GROUND-WATER HYDROLOGY AND

SIMULATED EFFECTS OF DEVELOPMENT

IN THE MILFORD AREA, AN ARID BASIN IN

SOUTHWESTERN UTAH

l *

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science 

USGS

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Ground-Water Hydrology and Simulated Effects of 

Development in the Milford Area, an Arid Basin in 

Southwestern Utah

By JAMES L. MASON

REGIONAL AQUIFER-SYSTEM ANALYSIS 

GREAT BASIN NEVADA AND UTAH

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1409-G

1998
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Thomas J. Casadevall, Acting Director

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

identification purposes only and does not constitute 

endorsement by the U.S. Government.

Library of Congress Cataloging-in-Publication Data

Mason, James L.

Ground-water hydrology and simulated effects of development in the Milford area, 

an arid basin in southwestern Utah / by J.L. Mason.

p. cm. - (Regional aquifer-system analysis-Great Basin, Nevada and Utah) (U.S. 

Geological Survey professional paper ; 1409-G) 

Includes bibliographical references 

Supt. of Docs, no.: I 19. 16: 1409-G

1. Ground-water flow--Utah--Milford Region. I. Title. II. Series. III. Series: 

Regional aquifer-system analysis-Great Basin, Nevada-Utah. 

GB1197.7.M374 1996

551.49'09792'4-dc21 97-13890

CIP 

ISBN 0-607-86818-X

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

Box 25286, Federal Center

Denver, CO 80225
FOREWORD

THE REGIONAL AQUIFER-SYSTEM ANALYSIS PROGRAM

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 to 

develop an understanding of the natural, undisturbed hydrologic system 

and the changes brought about in it by human activities and to provide a 

means of predicting the regional effects of future pumping or other stresses. 

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

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

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

study within the RASA Program is assigned a single Professional Paper 

number beginning with Professional Paper 1400.

L

Thomas J. Casadevall 

Acting Director

CONTENTS

	Page

Foreword............................................................................................. iii

Abstract............................................................................................... Gl

Introduction........................................................................................ 1

Purpose and scope ..................................................................... 2

Previous studies.......................................................................... 2

Well-numbering system used in Utah..................................... 4

Description of study area.......................................................... 4

Physiography........................................................................ 4

Geology.................................................................................. 4

Climate................................................................................... 6

Vegetation.............................................................................. 6

Surface water........................................................................ 7

Ground-water hydrology................................................................. 8

Consolidated rocks..................................................................... 8

Unconsolidated basin fill........................................................... 8

Description............................................................................ 8

Movement............................................................................. 8

Recharge................................................................................ 10

Discharge............................................................................... 11

Hydraulic properties........................................................... 11

Storage................................................................................... 11

Simulation of ground-water flow.................................................... 13

Model design............................................................................... 13

Model grid and layers......................................................... 13

Boundary conditions........................................................... 14

Initial conditions......................................................................... 15

	Page

Simulation of ground-water flow Continued 

Initial conditions Continued

Water levels........................................................................... G15

Recharge................................................................................. 15

Discharge............................................................................... 16

Hydraulic conductivity........................................................ 16

Storage coefficients............................................................... 17

Steady-state calibration.............................................................. 17

Transient calibration................................................................... 20

Sensitivity analysis..................................................................... 21

Limitations of model.................................................................. 32

Short-term predictive simulations............................................ 32

Simulation of hypothetical development alternatives.................. 39

Criteria.......................................................................................... 39

Development alternative Al..................................................... 40

Development alternative A2..................................................... 40

Development alternative A3..................................................... 44

Development alternative Bl...................................................... 48

Development alternative B2...................................................... 52

Development alternative B3...................................................... 52

Evaluation of development alternatives.................................. 61

Need for future studies..................................................................... 65

Summary............................................................................................. 67

References cited.................................................................................. 68

ILLUSTRATIONS

[Plates are in pocket]

PLATE 1. Map showing grid of the ground-water flow model of the basin-fill aquifer and active cells, specified boundary cells, and cells 

having pumped wells, Milford area, southwestern Utah.

2. Map showing areal extent of phreatophytes and location of cells in the ground-water flow model having discharge by 

evapotranspiration, Milford area, southwestern Utah.

Page

FIGURE 1. Map showing location and geographic features of study area................................................................................................................ G3

2. Diagram showing well-numbering system used in Utah......................................................................................................................... 5

3. Graph showing annual discharge of the Beaver River at Rocky Ford Dam, 1931-84........................................................................... 7

4. Map showing potentiometric surface of the principal aquifer, Milford area, 1983............................................................................... 9

5.-7. Graphs showing:

5. Percentage change from the preceding year in Beaver River flow and percentage of wells having water-level rises

the following spring for each year, 1953-82 ................................................................................................................................. 12

6. Annual ground-water withdrawals in the Milford area, 1931-82................................................................................................. 12

7. Water levels in two adjacent observation wells in the Milford area, 1932-83.............................................................................. 13

V
VI CONTENTS

Page

8.-11. Maps showing:

8. Steady-state contours for initial and computed water levels in layer 1....................................................................................... 18

9. Steady-state contours for initial and computed water levels in layer 2....................................................................................... 19

10. Potentiometric contours for the end of the historical transient simulation in layer 2 using constant recharge from

seepage of surface water and measured water levels in wells in March 1983........................................................................ 22

11. Model cells receiving constant and variable recharge from seepage of surface water during transient simulations and

location of observation wells from which measured water levels are compared to computed water levels..................... 23

12.-14. Graphs showing:

12. Measured and computed water-level changes during 1950-83 for 13 observation wells in the Milford area....................... 24

13. Measured and computed water-level changes during 1950-83 for seven observation wells in the Milford area that

show minimal differences (2 feet or less) in computed levels between constant and variable recharge from seepage... 28

14. Measured and computed water-level changes during 1950-83 for three observation wells in the Milford area that show

substantial differences (more than 2 feet) in computed levels between constant and variable recharge from seepage .. 30 

15.-19. Maps showing:

15. Boundary of active cells during model simulations and areal distribution of cells used for comparison during

sensitivity analysis........................................................................................................................................................................... 33

16. Projected water-level declines in the basin-fill aquifer for 1983-2020, assuming ground-water withdrawals equal to the

1979-82 average rate........................................................................................................................................................................ 35

17. Projected water-level declines in the basin-fill aquifer for 1983-2020, assuming ground-water withdrawals equal to 1.5

times the 1979-82 average rate....................................................................................................................................................... 36

18. Projected water-level declines in the basin-fill aquifer for 1983-2020, assuming ground-water withdrawals double the

1979-82 average rate........................................................................................................................................................................ 37

19. Simulated water-level declines after 300 years of pumping and areal distribution of cells simulating pumping for

development alternative Al........................................................................................................................................................... 41

20.-22. Graphs showing:

20. Simulated average water-level decline and recovery in model cells containing pumped wells for development

alternative Al ................................................................................................................................................................................... 42

21. Simulated changes in basin inflow and net outflow at general-head boundaries during pumping and recovery for

development alternative Al........................................................................................................................................................... 42

22. Simulated changes in the ratios of water removed from storage during pumping to recharge and water added to

storage during recovery to recharge for development alternative Al..................................................................................... 42

23. Map showing simulated residual water-level declines after 300 years of recovery for development alternative Al.................... 43

24. Graph showing simulated change in the ratio of natural discharge to recharge during pumping and recovery for

development alternative Al....................................................................................................................................................................... 44

25. Map showing simulated water-level declines after 300 years of pumping and areal distribution of cells simulating pumping

for development alternative A2 ................................................................................................................................................................ 45

26.-2S. Graphs showing:

26. Simulated average water-level decline and recovery in model cells containing pumped wells for development

alternative A2 ................................................................................................................................................................................... 46

27. Simulated changes in basin inflow and net outflow at general-head boundaries during pumping and recovery for

development alternative A2........................................................................................................................................................... 46

28. Simulated changes in the ratios of water removed from storage during pumping to recharge and water added to

storage during recovery to recharge for development alternative A2..................................................................................... 46

29. Map showing simulated residual water-level declines after 300 years of recovery for development alternative A2.................... 47

30. Graph showing simulated change in the ratio of natural discharge to recharge during pumping and recovery for

development alternative A2....................................................................................................................................................................... 48

31. Map showing simulated water-level declines after 300 years of pumping and areal distribution of cells simulating pumping

for development alternative A3 ................................................................................................................................................................ 49

32.-34. Graphs showing:

32. Simulated average water-level decline and recovery in model cells containing pumped wells for development

alternative A3 ......................................................................................._^ 50

33. Simulated changes in basin inflow and net outflow at general-head boundaries during pumping and recovery for

development alternative A3........................................................................................................................................................... 50

34. Simulated changes in the ratios of water removed from storage during pumping to recharge and water added to

storage during recovery to recharge for development alternative A3..................................................................................... 50

35. Map showing simulated residual water-level declines after 300 years of recovery for development alternative A3.................... 51

36. Graph showing simulated change in the ratio of natural discharge to recharge during pumping and recovery for

development alternative A3....................................................................................................................................................................... 52

37. Areal distribution of cells simulating pumping for development alternatives Bl, B2, and B3.......................................................... 53

38. Simulated water-level declines after 300 years of pumping for development alternative Bl............................................................ 54
CONTENTS VII

Page

39.-41. Graphs showing:

39. Simulated average water-level decline and recovery in model cells containing pumped wells for development

alternative Bl..................................................................................................................................................................................^ 55

40. Simulated changes in basin inflow and net outflow at general-head boundaries during pumping and recovery for

development alternative Bl............................................................................................................................................................ 55

41. Simulated changes in the ratios of water removed from storage during pumping to recharge and water added to

storage during recovery to recharge for development alternative Bl...................................................................................... 55

42. Map showing simulated residual water-level declines after 300 years of recovery for development alternative Bl...................... 56

43. Graph showing simulated change in the ratio of natural discharge to recharge during pumping and recovery for

development alternative Bl....................................................................................................................................................................... 57

44. Map showing simulated water-level declines after 300 years of pumping for development alternative B2.................................... 58

4S.-47. Graphs showing:

45. Simulated average water-level decline and recovery in model cells containing pumped wells for development

alternative B2..................................................................................................................................................................................... 59

46. Simulated changes in basin inflow and net outflow at general-head boundaries during pumping and recovery for

development alternative B2 .....................;...................................................................................................................................... 59

47. Simulated changes in the ratios of water removed from storage during pumping to recharge and water added to

storage during recovery to recharge for development alternative B2...................................................................................... 59

48. Map showing simulated residual water-level declines after 300 years of recovery for development alternative B2...................... 60

49. Graph showing simulated change in the ratio of natural discharge to recharge during pumping and recovery for

development alternative B2........................................................................................................................................................................ 61

50. Map showing simulated water-level declines after 50 years of pumping for development alternative B3...................................... 62

51. Simulated average water-level decline and recovery in model cells containing pumped wells for development alternative B3 63

52. Simulated changes in basin inflow and net outflow at general-head boundaries during pumping and recovery for

development alternative B3....................................................................................................................................................................... 63

53. Map showing simulated water-level declines after 300 years of pumping for development alternative B3.................................... 64

54. Graph showing simulated changes in the ratios of water removed from storage during pumping to recharge and water

added to storage during recovery to recharge for development alternative B3................................................................................. 65

55. Map showing simulated residual water-level declines after 300 years of recovery for development alternative B3...................... 66

56. Graph showing simulated change in the ratio of natural discharge to recharge during pumping and recovery for

development alternative B3....................................................................................................................................................................... 67

TABLES

Page

TABLE 1. Variation in water-budget components during historical transient simulations in the Milford area, Utah.................................. G20

2. Simulated steady-state (1927) and transient-state (1979-82) ground-water budget for the Milford area, Utah........................... 31

3. Results of sensitivity analysis for ground-water model, Milford area, Utah..................................................................................... 34

4. Projected changes in ground-water budget components due to increased ground-water withdrawals, Milford area, Utah.... 38

5. Cumulative total of simulated water removed from storage after pumping and recovery for each development

alternative in the Milford area, Utah...................................................................................................................................................... 65
VIII CONTENTS

CONVERSION FACTORS AND VERTICAL DATUM

__________Multiply inch-pound units_____________ By___________To obtain metric units__________

acre 0.4047 square hectometer

acre-foot (acre-ft) 0.001233 cubic hectometer

acre-foot per square mile (acre-ft/mi2) 476.1 cubic meter per square kilometer

acre-foot per year (acre-ft/yr) 0.001233 cubic hectometer per year

cubic foot per second (ft3 /s) 0.02832 cubic meter per second

foot (ft) 0.3048 meter

foot per day (ft/ d) 0.3048 meter per day

foot per mile (ft/mi) 0.1894 meter per kilometer

foot per second (ft/ s) 0.3048 meter per second

foot squared per day (ft2 /d) 0.0929 meter squared per day

foot squared per second (ft^/s) 0.0929 meter squared per second

gallon per minute (gal/min) 0.0631 liter per second

inch (in.) 25.4 millimeter

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

mile (mi) 1.609 kilometer

square foot (ft2) 0.0929 square meter

square mile (mi2) 2.59 square kilometer

In the first part of the text, all units involving time are given in the commonly used form; however, in the latter part of the text where model 

simulations are discussed, all units involving time are given in seconds the time unit used for all simulations. The commonly used units 

involving time are shown in parentheses.

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 a geodetic datum derived from a general adjustment 

of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929.
REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN

GROUND-WATER HYDROLOGY AND SIMULATED EFFECTS OF 

DEVELOPMENT IN THE MILFORD AREA, AN ARID BASIN IN

SOUTHWESTERN UTAH

BY JAMES L. MASON

ABSTRACT

A three-dimensional, finite-difference model was constructed to 

simulate ground-water flow in the Milford area. The purpose of the 

study was to evaluate present knowledge and concepts of the groundwater system, to analyze the ability of the model to represent past and 

current (1984) conditions, and to estimate the effects of various groundwater development alternatives. The alternative patterns of groundwater development might prove effective in capturing natural discharge from the basin-fill aquifer while limiting water-level declines.

Water levels measured during this study indicate that ground water 

in the Milford area flows in a northwesterly direction through consolidated rocks in the northern San Francisco Mountains toward Sevier 

Lake. The revised potentiometric surface shows a large area t-ir probable basin outflow, indicating that more water leaves the Milford area 

than the 8 acre-feet per year estimated previously.

Simulations made to calibrate the model were able to approximate 

steady-state conditions for 1927, before ground-water development 

began, and transient conditions for 1950-82, during which groundwater withdrawal increased. Basin recharge from the consolidated 

rocks and basin outflow were calculated during the calibration process. 

Transient simulations using constant and variable recharge from surface water were made to test effects of large flows in the Beaver River.

Simulations were made to project water-level declines over a 37- 

year period (1983-2020) using the present pumping distribution. 

Ground-water withdrawals were simulated at 1, 1.5, and 2 times the 

1979-82 average rate.

The concepts of "sustained" yield, ground-water mining, and the 

capture of natural discharge were tested using several hypothetical 

pumping distributions over a 600-year simulation period. Simulations 

using concentrated pumping centers were the least efficient at capturing natural discharge and produced the largest water-level declines. 

Simulations using strategically placed ground-water withdrawals in 

the discharge area were the most efficient at eliminating natural discharge with small water-level declines.

INTRODUCTION

The Great Basin Regional Aquifer-System Analysis 

(RASA) Program, which began in 1980, is the tenth in a series of 25 studies that represents a systematic effort to 

study regional-aquifer systems throughout the United 

States. The general objectives for all RASA studies are to 

describe the present ground-water system and the original ground-water system as it existed prior to development, analyze the changes to the system, synthesize 

results of this and earlier studies, and provide capabilities 

through which effects of future ground-water development can be estimated. Specific objectives of the Great Basin RASA (Harrill and others, 1983, p. 2) are as follows:

1. To develop a data base with sufficient data to support 

computer ground-water flow modeling of basins 

throughout the region.

2. To delineate and quantitatively describe ground-water 

basins that are hydraulically connected to form a 

flow system.

3. To develop a better understanding of recharge and 

discharge processes.

4. To develop computer ground-water flow models of 

basins or flow systems considered to be representative of the region.

5. To evaluate relative hydrologic effects of hypothetical 

development alternatives on the basins or flow systems for which ground-water flow models were 

constructed.

Gl
G2 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

6. To design and document generalized ground-water 

flow models that can be readily applied to similar 

systems throughout the region. 

The Great Basin RASA study area encompasses a series of north-trending mountain ranges separated by alluvial basins. Both the mountain ranges and the basins tend 

to be 5 to 15 mi wide. Most mountain ranges rise from 

1,000 to 5,000 ft above the adjoining basins and can extend 

for as much as 50 mi.

The Great Basin contains a regional aquifer in which 

most individual basins are linked hydrologically. Some 

basins form multibasin ground-water flow systems by the 

movement of water through permeable sedimentary deposits or consolidated rock, whereas, some basins are 

linked by rivers or surface-water drainages. The remaining basins function as hydrologically isolated basins. All 

of these basins occupy structural depressions that have 

been filled with alluvial deposits derived from the adjacent mountain ranges or lacustrine deposits derived from 

Quaternary lakes. The water supply is derived from precipitation on the adjacent mountains. Annual recharge to 

the ground-water systems is usually small in relation to 

the large volumes of water stored (Harrill and others, 

1983, p. 3).

Computer simulation of the ground-water system in 

the Milford area in southwestern Utah (fig. 1) was one of 

nine modeling efforts included in the Great Basin RASA 

Program. Like the other modeling efforts, information obtained from the model of the Milford area might be applicable to other parts of the Great Basin. The Milford area 

was selected for study because of extensive surface-water 

irrigation, substantial ground-water withdrawals and 

water-level declines since 1950, and subsurface inflow to 

and outflow from the basin.

PURPOSE AND SCOPE

The purpose of this report is to describe the groundwater hydrology of the Milford area, to document the development of the computer ground-water flow model, 

and to present the results of model simulations. The 

ground-water system prior to and changes since groundwater development began is described.

For the purposes of this report, the term "Milford area" is the entire study area, including the basin in the center and the surrounding mountain ranges. The term 

"basin" refers to the structural depression that contains 

unconsolidated basin-fill deposits and the associated 

ground-water system.

A three-dimensional, finite-difference model was constructed to simulate ground-water flow in the Milford 

area. The model was constructed using data obtained

mostly during the 1970's; aquifer-test and ground-waterwithdrawal data were reevaluated and some new interpretations were made. Additional data on ground-water 

levels and withdrawals were collected during 1981-83. 

Three observation wells were drilled in the northwestern 

part of the Milford area to define more clearly that part of 

the ground-water system.

The model, which was calibrated to known steadystate and transient conditions, was used for simulations 

to estimate future water-level declines using present, and 

multiples of present, ground-water withdrawals. Hypothetical ground-water-withdrawal alternatives were simulated similar to other basin studies as part of the Great 

Basin RASA Program.

PREVIOUS STUDIES

White (1932) estimated evapotranspiration in the Milford area on the basis of pan-evaporation data and diurnal water-level fluctuations in the vicinity of various 

types of vegetation. His report includes extensive waterlevel data that had not been published previously. Nelson (1950,1954) and Nelson and Thomas (1952) described 

the ground-water system and the extent of ground-water 

development in the Milford area. Their reports include 

ground-water-withdrawal data for individual wells during 1931-53. Criddle (1958) studied consumptive use and 

irrigation requirements in the area. He estimated consumptive use for each crop type and total consumptive 

use for the area. Sandberg (1962, 1966) provided additional information on the ground-water hydrology of the 

area, including well information, well logs, water-level 

measurements, and chemical analyses of ground water. 

