Simulation of Ground-Water

System Response to Proposed

Withdrawals from 1993 to 2043 in

the Northern Part of Juab Valley,

Juab County, Utah

Water-Resources Investigations Report 98–4262

Prepared in cooperation with the

Central Utah Water Conservancy District

U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

SIMULATION OF GROUND-WATER SYSTEM RESPONSE TO 

PROPOSED WITHDRAWALS FROM 1993 TO 2042

IN THE NORTHERN PART OF JUAB VALLEY, 

JUAB COUNTY, UTAH

By S.A. Thiros

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 98-4262

Prepared in cooperation with the

CENTRAL UTAH WATER CONSERVANCY DISTRICT

Salt Lake City, Utah

1999
U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

The use of trade, product, industry, or firm names is for descriptive purposes only and does not imply endorsement 

by the U.S. Government.

For additional information write to: 

District Chief

U.S. Geological Survey

Room 1016 Administration Building

1745 West 1700 South

Salt Lake City, Utah 84104

Copies of this report can be purchased from:

U.S. Geological Survey

Branch of Information Services

Box 25286

Denver Federal Center

Denver, Colorado 80225

Additional information about water resources in Utah is available on the World Wide Web at 

http://ut.water.usgs.gov
 iii

CONTENTS

Abstract ............................................................................................................................................................ 1

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

Purpose and scope.................................................................................................................................. 3

Ground-water hydrology........................................................................................................................ 3

Changes to existing ground-water flow model................................................................................................. 4

Simulation of additional pumping.................................................................................................................... 7

Limitations of revised models.......................................................................................................................... 13

Summary .......................................................................................................................................................... 15

References cited ............................................................................................................................................... 16

FIGURES

1. Map showing location of Juab Valley, Utah......................................................................................... 2

2. Map showing potentiometric surface for model layer 1 contoured from water levels computed

for 2022 of the revised model simulating no additional pumping in Juab Valley, Utah .................... 5

3. Hydrographs showing model-computed water-level change in selected model cells in 

the northern part of Juab Valley, Utah................................................................................................ 6

4-8. Maps showing: 

4. Computed water-level decline for model layer 1 between 1992 and 2022 of the revised

 model simulating no additional pumping in the northern part of Juab Valley, Utah .................. 9

5. Location of 30 additional pumped wells in the northern part of Juab Valley, Utah .................... 10

6. Computed water-level decline for model layer 1 between 2002 of the revised model

 simulating no additional pumping and 2002 of the revised model simulating additional

 pumping in the northern part of Juab Valley, Utah ..................................................................... 11

7. Computed water-level decline for model layer 1 between 2022 of the revised model 

simulating no additional pumping and 2022 of the revised model simulating additional 

pumping in the northern part of Juab Valley, Utah ...................................................................... 12

8. General location where computed water levels for model layer 1 are less than or equal to

10 feet below land surface in 1992 and 2022 of the revised model simulations in the 

northern part of Juab Valley, Utah...................................................................................................... 14

TABLE

1. Specified ground-water recharge and discharge, model-computed discharge, and 

change in flow rates for the original and revised ground-water flow models, 

northern part of Juab Valley, Utah...................................................................................................... 8
iv 

CONVERSION FACTORS

Multiply By To obtain

acre-foot (acre-ft) 0.001233 cubic hectometer

1,233 cubic meter

acre-foot per year (acre-ft/yr) 0.00003907 cubic meter per second

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

foot (ft) 0.3048 meter

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.
1

ABSTRACT

Information on the ground-water system in 

the northern part of Juab Valley, Utah, is needed 

by water managers to plan the optimal use of surface water that will be imported by the Central 

Utah Project and ground water pumped locally. 

The response of the ground-water system to an 

increase in withdrawal with no new sources of 

recharge was simulated to provide a baseline for 

comparing possible water-management plans and 

to determine their potential effects on wetlands in 

the area.

To assess the effects of additional withdrawal on the system, a 50-year-long stress period 

was added to the end of the existing three-dimensional, finite-difference, ground-water flow model. 

This stress period simulates recharge and discharge stresses determined for 1987-92. Another 

model was constructed by simulating 30 additional wells pumping a total of 4,000 acre-feet per 

year in the 50-year-long stress period. The 30 

additional wells were simulated in a north-south 

trending line along the eastern part of the valley 

and as pumping from the bottom model layer. The 

difference between model-computed water-level 

changes after 10, 30, and 50 years with and without the additional pumped wells was calculated 

for the uppermost model layer.

Water-level declines of more than 6 feet 

were computed for layer 1 in the area east of 

Mona Reservoir, and natural sources of groundwater discharge in the northern part of the valley 

decreased in response to 30 years of additional 

pumping. Discharge from springs and seeps computed in 2022 of the revised model simulating 

additional pumping decreased by about 7 percent 

and computed discharge by evapotranspiration 

decreased by about 23 percent relative to the same 

time in the revised model simulating no additional 

pumping.

INTRODUCTION

Surface water is to be imported to the northern 

part of Juab Valley as part of the Central Utah Project. 

The Central Utah Project is a plan approved by Congress to transport water from the Colorado River drainage basin in Utah to areas along the western side of the 

Wasatch Range for irrigation. Information on the 

ground-water system is needed by water managers to 

develop plans for the optimal use of ground- and surface-water resources. 

