Dissolved-Solids Contribution to the Colorado River 

from Public Lands in Southeastern Nevada, 

Through September 1993

By Craig L. Westenburg

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 94-4210

Prepared in cooperation with the 

BUREAU OF LAND MANAGEMENT

Carson City, Nevada 

1995
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

Any use of trade names in this publication is for descriptive purposes 

only and does not constitute endorsement by the U.S. Government.

For additional information 

write to:

District Chief

U.S. Geological Survey

333 West Nye Lane, Room 203

Carson City, NV 89706-0866

Copies of this report can be 

purchased from:

U.S. Geological Survey 

Earth Science Information Center 

Open-File Reports Section 

Box 25286, MS 517 

Denver Federal Center 

Denver, CO 80225-0046
CONTENTS

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

Introduction..............................................................................................................................................^ 1

Purpose and Scope..................................................................................................................................................... 2

Description of Study Area and Study Sites............................................................................................................... 2

Methods Used to Estimate Dissolved-Solids Concentration, Load, and Yield......................................................... 12

Estimated Dissolved-Solids Concentration, Yield, and Load............................................................................................... 15

Muddy River Subbasin.............................................................................................................................................. 15

Pahranagat Wash-White River Drainage Area............................................................................................... 15

Meadow Valley Wash Drainage Area............................................................................................................ 16

Lower Muddy River Drainage Area.............................................................................................................. 16

Estimated Annual Dissolved-Solids Discharge to the Colorado River.......................................................... 16

Comparison of Study-Period and Long-Term Data....................................................................................... 18

Las Vegas Wash Subbasin ........................................................................................................................................ 18

Estimated Annual Dissolved-Solids Discharge to the Colorado River.......................................................... 19

Comparison of Study-Period and Long-Term Data....................................................................................... 19

Other Subbasins.........................................^ 20

Estimated Annual Dissolved-Solids Discharge to the Colorado River.......................................................... 20

Comparison of Study-Period and Long-Term Data....................................................................................... 20

Estimated Annual Dissolved-Solids Yield and Load from Public Lands............................................................................. 21

Muddy River Subbasin.............................................................................................................................................. 21

Las Vegas Wash Subbasin ......................................................................................................................................... 21

Other Subbasins...................................................^ 21

Implication of Findings for Management of Dissolved-Solids Discharge from Public Lands............................................. 22

Muddy River Subbasin.............................................................................................................................................. 22

Las Vegas Wash Subbasin ......................................................................................................................................... 23

Other Subbasins......................................................................^ 23

Summary..............................................................................._ 24

References Cited................................................................................................................................................................... 25

FIGURES

1. Map showing location of public lands, drainage areas, study sites, and streams tributary

to Colorado River in southeastern Nevada............................................................................................................ 4

2-3. Graphs showing average streamflow for 1989-93 at study sites in:

2. Muddy River subbasin....................................................................................................................................... 6

3. Las Vegas Wash subbasin.................................................................................................................................. 8

4-6. Graphs showing:

4. Annual average streamflow at four study sites with long-term record.............................................................. 10

5. Relation between specific conductance and dissolved-solids concentration for water 

samples collected at study sites ......................................................................................................................... 13

6. Annual average dissolved-solids load at four study sites, 1989-93 .................................................................. 16

TABLES

1. Area of subbasins in study area, of subbasins upstream from study sites, and of public lands

within subbasins.................................................................................................................................................... 3

2. Annual average streamflow, specific conductance, dissolved-solids concentration, and

dissolved-solids load at selected study sites.......................................................................................................... 7

3. Data on drainage area, streamflow, and dissolved solids at study sites.........................;....................................... 9

4. Summary of average annual dissolved-solids yield, load, and discharge for drainage areas

and subbasins......................................................................................................................................................... 17

CONTENTS III
CONVERSION FACTORS AND ABBREVIATED WATER-QUALITY UNITS

Multiply

acre

acre-foot (acre-ft)

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

cubic foot per second (ft3/s)

mile (mi)

square mile (mi2)

ton

ton per square mile (ton/mi2)

ton per year (ton/yr)

By

4,047

1,233

1,233

0.02832

1.609

2.590

0.9072

0.3503

0.9072

To obtain

square meter

cubic meter

cubic meter per year

cubic meter per second

kilometer

square kilometer

tonne

tonne per square kilometer

tonne per year

Temperature: Degrees Celsius (°C) can be converted to degrees Fahrenheit (°F) by using the formula °F = [1.8(°C)]+32.

Water-quality units used in this report:

mg/L milligram per liter

(iS/cm microsiemens per centimeter at 25 degrees Celsius

IV CONTENTS
Dissolved-Solids Contribution to the Colorado River 

from Public Lands in Southeastern Nevada, 

Through September 1993

ByCraig L. Westenburg

ABSTRACT

The Bureau of Land Management administers about 9,300 square miles of public lands in 

southeastern Nevada that are part of the Colorado 

River Basin. About 6,200 square miles of public 

lands are in the Muddy River subbasin in Nevada. 

The estimated average dissolved-solids load contributed to the Colorado River from those lands 

was 28,000 tons per year from October 1988 

through September 1993. Subsurface flow contributed about 86 percent (24,000 tons per year) of that 

load.

About 730 square miles of public lands 

in the Las Vegas Wash subbasin contribute 

dissolved-solids load to the Colorado River. 

(About 120 square miles of public lands do not 

contribute to the river.) The estimated average 

dissolved-solids load contributed to the river from 

those lands was about 1,300 tons per year from 

October 1988 through September 1993. Subsurface flow contributed almost all of that load.

About 1,100 square miles of public lands are 

in the Virgin River subbasin in Nevada. The estimated average dissolved-solids load contributed to 

the Colorado River from Nevada public lands in 

the subbasin was 8,700 tons per year. Subsurface 

flow contributed almost the entire load.

About 1,200 square miles of Nevada public 

lands are in ephemeral tributaries that drain 

directly to the Colorado River or its impoundments (Lake Mead and Lake Mohave). The estimated average dissolved-solids load contributed to 

the river from those lands was 50 tons per year 

from surface runoff; however, the dissolved-solids 

load contributed by subsurface flow was not estimated.

From October 1992 through September 

1993, the Colorado River carried about 6,600,000 

tons of dissolved solids past a streamflow gaging 

station 0.3 mile downstream from Hoover Dam. 

In contrast, surface runoff and subsurface flow 

contribute an estimated average dissolved-solids 

load of 38,000 tons per year from public lands in 

southeastern Nevada to the Colorado River. Landmanagement practices probably would not substantially reduce this contribution.

INTRODUCTION

The Colorado River provides municipal and 

industrial water for more than 18 million people in 

seven states and irrigation water to more than 1.7 

million acres of land (U.S. Department of the Interior, 

1991, p. S-l). The dissolved-solids load (salt load) of 

the Colorado River is a concern in the United States 

and the Republic of Mexico. For example, from 

October 1992 through September 1993, the Colorado 

River carried about 6,600,000 tons of dissolved solids 

in about 7,000,000 acre-ft of water (average dissolvedsolids concentration of 690 mg/L and average streamflow of 9,700 ft3/s) past a streamflow gaging station 0.3 

mi downstream from Hoover Dam (U.S. Geological 

Survey, 1994, p. 94-95).

Public Laws 93-320 and 98-569 authorize the 

Secretaries of the Department of the Interior and the 

Department of Agriculture to enhance and protect the 

quality of water in the Colorado River for use in the 

United States and the Republic of Mexico (U.S. 

Department of the Interior, 1991, p. S-l). Public Law 

98-569 directs the Secretary of the Interior to develop a 

comprehensive program for minimizing dissolvedsolids contributions to the Colorado River from lands 

administered by the Bureau of Land Management (U.S. 

Department of the Interior, 1991, p. S-l and 52).

ABSTRACT 1
The Bureau of Land Management (BLM) administers about 75 percent (table 1) of lands in the Nevada 

part of the Colorado River Basin. Lands administered 

by BLM are herein referred to as public lands. In the 

Colorado River Basin of southeastern Nevada, about 

6,200 mi2 of public lands are in the Muddy River subbasin, about 850 mi are in the Las Vegas Wash subbasin, about 1,100 mi2 are in the Virgin River subbasin, 

and about 1,200 mi are drained by ephemeral tributaries to the Colorado River (table 1).

Municipal, industrial, and agricultural water uses 

downstream from public lands in the Muddy River and 

Las Vegas Wash subbasins are potential sources of 

dissolved-solids load. Data available prior to 1988 for 

the two subbasins were generally for locations downstream from all potential sources of dissolved solids 

and were insufficient to estimate dissolved-solids contributions from public lands only.

The U.S. Geological Survey (USGS), in cooperation with BLM, began a 5-year program in October 

1988 to assess the contribution of dissolved solids from 

public lands in the Colorado River Basin of southeastern Nevada. Four study sites were established in 

calendar year 1988 as part of this study one each on 

Pahranagat Wash, Muddy River, Meadow Valley Wash, 

and Las Vegas Wash (fig. 1) and data were collected 

through September 1993. Selected data collected at 

these sites through September 1991 are listed by 

Gortsema (1993). The streamflow, specific-conductance, and dissolved-solids data collected from October 

1988 to September 1993 are in annual reports by the 

U.S. Geological Survey (1990-94). In addition to data 

from these four sites, data from other sites were used in 

the assessment.

The data are reported herein by water year, 

which is the 12-month period from October 1 to 

September 30, designated by the calendar year in 

which it ends.

Purpose and Scope

The purpose of this report is to present an assessment of dissolved solids contributed from Nevada public lands drained by the Muddy River, Las Vegas Wash, 

Virgin River, and ephemeral tributaries, and the consequent dissolved-solids discharge to the Colorado River 

and its impoundments (Lake Mead and Lake Mohave).

The average annual dissolved-solids load from these 

subbasins and the average annual dissolved-solids load 

contributed from public lands in the subbasins are summarized.

The annual dissolved-solids discharge to the 

Colorado River for the study period (water years 1989- 

93) is compared with available long-term data to determine whether the assessment can be extended over a 

longer period. The surface runoff and subsurface flow 

components of the annual dissolved-solids contributions are discussed.

With adequate environmental information, 

sources of dissolved solids probably could be identified, and the need for salinity control in future land-use 

planning evaluated. The identification of specific 

sources of dissolved solids was not within the scope of 

this report. Sufficient data were collected, however, to 

provide a basis for more detailed identification of 

sources of dissolved solids on public lands if further 

evaluation becomes necessary.

Description of Study Area and Study Sites

The area of study discussed herein includes the 

following subbasins of the Colorado River Basin in 

Nevada: the entire Las Vegas Wash subbasin and the 

Nevada parts of the Muddy River subbasin, the Virgin 

River subbasin, and the ephemeral tributaries that drain 

to the river and its impoundments (fig. 1).