Mower and Cordova (1974) conducted a comprehensive 

study of the water resources of the Milford area, with 

emphasis on the ground-water system.

Numerous geophysical and geochemical studies that 

defined the Roosevelt Hot Springs Known Geothermal 

Resource Area (KGRA), located along the eastern margin 

of the Milford area at the base of the Mineral Mountains, 

were conducted by the University of Utah with funding 

from the U.S. Department of Energy. Brumbaugh and 

Cook (1977), Crebs and Cook (1976), and Thangsuphanich (1976) defined the alluvium-consolidated rock interface along the west margin of the Mineral Mountains by 

using gravity and ground-magnetic surveys. These geophysical surveys partly defined the depth of the basin fill 

and defined the interface between the alluvium and the 

consolidated rock along the Mineral Mountains. Gertson 

and Smith (1979) reported on an east-west seismic-refraction profile across the basin north of Milford. Smith 

(1980) studied the potential for water recharging the
INTRODUCTION G3

Great Basin RASA 

study area

110°

40° 

<^%A\ Las P 

VALLEY l\ ARIZONA

EXPLANATION

Consolidated rocks

Basin fill

Boundary of study area

0 20 40 60 MILES 

0 20 40 60 KILOMETERS

FIGURE 1. Location and geographic features of study area.
G4 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

Tushar Mountains, east of the Milford area, to flow at 

depth beneath the Mineral Mountains and to discharge in 

the Milford area. Smith used a vertical, two-dimensional, 

finite-element model to determine conditions necessary 

for the hypothesized flow regime, and concluded that 

flow beneath the Mineral Mountains was not likely. Rohrs and Bowman (1980) and Bowman and Rohrs (1981) 

studied the stable isotopes of spring and thermal waters 

from the Roosevelt Hot Springs. They concluded that the 

thermal waters had a meteoric origin and probably were 

from the higher altitudes of the Mineral Mountains.

WELL-NUMBERING SYSTEM USED IN UTAH

The system of numbering wells in Utah is based on 

the cadastral land-survey system of the U.S. Government. 

The number, in addition to designating the well, 

describes its position. The State is divided into four quadrants by the Salt Lake Base Line and the Salt Lake 

Meridian, and these quadrants are designated by A, B, C, 

and D, indicating respectively, the northeast, northwest, 

southwest, and southeast quadrants. Numbers designating the township and range, in that order, follow the 

quadrant letter, and all three are enclosed in parentheses. 

The number after the parentheses indicates the section 

and is followed by three letters indicating the quarter section, the quarter-quarter section, and the quarter-quarterquarter section generally 10 acres; the letters a, b, c, and 

d indicate, respectively, the northeast, northwest, southwest, and southeast quarters of each subdivision. The 

number after the section subdivisions is the serial number 

of the well within the smallest (10-acre) subdivision. 

Thus, (C-29-ll)27dad-l designates the first well constructed or visited in the SE1/4NE1/4SE1/4 sec. 27, T. 29 

S., R. 11 W. The numbering system is shown in figure 2.

DESCRIPTION OF STUDY AREA

PHYSIOGRAPHY

The Milford area, which lies within the Basin and 

Range physiographic province (Fenneman, 1931), covers 

1,160 mi2 in parts of Millard, Beaver, and Iron Counties, 

Utah (fig. 1). The center of the Milford area is a northtrending basin, which is bounded by the Mineral Mountains to the east, the Black Mountains to the south, and the 

San Francisco Mountains to the west. The Beaver Lake 

Mountains, Rocky Range, and Star Range are small 

mountain ranges on the west side of the basin. The basin 

is mostly between altitudes of 4,850 and 5,500 ft above sea 

level. Most of the mountainous areas are between 5,500

and 9,000 ft; the highest peak (9,660 ft) is in the San Francisco Mountains.

The Milford area is topographically open to the southwest, where no topographic features separate the Milford 

area from the adjacent Beryl-Enterprise area. Similarly, 

the north end of the Milford area is topographically open 

near Black Rock where it joins the Sevier Desert.

The basin is drained by the Beaver River and numerous ephemeral tributaries, which are a part of the Sevier 

River drainage that terminates in Sevier Lake. The Beaver 

River channel is normally dry within a short distance 

downstream from Minersville because of diversions for 

irrigation. The Beaver River flows westward into the Milford area from Beaver Valley through a narrow gap between the Mineral Mountains and the Black Mountains. 

The river channel extends north and exits the basin where 

it is constricted by a basalt flow. Cove Creek, an ephemeral stream, flows into the northeast part of the area 

through a gap that separates the north end of the Mineral 

Mountains from the same basalt flow. The Big Wash, an 

ephemeral stream, drains the area east of the San Francisco Mountains between the Beaver Lake Mountains and 

the Star Range.

GEOLOGY

The present physiography of the Milford area is the 

result of several phases of geologic evolution. Thick sequences of marine, miogeosynclinal strata were deposited from late Precambrian through Devonian time 

(Hintze, 1973, p. 8). Additional deposits accumulated 

from Mississippian through Early Triassic time but were 

generally thinner and representative of a near-shore depositional environment (Hintze, 1973, p. 9). During Late 

Triassic to early Cenozoic time, this part of western Utah 

was a rugged highland caused by thrust faulting and 

folding of the Sevier Orogeny (Hintze, 1973, p. 9). During 

the Oligocene, volcanic activity deposited extensive layers of ignimbrites, lava flows, and volcanic breccias in 

western Utah (Hintze, 1973, p. 9). From Miocene to Holocene time, the Oligocene volcanic rocks and the earlier 

miogeosynclinal strata were subjected to block-faulting 

and crustal extension, which resulted in north-trending, 

alternating mountain ranges and basins. Erosional debris 

partially filled the basins prior to and during the deposition of Lake Bonneville lacustrine sediments (Hintze, 

1973, p. 9).

Consolidated rocks in the mountains surrounding the 

basin vary in age and lithology from Precambrian 

metasediments to Quaternary basalt and rhyolites. The 

Mineral Mountains on the east are an uplifted horst, most 

of which is a granitic pluton. The pluton has been K-Ar 

(potassium-argon) dated between 9.4 and 14.0 m.y. (mil-
INTRODUCTION G5

Sections within a township

R.11 w.

T. 

29s 

S.

6

7

18

V

30

31

5

8

17

20

v

OCL

32

4

9

16

21

28 

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34

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26

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12

13

24

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. Q 7 Inlnmatnrc X. »

Tracts within a section

Sec. 27

(C-29-11)27dad-1

T. 29 S., R. 11 W.

Salt Lake

UTAH

Base Line

Salt Lake City

FIGURE 2. Well-numbering system used in Utah.
G6 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

lion years) (Armstrong, 1970, p. 217; Ward and others, 

1978, p. 1520) and has intruded gneisses of probable Precambrian age, which are exposed along the western margin of the pluton. Repeated igneous activity from middle 

Tertiary to Quaternary time is evident. Middle Tertiary 

lavas are exposed on the south flank of the Mineral 

Mountains. This volcanic activity was followed by the 

emplacement of rhyolite on the north and west flanks of 

the Mineral Mountains that postdates the pluton. The 

youngest rhyolites have been K-Ar dated between 0.8 and 

0.5 m.y. (Ward and others, 1978, p. 1520) and are distributed along the western flank. Paleozoic and Mesozoic 

sedimentary rocks crop out on the north and south ends 

of the Mineral Mountains.

In the north end of the San Francisco Mountains, Precambrian and Cambrian metasediments overlie Cambrian quartzites as a result of the Frisco Thrust (Lemmon 

and Morris, 1983). In the San Francisco Mountains and 

northern Beaver Lake Mountains, Precambrian and Cambrian metasediments overlie Ordovician through Mississippian limestone, dolomite, and quartzite due to the 

Beaver Lake Thrust (Lemmon and Morris, 1983). The 

southern San Francisco Mountains and Star Range are 

composed primarily of Tertiary latitic ignimbrites and 

late Tertiary basalt and andesite flows with a few exposures of upper Paleozoic carbonate rocks and Mesozoic 

sandstone (Hintze, 1980).

The Black Mountains are composed primarily of late 

Tertiary volcanic rocks with small, intermittent outcrops 

of basalt. Numerous faults are also present (Hintze, 

1980).

Condie and Barsky (1972, p. 337) indicated the Black 

Rock basalts predated Lake Bonneville. The basalts overlie white tuffaceous clay, silt, and marl of early Pleistocene age. The contact is exposed along cliff faces east of 

Black Rock in the north end of the study area.

On the basis of gravity data, Carter and Cook (1978, p. 

89) suggested that the basin-fill thickness is 1.5 km (about 

4,900 ft). In a later study, Gertson and Smith (1979, p. 83) 

estimated the basin-fill thickness to be 1.8 km (about 5,900 

ft).

On the basis of a seismic refraction profile, Gertson 

and Smith (1979, p. 57) defined two layers within the basin-fill deposits. The lower layer ranges in thickness from 

0 km at the margin of the basin to about 1.2 km (3,900 ft) 

in the center of the basin (Gertson and Smith, 1979, p. 89). 

The composition of the lower layer is unknown because 

no well has penetrated this layer; however, Gertson and 

Smith (1979, p. 58) reported that seismic velocity values 

recorded for the lower layer were similar to those that 

Amow and Mattick (1968, p. B80) assigned to Tertiary 

sediments. These higher velocity values generally are

related to greater cementation and compaction and lower 

porosity values.

The upper layer of the basin fill ranges in thickness 

from 0.1 to 0.6 km (about 300 to 2,000 ft)(Gertson and 

Smith, 1979, p. 89). The upper layer of the basin fill consists of lacustrine deposits of fine-grained clay, silt, and 

marl along the axis of the basin that are interlayered and 

intertongued with deltaic and alluvial deposits of clay, 

silt, sand, and gravel. On the basis of scant well-log data, 

the lacustrine deposits are more prevalent in the northern 

one-half of the basin. Along the margins of the basin near 

the mountain fronts alluvial fans are present. Well-log 

data from the eastern margin of the basin indicate deposits of mixed clay and sand; whereas well-log data from 

the western margin of the basin indicate alternating layers of clay and unsorted sand and gravel. Shoreline deposits of sand and gravel reworked from the alluvial fans 

are present to an altitude of 5,120 ft (Dennis, 1942, p. 124).

The basement rocks below the basin fill are assumed 

to be Precambrian gneisses. Gertson and Smith (1979, p. 

60) reported that seismic velocity values are similar to 

those recorded for a sonic log in a test well drilled into 

Precambrian gneisses on the western edge of the Mineral 

Mountains.

CLIMATE

The climate of the study area varies from semiarid on 

the basin floor to subhumid at higher altitudes in the surrounding mountains. The mean annual temperature at 

Milford is 49.3°F; summer highs sometimes exceed 100°F, 

and winter lows are sometimes less than -10°F (Mower 

and Cordova, 1974, p. 9). Average growing season is 126 

days, usually from mid-May to late September (Criddle, 

1958, p. 4). Average annual precipitation at Milford was 

8.79 inches for 1932-83 (Avery and others, 1984, p. 62). 

The 1931-60 normal annual precipitation was 26 in. in the 

Mineral Mountains and as much as 16 in. in the San Francisco Mountains (U.S. Weather Bureau, 1963). Mower 

and Cordova (1974, p. 9) reported that average pan evaporation for April-October during 1953-71 was 78 inches/yr. They attributed the high rate of evaporation to 

frequent wind.

VEGETATION

In the higher altitudes of the surrounding mountains, 

the predominant vegetation is juniper (Juniperus sp.) and 

pinyon pine (Pinus edulis); however, in the Mineral Mountains, scrub oak (Quercus gambelii Nutt.) is more prevalent. Along the margins of the basin, the predominant 

vegetation is sagebrush (Artemisia tridentata), with some 

rabbitbrush (Chrysoihamnus nauseosus) and shadscale 

(Atriplex confertfolia); all are low to the ground.
INTRODUCTION G7

130

120

LLJ

cr 100

LLJ 

Q_

t 9°

LLJ

LL

LLJ 80

CC

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2 7°

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1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985

FIGURE 3. Annual discharge of the Beaver River at Rocky Ford Dam, 1931-84.

Along the axis of the basin where the water table is 

shallow and the land is not irrigated, stands of greasewood (Sarcobatus vermiculatus), rabbitbrush, saltgrass 

(Distichlis stricta), and pickleweed (Allenrolfea occidentalis) 

are the principal phreatophytes; of these, greasewood is 

the most common. Willow (Salix sp.) and saltcedar (Tamarix gallica), which are phreatophytes, grow along the Beaver River channel and major canals. Mower and Feltis 

(1968, p. 14) reported that saltcedar was introduced into 

the Sevier Desert to the north prior to 1950, and saltcedar 

probably was introduced into the Milford area about the 

same time.

Cottonwood (Populus sp.) and willow grow in upland 

areas near springs. Cottonwood and other trees grow in 

the center of the valley where they were planted for shade 

and windbreaks.

SURFACE WATER

The Beaver River was a perennial stream through the 

Milford area until 1914, when Rocky Ford Dam was constructed to impound water 5 mi east of Minersville, outside the study area. Flow in the Beaver River channel 

below the reservoir now is small; practically all the water 

is diverted for irrigation. Only in wet years is the discharge from the reservoir great enough to cause extensive 

flow in the channel. In winter months, 5 ft3 /s or less 

flows in the channel (Nelson, 1950, p. 185).

Annual discharge of the Beaver River at Rocky Ford 

Dam (fig. 3) averaged 26,100 acre-ft/yr from 1931 to 1982 

(Appel and others, 1983, p. 77). During 1931-82, the minimum annual discharge, 9,150 acre-ft, occurred in 1960 

(Mower and Cordova, 1974, p. 11). Annual discharges of 

125,000 acre-ft in 1983 and 94,800 acre-ft in 1984, far larger 

than the maximum during 1931-82, were reported by 

Avery and others (1984, p. 60) and Seiler and others (1985, 

p. 61).

All other streams are ephemeral and ungaged. Only 

rarely (such as during intense rainfall) does any appreciable flow reach the lower part of the basin. Using the channel-geometry method of Moore (1968, p. 29-39), Mower 

and Cordova (1974, p. 11) estimated mean annual runoff 

from 13 ephemeral streams to be 7,100 acre-ft. These 13 

streams drain 160 mi2, producing an average yield of 

about 45 acre-ft/mi2. By applying this yield to the entire 

540 mi2 of mountainous area, Mower and Cordova (1974, 

p. 11) estimated mean annual runoff to be about 24,000 

acre-ft.
G8 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

Practically all flow entering the area in the Beaver River channel is diverted near Minersville. The water enters 

either the Utopia Ditch and Minersville Canal for irrigation in the area near Minersville, or into the Low Line Canal that carries water north toward Milford.

GROUND-WATER HYDROLOGY 

CONSOLIDATED ROCKS

The consolidated rocks in the Milford area can be 

divided into three hydrogeologic units. Precambrian 

gneiss and Tertiary and Quaternary granite and basalt are 

grouped into one unit because of their assumed overall 

low permeability and porosity. Although the hydrologic 

properties of basalt can be markedly different than gneiss 

and granite, there is no information in the Milford area to 

differentiate between these rock types. These consolidated rocks might contain water in widely spaced joints; and 

if the joints are large and well connected, the granite and 

basalt can accept large quantities of water. The consolidated rocks could contribute a substantial quantity of 

water to the unconsolidated basin fill by subsurface flow. 

Wells intersecting systems of open joints could produce 

moderate quantities of water.

The second unit includes Tertiary fine-grained extrusive rocks other than basalts, such as latitic ignimbrites 

and andesite flows. These rocks contain small quantities 

of water in poorly developed and poorly connected joints. 

This unit probably does not accept an appreciable quantity of water for recharge and would not yield water readily 

to wells.

The third unit includes Precambrian through Cretaceous carbonate rocks, sandstones, and metasedimentary 

rocks that have hydrologic properties similar to the Tertiary and Quaternary granite and basalt. These rocks 

could have joints and fractures that contain water but the 

carbonate rocks have the additional potential for storing 

and transmitting large quantities of water due to enlargement of the fractures through dissolution. The sandstones could have some primary permeability related to 

intergranular porosity, but it probably would be subordinate to secondary permeability from fracturing and jointing.

UNCONSOLIDATED BASIN FILL

DESCRIPTION

The ground-water system of the Milford area is made 

up of unconsolidated basin fill. The ground-water system 

is unconfined along the margins of the basin, but becomes 

confined in the center of the southern one-half of the 

basin. The upper 200 to 300 ft of the saturated basin fill in 

this area is under both unconfined and semiconfined conditions. The lateral extent of the confined aquifer is 

assumed to coincide with the main area of ground-water 

development. The confined aquifer might extend further 

to the southwest and toward the mountains, but this is 

unknown because of a lack of well data outside the developed area. The depth to the bottom of the main confining 

bed ranges from 200 to 300 ft as shown by Mower and 

Cordova (1974, pi. 2A and 2B). Because of the lack of data, 

a lower limit for the confined or principal basin-fill aquifer cannot be determined except by geophysical methods, 

which suggest a total thickness of 2,000 ft.

In the center of the northern one-half of the basin, 

water from the basin fill discharges in this area where the 

hydraulic head is near the land surface. Data are insufficient, however, to determine whether the ground-water 

system in the northern one-half of the basin is truly confined with a confining layer at depth, or whether the upward hydraulic gradient is associated only with upward 

movement of ground water to a discharge area at land 

surface.

Along the center of the southern one-half of the basin, 

the basin fill is composed of alternating clay, sand, and 

gravel. The basin fill along the eastern margin of the 

basin, for the most part, is composed of unsorted clay and 

sand with intermixed gravel in the alluvial fans. In some 

areas along the western margin of the basin, sequences of 

alternating clay, sand, and gravel are present, but no data 

are available to determine if any of the clay layers act as 

confining beds. Along the center of the northern one-half 

of the basin, the basin fill is generally composed of unsorted clay and sand.

MOVEMENT

The general direction of ground-water movement is 

from south to north with a strong east to west component, 

as shown in figure 4. Subsurface flow enters the groundwater system from the Beryl-Enterprise area to the 

southwest and from the southeast under the Beaver River 

channel and through its associated alluvial fan. Along the 

eastern margin of the basin, the hydraulic gradient indicates flow toward the axis of the basin.
GROUND-WATER HYDROLOGY G9

113°00' 112°50'

38°40' 

38°30'

38°20'

38°10' 

EA\lER COUNTY / ^ 

IRON COUNTY '

T. 24 S.

T. 25 S.

T. 26 S.

T. 27 S.

T. 28 S.

T.29S.

T. 30 S.

T. 31 S.

EXPLANATION

Consolidated rocks 

Basin fill

5,000 Potentiometric contour 

Shows altitude at which 

water level would have 

stood in tightly cased wells, 

March 1983. Dashed where 

approximately located. 

Contour interval is 50 feet. 

Datum is sea level

Boundary of study area

 Observation well

4,802 Observation well (dry) 

Number is altitude of bottom 

of well, in feet above sea level

R. 13 W. R. 12 W. R. 11 W. R. 10 W. R.9W.

10 MILES

10 KILOMETERS

FIGURE 4. Potentiometric surface of the principal aquifer, Milford area, 1983.
G10 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

Along the southwestern margin of the basin, limited 

water-level data indicate that the ground-water flow direction is basically to the north, paralleling the Star 

Range, with little movement to the east of these uplands. 