The hydrology of Juab Valley in central Utah 

(fig. 1) was studied from 1992 through 1994 by the 

U.S. Geological Survey in cooperation with the Central Utah Water Conservancy District and the East Juab 

Water Conservancy District (Thiros and others, 1996). 

A three-dimensional, finite-difference flow model 

(McDonald and Harbaugh, 1988) that simulated 

ground-water conditions during 1949-92 was developed to better understand the system. 

The Central Utah Water Conservancy District 

requested that the existing flow model be modified to 

include 4,000 acre-ft/yr of withdrawal from 30 additional wells in the northern part of Juab Valley. The 

capacity of the pipeline transporting Central Utah 

Project water to the northern part of the valley had not 

been finalized at the time of the request (May 1997). 

The response of the ground-water system to an 

increase in withdrawal with no new sources of 

recharge was simulated to provide a baseline for comparing possible water-management plans and to determine the potential effects on wetlands in the area. 

Simulation of Ground-Water System Response to

Proposed Withdrawals from 1993 to 2042 in the 

Northern Part of Juab Valley, Juab County, Utah

By S.A.Thiros
2 

15

15

132

28

28

112°00'

Goshen

111°45'

RANGE

Mona

UTAH COUNTY

JUAB COUNTY

39°52'30"

LONG RIDGE

WASATCH

Nephi

WEST HILLS

39°30'

Levan

JUAB COUNTY

SANPETE COUNTY

SAN PITCH MOUNTAINS

T.16 S.

T.14 S.

R.1 E.

R 11/2 W

111°52'30"

39°45'

39°22'30"

R.1 W.

T.15 S.

R 1 W

T.13 S.

39°37'30"

T.12 S.

T.11 S.

T.10 S.

Sevier Bridge

Reservoir

Salt Creek

West

Creek

Mona

Reservoir

Deep Creek

Creek

Chicken

Chicken Creek

Reservoir

Creek

Fourmile

Gardners

Fork

GardnerCreek

Birch Creek

North Creek

Base from U.S. Geological Survey digital line graph data, 1:100,000, 1980 and 1981

Universal Transverse Mercator projection,

Zone 12

132

Pigeon

Creek

Little

Salt

Creek

Chriss

Creek

Suttons Canyon Old Pinery

Canyon

Biglows Canyon

Quaking Asp

Canyon

Red Canyon

Pole Canyon

Bear Canyon

Creek

Currant

LEVAN RIDGE

R. 2 E.

Burriston

Ponds Currant

Creek

Willow

Creek

Mount Nebo

HILLS

SOUTH

UTAH

Approximate boundary of basin-fill

deposits—Area inside boundary represents

unconsolidated basin-fill deposits

U.S. Geological Survey streamflow-gaging

station 10146400, Currant Creek near

Mona, Utah

EXPLANATION

0 2 6 4 8 KILOMETERS

0 2 6 4 8 MILES

Wash Canyon

Couch Canyon

Birch Cr Little

Figure 1. Location of Juab Valley, Utah.
 3

Purpose and Scope

The objective of this study was to estimate, 

using modified versions of an existing ground-water 

model, the effects of an increase in ground-water withdrawal by pumped wells on water levels and on natural 

ground-water discharge to seeps and springs and by 

evapotranspiration in the northern part of Juab Valley. 

This report describes the effects on the simulated 

ground-water system in the northern part of the valley 

caused by the addition of a 50-year-long stress period 

to the end of the existing 1949-92 transient-state 

model. Another model was created by adding 30 wells 

pumped at a total rate of 4,000 acre-ft/yr to the 50-

year-long stress period.

Although the southern part of Juab Valley is 

included in the model, changes to the ground-water 

system simulated there are not presented because they 

were not the focus of this study. Additional sources of 

recharge to the ground-water system were not simulated, and pumping rates used for existing wells in the 

northern part of the valley during the 1987-92 stress 

period of the original model also were used in the 

additional stress periods of the revised simulations. 

The effects of pumping from the additional wells were 

compared to the effects of pumping from the existing 

wells. The difference between model-computed waterlevel changes after 10, 30, and 50 years with and without the additional pumping wells was calculated for 

the uppermost model layer. Changes made to the existing model, the effects of these changes, and the limitations of the revised models are discussed in this report.

Ground-Water Hydrology

This section is a summary of the ground-water 

system in the northern part of Juab Valley. A more 

detailed discussion of the ground-water system is presented in Thiros and others (1996).

Saturated unconsolidated basin-fill deposits 

form the principal ground-water system in the northern 

part of Juab Valley. Ground water generally is unconfined near the mountain fronts and above the uppermost confining layer in the subsurface. The confining 

layers are mostly within 50 ft of land surface, although 

their depth, thickness, and presence in the valley are 

variable. Most wells drilled in the valley are less than 

1,000 ft deep. Because the actual depth of the unconsolidated basin-fill deposits in Juab Valley is not 

known, the ground-water system is assumed to consist 

of the upper 1,000 ft of material.

Ground water in the unconsolidated basin-fill 

deposits in Juab Valley generally flows from recharge 

areas near the mountain fronts to discharge areas in the 

lower parts of the valley. The ground-water divide that 

separates the ground-water system into northern and 

southern parts has been determined to be just south of 

Levan Ridge (fig. 1), a topographic divide within the 

valley. The relatively small amount of water recharged 

at the ground-water divide flows in both the north and 

south directions.