The Muddy River subbasin, which is drained by 

the Muddy River, is divided into three drainage areas: 

Pahranagat Wash-White River, Meadow Valley Wash, 

and lower Muddy River (table 1, fig. 1). Three sites 

established as part of this study (Pahranagat Wash near 

Moapa, Muddy River near Moapa, and Meadow Valley 

Wash near Rox) in addition to the site on the Muddy 

River above Lake Mead near Overton constitute the 

study sites in the Muddy River subbasin (fig. 1). The 

Pahranagat Wash-White River drainage area consists 

of the White River, Pahranagat Wash, and their ephemeral tributaries within the drainage area. The Meadow 

Valley Wash drainage area consists of Meadow Valley 

Wash and its ephemeral tributaries upstream from the 

confluence with Muddy River. The lower Muddy River 

drainage area consists of the Muddy River and its 

ephemeral tributaries downstream from Pahranagat 

Wash and Meadow Valley Wash.

Dissolved-Solids Contribution to the Colorado River from Public Lands in Southeastern Nevada, Through September 1993
Table 1. Area of subbasins in study area, of subbasins upstream from study sites, and of public lands within subbasins

[Symbol: --, not applicable for specific designation]

_ . . . . . . .. . .. . /IJA ,1 Entire subbasin upstream Subbasins and hydrographlc areas in Nevada (HA)1 . .

Designation

Nevada part of Colorado River Basin

Muddy River subbasin

Pahranagat Wash- White River drainage area

Kane Springs Valley (HA 206)

White River Valley (HA 207)

Pahroc Valley (HA 208)

Pahranagat Valley (HA 209)

Coyote Spring Valley (HA 210)

Muddy River Springs area (HA 219)

Meadow Valley Wash drainage area

Dry Valley (HA 198)

Rose Valley (HA 199)

Eagle Valley (HA 200)

Spring Valley (HA 201)

Patterson Valley (HA 202)

Panaca Valley (HA 203)

Clover Valley (HA 204)

Lower Meadow Valley Wash (HA 205)

Lower Muddy River drainage area

Garnet Valley (HA 216)8

Hidden Valley (HA 217)8

California Wash (HA 21 8)

Lower Moapa Valley (HA 220)

Las Vegas Wash subbasin

Three Lakes Valley (HA 21 1)8

Las Vegas Valley (HA 21 2)

Other subbasins

Virgin River subbasin (HA 221, 222)

Ephemeral tributaries (HA 213-215, 223, 224)

Total area Area Percentage of 

(square (square » 

miles) miles)

12,371

37,225 47,230 100

3,865 5 3,830 99

234

1,607

508

768

657

91

32,559 62,384 93

3 113

12

52

3287

418

334

3 364

979

801

156

80

313

252

1,875 9 1,829 98

311

1,564

n l,099 125,980

U 2,172

Public lands In Nevada part of 

subbasin

Area2 

(square 

miles)

9,300

6,200

3,200

2,400

7560

10850

13 1,100

1,200

Percentage of 

total area

75

86

83

94

70

45

100

55

1 Hydrographic-area numbers, names, and areas from Rush (1968a).

2 U.S. Geological Survey digital data base, 1:750,000,1994, rounded to two significant figures. Areas include Nevada parts of subbasins only.

3 Nevada part of area only. About 5 square miles additional area of Muddy River subbasin are in Utah.

4 Muddy River above Lake Mead near Overton; includes Utah part of subbasin; approximate area (Robert E. Bostic, U.S. Geological Survey, oral commun., 

1994).

5 Paharangat Wash near Moapa (Robert E. Bostic, written commun., 1994).

6 Meadow Valley Wash near Rox (U.S. Geological Survey, 1994, p. 69).

7 Approximately 130 square miles of public lands are in noncontributing hydrographic areas; approximately 430 square miles of public lands contribute to 

Colorado River.

8 Noncontributing part of Colorado River Basin.

9 Las Vegas Wash near Henderson; includes 1,518 square miles that contribute directly to surface runoff (U.S. Geological Survey, 1993, p. 89), plus noncontributing Three Lakes Valley.

1 Approximately 120 square miles of public lands are in noncontributing hydrographic area; approximately 730 square miles of public lands contribute to 

Colorado River.

1 1 Nevada part of area only.

12 Virgin River above Halfway Wash near Riverside (U.S. Geological Survey, 1994, p. xii).

13 All but about 40 square miles in Nevada part of subbasin are public lands.

INTRODUCTION
115

114°

EXPLANATION

mm Public lands managed by Bureau of Land 

Management

r7i Ephemeral tributary area

Boundary of Colorado River Basin

.. Boundary between subbasins

Boundary between hydrographic areas 

within subbasin Numbers and names 

from Rush (1968a)

198 Dry Valley

199 Rose Valley

200 Eagle Valley201 Spring Valley202 Patterson Valley203 Panaca Valley204 Clover Valley

205 Lower Meadow Valley Wash206 Kanes Springs Valley207 White River Valley208 Pahroc Valley209 Pahranagat Valley210 Coyote Springs Valley

211 Three Lakes Valley212 Las Vegas Valley213 Colorado Valley 214PiuteValley215 Black Mountains Area216 Garnet Valley217 Hidden Valley218 California Valley

219 Muddy River Springs Area220 Lower Moapa Valley221 Tule Desert222 Virgin River Valley

223 Gold Butte Area224 Greasewood Basin

Nye County 

Lincoln County

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INTRODUCTION
The Pahranagat Wash study site (Pahranagat 

Wash near Moapa) is about 9 mi northwest of Moapa 

(fig. 1). Ephemeral runoff in Pahranagat Wash, a narrow channel that connects the lower part of the White 

River to the upper part of the Muddy River, flows past 

the gage. This study site is upstream from agricultural 

development. The drainage area upstream from the site 

is about 3,830 mi2 (Robert E. Bostic, U.S. Geological 

Survey, written commun., 1994), and the Pahranagat 

Wash-White River drainage area is about 3,865 mi2 

(table 1), all within Nevada. For water years 1990-93, 

annual streamflow averaged 0.92 ft3/s (table 2) and 

ranged from 0.21 ft3/s for 1992 to 1.5 ft3/s for 1991 and 

1993 (fig. 2).

The Muddy River study site near Moapa is about 

5 mi northwest of Moapa and 4 mi southeast and downstream from the Pahranagat Wash study site (fig. 1). 

(Intermittent surface runoff in Pahranagat Wash may 

not reach the Muddy River near Moapa except during 

infrequent periods of high flow.) The average annual 

streamflow of about 43 ft /s, for water years 1913-93 as 

reported by the USGS (1994, p. 65), includes a diversion of 3.5 ft /s upstream from the site during water 

years 1975-77 for cooling water at a power generation 

facility. The diversion began in 1975 and continued at 

least through 1993; however, for water years 1977-93, 

the streamflow records do not include that diversion. 

For water years 1989-93, the annual streamflow averaged 37 fr/s (table 2) and ranged from 34 ft3/s for 1989 

to 40 ft3/s for 1993 (fig. 2).

Streamflow at the Muddy River study site near 

Moapa is primarily from subsurface flow discharging 

at numerous springs upstream from the site. Water discharging from the springs is thought to be a mixture of 

water recharged from the White River flow system (40 

percent), the Sheep Range (38 percent), and the southern Meadow Valley Wash flow system (22 percent), on 

the basis of stable-isotope composition (Thomas and 

Welch, in press). The White River flow system includes 

the northern part of the Pahranagat Wash-White River 

drainage area. The Sheep Range borders the southwest 

side of the Pahranagat Wash-White River drainage 

area.

Some surface runoff contributes to the streamflow at the study site and may increase the average 

streamflow for some years (see 1993 in table 2). The 

long-term average streamflow, however, is probably 

increased only slightly by surface runoff. For the purposes of this report, all flow at the Muddy River study 

site is considered subsurface flow.

O

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Pahranagat Wash near Moapa 

 Average, 1990-93 (period 

of water-quality record)

Muddy River near Moapa 

_ _ Average , 1989-93

Meadow Valley Wash near Rox

 Average , 1989-93

Muddy River above Lake Mead

near Overton 

... Average , 1989-93

1989 1990 1991 1992 

WATER YEAR

1993

Figure 2. Average streamflow at study sites in Muddy River 

subbasin, Nevada, 1989-93.

The Meadow Valley Wash study site (Meadow 

Valley Wash near Rox) is about 14 mi north of Moapa 

(fig. 1) and is upstream from agricultural development. 

Streamflow is perennial at the site, but it is intermittent 

in some upstream and downstream reaches of the wash. 

Streamflow infiltrates about 3 mi downstream, and only 

during extreme snowmelt runoff or intense storms does 

surface runoff reach the Muddy River. Streamflow at 

Meadow Valley Wash near Rox is a combination of discharge from a spring several miles upstream from the 

site and surface runoff. However, all streamflow at the 

study site is assumed to be surface runoff for this report. 

Most of the surface runoff from the Meadow Valley 

Wash subbasin flows past this site. The drainage area

6 Dissolved-Sollds Contribution to the Colorado River from Public Lands In Southeastern Nevada, Through September 1993
Table 2. Annual average streamflow, specific conductance, dissolved-solids concentration, and dissolved-solids 

load at selected study sites in Nevada

[Values rounded to two significant figures. Abbreviations and symbol: ft3/s, cubic feet per second; mg/L, milligrams per liter; nS/cm, 

microsiemens per centimeter at 25 degrees Celsius; , data not available]

Streamflow

Water year ^ Average Number of

(ftVs) days of flow

Specific conductance

Average 

(nS/cm)

Number of 

days of cor 

record

Average 

lissolvedsollds 

icentration 

(mg/L)

Average 

dissolvedsolids load 3 

2 (tons per 

year)

Pahranagat Wash near Moapa

[average dissolved-solids concentration = (0.464)(average specific conductance)+50]

1989

1990

1991

1992

1993

Average, 1990-93

Muddy River near Moapa

0.01

.47

1.5

.21

1.5

.92

[average dissolved-solids concentration

1989

1990

1991

1992

1993

Average, 1989-93

34

37

36

36

40

37

1

7

11

9

13

230

240

220

210

220

0

4

11

9

13

160

160

150

150

160

Not determined

74

240

31

220

140

= (0.680)(average specific conductance)-46]

365

365

365

366

365

990

1,000

1,000

1,000

1,000

1,000

148

270

285

293

96

630

630

630

630

630

630

21,000

23,000

22,000

22,000

25,000

23,000

Meadow Valley Wash near Rox

[average dissolved-solids concentration

1989

1990

1991

1992

1993

Average, 1989-93

1.1

1.3

1.3

3.4

11

3.6

= (0.736)(average specific conductance)-80]

365

365

365

366

365

1,500

1,500

1,500

4 1,400

1,500

1,500

329

336

308

261

341

1,000

1,000

1,000

950

1,000

990

1,100

1,300

1,300

3,200

11,000

3,600

Las Vegas Wash above detention basin near North Las Vegas

[average dissolved-solids concentration

1989

1990

1991

1992

1993

Average, 1990, 1992-93

0.018

.011

.008

.020

.023

.018

= (0.633)(average specific conductance)-8.3]

3

4

4

6

4

._

160

170

110

150

0

2

0

6

2

._

93

100

61

85

Not determined

1.0

Not determined

2.0

1.4

1.5

1 Water year begins October 1, ends September 30, and is designated by calendar year in which it ends.

2 Computed from annual average specific conductance, using regression equation shown in brackets after each site name.

3 Average dissolved-solids load = (average dissolved-solids concentration)(average streamflow)(0.985).

4 For purposes of this report, 82 of 105 missing daily specific-conductance values were estimated using regression equation: 

specific conductance = (streamflow)(602)+904; ^=0.65. This equation was developed for flows ranging from 0.56 to 1.6 ftVs.