This suggests limited inflow from the consolidated rocks. 

Based on information from three test holes drilled during 

this project, the ground-water gradient in the northwest 

part of the basin indicates movement through the consolidated rocks in the north end of the San Francisco Mountains toward Sevier Lake.

RECHARGE

Subsurface inflow from consolidated rocks along the 

mountain fronts was estimated by Mower and Cordova 

(1974, p. 22) to be 16,000 acre-ft/yr. This estimate was derived by subtracting all known and estimated sources of 

recharge from the estimated total ground-water discharge under steady-state conditions, assuming that recharge equals discharge. They also assumed that 

subsurface inflow from consolidated rocks was distributed along the surrounding mountains. On the basis of the 

revised direction of ground-water flow (fig. 4) as compared to the direction of ground-water flow shown in 

Mower and Cordova (1974, pi. 4), the major source of subsurface inflow from consolidated rocks is from the Mineral Mountains. By using the approach of Maxey and Eakin 

(1949, p. 40), which consists of assuming that a percentage 

of precipitation over upland areas seeps into consolidated 

rocks, subsurface inflow from the Mineral Mountains was 

estimated to be more than 15,000 acre-ft/yr. This is almost equal to the recharge estimated for the whole area 

by Mower and Cordova. On the basis of ground-water 

flow direction, the mountains to the south and west do 

not contribute an appreciable quantity of subsurface inflow from consolidated rocks.

In the extreme northern part of the basin, east of Black 

Rock, an unknown but large quantity of subsurface inflow enters the unconsolidated basin-fill aquifer from basalt that overlies clastic deposits of early Pleistocene age. 

Mower and Cordova (1974, p. 62) estimated the discharge 

from one spring orifice to be from 500 to 1,000 gal/min.

Subsurface inflow from tributary basins was estimated by Mower and Cordova (1974, p. 16) to be 1,700 acreft/yr by using Darcy's Law. The contribution was estimated to be 1,000 acre-ft/yr from the Beryl-Enterprise 

area and 700 acre-ft/yr from Beaver Valley. Later, during 

calibration of a ground-water flow model for the BerylEnterprise area, Mower (1982, p. 47), estimated the outflow from that area toward Milford to be 2,100 acre-ft/yr. 

This study did not attempt to collect new field data to verify these estimates.

Through canal-loss measurements, Mower and Cordova (1974, p. 18) estimated that 34 percent of the water

diverted from the Beaver River infiltrates to the groundwater system. They reported that approximately 4 percent probably is consumed by vegetation, leaving 30 percent to recharge the ground-water system. Also, they 

reported that the long-term average annual recharge from 

losses along the 23 mi of canals in the Milford area was 

8,300 acre-ft/yr.

Seepage from irrigated lands contributes a substantial 

amount of water to the ground-water system. Willardson 

and Bishop (1967, p. 35) reported water-application efficiencies of 60 to 80 percent (losses between 40 and 20 percent) with furrow or flooding methods. Losses may 

decrease with more efficient irrigation practices. Assuming an average seepage loss of 30 percent of the water applied to irrigated lands (ground water and surface water), 

Mower and Cordova (1974, p. 15) estimated that 22,700 

acre-ft/yr infiltrates to the ground-water system, based 

on irrigation practices for 1970-71. They also estimated 

that infiltration from precipitation on irrigated lands was 

2,000 acre-ft/yr, and infiltration from lawns and gardens 

was 100 acre-ft/yr.

Mower and Cordova (1974, p. 18) assumed that 30 

percent of the annual runoff in ephemeral stream channels infiltrates to the ground-water system. Using the 

24,000 acre-ft/yr estimate for ephemeral streamflow reported in the surface-water section of this report, this 

yields 7,200 acre-ft/yr. This includes underflow along 

The Big Wash, which was estimated to be 2,200 acre-ft/yr. 

With the revised flow system, which is in contrast to the 

flow system shown in Mower and Cordova (1974, pi. 4), 

only recharge from the Mineral Mountains affects the entire ground-water system. The Mineral Mountains cover 

an area of 125 mi2, about 25 percent of the mountainous 

area. Using the assumptions of Mower and Cordova 

(1974, p. 18), 25 percent of 24,000 acre-ft, or 6,000 acre-ft, 

would run off the Mineral Mountains and would be available for recharge. Thirty percent of that figure gives 1,800 

acre-ft of recharge to the ground-water system from these 

mountains. Minimum flow in the Beaver River channel is 

about 5 ft3 /s during the winter (Nelson, 1950, p. 185), 

which is about 1,800 acre-ft/yr, assuming a 6-month lowflow period. All of this flow is assumed to recharge the 

ground-water system.

Water-level fluctuations in wells within the area of 

ground-water withdrawal are a response to the long-term 

trends of precipitation, recharge from the Beaver River 

and the associated surface-water irrigation system, and 

ground-water withdrawals. Water levels within this area 

declined steadily from 1950 to 1968. Since 1968, water levels generally have declined at a slower rate with some rises that probably are related to high flows in the Beaver 

River. Similar trends can be seen by comparing the percentage of rise or decline of flow in the Beaver River from
GROUND-WATER HYDROLOGY Gil

one year to the next to the percentage of wells that shows 

a rise during the following spring, especially for years 

with a substantial increase of flow in the Beaver River (fig. 

5). Water-level rises in wells near the Beaver River channel or near large canals could be the result of an increase 

in the infiltration of surface-water in combination with a 

decrease in ground-water withdrawals because of the 

availability of surface water.

DISCHARGE

Mower and Cordova (1974, p. 32) estimated evapotranspiration to be 24,000 acre-ft in 1971, compared to an 

estimated 33,000 acre-ft for 1927 that they obtained by adjusting White's 1932 estimate. As reported by Mower and 

Cordova (1974, table 10), the difference in evapotranspiration is due to declining water levels within the area of 

ground-water development. The phreatophyte area 

mapped by Mower and Cordova (1974, pi. 3) was field 

checked during this study and no substantial differences 

were found.

Subsurface outflow toward the north to the Sevier 

Desert was estimated to be 8 acre-ft/yr by Mower and 

Cordova (1974, p. 33) using Darcy's Law. A low estimate 

for transmissivity of 75 ftVd was used in the calculation; 

however, based on the new direction of ground-water 

flow as compared to the direction of ground-water flow 

shown in Mower and Cordova (1974, pi. 4), the main component of basin outflow is toward the northwest through 

the consolidated rocks at the north end of the San Francisco Mountains. Model simulations of the Milford area, 

discussed in a later section of this report, provided an estimate for this outflow.

Since 1931, the U.S. Geological Survey, in cooperation 

with the State of Utah, has estimated ground-water withdrawals in this area. The estimates were made from periodic discharge and power-consumption measurements 

and yearly power-consumption records, or from a summation of water from irrigation wells that have water 

meters. From 1931 through 1949, ground-water withdrawals averaged 16,100 acre-ft/yr, with a maximum of 

22,760 acre-ft in 1947, and a minimum of 10,860 acre-ft in 

1931. Discharge from wells began to increase markedly in 

1949 (fig. 6). From 1950 through 1982, ground-water 

withdrawals averaged 49,000 acre-ft/yr. Since 1949, the 

maximum withdrawal was 70,200 acre-ft in 1974, and the 

minimum withdrawal was 30,900 acre-ft in 1950. Associated with the increase in ground-water withdrawals, water levels began to decline after 1950 as shown by the 

hydrographs of two observations wells (fig. 7). The large 

fluctuations in the hydrographs are a result of seasonal 

variations due to pumping; however, the long-term trend 

of water-level decline is clearly visible.

HYDRAULIC PROPERTIES

The hydraulic properties of an aquifer describe its 

ability to transmit and store water. Transmissivity, which 

depends on the hydraulic conductivity and the saturated 

thickness of the porous medium, can be determined from 

aquifer-test data and estimated from specific capacities. 

Mower and Cordova (1974, p. 13) reported transmissivity 

values ranging from 1,000 to about 40,000 ft2 /d, based on 

their analysis of aquifer-test data by the Theis curvematching procedure (Lohman, 1972, p. 34) and the Cooper and Jacob straight-line solution (Lohman, 1972, p. 19). 

As part of this study, aquifer-test data collected by Mower 

and Cordova were analyzed using the Hantush modified 

method (Lohman, 1972, p. 32). Transmissivity values 

ranged from about 1,000 to 55,000 ft2 /*! with the highest 

values in the south end of the developed area as indicated 

by the concentration of observation wells in figure 4.

Mower and Cordova (1974, p. 13) reported specificyield values from 0.04 for clayey silt to 0.2 for sandy gravel. They determined the values from short-term aquifer 

tests and the neutron-radiation method described by 

Keys and MacCary (1971, p. 74-86). They also reported a 

storage coefficient value of 1.0 X 10"3 for the confined 

aquifer in the central part of the basin. Storage coefficient 

values were determined in the present study from aquifer-test data using the Hantush modified method. Values 

ranged from 0.002 to 6.0 X 10'5.

STORAGE

Mower and Cordova (1974, p. 24) estimated that 40 

million acre-ft of ground water is stored in the groundwater system. They derived this estimate by multiplying 

the volume of saturated materials, 95 million acre-ft, by 

an average water content of 40 percent by volume. They 

also estimated water content for different lithologies from 

110 relatively undisturbed soil samples and from neutron 

moisture-probe measurements. Lithologic logs and the 

estimated values for water content were used to determine average water content for the entire ground-water 

system. Their estimated volume of saturated materials, 

however, was based on a maximum depth of slightly over 

500 ft. Drilling since the early 1970's has shown that the 

depth of saturated materials is greater than 500 ft and that 

the bottom of the ground-water system has not been 

reached; therefore, the amount of water in storage probably is greater than the value estimated by Mower and 

Cordova.

Mower and Cordova (1974, p. 27) reported that less 

than one-half of the estimated 40 million acre-ft stored in 

the ground-water system may be recoverable. The 

amount of recoverable water in storage is determined 

from the volume of the ground-water system and the spe-
G12 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

150

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1950 1955 1960 1965 197O 1975 198O 1985 

FIGURE 5. Percentage change from the preceding year in Beaver River flow and percentage of wells having water-level rises

the following spring for each year, 1953-82.

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FIGURE 6. Annual ground-water withdrawals in the Milford area, 1931-82.
SIMULATION OF GROUND-WATER FLOW G13

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(1932-53) Well

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(1954-83)

1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 

FIGURE 7. Water levels in two adjacent observation wells in the Milford area, 1932-83.

1980 1984

cific yield, assuming that the water levels will have been 

lowered so that the confined aquifers have been dewatered; thus, a specific yield representative of water-table 

conditions will determine the amount of water released 

from storage. The ground-water system in the Milford 

area covers approximately 550 mi2. Assuming an average 

saturated thickness of 400 ft for the basin fill and a specific 

yield of 0.15, the amount of recoverable water in storage 

was estimated to be 21 million acre-ft.

SIMULATION OF GROUND-WATER FLOW

A three-dimensional, finite-difference computer program developed by McDonald and Harbaugh (1988) was 

used to describe ground-water flow in the basin fill in the 

Milford area. The finite-difference algorithm used in 

their computer program can generate only an approximate solution to the partial-differential equation that describes ground-water flow; therefore, the model needs to 

be considered a tool to help describe the ground-water 

system. The ground-water model was used to (1) verify 

or improve estimates of recharge and discharge and the 

hydraulic properties that describe the basin-fill aquifer; 

and (2) simulate past and future stresses on the basin-fill 

aquifer. Both short-term stresses using the present pattern of ground-water withdrawal, and long-term stresses 

using hypothetical distributions of ground-water withdrawal were simulated. The short-term simulations projected effects of present withdrawals and potential 

increases in withdrawals. The long-term simulations tested the effects of three kinds of ground-water development: "sustained" yield, ground-water mining, and the 

capture of natural discharge.

MODEL DESIGN

The three-dimensional, ground-water flow model 

uses a block-centered or cell-oriented grid system as described by McDonald and Harbaugh (1988, p. 5-1). The 

grid used for the Milford model consists of 55 rows and 

29 columns. Cell spacing ranged from 0.5 to 1.5 mi. The 

smallest cells, located in the area with numerous wells, 

cover 0.25 mi2; largest cells cover 1.5 mi . The area of active cells (those actually included in the model calibrations) used in the final model design are shown on plate 1.

The original model design included two layers; an unconfined upper layer and a confined lower layer, except
G14 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

unconfined at the margins of the basin where water levels 

were below the base of the upper layer. Thickness for the 

upper layer was held constant at 200 ft, conforming to 

surface topography.

In some cells along the active edge of the upper layer, 

the saturated thickness of the porous medium was small. 

During initial transient simulations, many of these active 

cells went dry within a short period of time, probably 

causing adjacent cells to go dry prematurely. In the actual 

system, water levels do not decline this abruptly, so the 

ground-water model was redesigned to prevent cells 

from going dry prematurely by including three layers. 

The upper layer (layer 1), which represents the unconfined basin fill, was deepened to 250 ft below land surface 

along the axis of the basin. The bottom of layer 1 was inclined in a north direction to parallel the natural inclination of the land surface. Also, the bottom of layer 1 was 

made uniform in an east and west direction from the axis, 

thus increasing its thickness toward the mountains. This 

design eliminated the problem of cells going dry because 

almost all cells in layer 1 have large saturated intervals, 

except in the extreme northwest corner. Due to the steep 

hydraulic gradient in that area, a few cells have small saturated intervals, and some cells are inactive because the 

water level is below the bottom of layer 1.

The middle layer (layer 2) generally represents a confined aquifer. Only those cells in the extreme northwest 

corner, which lie under the inactive (dry) cells of layer 1, 

simulate unconfined conditions. The confining bed is not 

simulated; therefore, the top of layer 2 coincides with the 

bottom of layer 1. Because of the lack of data defining the 

base of the ground-water system, the thickness of layer 2 

was not specified; therefore, constant transmissivity had 

to be used for this layer during all simulations, rather 

than computing transmissivity from hydraulic conductivity and saturated thickness.

After initial transient simulations, the bottom layer 

(layer 3) was added in order to provide a source of water 

for upward leakage into layer 2. Without this layer, computed water-level declines in layer 1 and layer 2 were almost twice the historical water-level declines. Layer 3 

represents a confined aquifer with a constant transmissivity as in layer 2; thus, no top or bottom surfaces had to be 

specified.

BOUNDARY CONDITIONS

Boundary conditions during model simulations are of 

three types: constant head, constant flux, and mixed. 

Constant-head cells maintain the specified head for the 

entire simulation. Fluxes entering or leaving the groundwater system through the constant-head cells are calculated based on the head gradient and transmissivity between the boundary and interior cells. Constant-flux cells 

maintain the specified flux for the entire simulation; the 

heads are calculated. An impermeable or no-flow boundary can be simulated by constant-flux cells with a specified flux of zero. Mixed boundary conditions are handled 

by the general-head boundary module in the ground-water flow model of McDonald and Harbaugh (1988, p. 11- 

1), wherein the head and flux are calculated at the model 

boundary using a specified conductance and head at 

some distance outside the boundary. The conductance 

can be determined by multiplying the hydraulic conductivity along the flow path from the model boundary to the 

specified head by the cross-sectional area of the cell at the 

model boundary and dividing by the length of the flow 

path. If transmissivity is used instead of hydraulic conductivity, then transmissivity is multiplied by the length 

of the cell rather than cross-sectional area.

During steady-state calibration, constant-head, constant-flux, and mixed (general-head) cells were used at 

the boundaries. Constant-head cells were used in layer 1 

along recharge boundaries where the estimated head and 

hydraulic conductivity were considered to be more accurate than any estimate of recharge. As shown in plate 1, 

constant-head cells were placed along the entire length of 

the eastern boundary from the north end of the simulated 

area near Black Rock to south of the Beaver River near 

Minersville.

Constant-flux cells in layer 1 were placed along 

boundaries where the potentiometric surface indicated 

that no appreciable subsurface inflow enters the groundwater system, and were assigned a flux value of zero. 

This type of boundary condition generally exists along 

the Black Mountains/basin-fill interface in the south and 

most of the San Francisco Mountains/basin-fill interface 

on the west.

The general-head (mixed) boundary was used along 

two model boundaries where subsurface flow into or out 

of the basin occurs. This type of boundary was chosen in 

order to quantify any changes in basin inflow and outflow due to declining water levels during transient simulations. All flow was assumed to enter or leave through 

layer 2; therefore, cells in layers 1 and 3 along this type of 

boundary were specified as no-flow. One general-head 

boundary was placed along the southwest edge where 

basin inflow enters from the Beryl-Enterprise area. The 

other general-head boundary was placed along the northwest boundary at the San Francisco Mountains/basin-fill 

interface and along the north edge of the simulated area 

near Black Rock. The general-head boundary was not 

used where interbasin flow enters the basin along Cove 

Creek and the Beaver River. Because of the small number 

of cells and the small area involved, any change in head 

would not make a substantial difference in computed in-
SIMULATION OF GROUND-WATER FLOW G15

flow. All boundary cells in layer 2 not specified as general 

head, and all boundary cells in layer 3 were simulated as 

no-flow.

INITIAL CONDITIONS

WATER LEVELS

Within the area of ground-water development, initial 

water levels used for steady-state calibration were measured in 1927 and reported by White (1932, p. 58). Additional water levels measured in wells through 1983 were 

used outside the developed area, where data were few, 

and at margins of the basin where steady-state conditions 

were assumed at the time of measurement.

RECHARGE

Simulated recharge includes subsurface inflow from 

consolidated rocks, seepage losses from canals and unconsumed irrigation water, infiltration from perennial 

and ephemeral streams, subsurface inflow from adjoining 

basins through basin-fill deposits, and precipitation on 

basin-fill deposits at margins of the basin. On the basis of 

estimated-head values along the southern and western 

margins of the basin, no appreciable subsurface inflow 

enters from the consolidated rocks of the Black Mountains and San Francisco Mountains. Apparently, all subsurface inflow from consolidated rocks is from the 

Mineral Mountains and from the basalt east of Black 

Rock. Although this inflow was estimated to be 15,000 

acre-ft/yr, the model computed this inflow using a constant-head boundary during steady-state calibration.

Seepage losses from canals and unconsumed irrigation water is another major component of recharge to the 

ground-water system. Seepage losses from canals, reported by Mower and Cordova (1974, p. 18), vary with the 

quantity of flow in the canals. On the basis of annual diversions, they reported a weighted average loss of 14 percent of the water diverted in a test reach, or 1.5 percent per 

mile. This average rate of loss was assumed to apply for 

the total 23 mi of canals in the area; thus 34 percent of all 

diversions from the Beaver River is lost. An estimated 4 

percent of the loss is assumed to be transpired by vegetation, leaving 30 percent to recharge the ground-water system. The rate of recharge to the ground-water system is 

thus estimated to be 1.3 percent per mile of canal. This 

rate, which is used for all major canals, is assumed to be 

constant for both steady-state and transient conditions 

despite yearly changes in flow. Losses from major canals 

were calculated by multiplying 0.013 times the continually decreasing flow for each mile of canal. These losses 

were then distributed to the appropriate cells based on

the length of the canal in a cell. Losses from small canals 

were assumed to be part of unconsumed water applied to 

irrigated lands.

The amount of discharge in the Beaver River, which is 

regulated upstream at the Rocky Ford Dam, determines 

the distribution for irrigation. By prior rights, the area 

near Minersville is allocated 13.8 ft3 /s (10,000 acre-ft/yr). 

