well in 

SE14 sec. 4, T. 17 N., R. 23 E.; well depth 339 feet and top of 

open interval at 287 feet; cell (9,13) in layer 2 used for simulation. B, Well in NW!4 sec. 10, T. 17 N., R. 23 E.; well depth 

300 feet and top of open interval at 234 feet; cell (9,14) in 

layer 2 used for simulation. C, Well in SE14 sec. 7, T. 17 N., R. 

23 E.; well depth 386 feet and top of open interval at 12 feet; 

cell (12,8) in layer 2 used in simulation. D, Well in SE/4 sec. 

18, T. 17 N., R. 23 E.; well depth 273 feet and top of open 

interval at 137 feet; cell (14,8) in layer 2 used for simulation. 

E, Well in NEK sec. 27, T. 17 N., R. 23 E.; well depth 220 feet 

and top of open interval at 180 feet; cell (17,15) in layer 2 

used for simulation.

(pre-1971) conditions and for conditions during the 

period spring 1981 to spring 1982. Two sets of figures were used for long-term natural conditions; 

one was estimated using field observations and 

analysis of empirical data, and the other was calculated using the calibrated steady-state model. Most 

of the model results are at least one-third larger 

than the empirically estimated values. Most of this 

difference is in values of subsurface inflow and outflow, which in several cases were considered negligible in the budget on the basis of field 

observations and analysis of empirical data.

The 11 pumping seasons from spring 1971 

through spring 1982 had discernible effects on the 

water budget for the basin-fill aquifer. During the 

1981 pumping season about 1,100 acre-ft/yr was 

being pumped, of which about 150 acre-ft was being 

recirculated back to the basin-fill aquifer as irrigation-return flow (table 7). This resulted in a net 

pumpage of about 950 acre-ft/yr. About 48 percent 

of the net pumpage was supplied by reductions in 

evapotranspiration, about 3 percent by increased 

subsurface inflow from the Carson River, and about 

2 percent by reduced subsurface outflow to 

Churchill Valley and Carson River (downstream 

reach). The remaining 47 percent of the net 

pumpage was supplied from ground-water storage, 

causing the declines in ground-water levels shown 

in figure 11.

SENSITIVITY ANALYSIS

Twenty model simulations were made to determine the sensitivity of model results to the uncertainty in the determination of five parameters. 

Consecutively each of the five parameters was varied by 20 percent above and below its final calibrated value while the other four parameters were 

kept at the calibrated values (table 8). The model 

then was run for steady-state conditions, and the 

average of the absolute differences between simulated and measured values of head was determined. 

The average of the absolute differences obtained 

with the varying parameter then was compared 

with the average of the absolute differences that 

existed in the calibrated steady-state model. The 

extent to which the average difference of head 

changed in response to the varying parameter was 

used as an index of sensitivity. The head-dependent 

fluxes at the boundaries were evaluated the same 

way and compared with fluxes computed by the
H42 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

TABLE 7. Predevelopment (pre-1971) and 1981-82 ground-water budgets based on field observations and empirical

analysis and on steady-state and transient simulations

[All data given in acre-feet per year. Negative values indicate that water is being added to storage. All values are rounded to two

significant figures. , negligible or not applicable]

Predevelopment conditions

Based on field 

observaions and 

empirical analysis

Based on 

steady-state 

simulation

Spring 1981 

to spring 1982 

conditions, based 

on transient 

simulation

Inflow

Inflow from Carson River (upstream reach) ............

Inflow from Carson River below Table Mountain 

(downstream reach). 

Recirculated from irrigation return...........................

Total.........................................................................

440-580

130-170

570-750

550 

280

86

920

550 

300

98 

150

1,100

Outflow

Outflow to Churchill Valley ........................................

Outflow to Carson River (downstream reach)..........,

Total.........................................................................

700

700

630

170 

120

920

180 

1,100 

160 

110

1,600

Net results

-50 to 130 450 

460

calibrated model. The change in flux was also used 

as an index of sensitivity. These changes are summarized in table 8.

A general conclusion that can be drawn from this 

sensitivity analysis is that the head distribution 

simulated by the model is not highly sensitive to 

moderate uncertainties in values of hydrologic 

parameters except the evapotranspiration extinction depth. Changes of ±20 percent in the other four 

hydrologic parameters generally produced a change 

in head of less than 15 percent. The high sensitivity 

to evapotranspiration extinction depth is probably 

because small changes in head in the center of the 

valley, caused by changes in extinction depth, also 

cause changes in inflow to and outflow from the 

Carson River. Moreover, the initial quantities of inflow and outflow are small, so minor changes in 

flow rates could cause large percentage changes. 

Also, boundary fluxes calculated by the model are 

generally more sensitive than calculated heads to 

uncertainties in values of the model parameters. 

Consequently, a close fit between observed and 

simulated heads does not guarantee accuracy. For 

instance, estimates of flow to and from the Carson 

River and flow to Churchill Valley may be somewhat in error because of moderate errors in determining key hydrologic parameters such as transmissivity.

LIMITATIONS OF THE MODEL

The digital computer model is a simplified representation of the basin-fill aquifer of Stagecoach 

Valley. It was calibrated for predevelopment steadystate conditions on the basis of sparse data available in the early 1970's and for transient pumping 

conditions during a relatively short period of 11 

pumping seasons. Limited hydrologic data are 

available for the area, so hydrologic conditions had 

to be inferred for some parts of the aquifer, especially beneath the playa, along the south and east 

margins of the valley, and at depths greater than 

about 350 ft in the basin fill.

The model-simulated head distributions and 

fluxes were similar to those measured during the 

period spring 1971 to spring 1982. If the well distribution and associated pumping rates remained 

about the same as during the calibration period, 

then simulations for relatively short periods (5-10 

yr) of future pumping would indicate water-level 

declines and flux changes with the same degree of 

accuracy as calculated for the 1971 to 1982 period.
TABLE 8. Summary of model-sensitivity runs 

[ET, evapotranspiration rate; , none]

Parameter 

varied

Part of Change 

model applied to 

affected parameter 

(percent)

Difference between observed 

and simulated head 

(feet (percent change))

Layer 1 Layer 2

Flux at head-dependent boundaries 

(cubic feet per second (percent change)

Upstream reach 

Carson River, 

net flux

Downstream reach 

Carson River, 

net flux

Outflow t

Churchil

Valley

Steady-state calibration

All IQVPTQ 3.63 ( ) 3.84 (-) 0.39165 ( ) -0.04200 ( ) 0.22869 

Sensitivity analysis

Transmissivity:

Vertical 

hydraulic 

conductivity.

Recharge rate:

Maximum ET 

rate.

Maximum ET 

depth.

Layer 1 ...............

Layer 2 ...............

LayerS ...............

All layers ............

Interface between 

layers 1 and 2.

Interface between 

layers 2 and 3.

Layer 1 ...............

Layer 1 ...............

Corresponding 

depth in layer 1.

+20 

-20

+20 

-20

+20 

-20

+20 

-20

+20 

-20

+20 

-20

+20 

-20

+20 

-20

+20 

-20

+20 

-20

3.43 

3.93

3.45 

3.84

3.60 

3.68

3.62 

3.65

3.51 

3.84

3.61 

3.67

3.53 

3.80

4.06 

3.31

3.61 

3.67

5.13 

4.97

(5.5) 

(8.3)

(5.0) 

(5.8)

(.8) 

(1.4)

(.3) 

(.6)

(3.3) 

(5.8)

(.6) 

(1.1)

(2.8) 

(4.7)

(11.8) 

(8.8)

(.6) 

(1.1)

(41.3) 

(36.9)

3.72 

4.10

3.66 

4.08

3.87 

3.83

3.82 

3.87

3.71 

4.09

3.78 

3.93

3.76 

4.00

4.34 

3.48

3.76 

3.96

4.48 

5.56

(3.1) 

(6.8)

(4.7) 

(6.2)

(.8) 

(.3)

(.5) 

(.8)

(3.4) 

(6.5)

(1.6) 

(2.3)

(2.1) 

(4.2)

(13.0) 

(9.4)

(2.1) 

(3.1)

(16.7) 

(44.8)

0.46271 

.31889

.44668 

.33568

.40757 

.37493

.39191 

.39138

.39520 

.38727

.39494 

.38756

.39191 

.39137

.38869 

.39485

.39660 

.38504

.44411 

.33272

(18.1) 

(18.6)

(14.1) 