INTRODUCTION
*J

upstream from the study site is 2,384 mi (U.S. 

Geological Survey, 1994, p. 69), and the overall 

Meadow Valley Wash drainage area in Nevada is 2,559 

mi2 (table 1). About 5 mi2 of the Meadow Valley Wash 

drainage is in Utah. For water years 1989-93, annual 

streamflow averaged 3.6 ft3/s (table 2), and ranged 

from 1.1 ft3/s for 1989 to 11 ft3/s for 1993 (fig. 2).

The Muddy River study site above Lake Mead, 

about 1.9 mi southeast of Overton, is near the mouth of 

the Muddy River, which flows into Lake Mead (an 

impoundment of the Colorado River). Most surface 

runoff from the Muddy River subbasin flows past the 

site. The drainage area for the study site is about 

7,230 mi2 (Robert E. Bostic, U.S. Geological Survey, 

written commun., 1994), including about 5 mi in 

Utah. About 7,225 mi2 of the Muddy River subbasin is 

in Nevada (table 1). For water years 1979-93, annual 

streamflow averaged 9.2 ft3/s; for 1989-93, annual 

streamflow averaged 10 ft /s (table 3).

The annual average streamflows in the Muddy 

River near Moapa (water years 1977-93) and in the 

Muddy River above Lake Mead near Overton (water 

years 1979-93) are shown in figure 4. Average annual 

streamflow near Moapa (water years 1977-93) was 

about four times greater than at Overton (water years 

1979-93).

The Las Vegas Wash subbasin is drained by Las 

Vegas Wash (fig. 1). The study sites in the Las Vegas 

Wash subbasin are Las Vegas Wash above detention 

basin (flood control) near North Las Vegas and Las 

Vegas Wash near Henderson.

The Las Vegas Wash study site near North Las 

Vegas (fig. 1) is upstream from urban development. 

Streamflow is ephemeral, and small flows may be contained in a manmade flood detention basin about 1/2 mi 

downstream from the site. Larger streamflows reach 

and pass through the detention-basin outlet. For water 

years 1989-93, annual streamflow averaged 0.016 ft3/s 

and ranged from 0.008 ft3/s for 1991 to 0.023 ft3/s for 

1993 (fig. 3).

The Las Vegas Wash study site near Henderson is 

about 6.0 mi upstream from Lake Mead and 3.5 mi 

north of Henderson, and includes surface runoff, subsurface return flows from urban landscape irrigation, 

and treated sewage effluent from the urbanized parts of 

Las Vegas Valley. The drainage area upstream from the

study site is about 1,829 mi2 (table 1; U.S. Geological 

Survey, 1993, p. 89), all within Nevada. For water 

years 1977-92, annual streamflow averaged 110 ft /s 

and for water years 1989-92, annual streamflow o

averaged 150 ft /s (table 3), reflecting a continuous 

trend in increasing surface returns from the expanding 

urban areas. The annual average stream-flows in Las 

Vegas Wash near Henderson (water years 1977-93), 

shown in figure 4, are based on continuous streamflow 

data from 1977 to 1988 and periodic streamflow 

measurements or estimates from 1989 to 1992 (U.S. 

Geological Survey, 1978-93). Annual dissolved-solids 

concentrations are based on periodic analysis of water 

samples. Some subsurface flow and surface runoff may 

bypass the study site, but the relatively small amount 

was disregarded for this study.

O 0.03

O 

O 

UJ <f) 

rr 0.02

UJQ_

UJ 

UJ "- 0.01 

O

m

ID O

O

UJ 

DC

C/3 

UJ 

CD 

<

DC 

UJ

0.00

200

150

100

50

Las Vegas Wash above detention basin near

North Las Vegas 

 Average, 1990,1992-93 (period of water-quality record)

Las Vegas Wash near Henderson

(no data for 1993)

 Average, 1989-92

1989 1990 1991 1992 

WATER YEAR

1993

Figure 3. Average streamflow at study sites in Las Vegas 

Wash subbasin, Nevada, 1989-93.

8 Dissolved-Sollds Contribution to the Colorado River from Public Lands in Southeastern Nevada, Through September 1993
Table 3. Data on drainage area, streamflow, and dissolved solids at study sites in Nevada

[Streamflow and dissolved-solids values rounded to two significant figures. Abbreviation and symbol: ftVs, cubic feet per second; 

--, data not available for part of period]

Study site name and 

station number1

Muddy River subbasin

Pahranagat Wash near Moapa 

(09415850)

Muddy River near Moapa 

(09416000)

Meadow Valley Wash near Rox 

(09418700)

Muddy River above Lake Mead 

near Overton (09419515)

Las Vegas Wash subbasin

Las Vegas Wash above detention 

basin near North Las Vegas 

(09419648)

Las Vegas Wash near Henderson 

(09419700)

Virgin River subbasin

Virgin River at Littlefield 

(09415000)

Virgin River above Halfway Wash 

near Riverside (09415230)

Drainage 

area 

(square 

miles)

3,830

23,820

2,384

7,230

(3)

1,829

55,090

55,980

Streamflow

Average 

annual 

(ftVs)

0.92

38 

37

3.6

9.2 

10

4.67

110 

150

300 

360

360

Period 

of 

record

1990-93

1977-93 

1989-93

1989-93

1979-93 

1989-93

1963-78

1977-92 

1989-92

1978-93 

1978-86

1978-86

Dissolved solids

Average 

annual load 

(tons per 

year)

140

23,000

3,600

21,000 

21,000

59

170,000 

210,000

560,000 

640,000

710,000

Period 

of 

record

1990-93

1989-93

1989-93

1979-93 

1989-93

1990, 

1992-93

1977-92 

1989-92

1978-93 

1978-86

1978-86

Average 

annual yield 

(tons per 

square mile)

0.036

6.0

1.5

2.9 

2.9

.045

98 

110

110 

130

120

1 Eight-digit number is used to identify each study site. For example, station number 09419700 consists of two-digit part number 

(09) followed by six-digit downstream-order number (419700). Part refers to drainage area or group of areas that is generally regional 

in extent. Records in this report are for sites in Part 09 (Colorado River Basin). Downstream-order number is assigned according to 

geographic location of station in drainage network; larger number stations are downstream from smaller number stations. All sites are in 

Nevada, except Virgin River at Littlefield, which is in Arizona.

2 Approximate area (U.S. Geological Survey, 1994, p. 65).

3 Area not determined.

4 Average streamflow is from earlier, longer term records for gaging station about 6 miles downstream from study site (station 

09419650); is thought to be more representative of flow in this reach of Las Vegas Wash (see text).

5 Includes parts of Arizona, Utah, and Nevada. .

INTRODUCTION
50

40

30

Q

Z

o 

o

UJ

w 

rr

UJ 

D_

LL. 

O

CO=) 

o

o

UJ

cc

W

UJ

10

Muddy River near Moapa 

Average, 1977-93

H Muddy River above Lake Mead near Overton

(no data for 1977,1978,1984) 

 Average, 1979-93

1977 1979 1981 1983 1985 1987 1989 1991 1993

WATER YEAR

200

175

£ 15°

< 125

=)

Z

< 100

75

50

25

i I I I I I \ \ I I I I T 

Las Vegas Wash near Henderson

Continual record (no data for 1984-85)

|__| Weekly or monthly measurement or estimate (no data for 1993) 

 Average, 1977-83, 1986-92

1977 1979 1981 1983 1985 1987 1989 1991 1993

WATER YEAR

Figure 4. Annual average streamflow for Muddy River and Las Vegas Wash, Nevada, at four study sites with 

long-term record.

10 Dissolved-Solids Contribution to the Colorado River from Public Lands in Southeastern Nevada, Through September 1993
Q

Z

o 

o

LLJ 

V)

or

HI 

D_

tD

LLJ 

LJL

O

m

ID 

o

o

ID 

Z

800

700

600

500

400

Virgin River at Littlefield, Ariz.

------ Average, 1978-86

 Average, 1978-93

LU 300 

cc

C/3

111

CJ 200

or LU 

>

100

1977 1979 1981 1983 1985 1987 1989 1991 1993

WATER YEAR

Figure 4. Continued.

The Virgin River study site at Littlefield is about 

36 mi upstream from Lake Mead and 0.4 mi upstream 

from Littlefield, Ariz. The drainage area upstream from 

the study site is about 5,090 mi2 (U.S. Geological 

Survey, 1993, p. 52), including parts of Arizona and 

Utah (table 3). Annual streamflow averaged 300 f1?/s 

for water years 1978-93 and annual streamflow 

averaged 360 ft3/s for water years 1978-86 (table 3). 

The annual average streamflows in Virgin River at 

Littlefield (water years 1978-93), shown in figure 4, are 

based on continuous streamflow data from 1978 to 

1993 (U.S. Geological Survey, 1979-94).

The Virgin River study site above Halfway Wash 

is about 8 mi upstream from Lake Mead. The drainage 

area upstream from the study site is about 5,980 mi2 

(U.S. Geological Survey, 1994, p. xii). For water years 

197 8-86,'periodically measured streamflow averaged 

360 ft3/s (table 3; U.S. Geological Survey, 1979-88).

Ephemeral tributaries in Nevada that drain to the 

Colorado River and its impoundments lie within the 

following hydrographic areas (fig. 1): Colorado Valley 

(area 213), Piute Valley (214), Black Mountains Area 

(215), Gold Butte Area (223), and Greasewood Basin 

(224). All but Piute Valley and Greasewood Basin 

drain directly to the river or its impoundments in 

Nevada. In contrast, surface runoff and subsurface flow 

in Piute Valley drain southward into California before 

reaching the river; in Greasewood Basin, the runoff and 

subsurface flow drain eastward into Arizona before 

reaching the river. This report deals only with the 

Nevada parts of the two hydrographic areas. However, 

the dissolved-solids loads generated in Nevada are 

assumed to ultimately reach the river in California and 

Arizona, respectively.

INTRODUCTION 11
Ranges in recorded streamflow and specific conductance at the four sites that were established as part 

of this study are listed below for the overall periods 

during which specific-conductance data are available.