The remainder of the total discharge is available for use in 

the area near Milford, up to 21.4 ft3 /s (15,500 acre-ft/yr), 

the maximum quantity that can be transported in the Low 

Line Canal. Discharge exceeding the total 35.2 ft /s 

(25,500 acre-ft/yr) is allowed to flow down the Beaver 

River channel.

For steady-state calibration, the total 1927 discharge 

of 31.8 ft3 /s (23,000 acre-ft/yr) (Mower and Cordova, 

1974, fig. 3) was used. As mentioned above, 13.8 ft3 /s 

(10,000 acre-ft/yr) is allotted to the area near Minersville. 

Along the 4-mile reach of the Minersville Canal, 0.7 ft3 /s 

(510 acre-ft/yr) was lost to the ground-water system, thus 

leaving 13.1 ft3 /s (9,480 acre-ft/yr) for irrigation. Assuming 30 percent infiltration of applied irrigation water, 3.9 

ft3 /s (2,820 acre-ft/yr) infiltrated to the ground-water 

system and was distributed to cells that cover the currently irrigated area.

After subtracting canal losses of 2.2 ft3 /s (1,600 acreft/yr) from the 18.0 ft3 /s (13,000 acre-ft/yr) diverted into 

the Low Line Canal, the amount of Beaver River water 

available for irrigation in the area near Milford was 15.8 

ft3 /s (11,400 acre-ft/yr), of which 4.7 ft3 /s (3,400 acreft/yr) infiltrated to the ground-water system. This water 

was divided among cells that coincide with lands irrigated with surface water as shown by Nelson (1950, fig. 11).

Seepage from irrigated lands using ground water was 

assumed to be 30 percent as suggested by Mower and 

Cordova (1974, p. 21). White (1932, p. 88) reported 6.9 

ft3 /s (5,000 acre-ft/yr) of ground water was used for irrigation in 1927, of which 30 percent or 2.1 ft3 / s (1,500 acreft/yr) was assumed to be recharge. This seepage was applied by using the distribution shown by White (1932, fig. 

2).

Stream infiltration from the Beaver River is a minor 

source of recharge except in wet years, when the flow 

downstream from Rocky Ford Reservoir is substantially 

greater than the 35.2 ft3 /s (25,500 acre-ft/yr) diverted for 

irrigation. Winter minimum flows are 5 ft / s or less as reported by Nelson (1950, p. 185). For steady-state simulation purposes, an average of 2.1 ft3 /s (1,500 acre-ft/yr) is 

assumed to infiltrate to the ground-water system and is 

distributed along 5 mi of river channel.

All recharge from stream and canal losses and seepage from irrigated lands was simulated as recharging 

wells with a fixed flux. Stream and canal losses were not
G16 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

simulated as head dependent because water levels are below the streambeds or canals.

Subsurface inflow from the Beryl-Enterprise area was 

computed during model simulations using the generalhead boundary module of McDonald and Harbaugh 

(1988, p. 11-1). This inflow increased during transient 

simulations when water-level declines extended to the 

boundary.

Recharge from precipitation was simulated using the 

recharge module (McDonald and Harbaugh, 1988, p. 7-1) 

in the eastern part of the basin where precipitation is 

greater than 10 inches /yr. Only 5 percent of the precipitation is assumed to infiltrate to the ground-water system 

because of high evaporation rates and consumption by 

vegetation. Recharge from precipitation is estimated to 

be 5.1 ft3 /s (3,700 acre-ft/yr), which is greater than the 2.8 

ft/s (2,000 acre-ft/yr) reported by Mower and Cordova 

(1974, p. 21). Recharge for each cell was entered as ft3 /s 

per ft2 of area, or ft/s for each cell.

DISCHARGE

Initial discharge from the ground-water system was 

simulated as evapotranspiration, withdrawal from wells, 

and basin outflow through the northwest general-head 

boundary. Evapotranspiration was simulated in cells 

where the water table is within 30 ft of land surface. Using this extinction depth, the area simulating evapotranspiration (pi. 2) corresponds to the phreatophyte area 

mapped by Mower and Cordova (1974, pi. 3). A maximum evapotranspiration rate is assigned to each cell 

within the phreatophyte area. The computed evapotranspiration is based on a linear proportion of the maximum 

rate and the depth of water below land surface at each cell 

(McDonald and Harbaugh, 1984, p. 317). Evapotranspiration rates used during model simulations ranged from 8.2 

x 10'9 ft/s (3 inches/yr) to 9.8 x 10'8 ft/s (37 inches/yr). 

These rates are similar to the rates determined by White 

(1932, p. 86).

Ground-water withdrawal from wells was estimated 

by White (1932, p. 88) to be 5,000 acre-ft for 1927. The areal distribution for withdrawal from wells determined by 

White (1932, fig. 2) was used for steady-state calibration.

Basin outflow to the northwest was calculated during 

steady-state simulations using a general-head boundary. 

By calibrating computed heads to estimated heads and 

assuming the estimated distribution of transmissivity approximates reality, a reasonable estimate for basin outflow can be determined.

HYDRAULIC CONDUCTIVITY

Horizontal hydraulic-conductivity values for the upper water-table layer (layer 1) were estimated from drillers' logs using a weighted average for all lithologies, and 

from specific capacities determined from tests conducted 

at time of drilling. These hydraulic-conductivity values 

are multiplied by the saturated thickness in each cell during model computations. Hydraulic-conductivity values 

range from 2.3 x 10' 5 ft/s (2 ft/d) to 6.9 x 10' 4 ft/s (60 

ft/d) and were changed by trial-and-error during steadystate calibration. The middle layer (layer 2) was simulated as a confined-unconfined aquifer using a constant 

transmissivity rather than calculating transmissivity from 

the saturated thickness. Transmissivity values in layer 2 

range from 9.3 x 10'3 ft2 /s (800 ft 2 /d) to 5.4 x 10'1 ft2 /s 

(47,000 n^/d) and were similar to the distribution reported by Mower and Cordova (1974, fig. 4). The bottom layer 

was simulated as a confined system. Hydraulic properties of this layer are unknown because this part of the 

aquifer lies below the level of present development. 

Transmissivity values were arbitrarily assumed to be onethird of those used in the middle layer.

Most irrigation wells in the Milford area are completed in multiple permeable zones, thus maximizing production. The lack of wells with completion in a specific 

zone limits the ability to determine vertical hydraulic conductivity and vertical head gradient. For this reason, no 

estimates of vertical hydraulic conductivity and vertical 

head gradient were reported by Mower and Cordova 

(1974) and no aquifer tests were designed to determine 

vertical hydraulic conductivity during this study. From 

limited water-level data representative of specific zones, 

the difference in head between the water-table or semiconfined aquifer (layer 1) and the underlying confined 

aquifer (layer 2) was estimated to range from 1 to 10 ft in 

the center of the basin.

The model calculates vertical flow between layers 

from data incorporating vertical hydraulic conductivity 

and aquifer thickness. The resulting term, known as vertical leakance (McDonald and Harbaugh, 1988, p. 5-12), is 

calculated by dividing the estimated vertical hydraulic 

conductivity by the distance between the centers of adjoining model layers. Vertical hydraulic conductivity can 

be assumed to be one to two orders of magnitude smaller 

than horizontal hydraulic conductivity. Although the 

model was designed with unspecified thicknesses for layers 2 and 3, the distance between the centers of adjoining 

model layers can be assumed to be a few hundred feet. 

Initial vertical leakance between layers, therefore, was estimated to range between 1.0 to 5.0 x 10"9 /s (8.6 x 10"5 to 

4.3 x 10"4 / d). The larger values were distributed at the basin margin where vertical leakage is larger than in the 

center of the basin. These values were adjusted during
SIMULATION OF GROUND-WATER FLOW G17

calibration to maintain the estimated head differences between layers 1 and 2.

STORAGE COEFFICIENTS

An average value of 0.20 for specific yield as reported 

by Mower and Cordova (1974, p. 15) was used for the entire upper layer (layer 1). In the middle layer (layer 2), 

two storage-coefficient arrays are necessary because it is 

simulated as a confined-unconfined system. The primary 

array contains the storage-coefficient values for the confined aquifer that range from 5.0 x 10" 4 to 1.5 x 10" 3. The 

secondary storage-coefficient array is necessary when 

cells in layer 1 become dry and the underlying cells in layer 2 simulate an unconfined aquifer. Because of greater 

compaction at depth, the secondary storage-coefficient 

array was assigned an average value of 0.10. The bottom 

layer (layer 3) is confined throughout the simulated area 

and was assigned values an order of magnitude less than 

the primary storage-coefficient array for layer 2.

STEADY-STATE CALIBRATION

The model was first calibrated to steady-state heads 

known to exist prior to large-scale ground-water development. Hydraulic conductivity and transmissivity in all 

layers were varied along with vertical leakance during 

steady-state calibration to obtain a best fit to initial heads. 

Evapotranspiration rates also were adjusted to get a better match to initial heads; however, all adjusted values remained within the initial ranges.

In the calibration process, the vertical leakance values 

between layers were adjusted so that the estimated head 

differences between layers 1 and 2 were maintained and 

the necessary quantity of water from layer 3 moved upward. Calibrated vertical leakance values between layers 

1 and 2 range from 4.8 x 10"10 to 6.1 x 10"8 /s (4.1 x 10'5 to 

5.3 x 10"3 /d). Calibrated vertical leakance values between 

layers 2 and 3 range from 1.2 x 10"9 to 7.2 x 10"8 /s (1.0 x 

10"4 to6.2xlO"3 /d).

Initial conductance values were varied at both general-head boundaries. At the southwestern boundary, the 

conductances were varied to match computed heads and 

fluxes to known heads and to the total estimated subsurface inflow of 2.9 ft3 /s (2,100 acre-ft/yr) (Mower, 1982, p. 

47). At this boundary, the final conductances range from 

4 x 10' 3 to 2.5 x 10" 2 ft 2 /s (345 to 2,160 f^/d). Through 

this process, the computed steady-state heads were within 20 ft of the initial heads estimated from field data and 

the total computed subsurface inflow was only 0.2 ft3 /s 

(145 acre-ft/yr) below the initial estimate.

Because no estimate had ever been made for subsurface outflow along the northwestern general-head boundary, the conductances were varied in order to match 

estimated heads in the boundary cells. Most of the computed heads were within 30 ft of the estimated heads in 

this area; a 65-ft difference was the largest deviation. 

These computed heads are considered to be within calibration limits given that the estimated head gradient is 

greater than 100 ft/mi, which is based on very limited 

data and large cell size in this area. The model -calculated, 

steady-state subsurface outflow for this boundary is 15.8 

ft3 /s (11,400 acre-ft/yr). In most cases, the conductance 

for each cell was increased by three times the original estimate. The final conductances at the northwest boundary range from 1 x 10" 3 to 4 x 10"2 ft2 / s (86 to 3,460 ft2 / d).

Steady-state calibration criteria included a match to 

within 5 ft of initial heads in the area of ground-water development and a reasonable match in other areas depending on hydraulic gradient, topography, and quantity of 

data. Within a 309-cell area, where sufficient data were 

available to make a reasonable estimate of steady-state 

water levels or where the estimated hydraulic gradient 

was small, the average difference between initial head 

and computed head was less than 2 ft for all three layers. 

Along most of the margins of the basins, a match to within 

20 ft was considered to be within calibration limits. In a 

few areas, such as the southeast recharge area near Minersville and in the northwestern outflow area, the difference between initial and computed heads was greater 

than 20 ft. This can be attributed to the steep hydraulic 

gradient, large cell size, and uncertainty in estimated initial heads.

Recharge from consolidated rocks was simulated by 

using constant-head cells along the eastern boundary of 

the area. The steady-state calibrated model is just one of 

many possible solutions because recharge is unbounded. 

The calibrated model, however, is a reasonable approximation of the ground-water system under steady-state 

conditions because hydraulic conductivity was varied 

within reasonable limits along this boundary in order to 

match initial heads. The original estimate for recharge 

from consolidated rocks was calculated to be 20.7 ft /s 

(15,000 acre-ft/yr). By not assigning this recharge as constant flux along this boundary, the model calculated the 

recharge to be 32.9 ft3 /s (23,800 acre-ft/yr).

Computer-generated steady-state contours for initial 

and computed heads in layers 1 and 2 are shown in figures 8 and 9. The similarity in the figures is due to the relatively small head differences between the two layers, 

except in the center of the basin, where estimated head 

differences are assumed to be 1 to 10 ft.

Prior to transient calibration, all constant-head cells 

along the eastern boundary of the simulated area were
G18 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

113°00' 112°50'

38°40'

38°30'

38°20'

38°10'

T. 24 S.

EXPLANATION

Consolidated rocks 

Basin fill

 4,900 -^ Potentiometric contour

Shows altitude of 

computer-generated 

potentiometric surface of 

initial water levels

T. 25 s. interpolated mostly from 

water levels measured by 

White (1932). 

Contour interval is 50 feet. 

Datum is sea level

T. 26 S.

 -4,900- Potentiometric contour 

Shows altitude of 

computer-generated 

potentiometric surface of 

computed water levels. 

Contour interval is 50 feet. 

Datum is sea level

T. 27 S.

T. 28 S.

T. 29 S.

T. 30 S.

T. 31 S.

Boundary of study area

R. 13 W. R. 12 W. R. 11 W. R. 10 W. R. 9W.

10 MILES

_I

10 KILOMETERS

FIGURE 8. Steady-state contours for initial and computed water levels in layer 1.
SIMULATION OF GROUND-WATER FLOW G19

112°50'

38°40' 

38°30'

38°20'

38°10' 

T. 24 S.

EXPLANATION

Consolidated rocks 

Basin fill

T. 25 S.

T. 26 S.

-4,900 Potentiometric contour 

Shows altitude of 

computer-generated 

potentiometric surface of 

initial water levels 

interpolated mostly from 

water levels measured by 

White (1932). 

Contour interval is 50 feet. 

Datum is sea level

-4,900- Potentiometric contour 

Shows altitude of 

computer-generated 

potentiometric surface of 

computed water levels. 

Contour interval is 50 feet. 

Datum is sea level

T. 27 S.

T. 28 S.

T. 29 S.

T. 30 S.

T. 31 S.

Boundary of study area

R. 13 W. R. 12 W. R. 10 W. R.9W.

10 MILES

_I

10 KILOMETERS

FIGURE 9. Steady-state contours for initial and computed water levels in layer 2.
G20 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

converted to constant-flux cells with all model-calculated 

fluxes entered into the same recharge array as infiltration 

from precipitation. As a transition step from steady-state 

to transient calibration, arrays containing the necessary 

storage-coefficient values were entered and a 100-year 

simulation was made using steady-state conditions. This 

simulation verified that the model-calculated boundary 

fluxes did not vary with time.

TRANSIENT CALIBRATION

Transient calibration involved the use of time-dependent data such as storage, known ground-water withdrawals, and varying seepage from the Beaver River 

channel and irrigated lands. Storage was adjusted in order to match known water-level fluctuations. Steadystate conditions were assumed to have prevailed in the 

Milford area until 1950 when ground-water withdrawals 

began to increase rapidly. Withdrawals varied from 15.0 

ft3 /s (10,900 acre-ft/yr) to 31.5 ft3 /s (22,800 acre-ft/yr) 

during 1931-49. After 1950, withdrawals did not drop below 44.2 ft3 /s (32,000 acre-ft/yr) (fig. 6). Coincident with 

this increase, water levels in observation wells 

(C-29-10)6ddc-l and (C-29-10)6ddc-2 began to decline after 1950 (fig. 7). The model-calculated, steady-state heads 

were assumed to be representative of the ground-water 

system prior to 1950 and were used as initial heads for 

transient calibration.

Seven pumping or stress periods were selected for the 

transient calibration: 1950-52,1953-60,1961-67,1968-72, 

1973, 1974-78, and 1979-82. During these intervals, discharge from wells was relatively constant. The fifth stress 

period, 1973, was a year of high flows in the Beaver River 

and decreased pumping. By defining a single-year stress 

period, the model could be tested for its response to increased recharge and decreased ground-water withdrawals. Water-level changes were computed for the end of 

each stress period within the 33-year transient-simulation 

period, starting from the calibrated, steady-state water 

levels. The computed changes in water levels for each 

stress period were compared to water-level changes calculated from measurements made in March of the year after each stress period.

Differences between measured and computed waterlevel changes may reflect the response of the aquifer to a 

large change in the last year of a stress period rather than 

the overall trend for the entire stress period. Also, in 

some observation wells, the measured water levels are 

representative of both the unconfmed and confined aquifers, depending on the location of the perforated intervals; whereas computed water levels are representative of

either the unconfined or confined aquifers, depending on 

location and model layer.

The average ground-water withdrawals applied during each stress period are shown in table 1. Annual 

ground-water withdrawals for each well were averaged 

over each stress period. If a well penetrated more than 

one model layer, the average withdrawal was divided 

proportionally between the layers based on the percent of 

perforated interval in each layer. Finally, average withdrawals for all wells were combined for each cell in a 

model layer.

Two simulations were made for the transient calibration, each treating recharge from seepage to the groundwater system differently. In both cases, seepage was 

based on the mean annual flow in the Beaver River as 

measured at Rocky Ford Dam. For the first transient simulation, seepage from surface-water irrigation, canal losses, and infiltration from the Beaver River were averaged 

for each stress period. As mentioned previously, the 13.8 

ft3 /s (10,000 acre-ft/yr) of surface water diverted to the 

area near Minersville remained constant due to prior 

rights. In 1960, the flow in the Beaver River was slightly 

below the amount allocated to the Minersville area (fig.

TABLE 1. Variation in water-budget components during historical transient 

simulations in the Milford area, Utah

[Data are in cubic feet per second; acre-feet per year shown in parentheses]

Stress 

period 

(years)

1950-52

1953-60

1961-67

1968-72

1973

1974-78

1979-82

Ground-water 

withdrawals

42.8

(31,000)

56.5

(40,900)

61.5

(44,500)

74.2

(53,700)

69.0

(50,000)

83.0

(60,100)

63.6

(46,000)

Recharge from seepage to 

ground-water system

Variable2

30.4

(22,000)

28.6

(20,700)

27.4

(19,800)

39.9

(28,900)

60.6

(43,900)

42.9

(31,100)

51.8

(37,600)

Constant3

26.4

(19,100)

30.5

(22,100)

32.0

(23,200)

35.8

(26,000)

34.2

(24,800)

38.4

(27,800)

32.6

(23,600)

'Sum of seepage from irrigated lands using surface and ground water, canal losses, 

and infiltration from the Beaver River.

2Based on the mean annual flow in the Beaver River and associated canals during each 

stress period.

3Based on the mean annual flow in the Beaver River and associated canals during the 

entire simulation period.
SIMULATION OF GROUND-WATER FLOW G21

3); however, the mean annual flow for any one stress period was never lower than that allocation.

A ratio was calculated by which the seepage in the 

area near Milford was adjusted for each stress period. The 

diversion to the area near Minersville was subtracted 

from the mean annual flow in the Beaver River as measured at Rocky Ford Dam. The remaining flow, up to a 

maximum of 21.4 ft3 /s (15,500 acre-ft/yr), was divided by 

the flow that was diverted to the area near Milford in the 

steady-state calibration. This ratio was then multiplied by 

the steady-state seepage for each affected cell, thus increasing or decreasing the seepage for each stress period 

from the steady-state seepage. The same distribution of 

surface-water irrigated lands was used for each stress period. If the mean annual flow in the Beaver River was in 

excess of the 35.2 ft3 /s (25,500 acre-ft/yr) diverted for irrigation in any stress period, then the entire amount of excess flow was assumed to recharge the ground-water 

system and was distributed among the cells along the 

Beaver River channel.

