Table Of ContentConceptual Evaluation of Regional Ground-Water Flow in
the Carbonate-Rock Province of the Great Basin,
Nevada, Utah, and Adjacent States
U.S. GEOLOGICAL SURVEY
Open-File Report 93-170
(revision of Open-File Report 90-560)
A product ofthe Regional
Aquifer-System Analysis ofthe
Great Basin
Carson City, Nevada
1993
Conceptual Evaluation of Regional Ground-Water Flow in
the Carbonate-Rock Province of the Great Basin,
Nevada, Utah, and Adjacent States
By David E. Prudic, James R. Harrill, and Thomas J. Burbey
U.S. GEOLOGICAL SURVEY
Open-File Report 93-170
(revision of Open-File Report 90-560)
A product ofthe Regional
Aquifer-System Analysis ofthe
Great Basin
Carson City, Nevada
1993
U.S. DEPARTMENT OF THE INTERIOR
BRUCE BABBITT, Secretary
GEOLOGICAL SURVEY
U.S.
Robert M. Hirsch, Acting Director
Any use oftrade, product, or firm names in this publication is for
descriptive purposes only and does not constitute endorsement by
the U.S. Government
For additional information Copies of this report may be
write to: purchased from:
District Chief U.S. Geological Survey
U.S. Geological Survey Earth Science Information Center
333 W. Nye Lane, Rm 203 Open-File Reports Services
Carson City, NV 89706-0866 Federal Center, MS 517
Box 25286
Denver, CO 80225-0046
CONTENTS
Abstract 1
Introduction 2
Purpose and Scope 4
Previous Investigations 6
Description of the Carbonate-Rock Province 7
Physiography 7
Climate 7
Surface Water 8
Acknowledgments 11
Ground Water in the Carbonate-Rock Province 11
Hydrogeology 11
Occurrence and Movement of Ground Water 13
Conceptual Evaluation of Ground-Water Flow 15
General Assumptions 15
Model Development 17
Application of Finite-Difference Equations 17
Model Grid 18
Representation as a Two-Layer System 18
Boundary Conditions 18
Modeling Approach 21
Estimates of Recharge 23
Initial Estimates of Transmissivity and Leakance 26
Model Calibration 26
Limits of Calibration 35
Simulation Results 35
Estimated Transmissivities 38
Correlation of Simulated Ground-Water Flow to Regional Geologic Features 39
Distribution of Flow into Regions 48
Flow Regions 55
Death Valley Region 55
Inflow 56
Outflow 56
Description of Subregions 56
Big Smoky Subregion 56
Clayton Subregion 57
Mesquite Subregion 60
Pahrump-Amargosa Subregion 60
Ground-Water Flow to Furnace Creek 61
Ground-Water Flow to Ash Meadows 62
Colorado River Region 63
Inflow 65
Outflow 65
Description of Subregions 65
Penoyer Subregion 65
Las Vegas Subregion 68
Virgin River Subregion 68
White River Subregion 69
Bonneville Region 72
Inflow 72
Outflow 75
Contents
iii
. .