[Abbreviations: e, estimated; |O.S/cm, microsiemens per centimeter at 25 

degrees Celsius]

Streamflow 

(cubic feet 

per second)

Specific

conductance

(jaS/cm)

Study Site 

(water years)

Maximum 

instantaneous

Minimum 

daily

Maximum Minimum 

recorded recorded

Pahranagat Wash 

near Moapa 

(1990-93)

Muddy River 

near Moapa 

(1989-93)

Meadow Valley 

Wash near Rox 

(1989-93)

Las Vegas Wash 

above detention 

basin near North 

Las Vegas 

(1990, 1992-93)

e3,350 0.00

e5,760 26

el,620

e278

.14

.00

550

1,490

7,460

286

109

496

204

79

Methods Used to Estimate Dissolved-Solids 

Concentration, Load, and Yield

Annual dissolved-solids concentrations can be 

estimated from measurements of specific conductance 

and dissolved-solids concentration of periodically collected samples. Conductance is the ability of a solution 

to conduct an electrical current due to the presence of 

dissolved, ionized constituents. As the concentration 

of dissolved constituents increases, the conductance of 

the solution also increases. The specific-conductance 

measurement, therefore, is an approximate measure of 

the dissolved-solids concentration (Hem, 1985, p. 66- 

69).

Water samples were collected intermittently at 

Pahranagat Wash near Moapa, Muddy River near 

Moapa, Meadow Valley Wash near Rox, and Las 

Vegas Wash near North Las Vegas and analyzed for 

dissolved-solids concentration, determined by residue 

upon evaporation at 180°C, at the USGS National 

Water-Quality Laboratory in Arvada, Colo. Specific 

conductance of the sample also was measured at the

laboratory. Streamflow data and specific-conductance 

data were recorded half-hourly at Pahranagat Wash 

near Moapa and Las Vegas Wash near North Las Vegas 

and hourly at Muddy River near Moapa and Meadow 

Valley Wash near Rox (Gortsema, 1993, p. 2). Specific 

conductance was not recorded for 1989 at Pahranagat 

Wash near Moapa and for 1989 and 1991 at Las Vegas 

Wash near North Las Vegas, and thus, dissolved-solids 

concentration could not be computed for those years.

Measurements of specific conductance and 

dissolved-solids concentration were plotted for 

Pahranagat Wash near Moapa, Muddy River near 

Moapa, Meadow Valley Wash near Rox, and Las Vegas 

Wash near North Las Vegas to establish a regression 

line for each site. Specific conductance was plotted as 

the independent variable and dissolved-solids concentration as the dependent variable (fig. 5). An 

equation for each of the simple-regression lines was 

developed, which predicts a dissolved-solids concentration for a given specific-conductance measurement. The regression equations (shown in table 2) 

were then used to compute the annual average 

dissolved-solids concentration from the annual average 

specific conductance, which was determined from the 

continual specific-conductance record. The variance 

between the observed and predicted dissolved-solids 

concentration also was plotted to determine if the 

observed values were reasonably close to the predicted 

values. For the most part they were, which provides 

confidence in the use of simple-regression equations.

The annual average dissolved-solids load was 

computed for each year that average specific conductance and average streamflow data were available 

for Pahranagat Wash near Moapa, Muddy River near 

Moapa, Meadow Valley Wash near Rox, and Las Vegas 

Wash near North Las Vegas. The annual dissolvedsolids loads for each site were averaged to compute the 

average annual dissolved-solids load.

The average annual dissolved-solids yield (tons 

per square mile) was computed by dividing the average 

annual dissolved-solids load (tons per year) by the area 

upstream from the study site (square miles). This yield 

is assumed to represent the average annual yield for the 

entire drainage area and public lands within the drainage area, though it may not apply to small areas within 

the drainage area. Most values of loads and yields are 

rounded to two significant figures (a few are rounded to

12 Dissolved-Sollds Contribution to the Colorado River from Public Lands in Southeastern Nevada, Through September 1993
DC 

LLJ 

H

_J

DC 

LJJ 

CL

DC 

CD

O

<

DC

LJJ 

O 

Z 

O 

O 

COQ

_i

O 

COI

Q 

LJJ

O 

CO 

CO

Q

300

250

200

150

100

50

Pahranagat Wash near Moapa

D=(0.464S)+50 

1^=0.93

100 200 300 400 500

1,000

800

600

400

200

Muddy River near Moapa

D=(0.680S)-46 

^=0.91

600 800 1,000 1,200 1,400

SPECIFIC CONDUCTANCE (S), IN MICROSIEMENS PER CENTIMETER AT

25 DEGREES CELSIUS

Figure 5. Relation between specific conductance and dissolved-solids concentrations for water samples collected at 

study sites in Nevada. Symbol: r2, statistical coefficient indicating decimal percentage of total variation in dissolved 

solids that can be attributed to relation with specific conductance.

INTRODUCTION 13
ooc

CO

toc

(D

cn

O o

CD 

Q.

DISSOLVED-SOLIDS CONCENTRATION (D), IN MILLIGRAMS PER LI

05 

TJ m

33 Om

m m

33

cn o

o o

cn o

IV)

o o

o 

o o

o 

o o

cn o

o o

05 

TJ

m 

O 

nn 

O 

O 

O 

z: D

C O2

01 - 

D 05

33 *-

m ^ _^

m F; ^ CO t ) O

05 m

05

IV)

o o

ro

cn o
only one significant figure) because of measurement 

inaccuracies inherent in all hydrological data collection. Significant figures cited from references, however, are retained.

Water samples from Muddy River above Lake 

Mead near Overton have been analyzed periodically 

for dissolved-solids concentrations since 1979. Average annual dissolved-solids concentrations were computed for water years 1979-93 and 1989-93.

Water samples from Las Vegas Wash near 

Henderson were analyzed for dissolved-solids concentrations from 1970 to 1985. In addition, 327 field 

measurements of specific conductance are available for 

1970 to 1992, when data collection ceased. The field 

specific-conductance values were plotted against the 

dissolved-solids concentrations for 1970-85 to show 

their relation and develop a regression equation. 

Dissolved-solids concentrations were then computed 

from the field measurements of specific conductance 

for 1986-92, when only specific-conductance data were 

available. Average annual concentrations were 

computed for 1977-92 and 1989-92 (to approximately 

correspond to period of data available for the Muddy 

River and study period).

Water samples from Virgin River at Littlefield 

have been analyzed periodically for dissolved-solids 

concentrations since 1949. During water years 1978- 

93, dissolved-solids concentrations of water samples 

were determined from residue on evaporation at 180°C 

(ROE at 180°C). Average dissolved-solids concentrations (ROE at 180°C) were computed for water years 

1978-93 and 1978-86 (to correspond with the period of 

data availability for the Virgin River above Halfway 

Wash near Riverside).

Water samples from Virgin River above Halfway 

Wash near Riverside were analyzed periodically for 

dissolved-solids concentrations during water years 

1978-86. Average dissolved-solids concentrations 

were computed for the same period.

The dissolved-solids load, expressed in terms of 

tons per year in this report, was computed by using the 

equation: average dissolved-solids load, in tons per 

year=(average dissolved-solids concentration, in milligrams per liter)(average streamflow, in cubic feet per 

second)0.985.

ESTIMATED DISSOLVED-SOLIDS 

CONCENTRATION, YIELD, AND LOAD

Muddy River Subbasin

Pahranagat Wash-White River Drainage Area

For water years 1990-93, the estimated annual 

dissolved-solids concentration averaged 160 mg/L and 

ranged from 150 mg/L in 1992 and 1993 to 160 mg/L 

in 1990 and 1991 (table 2) for surface runoff at the 

Pahranagat Wash study site. Dissolved-solids load 

averaged 140 tons/yr for water years 1990-93 (table 2) 

and ranged from 31 tons in 1992 to 240 tons in 1991 

(fig. 6). The average annual dissolved-solids yield was 

about 0.036 ton/mi2 (table 4). The yield was applied to 

the entire Pahranagat Wash-White River drainage area 

to determine the average dissolved-solids load of 140 

tons/yr (table 4).

As was mentioned in the section "Description of 

Study Area and Study Sites," streamflow at the Muddy 

River study site near Moapa is thought to be a mixture 

of subsurface flow from the Pahranagat Wash-White 

River and Meadow Valley Wash drainage areas. On the 

basis of the contributions to springflow only, 78 percent or 18,000 tons/yr of the load for Muddy River near 

Moapa (total, 23,000 tons/yr; table 3) may originate in 

the Pahranagat Wash-White River drainage area (table 

4). 1

Combined surface runoff and subsurface flow 

contributed an estimated total of 18,000 tons/yr 

(rounded) of dissolved-solids from the Pahranagat 

Wash-White River drainage area.

Recharge in the White River flow system and recharge 

from the Sheep Range are thought to contribute about 40 percent 

and 38 percent, respectively, of the total springflow. Recharge in 

the Meadow Valley Wash drainage area is thought to contribute 

about 22 percent of the total springflow, on the basis of stableisotope composition (Thomas and Welch, in press). These 

percentages, as applied to dissolved-solids load, assume that the 

ground-water contribution from each recharge area has about the 

same dissolved-solids concentration. The validity of this 

assumption is unknown, given the lack of available data on 

ground-water quality.

ESTIMATED DISSOLVED-SOLIDS CONCENTRATION, YIELD, AND LOAD 15
DC 

LLI 

Q.

(f)

o

a 

< 

o

in

9

o

°?

a

UJ

>

O

C/D 

</)

a

LLI

(D

<

rr

LU

D 

Z 

Z 

<

400

300

200

100

0

40,000

30,000

20,000

10,000

0

12,000

10,000

8,000

6,000

4,000

2,000

0

4

3

2

Pahranagat Wash near Moapa 

(no data for 1989) 

 Average, 1990-93

11111111

|:|SJfi| S ftij ftijijij - - - -

SiS&SSSliS&S

xl:*:*:;:;:*:t;f!::::!±'::::::

-

Mu ddy River near Moapa 

-Average, 1989-93

§:5:-85SW:W&: 3:5i§:5:?: : £?:£ :88 ?:&:&:& ': 

¥:¥SSS:::o:;:¥:i: :::::?: : : : :: :' $$£ :W:|: |:|:|: ¥ : : :$$ 

. Meadow Valley Wash near Rox 

 Average, 1989-93

:wmtefv<kxmmm3mmmm

:8§&?:888§8

iiilliili -

Las Vegas Wash above detention basin near 

North Las Vegas 

(no data for 1989, 1991) 

- - Average, 1990, 1992-93

_ _ _ _

x:j:|::: ::;: : : ::v:;:v:

::;:;:::::::::::::::::::::;::::::: 

:|:|:|i|:|:¥:|:|:$:|:;:j:j|:| illflll! -

1989 1990 1991 1992 1993 

WATER YEAR

Figure 6. Annual average dissolved-solids load at four 

study sites in Nevada, 1989-93.