A second simulation was made in which one set of average values was used for seepage to the ground-water 

system during the entire simulation period rather than a 

different set of values for each stress period. In this simulation, seepage to the ground-water system in the area 

near Minersville remained the same as in the previous 

simulation.

Seepage from land irrigated with ground water was 

simulated for each stress period by assuming that 30 percent of the water withdrawn from each cell returned to 

the ground-water system. Because this type of recharge 

is independent of the surface-water system, the percentage of seepage remained constant for each transient simulation. Computer-generated contours of computed 

water levels for 1983, at the end of the transient simulation using constant recharge, are reasonably close to water levels measured in wells for that year (fig. 10).

Differences in simulated water levels for the two transient simulations using constant and varying recharge 

from seepage for each stress period are considered to be 

substantial if greater than 2 ft. These differences are 

found in or near areas of recharge from seepage of surface 

water as shown in figure 11. Measured and computed 

water-level changes for 13 observation wells that have 

data for most or all of the stress periods are shown in figure 12. These observation wells are located in the north 

and west parts of the developed area where the effects of 

seepage from surface-water irrigation are negligible; 

therefore, only computed water-level changes using constant recharge are compared to measured water-level 

changes. Measured and computed water-level changes 

for seven observation wells in which there are some, but 

minimal, differences are shown in figure 13. Simulated

water-level changes for three observation wells where 

there are substantial differences between the two types of 

computed water-level changes are shown in figure 14. 

These observation wells are located in the southeastern 

part of the developed area, closest to the area of surfacewater recharge. The computed water levels from the 

transient simulation using constant seepage from surfacewater irrigation show a steady decline. This decline 

might be the result of withdrawals in the main pumping 

center to the north. By varying the recharge for each 

stress period, recharge becomes the dominant influence 

on the ground-water system in this area, although the 

long-term decline still occurs. The computed water-level 

changes follow the same trends as those shown by the 

measured water-level changes; however, overall waterlevel declines obtained from constant recharge show a 

better match to the total measured declines.

When seepage to the ground-water system from surface-water sources was varied, model-calculated, waterbudget components of evapotranspiration and basin outflow were not substantially different than those calculated when seepage for each stress period was constant 

(table 2). In the last stress period with varying seepage, 

however, the large increase in seepage from the Beaver 

River resulted in a net increase of almost 5 ft /s (3,620 

acre-ft/yr) of water going into storage. In addition, the 

three observation wells that show substantial water-level 

changes are located near the Beaver River. This would indicate that the greatest effect on computed water levels is 

the result of excess flow in the Beaver River channel recharging the ground-water system.

Historical transient simulations using both varying 

and constant recharge from seepage of surface-water irrigation show water-level declines of nearly 22 ft along the 

eastern constant-flux boundary; however, limited waterlevel data in this area indicate that there have been no actual water-level declines during the 1950-82 simulation 

period. Adjusting the constant-flux rates based on the 

variation from average precipitation for each stress period still gave computed water-level declines of nearly 16 ft 

along the eastern boundary. The simulated boundary effects are therefore probably due to the grid spacing in this 

narrow basin and large simulated ground-water withdrawals, rather than the flux rates at the boundary.

SENSITIVITY ANALYSIS

Numerous simulations were made to determine the 

sensitivity of the calibrated, steady-state model to changes in input data. Each parameter was increased and decreased by 20 percent of its final calibrated value for all 

layers simultaneously and for each layer separately.
G22 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

113°00' 112°50'

38°40' 

38°30'

38°20'

38°10' 

T. 24 S.

5,000 '

T.25S.

T. 26 S.

T. 27 S.

T. 28 S.

T. 29 S.

T. 30 S.

T. 31 S.

EXPLANATION

Consolidated rocks 

Basin fill

 Potentiometric contour 

Shows altitude of computergenerated potentiometric 

surface for layer 2 at end 

of historical transient 

simulation. Contour interval 

is 50 feet. Datum is sea level

Boundary of study area

4 998 ' Observation well Number 

is altitude of water level, 

in feet above sea level

O4'802 Observation well (dry) 

Number is altitude of 

bottom of well, in feet 

above sea level

R. 13 W. R. 12 W. R. 11 W. R. 10 W. R. 9W.

10 MILES

10 KILOMETERS

FIGURE 10. Potentiometric contours for the end of the historical transient simulation for layer 2 using constant 

recharge from seepage of surface water and measured water levels in wells in March 1983.
SIMULATION OF GROUND-WATER FLOW G23

38°40'

38°30'

38°20'

38°10' 

EAVER COUNTY/ 

IRON COUNTY '

T.24S.

T.25S.

T. 26 S.

T. 27 S.

T. 28 S.

T. 29 S.

T. 30 S.

T. 31 S.

EXPLANATION

Consolidated rocks

Basin fill

Boundary of study area

Cell simulating recharge 

from seepage of surfacewater irrigation, associated 

canals, and direct seepage 

from Beaver River

Observation well Showing 

no difference in water level 

between constant and variable 

recharge from seepage

Observation well Showing 

minimal difference (2 feet or 

less) in water level between 

constant and variable recharge 

from seepage

Observation well Showing 

substantial difference (more than 

2 feet) in water level between 

constant and variable recharge 

from seepage

R. 13 w. R. 12 w. R.11 w. R. 10 W. R.9W.

10 MILES

10 KILOMETERS

FIGURE 11. Model cells receiving constant and variable recharge from seepage of surface water during transient simulations 

and location of observation wells from which measured water levels are compared to computed water levels.
G24 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

o

10

en.

O CO

00 00

en en

+16

+8

0

-8

-16

-24 

+8

0

-8

LLJ

LU -16

Well (C-28-10)8cac-2 Measured

- Computed

LU 

CD

I 

O

_l 

LU

LU

r± LU

I

-24

-32 

+8

-8

-16

-24

-32 

+8

0

-8

-16

-24

-32

-40

Well (C-28-10)16cda-1 Measured 

Computed

i i i i i i i i i i i i i i i i i i

Well (C-28-10)18cab-1

Well (C-28-10)28cdd-1

 Measured

 Computed

O CO

00 00

en en

FIGURE 12. Measured and computed water-level changes during 1950-83 for 13 observation wells in the Milford area.
SIMULATION OF GROUND-WATER FLOW G25

O CO

00 CO

O) O)

+8

Well(C-28-10)30cdc-2 Measured 

Computed

-8

-16

-24 i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i

LU 

LU

U_

LU 

O

<

O

_J 

LU

LU 

_J

tr

LUI

+8

Well(C-28-10)32ddd-1

Measured 

Computed

-8

-16

-24

+8

i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i

i i i i i i i i i i i i i i i i i i i i i i i i i i i i i r i i i

 Measured

Well(C-29-11)1add-2

Computed

-8

-16

-24 i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i

FIGURE 12. Measured and computed water-level changes during 1950-83 for 13 observation wells in the Milford area Continued.
G26 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

O CO

CO CO

O) O)

+8

Measured 

Computed

-8

-16

-24 

+8

0

-8

-16

-24

-32

-40 

+8

0

-8

-16

-24

-32

-40

i i i i

LJJ 

LJJ

LJJ

I 

O 

_l 

LJJ

LJJ

_J

QC 

LJJ

I

i i > i i i i i i i i i i r T i i i i i i i i i i i i i i i i i i

Measured 

Computed

Well(C-29-11)27dad-1

i i i i i i i i i i I I I I i i i i i i i i i i i

FIGURE 12. Measured and computed water-level changes during 1950-83 for 13 observation wells in the Milford area Continued.
SIMULATION OF GROUND-WATER FLOW G27

O CO

00 00

en o>

+8

Well (C-29-12)35ddd-1

-8

-16 

+8

 Measured

 Computed

LJJ 

LJJ LL.

UJ

CD

Z 

<

5 -8

LJJ

LJJ -16

CC

LJU

-24 

+8

Measured 

Computed

Well(C-30-11)12bbb-1

i i i i i

-8

-16

-24

Well(C-30-11)24ccb-1

i i i i i r i i r i i i i i i i i i i

 Measured

Computed

i i i i i i i i i i i i i i i i i i i i i i i i

o in

O)

m mO)

in

CO 

O)

in 

fe

CO 

00 

O)

FIGURE 12. Measured and computed water-level changes during 1950-83 for 13 observation wells in the Milford area Continued.
G28 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

in

CO01 S

CO 

oo 01 01

+8

Well(C-28-11)25dcd-1

-8

-16

-24

-32 i i i i i i i i i i i i

Measured

Computed using variable recharge

Computed using constant recharge

+8 

0 

-8

UJ -16

HI

0

I 

o

HI 

HI

DC 

HI

I

-24

-32 

+8

Well (C-29-10)6ddc-2 Measured

Computed using variable recharge

Computed using constant recharge

i i i i i i i i i i i

Well (C-29-10)15bdc-1 Measured

Computed using variable recharge

Computed using constant recharge

-16

-24

-32 i i i i i i i i

-8 |_ Well (C-29-10)19ddd-1

-16

-24

-32

-40 i i i i i i i

i i i i i i i i i i i i i i i

 Measured

 * Computed using variable recharge 

Computed using constant recharge

o 10 in in

o> o>

FIGURE 13. Measured and computed water-level changes during 1950-83 for seven observation wells in the Milford area 

that show minimal differences (2 ft or less) in computed levels between constant and variable recharge from seepage.
SIMULATION OF GROUND-WATER FLOW G29

CO 

00 

O5

+8 

0 

-8

-16

-24

-32

-40 

+8

Well(C-29-11)13add-1 Measured

Computed using variable recharge

Computed using constant recharge

i i i i i i i i i i i i i i i i i i i i i i i i i

LLJ 

LLJ

LJJ 

CD

O

_J 

LU

LU

_J

ri LU

I

Well(C-30-10)6ddd-1

-8

-16

-24 I I L

Measured

Computed using variable recharge

Computed using constant recharge

+32

+24

+16

+8

0

-8

-16

-24

-32

i i i i i i i i i i i i i i i r i i i i i r i i i i i i i i i

 Measured

 * Computed using variable recharge

 i Computed using constant recharge

Well(C-30-10)8ddd-1

i i i i i i i i i i i i i i i i i i i i i i i i

FIGURE 13. Measured and computed water-level changes during 1950-83 for seven observation wells in the Milford area that 

show minimal differences (2 ft or less) in computed levels between constant and variable recharge from seepage Continued.
G30 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

o m 

co co

+16

+8

0

-8

-16

-24 

+32 

+24 

+16

+8 

0

-8

-16

-24

-32 

+32

+24

+16

+8

-8

Well(C-29-10)33bbb-1 Measured

 Computed using variable recharge

 Computed using constant recharge

i i i i i i i i i i i i

LLJ 

LL

2 

III

O

_l 

LLJ

LLJ

DC 

LJJ

I

Well(C-29-10)35ccd-1

\ I I I I I I I T

 Measured

n i i i i i i

 Computed using variable recharge

 Computed using constant recharge

i i i i i i i i

Well (C-30-10)1 Oabb-1 Measured

 Computed using variable recharge

 Computed using constant recharge

i i i i i i i i

FIGURE 14. Measured and computed water-level changes during 1950-83 for three observation wells in the Milford area that 

show substantial differences (more than 2 ft) in computed levels between constant and variable recharge from seepage.
SIMULATION OF GROUND-WATER FLOW G31

TABLE 2. Simulated steady-state (1927) and transient-state (1979-82) ground-water budget for the Milford area, Utah 

[Data are in cubic feet per second; acre-feet per year shown in parentheses. Dashes ( ) indicate not applicable]

Budget 

component

Steady-state 

(1927)

Transient-state 

(end of 1979-82 stress period)

Variable 

seepage

Constant 

seepage

Recharge:

Subsurface inflow from consolidated 

rocks in the Mineral Mountains.

Subsurface inflow from adjoining areas: 

Beryl-Enterprise ..................................

Beaver Valley.. 

Cove Fort area.

32.9 

(23,800)

...2.67 

(1,930) 

...5.02 

(3,630) 

...2.37 

(1,720)

Seepage from canals, streams, and 

unconsumed irrigation water. 

Unconsumed irrigation water derived

from ground-water sources. 2.08

(1,500) 

Unconsumed irrigation water derived

from surface-water sources. 6.24

(4,520) 

Seepage from canals........................................... 1.92

(1,390) 

Seepage from the Beaver River ........................2.07

(1,500) 

Infiltration from precipitation.................................4.77

(3,450)

Total recharge.................................................60.0

(43,400)

Discharge:

Wells........................................................................... 6.95

(5,000) 

Evapotranspiration................................................... 37.2

(26,900) 

Subsurface outflow to adjoining areas

on northwestern boundary. 15.8

(11,400)

Total discharge...............................................60.0

(43,400)

Change in storage:

Water entered into storage....................................... 

Water removed from storage................................... 

Net change in storage equals difference 

between water entered into storage 

and water removed from storage.

32.9 

(23,800)

3.52 

(2,550)

5.02 

(3,630)

2.37 

(1,720)

19.1 

(13,800)

9.80 

(7,100)

2.78 

(2,010)

20.1 

(14,500)

4.77 

(3,450)

100 

(72,400)

63.6 

(46,000)

16.8 

(12,200)

15.2 

(11,000)

95.6 

(69,200)

13.8 

(9,990)

9.00 

(6,520)

-4.8 

(-3,480)

32.9 

(23,800)

3.44 

(2,490)

5.02 

(3,630)

2.37 

(1,720)

19.1 

(13,800)

8.78 

(6,360)

2.66 

(1,930)

2.07 

(1,500)

4.77 

(3,450)

81.1 

(58,700)

63.6 

(46,000)

17.0 

(12,300)

15.2 

(11,000)

95.8 

(69,400)

0.45

(325)

15.1 

(10,900)

14.6 

(10,600)
G32 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

These changes are considered to be a reasonable estimate 

of error for each parameter, although the estimate of error 

may be much greater in areas with few data. After each 

simulation, the average difference between computed 

and calibrated steady-state heads was determined for 

each layer in a 309-cell area (fig. 15). The average differences obtained using the adjusted data were compared to 

the average differences that existed in the calibrated model between the calibrated steady-state heads and the initial heads. In addition, the new head-dependent fluxes 

were compared to the fluxes computed by the calibrated 

model. The results of all simulations are summarized in 

table 3.

The largest changes in computed-head distributions 

were due to variations in recharge at the eastern boundary, maximum evapotranspiration rates, and evapotranspiration extinction depths; however, the difference 

between the newly computed and calibrated steady-state 

heads within the 309-cell area show relatively minor 

changes compared to the calibrated-model values. The 

largest changes in flux at head-dependent boundaries 

were due to variations in recharge at the eastern boundary, maximum evapotranspiration rates, and extinction 

depths, in addition to transmissivity. Variations in recharge caused substantial changes in evapotranspiration. 

Variations in evapotranspiration rates and extinction 

depths changed the flux at the basin inflow boundary and 

variations in transmissivity caused changes in flux at both 

the inflow and outflow boundaries. In conclusion, the 

flux at head-dependent boundaries seems to be moderately sensitive to variations in some of the data. Consequently, even though the changes in computed head that 

result from errors in estimation of data are relatively 

small, the model-calculated water-budget components 

might change.

LIMITATIONS OF MODEL

The limitation to the ground-water model of the Milford area is the uncertainty of water levels and values for 

hydraulic properties in the northern one-half of the basin 

and along the margins of the basin. Because of the uncertainty in the potentiometric surface and hydraulic properties, our understanding of ground-water flow in these 

parts of the basin is limited. Constant-head cells were 

used initially along the eastern recharge boundary to determine the flux entering the system from the consolidated rocks and any uncertainty in the values for head and 

hydraulic conductivity would lead to uncertainty in the 

computed flux. By maintaining all parameters within 

reasonable limits, the computed flux along the recharge 

boundary was similar to the value estimated previously.

Steep hydraulic gradients and larger cell size in the 

southeast and the northwest parts of the simulated area 

cause some differences between initial and computed 

heads. These values were much larger than the generally 

accepted calibration limits. Although the computed 

heads were considerably different from measured heads, 

the initial and computed hydraulic gradients in these areas are similar. Consequently, during transient simulations, computed head changes between stress periods 

were similar to actual head changes in the southeast. If 

future model simulations were to consider the effects of 

seepage from surface-water irrigation in the southeast 

part of the simulated area and more data were available, 

then model cell size in that part of the basin could be 

made smaller to ensure greater accuracy.

On the basis of canal-loss studies, 30 percent of all surface water and ground water used for irrigation was assumed to seep into the ground-water system. In making 

this simplistic assumption, variations in seepage due to 

the use of different methods of irrigation and differences 

in soil conditions were not taken into account. This assumption probably does not make a substantial difference in the overall accuracy of the calibrated model, but 

could make a difference in the accuracy of a computed 

head of a specific cell.

The effects on layer 1 due to increased withdrawals in 

layer 2 could not be tested accurately without additional 

water-level and aquifer-test data from wells completed 

only in deeper zones of the basin-fill aquifer. These data 

would be necessary to define and calibrate the verticalhead gradient and flux within the area of ground-water 

development.

SHORT-TERM PREDICTIVE SIMULATIONS

The model of the Milford area was used to project the 

effects of ground-water withdrawals from 1983 to 2020. 

Computed water levels at the end of the 1979-82 stress 

period, derived from the historical transient simulation, 

were used as the starting point for the short-term predictive simulations. As in the transient simulation, average 

values for seepage were used for all stress periods. Because the model was designed principally to simulate relative declines and possible trends in ground-water levels, 

no attempt was made to simulate future variations of flow 

in the Beaver River and its associated irrigation-canal system. Also, the extremely high flows in the Beaver River 

for 1983 and 1984 were not simulated.

The model was used to simulate the response of the 

ground-water system to three rates of ground-water 

withdrawal. The areal and vertical distributions of the 

withdrawals for 1979-82 were used for all simulations. In
SIMULATION OF GROUND-WATER FLOW G33

113°00' 112°50'

38°40' -

38°30'

38°20'

38°10' 

T. 24 S.

T. 25 S.

T. 26 S.

T. 27 S.

T. 28 S.

T. 29 S.

T.30S.

T. 31 S.

EXPLANATION

Consolidated rocks 

Basin fill

Cell used for 

comparison in 

sensitivity analysis

Boundary of active cells 

 Boundary of study area

R. 13 W. R. 12 W. R. 11 W. R. 10 W. R. 9W.

10 MILES

10 KILOMETERS

FIGURE 15. Boundary of active cells during model simulations and areal distribution of cells used for comparison

during sensitivity analysis.
G34 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

TABLE 3. Results of sensitivity analysis for ground-water model, Milford area, Utah

[Percent change of new computed value, compared to calibrated model given in parentheses]

Hydraulic 

property

Percent 

change

Difference between initial 

and computed head 

difference1 (feet)

Layer 1

Calibrated model

Transmissivity

(all layers).

Hydraulic conductivity

(layer 1).

Transmissivity

(layer 2).

Transmissivity

(layer 3).

Vertical conductivity

(all layers).

Vertical conductivity

(layers 1-2).

Vertical conductivity

(layers 2-3).

Recharge

Maximum

evapotranspiration.

Evapotranspiration

extinction depth.

