Focused Ground-Water Recharge in the Amargosa 

Desert Basin

USGS Professional Paper 1703—Ground-Water Recharge

in the Arid and Semiarid Southwestern United States—

Chapter E

By David A. Stonestrom, David E. Prudic, Michelle A. Walvoord, Jared D. Abraham, Amy E. Stewart-Deaker1, 

Patrick A. Glancy, Jim Constantz, Randell J. Laczniak, and Brian J. Andraski

Abstract 

The Amargosa River is an approximately 300-kilometer-long regional drainage connecting the northern highlands 

on the Nevada Test Site in Nye County, Nev., to the floor 

of Death Valley in Inyo County, Calif. Streamflow analysis 

indicates that the Amargosa Desert portion of the river is dry 

more than 98 percent of the time. Infiltration losses during 

ephemeral flows of the Amargosa River and Fortymile Wash 

provide the main sources of ground-water recharge on the 

desert-basin floor. The primary use of ground water is for irrigated agriculture. The current study examined ground-water 

recharge from ephemeral flows in the Amargosa River by 

using streamflow data and environmental tracers. The USGS 

streamflow-gaging station at Beatty, Nev., provided highfrequency data on base flow and storm runoff entering the 

basin during water years 1998–2001. Discharge into the basin 

during the four-year period totaled 3.03 million cubic meters, 

three quarters of which was base flow. Streambed temperature 

anomalies indicated the distribution of ephemeral flows and 

infiltration losses within the basin. Major storms that produced 

regional flow during the four-year period occurred in February 

1998, during a strong El Niño that more than doubled annual 

precipitation, and in July 1999. The study also quantified 

recharge beneath undisturbed native vegetation and irrigation return flow beneath irrigated fields. Vertical profiles of 

water potential and environmental tracers in the unsaturated 

zone provided estimates of recharge beneath the river channel 

(0.04–0.09 meter per year) and irrigated fields (0.1–0.5 meter 

per year). Chloride mass-balance estimates indicate that 12–15 

percent of channel infiltration becomes ground-water recharge, 

together with 9–22 percent of infiltrated irrigation. Profiles of 

potential and chloride beneath the dominant desert-shrub vegetation suggest that ground-water recharge has been negligible 

throughout most of the basin since at least the early Holocene. 

Surface-based electrical-resistivity imaging provided areal 

extension of borehole information from sampled profiles. 

These images indicate narrowly focused recharge beneath the 

Amargosa River channel, flanked by large tracts of rechargefree basin floor.

1

 Present address Berkeley, California (amystew@gmail.com).

Introduction and Setting

The Amargosa Desert Basin contains a large quantity of 

high quality ground water (Walker and Eakin, 1963; Claassen, 1985; Kilroy, 1991). Beneficial uses of ground water 

include sustenance of wildlife at discharge points within Ash 

Meadows National Wildlife Refuge and support of irrigated 

agriculture within the Amargosa Farms area (fig. 1). Recharge 

of ground water is a relatively uncharacterized component of 

the hydrologic budget. The basin is part of the larger Death 

Valley regional ground-water flow system. While numerous 

studies have examined the Death Valley system at a regional 

scale (Winograd and Thordarson, 1975; Harrill and others, 

1988; D’Agnese and others, 1999; Tiedeman and others, 

2004), the sparsely populated Amargosa Desert Basin—especially its upper reaches—has received relatively little study. 

Considerable uncertainties remain in subsurface residence 

times and fluxes under current climatic and land-use conditions. Appraisal of ground-water resources and management 

of competing demands from developing land-use patterns 

requires an improved understanding of ground-water recharge 

in this desert environment. 

Population, Land Use, and Water Withdrawals

The Amargosa Desert Basin is sparsely populated and 

relatively undeveloped. The average population density is less 

than one person per square kilometer. Primary land uses are 

farming and recreation. The town of Beatty straddles the Amargosa River just upstream of its entry into the basin (fig. 1). 

The estimated population of Beatty in 2000 was 1,085 (U.S. 

Census Bureau, 2003). The Amargosa Farms area spreads 

across the outlet of the basin. The census division that includes 

the farms area, Amargosa Valley, had an estimated population 

in 2000 of 1,142.

In view of rapid population growth in nearby areas, the 

Amargosa Desert Basin has substantial potential for growth. 

Population estimates at the county level extend back to 1870. 