Meadow Valley Wash Drainage Area

For water years 1989-93, the estimated annual 

dissolved-solids concentrations averaged 990 mg/L and 

ranged from 950 mg/L in 1992 to 1,000 mg/L in 1989- 

91 and 1993 (table 2) for surface runoff at the Meadow 

Valley Wash study site. Dissolved-solids load averaged 

3,600 tons/yr for water years 1989-93 (table 2) and 

ranged from 1,100 tons in 1989 to 11,000 tons in 1993 

(fig. 6). The average annual dissolved-solids yield was 

about 1.5 tons/mi2 (tables 3,4). The yield was applied 

to the entire Meadow Valley Wash drainage area to 

determine the average dissolved-solids load of 3,800 

tons/yr (table 4).

On the basis of stable-isotope data, about 22 percent (Thomas and Welch, in press) or 5,000 tons/yr of 

the dissolved-solids load for Muddy River near Moapa 

may be contributed from the Meadow Valley Wash 

drainage area (table 4). Combined surface runoff and 

subsurface flow contributed an estimated total of 8,800 

tons/yr of dissolved solids to the Muddy River subbasin 

from the Meadow Valley Wash drainage area (table 4).

Lower Muddy River Drainage Area

Additional surface runoff and subsurface flow in 

the lower Muddy River drainage area contributed dissolved solids to the dissolved-solids load of the Muddy 

River. The average annual dissolved-solids yield of 

0.04 ton/mi2, determined from data collected at the 

Pahranagat Wash study site (0.036 ton/mi2, rounded), 

was used to estimate the contribution of dissolvedsolids load of surface runoff in the lower Muddy River 

drainage area. About 565 mi2 of the lower Muddy 

River drainage area contributes 

99

to the Colorado River.

An annual yield of 0.04 ton/mi for 565 mi produces 

about 20 tons of dissolved solids from surface runoff 

(table 4). Rush (1968b, p. 26) estimated about 800 acreft/yr of subsurface flow from Garnet and Hidden 

Valleys (hydrographic areas 216 and 217, respectively) 

into the Muddy River subbasin. Data reported by Rush 

(1968b, p. 44) for wells and seeps in California Wash 

are used to determine an average dissolved-solids concentration of 1,300 mg/L. Using these values, about 

1,400 tons/yr (table 4) of dissolved solids were contributed by subsurface flow within the lower Muddy River 

drainage area. Combined surface runoff and subsurface 

flow in the lower Muddy River drainage area contributed an estimated 1,400 tons/yr (rounded) of dissolved 

solids to the Muddy River (table 4).

Estimated Annual Dissolved-Solids Discharge to 

the Colorado River

Dissolved-solids load of streamflow discharging 

to the Colorado River from the Muddy River subbasin 

averaged 21,000 tons/yr for water years 1989-93 (table 

3). For comparison, an earlier study determined 

average dissolved-solids load of 19,770 tons/yr for 

1979-83 in the Muddy River (Panian and others, 1987, 

p. 8). Rush (1968b, p. 44) lists dissolved-solids concentrations of ground-water samples from 12 sites in 

the lower Moapa Valley; the average concentration is 

1,970 mg/L.

16 Dissolved-Solids Contribution to the Colorado River from Public Lands in Southeastern Nevada, Through September 1993
Table 4. Summary of average annual dissolved-solids yield, load, and discharge for drainage areas and subbasins in Nevada

[Most dissolved-solids values rounded to two significant figures. Abbreviations: acre-ft/yr, acre-feet per year; ft /s, cubic feet per second; mg/L, milligrams per 

liter; tons/mi2, tons per square mile; tons/yr, tons per year]

Average Nevada drainage

Subbasin or drainage area

Muddy River subbasin

Pahranagat Wash- White River drainage area

Surface runoff

Subsurface flow

Total (rounded)

Meadow Valley Wash drainage area

Surface runoff

Subsurface flow

Total (rounded)

Lower Muddy River drainage area

Surface runoff

Subsurface flow (rounded)

Total (rounded)

Total surface runoff (rounded)

Total subsurface flow (rounded)

Total (rounded)

Las Vegas Wash subbasin

Surface runoff

Subsurface flow (rounded)

Total (rounded)

Other subbasins

Virgin River

Surface runoff

Subsurface flow (rounded)

Total (rounded)

Ephemeral tributaries 11

Surface runoff

Totals for Colorado River Basin

Surface runoff (rounded)

Subsurface flow (rounded)

Total (rounded)

annual .

" 1*1 /\i68

yiel contributing 

(tons to discharge 

per of dissolved 

8q"a~ solids (square 

mlle> miles)

0.036 3,865

1.5 2,559

2.04 3 565

3 6,989

50.045 6 1,564

20.04 1,099

2.04 2,172

11,824

Dissolvedsolids 

load 

(tons per 

year)

140

1 18.000

18,000

3,800

^.000

8,800

20

4 1.400

1,400

4,000

24.000

28,000

70

7 1.300

1,400

40

8.700

8,700

90

4,200

34.000

38,000

Nevada public lands

contributing 

to discharge 

of dissolved 

solids (square 

miles)

3,200

2,400

3430

3 6,000

6730

9 1,100

1,200

9,000

Dissolvedsolids 

load 

(tons per 

year)

120

18.000

18,000

3,600

5.000

8,600

20

4 1.400

1,400

3,700

24.000

28,000

33

8 1.300

1,300

40

8.700

8,700

50

3,800

34.000

38,000

Total

dissolved solids 

discharge to 

Colorado River 

(tons per year)

3,000

21.000

24,000

210,000

1.300

210,000

10710,000

120.000

830,000

90

920,000

140.000

1,100,000

1 See section "Estimated Dissolved-Solids Concentration, Yield, and Load" for explanation.

2 Yield assumed to be about the same as that for areas drained by Pahranagat Wash near Moapa and Las Vegas Wash near North Las Vegas, rounded.

3 Excludes about 236 square miles of noncontributing (surface runoff) part of drainage area (Garnet and Hidden Valleys; hydrographic areas 216 and 217, 

respectively), of which about 130 square miles are public lands.

4 Computed with data from Rush (1968b), average dissolved solids of 1,300 mg/L for wells and seeps in California Wash and estimated 800 acre-ft/yr 

subsurface discharge into California Wash from Garnet and Hidden Valleys (hydrographic areas 216 and 217, respectively); 1,400 tons/yr (rounded)=(l,300 

mg/L)(800 acre-ft/yr)(0.00136).

5 Average annual yield was determined thus: 59 tons/yr=(90 mg/L)(0.67 ft3/s)(0.985); 0.045 tons/mi2=(59 tons)/(l,300 mi2). This yield closely compares 

with that computed for Pahranagat Wash near Moapa (0.036 tons/mi2). See text section "Estimated Dissolved-Solids Concentration, Yield, and Load" for discussion of Las Vegas Wash subbasin.

6 Does not include about 311 square miles of noncontributing part of drainage from Three Lakes Valley (hydrographic area 211; Rush, 1968a), of which 

about 120 square miles are public lands.

7 Computed from dissolved-solids concentration data from Derringer (1987, tables 1 and 2) and subsurface flow under Frenchman Mountain from Morgan 

and Dettinger (1994, p. 84); 1,300 tons/yr (rounded)=(460 mg/L)(2,000 acre-ft/yr)(0.00136).

8 All subsurface flow is assumed to originate from public lands, because much of the recharge area is public land.

9 Rounded to two significant figures. All but about 40 mi2 of subbasin in Nevada are public lands.

Most of dissolved-solids load originates in Arizona and Utah. 

11 No estimate made for subsurface flow.

ESTIMATED DISSOLVED-SOLIDS CONCENTRATION, YIELD, AND LOAD 17
Subsurface flow of 1,100 acre-ft/yr (Rush, 19685, 

p. 41) was assumed to have a dissolved-solids 

concentration of 2,000 mg/L (1,970 mg/L rounded). 

Thus, an additional 3,000 tons/yr of dissolved solids 

discharged from the Muddy River subbasin to the 

Colorado River by subsurface flow. Combined surface 

runoff and subsurface flow discharged an estimated 

24,000 tons/yr (table 4) of dissolved solids to the 

Colorado River from the Muddy River subbasin.

Comparison of Study-Period and Long-Term Data

For the purposes of this report, streamflow data 

for water years 1977-93 for Muddy River near Moapa 

are considered long-term data. Some data prior to this 

period includes flow that is diverted upstream. Data for 

the period of record for Muddy River near Overton, 

water years 1979-93, are considered long-term data.

Streamflow for the 5-year study period (water 

years 1989-93) was compared with the long-term 

record for Muddy River near Moapa (water years 1977- 

93) and Muddy River above Lake Mead near Overton 

(water years 1979-93). At Muddy River near Moapa, 

the average annual streamflow for the study period, 

37 ft3/s, was only 3 percent less than the long-term 

average annual streamflow of 38 ft /s. At Muddy River 

above Lake Mead near Overton, the average annual 

streamflow for the study period, 10 ft /s, was 8 percent 

more than the long-term average annual streamflow of 

9.2 ft3/s.

The average annual dissolved-solids load of the 

Muddy River above Lake Mead near Overton was 

21,000 tons/yr for both the study period, water years 

1989-93, and the long-term period, water years 1979- 

93 (table 3). Specific conductance for Muddy River 

near Moapa was reported as 1,090 jiS/cm by Eakin 

(1964, p. 28) and as 940 to 1,100 uS/cm by Bateman 

(1976, p. 21). These data are comparable to the average 

specific conductance of 1,000 uS/cm for 1989-93, indicating no appreciable overall change in dissolvedsolids concentrations.

The comparisons indicate that the dissolvedsolids load for the study period is comparable to 

dissolved-solids load in the long term. Thus, contributions of dissolved-solids load and discharge for the 

Muddy River subbasin determined by this study can 

probably be used to represent long-term values, 

provided land or water use do not change significantly 

within the area.

Las Vegas Wash Subbasin

Streamflow in Las Vegas Wash at the North Las 

Vegas study site averaged 0.016 ft3/s for water years 

1989-93 and 0.018 for the water years having specificconductance data (1990, 1992-93; table 2). This 

average is much less than the average annual streamflow of 0.67 ft3/s at the now-discontinued gaging 

station about 6 mi downstream for water years 1963-78 

(Las Vegas Wash at North Las Vegas, sta. 09419650; 

U.S. Geological Survey, 1979, p. 56). The average 

annual streamflow at the downstream gage is thought to 

be a better representation of streamflow for this general 

reach of Las Vegas Wash.