0

-20

+20

-20

+20

-20

+20

-20

+20

-20

+20

-20

+20

-20

+20

-20

+20

-20

+20

-20

+20

1.63

0.41

2.61

1.11

2.04

1.09

2.11

1.50

1.75

1.60

1.65

1.60

1.65

1.63

1.63

4.67

-1.40

-1.65

3.82

-1.19

4.39

(0.0)

(74.8)

(60.1)

(31.9)

(25.2)

(33.1)

(29.4)

(8.0)

(7.4)

(1.8)

(1.2)

(1.8)

(1-2)

(0.0)

(0.0)

(186)

(186)

(201)

(134)

(173)

(169)

Layer 2

1.76 (0.0)

0.08 (95.5)

3.12 (77.3)

0.77 (56.3)

2.56 (45.5)

1.25 (29.0)

2.24 (27.3)

1.63 (7.4)

1.89 (7.4)

1.28 (41.3)

2.13 (21.0)

1.27 (27.8)

2.13 (21.0)

1.76 (0.0)

1.76 (0.0)

5.26 (199)

-1.70 (197)

-1.34 (176)

3.83 (118)

-1.07 (161)

4.53 (157)

Layer 3

1.53 (0.0)

-0.18 (111.0)

2.91 (90.2)

0.52 (66.0)

2.35 (53.6)

0.99 (35.3)

2.05 (34.0)

1.43 (6.5)

1.63 (6.5)

1.02 (33.3)

1.92 (25.5)

1.07 (30.1)

1.89 (23.5)

1.49 (2.0)

1.56 (2.0)

5.06 (231)

-1.95 (228)

-1.56 (202)

3.59 (135)

-1.29 (184)

4.30 (181)

Flux at head-dependent 

boundaries 

(cubic feet per second)

Basin 

inflow

2.67

2.48

2.85

2.57

2.77

2.61

2.75

2.65

2.69

2.67

2.68

2.67

2.68

2.67

2.67

2.76

2.64

2.51

2.82

2.41

2.96

(0.0)

(7.1)

(6.7)

(3.7)

(3.7)

(2.2)

(3.0)

(0.7)

(0.7)

(0.0)

(0.4)

(0.0)

(0.4)

(0.0)

(0.0)

(3.4)

(1.1)

(6.0)

(5.6)

(9.7)

(10.9)

Basin 

outflow

15.82

13.76

17.60

15.33

16.32

14.63

16.89

15.54

16.10

15.87

15.78

15.87

15.78

15.82

15.82

15.04

16.57

16.38

15.48

16.37

15.33

(0.0)

(13.0)

(11.3)

(3.1)

(3.2)

(7.5)

(6.8)

(1.8)

(1.8)

(0.3)

(0.3)

(0.3)

(0.3)

(0.0)

(0.0)

(4.9)

(4.7)

(3-5)

(2.1)

(3-5)

(3.1)

Evapotranspiration

37.25

39.12

35.66

37.65

36.86

38.37

36.26

37.52

36.99

37.20

37.30

37.20

37.29

37.25

37.25

30.60

43.98

36.54

37.75

36.43

38.04

(0.0)

(5.0)

(4.3)

(1.1)

(1.0)

(3.0)

(2.7)

(0.7)

(0.7)

(0.1)

(0.1)

(0.1)

(0.1)

(0.0)

(0.0)

(17.9)

(18.1)

(1.9)

(1.3)

(2.2)

(2.1)

Average of the absolute difference between the initial-head distribution and the computed-head distribution in the 309-cell area where enough data were available to make a 

reasonable estimate of steady-state water levels or where the estimated hydraulic gradient was small (fig. 15). Negative values for difference in head indicate computed head is 

above initial head.

the first simulation, withdrawals equal to the 1979-82 

average rate caused water-level declines of more than 12 

ft near the south end of the Mineral Mountains and declines of 6 to 10 ft in the area of pumping (fig. 16). The 

smaller water-level declines in the area of pumping can 

be attributed to decreased evapotranspiration and to decreased storage depletions (table 4), indicating that the 

ground-water system could conceivably be approaching 

a new equilibrium condition. The projected water-level 

declines along the eastern margin of the simulated area 

are a continuation of the boundary effects that were simulated at the end of the historical transient simulation.

In the second simulation, ground-water withdrawals 

were increased to 1.5 times the 1979-82 average rate. This 

rate of ground-water withdrawal is about 15 percent larger than the maximum average rate applied in the historical, transient simulation for 1974-78 (table 1) and it is 

equal to the largest annual rate of withdrawal reported 

for 1974 (fig. 6). Although long-term ground-water withdrawals probably would not remain this large, it could 

approach this level for short periods as it has in recent 

years. This simulation resulted in projected water-level 

declines of more than 35 ft at the center of a well-defined 

cone of depression that covered the entire southern onehalf of the basin (fig. 17). As would be expected with the 

extent of projected water-level declines, evapotranspiration decreased and storage depletion and basin inflow at 

the southwest boundary increased (table 4). Minor water-level rises of less than 1 ft were projected for the extreme north end of the basin. These rises probably are 

due to minor flux imbalances at the northern boundary.

The third simulation used ground-water withdrawals at double the 1979-82 rate. This simulation projected 

water-level declines of more than 70 ft at the center of a 

well-defined cone of depression (fig. 18). Water-level declines of more than 40 ft were projected at the eastern and 

western boundaries of the basin. Storage depletion becomes a large component in the water budget at this rate 

of withdrawal (table 4). Pumping at this rate with the current (1984) distribution of wells would be a worst-case 

possibility. Pumping could not approach this rate without considerable development in the north part of the basin. If substantial development did occur in the north 

part of the basin, the overall water-level declines would 

be less because withdrawals would be distributed 

throughout the basin rather than being restricted to the 

southern one-half.
SIMULATION OF GROUND-WATER FLOW G35

112°50'

38°40' -

38°30'

38°20'

38°10' 

MILCSRDTOUN 

BEAVER COTO, TY

T. 24 S.

T. 25 S.

T. 26 S.

T. 27 S.

T.28S.

T. 29 S.

T. 30 S.

T. 31 S.

EXPLANATION

Consolidated rocks 

Basin fill

 2 Line of equal water-level

decline Interval is 2 feet

Boundary of study area

R. 13 W. R. 12 W. R. 11 W. R. 10 W. R.9W.

10 MILES

10 KILOMETERS

FIGURE 16. Projected water-level declines in the basin-fill aquifer for 1983-2020, assuming ground-water 

withdrawals equal to the 1979-82 average rate.
G36 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

113°00' 112°50'

38°40'

38°30

38°20'

38°10' -

T. 24 S.

T.25S.

T. 26 S.

T. 27 S.

T. 28 S.

T. 29 S.

T. 30 S.

T. 31 S.

EXPLANATION

Consolidated rocks 

Basin fill

 5 Line of equal water-level 

decline Interval is 5 feet

Boundary of study area

R. 13 W. R. 12 W. R. 11 W. R. 10 W. R.9W.

10 MILES

10 KILOMETERS

FIGURE 17. Projected water-level declines in the basin-fill aquifer for 1983-2020, assuming ground-water 

withdrawals equal to 1.5 times the 1979-82 average rate.
SIMULATION OF GROUND-WATER FLOW G37

113°00' 112°50'

38°40r -

38°30'

38°20

38°10' 

MILLARDCO 

BEAVER COUNTY

T. 24 S.

T. 25 S.

T. 26 S.

T. 27 S.

T. 28 S.

T. 29 S.

T. 30 S.

T. 31 S.

EXPLANATION

Consolidated rocks 

Basin fill

- Line of equal water-level 

decline Interval is 10 feet

Boundary of study area

R. 13 W. R. 12 W. R.11 W. R. 10 W. R. 9W.

10 MILES

10 KILOMETERS

FIGURE 18. Projected water-level declines in the basin-fill aquifer for 1983-2020, assuming ground-water 

withdrawals double the 1979-82 average rate.
G38 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

TABLE 4. Projected changes in ground-water budget components due to increased ground-water withdrawals,

Milford area, Utah

[Data are in cubic feet per second; acre-feet per year shown in parentheses]

Budget component

Transient-state

(end of 1979-82

stress period)

average

seepage

Projected water-budget rates at 

year 2020 using 1979-82 average 

ground-water withdrawal times

1.0 1.5 2.0

Recharge:

Subsurface inflow from consolidated 32.9 32.9

rocks in the Mineral Mountains. (23,800) (23,800) 

Subsurface inflow from adjoining areas:

Beryl-Enterprise............................................................. 3.44 4.41

(2,490) (3,190) 

Beaver Valley.................................................................. 5.02 5.02

(3,630) (3,630) 

Cove Fort area................................................................. 2.37 2.37

(1,720) (1,720) 

Seepage from streams, canals, and 

unconsumed irrigation water. 

Seepage from the Beaver River.................................... 2.07 2.07

(1,500) (1,500) 

Seepage from canals....................................................... 2.66 2.66

(1,930) (1,930) 

Unconsumed irrigation water derived 19.1 19.1

from ground-water sources. (13,800) (13,800) 

Unconsumed irrigation water derived 8.78 8.78

from surface-water sources. (6,360) (6,360) 

Infiltration from precipitation..............................................4.77 4.77

(3,450)______(3,450)

Total recharge....................................................... 81.1 82.1

(58,700)_____(59,400)

Discharge: 

Subsurface outflow to adjoining areas 15.2 15.1

on northwestern boundary. (11,000) (10,900) 

Wells.....................................................................................63.6 63.6

(46,000) (46,000) 

Evapotranspiration.............................................................17.0 13.3

(12,300)_____(9,630)

Total discharge..................................................... 95.8 92.0

.............................................................................................(69,400) (66,600)

Change in storage:

Water entered into storage ...................................................0.45 0.0

(325) 

Water removed from storage...............................................15.1 9.93

(10,900) (7,200)

Net change in storage equals difference 14.6 9.93 

between water entered into storage and (10,600) (7,200) 

water removed from storage.

32.9 

(23,800)

5.85 

(4,240)

5.02 

(3,630)

2.37 

(1,720)

2.07 

(1,500)

2.66 

(1,930)

28.6 

(20,700)

8.78 

(6,360) 

4.77 

(3,450)

93.0 

(67,300)

15.1 

(10,900)

95.4 

(69,100)

10.4 

(7,530)

121 

(87,600)

0.0

27.8 

(20,100)

27.8 

(20,100)

32.9 

(23,800)

7.34 

(5,310)

5.02 

(3,630)

2.37 

(1,720)

2.07 

(1,500)

2.66 

(1,930)

38.1 

(27,600)

8.78 

(6,360)

4.77 

(3,450)

104 

(75,300)

15.1 

(10,900)

127 

(92,000)

8.88 

(5,950)

151 

(109,000)

0.0

47.0 

(34,000)

47.0 

(34,000)
SIMULATION OF HYPOTHETICAL DEVELOPMENT ALTERNATIVES G39

SIMULATION OF HYPOTHETICAL 

DEVELOPMENT ALTERNATIVES

CRITERIA

The calibrated flow model for the Milford area was 

used to project the long-term effects of ground-water 

withdrawals under different applied stresses. Alternatives were designed to test the effects of withdrawals at a 

rate equal to the "sustained" yield of the ground-water 

system and to simulate development necessary for the 

capture of natural discharge. In most cases, the pumping 

distributions do not have practical applications. The concept of "sustained" yield is used by the States of Nevada 

and Utah, by which water rights generally are allocated 

on the basis of the estimated, average annual recharge to 

the basin in order to prevent long-term "mining" of 

ground water. Model-simulated responses of water-level 

declines and recovery and changes in discharge and storage were used to compare the effect of different applied 

stresses on the ground-water system.

Each development alternative was simulated for an 

arbitrary period of 600 years. The first 300 years simulated pumping, followed by 300 years of recovery. The long 

simulation period allowed the system to respond to the 

new stress and to approach a new equilibrium.

Each hypothetical development alternative was constrained by the following arbitrary requirements: Pumping wells were not located (1) where the depth to water 

exceeds 200 ft, (2) where land-surface slopes are larger 

than 200 ft/mi, (3) where the saturated thickness in any 

model cell is less than 200 ft, and (4) where cells are 

bounded on two sides by consolidated rocks. Within the 

simulated area, no cells had transmissivity values that 

were considered to be too small for pumping (less than 

1.2 xlO" 2 ft 2 /s). Pumping requirements included (1) one 

well per 160 acres, (2) a maximum average rate of 0.552 

ft3 /s (400 acre-ft/yr) for each well, and (3) withdrawals 

equally divided between the upper two model layers. All 

simulations assumed net ground-water withdrawal, so it 

was not necessary to simulate the recirculation of 

pumped water to the aquifer.

Hypothetical development alternatives simulated for 

the basin were as follows:

A. Concentrated pumping centers, withdrawing 

ground water at a rate equal to the estimated average annual recharge Alternative Al concentrated pumping in 

the southern one-half of the simulated area; alternative 

A2 concentrated pumping in the northern one-half of the 

simulated area; and alternative A3 concentrated pumping 

in two equal centers, one in the south and one in the 

north.

B. Strategically placed distribution of withdrawals 

that efficiently captured natural discharge, which includes evapotranspiration and basin outflow Alternative Bl maintained pumping at a rate equal to the 

estimated average annual recharge; alternative B2 maintained pumping at 1.25 times the estimated average annual recharge; and alternative B3 maintained pumping at 

1.75 times the estimated average annual recharge for the 

first 50 years and then at a rate equal to the estimated annual recharge for the remaining 250 years.

Specific economic considerations were not addressed, 

but were indirectly considered when placing constraints 

on the model simulations. Possible degradation of water 

quality due to recirculation of pumped water was not 

considered in the simulations.

For each development alternative, a set of four plots 

was made to graphically portray the response of the 

ground-water system to the applied stress. The first plot 

shows the average water-level decline within all pumped 

cells at the end of each stress period. The second plot 

shows the change in basin inflow and outflow through 

the two general-head boundaries. In the other two plots, 

the net change in storage and natural discharge at the end 

of each stress period are divided by total recharge. Total 

recharge was calculated at the end of each stress period 

by adding any increase in basin inflow entering through 

the southwest general-head boundary to the other sources of recharge that remain constant throughout the simulation. Natural discharge includes evapotranspiration 

and basin outflow. If the ground-water gradient was reversed due to declining water levels in the northern onehalf of the basin, the computed basin inflow from the 

northwest general-head boundary was subtracted from 

the basin outflow to get the net basin outflow that was 

then used to determine natural discharge. The simulated 

inflow at the north end of the basin was not added to the 

total recharge because it was accounted for by reducing 

outflow. During the recovery phase of each simulation, 

steady-state ground-water withdrawal, which was defined as part of the steady-state conditions, was included 

with natural discharge; otherwise, the potentiometric surface at the end of each simulation would be higher than 

the original steady-state potentiometric surface.

Plots of storage versus recharge and natural discharge 

versus recharge can be used to evaluate the effectiveness 

of each development alternative to approach a new equilibrium condition, to capture natural discharge, and to let 

ground-water levels recover. Ideally, if a new equilibrium condition is achieved during the 300 years of pumping, then the ratio of water removed from storage to 

recharge and the ratios of natural discharge to recharge 

would stabilize. If all natural discharge was captured 

during pumping, then the ratios would equal zero. If full
G40 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

recovery was achieved at the end of the 600-year simulation, then the ratio of water entered into storage to recharge would equal zero and the ratio of natural 

discharge to recharge would equal one.

All hypothetical simulations used calibrated, steadystate conditions for the initial conditions. The simulations 

were designed to test the effects of hypothetical groundwater development patterns and did not incorporate the 

present pattern.

DEVELOPMENT ALTERNATIVE Al

In this simulation, net ground-water withdrawals 

were held equal to the estimated annual recharge. 

Ground water was withdrawn from a concentrated 

pumping center covering 105 cells that was located in the 

southern one-half of the simulated area (fig. 19). Withdrawals were divided evenly between the upper two 

model layers. The withdrawal for each cell depended on 

its size and ranged from 0.552 ft3 /s (400 acre-ft/yr) to 

0.828 ft3 /s (599 acre-ft/yr).

After 300 years of pumping, a distinct cone of depression had developed covering the entire southern one-half 

of the simulated area and extending into the northern 

one-half (fig. 19). Computed water-level declines at the 

basin boundaries were locally more than 100 ft. The average water-level decline within the pumped area was 

about 160 ft (fig. 20). Boundary effects at both generalhead boundaries began to occur after 25 years of pumping (fig. 21). Basin inflow from the Beryl-Enterprise area 

increased from 2.65 ft3 /s (1,920 acre-ft/yr) as pumping 

began, to about 4.65 ft3 /s (3,370 acre-ft/yr) by 300 years. 

Although the computed basin outflow did not decrease 

substantially, the net basin outflow at the northwest general-head boundary decreased 7.60 ft3 /s (5,500 acre-ft/yr) 

because of the reversal of the hydraulic gradient at the 

southern end of this boundary.

After pumping ended at 300 years, water levels initially recovered rapidly with most of the water recharging 

the basin going into storage (figs. 20, 22). After the full 

300 years of recovery, water levels had returned to within 

3 ft of the original level throughout most of the basin. 

Only in the extreme southeast part were residual waterlevel declines more than 5 ft; in this area, only a small 

quantity of water was entering the basin fill from the consolidated rocks (fig. 23).

This development alternative is not the most efficient 

for capturing natural discharge only 80 percent was 

eliminated (fig. 24). With water-level declines of less than 

25 ft for most of the northern one-half of the basin, evapotranspiration was not completely eliminated. Although 

net basin outflow through the general-head boundary

was reduced, the computed basin outflow was reduced 

only slightly. A new equilibrium condition was not 

reached as shown in figures 20, 21, 22, and 24; therefore, 

water was removed from storage throughout the 300 

years of pumping. As a result, almost 25 years of recovery 

were required to replenish the ground-water system before natural discharge began to increase.

DEVELOPMENT ALTERNATIVE A2

The net ground-water withdrawals for development 

alternative A2, like development alternative Al, were 

held equal to the estimated annual recharge. Ground water was withdrawn from a concentrated pumping center 

in the northern one-half of the simulated area. As shown 

in figure 25, 55 cells were pumped at a rate of 1.104 ft3 /s 

(799 acre-ft/yr) per cell, evenly divided between the upper two layers.

As with development alternative Al, 300 years of 

pumping produced a cone of depression that enveloped 

the entire northern one-half of the basin (fig. 25). Because 

of smaller transmissivity values in this part of the basin, 

the water-level declines were much larger, averaging 

nearly 220 ft in the pumped area (figs. 25, 26). After 25 

years, large boundary effects began to occur along the 

northwest general-head boundary (fig. 27). After 300 

years of pumping, the hydraulic gradient had been reversed along part of this boundary so that basin inflow 

was approaching basin outflow, thus making net basin 

outflow small.

In the initial stages of recovery, water levels began to 

rise rapidly with most of the water going into storage 

(figs. 26,28). In this development alternative, more water 

than usual went into storage due to the increased basin inflow along the northern general-head boundary. At the 

end of the full recovery period, water levels had returned 

to within 5 ft of the starting level throughout most of the 

pumped area (fig. 29); however, residual water-level declines were larger than 30 ft in the northeast corner where 

the Cove Creek drainage enters the basin. The eastern 

model boundary in this area has a fixed flow rate while 

the northern boundary has no flow entering the groundwater system. The boundary conditions as defined might 

be unrealistic; but the lack of data prevents the use of any 

other type of boundary. The residual water-level declines 

for this simulation probably represent a worst-case 

situation.