(14.3)

(4.1) 

(4.3)

(.1) 

(.1)

(.9) 

(1.1)

(.8) 

(1.0)

(.1) 

(.1)

(.8) 

(.8)

(1.3) 

(1.7)

(13.4) 

(15.0)

-0.04888 

-.03568

-.04105 

-.04293

-.05036 

-.03390

-.04086 

-.04307

-.04136 

-.04302

-.04035 

-.04400

-.04300 

-.04099

-.04817 

-.03554

-.03898 

-.04608

.02927 

-.09627

(16.4) 

(15.0)

(2.3) 

(2.2)

(19.9) 

(19.3)

(2.7) 

(2.5)

(1.5) 

(2.4)

(3.9) 

(4.8)

(2.4) 

(2.4)

(14.7) 

(15.4)

(7.2) 

(9.7)

(169.7) 

(129.2)

0.25303 

.20115

.23436 

.21544

.23293 

.22437

.23761 

.21925

.23990 

.21352

.22900 

.22817

.23596 

.21397

.23768 

.21986

.22682 

.23116

.20500 

.25222

(1

(1

(

(

(

(

(

(

(

(

(

(

(

(

(

(

(1

(1

Average of absolute difference between observed-head distribution and simulated-head distribution in 120-cell area of layers 1 and 2 where there were enough data to m

predevelopment water levels (fig. 17).
H44 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

Longer periods of pumping and different well distributions and pumping rates can be evaluated, but 

the results should be considered reliable only in 

terms of the general response of the basin-fill aquifer to the pumping. Actual pumping for long periods 

of time may produce aquifer responses different 

from those simulated and discussed in this report; 

however, the general changes and trends should be 

similar.

SIMULATED RESPONSE TO HYPOTHETICAL 

DEVELOPMENT SCENARIOS

The general response of the basin-fill aquifer of 

Stagecoach Valley to nine hypothetical pumping 

scenarios was simulated and then evaluated using 

the calibrated flow model. Model simulations were 

made for an arbitrary period of 600 yr, 300 yr of 

pumping and 300 yr of recovery to allow the flow 

system to respond to sustained stresses and to 

approach a new equilibrium by the end of the 600 

yr of pumping and recovery. In the model, transmissivity of the top layer was arbitrarily held constant 

instead of being allowed to vary in response to 

changing water levels. This was done to avoid difficulties with model cells going dry (during some of 

the scenarios that involved heavy pumping) and 

then becoming saturated again during subsequent 

periods of recovery. To test the effect of assuming a 

constant transmissivity, the 11 pumping seasons, 

from 1971 to 1982, were also simulated without 

varying transmissivity. Drawdowns in the most 

heavily pumped cells were within 1 to 2 ft of the 

calibrated drawdowns (figs. 22, 24). Drawdown in 

areas distant from the heavily pumped wells agreed 

closely with drawdown obtained during calibration. 

Consequently, for moderate drawdown, the assumption of constant transmissivity is valid for the purpose of this report. However, some pumping 

scenarios involved great pumping rates, and large 

drawdowns were simulated for some areas near 

pumping cells. In two scenarios, the localized drawdown exceeded 100 ft but decreased rapidly away 

from pumping centers. In these scenarios, the simulated drawdown in the vicinity of pumping centers 

may be erroneously small. However, these errors 

would be restricted to localized areas and the 

assumption of constant transmissivity for layer 1 

probably is acceptable, as a first approximation, for 

evaluation of valleywide response to the pumping 

scenarios.

Hypothetical pumping scenarios were constrained 

using the following limitations:

1. Pumping wells were not located where finegrained deposits have low transmissivity, where the 

predevelopment depth to water exceeded 200 ft, 

where the thickness of saturated basin fill is less 

than 200 ft, where model cells are bounded on two 

or more sides by consolidated rock, or where landsurface slopes are greater than 200 ft/mi. Stagecoach Valley is partly drained by subsurface 

outflow, and no significant areas of saline water are 

known to be present; consequently, water quality 

was not used as a constraint in siting wells.

2. Pumping cells were distributed according to 

two general strategies. One is to distribute pumping cells strategically in or adjacent to areas of 

large estimated evapotranspiration to facilitate capture of the water consumed by natural evapotranspiration. This strategy is termed "strategically 

distributed." The other strategy is to form a single 

pumping center where pumping is concentrated in a 

few specific cells that are adjacent to each other. 

This strategy is termed "concentrated."

3. To avoid the necessity of quantifying and simulating the rate of irrigation-return flow from 

pumped water, all model simulations were based on 

net pumpage.

4. The range of pumping rates assigned to wells 

in an individual model cell was constrained. The 

maximum allowable rate prevented massive 

overpumping in individual cells, and the minimum 

rate avoided assignment of unrealistically low 

pumpage in numerous individual cells. The maximum pumping rate for each pumping cell was estimated on the assumption that a draft of about 3 ft/yr 

of water is evenly applied to the entire cell area. This 

rate of 3 ft/yr is the average rate of consumption by 

irrigation in the valley. Four pumping cells (three 

pumping at the maximum rate and one pumping at 

about half the maximum rate) are required to withdraw water at a total rate equal to the estimated 

predevelopment inflow and outflow (920 acre-ft/yr). 

The minimum rate for each pumping cell was about 

half of the maximum rate; therefore, seven pumping cells are required to withdraw water at a total 

rate equal to the estimated predevelopment inflow 

and outflow. In the model, all pumping was from 

layer 2.

The nine simulated development scenarios (A 

through I), grouped in table 9 by strategic distribution of pumping cells, were selected to illustrate 

how the general response of the basin-fill aquifer of 

Stagecoach Valley might change under a variety of 

imposed pumping stresses. Scenarios A, C, D, F, 

and H also provide a general test of the feasibility 

of the concept of sustained yield, in which pumping
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H45

TABLE 9. Simulated development scenarios

Distribution of pumping cells

Pumping cells are strategically located to

evapotranspiration.

Pumping cells are concentrated at north end

of Staeecoach Vallev.

Scenario

A........

B ........

C1 .......

D. .......

E........

F ........

G........

Pumping

rate

(acre-feet

per year)

.... 920

.... 1,840

.... 1,840

920

.... 920

.... 1,840

.... 920

.... 1.840

Drawdown

time

(years)

300

300

50

250

300

300

300

300

Recovery

time

(years)

300

300

300

300

300

300

300

Pumping cells are concentrated in south- H, 

eastern part of Stagecoach Valley, near 

Carson River.

Pumping cells have same general distribution I.. 

(and pumping rates) as 1981 pumping wells.

920

970

300

300

300

300

Scenario C incorporates two phases of pumping (a 50-year phase succeeded by a 250-year phase) characterized by different pumping rates; 300-year recovery begins after 300-year drawdown.

is maintained at a rate equal to the capture, which 

is the increase in recharge plus the decrease in discharge (Lohman and others, 1972). The scenarios 

for Stagecoach Valley test the sustained-yield concept in situations where not only may water be captured from more than one source but also where 

additional water may actually be induced to flow 

into the area. The scenarios were also selected to 

illustrate how the location of pumping wells affects 

the long-term aquifer response to development.

Scenarios B, E, and G illustrate the aquifer 

response to pumping rates substantially greater 

than the average annual recharge. Scenario I was 

included so that the general long-term response to 

a development pattern similar to the 1981 pumping 

pattern could be compared with the simulated scenarios. In all nine scenarios, neither economic and 

legal consideration nor possible salt buildup in the 

soil, caused by irrigation, was considered.

SIMULATION RESULTS

Simulation results of the various development 

scenarios are presented in figures 26 to 34 and in 

tables 10 to 18. (These figures and tables follow the 

"References Cited" section of this report.) Simulation of long-term response of the aquifer is only 

intended to show the nature of the response; therefore, only those factors that indicate general trends

are presented in the tables and figures. These factors are areal distribution of pumping cells and 

associated drawdown after 300 yr of pumping; 

changes in average drawdown of pumping cells, 

storage, evapotranspiration, and subsurface inflow 

and outflow during 300 yr of pumping succeeded by 

300 yr of recovery; and the sources of pumped 

water after specified periods of pumping (ranging 

from 1.5 to 300 yr).

The areal distribution of cells with associated 

pumping rates and the distribution of drawdown in 

layer 2 after 300 yr of pumping (shown in part A of 

figs. 26-34) are used to illustrate the general 

relation between distributed pumping and areal 

patterns of drawdown. Drawdowns in layers 1 and 

3 have similar patterns, but their magnitude is 

generally less.