Estimated dissolved-solids concentration in 

streamflow at the study site averaged 85 mg/L for water 

years 1990 and 1992-93 (no data for 1989 and 1991) 

and ranged from 61 mg/L for 1993 to 100 mg/L for 

1992 (table 2). For streamflows less than 20 fl?/s at the 

study site, specific-conductance data indicate that the 

dissolved-solids concentration most commonly ranges 

from 80 to 95 mg/L and averages about 90 mg/L. For 

this study, the relations between streamflow and 

dissolved-solids concentration at the study site and at 

the gage about 6 mi downstream are assumed to have 

been about the same during the respective periods of 

record. However, if instead the average dissolvedsolids concentration at the former downstream gage 

were twice that of the upstream site, the resultant 

additional load would amount to less than 10 percent of 

the total from public lands for this subbasin.

An average dissolved-solids load of 59 tons/yr for 

the Las Vegas Wash study site near North Las Vegas 

(table 3) was estimated using the average annual 

streamflow of 0.67 ft3/s for the downstream gage and 

an average dissolved-solids concentration of 90 mg/L 

for the study site. An average annual yield of 0.045 

ton/mi was computed from the average dissolvedsolids load of 59 tons/yr, and 1,300 mi2 area upstream 

from the lower gage. This average annual yield of 

0.045 ton/mi is comparable to the average annual 

yield of 0.036 ton/mi estimated for the Pahranagat 

Wash study site.

This comparability of yields for the two drainage 

areas indicates that an annual yield of about 0.04 

ton/mi2 may be applicable within the study area to 

other drainages with ephemeral streamflow to estimate 

average annual dissolved-solids load.

18 Dissolved-Sollds Contribution to the Colorado River from Public Lands In Southeastern Nevada, Through September 1993
Surface runoff contributed an estimated 70 tons 

of dissolved solids annually to Las Vegas Wash, based 

on 0.045 ton/mi2 yield and 1,564 mi2 subbasin area 

(table 4). Subsurface flow from Las Vegas Wash subbasin toward the Colorado River, beneath Frenchman 

Mountain on the east side of the Las Vegas Wash 

subbasin, was estimated as about 2,000 acre-ft/yr by 

Morgan and Dettinger (1994, p. 84). Although the 

estimate was made for predevelopment conditions in 

Las Vegas Valley, it is thought to be an adequate 

approximation for current conditions as well (James R. 

Harrill, U.S. Geological Survey, oral commun., 1994). 

Data reported by Dettinger (1987, tables 1 and 4, sites 

3, 19, 20, and 47 west of Frenchman Mountain) are 

used to determine an average dissolved-solids 

concentration of 460 mg/L. Subsurface flow of about 

2,000 acre-ft/yr with a dissolved-solids concentration 

of 460 mg/L would contribute an additional 1,300 

tons/yr (rounded) of dissolved solids from the Las 

Vegas Wash subbasin. Surface runoff and subsurface 

flow contributed a combined 1,400 tons/yr (rounded) of 

dissolved solids from the Las Vegas Wash subbasin 

(table 4). The subsurface flow used to calculate 

dissolved-solids load in this report is natural flow under 

Frenchman Mountain on the northeast side of the 

valley. Surface runoff evaluated in this report is that 

resulting from precipitation.

Estimated Annual Dissolved-Solids Discharge to 

the Colorado River

Dissolved-solids load in Las Vegas Wash near 

Henderson (fig. 1) averaged 210,000 tons/yr for water 

years 1989-92 (table 3). An estimated 1,300 tons/yr of 

dissolved solids moves from the Las Vegas Wash subbasin toward the Colorado River by subsurface outflow 

(see previous paragraph). Combined surface runoff and 

subsurface flow discharged about 210,000 tons/yr 

(rounded) of dissolved solids from the Las Vegas Wash 

subbasin (table 4). For comparison, an earlier study 

determined an average dissolved-solids load of 

196,047 tons/yr for 1979-83 in Las Vegas Wash 

(Panian and others, 1987, p. 8).

Most of the dissolved-solids discharge in Las 

Vegas Wash is related to water imported from Lake 

Mead and native water pumped from the Las Vegas 

Valley ground-water system that return to the wash by 

way of urban landscape irrigation and treated sewage 

effluent. In 1991, an estimated 268,000 acre-ft of water 

was imported and an estimated 47,000 acre-ft was

pumped (Johnson, 1992). Evaluation of the dissolvedsolids load of this water is beyond the scope of this 

report.

Comparison of Study-Period and Long-Term Data

For the purposes of this report, streamflow data 

for water years 1977-92 for Las Vegas Wash near 

Henderson is considered long-term data (no data available for water year 1993). This period closely corresponds to the periods used for long-term data for study 

sites in the Muddy River subbasin.

Streamflow for the study period (water years 

1989-92) was compared with the streamflow for 

1977-92. The streamflow for the study period was 150 

ft3/s, compared with 110 ft3/s for the long-term period 

(table 3). The generally steady increase in streamflow 

in Las Vegas Wash is due to increasing water use in the 

Las Vegas Valley. The estimated average annual 

dissolved-solids load in Las Vegas Wash near 

Henderson was 210,000 tons/yr for water years 1989- 

92 and was 170,000 tons/yr for the long-term period 

1977-92 (table 3). The increase in load corresponded 

with an increase in streamflow.

Comparison of study-period and long-term data 

indicates that the average annual streamflow and 

dissolved-solids load in lower Las Vegas Wash for the 

study period are not comparable to long-term 

conditions, because of the continued expansion of 

urbanized areas in Las Vegas Valley. However, average 

streamflow at the USGS gaging station about 6 mi 

downstream from the upper study site, near North Las 

Vegas, probably is representative of long-term average 

streamflow for undeveloped areas of public lands in the 

Las Vegas Wash subbasin. The annual average 

dissolved-solids concentration of Las Vegas Wash near 

North Las Vegas was generally low, ranging from 61 

mg/L to about 100 mg/L. This low concentration of 

surface runoff from public lands probably is due to the 

short time runoff is in contact with the soil and rocks. 

Average annual dissolved-solids concentration of 

about 90 mg/L may be a rough representation of the 

dissolved-solids concentration of surface runoff in 

undeveloped areas of the Las Vegas Valley. Characterization of the effects of urbanization in Las Vegas 

Valley on changes in dissolved-solids loads to Lake 

Mead is beyond the scope of this study and report.

ESTIMATED DISSOLVED-SOLIDS CONCENTRATION, YIELD, AND LOAD 19
Other Subbasins Estimated Annual Dissolved-Solids Discharge to 

the Colorado River

Although the Virgin River subbasin was not 

studied in detail, available data were used to compute 

rough estimates of dissolved-solids contribution. An 

estimated 40 tons (rounded) of dissolved solids in 

surface runoff may be contributed annually to the

/^

Virgin River in Nevada, on the basis of 0.04 ton/mi

/^

annual yield (see p. 20) and 1,099 mi subbasin area. 

Subsurface flow into the Lower Virgin River Valley of 

Nevada was estimated as 2,900 acre-ft/yr (Glancy and 

Van Denburgh, 1969, p. 51, 54). Water-quality data for 

samples from 16 wells along the Virgin River (Glancy 

and Van Denburgh, 1969, table 17) are used to 

determine an average dissolved-solids concentration of 

2,200 mg/L for subsurface flow. This concentration 

compares closely with the average concentration of 

dissolved solids in the Virgin River above Halfway 

Wash near Riverside (2,000 mg/L) for the period of 

record there (water years 1978-86). Subsurface flow of 

2,900 acre-ft/yr with a dissolved-solids concentration 

of 2,200 mg/L contributes an estimated 8,700 tons/yr 

(rounded; table 4) of dissolved solids to the Nevada 

part of the Virgin River. Surface runoff and subsurface 

flow in Nevada may contribute a combined 8,700 

tons/yr (rounded) of dissolved solids to the Virgin 

River from surface runoff and subsurface flow in 

Nevada.

Surface runoff in ephemeral tributaries (fig. 1) 

also contributes dissolved solids. A rough estimate of 

average dissolved-solids load of surface runoff from 

ephemeral tributaries is about 90 tons (rounded), on the 

basis of 0.04 ton/mi2 annual yield and 2,172 mi2 area. 

This estimate should be used with caution because of 

the variety of hydrogeologic conditions in the 2,172

/^

mi drained by ephemeral tributaries, which would 

affect the dissolved-solids yield. For example, limited 

water-quality data (Rush, 1968b, table 16) and geologic 

information suggest that surface runoff in the Black 

Mountains area (fig. 1) may be quite saline (A.S. 

Van Denburgh, U.S. Geological Survey, oral commun., 

1994).

Hydrologic data are not available to estimate 

dissolved-solids load in subsurface flow from the 

ephemeral tributaries.

The dissolved-solids load in the Virgin River 

above Halfway Wash near Riverside, which was about 

710,000 tons/yr for water years 1978-86, may 

approximate the dissolved-solids load discharged to the 

Colorado River by streamflow. As much as 40,000 

acre-ft/yr of subsurface flow may enter Lake Mead 

from the Virgin River subbasin (Glancy and Van 

Denburgh, 1969, p. 51). Assuming a dissolved-solids 

concentration of 2,200 mg/L for subsurface flow (see 

previous section), an average dissolved-solids load of 

120,000 tons/yr may discharge into the Colorado River 

by subsurface flow. Combined surface runoff and 

subsurface flow may contribute about 830,000 tons/yr 

of dissolved solids to the Colorado River.

The average dissolved-solids load in surface 

runoff from ephemeral tributaries, about 90 tons/yr, is 

an estimate of dissolved-solids load discharged to the 

Colorado River. Adequate hydrologic data are not 

available to estimate the dissolved-solids load in 

subsurface flow from ephemeral tributaries discharged 

to the Colorado River.

Comparison of Study-Period and Long-Term Data

The annual concentration of dissolved solids in 

the Virgin River at Littlefield, Ariz. (fig. 1), averaged 

1,900 mg/L for water years 1978-93 and 1,800 mg/L 

for water years 1978-86. The average annual dissolvedsolids concentrations are based on analyses of periodic 

water samples. The average dissolved-solids load was 

about 560,000 tons/yr for water years 1978-93 (table 

3), on the basis of about 300 ft3/s average streamflow 

and about 1,900 mg/L average dissolved-solids concentration. For comparison, an earlier study determined 

an average dissolved-solids load of 541,037 tons/yr for 

1979-83 in the Virgin River (Panian and others, 1987, 

p. 8). The average dissolved-solids load was about 

640,000 tons/yr for water years 1978-86 (table 3), on 

the basis of 360 ft3/s average streamflow and 1,800 

mg/L average dissolved-solids concentration. Most of 

the dissolved-solids load in the Virgin River at Littlefield study site originates in Arizona and Utah.

The annual concentration of dissolved solids in 

the Virgin River above Halfway Wash near Riverside 

averaged 2,000 mg/L for water years 1978-86. The 

dissolved-solids load averaged about 710,000 tons/yr 

for water years 1978-86 (table 3). Thus, the load

20 Dissolved-Sollds Contribution to the Colorado River from Public Lands in Southeastern Nevada, Through September 1993
increased by an average of about 70,000 tons/yr 

between the Littlefield and Riverside gages during 

water years 1978-86. This 9-year period was wetter 

than average: at the Littlefield gage, flow for the entire 

period of record (water years 1930-93) averaged 241 

ft3/s (U.S. Geological Survey, 1994, p. 52), in contrast 

to about 360 ft3/s for 1978-86 (table 3).