Like development alternative Al, this development 

alternative is not efficient at capturing natural discharge, 

eliminating only 80 percent (fig. 30). Although basin outflow through the general-head boundary was reduced 

and evapotranspiration eliminated in the northern one-
SIMULATION OF HYPOTHETICAL DEVELOPMENT ALTERNATIVES G41

113°00' 112°50'

38°40' -

38°30'

38°20'

38°10r 

IS/lDlARDCO 

BEAVER COWMFi

/BEAVER CO 

y/PlRONCO

<S\

T. 24 S.

T. 25 S.

T. 26 S.

T. 27 S.

T. 28 S.

T. 29 S.

T. 30 S.

T. 31 S.

EXPLANATION

Consolidated rocks 

Basin fill

ED Cell simulating pumping

-25 Line of equal water-level 

decline after 300 years 

of pumping Interval is 

25 feet

 Boundary of study area

R. 13 W. R. 12 W. R.11 W. R. 10 W. R. 9W.

10 MILES

10 KILOMETERS

FIGURE 19. Simulated water-level declines after 300 years of pumping and areal distribution of cells simulating

pumping for development alternative Al.
G42 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

PUMPING RECOVERY

-200

100 200 300

TIME, IN YEARS

400 500 600

FIGURE 20. Simulated average water-level decline and recovery in model cells containing pumped wells for

development alternative Al.

PUMPING RECOVERY

0 100 200 300 400 500

TIME, IN YEARS

FIGURE 21. Simulated changes in basin inflow and net outflow at general-head boundaries during pumping and

recovery for development alternate Al.

PUMPING RECOVERY

600

LU

O 

CC

I 

O 

LLJ 

CC

O

LLJ 

O

CC 

O

LL

O 

O

100 200 300 

TIME, IN YEARS

400 500 600

FIGURE 22. Simulated changes in the ratios of water removed from storage during pumping to recharge and water added to 

storage during recovery to recharge for development alternative Al.
SIMULATION OF HYPOTHETICAL DEVELOPMENT ALTERNATIVES G43

113°00' 112°50'

38°40' -

38°30'

38°20

38°10' 

BLACK MOUNTAINS

T. 24 S.

EXPLANATION

Consolidated rocks 

Basin fill

T. 25 S.

T. 26 S.

T. 27 S.

T.28S.

T. 29 S.

T. 30 S.

T. 31 S.

' 1 Line of equal residual 

water-level decline 

after 300 years of 

recovery Interval is 1 foot

Boundary of study area

R. 13 W. a 12 W. a 11 w. a 10 w. a 9W.

10 MILES

10 KILOMETERS

FIGURE 23. Simulated residual water-level declines after 300 years of recovery for development alternate Al.
G44 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

PUMPING RECOVERY

100 200 300

TIME, IN YEARS

400 500 600

FIGURE 24. Simulated change in the ratio of natural discharge to recharge during pumping and recovery for

development alternative Al.

half of the basin, evapotranspiration remained substantial 

in the southern one-half. A new equilibrium was not 

reached, with changes in storage and natural discharge 

still occurring (figs. 26, 27, 28, 30). Because large quantities of water were removed from storage, over 25 years of 

recovery were required before substantial increases in 

natural discharge began to appear.

DEVELOPMENT ALTERNATIVE A3

In this simulation, there were two centers of concentrated pumping, one in the north and one in south as 

shown in figure 31. Ground-water withdrawals were 

split evenly between the two areas and held equal to the 

estimated annual recharge. A total of 84 cells have simulated withdrawals with 0.552 ft3 /s (400 acre-ft/yr) withdrawn from each cell in the south and 1.104 fr/s (799 

acre-ft/yr) withdrawn from each cell in the north. The 

large withdrawals in each cell were evenly divided between the upper two layers.

When ground-water withdrawals were concentrated 

in two areas, two cones of depression developed during 

the pumping period (fig. 31). The cone of depression in 

the north is well defined; whereas the cone of depression 

in the south is shallower and less well defined. This is the 

result of much smaller transmissivity values in the north. 

The maximum water-level decline in the north was more 

than 160 ft; in the south it was about 60 ft. The average 

water-level decline at the end of pumping for both areas

was almost 76 ft (fig. 32). Unlike the two previous development alternatives, substantial water-level declines 

were present along the entire eastern boundary (fig. 31). 

By dividing the withdrawals into two centers, effects at 

the general-head boundaries were moderated. Basin inflow increased slightly, whereas net basin outflow decreased substantially, but not as much as in development 

alternative A2 (fig. 33).

Because of the smaller water-level declines, which 

were distributed over a larger area, water levels recovered more rapidly than in the previous development alternatives. More water initially went into storage (figs. 32 

and 34). Like development alternative A2, residual water-level declines after the full recovery period were 

large more than 12 ft in the extreme northeast corner 

(fig. 35). The entire southern one-half and the central part 

of the northern one-half of the basin recovered to within 

2 ft of the original potentiometric surface. As shown in 

figure 33, water levels had recovered sufficiently so that 

the general-head boundaries had essentially returned to 

near steady-state conditions after 100 years.

This development alternative shows the benefits of 

distributing rather than concentrating ground-water 

withdrawals. This development alternative was 86 percent effective in eliminating natural discharge, substantially better than development alternatives Al and A2. As 

shown in figures 34 and 36, the rate of change in water removed from storage and natural discharge became small 

after 100 years as a new equilibrium was approached.
SIMULATION OF HYPOTHETICAL DEVELOPMENT ALTERNATIVES G45

113°00' 112°50'

38°40' -

38°30'

38°20'

38°10' -

T. 24 S.

T. 25 S.

T. 26 S.

T. 27 S.

T. 28 S.

T.29S.

T.30S.

T. 31 S.

EXPLANATION

Consolidated rocks

Basin fill

Cell simulating pumping

 250^ Line of equal water-level 

decline after 300 years 

of pumping Interval is 

50 feet

 Boundary of study area

R. 13 W. R. 12 W. R. 11 W. R. 10 W. R.9W.

10 MILES

10 KILOMETERS

FIGURE 25. Simulated water-level declines after 300 years of pumping and areal distribution of cells simulating

pumping for development alternative A2.
G46 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

PUMPING RECOVERY

-250

100 200 300

TIME, IN YEARS

400 500 600

FIGURE 26. Simulated average water-level decline and recovery in model cells containing pumped wells for

development alternative A2.

PUMPING RECOVERY

£-\J

Q

g z 15 '

0 g

? cr 10

-LJJ

> 0.

OH

 ' LJJ t- LJ- LJJ 5 

LJ_

i

n

i i i I i i i 1 i i i I i i i I i i i i i i i

^ ~4

: ^^ OUTFLOW ^.-"" :

- A ^ / A-*"* ~~

^* «« / x ~

""" ». ^ ~

 «. x

INFLOW "A ^ x^

r < ^ - ^ ^ X ~

W^A A A A ^^ A "^^ gSnrr A A A A -r

Sl4_li_l i_l i_l £_i ftKLii-l i_l i_i i_l i

1 , , , 1 ,,,!,,,!,,,"

0 100 200 300 400 500 600

TIME, IN YEARS

FIGURE 27. Simulated changes in basin inflow and net outflow at general-head boundaries during pumping and

recovery for development alternative A2.

PUMPING RECOVERY

100 200 300 400 500 600

TIME, IN YEARS

FIGURE 28. Simulated changes in the ratios of water removed from storage during pumping to recharge and water added 

to storage during recovery to recharge for development alternative A2.
SIMULATION OF HYPOTHETICAL DEVELOPMENT ALTERNATIVES G47

112°50T

38°40' 

38°30'

38°20

38°10' 

IRON COUNTY ! J

s 'BLACK MOUNTINS

T. 24 S.

EXPLANATION

Consolidated rocks 

Basin fill

-30^ Line of equal residual 

water-level decline 

after 300 years of 

recovery Interval is 5 feet

T. 25 S.

T. 26 S.

T. 27 S.

T. 28 S.

T. 29 S.

T. 30 S.

T. 31 S.

< Boundary of study area

R. 13 W. R. 12 W. R. 11 W. R. 10 W. R. 9W.

10 MILES

10 KILOMETERS

FIGURE 29. Simulated residual water-level declines after 300 years of recovery for development alternative A2.
G48 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

PUMPING RECOVERY

100 200 300

TIME, IN YEARS

400 500 600

FIGURE 30. Simulated change in the ratio of natural discharge to recharge during pumping and recovery for

development alternative A2.

DEVELOPMENT ALTERNATIVE Bl

In this development alternative, an entirely different 

approach was taken for distributing ground-water withdrawals. A trial-and-error method was used to find the 

pumping distribution most efficient at eliminating natural discharge. Knowledge gained from the previous 

development alternatives and the fact that evapotranspiration occurs throughout the length of the simulated area 

provided the basis for the initial distribution of groundwater withdrawals. After each simulation, the distribution of ground-water withdrawals was modified in order 

to eliminate evapotranspiration and to balance basin outflow with basin inflow at the northwest general-head 

boundary. The original constraints on ground-water 

withdrawals were maintained during the process.

The final distribution of ground-water withdrawals, 

which is one of many possible, used 96 cells distributed 

along the axis of the basin (fig. 37). This distribution coincides with the area of evapotranspiration as shown on 

plate 2. As in previous development alternatives, the net 

ground-water withdrawals equaled the estimated annual 

recharge. The cells had ground-water withdrawals ranging from 0.552 ft3 /s (400 acre-ft/yr) to 1.104 ft3 /s (799 

acre-ft/yr). Ground-water withdrawals from cells near 

the southwest corner were necessary to eliminate evapotranspiration; and in all simulations using this distribution, the adjacent general-head boundary was affected

immediately, thus increasing basin inflow. Ground-water withdrawals were simulated in cells near the northwest general-head boundary for the purpose of balancing 

basin outflow with inflow.

After 300 years of pumping, cones of depression had 

developed in the north and the southwest corners of the 

basin with a discernible trough along the axis of the basin 

(fig. 38). The maximum water-level decline was more 

than 60 ft and the average water-level decline was almost 

45 ft (fig. 39). The general-head boundaries were affected 

immediately because of the strategically placed groundwater withdrawals (fig. 40).

Unlike previous development alternatives, strategically placed ground-water withdrawals resulted in distributed water-level declines throughout the basin, thus 

maximizing the area for potential recharge when pumping ceased. During recovery, more water initially went 

into storage (fig. 41), thus allowing water levels to rise 

rapidly and recovery to be more complete; however, like 

the development alternatives A2 and A3, which have 

ground-water withdrawals in the north, residual waterlevel declines are present only in the northern one-half of 

the basin with maximum residual water-level declines of 

more than 5 ft in the extreme northeast corner (fig. 42).

This development alternative was efficient at capturing natural discharge with most of the decrease occurring 

in the first 50 years of pumping (fig. 43). By the end of 300 

years of pumping, 89 percent of the natural discharge had
SIMULATION OF HYPOTHETICAL DEVELOPMENT ALTERNATIVES G49

38°40' -

38°30'

38°20'

38°10' 

EAVERTCOUNTY/. Vj^J^

T. 24 S.

T. 25 S.

T. 26 S.

T. 27 S.

T. 28 S.

T. 29 S.

T. 30 S.

T. 31 S.

EXPLANATION

Consolidated rocks

Basin fill

Cell simulating pumping

 70 Line of equal water-level 

decline after 300 years 

of pumping Interval is 

10 and 20 feet

Boundary of study area

R. 13 W. R. 12 W. R. 11 W. R. 10 W. R. 9W.

10 MILES

_I

10 KILOMETERS

FIGURE 31. Simulated water-level declines after 300 years of pumping and areal distribution of cells simulating pumping for

development alternative A3.
G50 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

PUMPING RECOVERY

-200

100 200 300 400 500

TIME, IN YEARS

FIGURE 32. Simulated average water-level decline and recovery in model cells containing pumped wells for

development alternative A3.

PUMPING RECOVERY

600

OZ 15 '

§8

0 C/D

ZQ: 10

-UJ

^ Q.

rr" lil 5

U- LU 

LL

^

n

i i i i i i i I i i i I i i i I i i i I i i i

I XA- ^ OUTFLOW ^ ^ - ' ' ' I

f "~~~~A-.___ «'*' -

INFLOW ^

i , , , i , , , i , , , i , , , i , , , ~

0 100 200 300 400 500

TIME, IN YEARS 

FIGURE 33. Simulated changes in basin inflow and net outflow at general-head boundaries during pumping

600

and recovery for development alternative A3.

PUMPING RECOVERY

100 200 300 400 

TIME, IN YEARS

500 600

FIGURE 34. Simulated changes in the ratios of water removed from storage during pumping to recharge and water added 

to storage during recovery to recharge for development alternative A3.
SIMULATION OF HYPOTHETICAL DEVELOPMENT ALTERNATIVES G51

113°00' 112°50'

38°40'

38°30'

38°20'

38°10'

T. 24 S.

 12-

T. 25 S.

T. 26 S.

T. 27 S.

T. 28 S.

T. 29 S.

T.30S.

T. 31 S.

EXPLANATION

Consolidated rocks 

Basin fill

- Line of equal residual 

water-level decline 

after 300 years of 

recovery Interval is 2 feet

- Boundary of study area

R. 13 W. R. 12 W. R. 11 W. R. 10 W. R.9W.

10 MILES

10 KILOMETERS

FIGURE 35. Simulated residual water-level declines after 300 years of recovery for development alternative A3.
G52 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

PUMPING RECOVERY

100 200 300 

TIME, IN YEARS

400 500 600

FIGURE 36. Simulated change in the ratio of natural discharge to recharge during pumping and recovery for

development alternative A3.

been eliminated. Evapotranspiration had ceased, thereby 

leaving net basin outflow as the only form of natural discharge. The ground-water system approached a new 

equilibrium after 200 years. For the remaining 100 years 

of pumping, there was no substantial change in the quantity of water removed from storage. Similarly, recovery 

was rapid with most of it occurring in the first 100 years.

DEVELOPMENT ALTERNATIVE B2

This development alternative uses the same distribution of withdrawals as development alternative Bl but increases the net ground-water withdrawals by a factor of 

1.25. Originally, this simulation used a factor of 1.5; but 

cells in the upper layer near the northwest general-head 

boundary began to go dry after 100 years of pumping. After several cells had gone dry, they became inactive for 

the remainder of the simulation, including the recovery 

period; therefore, the simulation could not approximate 

the response of the ground-water system to the hypothetical stress. By using the smaller increase, this problem 

was not encountered.

As in development alternative Bl, a well-defined cone 

of depression developed in the southwest corner of the 

basin, with water-level declines of more than 70 ft after 

300 years of pumping (fig. 44). A broad trough developed 

through the center of the area with maximum declines of 

more than 90 ft in the north and 80 ft in the south. The average water-level decline was more than 80 ft within the 

entire pumped area (fig. 45). Substantial water-level

declines were present at all boundaries. The general-head 

boundaries were affected immediately and changes in the 

rate of basin inflow and outflow continued throughout 

the pumping period (fig. 46).

Due to the broad area of water-level declines and 

large quantities of water removed from storage, almost 50 

years of recovery were necessary before substantial quantities of water went into storage (fig. 47). After 300 years 

of recovery, residual water-level declines were less than 2 

ft throughout most of the area (fig. 48). As in previous 

development alternatives that pumped from the north 

part of the basin, substantial residual water-level declines 

were present in the northeast corner.

The ratio of storage versus recharge declined drastically during the first 50 years of pumping (fig. 47). During the remaining 250 years, this ratio continued to 

decline, but at a much slower rate. Eighty-six percent of 

the natural discharge was eliminated after 100 years with 

most of the remaining 14 percent eliminated in the last 

200 years of pumping (fig. 49). By comparing the ratios of 

storage and natural discharge to recharge, it is apparent 

that as natural discharge was eliminated, less water was 

removed from storage.

DEVELOPMENT ALTERNATIVE B3

In the final development alternative, ground-water 

withdrawals were varied during the pumping phase. For 

the first 50 years, the applied stress was 1.75 times the 

estimated annual recharge, and was held equal to re-
SIMULATION OF HYPOTHETICAL DEVELOPMENT ALTERNATIVES G53

112°50'

38°40' -

38°30'

38°20'

38°10' 

T. 24 S.

T. 25 S.

T. 26 S.

T. 27 S.

T. 28 S.

T. 29 S.

T. 30 S.

T. 31 S.

EXPLANATION

Consolidated rocks 

Basin fill 

 Boundary of study area

Cell simulating pumping 

from one well

Cell simulating pumping 

from two wells

R. 13 W. R. 12 W. R.11 W. R. 10 W. R. 9W.

10 MILES

10 KILOMETERS

FIGURE 37. Areal distribution of cells simulating pumping for development alternatives Bl, B2, and B3.
G54 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

112°50'

38°40' -

38°30'

38°20'

38°10' -

T.24S.

T.25S.

T.26S.

T. 27 S.

T. 28 S.

T. 29 S.

T. 30 S.

T. 31 S.

EXPLANATION

Consolidated rocks 

Basin fill

-20 Line of equal water-level 

decline after 300 years of 

pumping Interval is 10 feet

Boundary of study area

R. 13 W. R. 12 W. R. 11 W. R. 10 W. R. 9W.

10 MILES

10 KILOMETERS

FIGURE 38. Simulated water-level declines after 300 years of pumping for development alternative Bl.
SIMULATION OF HYPOTHETICAL DEVELOPMENT ALTERNATIVES G55

PUMPING RECOVERY 1 &

-200

100 200 300 400 500

TIME, IN YEARS 

FIGURE 39. Simulated average water-level decline and recovery in model cells containing pumped wells for

600

development alternative Bl.

PUMPING RECOVERY

100 200 300

TIME, IN YEARS

400 500 600

FIGURE 40. Simulated changes in basin inflow and net outflow at general-head boundaries during pumping and

recovery for development alternative Bl.

PUMPING RECOVERY

100 200 300

TIME, IN YEARS

400 500 600

FIGURE 41. Simulated changes in the ratios of water removed from storage during pumping to recharge and water added 

to storage during recovery to recharge for development alternative Bl.
G56 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

113°00' 112°50T

38°40' -

38°30'

38°20'

38°10' 

>BEA¥ER COUNTY / 

IRON COUNTY ' '" i

T. 24 S.

T. 25 S.

T. 26 S.

T. 27 S.

T. 28 S.

T. 29 S.

T. 30 S.

T. 31 S.

EXPLANATION

Consolidated rocks 

Basin fill

- Line of equal residual 

water-level decline 

after 300 years of 

recovery Interval is 1 foot

- Boundary of study area

R. 13 W. R. 12 W. R. 11 W. R. 10 W. R. 9W.

10 MILES

10 KILOMETERS

FIGURE 42. Simulated residual water-level declines after 300 years of recovery for development alternative Bl.
SIMULATION OF HYPOTHETICAL DEVELOPMENT ALTERNATIVES G57

PUMPING RECOVERY

100 200 300

TIME, IN YEARS

400 500 600

FIGURE 43. Simulated change in the ratio of natural discharge to recharge during pumping and recovery for

development alternative Bl.

charge for the remaining 250 years. The same distribution 

of ground-water withdrawals derived for development 

alternative Bl was used. The response of the groundwater system to this hypothetical stress was quite different compared to the previous development alternatives.

As in development alternatives Bl and B2, a welldefined cone of depression, with water-level declines of 

more than 50 ft, developed in the southwest corner of the 

area. In this case, however, the cone of depression developed after only 50 years of pumping (fig. 50). An elongate 

trough of water-level declines developed along the axis of 

the basin with maximum declines of more than 60 ft in 

three separate areas. Water-level declines developed 

along all basin boundaries. A small trough of water-level 

declines developed in the extreme north end of the basin 

near Black Rock. Under actual conditions, water-level 

declines in that area probably would be less because the 

basalt near Black Rock could provide more water than the 

constant flux allowed in these simulations.