Average recharge to the unconsolidated basinfill deposits in the northern part of the valley was estimated to be about 42,000 acre-ft/yr for 1963-93. 

Sources of recharge are seepage from streams, unconsumed irrigation water, and distribution systems (51 

percent); infiltration of precipitation (9 percent); and 

subsurface inflow from consolidated rocks that surround the valley (40 percent). 

Discharge from the unconsolidated basin-fill 

deposits in the northern part of the valley is by wells 

(39 percent), springs and seeps (35 percent), evapotranspiration (24 percent), and subsurface outflow to 

consolidated rocks (2 percent). Ground water is used 

mostly to supplement surface water for irrigation, and 

pumping of wells capable of yielding large amounts of 

water generally begins after snowmelt runoff ends. The 

1963-93 average annual ground-water discharge by 

pumped wells for irrigation and public supply is about 

14,500 acre-ft/yr.

Ground-water discharge from springs and 

seeps occurs mostly in low-lying areas where the 

hydraulic head of the ground water is above land surface. This discharge provides much of the base flow in 

West and Currant Creeks and much of the inflow to 

Mona Reservoir. The area delineated as wetlands by 

the U.S. Department of Agriculture, Soil Conservation 

Service (written commun., 1993) is generally oriented 

along the axis of the valley and corresponds to where 

ground water is discharged by evapotranspiration. 

About 4,800 acres were mapped as wetlands in the 

northern part of the valley in 1988. Discharge by 

springs, seeps, evapotranspiration, and flowing wells 

has decreased in the valley in response to an increase 

in withdrawals from pumped wells as the groundwater system approaches a new equilibrium.
4 

CHANGES TO EXISTING GROUNDWATER FLOW MODEL

The existing numerical ground-water flow 

model was calibrated to the transient-state conditions 

that existed in the ground-water system of Juab Valley 

during 1949-92. It contains eight multi-year stress 

periods that represent similar climatic and pumping 

conditions (Thiros and others, 1996, fig. 32). The 

length of each stress period was chosen on the basis of 

a visual inspection of the estimated annual groundwater pumpage from wells in Juab Valley. Recharge 

and discharge stresses to the system were averaged for 

the years within a stress period and then applied to the 

model on a yearly (time-step) basis. More information 

on the existing numerical ground-water flow model for 

Juab Valley is presented in Thiros and others (1996).

The hydrologic effects of additional pumping 

can be estimated by comparing changes in water levels 

and natural discharge with those of the model with no 

additional pumping. As a first step, the existing 1949-

92 transient-state model was extended to 2042 using 

1987-92 stresses. This was accomplished by adding 

one 50-year-long stress period consisting of 50 time 

steps to the end of the original model. The second step 

was to simulate the same 50-year-long period from 

1993-2042 with an additional 4,000 acre-ft/yr of withdrawal from 30 proposed wells. Then, the results of 

these two simulations were compared to quantify and 

evaluate the effects of the proposed additional pumpage.

Recharge and natural discharge simulated in 

the stress period representing 1987-92 were generally 

less than the long-term average because of less-thannormal precipitation. Pumping for irrigation during 

this period was correspondingly greater than the 1963-

93 average in both the southern and northern parts of 

Juab Valley. Therefore, the revised model simulates a 

prolonged period of less-than-normal precipitation and 

greater-than-average pumping. An averaged set of 

recharge and discharge stresses was not constructed 

for use in the revised model because of limitations in 

the scope of the study.

Model layer 1, the uppermost layer, represents 

unconfined ground-water conditions in the valley. 

Changes in simulated recharge and discharge cause the 

saturated thickness of the uppermost layer to vary. A 

result of using 1987-92 stresses for an extended period 

is that some water levels simulated in the valley 

dropped below the bottom of model layer 1 and model 

cells in those areas and layer became dewatered (inactive). Areal recharge was then applied to the cell in the 

next layer at that location. Adjacent cells in layer 1 can 

become dewatered because no flow is simulated across 

the interval between an inactive cell and any adjacent 

cell. Recharge from subsurface inflow from consolidated rocks and discharge from wells cannot be redistributed to the uppermost active cell in the event that 

cells become dewatered. These stresses applied to an 

inactive cell are not simulated.

As noted earlier, assessment of the effects of 

additional withdrawal on water levels in the northern 

part of Juab Valley was the focus of this investigation. 

Therefore, pumping simulated in the southern part was 

halved from 3,270 to 1,635 acre-ft/yr to reduce the 

number of dewatered cells so that the model could 

complete calculations for all nine stress periods. This 

change in the model did not substantially affect simulated water levels in the northern part of the valley 

because of the presence of the ground-water divide 

(fig. 2). An area south of Levan adjacent to the eastern 

mountain front still became dewatered during the additional stress period (fig. 2). This area received simulated recharge from infiltration of precipitation and 

subsurface inflow from consolidated rocks. No pumping wells were simulated in the dewatered area. 

Areas where cells dewatered in the northern 

part of the revised model are northeast of Levan Ridge 

near the ground-water divide and near Nephi (fig. 2). 