For water years 1989-93, the total contribution of 

dissolved solids from public lands in the Muddy River 

subbasin averaged about 28,000 tons/yr (rounded). 

Subsurface flow contributed 24,000 tons/yr of dissolved solids. The annual dissolved-solids yield for 

public lands in the Muddy River subbasin was about 

4.5 tons/mi2 [determined from (28,000 tons/yr) / (6,200 

mi2)] for the same period.

ESTIMATED ANNUAL DISSOLVEDSOLIDS YIELD AND LOAD FROM PUBLIC 

LANDS

Muddy River Subbasin

Public lands constitute 86 percent of the Muddy 

River subbasin, as shown in table 1. This land includes 

83 percent of Pahranagat Wash-White River drainage 

area, 94 percent of Meadow Valley Wash drainage area, 

and 70 percent of the lower Muddy River drainage 

area. The dissolved-solid load contributed by surface 

runoff from public lands was computed by applying the 

dissolved-solids yield for the entire drainage area to the 

part that consists of public lands. For the lower Muddy 

River drainage area, the yield was applied to 430 mi ,

9 9

instead of 560 mi , because about 130 mi are in hydrologic areas that do not contribute surface runoff to the 

Colorado River. The dissolved-solids loads contributed 

by public lands to the Muddy River subbasin from surface runoff in the drainage areas are 120 tons/yr from 

Pahranagat Wash-White River drainage area, 3,600 

tons/yr from Meadow Valley Wash drainage area, and 

only 20 tons/yr from the lower Muddy River drainage 

area (table 4).

The source of subsurface flow is not identified in 

this report, but the general areas of recharge may be 

mountain slopes and channels, alluvial fans, and valley 

bottoms. The dissolved-solids load from subsurface 

flow is attributed entirely to public lands because 

almost 90 percent of the Muddy River subbasin is public lands. Dissolved-solids loads contributed by subsurface flow were 18,000 tons/yr from Pahranagat WashWhite River, 5,000 tons/yr from Meadow Valley Wash, 

and 1,400 tons/yr from the lower Muddy River drainage (table 4).

Las Vegas Wash Subbasin

Public lands are 45 percent of the Las Vegas Wash 

subbasin, as shown in table 1. The dissolved-solids 

load contributed by surface runoff from public lands 

was computed by applying the annual dissolved-solids 

yield of 0.045 ton/mi to the area of public lands within 

the drainage area. Approximately 730 mi2 of public 

lands contribute dissolved solids in the Las Vegas Wash 

subbasin. An additional 120 mi2 of public lands are in 

a hydrographic area, Three Lakes Valley (hydrographic 

area 211), that is a noncontributing part of the Colorado 

River Basin. The total average dissolved-solids load 

contributed by surface runoff from public lands was 33 

tons/yr.

The source of subsurface flow from public lands 

is the ground-water system of the Las Vegas Valley. 

Recharge to the ground-water system is from precipitation in the Spring Mountains that border the west 

side of the valley and in the Sheep Range that borders 

the north side of the valley (Harrill, 1976, p. 2). 

Dissolved-solids load from subsurface flow is 

attributed entirely to public land because much of the 

recharge area and the flow path downgradient 

therefrom underlie public land. Dissolved-solids load 

contributed to the Las Vegas Wash subbasin from 

subsurface flow in the drainage area was approximately 

1,300 tons/yr. The combined total from surface runoff 

and subsurface flow is about 1,300 tons/yr (rounded). 

The annual dissolved-solids yield for public lands in 

the Las Vegas Wash subbasin was almost 2 tons/mi2 

[determined from (1,300 tons/yr) / (730 mi2)].

Other Subbasins

All but about 40 mi2 of the Virgin River subbasin 

within Nevada consists of public lands. Surface runoff 

from public lands in the Virgin River subbasin may 

contribute an estimated 40 tons/yr of dissolved solids,

ESTIMATED ANNUAL DISSOLVED-SOLIDS YIELD AND LOAD FROM PUBLIC LANDS 21
r\

on the basis of 0.04 ton/mi annual yield and about 

1,100 mi2 of public lands. Dissolved-solids load from 

subsurface flow in Nevada is attributed entirely to public land. Subsurface flow from public lands may contribute an estimated 8,700 tons/yr of dissolved solids. 

Combined dissolved-solids load from public lands is 

about 8,700 tons/yr (rounded) and annual dissolvedsolids yield for public lands is about 7.9 tons/mi2 

[determined from (8,700 tons/yr) / (1,100 mi2)].

A rough estimate of average dissolved-solids load 

in surface runoff from public lands in ephemeral 

tributaries is 50 tons/yr [determined from (0.04 

ton/yr)( 1,200 mi2)]. No estimate was made for 

dissolved-solids load in subsurface flow from these 

lands.

IMPLICATION OF FINDINGS FOR 

MANAGEMENT OF DISSOLVED-SOLIDS 

DISCHARGE FROM PUBLIC LANDS

Subsurface flow contributes about 87 percent of 

the dissolved-solids load from public lands in the 

Muddy River and Las Vegas Wash subbasins, whereas 

surface runoff contributes the remaining 13 percent of 

the load. Although about 7,000 mi2 of the two subbasins are public lands, the arid climate of the study 

area and low annual runoff limit the contributions of 

dissolved solids from surface runoff. The low concentration of dissolved solids normally associated with 

surface runoff also limits the contribution.

Surface runoff and subsurface flow from public 

lands in the Nevada part of the Colorado River Basin 

contribute an estimated average total of 38,000 tons/yr 

(rounded) 28,000 tons/yr in the Muddy River subbasin, 1,300 tons/yr in Las Vegas Wash subbasin, 8,700 

tons/yr in the Virgin River subbasin, and 50 tons/yr in 

areas drained by ephemeral tributaries. Hydrologic 

conditions that are unique to the subbasins are discussed in the following sections.

Muddy River Subbasin

The BLM manages about 6,200 mi2 of land in the 

Muddy River subbasin of Nevada (table 1). The Muddy 

River flows into Lake Mead (an impoundment of the 

Colorado River) and discharges dissolved solids into 

the lake. Contributions of dissolved-solids load from 

the public lands were estimated from data collected at

study sites within the subbasin and data compiled from 

other sources. About 28,000 tons/yr of dissolved solids 

were contributed by surface runoff and subsurface flow 

from public land during water years 1989-93.

An estimated 86 percent of the dissolved-solids 

load (24,000 tons/yr) was contributed by subsurface 

flow from public lands (table 4). The percentage actually may be somewhat higher, because streamflow at 

the Meadow Valley Wash study site was assumed to be 

surface runoff, although discharge from a spring 

upstream provided most of the total annual flow.

Because surface runoff contributes less than 15 

percent of the total dissolved-solids load from public 

lands, management practices in these lands probably 

would not substantially reduce the overall load.

Hydrologic data collected at the Meadow Valley 

Wash study site show occasional spikes of specific conductance to a recorded maximum of 7,460 |iS/cm (U.S. 

Geological Survey, 1994, p. 70). Perhaps related to the 

periodic conductance spikes is the tendency at flows 

less than 5 ft3/s for dissolved-solids concentration to 

increase with increased flow (in most streams, dissolved-solids concentration is inversely proportional to 

flow, owing to dilution). This unusual hydrologic phenomenon may be due at least in part to local input of 

salts directly and indirectly related to dense stands of 

riparian saltcedar upstream from the Meadow Valley 

Wash study site (Hem, 1967, p. 6).

A 1975 study by Desert Research Institute (DRI) 

for BLM (Bateman, 1976) included the Muddy River 

and Virgin River subbasins. Bateman collected or compiled data on dissolved-solids concentrations at 169 

sites including wells, springs, streams, and irrigation 

return flow. Future investigations, using detailed data 

for the Meadow Valley Wash study site (present study) 

and the DRI study, may identify specific sources of discharge or land areas that could be managed for reduction of dissolved-solids load. Any such reduction may 

not substantially affect the overall dissolved-solids 

contribution to the Muddy River subbasin, however, 

because the contribution from an individual specific 

source would be relatively minor compared to the total 

basin load.

Agricultural land use downstream from public 

lands may potentially affect dissolved-solids discharge 

to the Colorado River. About 4,900 acres of crops and 

pasture lands are irrigated in lower Meadow Valley 

Wash, upper Moapa Valley, and lower Moapa Valley 

(U.S. Soil Conservation Service, 1993, p. ii). Water is 

diverted from the Muddy River for irrigation. Average 

annual streamflow of 38 ft /s near Moapa is reduced to

22 Dissolved-Solids Contribution to the Colorado River from Public Lands in Southeastern Nevada, Through September 1993
about 10 ft3/s above Lake Mead near Overton. Part of 

the reduction is due to evapotranspiration along the 

stream, but a large part of the loss is due to diversion of 

water for irrigation and subsequent evapotranspiration 

losses from crops and pastures and evaporation losses 

from irrigation ditches and reservoirs. Accumulation of 

the dissolved solids in the agriculture areas may partly 

reduce the total contribution of 28,000 tons/yr of dissolved solids from the upstream parts of the Muddy 

River subbasin to 24,000 tons/yr of discharge to the 

Colorado River. The apparent loss of 4,000 tons/yr of 

dissolved solids in the Lower Muddy River subbasin 

also may be due at least in part to the limited accuracy 

of the method used to estimate dissolved-solids contributions. More detailed studies of water chemistry in the 

lower Muddy River subbasin may provide additional 

information for evaluating changes in dissolved-solids 

concentration and load.

The U.S. Soil Conservation Service (USSCS) 

studied the lower Muddy River subbasin to determine 

dissolved-solids load in the lower Muddy River subbasin and discharge to Lake Mead (U.S. Soil Conservation Service, 1993). The surface-runoff component of 

dissolved-solids discharge as determined by the 

USSCS study (p. 26) was 14,300 tons/yr on the basis of 

average streamflow of 8.42 ft3/s and average dissolvedsolids concentration of 1,735 mg/L. The present (1994) 

study determined 21,000 tons/yr on the basis of average streamflow of 9.2 ft3/s and dissolved-solids concentration of 2,300 mg/L. However, the USSCS reports 

a discharge of 42,200 tons/yr of dissolved solids due to 

subsurface flow (U.S. Soil Conservation Service, 1993, 

p. 26). In contrast, this present study determined a discharge of only 3,000 tons/yr (table 4) of dissolved solids from subsurface flow. Differing estimates of 

subsurface flow and dissolved-solids concentrations 

resulted in large differences in estimates of dissolvedsolids loads. More detailed estimates of subsurface 

flow and dissolved-solids concentrations are needed to 

resolve these differences.