When the net ground-water withdrawals were 

reduced, the average water level rose in the pumped cells 

for the next 50 years and then stabilized for the remaining 

200 years (fig. 51). Similarly, effects at both general-head 

boundaries stabilized after the first 50 years (fig. 52). 

After the full 300 years of pumping, the computed waterlevel declines (fig. 53) are different from the computed 

water-level declines after 50 years of pumping. Although 

water levels rose in the southern one-half of the basin, the 

cone of depression in the southwest corner remained well 

defined. Similarly, water-level declines at the southern

boundaries were reduced. In contrast, water levels continued to decline throughout the northern one-half of the 

basin. Although the maximum water-level decline did 

not decrease substantially, the effects of continued pumping at the reduced rate can be seen by the increased waterlevel declines at the northern basin boundaries. The continued water-level declines are due to smaller transmissivity values and less recharge compared to the southern 

one-half of the basin.

Initially, the quantity of water removed from storage 

was large; but, after 25 years, it began to stabilize. When 

the net ground-water withdrawals were reduced for the 

remaining 250 years, the quantity of water removed from 

storage decreased drastically with the net change in storage approaching zero (fig. 54). With partial recovery in 

the last 250 years of pumping, water levels were able to 

recover more rapidly after pumping ceased. As shown in 

figure 55, most of the area recovered to within 1 ft of the 

original water levels. Residual water-level declines of 

more than 6 ft are found in the extreme northeast corner 

of the basin.

In the first 50 years of the simulation, natural discharge was captured efficiently, eliminating 86 percent. 

For the remainder of the pumping period, only another 5 

percent of the natural discharge was eliminated (fig. 56). 

After 200 years, all evapotranspiration had ceased, thus 

natural discharge for the remaining 100 years was composed entirely of net basin outflow. After 50 years, with 

natural discharge mostly captured and ground-water 

withdrawals reduced to a quantity equal to recharge,
G58 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

113°00' 112°50'

38°40' 

38°30'

38°20'

38°10' 

T. 24 S.

EXPLANATION

Consolidated rocks 

Basin fill

 30^^ Line of equal

water-level decline 

after 300 years of 

pumping Interval is 10 feet

T. 25 S.

T. 26 S.

T. 27 S.

T. 28 S.

T. 29 S.

T. 30 S.

T. 31 S.

Boundary of study area

R. 13 W. R. 12 W. R. 11 W. R. 10 W. R. 9W.

10 MILES

10 KILOMETERS

FIGURE 44. Simulated water-level declines after 300 years of pumping for development alternative B2.
SIMULATION OF HYPOTHETICAL DEVELOPMENT ALTERNATIVES G59

PUMPING RECOVERY

QCLLJ -100

-150

-200

100 200 300

TIME, IN YEARS

400 500 600

FIGURE 45. Simulated average water-level decline and recovery in model cells containing pumped wells for

development alternative B2.

PUMPING RECOVERY

100 200 300

TIME, IN YEARS

400 500 600

FIGURE 46. Simulated changes in basin inflow and net outflow at general-head boundaries during pumping and

recovery for development alternative B2.

PUMPING RECOVERY

100 200 300 400 500 600

TIME, IN YEARS

FIGURE 47. Simulated changes in the ratios of water removed from storage during pumping to recharge and water added 

to storage during recovery to recharge for development alternative B2.
G60 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

113°00' 112°50'

38°40'

38°30'

38°20'

38°10'

T. 24 S.

T. 25 S.

T. 26 S.

T. 27 S.

T. 28 S.

T. 29 S.

T. 30 S.

T. 31 S.

EXPLANATION

Consolidated rocks 

Basin fill

 10 Line of equal residual 

water-level decline 

after 300 years of 

recovery Interval is 

2 feet

Boundary of study area

R. 13 W. R. 12 W. R. 10 W. R. 9W.

10 MILES

5 10 KILOMETERS

FIGURE 48. Simulated residual water-level declines after 300 years of recovery for development alternative B2.
SIMULATION OF HYPOTHETICAL DEVELOPMENT ALTERNATIVES G61

PUMPING RECOVERY

CC

100 200 300 

TIME, IN YEARS

400 500 600

FIGURE 49. Simulated change in the ratio of natural discharge to recharge during pumping and recovery for

development alternative B2.

water removed from storage was about equal to the quantity of water exiting the basin through the general-head 

boundary.

EVALUATION OF DEVELOPMENT ALTERNATIVES

Four different distributions of ground-water withdrawals were used in "sustained"-yield simulations to 

determine (1) their efficiency in reducing or eliminating 

natural discharge, (2) their effect on water-level declines, 

and (3) their residual effects on water-level recoveries and 

resumption of natural discharge after pumping ceased. 

Two additional simulations tested the effects of groundwater withdrawals greater than the average annual 

recharge.

All development alternatives resulted in declining 

water levels and reduced natural discharge during 

pumping; but in most cases, water levels and natural discharge recovered to near pre-pumping conditions after 

pumping had ceased. The extent of water-level declines 

and the rate of reduction of natural discharge was most 

dependent on the areal distribution of withdrawals. 

Because increased pumping above average annual recharge goes beyond the concept of "sustained" yield, 

variations in the rate of pumping were not tested for development alternatives that have concentrated pumping 

centers. Increasing the rate of pumping for these development alternatives would have formed deeper cones of 

depression and would not have decreased natural discharge substantially.

During the 300-year recovery phase, the rates at 

which water levels recovered and natural discharge 

increased were dependent on (1) the areal distribution of 

ground-water withdrawals relative to recharge boundaries, (2) the areal distribution of transmissivity, and (3) 

the quantity of water removed from storage.

"Sustained"-yield simulations involving concentrated pumping centers (development alternatives Al, A2, 

and A3) were least effective in reducing natural discharge, and formed well-defined cones of depression 

with large water-level declines. Development alternatives Al and A2 had the largest water-level declines and 

the largest amount of water removed from storage (table 

5). Development alternative Al, with its concentrated 

pumping center in the southern one-half of the basin area, 

had the advantage of larger transmissivity values in the 

pumped area and closer proximity to the main sources of 

recharge than alternative A2 with its pumping center in 

the north; therefore, water-level declines were less and recovery was faster for development alternative Al. 

Because natural discharge occurs throughout the basin 

area, neither development alternative Al or A2 were 

completely effective in reducing natural discharge. 

Development alternative A3, which equally divided 

pumping between two centers, began to approach the 

optimum development pattern by more effectively reducing natural discharge, coupled with smaller water-level 

declines and less water removed from storage. These 

conditions allowed for faster recovery after pumping 

ceased.
G62 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

113°00' 112°50'

38°40'

38°30'

38°20'

38°10'

T.24S.

EXPLANATION

Consolidated rocks 

Basin fill

T.25S.

T. 26 S.

T.27S.

T. 28 S.

T. 29 S.

T.30S.

T. 31 S.

 10 Line of equal

water-level decline after 

50 years of pumping 

Interval is 10 feet

Boundary of study area

R. 13 W. R. 12 W. R. 11 W. R. 10 W. R.9W.

10 MILES

10 KILOMETERS

FIGURE 50. Simulated water-level declines after 50 years of pumping for development alternative B3.
SIMULATION OF HYPOTHETICAL DEVELOPMENT ALTERNATIVES G63

PUMPING RECOVERY -I &

-200

100 200 300 400 500

TIME, IN YEARS

FIGURE 51. Simulated average water-level decline and recovery in model cells containing pumped wells for

development alternative B3.

600

PUMPING RECOVERY

0 100 200 300 400 500

TIME, IN YEARS

FIGURE 52. Simulated changes in basin inflow and net outflow at general-head boundaries during pumping and

recovery for development alternative B3.

600

A development alternative with withdrawals strategically distributed, such as development alternative Bl, 

proved to be the most effective in reducing natural discharge, eliminating 89 percent of the total evapotranspiration and basin outflow as the ground-water system 

approached a new equilibrium. This was accomplished 

with minimal water-level declines throughout the basin 

and the least amount of water removed from storage 

(table 5). By removing ground water normally lost to 

evapotranspiration and basin outflow, the ground-water 

system was not substantially depleted, thus allowing for 

rapid recovery.

Development alternatives B2 and B3 provided some 

insight into the effects of ground-water mining by withdrawing more ground water than the average annual 

recharge. Net ground-water withdrawals for development alternative B2 were 1.25 times larger than the estimated average annual recharge for the basin. This 

development alternative almost eliminated natural discharge after 200 years of pumping, but it also produced 

water-level declines throughout the basin, especially in 

the north. Pumping at a large rate for the first 50 years, 

such as development alternative B3, proved to be effective in eliminating natural discharge in a short time. 

When the pumping rate was reduced to the estimated average annual recharge for the remaining 250 years of 

pumping, water levels partially recovered and then stabilized. This development alternative had two additional 

advantages: (1) it removed virtually no water from storage after the first 100 years of pumping, and (2) it produced the second smallest water-level declines after the 

full 300 years of pumping. Along with development 

alternative Bl, this alternative could be another viable 

development option for the beneficial use of ground 

water before it is consumed by evapotranspiration or is 

lost by flowing out of the basin, despite the initial disadvantage of large water-level declines that might promote 

the compaction of sediments and land subsidence.
G64 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

38°40' -

38°30'

38°20'

38°10' 

T. 24 S.

EXPLANATION

Consolidated rocks 

Basin fill

-30 Line of equal water-level 

decline after 300 years of 

pumping Interval is 10 feet

T. 25 S.

T. 26 S.

T. 27 S.

T. 28 S.

T. 29 S.

T. 30 S.

T. 31 S.

Boundary of study area

R. 13 W. R. 12 W. R. 11 W. R. 10 W. R. 9W.

10 MILES

10 KILOMETERS

FIGURE 53. Simulated water-level declines after 300 years of pumping for development alternative B3.
NEED FOR FUTURE STUDIES G65

PUMPING RECOVERY

100 200 300 400 500 600

TIME, IN YEARS

FIGURE 54. Simulated changes in the ratios of water removed from storage during pumping to recharge and water added to 

storage during recovery to recharge for development alternative B3.

TABLE 5. Cumulative total of simulated water removed from storage

after pumping and recovery for each development alternative in the

Milford area, Utah

[Data are in cubic feet; acre-feet shown in parentheses]

Development 

alternative

Al

A2

A3

Bl

B2

B3

Following 

pumping

1.88X1011

(4,320,000)

2.20xlOn

(5,050,000)

1.53xlOn

(3,510,000)

l.llxlO11

(2,550,000)

2.06xlOn

(4,730,000)

1.39xlOn

(3,190,000)

Following 

recovery

4.53xl09

(104,000)

1.73xl010

(397,000)

6.85xl09

(157,000)

3.08xl09

(70,700)

7.21xl09

(166,000)

4.23xl09

(97,100)

NEED FOR FUTURE STUDIES

Transient simulations produced water-level declines 

at the basin fill-consolidated rock interface that might not 

occur if the consolidated rocks are able to yield and transmit water readily to the basin fill. In this study, the flux 

entering the ground-water system from consolidated 

rocks at the margin of the basin was determined initially 

by using constant-head cells along this boundary. 

Because of the lack of data, the estimated water levels at 

these cells may lead to uncertainty in the estimated flux. 

Additional well data and, if possible, aquifer-test data 

would help define the hydraulic properties of the basin 

fill at these boundaries and permit a better estimate for 

this uncertain component of the water budget.

This study redefined the flow direction in the northern one-half of the study area, using limited test-hole 

data. Additional data might better define the extent and 

quantity of basin outflow along the northwest boundary.

The vertical head gradient within the area of present 

ground-water development had to be estimated because 

water-level data solely from the confined aquifer were 

lacking. Data from newer wells completed only in the 

confined aquifer, without multiple perforated zones, 

might permit a refined conceptualization of the groundwater system. Aquifer tests using wells with limited perforated zones might permit better estimates of vertical 

hydraulic conductivity and vertical hydraulic gradient. 

With this information, transient simulations could project 

effects of future ground-water withdrawals within the 

developed area with greater accuracy.
G66 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

112°50'

38°40' -

38°30'

38°20'

38°10' 

T. 24 S.

T. 25 S.

T. 26 S.

T. 27 S.

T. 28 S.

T. 29 S.

T. 30 S.

T. 31 S.

EXPLANATION

Consolidated rocks 

Basin fill

- Line of equal residual 

water-level decline after 

300 years of recovery 

Interval is 1 foot

Boundary of study area

R. 13 W. R. 12 W. R. 11 W. R. 10 W. R. 9W.

10 MILES

10 KILOMETERS

FIGURE 55. Simulated residual water-level declines after 300 years of recovery for development alternative B3.
SUMMARY G67

PUMPING RECOVERY

100 200 300

TIME, IN YEARS

400 500 600

FIGURE 56. Simulated change in the ratio of natural discharge to recharge during pumping and recovery for

development alternative B3.

SUMMARY

As part of the Great Basin Regional Aquifer-System 

Analysis program, a three-dimensional, finite-difference 

model was constructed to simulate the ground-water system in the Milford area of southwestern Utah. The calibrated model was used to make short-term predictive 

simulations to estimate water-level declines using the 

current (1984) pumping distribution, and hypothetical 

long-term simulations using several different pumping 

distributions.

Ground-water movement in the basin-fill aquifer generally is from south to north with a prominent east-west 

component of flow from the eastern recharge boundary 

along the Mineral Mountains toward the center of the 

basin. Recharge from the western boundary appears to be 

inconsequential; therefore, the flow direction along the 

western margin basically parallels the main flow direction in the center of the basin. Measured and inferred 

water levels from new test holes in the northwest part of 

the basin indicate that ground water exits the basin in a 

northwesterly direction through the north end of the San 

Francisco Mountains rather than as underflow following 

the Beaver River drainage to the north.

The basin-fill aquifer was simulated by using three 

layers to represent the three-dimensional system. After 

the model was calibrated, simulations were able to 

approximate steady-state conditions for 1927 and transient conditions from 1950-82. Through steady-state calibration, subsurface inflow from consolidated rocks along 

the Mineral Mountains was computed to be almost 24,000

acre-ft/yr. Basin outflow to the northwest was computed 

to be more than 11,000 acre-ft/yr and evapotranspiration 

was computed to be almost 27,000 acre-ft/yr. Two transient simulations using constant and varying recharge 

from surface water for each stress period were made to 

test the effects of these conditions on the ground-water 

system. With the present model-grid configuration, substantial differences in computed water-level changes 

between the two methods of simulating recharge are indicated in the vicinity of the Beaver River in the southeast 

part of the area; but, for most of the simulated area, minimal or no differences in water levels were indicated.

Sensitivity analysis showed that the largest changes in 

the computed-head distributions were caused by changes 

in recharge at the eastern boundary, evapotranspiration 

rates, and evapotranspiration extinction depths. Similarly, the largest changes in ground-water flow at headdependent boundaries, such as the general-head boundaries and the area of evapotranspiration, were caused by 

changes in recharge at the eastern boundary, evapotranspiration rates and extinction depths, and transmissivity 

values.

The calibrated ground-water flow model was used to 

make short-term predictive simulations over a 37-year 

period from 1983 to 2020. Three simulations were made 

using rates of ground-water withdrawal equal to 1, 1.5, 

and 2 times the 1979-82 average rate. Water-level declines 

of about 6 to 12 ft were projected using the average rate 

for 1979-82. The declines are minimal primarily because 

the average rate of withdrawal for 1979-82 is virtually
G68 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN NEVADA AND UTAH

equal to the estimated average annual recharge. At 1.5 

times the 1979-82 average rate, projected maximum 

water-level declines increased to more than 35 ft. 

Although this rate of withdrawal was reached only once 

(1974) in the Milford area, future long-term average withdrawals could conceivably approach this level. As a 

worst-case simulation, maximum water-level declines of 

more than 70 ft were projected using withdrawals equal 

to twice the 1979-82 average rate.

In order to test the concepts of "sustained" yield, 

ground-water mining, and the capture of natural discharge, several 600-year simulations were made using 

hypothetical distributions of ground-water withdrawals. 

Simulations using concentrated pumping centers were 

the least efficient at eliminating natural discharge and 

approaching new equilibrium conditions, and produced 

the largest water-level declines. Simulations using a distribution with ground-water withdrawals strategically 

placed in discharge areas were the most efficient at eliminating natural discharge, and in some cases approached a 

new equilibrium condition.

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Appel, C.L., and others, 1983, Ground-water conditions in Utah,

spring of 1983: Utah Division of Water Resources Cooperative 

Investigations Report No. 23, 97 p.

Armstrong, R.L., 1970, Geochronology of Tertiary igneous rocks, eastern Basin and Range Province, western Utah, eastern Nevada, 

and vicinity, U.S.A.: Geochimica et Cosmochimica Acta, v. 34, p. 

203-232.

Arnow, Ted, and Mattick, R.E., 1968, Thickness of valley fill in the Jordan Valley east of Great Salt Lake, Utah: U.S. Geological Survey 

Professional Paper 600-B, p. B79-B82.

Avery, C.F., and others, 1984, Ground-water conditions in Utah,

spring of 1984: Utah Division of Water Resources Cooperative 

Investigations Report No. 24, 79 p.

Bowman, J.R., and Rohrs, D.T., 1981, Light stable isotope studies of 

spring and thermal waters from the Roosevelt Hot Springs and 

Cove Fort/Sulphurdale thermal areas and of clay minerals from 

the Roosevelt Hot Springs thermal area: U.S. Department of 

Energy Report No. ID/12079-44, Department of Geology and 

Geophysics, University of Utah, 36 p.

Brumbaugh, W.D., and Cook, K.L., 1977, Gravity survey of the Cove 

Fort-Sulphurdale KGRA and the north Mineral Mountains area, 

Millard and Beaver Counties, Utah: U.S. Department of Energy 

Technical Report v. 77-4, contract EY-76-S-07-1601, Department 

of Geology and Geophysics, University of Utah, 130 p.

Carter, J.A., and Cook, K.L., 1978, Regional gravity and aeromagnetic 

surveys of the Mineral Mountains and vicinity, Millard and Beaver Counties, Utah: U.S. Department of Energy Final Report v. 

77-11, contract EY-76-S-07-1601, Department of Geology and 

Geophysics, University of Utah, 179 p.

Condie, K.C., and Barsky, C.K., 1972, Origin of Quaternary basalts 

from the Black Rock Desert region, Utah: Geological Society of 

America Bulletin, v. 83, no. 2, p. 333-352.

Crebs, T.J., and Cook, K.L., 1976, Gravity and ground magnetic surveys of the central Mineral Mountains, Utah: Final Report v. 6,

National Science Foundation Grant GI-43741, Department of 

Geology and Geophysics, University of Utah, 129 p.

Criddle, W.D., 1958, Consumptive use and irrigation water requirements of Milford Valley: U.S. Department of Agriculture, Agriculture Research Service, 41-14, 45 p.

Dennis, P.E., 1942, Shorelines of the Escalante Bay of Lake Bonneville: 

Utah Academy of Science, Arts, and Letters Proceedings, v. 19, 

p. 121-124.

Fenneman, N.M., 1931, Physiography of the western United States: 

New York, McGraw-Hill, 534 p.

Gertson, R.C., and Smith, R.B., 1979, Interpretation of a seismic refraction profile across the Roosevelt Hot Springs, Utah and vicinity: 

U.S. Department of Energy Report No. ADO/78-1701.a.3, 

Department of Geology and Geophysics, University of Utah, 

120 p.

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.

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