In the graphs showing changes with time (parts 

B through E of figs. 26-34), the rate of change of 

each factor probably is more significant than a particular value at any given time. Generally, rapid 

changes suggest that the aquifer is strongly out of 

equilibrium and indicate that most of the pumped 

water is being derived from storage. On the other 

hand, small changes with time suggest that the 

aquifer may be gradually approaching a new 

equilibrium when little or no change in storage 

will occur. The potential sources of pumped water 

are shown in the pie diagrams (part F) of figures 

26 to 34.
H46 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

Ground-water budgets (tables 10-18) are used to 

describe the overall hydrologic effects after 1.5, 25, 

50, 100, and 300 yr of pumping. A summary of 

predevelopment conditions is included in each budget table for comparison.

DISCUSSION OF RESULTS

One of the objectives of the study of the basin-fill 

aquifer of Stagecoach Valley was to test the general 

feasibility of sustained yield. A comparison of the 

aquifer responses to the nine development scenarios 

is presented in table 19. Results of scenarios A, C, 

D, F, and H (figs. 26, 28, 29, 31, and 33, respectively) indicate that sustained yield is possible in 

Stagecoach Valley. In scenarios A, D, F, and H, 

where net pumping rate was held equal to the 

simulated rate of predevelopment total inflow to or 

total outflow from the basin-fill aquifer (920 acre-ft/yr), 

the model reached or almost reached a new equilibrium condition by the end of the 300-yr simulation. 

Siting (location and concentration) of pumping wells 

played a major role in determining the magnitude 

of the drawdown and what sources of water would 

be most readily captured; however, none of the scenarios used in this analysis produced adverse effects severe enough to prevent the aquifer from 

approaching a new equilibrium. A significant assumption in the simulations was that the Carson 

River added "new" water to the basin-fill aquifer in 

proportion to the amount of drawdown in the river 

cells; this balanced inflow and the small size of 

Stagecoach Valley were significant factors in the 

aquifer's closely approaching a new equilibrium. If 

the aquifer had been bounded entirely by no-flow 

boundaries in the model, the results would have 

been substantially different. The assumed inflow of 

water from the boundaries plus the small size of 

the area facilitated a complete recovery within the 

300-yr period after pumping had ceased.

Scenarios B, E, and G illustrate the response of 

the aquifer to a rate of pumping twice the estimated average annual recharge or discharge (table 

19; figs. 27, 30, 32). Drawdowns were from two to 

six times as great as those due to pumping at the 

lower rate of 920 acre-ft/yr; however, the aquifer 

was still nearing a new equilibrium in each of the 

three scenarios. This was possible only because of 

"new" water brought into the aquifer, either from 

induced infiltration through deposits along the 

Carson River or by capturing ground water that formerly flowed toward Churchill Valley. In this regard the limiting factor on sustained development

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GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H47

is not simply the ability to obtain water by pumping; rather, the limiting factor is the extent of 

allowable adverse effects on other water users. Virtually all water in the Carson River is appropriated, and increasing the subsurface flow from the 

river into the basin-fill aquifer of Stagecoach Valley 

would affect downstream users along the Carson 

River. Similar effects on ground-water users could 

conceivably occur in Churchill Valley.

Determining the extent to which effects on areas 

outside Stagecoach Valley can be tolerated is a legal 

matter and is beyond the scope of this report. Moreover, limiting pumping to the natural (predevelopment) inflow rate of 920 acre-ft/yr does not 

guarantee that conflicts with surface-water users 

along the Carson River will be avoided. The natural 

ground-water budget includes some ground-water 

outflow to the downstream reach of the river, 

which, if captured by pumping, could adversely affect the downstream river flows. The quantity 

would be small in relation to the average flow of 

the river and probably would not cause a detectable 

change except during low-flow periods. The location 

of pumping wells also significantly affects downstream users. For example, from scenario H (fig. 

33) the effects on stream flow near the south end of 

Stagecoach Valley are much greater and occur more 

rapidly than the effects from either scenarios A or 

D (figs. 26 and 29, respectively) in the north-central 

part of the valley, even though the net rate of 

pumping is the same.

One factor that is common to all the scenarios is 

that the leaky boundary conditions of the basin-fill 

aquifer strongly influence the results of the simulation. In order to apply the general findings of this 

analysis to other small basins within the Great 

Basin, considerable effort should be expended on 

defining boundary conditions, which might not be 

required for the study of a large area.

In summary, the simulated effects of pumping 

spread quickly throughout the entire basin-fill aquifer in all scenarios, and the capture of discharge 

probably proceeded more rapidly than it would have 

in a larger basin. When the aquifer was stressed by 

pumping, additional inflow induced from the 

Carson River and to a small extent from Churchill 

Valley tended to reduce water-level declines. Consequently, if water-level changes alone are used to 

evaluate the sensitivity of the model to variations 

in pumping rates, then sensitivity is underestimated; changes in subsurface inflow and outflow 

also must be included in any evaluation of how the 

basin-fill aquifer responds to heavy pumping. Moreover, this additional inflow ultimately causes the

simulated aquifer to attain a new equilibrium in 

response to a relatively wide range of pumping 

rates. The predevelopment flux through the basinfill aquifer is not necessarily the limiting criterion 

in determining the maximum sustained pumping 

rate; the limiting factor probably is the degree to 

which adverse effects on Carson River flows can be 

tolerated.

SUMMARY AND CONCLUSIONS

Stagecoach Valley is a small, topographically 

closed basin in western Nevada with a total area of 

about 70 mi2. About 33 mi2 of the area is underlain 

by basin-fill deposits; the remainder is underlain by 

consolidated rock. Surface drainage is from mountains that border most of the area toward Misfits 

Flat in the south-central part of the valley. Most 

locally derived runoff and recharge is generated in 

the Flowery Range, which forms the northwest border and contains the highest altitudes in the area. 

Churchill Butte and some relatively small unnamed 

mountains form the east and west boundaries of the 

area.

The south boundary is more complex. A topographic divide that traverses a series of small 

mountains and alluvial and lake deposits forms the 

topographic boundary of the basin. However, local 

subsurface hydraulic continuity exists between 

andesitic and basaltic rocks and alluvium beneath 

the topographic divide. Flood-plain deposits of the 

Carson River lie immediately south of this topographic divide; thus, the true hydrologic boundary 

of the basin-fill aquifer of Stagecoach Valley is the 

Carson River.

The structural depression that underlies Stagecoach Valley is partly filled by deposits of sand, 

gravel, silt, and clay that form the basin-fill aquifer. 

The fill is at least 500 ft thick throughout most of 

the area and attains a maximum thickness of about 

3,000 ft. The estimated average hydraulic conductivity of the basin-fill deposits ranges from l.OxlO"6 

ft/s for the finer grained deposits to as much as 

1.7xlO~3 ft/s for the coarser grained deposits.

The amount of ground water in storage under 

natural conditions, presumed to correspond to estimated pre-1971 (predevelopment) conditions, is 

about 1 million acre-ft; however, most of this stored 

water probably cannot be economically pumped because of excessive lifts and probable effects on the 

Carson River. Also estimated from predevelopment 

conditions, 89,000 acre-ft of water is stored in the 

upper 200 ft of saturated basin fill in the area that
H48 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

was developed as of 1982. This amount of water 

might be economically pumped. However, constraints related to potential effects on Carson River 

flow may limit storage depletion to significantly 

less than this amount.

A numerical model described by McDonald and 

Harbaugh (1988) was used to simulate the basin-fill 

aquifer; the aquifer was discretized into three layers. The top model layer (layer 1) approximates the 

water-table portion of the basin-fill deposits and 

thus represents the aquifer under unconfined conditions. The processes of recharge from precipitation 

and irrigation-return flow, evapotranspiration of 

ground water, interaction with flow in the Carson 

River, and depletion of storage by ground-water 

withdrawals all occur in layer 1, which is assumed 

to be about 50 ft thick. The middle layer (layer 2) 

represents that part of the basin fill most affected 

by pumping and is considered to represent the saturated zone at depths of 50 to about 300 ft below the 

water table. In this study, all pumping is assumed 

to be from layer 2. The lowest layer (layer 3) consists of saturated basin fill below layer 2, and its 

thickness varies laterally.