The early population of the county jumped roughly six-fold 

after prospectors found gold near Beatty in 1904, and rose again 

in the 1950s and 1960s during expansion of irrigated agriculture 

and defense activities at the Nevada Test Site (fig. 2). Even so, 

total county population remained below 10,000 before 1981. 
108 Focused Ground-Water Recharge in the Amargosa Desert Basin

0 5 10 15 Kilometers 20

116°45' 116°30' 116°15' 116°0'

36°30'

36°45'

37°0'

37°15'

 

 

NEVADA TEST SITE

Yucca F al t

Pahute Mesa

NEVADA

AMARGOSA D ESERT

CAL FI ORN AI

Amargosa

Farms

As

M

h

eadows

BEATTY

Amargosa 

Valley

MERCURY

ADRS

Devils Hole

Oasis

Valley

120° 118° 116° 114°

36°

38°

40°

42°

NEVADA

HATU

OREGON IDAHO

CAL FI ORN AI

Map

Area

yttaeB

Wash

Amargosa R vi er

Fo ytr m eli Wash

Figure 1. Physiographic and cultural features in the Amargosa Desert study area and vicinity, Nye County, Nev., and Inyo 

County, Calif. During the study, an active streamflow-gaging station was located in Beatty, Nev. Weather stations were 

located at Beatty, Nev., Amargosa Valley, Nev., Amargosa Farms, Nev., and at the ADRS (Amargosa Desert Research Site; 

Andraski and Stonestrom, 1999). Figure 9 shows channel- and borehole-sampling locations.
Introduction and Setting 109

The county grew substantially starting in the late 1970s due to 

migration into Pahrump Valley, an adjacent basin southeast of 

Ash Meadows.

The primary use of ground water in the Amargosa Desert 

Basin is for irrigation. Irrigation began around 1917 and continued on a modest scale until 1954. Between 1954 and 1965, 

the number of wells grew by about 150 to support agricultural 

production. Irrigation withdrawals have fluctuated since 1965, 

but maximum withdrawals about 20 million cubic meters per 

year (Mm3 yr-1) rival the natural discharge of ground water at 

Ash Meadows (about 22–26 Mm3 yr-1; Laczniak and others, 

1999; Stonestrom, Prudic, and others, 2003).

Hydrogeologic Setting

The Amargosa Desert Basin is bounded by large mountain 

blocks comprised of rocks ranging from Precambrian through 

Tertiary. Dominant rock types include Precambrian to Cambrian quartzite, Precambrian to Devonian massive dolomite 

and limestone, Carboniferous interbedded limestone and shale, 

and Tertiary rhyolites and basalts. Late Tertiary to Quaternary 

sediments form poorly indurated to unconsolidated basin-floor 

deposits (Winograd and Thordarson, 1975; Nichols, 1987; 

Sweetkind and others, 2001; Workman and others, 2002).

The present basin configuration resulted from distinct 

episodes and styles of tectonic deformation (Carr and Yount, 

1984; Hamilton, 1987; Glazner and others, 2002; Park and 

Wernicke, 2003). Cretaceous folding and thrusting imparted 

an east-to-northeasterly grain to the Paleozoic bedrock. Tear 

faulting of low-angle overthrusted slabs followed, ending in 

mid-Tertiary (Carr and Yount, 1984). Tear faulting impacted 

the entire area, creating northwesterly striking offsets (tears) 

in bedrock units of tens of kilometers. A northeasterly trending corridor of folding and faulting divides the Amargosa 

Desert Basin into upper and lower regions. This corridor, 

marked by the lower reaches of Fortymile Wash, appears to 

have formed by the early Tertiary (Carr and Yount, 1984). 

Low-angle detachment faulting starting in mid Tertiary 

accompanied subcontinental extension, producing the horst 

and graben topography characteristic of the southern Great 

Basin (Hamilton, 1987). Horst and graben-style faulting 

associated with large-scale detachments locally activated preexisting northeasterly and northwesterly trending structures, 

forming deep basins that filled with alluvium. Widespread 

volcanism accompanied extension (Workman and others, 

2002). Active deformation of 9 mm yr-1 north-northwesterly 

trending right-lateral shear continues to shape the region 

(Park and Wernicke, 2003). Small blocks of bedrock crop out 

through basin-floor alluvium along a northwesterly trending 

line through the Amargosa Desert Research Site (Stonestrom 

and others, 2004). Tectonic subsidence in the central part 

of the Amargosa Farms area is roughly matched by alluvial 

deposition from the Amargosa River and Fortymile Wash 

(Stonestrom, Prudic, and others, 2003).

As part of the Mojave Desert ecosystem, the Amargosa 

Desert Basin is one of the driest areas in the United States. 