Bonneville Region-Continued
Description of Subregions 75
Escalante Subregion 75
Spring-Steptoe Subregion 77
Ruby Subregion 78
Clover-Independence Subregion 79
Utah Lake Subregion 80
Great Salt Lake Desert Subregion 80
Railroad Valley Region 83
Inflow 83
Outflow 85
Description of Ground-Water Flow 86
Upper Humboldt River Region 87
Inflow 87
Outflow 89
Description of Subregions 90
Diamond Subregion 90
Humboldt Subregion 90
Potential Uses of Model 91
Summary and Conclusions 92
References Cited 96
FIGURES
1 Map showing location and geographic features of study areas for Great Basin Regional
Aquifer-System Analysis (RASA) and carbonate-rock province 3
2. Map showing hydrographic areas and location of Nevada Test Site 5
3. Graph showing population growth in study area between 1900 and 1990 6
4. Map showing distribution of average annual precipitation 9
5. Map showing distribution of rivers and lakes in and adjacent to study area for Great Basin
Regional Aquifer-System Analysis 10
6. Geologic sections of Precambrian and Paleozoic rocks in carbonate-rock province 12
7. Map showing principal source areas for ground-water recharge, areas where ground water
is consumed by evapotranspiration, and regional springs 14
8. Map showing distribution of estimated grcund-water withdrawals by hydrographic areas
for 1975 16
9. Map showing finite-difference grid network 19
10. Diagrams showing simulations of evapotranspiration as a function of water level 21
11-20. Maps showing:
1 1 Cells used to simulate spring discharge from lower model layer 22
12. Wells tapping basin fill for which water-level data are available 24
13. Wells, test holes, and mine shafts tapping consolidated rocks for which water-level
data are available 25
14. Distribution of recharge assigned to cells in upper model layer, and simulated recharge
from rivers and lakes through general-head boundaries 27
15. Principal rock types assigned to cells in upper model layer, and initial
transmissivities used 28
16. Estimated vertical leakance between cells in upper and lower model layers 30
17. Simulated evapotranspiration rates in cells in upper model layer, and simulated
discharge from rivers, lakes, and Death Valley through general-head boundaries 33
18. Areas where ground water is consumed by evapotranspiration 34
19. Simulated steady-state ground-water levels, upper and lower model layers 36
20. Estimated transmissivities, upper and lower model layers 40
egional Ground-Water Flow in the Carbonate-Rock Province
21. Graphs showing frequency distributions of estimated transmissivities for cells in
upper model layer on basis of principal rock type, and for all cells in lower model layer 42
22-25. Maps showing:
22. Relation between selected geologic features and simulated ground-water levels,
areas of evapotranspiration, and location of springs simulated in model 44
23. Distribution of shallow-flow regions delineated in upper model layer in relation
to: Areas where ground water is consumed by evapotranspiration, simulated water
levels in upper model layer, and outcrops of low-permeability rocks 47
24. Distribution of deep-flow regions and subregions delineated in lower model layer in
relation to: (A) metamorphic core complexes, low-permeability rocks, and magnetic
source bodies; and (B) generalized directions of deep ground-water flow 50
25. Distribution of high transmissivities in lower model layer in relation to springs
simulated in model and to boundary of central corridor of thick carbonate
rocks in south-central Nevada 52
26. Schematic diagrams showing (A) conceptualization of ground-water flow from recharge
areas in mountains to discharge areas on basin floors; (B) same conceptualization,
as represented in finite-difference computer model; and (C) summary of water budget
within area encompassed by a deep-flow region on basis of computer-model output 53
27-35. Maps showing:
27. Distribution of vertical flow between model layers 54
28. Areas of assigned recharge, simulated discharge from upper model layer, and simulated
discharge from regional springs in Death Valley region 58
29. Simulated direction of ground-water flow for both upper and lower model layers in
Death Valley region 59
30. Areas of assigned recharge, simulated discharge from upper model layer, and
simulated discharge from regional springs in Colorado River region 64
31. Simulated direction of ground-water flow for both upper and lower model layers in
Colorado River region 67
32. Areas of assigned recharge, simulated discharge from upper model layer, and
simulated discharge from regional springs in Bonneville region 73
33. Simulated direction of ground-water flow for both upper and lower model layers
in Bonneville region 76
34. Areas of assigned recharge, simulated discharge from upper model layer, simulated
discharge from regional springs, and simulated direction of ground-water flow
for both upper and lower model layers in Railroad Valley region 84
35. Areas of assigned recharge, simulated discharge from upper model layer, simulated
discharge from regional springs, and simulated direction of ground-water flow
for both upper and lower model layers in upper Humboldt River region 88
TABLES
1. Estimated discharge ofregional springs, compared with simulated discharge following model
calibration 32
2. Selected statistics of estimated transmissivities in both model layers 39
3. Summary of estimated transmissivities for model cells corresponding to selected rock types
in both model layers 39
4-9. Simulated ground-water flow budgets for:
4. Death Valley region 57
5. Colorado River region 66
6. Bonneville region ' 74
7. Railroad Valley region 85
8. Upper Humboldt River region 89
9. Five deep-flow regions of modeled area 94
Contents v
CONVERSION FACTORS AND ALTITUDE DATUM
Multiply By To obtain
acre-foot (acre-ft) 0.001233 cubic hectometer
acre-foot per year (acre-ft/vr) 0.001233 cubic hectometer per year
cubic foot per second (fr/s) 0.02832 cubic meter per second
foot (ft) 0.3048 meter
foot per mile (ft/mi) 0.1894 meter per kilometer
gallon per day per foot (gal/d/ft) 0.01242 square meter per day
inch (in.) 25.40 millimeter
inch per year (in/yr) 25.40 millimeter per year
mile (mi) 1.609 kilometer
foot squared per second (ft /s) 0.0929 meter squared per second
foot squared per day (ft /d) 0.0929 meter squared per day
square mile (mi 2.590 square kilometer
)
Temperature: Degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) by using the formula
°C = 0.5556 (°F -32).
Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929,
formerly called "Sea-level Datum of 1929"), which is derived from a general adjustment of the first-order
leveling networks of the United States and Canada.
iegional Ground-Water Flow in the Carbonate-Rock Province
Conceptual Evaluation of Regional Ground-Water Flow in
the Carbonate-Rock Province of the Great Basin,
Nevada, Utah, and Adjacent States
By David E. Prudic, James R. Harrill, and Thomas J. Burbey
ABSTRACT The conceptualization and simulation of
regional ground-water flow includes several
The carbonate-rock province of the Great simplifying assumptions: Flow through fractures
Basin, mainly in eastern Nevada and western and solution openings in consolidated rocks is
Utah, is characterized by thick sequences of approximately equivalenttoflow through aporous
carbonate rocks of Paleozoic age. These rocks medium; Darcy's Law is applicable from aregion-
overlie clastic and crystalline rocks of Cambrian al perspective; steady-state conditions exist, in
and Precambrian age, respectively. Since the which estimates of present-day recharge equal
carbonate rocks were deposited, structural com- natural discharge prior to ground-water with-
pression and extension, intrusive and volcanic drawals; transmissivity is heterogeneous over the
episodes, and erosion have greatly modified their region but is homogeneous and isotropic in each
distribution and thickness, and a variety of youn- 37.5-square-mile model cell; recharge is from
ger rocks and deposits have been emplaced within precipitation in the mountain ranges and percola-
and above them. The most notable present-day tion from rivers and lakes; and discharge is by
physiographic features in the area are associated evapotranspiration, seepage to rivers and lakes,
with normal faults caused by tensional forces and flow from regional springs. Although the
during Tertiary time: The faulting has formed the assumptions are probably valid for parts of the
north- to northeast-trending mountain ranges and province, the validity of each assumption is
adjacent sedimentary basins that characterize the unknown for the province as a whole. Therefore,
terrane. The 100,000-square mile study area, with the simulation results do not completely replicate
its abundant carbonate rocks, is referred to in this actual ground-waterflow throughout the province;
report as the carbonate-rock province ofthe Great rather, the intent of the simulations is to provide
Basin. a conceptual evaluation of regional ground-water
Regional ground-water flow in the province flow.
has been studied as part of the Great Basin The model was calibrated by adjusting the
Regional Aquifer-System Analysis. The flow transmissivities of cells in both model layers and
system is conceptualized as having (1) a relatively the vertical leakance of cells between layers
shallow component, moving primarily from during repeated simulations. Calibration proceed-
mountain ranges to basin fill beneath adjacent ed until simulated water levels and simulated
valley floors, which is superimposed upon (2) a discharge as evapotranspiration and regional-
deeper component, moving primarily through spring flow generally agreed with available water
carbonate rocks. A computer model has been levels, the mapped distribution and estimated
developed to simulate and thereby evaluate the quantity of evapotranspiration, and the estimated
regional flow. Two model layers are used to flow at regional springs. Because of (1) the
simulate the two components. The layers are scarcity of available water-level data, particularly
divided into cells with dimensions of 5 miles by forthe carbonate-rock aquifers, (2) the uncertainty
7.5 miles, elongated in a north-northeastward in the extent and thickness of the carbonate-rock
direction. The maximum depth of flow in the aquifers, and (3) the uncertainty in the estimates
province is unknown, but freshwater has been of ground-water recharge and evapotranspiration,
detected at depths as great as 10,000 feet. other distributions and estimates of transmissiv-
Abstract 1
ities and vertical leakances than those calibrated In conclusion, most ground-water flow is
may also adequately simulate waterlevels and dis- relatively shallow, moving from recharge areas in
charge in the province. Nonetheless, several the mountain ranges to discharge areas in adjacent
inferences can be made regarding ground-water valleys. Directions of shallow ground-water flow