The simulation of predevelopment conditions indicated that the flux through the basin-fill aquifer 

was about 920 acre-ft/yr. This total inflow to the 

system included about 550 acre-ft/yr recharge from 

precipitation, about 280 acre-ft/yr subsurface inflow 

from flood-plain deposits beneath the upstream 

reach of the Carson River, and about 90 acre-ft/yr 

subsurface inflow from flood-plain deposits in the 

downstream reach of the Carson River. Total outflow from the system included about 640 acre-ft/yr 

by evapotranspiration, about 170 acre-ft/yr by subsurface flow to Churchill Valley, and about 120 

acre-ft/yr by subsurface flow to deposits beneath the 

downstream reach of the Carson River.

Ground-water development began in 1971, when 

about 310 acre-ft of water was pumped. Pumpage 

increased steadily until 1977, when about 1,600 

acre-ft was pumped and then decreased slightly in 

the following years. In 1981 about 1,100 acre-ft of 

water was pumped. This included about 930 acre-ft 

for irrigation, about 30 acre-ft for domestic and 

stock use, and about 130 acre-ft for public supply.

During the 11 pumping seasons from spring 1971 

through spring 1982, slightly more than 11,000 

acre-ft of ground water was pumped in Stagecoach 

Valley. Of this total, slightly less than 1,000 acre-ft 

was recirculated to the aquifer by irrigation-return 

flow, resulting in a net pumpage of about 10,000 

acre-ft. About 3,000 acre-ft of the net pumpage resulted from reductions in evapotranspiration and

from changes in subsurface inflow and outflow; the 

remaining 7,000 acre-ft was removed from aquifer 

storage. In response to this pumpage, water levels 

declined by 1 ft or less near the Carson River to 

more than 15 ft near pumping wells.

Model simulation of the ground-water system for 

the 11 pumping seasons (spring 1971 to spring 

1982) indicates that the rate of evapotranspiration 

of ground water had decreased by about 460 acre-ft/yr 

by spring 1982. Subsurface inflow from the upstream reach of the Carson River had increased by 

about 20 acre-ft/yr, inflow from the downstream 

reach of the Carson River had increased by about 

10 acre-ft/yr, and subsurface outflow to the downstream reach of the Carson River had decreased by 

about 7 acre-ft/yr. Subsurface outflow to Churchill 

Valley had decreased by about 8 acre-ft/yr. A total 

of about 450 acre-ft/yr was estimated to be captured 

by the pumping.

The potential response to pumping stresses over a 

300-yr period was evaluated using nine hypothetical 

development scenarios. Eight of the scenarios involved pumping at the rate of 920 or 1,840 acre-ft/yr 

(equal to or twice the predevelopment flux) or 

pumping at a mixed rate. Assumed pumping strategies for these eight scenarios included distributing 

pumping wells over a relatively large area, concentrating pumping in one area, strategically locating 

pumping wells with respect to areas of natural discharge, concentrating pumping at the north end of 

Stagecoach Valley, and concentrating pumping at 

the south end of the valley near the Carson River. 

The ninth scenario used a well distribution and average pumping rate similar to those in use in 1981. 

A 300-yr pumping period and a subsequent 300-yr 

recovery period were simulated for each scenario. 

The following general statements can be made on 

the basis of the simulation results:

1. The concept of sustained yield appears to be 

viable for hydrologic conditions like those in Stagecoach Valley. When simulated pumping was held to 

the predevelopment (natural) inflow or outflow rate 

of 920 acre-ft/yr, the aquifer essentially attained a 

new equilibrium after 300 yr of pumping. Moreover, 

water-level declines in and adjacent to the areas of 

pumping were generally less than 40 ft, and the 

greatest declines occurred during the first 50 yr of 

the simulation. When pumping rates were mixed 

(50 yr at 1,840 acre-ft/yr and 250 yr at 920 acre-ft/yr), 

the system also attained a new equilibrium after 

300 yr. In the scenarios where the pumping rate 

was held at 1,840 acre-ft/yr, the aquifer also approached a new equilibrium after 300 yr of pumping even though maximum drawdowns ranged from
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H49

90 to 186 ft, depending on the distribution of the 

pumping wells. In these scenarios additional subsurface inflow was induced from the Carson River 

and to a small extent from adjacent Churchill 

Valley; such induced inflow makes achieving a new 

equilibrium at least theoretically possible. Because 

the simulated aquifer ultimately attains a new 

equilibrium in response to a relatively wide range 

of pumping rates, the predevelopment flux is not 

necessarily the limiting criterion in determining the 

sustained pumping rate. The limiting factor probably is the degree to which reduction in Carson 

River flows can be tolerated.

2. In the model, the basin-fill aquifer was sensitive to pumping rates in that the maximum simulated drawdowns under a pumping rate of 1,840 

acre-ft/yr were as much as two to six times as great 

as those under a pumping rate limited to the 

predevelopment inflow rate of 920 acre-ft/yr. Substantial additional water inflow that was induced 

from the Carson River tended to attenuate the 

rates of water-level decline. If change in water level 

is the only criterion used to evaluate the sensitivity 

of the model to variations in pumping rates, then 

the sensitivity is underestimated. Changes in subsurface inflow and outflow also must be included in 

any evaluation.

3. In the model simulation, the aquifer also was 

sensitive to the location of the pumping wells. As 

previously mentioned, both water-level changes and 

variations in inflow and outflow must be evaluated 

to judge the full sensitivity of the aquifer response. 

Generally, minimal water-level declines occurred in 

the scenarios where pumping wells were located 

near areas of natural discharge or near potential 

sources of induced recharge. Conversely, when 

pumping wells were located away from these areas, 

water-level declines were significantly greater.

4. In the model simulation, the effects of pumping 

spread quickly throughout the entire aquifer, and 

the capture of discharge probably proceeds more 

rapidly in a basin the size of Stagecoach Valley 

than it would in a larger basin. The characteristics 

of the boundaries of the basin-fill aquifer, as modeled, greatly affected the simulated aquifer response. During pumping, additional inflow induced 

from the Carson River, and to a small extent from 

Churchill Valley, tended to reduce water-level declines. If a basin of similar size had no-flow conditions at all boundaries, the boundary effects 

probably would result in water-level declines much 

greater than those simulated for Stagecoach Valley. 

The general conclusion is that in small alluvial 

basins similar in hydrologic setting to Stagecoach

Valley, the boundary conditions of the aquifers probably are much more significant in determining the 

response to pumping stresses than they are in 

larger but hydrologically similar basins.

REFERENCES CITED

Axelrod, D.I., 1956, Mio-Pliocene floras from west-central 

Nevada: University of California Publications in Geological 

Sciences, v. 33, p. 91-160.

Benson, L.V., 1978, Fluctuations in the level of Lake Lahontan 

during the last 40,000 years: Quaternary Research, v. 9, 

p.300-318.

Bonham, H.F., 1969, Geology and mineral deposits of Washoe 

and Storey Counties, Nevada: Nevada Bureau of Mines 

and Geology Bulletin 70, 140 p.

Chow, V.T., ed., 1964, Handbook of applied hydrology: New 

York, McGraw-Hill, 1453 p.

Cordell, L.E., and Henderson, R.G., 1968, Iterative three-dimensional selection of gravity anomaly data using a digital 

computer: Geophysics, v. 33, no. 4, p. 596-601.

Dettinger, M.D., 1989, Reconnaissance estimates of natural recharge to desert basins in Nevada, U.S.A., by using chloride-balance calculations: Journal of Hydrology, v. 106, p. 

55-78.

Eakin, T.E., Maxey, G.B., Robinson, T.W, Fredericks, J.C., and 

Loeltz, O.J., 1951, Contributions to the hydrology of eastern Nevada: Nevada State Engineer, Water-Resources Bulletin, v. 12, 171 p.

Edwards, M.D., 1987, NAWDEX A key to finding water data: 

U.S. Geological Survey, 15 p.

Frisbie, H.R., La Camera, R.J., Riek, M.M., and Wood, D.B., 

1983, Water-resources data for Nevada, water year 1982: 

U.S. Geological Survey Water-Data Report NV-82-1, 366 p.

Glancy, PA., and Katzer, T.L., 1975, Water-resources appraisal 

of the Carson River basin, western Nevada: Nevada Division of Water Resources, Water-Resources Reconnaissance 

Report 59, 126 p.

Hardman, George, and Mason, H.G., 1949, Irrigated lands of 

Nevada: Reno, University of Nevada, Agricultural Experiment Station Bulletin 183, 57 p.