The area near the ground-water divide does not contain 

large-yield wells but is affected by relatively small 

amounts of recharge and pumpage in the Nephi and 

Levan areas. The effects of these dewatered cells on 

water levels computed for the rest of the model is 

minor because of the small amount of recharge from 

subsurface inflow lost from the system. Dewatered 

model cells in layer 1 near Nephi resulted in a reduction of 480 and 310 acre-ft/yr in specified discharge 

from pumped wells beginning in 2018 and 2029, 

respectively. Therefore, specified discharge in 2022 

and 2042 of the simulation with no additional pumping 

was 480 and 790 acre-ft/yr less, respectively, than was 

simulated in 2002 when there were no dewatered cells 

in the northern part of the valley. 

The ground-water system in most of the northern part of Juab Valley approached equilibrium with 

the change in water levels stabilizing after about 25 

years (2017) of the 50-year stress period (fig. 3). The 

change in water levels computed for selected cells in 

model layer 1 is similar to changes for the same cells 

in the other three layers shown in figure 3. Steady-state 

conditions result when the amount of simulated 
 5

Creek

North

Creek

Currant

111°45' 112°00'

39°52'30"

39°30'

0 2 4 MILES

0 2 4 KILOMETERS

5

ROWS 10 15 20 25 30

COLUMNS

70

75

80

85

90

95

100

105

110

115

120

125

130

135

140

145

150

155

5

10

15

20

25

30

35

40

45

50

55

60

65

Mona

Reservoir

Mona

Nephi Salt Creek

JUAB

VALLEY Chicken

Creek

Reservoir

Little Salt

EXPLANATION

Approximate location of ground-water divide

determined from water levels computed for

model layer 1, 1992 of the original model

Potentiometric contour—Shows altitude of the

potentiometric surface contoured from water

levels computed for model layer 1, 2022 of the

revised model simulating no additional pumping.

Contour interval 20 feet. Datum is sea level

Boundary of active cells

Location of existing pumped well simulated in

1992 of the original model and in 1993–2042

of the revised model simulating no additional

pumping

Location of dewatered model cell simulated in

layer 1, 2022 of the revised model simulating

no additional pumping

Creek

5,000

4,940

4,960

4,900

4,920

4,940

4,960

4,980

5,000

5,020

5,040

5,060

5,080

5,100

5,120

5,140

5,140

5,120

5,100

5,080

5,060

5,140

5,160

Figure 2. Potentiometric surface for model layer 1 contoured from water levels computed for 2022 of the revised model 

simulating no additional pumping in Juab Valley, Utah.
6 

Boundary of active cells

Hydrographs showing modelcomputed water-level change

Computed water-level change

in 1949–92 of original model

Computed water-level change

in 1993–2042 of revised model

simulating no additional wells

Computed water-level change

in 1993–2042 of revised model

simulating additional wells

Location of cell showing modelcomputed water-level change

Creek

Currant 111°52'30" 111°45'

39°52'30"

0 2 4 MILES

0 2 4 KILOMETERS

5

ROWS 10 15 20 25 30

COLUMNS

110

115

120

125

130

135

140

145

150

155

Mona Reservoir

North

Creek

Mona

Nephi Salt Creek

JUAB

VALLEY

EXPLANATION

WATER-LEVEL CHANGE, IN FEET

194919551960196519701975198019851990199520002005201020152020202520302035204020452047

25

0

-25

-50

25

0

-25

-50

-75

25

0

-25

-50

20

0

-20

-40

10

0

-5

-10

5

20

0

-20

-40

39°45'

Row 25, Column 94, Layer 3

Row 16, Column 97, Layer 4

Row 14, Column 124, Layer 2

Row 17, Column 87, Layer 2

Row 16, Column 104, Layer 4

Row 18, Column 143, Layer 3

1-YEAR TIME STEPS

Figure 3. Model-computed water-level change in selected model cells in the northern part of Juab Valley, Utah.
 7

recharge to the system is equal to the amount of simulated discharge—there is no net change in storage. 

About 810 acre-ft/yr of water was removed from storage (2 percent of simulated recharge) in 2022 and 

about 210 acre-ft/yr (0.5 percent of simulated 

recharge) in 2042 of the revised model simulating no 

additional pumping (table 1). Water-level declines simulated in layer 1 in 2022 of the revised model simulating no additional pumping generally ranged from 

about 5 ft in the area near Currant Creek to about 30 ft 

in the area south of Nephi (fig. 4). 

Simulated discharge from springs, seeps, 

evapotranspiration, and flowing wells in the northern 

part of the valley decreased in response to the decline 

in water levels. Total model-computed discharge 

decreased about 38 percent (12,640 acre-ft/yr) from 

33,610 acre-ft in 1992, the last year of the original 

model, to 20,970 acre-ft in 2022, the 30th year of the 

additional stress period (table 1). Model-computed discharge by evapotranspiration and from springs and 

seeps decreased by about 53 percent (6,070 acre-ft/yr) 

and 29 percent (6,260 acre-ft/yr), respectively, from 

1992 to 2022. Simulated spring discharge includes 

ground-water discharge to Mona Reservoir, Burriston 

Ponds, West Creek, and Currant Creek. The budget 

element listed as ‘Seepage to Currant Creek upstream 

from streamflow-gaging station 10146400’ in table 1 

includes simulated spring discharge to Burriston Ponds 

and seepage to West Creek. Although the decrease in 

model-computed discharge is substantial, it is thought 

to be acceptable for the purpose of determining the 

effects of additional pumping on the system.