flow in the province from the model results. do not correspond everywhere to directions of
Transmissivities in the upper model layer are deep flow. Deep ground-water flow mostly
generally greater in cells corresponding to basin discharges at regional springs or in areas of
fill and carbonate rocks, and are less in cells evapotranspiration upgradient from the terminal
corresponding to other consolidated rocks (clastic, sinks (the Great Salt Lake, the Great Salt Lake
metamorphic, igneous, and volcanic). In the Desert, the Railroad Valley and Death Valley
lower layer, transmissivities are greatest near playas, and the Colorado, Virgin, and Humboldt
regional springs and in the vicinity of basins Rivers). Interbasin movement of ground water to
where ground-water discharge is considerably the larger regional springs is through permeable
more than the estimated recharge from the imme- carbonate rocks in areas where the rocks are thick
diately surrounding drainage area. and continuous; elsewhere consolidated rocks
Simulated inflow to the modeled area is beneath the valleys and surrounding mountains are
about 1.5 million acre-feet per year, which is only not highly transmissive, suggesting that not all
3 percent ofthe estimated total precipitation. This carbonate rocks are highly permeable or that not
inflow does not include recharge that is dis- all valleys and surrounding mountains are under-
charged locally (that is, within the same 37.5- lain by carbonate rocks.
square-mile model cell). Most ground-water flow
is simulated in the upper model layer; it moves
INTRODUCTION
from mountainous recharge areas to adjacent
valley lowlands where it is discharged by evapo-
transpiration. A total of 45 shallow-flow regions Ground-water flow within an area dominated by
are identified on the basis of horizontal flow basin-fill and carbonate-rock aquifers was studied as
between model cells. part of the Great Basin Regional Aquifer System
In the lower layer, simulated flow is 428,000 Analysis (RASA). The Great Basin RASA project
began in 1980 as a component of a national program
acre-feet per year, or only 28 percent of the total
designed to systematically study large aquifer systems
inflow. About half of the flow is discharged to
that constitute a major part of the Nation's water
regional springs that represent the discharge of
deep flow through carbonate rocks. A total of 17 Gsrueppalty B(HaasrirnillRaAndSAotheprrso,jec1t9,83,inp.a2d)d.itRieosnulttos otfhotshee
deep-flow subregions are identified on the basis of described in this report, include detailed studies of
horizontal flow between model cells. These ground-water flow in selected basins and analyses of
subregions are further grouped into five deep-flow regional hydrogeology and geochemistry.
regions on the basis of water-level patterns. The area of the Great Basin RASA project is
Simulated flow in the lower layer is generally about 140,000 mi and includes most of Nevada, the
southward and northward from a large, topograph- western half of Utah, and small parts of California,
ically high area in east-central Nevada and south- Oregon, Idaho, and Arizona (fig. 1). The project area
western Utah. Southward flow is toward Death is characterized by northeast-trending mountains and
Valley and the Colorado and Virgin Rivers; adjoining basins that are partly filled with sediments
northward flow is toward the Great Salt Lake derived from the mountains. Ground-waterflow in this
area is typically from recharge areas in and adjacent to
Desert and the upper Humboldt River. However,
the mountains todischargeareas in the valley lowlands.
only small quantities of deep flow are simulated
Carbonate rocks, deposited in a shallow sea during the
as discharge to the Death Valley playa, the Colo-
Paleozoic Era, underlie large areas in the eastern two-
rado and Virgin Rivers, the Humboldt River, and thirds of the Great Basin. These rocks can be highly
the Great Salt Lake Desert. Instead, most of the permeable where thick sequences are present, thereby
flow is discharged upgradient from these sinks. providing conduits for the interbasin movement of
Within the topographically high area of east- ground water (Eakin, 1966; Mifflin, 1968; Winograd
central Nevada, some deep ground water flows to and Thordarson, 1975; Gates, 1984 and 1987; and
a land-surface depression in Railroad Valley. Dettinger, 1989).
Regional Ground-Water Flow in the Carbonate-Rock Province