Harrill, J.R., 1986, Ground-water storage depletion in Pahrump 

Valley, Nevada-California, 1962-75: U.S. Geological Survey 

Water-Supply Paper 2279, 53 p.

Harrill, J.R., Welch, A.H., and Preissler, A.M., 1984, 

Hydrogeologic controls on ground-water flow in Stagecoach 

Valley, Nevada, in v. 3 of Lintz, Joseph, Jr., ed., Western 

geological excursions [in conjunction with Geological Society of America Annual Meeting, 97th, Reno, Nev.]: Reno, 

University of Nevada, p. 117-120.

 1993, Hydrogeochemical evidence for subsurface inflow to 

Stagecoach Valley, Lyon County, Nevada, in Selected Papers in the Hydrologic Sciences, 1988-92: U.S. Geological 

Survey Water-Supply Paper 2340, p. 179-193.

Harrill, J.R., Welch, A.H., Prudic, D.E., Thomas, J.M., Carman, 

R.L., Plume, R.W., Gates, J.S., and Mason, J.L., 1983, 

Aquifer systems in the Great Basin region of Nevada, 

Utah, and adjacent States A study plan: U.S. Geological 

Survey Open-File Report 82-445, 49 p.

Holzer, T.L., 1981, Preconsolidation stress of aquifer systems in 

areas of induced land subsidence: Water-Resources Research, v. 17, no. 3, p. 693-704.
H50 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

Kohler, M.S., Mordenson, T.J., and Baker, D.R., 1959, Evaporation maps of the United States: U.S. Weather Bureau Technical Publication 37, 13 p.

Lohman, S.W., 1972, Ground-water hydraulics: U.S. Geological 

Survey Professional Paper 708, 70 p.

Lohman, S.W., and others, 1972, Definitions of selected groundwater terms Revisions and conceptual refinements: U.S. 

Geological Survey Water-Supply Paper 1988, 21 p.

Maxey, G.B., and Eakin, T.E., 1949, Ground water in White 

River Valley, White Pine, Nye, and Lincoln Counties, Nevada: State of Nevada, Office of the State Engineer, WaterResources Bulletin no. 8, 59 p.

McDonald, M.G., and Harbaugh, A.W., 1988, A modular threedimensional finite-difference ground-water flow model: U.S. 

Geological Survey Techniques of Water-Resources Investigations, Book 6, Chap. A-l, 586 p.

Moore, J.G., 1969, Geology and mineral deposits of Lyon, Douglas, 

and Ormsby Counties, Nevada: Nevada Bureau of Mines and 

Geology Bulletin 75, 45 p.

Morris, D.A., and Johnson, A.I., 1967, Summary of hydrologic 

and physical properties of rock and soil materials, as analyzed by the hydrologic laboratory of the U.S. Geological 

Survey, 1948-60: U.S. Geological Survey Water-Supply 

Paper 1839-D, 42 p.

Rogers, O.K., 1975, Environmental geology of northern Carson 

City, Nevada: Reno, University of Nevada, M.S. thesis, 133 p.

Rose, R.L., 1969, Geology of parts of the Wadsworth and 

Churchill Butte quadrangles, Nevada: Nevada Bureau of 

Mines and Geology Bulletin 71, 27 p.

Schaefer, D.H., 1983, Gravity survey of Dixie Valley, west-central 

Nevada: U.S. Geological Survey Open-File Report 82-111, 17 p.

 1988, Bouguer gravity anomaly maps of Paradise, Stagecoach, Dixie, Fairview, and Stingaree Valleys, northwestern 

Nevada: U.S. Geological Survey Geophysical Investigations 

Map GP-985, scale 1:100,000.

Schaefer, D.H., Duffrin, E.G., and Plume, R.W., 1986, Principal 

facts for gravity stations in Paradise and Stagecoach Valleys, Humboldt and Lyon Counties, Nevada: U.S. Geological 

Survey Open-File Report 85-694, 15 p.

Schroer, C.V, and Moosburner, O.M., 1978, Nevada streamflow 

characteristics: Nevada Department of Conservation and 

Natural Resources, Division of Water Resources, Information Series Report 28, 478 p.

Shawe, D.R., 1965, Strike-slip control of basin-range structure 

indicated by historical faults in western Nevada: Geological 

Society of America Bulletin, v. 76, no. 12, p. 1361-1377.

Slemmons, D.B., Van Wormer, Douglas, Bell, E.J., and 

Silberman, M.N., 1979, Recent crustal movements in the 

Central Sierra Nevada-Walker Lane region of CaliforniaNevada Pt. I, Rate and style of deformation, in Whitten, 

C.A., ed., Recent crustal movements 1977: Tectonophysics, 

v. 52, nos. 14, p. 561-570.

Thompson, G.A., 1956, Geology of the Virginia City quadrangle, 

Nevada: U.S. Geological Survey Bulletin 1042-C, p. 45-75.

U.S. Department of Commerce, 1983, 1980 census of housing, detailed housing characteristics, Nevada: U.S. Bureau of the 

Census [Report] HC80-1-B30, 70 p.
FIGURES 26-34 AND TABLES 10-18
H52

119°30'

REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

119°25' 119°20'

39°25'

39°20'

Base from U.S. Geological Survey 

Churchill Butte. 1:62,500.1957

234 KILOMETERS 

EXPLANATION

BASIN FILL

CONSOLIDATED ROCK

FIGURE 26. Scenario A: Simulated response with pumping cells 

strategically located to capture evapotranspiration. Pumping 

rate is equal to estimated average predevelopment inflow and 

outflow (steady-state pumping rate of 920 acre-feet per year).

PUMPING CELL

 20 LINE OF EQUAL SIMULATED 

DRAWDOWN IN LAYER 2 

AFTER 300 YEARS OF 

PUMPING Interval, 2.5 feet

A, Predicted drawdown in layer 2 after 300 years of pumping. 

B, Average drawdown of pumping cells. C, Cumulative storage 

depletion. D, Evapotranspiration rates. E, Rates of subsurface 

inflow and outflow. F, Sources of pumped water.
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H53

0

0=1

OLD

50

100

150

200

0

g

uJ. uJ 50,000

2< 

OLU

I-LU

25

100,000

150,000

1000

750

2000

1000

£^^9y

1000

I I I I 

^r Predevelopment evapotranspiration rate = 630 acre-feet per year D

I I I

~ f Inflow from Carson River (upstream reach) s

I I

£

Total capture (inflow or outflow) ~~

''

Outflow to Churchill Valley/ 

I

/ --"-------

Net inflow/outflow, Carson

I I ! I

100 200 300 400 

ELAPSED TIME, IN YEARS

500 600

After 1.5 years After 25 years After 100 years After 300 years

EXPLANATION

INCREASED INFLOW FROM CARSON RIVER Upstream reach

INCREASED INFLOW FROM CARSON RIVER Downstream reach

CAPTURED EVAPOTRANSPIRATION

STORAGE DEPLETION

DECREASED OUTFLOW TO CHURCHILL VALLEY

FIGURE 26. Continued.
H54 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

1190301 119°20'

39°25'

39°20'

Base from U.S. Geological Survey 

Churchill Butte, 1:62.500,1957

1 2 3 4 KILOMETERS 

EXPLANATION

BASIN FILL

CONSOLIDATED ROCK

PUMPING CELL

FIGURE 27. Scenario B: Simulated response with pumping cells 

strategically located to capture evapotranspiration. Pumping 

rate is 1,840 acre-feet per year (equal to twice estimated average predevelopment inflow or outflow). A, Predicted drawdown

 20 LINE OF EQUAL SIMULATED 

DRAWDOWN IN LAYER 2 

AFTER 300 YEARS OF 

PUMPING Interval, 5 feet

in layer 2 after 300 years of pumping. B, Average drawdown of 

pumping cells. C, Cumulative storage depletion. D, Evapotranspiration rates. E, Rates of subsurface inflow and outflow. 