SIMULATION OF ADDITIONAL 

PUMPING

To assess the effects of an additional 4,000 

acre-ft/yr of pumping in the northern part of Juab Valley, 30 wells were added to stress period 9 (1993-

2042) of the revised flow model. Each of the 30 wells 

was assigned a pumping rate of 133 acre-ft/yr. For a 

possible water-management option that requires the 

additional ground water during the month of July only, 

this equates to about 2.2 ft3

/s for each well. The wells 

were simulated in a line along the eastern part of the 

valley (fig. 5) where the unconsolidated basin-fill 

deposits probably are thicker and were screened in 

model layer 4 to tap the thickest and most transmissive 

part of the ground-water system. The spacing of the 

wells decreased in the area west of Nephi to take 

advantage of the large amount of simulated recharge 

by subsurface inflow from consolidated rocks. Wells 

were not added to the southern part of the valley.

Water-level declines of more than 5 ft were 

simulated in layer 1 in the area east of Mona Reservoir 

in response to 10 years of pumping the additional 

wells (fig. 6). Total model-computed discharge 

decreased by about 9 percent, from 24,130 acre-ft in 

2002 of the revised model simulating no additional 

pumping to 22,000 acre-ft for the same time in the 

revised model simulating additional pumping (table 1). 

Model-computed discharge to head-dependent boundaries such as evapotranspiration, springs, and seeps 

decreased by about 16 percent (1,100 acre-ft/yr) and 6 

percent (950 acre-ft/yr), respectively, for the same 

period because of reduced water levels. Model-computed discharge by flowing wells decreased by about 

22 percent (80 acre-ft/yr). Water removed from storage 

was about 15 percent (5,540 acre-ft/yr) of the recharge 

specified in 2002 of the revised model simulating no 

additional pumping. 

The model-computed water-level change that 

resulted from additional pumping and specified 

recharge and pumping rates representing 1987-92 conditions also approached equilibrium in most of the 

northern part of Juab Valley after about 25 years (fig. 

3). About 1,200 acre-ft/yr of water was removed from 

storage in 2022 and about 260 acre-ft/yr in 2042 of the 

revised model simulating additional pumping (table 1). 

Water-level declines of more than 6 ft were computed 

for layer 1 in the area east of Mona Reservoir in 

response to 30 years of pumping from the additional 

wells (fig. 7). 

A comparison between results of the two 

revised models indicates a decrease in model-computed discharge components caused by the additional 

pumping. Total model-computed discharge decreased 

by about 12 percent, from 20,970 acre-ft in 2022 of the 

revised model simulating no additional pumping to 

18,550 acre-ft in 2022 of the revised model simulating 

additional pumping (table 1). Model-computed discharge from head-dependent boundaries such as 

evapotranspiration, springs, and seeps decreased by 

about 23 percent (1,230 acre-ft/yr) and 7 percent 

(1,100 acre-ft/yr), respectively, for the same comparison. 

An inactive or dewatered cell cannot simulate 

recharge from subsurface inflow from consolidated 

rocks or discharge from pumping wells. Five cells 

became dewatered in the Nephi area during and after 

2022 of the model simulating additional pumping. A 

consequence of the dewatered cells is that the total 
8 

ground-water flow models, ow rates for the original and revised 

, Utah

ound-water recharge and discharge, model-computed discharge, and change in fl

alley t of Juab V

 Specified gr

n parthernor

le 1.baT

Flow, in acre-feet per year

1992 

Time step 2002 2022 2042

6, stress Time step 10, stress period 9 Time step 30, stress period 9 Time step 50, stress period 9

period 8

 Budget element 50th year of 

10th year of 10th year of 30th year of 30th year of revised 50th year of Difference Original and revised revised Difference revised revised Difference model with revised model between

revised model with model with between model with model with between no with additional models models no addtional additional models no additional additional models additional pumping

pumping pumping pumping pumping pumping

Specified rechargeSeepage from streamflow, unconsumed irriga- 23,310 23,310 23,310 0 23,310 23,310 0 23,310 23,310 0

tion, and infiltration from precipitation

Subsurface inflow to east side of Juab Valley 9,970 9,970 9,970 0 9,970 9,850 -120 9,970 9,840 -130

Subsurface inflow to west side of Juab Valley 3,790 3,790 3,790 0 3,790 3,790 0 3,790 3,790 0

Total specified recharge 37,070 37,070 37,070 0 37,070 36,950 -120 37,070 36,940 -130

Specified dischargeWithdrawal from wells pumped for irrigation and 17,220 17,220 21,220 4,000 16,740 20,430 3,690 16,430 19,800 3,370

public supply

Subsurface outflow to consolidated rock/ unconsolidated basin-fill deposits boundary 900 900 900 0 900 900 0 900 900 0

Total specified discharge 18,120 18,120 22,120 4,000 17,640 21,330 3,690 17,330 20,700 3,370

Model-computed dischargeSprings and seeps

 Seepage to Mona Reservoir 8,800 7,230 6,490 -740 6,760 5,890 -870 6,700 5,820 -880

 Seepage to Currant Creek upstream from 

streamflow-gaging station 101464001 9,480 6,760 6,750 -10 5,800 5,790 -10 5,700 5,690 -10