Las Vegas Wash Subbasin

Factors that may affect the runoff from public 

lands in the Las Vegas Wash subbasin are the flooddetention basins on major channels draining public 

lands and the large urban area between most of the public lands and the mouth of Las Vegas Wash. Large 

streamflows in Las Vegas Wash during rainfall consist 

mostly of runoff from the urban area. Most public lands

in the Las Vegas Wash subbasin that are transferred to 

private ownership are subsequently developed, thus, 

adding to the total urban area; this urbanization could 

increase the dissolved-solids load. An evaluation of the 

effects of urbanization in Las Vegas Valley on dissolved-solids loads to Las Vegas Wash is beyond the 

scope of the current study.

The relatively small amount of subsurface flow 

from the Las Vegas Wash subbasin (Harrill, 1976, p. 2) 

limits the contribution of dissolved solids from public 

lands to the Colorado River. Prior to development, 

almost all the recharge from natural sources in the subbasin (25,000 acre-ft; Malmberg, 1961, p. 17), was lost 

because of evapotranspiration and spring discharge.

Land-management practices, implemented to 

reduce the contribution of dissolved solids from public 

lands, probably would not substantially reduce the dissolved-solids discharge to the Colorado River, considering the small amount of natural subsurface flow to the 

Colorado River and the extensive development of the 

ground-water system, the presence of flood-detention 

basins, and the continued expansion of the large urban 

area in the subbasin.

The average discharge of dissolved solids to the 

Colorado River from Las Vegas Wash was about 

210,000 tons/yr for 1989-92. The average dissolvedsolids concentration of discharge from Las Vegas Wash 

(about 1,400 mg/L) was higher than the concentration 

in public-supply water imported from Lake Mead 

(about 600-800 mg/L) or pumped from native ground 

water (about 300 mg/L; Jeffrey A. Johnson, Las Vegas 

Valley Water District, and Ray J. Hoffman, U.S. 

Geological Survey, written communs., 1994). As the 

population of the valley increases, the dissolved-solids 

load of the Wash is expected to increase.

Other Subbasins

Combined surface runoff and subsurface flow in 

the Virgin River subbasin may discharge about 830,000 

tons/yr of dissolved solids to the Colorado River (table 

4). The dissolved-solids load increased by an average 

of about 70,000 tons/yr between the Littlefield and Riverside gages during the wetter-than-average period of 

concurrent record (water years 1978-86; see table 3). 

Dissolved-solids contributions from surface runoff due 

to precipitation and from subsurface flow within 

Nevada, calculated as about 8,700 tons/yr (table 4), 

account for only about 12 percent of this increase.

IMPLICATION OF FINDINGS FOR MANAGEMENT OF DISSOLVED-SOLIDS DISCHARGE FROM PUBLIC LANDS 23
Efforts to reduce dissolved-solids contribution from 

public lands in the Nevada part of the Virgin River subbasin probably would not substantially affect the dissolved-solids discharge to the Colorado River.

The public land area drained by ephemeral tributaries (1,200 mi ) is widespread with numerous individual channels tributary to the river, Lake Mead, or 

Lake Mohave. The average annual yield for the public 

lands is assumed to be 0.04 ton/mi2. Because of the low 

yield and numerous individual tributaries, landmanagement practices in these areas probably would 

not substantially reduce the contribution of dissolved 

solids from the public lands drained by ephemeral tributaries.

SUMMARY

About 9,300 of the 12,400 mi2 (75 percent) of 

Colorado River Basin in Nevada are administered by 

the Bureau of Land Management. The administered 

tracts are referred to as public lands and are subject to 

Public Law 98-569, which directs the Secretary of the 

Interior to develop a comprehensive program for 

minimizing dissolved-solids contributions to the 

Colorado River from public lands. About 6,200 mi of 

public lands are in the Muddy River subbasin and about 

850 mi2 are in the Las Vegas Wash subbasin. Data 

available prior to 1988 for the two subbasins were 

generally for locations downstream from all potential 

sources of dissolved solids and were insufficient to 

estimate dissolved-solids contributions from public 

lands only.

Four study sites were established in calendar year 

1988, in cooperation with the Bureau of Land 

Management, to assess the dissolved-solids loads from 

public lands in the Nevada part of the Colorado River 

Basin. The study sites were on Pahranagat Wash, 

Muddy River, Meadow Valley Wash, and Las Vegas 

Wash. Water samples were collected during site visits 

and analyzed for specific conductance and for 

dissolved-solids concentration. Additional water 

samples were collected during periods of storm runoff. 

Streamflow and specific-conductance data were 

recorded half-hourly at Pahranagat Wash near Moapa 

and Las Vegas Wash near North Las Vegas and hourly 

at Muddy River near Moapa and Meadow Valley Wash 

near Rox. Data were collected at the study sites through 

September 1993. These data and additional

information compiled for other sites were used to 

estimate the dissolved-solids contributions from 

Nevada public lands.

The average dissolved-solids discharge from the 

Muddy River subbasin to the Colorado River, from 

October 1988 to September 1993, was about 24,000 

tons/yr, including that from subsurface flow. The estimated average dissolved-solids load that was contributed from Nevada public lands in the Muddy River 

subbasin was 28,000 tons/yr for the same period, of 

which subsurface flow contributed about 86 percent 

(24,000 tons/yr). The difference of 4,000 tons/yr may 

be partially due to salt losses in agriculture areas in the 

lower parts of the basin, inaccuracies in the methods 

used to estimate dissolved-solids load, or both.

The average dissolved-solids discharge from the 

Las Vegas Wash subbasin to the Colorado River, from 

October 1988 to June 1992, was about 210,000 tons/yr, 

including that from subsurface flow. The estimated 

average dissolved-solids load contributed from public 

lands in the Las Vegas Wash subbasin was 1,300 

tons/yr for October 1988 through September 1993.

Available data were compiled to estimate dissolved-solids loads in the Virgin River subbasin. All 

but about 40 mi2 of the subbasin within Nevada is public lands. An estimated 40 tons/yr of dissolved solids 

may be contributed to the Virgin River by surface runoff from those lands. About 8,700 tons/yr of dissolved 

solids may be contributed to the Virgin River by subsurface flow from public lands. Thus, the combined 

dissolved-solids load from public lands is about 8,700 

tons/yr (rounded).

The average dissolved-solids load in surface runoff from Nevada public lands in ephemeral tributaries 

to the Colorado River and its impoundments is estimated as 50 tons/yr. Available information was insufficient to permit an estimate of dissolved-solids load in 

subsurface flow from those lands.

In summary, a total of about 38,000 tons 

(rounded) of dissolved solids is contributed annually to 

the Colorado River Basin by surface runoff and subsurface flow from public lands in Nevada. Land-management practices probably would not substantially reduce 

this contribution.

24 Dissolved-Solids Contribution to the Colorado River from Public Lands in Southeastern Nevada, Through September 1993
REFERENCES CITED

Bateman, R.L., 1976, Inventory and chemical quality of 

ground water in the White River-Muddy RiverMeadow Valley Wash area, southeastern Nevada: 

University of Nevada, Desert Research Institute Project 

Report 40, 44 p.

Dettinger, M.D., 1987, Ground-water quality and geochemistry of Las Vegas Valley, Clark County, Nevada, 1981- 

83 Implementation of a monitoring network: U.S. 

Geological Survey Water-Resources Investigations 

Report 87-4007, 69 p.

Eakin, T.E., 1964, Ground-water appraisal of Coyote Spring 

and Kane Spring Valleys and Muddy River Springs 

area, Lincoln and Clark Counties, Nevada: Nevada 

Department of Conservation and Natural Resources, 

Ground-Water Resources - Reconnaissance Report 25, 

40 p.

Glancy, P.A., and Van Denburgh, A.S., 1969, Waterresources appraisal of the lower Virgin River Valley 

area, Nevada, Arizona, and Utah: Nevada Division of 

Water Resources, Reconnaissance Report 51, 87 p.

Gortsema, G.C., 1993, Selected data on water quantity and 

quality at four sites on streams draining public lands, 

Colorado River Basin, southeastern Nevada, October 

1988 - September 1991: U.S. Geological Survey OpenFile Report 93-439, 31 p.

Harrill, J.R., 1976, Pumping and ground-water storage 

depletion in Las Vegas Valley, Nevada, 1955-74: 

Nevada Division of Water Resources, Bulletin 44,70 p.

Hem, J.D., 1967, Composition of residues on leaves and 

stems of saltcedar (Tamarixpentandra Pallas): U.S. 

Geological Survey Professional Paper 491-C, 9 p.

 1985, Study and interpretation of the chemical 

characteristics of natural water [3d ed.]: U.S. 

Geological Survey Water Supply Paper 2254, 283 p.

Johnson, Michael, 1992, Ground-water conditions in the Las 

Vegas Valley: Association of Engineering Geologists, 

Southwestern Section, Geologic and Hydrologic Hazards in the Las Vegas Valley A One-Day Workshop, 

Las Vegas, December 1992, unpaginated.

Malmberg, G.T., 1961, A summary of the hydrology of the 

Las Vegas ground-water basin, Nevada, with special 

reference to the available supply: Nevada Department 

of Conservation and Natural Resources, Water 

Resources Bulletin 18, 23 p.

Morgan, D.S., and Dettinger, M.D., 1994, Ground-water 

conditions in Las Vegas Valley, Clark County, Nevada. 

Part II, Geohydrology and simulation of ground-water 

flow: U.S. Geological Survey Open-File Report 90- 

179, 151 p.

Panian, T., Miller, WW, and Gifford, G.F., 1987, Salinity 

contribution to Colorado River from Nevada basin 

components: Reno, Nev., Bureau of Land Management 

Report BLMNVPT87077200, 33 p.

Rush, F.E., 1968a, Index of hydrographic areas in Nevada: 

Nevada Division of Water Resources, Information 

Report 6, 38 p.

 1968b, Water-resources appraisal of the Lower MoapaLake Mead area, Clark County, Nevada: Nevada 

Division of Water Resources, Reconnaissance Report 

50, 66 p.

Thomas, J.M., and Welch, A.H., (in press), Geochemistry 

and isotope hydrology of representative aquifers in the 

Great Basin region of Nevada, Utah, and adjacent 

states: U.S. Geological Survey Professional Paper 

1409-C.

U.S. Department of the Interior, 1991, Quality of water, 

Colorado River Basin: Bureau of Reclamation, 

Progress Report 15, 103 p.

U.S. Geological Survey, 1978-94, Water resources data, 

Nevada, water years 1977-93: U.S. Geological Survey 

Water-Data Reports NV-77-1 to NV-93-1 (published 

annually).

U.S. Soil Conservation Service, 1993, Salinity control plan 

and final environmental impact statement, Moapa 

Valley unit, Colorado River Basin Salinity Control 

Program, Clark County, Nevada: Reno, Nev., 185 p.

REFERENCES CITED 25