F, Sources of pumped water.
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY. NEVADA H55

100 -

150 -

200

50,000

100,000

o"§

pCLLLJ 

C0|- 

Z LU

ccH"

I-LU

150,000

1000

750

500

250

2000

1000

-1000

L

I 1 I

' Inflow from Carson River (upstream reach)

I I I I I 

Predevelopment evapotranspiration rate = 630 acre-feet per year

Total capture (inflow or outflow)

k Outflow to Churchill Valley

______I_________

 Net inflow/outflow, Carson River (downstream reach)

I__________I__________I_______

100 200 300 400 

ELAPSED TIME, IN YEARS

500 600

After 1.5 years After 25 years After 100 years After 300 years

EXPLANATION

INCREASED INFLOW FROM CARSON RIVER Upstream reach

INCREASED INFLOW FROM CARSON RIVER Downstream reach

CAPTURED EVAPOTRANSPIRATION

STORAGE DEPLETION

DECREASED OUTFLOW TO CHURCHILL VALLEY

FIGURE 27. Continued.
H56 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

119°30' 

39°25'

119°25' 119°20'

39°20'

Base from U.S. Geological Survey 

Churchill Butte. 1:62,500.1957 1 3 MILES

J

1 2 3 4 KILOMETERS 

EXPLANATION

BASIN FILL PUMPING CELL

CONSOLIDATED ROCK

FIGURE 28. Scenario C: Simulated response with pumping cells 

strategically located to capture evapotranspiration and pumping rate varied over time (50 years at 1,840 acre-feet per year, 

twice estimated average predevelopment inflow or outflow, 

then 250 years at 920 acre-feet per year, equal to estimated

 20 LINE OF EQUAL SIMULATED 

DRAWDOWN IN LAYER 2 

AFTER 300 YEARS OF 

PUMPING Interval, 5 feet

average annual predevelopment inflow or outflow). A, Predicted drawdown in layer 2 after 300 years of pumping. B, 

Average drawdown of pumping cells. C, Cumulative storage 

depletion. D, Evapotranspiration rates. E, Rates of subsurface 

inflow and outflow. F, Sources of pumped water.
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H57

QLJJ

50

100

150

200

0

50,000

<2 100,000

o

150,000

1000

750

zt 500

I-LU 

Q-O 

>^

250

0

2000

1000

m<o 

^ <

-1000

B

. Predevelopment evapotranspiration rate = 630 acre-feet per year

 Inflow from Carson River (upstream reach) 'Total capture (inflow or outflow)

^Outflow to Churchill Valley

______I__________

'Net inflow/outflow, Carson River (downstream reach) 

I__________I__________I

100 200 300

ELAPSED TIME, IN YEARS

400 500 600

After 1.5 years After 25 years After 100 years After 300 years

EXPLANATION

INCREASED INFLOW FROM CARSON RIVER Upstream reach

INCREASED INFLOW FROM CARSON RIVER Downstream reach

CAPTURED EVAPOTRANSPIRATION

STORAGE DEPLETION

DECREASED OUTFLOW TO CHURCHILL VALLEY

FIGURE 28. Continued.
H58

119°30' 

39°25' R

REGIONALAQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

119°25' 119°20'

39°20'

Base from U.S. Geological Survey 

Churchill Butte, 1:62.500,1957 3 MILES

I I I 

234 KILOMETERS

EXPLANATION

BASIN FILL

CONSOLIDATED ROCK

PUMPING CELL

FIGURE 29 Scenario D: Simulated response with pumping cells 

concentrated in area of evapotranspiration. Pumping rate is 

920 acre-feet per year, equal to estimated average 

predevelopment inflow or outflow. A, Predicted drawdown in

 20 LINE OF EQUAL SIMULATED 

DRAWDOWN IN LAYER 2 

AFTER 300 YEARS OF 

PUMPING Interval, 5 feet

layer 2 after 300 years of pumping. B, Average drawdown of 

pumping cells. C, Cumulative storage depletion. D, Evapotranspiration rates. E, Rates of subsurface inflow and outflow. 

F, Sources of pumped water.
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY NEVADA H59 

0

0 

QLU

s£

50

100

150

200

0

g

LU LU 50,000

<z 100,000

o

150,000

1000

z< 

OLU

750

500

250

B

 Predevelopment evapotranspiration rate = 630 acre-feet per year

g _£

 'd. 

UJLL.

^ Q i n

I) <

W 2

u 

2000

1000

0

-innn

1 1 1 1 1

£

~ x Inflow from Carson River (upstream reach) s Total capture (inflow or outflow) ~~

_,... , ,- , ;,,, *^««fa»^.-, ^

________ -- _____________ .^. _ _

Outflow to Churchill Valley/ Net inflow/outflow, Carson River (downstream reach)/ 

1 1 1 1 1

100 200 300 400 

ELAPSED TIME, IN YEARS

500 600

After 1.5 years After 25 years After 100 years After 300 years

4

EXPLANATION

INCREASED INFLOW FROM CARSON RIVER Upstream reach

INCREASED INFLOW FROM CARSON RIVER Downstream reach

CAPTURED EVAPOTRANSPIRATION

STORAGE DEPLETION

DECREASED OUTFLOW TO CHURCHILL VALLEY

FIGURE 29. Continued.
H60 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

119°25' 119°20'

39°20'

Base from U.S. Geological Survey 

Churchill Butte, 1:62.500,1957 1 3 MILES

J

1 2 3 4 KILOMETERS 

EXPLANATION

BASIN FILL

I CONSOLIDATED ROCK

FIGURE 30. Scenario E: Simulated response with pumping cells 

concentrated in area of evapotranspiration. Pumping rate is 

1,840 acre-feet per year, equal to twice estimated average 

predevelopment inflow or outflow. A, Predicted drawdown in

PUMPING CELL

 20 LINE OF EQUAL SIMULATED 

DRAWDOWN IN LAYER 2 

AFTER 300 YEARS OF 

PUMPING Interval, 10 feet

layer 2 after 300 years of pumping. B, Average drawdown of 

pumping cells. C, Cumulative storage depletion. D, Evapotranspiration rates. E, Rates of subsurface inflow and outflow. 

F, Sources of pumped water.
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY NEVADA H61 

0

0

OLD

z 

gHILULU -JLU

D-LL

50

100

150

200

50,000

100,000 -

B

150,000 l 

1000

C

z<02

EDCO i750 -

500

250

2000

1000

~i i r i 

Predevelopment evapotranspiration rate = 630 acre-feet per year

13 <

co z

-1000

Inflow from Carson River (upstream reach)

'Total capture (inflow or outflow) _

^Outflow to Churchill Valley

I__________

Net inflow/outflow, Carson River (downstream reach)

I__________I__________I_______

100 200 300 400 

ELAPSED TIME, IN YEARS

500 600

After 1.5 years After 25 years After 100 years After 300 years

EXPLANATION

INCREASED INFLOW FROM CARSON RIVER Upstream reach

INCREASED INFLOW FROM CARSON RIVER Downstream reach

CAPTURED EVAPOTRANSPIRATION

STORAGE DEPLETION

DECREASED OUTFLOW TO CHURCHILL VALLEY

FIGURE 30. Continued.
H62

119°30'

REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

119°25' 119°20'

39°25'

39°20'

Base from U.S. Geological Survey 

Churchill Butte, 1:62,500,1957 1 3 MILES

1 2 3 4 KILOMETERS 

EXPLANATION

BASIN FILL PUMPING CELL

CONSOLIDATED ROCK

FIGURE 31. Scenario F: Simulated response with pumping cells 

concentrated at north end of valley. Pumping rate is 920 acrefeet per year, equal to estimated average predevelopment 

inflow or outflow. A, Predicted drawdown in layer 2 after 300

 20 LINE OF EQUAL SIMULATED 

DRAWDOWN IN LAYER 2 

AFTER 300 YEARS OF 

PUMPING Interval, 5 feet

years of pumping. B, Average drawdown of pumping cells. C, 

Cumulative storage depletion. D, Evapotranspiration rates. E, 

Rates of subsurface inflow and outflow. F, Sources of pumped 

water.
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H63 

0

§co

01 

OLLJ

<C3LLJ

50

100

150

200

uj UJ 50,000

Q-LL

z< oS

COI100,000

150,000

1000

750

500

250

2000

1000

oi-i-

-1000

B

C

 Predevelopment evapotranspiration rate = 630 acre-feet per year D

Inflow from Carson River (upstream reach) 'Total capture (inflow or outflow)

^Outflow to Churchill Valley Net inflow/outflow, Carson River (downstream reach)

100 200 300 400 

ELAPSED TIME, IN YEARS

500 600

After 1.5 years After 25 years After 100 years After 300 years

 *

EXPLANATION

INCREASED INFLOW FROM CARSON RIVER Upstream reach

INCREASED INFLOW FROM CARSON RIVER Downstream reach

CAPTURED EVAPOTRANSPIRATION

STORAGE DEPLETION

DECREASED OUTFLOW TO CHURCHILL VALLEY

FIGURE 31. Continued.
H64 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

119°25' 119°20'