 Seepage to Currant Creek downstream from 

streamflow-gaging station 10146400 3,390 2,980 2,780 -200 2,850 2,630 -220 2,840 2,610 -230

 Springs and seeps total 21,670 16,970 16,020 -950 15,410 14,310 -1,100 15,240 14,120 -1,120

Flowing wells 600 370 290 -80 290 200 -90 280 190 -90

Evapotranspiration 11,340 6,790 5,690 -1,100 5,270 4,040 -1,230 5,130 3,910 -1,220

Total model-computed discharge 33,610 24,130 22,000 -2,130 20,970 18,550 -2,420 20,650 18,220 -2,430

Water going out from storage 13,550 4,470 5,540 1,070 810 1,200 390 210 260 50

Water going into storage 60 0 0 0 0 0 0 0 0 0

Recharge from southern part of Juab Valley 2,050 2,270 2,290 20 2,400 2,450 50 2,360 2,420 60

Discharge to southern part of Juab Valley 620 600 600 0 570 570 0 560 550 -10

est Creek. and seepage to W onds iston P ing discharge to Burr ulated spr w-gaging station 10146400 includes sim o Seepage to Current Creek upstream from streamfl 1
 9

Line of equal water-level decline—

Contour interval 5 feet

Boundary of active cells

Location of existing pumped well

simulated in 1992 of the original

model and in 1993–2042 of the

revised model simulating no

additional pumping

Location of dewatered model cell

simulated in layer 1, 2022 of the

revised model simulating no

additional pumping

0

-25

-25

-15

-20

-15

-10

-5

-10

-15

-20

-25 -30

-25

112°00'

39°52'30"

111°45'

0 2 4 MILES

0 2 4 KILOMETERS

5

ROWS 10 15 20 25 30

COLUMNS

70

75

80

85

90

95

100

105

110

115

120

125

130

135

140

145

150

155

Currant

Creek

Mona

Reservoir

North

Creek

Mona

Nephi Salt Creek

JUAB

VALLEY

EXPLANATION

-10

39°37'30"

Figure 4. Computed water-level decline for model layer 1 between 1992 and 2022 of the revised model simulating no 

additional pumping in the northern part of Juab Valley, Utah.
10 

112°00'

39°52'30"

111°45'

0 2 4 MILES

0 2 4 KILOMETERS

5

ROWS 10 15 20 25 30

COLUMNS

70

75

80

85

90

95

100

105

110

115

120

125

130

135

140

145

150

155

Currant

Creek

Mona

Reservoir

North

Creek

Mona

Nephi

Salt Creek

JUAB

VALLEY

EXPLANATION

Model cell simulating additional

pumped well—Simulates discharge at

a specified rate to a well added to revised

model simulating pumping from

additional wells

Model cell simulating existing pumped

well—Simulates discharge at a specified

rate to a well existing in the original

model

Boundary of active cells

39°37'30"

Figure 5. Location of 30 additional pumped wells in the northern part of Juab Valley, Utah.
 11

112°00'

39°52'30"

111°45'

0 2 4 MILES

0 2 4 KILOMETERS

5

ROWS 10 15 20 25 30

COLUMNS

70

75

80

85

90

95

100

105

110

115

120

125

130

135

140

145

150

155

Mona

Reservoir

North

Creek

Mona

Nephi

Salt Creek

JUAB

VALLEY

EXPLANATION

Currant

Creek

Line of equal water-level decline—

Contour interval 1 foot

Boundary of active cells

Location of existing pumped well

simulated in 1993–2042 of the

revised model simulating no

additional pumping

Location of additional pumped well

simulated in 1993–2042 of the

revised model simulating

additional pumping

39°37'30"

-1

-4

-2

-3

-4

-5

-4

-2

-2

-1

-1 -3

-4

-2

-3

-1

-3

Figure 6. Computed water-level decline for model layer 1 between 2002 of the revised model simulating no additional 

pumping and 2002 of the revised model simulating additional pumping in the northern part of Juab Valley, Utah.
12 

112°00'

39°52'30"

111°45'

0 2 4 MILES

0 2 4 KILOMETERS

5 10 ROWS

15 20 25 30

COLUMNS

70

75

80

85

90

95

100

105

110

115

120

125

130

135

140

145

150

155

Currant

Creek

Mona

Reservoir

North

Creek

Mona

Nephi Salt Creek

JUAB

VALLEY

EXPLANATION

Line of equal water-level decline—

Contour interval 1 foot

Boundary of active cells

Location of existing pumped well

simulated in 1993–2042 of the

revised models

Location of additional pumped well

simulated in 1993–2042 of the

revised models

Location of dewatered model cell

simulated in layer 1, 2022 of the

revised models

Location of dewatered model cell

simulated in layer 1, 2022 of the

revised model simulating additional

pumping

39°37'30"

-4

-1

-5

-5

-4

-6

-4

-3

-1

-2

-2

-5

-4

-4

-3

-4

-3

-1 -2

-5

-4

-5

-5

-4

Figure 7. Computed water-level decline for model layer 1 between 2022 of the revised model simulating no addtional

pumping and 2022 of the revised model simulating additional pumping in the northern part of Juab Valley, Utah. 
 13

specified recharge applied in 2022 and 2042 of the 

simulation with additional pumping was about 0.3 percent less (120 and 130 acre-ft/yr, respectively) than the 

amount applied in the simulation with no additional 

pumping. The loss of specified recharge from subsurface inflow caused by the dewatered cells results in 

more model-computed water-level decline than if the 

cells were active. 