39°20'

Base from U.S. Geological Survey 

Churchill Butte, 1:62.500,1957

1 2 3 4 KILOMETERS

EXPLANATION

BASIN FILL 

CONSOLIDATED ROCK

PUMPING CELL

 20 LINE OF EQUAL SIMULATED 

DRAWDOWN IN LAYER 2 

AFTER 300 YEARS OF 

PUMPING Interval, 10 feet

FIGURE 32. Scenario G: Simulated response with pumping cells layer 2 after 300 years of pumping. B, Average drawdown of

concentrated at north end of valley. Pumping rate is 1,840 

acre-feet per year, equal to twice estimated average

pumping cells. C, Cumulative storage depletion. D, Evapotranspiration rates. Et Rates of subsurface inflow and outflow.

predevelopment inflow or outflow. A, Predicted drawdown in F, Sources of pumped water.
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H65

<OuJ

g 1-1-

o

50

100

150

200

50,000

100,000

150,000

1000

OLJJ

ZUJ 

<UJ SHI-UJ

750 -

500

250

2000

1000

m<u 

13 <

-1000

B

C

I I I i

Predevelopment evapotranspiration rate = 630 acre-feet per year

1 I I 

Inflow from Carson River (upstream reach) Total capture (inflow or outflow)

k Outflow to Churchill Valley Net inflow/outflow, Carson River (downstream reach) 

I I__________I_________

100 200 300 400 

ELAPSED TIME, IN YEARS

500 600

After 1.5 years After 25 years After 100 years After 300 years

EXPLANATION

INCREASED INFLOW FROM CARSON RIVER Upstream reach

INCREASED INFLOW FROM CARSON RIVER Downstream reach

CAPTURED EVAPOTRANSPIRATION

STORAGE DEPLETION

DECREASED OUTFLOW TO CHURCHILL VALLEY

FIGURE 32. Continued.
H66

119°30'

REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

11925" 119°20'

39°25'

r % yw vi ?

T '* <?' °±-^-- I- I t?

Base from U.S. Geological Survey 

Churchill Butte. 1:62.500,1957 1 3 MILES

1 2 3 4 KILOMETERS 

EXPLANATION

BASIN FILL 

CONSOLIDATED ROCK

PUMPING CELL

 20 LINE OF EQUAL SIMULATED 

DRAWDOWN IN LAYER 2 

AFTER 300 YEARS OF 

PUMPING Interval, 5 feet

FIGURE 33. Scenario H: Simulated response with pumping cells pumping. B, Average drawdown of pumping cells. C, Cumulaconcentrated near Carson River. Pumping rate is 920 acre-feet tive storage depletion. D, Evapotranspiration rates. E, Rates 

per year, equal to estimated average predevelopment inflow or of subsurface inflow and outflow. F, Sources of pumped water, 

outflow. A, Predicted drawdown in layer 2 after 300 years of
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H67

0

o=j

OLLJ

tr LUO

z< 

gS

wiZLU 

<LU C4-

I-LU

25

50,000

100,000

150,000

1000

750

500

250

2000

1000

-1000

I I I I

Predevelopment evapotranspiration rate = 630 acre-feet per year D

Inflow from Carson River (upstream reach) /Total capture (inflow or outflow)

LlL'-ljt^iyjS^-f&^iV^JP.lsftC^'.W?^

 Outflow to Churchill Valley Net inflow/outflow, Carson River (downstream reach) 

I__________I__________I______

100 200 300 400 

ELAPSED TIME, IN YEARS

500 600

After 1.5 years After 25 years After 100 years After 300 years

EXPLANATION

INCREASED INFLOW FROM CARSON RIVER Upstream reach 

INCREASED INFLOW FROM CARSON RIVER Downstream reach

CAPTURED EVAPOTRANSPIRATION

STORAGE DEPLETION

DECREASED OUTFLOW TO CHURCHILL VALLEY

FIGURE 33. Continued.
H68

1 ^"SOREGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

119°25' 119°20

39°25'

Base from U.S. Geological Survey 

Churchill Butte. 1:62.500.1957

1 2 3 4 KILOMETERS 

EXPLANATION

BASIN FILL 

CONSOLIDATED ROCK

PUMPING CELL Pumpage greater 

than 0.01 cubic feet per second

 20 LINE OF EQUAL SIMULATED 

DRAWDOWN IN LAYER 2 

AFTER 300 YEARS OF 

PUMPING Interval, 5 feet

FIGURE 34. Scenario I: Simulated response using 1981 well loca- Cumulative storage depletion. D, Evapotranspiration rates. E, 

tions. Net pumping rate is equal to 1981 rate (about 966 Rates of subsurface inflow and outflow. F, Sources of pumped 

acre-feet per year). A, Predicted drawdown in layer 2 after 300 water, 

years of pumping. B, Average drawdown of pumping cells. C,
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H69 

0

DLLJ

50 -

100 -

Luiij 50,000

Q.LL

100,000 -

150,000

1000

750

500

250

O .L

'Predevelopment evapotranspiration rate = 630 acre-feet per year

2000

1000

0

-inrtn

I I I I I

E

~ / Inflow from Carson River (upstream reach) x Total capture (inflow or outflow) ~

- - -- *"

Outflow to Churchill Valley \ Net inflow/outflow, Carson River (downstream reach)

I I I I I

100 200 300 400 

ELAPSED TIME, IN YEARS

500 600

After 25 years After 100 years After 300 years

c

fc. At 

EXPLANATION

INCREASED INFLOW FROM CARSON RIVER Upstream reach

INCREASED INFLOW FROM CARSON RIVER Downstream reach

CAPTURED EVAPOTRANSPIRATION

STORAGE DEPLETION

DECREASED OUTFLOW TO CHURCHILL VALLEY

FIGURE 34. Continued.
H70 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

TABLE 10. Ground-water budgets for scenario A 

[All data values are in acre-feet per year and are considered reasonable only to two significant figures. , none or negligible]

Pre-19 

conditio

71 

ns1

1.5 

years

Simulated elapsed pumping time

25

years

50 

years

100 

years

300 

years

Inflow

Recharge from precipitation ....................................

Inflow from Carson River (upstream reach) .........

Inflow from Carson River (downstream reach)..... 

Subsurface inflow from Churchill Valley ...............

Total......................................................................

547 

283 

86

. 916

547 

287 

88

922

547 

324 

110

981

547 

338 

122

1,007

547 

356 

139

1,042

547 

379 

164

1,090

Outflow

Subsurface outflow to Churchill Valley ..................

Net pumpage. .............................................................

Evapotranspiration ...................................................

Total......................................................................

166

635 

116

. 917

165 

920 

447 

115

1,647

153 

920 

71 

107

1,251

141 

920 

23 

104

1,188

127 

920 

4 

101

1,152

109 

920

95

1,124

Net results

Net outflow-inflow ................................................... 1 725 

717

270 

265

181 

176

110 

106

34 

20

Predevelopment conditions, based on steady-state simulation.

Ideally, the difference between simulated estimates of inflow and outflow is equal to simulated storage depletion, assuming outflow 

exceeds inflow. Discrepancies represent errors due primarily to truncation and rounding during iterative calculations performed by 

computer. These errors are independent of errors associated with estimation of recharge, discharge, or aquifer properties.

TABLE 11. Ground-water budgets for scenario B 

[All data values are in acre-feet per year and are considered reasonable only to two significant figures. , none or negligible]

Pre-19 

conditio

71

ns1 11 a

1.5 

years

Simulated elapsed pumping time

25 

years

50 

years

100 

years

300 

years

Inflow

Recharge from precipitation ....................................

Inflow from Carson River (downstream reach)..... 

Subsurface inflow from Churchill Valley ...............

Total......................................................................

547 

283 

86

, 916

547 

302 

91

940

547 

424 

162

1,133

547 

510 

238

1,295

547 

610 

340

1,497

547 

738 

478 

40

1,803

Outflow

Subsurface outflow to Churchill Valley..................

Outflow to Carson River (downstream reach)....... 

Total......................................................................

166

635 

116

917

164 

1,840 

299 

113

2,416

132 

1,840

95

2,067

94 

1,840

88

2,022

40 

1,840

81

1,961

1,840 

72

1,912

Net results

Simulated storage depletion ....................................