Dewatered model cells in layer 1 near Nephi 

resulted in 630 acre-ft/yr less specified discharge from 

pumped wells between 2022 and 2042 of the simulation with additional pumping. This is in addition to the 

790 acre-ft/yr of specified discharge from pumped 

wells lost to dewatered cells in the simulation with no 

additional pumping. The loss of specified discharge 

caused by the dewatered cells results in a reduction in 

the amount of water-level decline computed by the 

model. Computed water-level declines would be 

greater if the simulated wells continued to withdraw 

water rather than becoming inactive.

The area where computed water levels for 

model layer 1 are less than or equal to 10 ft below land 

surface in 1992 and 2022 of the revised model simulations is shown in figure 8. Natural discharge by evapotranspiration and seepage to springs, streams, and 

Mona Reservoir generally occurs within this area. Discharge by evapotranspiration is dependent on the depth 

of the water table and is, therefore, a head-dependent 

process. The evapotranspiration rate varies linearly 

from a maximum when the water level is near or at 

land surface to zero when the water level is below a 

subjectively set extinction depth of 10 ft. The area 

decreased in size in the revised models, mostly 

because water levels declined throughout the additional stress periods. The area where ground water was 

within 10 ft of land surface as computed by the simulation with additional pumping was less than the area 

computed by the simulation with no additional pumping. The areas where model-computed water levels for 

model layer 4 are greater than for model layer 1 in the 

revised models is roughly similar to the areas shown in 

figure 8. 

LIMITATIONS OF REVISED MODELS

This investigation compares the effects of 

pumping from existing and additional wells in the 

northern part of Juab Valley. To distinguish between 

the effects of the two simulations, specified recharge 

and specified discharge from existing wells was simulated until the resulting water-level changes stabilized. 

The application of the stresses used in the last stress 

period of the original model to the added stress period 

of the revised models caused relatively large changes 

in water levels and natural discharge. Because of limitations in the scope of the study, a more representative 

set of specified recharge and discharge stresses was not 

constructed for the revised models. This set of stresses 

could be derived from a more normal period of precipitation and from annual average pumping volumes for 

the wells that existed in 1992. Although the effects of 

pumping from existing wells are large in the revised 

models (some model cells became dewatered, and the 

model required about 25 years to approach equilibrium), the general effects of additional pumping on 

water levels and natural discharge could be estimated 

using these stresses.

Because yearly time steps are used in these 

simulations, the additional withdrawal of 4,000 acre-ft/

yr is distributed equally throughout the year rather than 

seasonally or monthly as would be required by the 

hypothetical water-management option. In reality, 

pumping at a higher rate during the summer months 

would likely produce much greater localized drawdown than is simulated by the model using annualized 

pumping rates and yearly time steps.

Recharge to the valley from subsurface inflow 

from the surrounding consolidated rocks is simulated 

as specified flux. A specified-flux boundary condition 

fixes the amount of recharge and discharge across the 

boundary and does not allow more water to enter or 

leave the active model area as a result of head-gradient 

changes. Additional pumping simulated near the edges 

of the modeled area does not cause recharge from subsurface inflow at the model edge to increase or discharge by subsurface outflow at the model edge to 

decrease to compensate for the ground-water withdrawals. More water could recharge the system and 

simulated water-level declines would be less if a headdependent boundary were used to simulate subsurface 

inflow from consolidated rocks instead of a specifiedflux boundary. 

Recharge from unconsumed irrigation water 

and distribution-system losses was assumed to be 10 

percent of the ground water pumped from wells in the 

original model (Thiros and others, 1996, p. 58). The 

amount of recharge from unconsumed irrigation water 

and distribution-system losses specified in the revised 

model simulating additional pumping was not 

increased as a percentage of the additional ground 

water pumped. Assuming no changes in water-application practices used in the valley, the amount of water-
14 

112°00'

39°52'30"

111°45'

0 2 4 MILES

0 2 4 KILOMETERS

5 ROWS 10 15 20 25 30

COLUMNS

70

75

80

85

90

95

100

105

110

115

120

125

130

135

140

145

150

155

Currant

Creek

Mona

Reservoir

North

Creek

Currant

Creek

Mona

Nephi

Salt Creek

JUAB

VALLEY

EXPLANATION

Area where model-computed water

levels for layer 1 are less than or

equal to 10 feet below land surface

in 1992 of the original and revised

models

Area where model-computed water

levels for layer 1 are less than or

equal to 10 feet below land surface

in 1992 of the original and revised

models and in 2022 of the revised

model simulating no additional

pumping wells

Area where model-computed water

levels for layer 1 are less than or

equal to 10 feet below land surface

in 1992 of the original and revised

models and in 2022 of the revised

models

Boundary of active cells

39°37'30"

Figure 8. General location where computed water levels for model layer 1 are less than or equal to 10 feet below land 

surface in 1992 and 2022 of the revised model simulations in the northern part of Juab Valley, Utah.
 15

level decline caused by the additional pumping is more 

than if recharge from unconsumed irrigation water and 

distribution-system losses were included.