1 1,476 

1,471

934 

927

727 

720

464 

457

109 

99

Predevelopment conditions, based on steady-state simulation. 

2See footnote 2 of table 10.
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H71

TABLE 12. Ground-water budgets for scenario C

[All data values are in acre-feet per year and are considered reasonable only to two significant figures; negative values indicate that

water is being added to storage. , none or negligible]

Pre-1971 

conditions

Simulated elapsed pumping time

1.5 

years

25 

years

50 

years

100 

years

300 

years

Inflow

Recharge from precipitation ....................................

Inflow from Carson River (upstream reach) .........

Inflow from Carson River (downstream reach)..... 

Subsurface inflow from Churchill Valley ...............

547

283

86

547

302

91

547

424

162

547

510

238

547

435

218

547

403

186

Total 916 940 1,133 1,295 1,200 1,136

Outflow

Subsurface outflow to Churchill Valley .................

Net pumpage .............................................................

Evapotranspiration ..................................................

Outflow to Carson River (downstream reach)......

. 166

. 635

. 116

164

1,840

299

113

132

1,840

95

94

1,840

88

82

920

89

91

920

94

Total 917 2,416 2,067 2,022 1,091 1,105

Net results

Net outflow-inflow2 ..................

Simulated storage depletion

1 1,476 

- 1,471

934

927

727

720

-109

-104

-31

-12

Predevelopment conditions, based on steady-state simulation. 

2See footnote 2 of table 10.

TABLE 13. Ground-water budgets for scenario D 

[All data values are in acre-feet per year and are considered reasonable only to two significant figures. , none or negligible]

Pre-1971 Simulated elapsed pumping time

conditions 

1.5 

years

25 

years

50 

years

100 

years

300 

years

Inflow

Inflow from Carson River (downstream reach)..... 

Subsurface inflow from Churchill Valley ...............

547

283

86

547

277

89

547

298

112

547

310

129

547

324

152

547

346

184

Total...................................................................... 916 913 957 986 1,023 1,077

Outflow

Subsurface outflow to Churchill Valley............

Net pumpage.......................................................

Evapotranspiration ............................................

Outflow to Carson River (downstream reach).

166

635

116

165

920

460

115

151

920

101

106

136

920

62

103

Total 917 1,660 1,278 1,221

117

920

30

98

1,165

94

920

8

91

1,113

Net results

Net outflow-inflow2 ..................

Simulated storage depletion

747

745

321

315

235

229

142

134

36

25

Predevelopment conditions, based on steady-state simulation. 

2See footnote 2 of table 10.
H72 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

TABLE 14. Ground-water budgets for scenario E 

[All data values are in acre-feet per year and are considered reasonable only to two significant figures. , none or negligible]

Pre-1971 

conditions1

Simulated elapsed pumping time

1.5 

years

25 

years

50 

years

100 

years

300 

years

Inflow

Recharge from precipitation.................................... 547 547 547 547 547 547

Inflow from Carson River (upstream reach) ......... 283 278 331 395 495 637

Inflow from Carson River (downstream reach)..... 86 92 171 255 368 523

Subsurface inflow from Churchill Valley............... 84

Total 916 917 1,049 1,197 1,410 1,791

Outflow

Subsurface outflow to Churchill Valley............

Net pumpage .......................................................

Evapotranspiration ............................................

Outflow to Carson River (downstream reach).

Total ...............................................................

166 164

 1,840

635 321

116 113

123

1,840

23

93

76

1,840

86

917 2,438 2,079 2,002

11

1,840

79

1,930

1,840

69

1,909

Net results

Net outflow-inflow2 ..................

Simulated storage depletion

1 1,521 

- 1,516

1,030

1,024

805

798

520

513

118

113

Predevelopment conditions, based on steady-state simulation. 

2See footnote 2 of table 10.

TABLE 15. Ground-water budgets for scenario F 

[All data values are in acre-feet per year and are considered reasonable only to two significant figures. , none or negligible]

Pre-1971 

conditions 1

Simulated elapsed pumping time

1.5 

years

25 

years

50 

years

100 

years

300 

years

Inflow

Inflow from Carson River (downstream reach)..... 

Inflow from Carson River (downstream reach)..... 

Subsurface inflow from Churchill Valley ...............

547

283 

86

547

274 

86

547

284 

102

547

292 

119

547

306 

144

547

326 

183

Total 916 907 933 958 997 1,056

Outflow

Subsurface outflow to Churchill Valley............

Net pumpage .......................................................

Evapotranspiration ............................................

Outflow to Carson River (downstream reach).

166

635

116

164

920

563

116

140

920

204

109

116

920

117

105

Total...................................................................... 917 1,763 1,373 1,258

88

920

66

99

1,173

57

920

26

91

1,094

Net results

Net outflow-inflow2 ..................

Simulated storage depletion

856

849

440

434

300

294

176

170

38

31

^redevelopment conditions, based on steady-state simulation. 

2See footnote 2 of table 10.
GROUND-WATER FLOW AND SIMULATED EFFECTS OF DEVELOPMENT IN STAGECOACH VALLEY, NEVADA H73

TABLE 16. Ground-water budgets for scenario G 

[All data values are in acre-feet per year and are considered reasonable only to two significant figures. , none or negligible]

Pre-1971 

conditions1

Simulated elapsed pumping time

1.5 

years

25 

years

50 

years

100 

years

300 

years

Inflow

Recharge from precipitation ....................................

Inflow from Carson River (downstream reach).....

547

283

86

547

274

87

547

300

138

547

338

211

547

429

328 

43

547

582

499 

148

Total 916 908 985 1,026 1,347 1,776

Outflow

Net pumpage. ............................................................

Evapotranspiration ..................................................

. 166

. 635

116

163

1,840

497

115

99

1,840

79

100

36

1,840

14

89

1,840

14

81

1,840

70

Total 917 2,615 2,118 1,979 1,935 1,910

Net results

Net outflow-inflow2 ..................

Simulated storage depletion

1,707

1,700

1,133

1,127

883

878

588

566

134

125

^redevelopment conditions, based on steady-state simulation. 

2See footnote 2 of table 10.

TABLE 17. Ground-water budgets for scenario H 

[All data values are in acre-feet per year and are considered reasonable only to two significant figures. , none or negligible]

Pre-1971 

conditions

Simulated elapsed pumping time

1.5 

years

25 

years

50 

years

100 

years

300 

years

Inflow

Recharge from precipitation ....................................

Inflow from Carson River (upstream reach) .........

Inflow from Carson River (downstream reach)..... 

Subsurface inflow from Churchill Valley ...............

547

283

86

547

274

323

547

280

607

547

281

635

547

281

643

547

282

645

Total 916 1,144 1,434 1,463 1,471 1,474

Outflow

Net pumpage.............................................................

Outflow to Carson River (downstream reach)......

. 166

. 635

. 116

165

920

567

77

162

920

400

60

160

920

367

58

159

920

352

58

159

920

350

58

Total 917 1,729 1,542 1,505 1,489 1,487

Net results

Net outflow-inflow2 ..................

Simulated storage depletion

585

582

108

103

42

38

18

9

13

1

Predevelopment conditions, based on steady-state simulation. 

2See footnote 2 of table 10.
H74 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

TABLE 18. Ground-water budgets for scenario I 

[All data values are in acre-feet per year and are considered reasonable only to two significant figures. , none or negligible]

Pre-1971 Simulated elapsed pumping time

Recharge from precipitation ....................................

Inflow from Carson River (upstream reach) .........

Inflow from Carson River (downstream reach) .....

conditions

Inflow

547

283

86

1.5 

years

547

282

88

25 

years

547

314

108

50 

years

547

327

124

100 

years

547

346

145

300 

years

547

377

180

Total...................................................................... 916_____917_____969_____998 1,038 1,104

Outflow

Net pumpage. ............................................................

Outflow to Carson River (downstream reach)......

. 166

. 635

. 116

164

966

492

115

146

966

93

107

130

966

34

104

110

966

9

99

85

966

92

Total...................................................................... 917 1,737 1,312 1,234 1,184 1,143

Net results

Net outflow-inflow2 ........................................................... 1 820 343 236 146 39

Simulated storage depletion.................................... 818 339 232 139 29

^redevelopment conditions, based on steady-state simulation. 

2See footnote 2 of table 10.

* U.S. QOVHOMOT PRIWTING OFFICE: 1994-583/048/80019
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