Dewatered cells cause the loss of some 

recharge and discharge specified in the revised models. 

The loss of specified discharge from model layer 1 

simulated by four existing pumped wells in the Nephi 

area resulted in less model-computed water-level 

decline than if the cells had not been dewatered. The 

effect of this underestimation extends to the headdependent cells used to simulate discharge from 

springs, flowing wells, leakage to streams, and evapotranspiration. Therefore, model-computed discharge 

was increased by the amount of specified discharge not 

simulated by the dewatered cells with the existing 

pumped wells.

As was stated in the documentation of the 

original numerical ground-water flow model for Juab 

Valley, data are not available to estimate discharge to 

springs, evapotranspiration, and flowing wells. Therefore the numerical model was calibrated to match 

water levels rather than flow rates in discharge areas 

(Thiros and others, 1996, p. 96). The accuracy of 

model-computed flow for individual components of 

discharge is not known and should be considered an 

approximation. Additional data on recharge and discharge components are needed to improve the original 

ground-water flow model and any revisions to it.

SUMMARY

Information on the ground-water system in 

northern Juab Valley, Utah, is needed by water managers to plan the optimal use of surface water that will be 

imported by the Central Utah Project and existing 

ground and surface water. The response of the groundwater system to an increase in withdrawal with no new 

sources of recharge was simulated to provide a baseline for comparing possible water-management plans 

and to determine the potential effects on wetlands in 

the area. As a first step, the existing 1949-92 transientstate model was extended to 2042 using 1987-92 

stresses. This was accomplished by adding one 50-

year-long stress period to the end of the original 

model. The second step was to simulate the same 50-

year-long period from 1993-2042 with an additional 

4,000 acre-ft/yr of withdrawal from 30 proposed wells. 

Then, the results of these two simulations were compared to quantify and evaluate the effects of the proposed additional pumpage.

The ground-water system in most of the northern part of Juab Valley approached equilibrium with 

the change in water levels stabilizing after about 25 

years of the 50-year stress period. Water-level declines 

simulated in layer 1 in 2022 of the revised model simulating no additional pumping generally ranged from 

about 5 ft in the area near Currant Creek to about 30 ft 

in the area south of Nephi. Simulated discharge from 

springs, seeps, evapotranspiration, and flowing wells 

in the northern part of the valley decreased in response 

to the decline in water levels. Total model-computed 

discharge decreased about 38 percent (12,640 acre-ft/

yr) from 33,610 acre-ft in 1992, the last year of the 

original model, to 20,970 acre-ft in 2022, the 30th year 

of the additional stress period. Although the decrease 

in model-computed discharge is substantial, it is 

thought to be acceptable for the purpose of determining the effects of additional pumping on the system.

An additional 4,000 acre-ft/yr of pumping was 

simulated from 30 wells in the northern part of Juab 

Valley from 1993-2042. These wells were simulated in 

a line along the eastern part of the valley and were 

screened in model layer 4 to tap the thickest and most 

transmissive part of the ground-water system. The 

model-computed water-level change that resulted from 

additional pumping and specified recharge and pumping rates representing 1987-92 conditions also 

approached equilibrium in most of the northern part of 

the valley after about 25 years.

Water-level declines of more than 6 ft were 

computed for layer 1 in the area east of Mona Reservoir in response to 30 years of additional pumping. 

Total model-computed discharge decreased by about 

12 percent, from 20,970 acre-ft in 2022 of the revised 

model simulating no additional pumping to 18,550 

acre-ft in 2022 of the revised model simulating additional pumping. Discharge from springs and seeps 

computed in 2022 of the model with additional pumping decreased by about 7 percent and computed discharge by evapotranspiration decreased by about 23 

percent relative to the same time in the model with no 

additional pumping. The area where the simulated 

depth to water was less than or equal to 10 ft below 

land surface decreased in size in the revised models. 

A limitation of the revised models is that the 

application of the stresses determined for the last stress 

period of the original model to the added stress period 

of the revised models caused relatively large changes 

in water levels and natural discharge. Because of limitations in the scope of the study, a more representative 

set of specified recharge and discharge stresses was not 
16 

constructed for the revised models. More water could 

recharge the system and simulated water-level declines 

would be less if a head-dependent boundary were used 

to simulate subsurface inflow from consolidated rocks 

instead of a specified-flux boundary. The accuracy of 

model-computed flow for individual components of 

discharge is not known and should be considered an 

approximation. Additional data on recharge and discharge components are needed to improve the original 

ground-water flow model and any revisions to it.

REFERENCES CITED

McDonald, M.G., and Harbaugh, A.W., 1988, A modular three-dimensional finite-difference groundwater flow model: Techniques of WaterResources Investigations of the U.S. Geological Survey, book 6, chap. A1.

Thiros, S.A., Stolp, B.J., Hadley, H.K., and Steiger, 

J.I., 1996, Hydrology and simulation of 

ground-water flow in Juab Valley, Juab 

County, Utah: Utah Department of Natural 

Resources Technical Publication No. 114, 

100 p.

S.A. Thiros—Simulation of Ground-Water System Response to Proposed Withdrawals from 1993 to 2043 in the Northern Part of Juab V

Utah—Water-Resources Investigations Report 98–4262

alley, Juab County,

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