Gold discovered near Beatty; 

Beatty founded, 1904 First nuclear detonation at 

NevadaTest Site, 1951 

Pahrump opens first 

public high school, 1972 

U.S. Census Bureau 

2000 population (32,485) 

Nevada Division of Water Planning 

projected population, 1998–2005 

Nevada gains statehood, 1864 

NYE COUNTY POPULATION, IN THOUSANDS 

YEAR

50 

40 

30 

20 

10 

0 

1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 

Figure 2. The population of Nye County, Nev., increased exponentially from the mid 1950s through mid 1990s, at about six 

percent per year (thin curved line). Early data (squares) are from the University of Virginia’s Fisher Library (http://fisher.lib.

virginia.edu/census, last accessed June 10, 2003). Later estimates (circles, 1950–1997) and forecasts (thick line, 1998–2005) 

are from the Nevada Division of Water Planning (http://www.water.nv.gov/waterPlanning/wat-plan/con-main.cfm; last 

accessed March 1, 2005).
110 Focused Ground-Water Recharge in the Amargosa Desert Basin

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4EMPERATURE

The present climate is arid-thermic, with moderate seasonality with respect to precipitation and strong seasonality with 

respect to temperature (Bull, 1991). Daily average temperatures range from 33 degrees Celsius (oC) in August to 3oC in 

December (fig. 3). Precipitation on the basin floor averages 

about a tenth of a meter per year based on long-term records 

at Amargosa Farms (1971–2000; 99.6 mm yr-1; NOAA, 

2002) and at the Amargosa Desert Research Site (1981–2005; 

112 mm yr-1; Johnson and others, 2007). About 60 percent 

of annual precipitation arrives in frontal systems during the 

months of December through March, with enhanced amounts 

during moderate to strong El Niño events (fig. 4).

Ground-water discharge maintains perennial flow in the 

Amargosa River at Beatty, near the entrance to the basin. Base 

flow dissipates within a few kilometers downstream. Speculation that no modern-day flows were capable of completely 

traversing the Amargosa Desert Basin was falsified by field 

reconnaissance following storms in March 1995 that produced 

continuous flow from the Nevada Test Site to Death Valley 

(Beck and Glancy, 1995).

Except for storm-generated runoff, the Amargosa River 

is usually dry downstream of Beatty. Storm flows are brief—

despite an upstream drainage area of about 1,200 square 

kilometers—as shown by 15-minute discharge data at Beatty 

during the study period (fig. 5). Ephemeral flow is generated 

primarily by runoff from the mountains surrounding Oasis 

Valley, but runoff from Bare Mountain (which forms the 

northeastern side of the basin), the Bullfrog Hills (northern 

side), the Funeral Mountains (southwestern side), as well 

as runoff from the basin floor itself can contribute flow in 

unnamed tributaries. Ephemeral flows exhibit extreme variability in magnitude, as shown by annual peak flows at the 

basin inlet (fig. 6). 

The dominant plant in the Mojave Desert is creosote bush 

(Larrea tridentata; Smith, Monson, and others, 1997), which 

covers nearly the entire Amargosa Desert Basin floor. Saltbush 

(Atriplex) co-dominates, becoming dominant beside channel 

reaches that were scoured by major flooding in the past. The 

active channel is largely vegetation free. On surfaces more than 

a few meters away from the channel, the native vegetation has 

likely been undisturbed for many centuries. Creosote and saltbush plants are perennial, with several meters typically separating the above-ground portions of adjacent plants. Typical 

mature heights are 0.5 m (saltbush) to 1–2 m (creosote bush). 

Figure 3. Mean monthly temperature and precipitation for 1965–2000 at Amargosa Farms, Nev. (National Weather Service 

cooperative station 260150). Altitude of station is 747 meters above sea level (National Geodetic Vertical Datum of 1929).
Introduction and Setting 111

 

1982 

1983 

1984 

1985 

1986 

1987 

1988 

1989 

1990 

1991 

1992 

1993 

1994 

1995 

1996 

1997 

1998 

1999 

2000 

2001 

2002 

PRECIPITATION, IN MILLIMETERS 

WATER YEAR

0 

100 

200 

300 

* = Strong El Niños, with sea-surface-temperature anomaly 

 index values greater than 2 degrees Celsius 

* 

* 

Study Period 

Average annual 

precipitation is 

112 mm 

Figure 4. Annual precipitation at the Amargosa Desert Research Site (ADRS) for water years 1982–2002 (Johnson and 

others, 2007). El Niño index is from McPhaden and others (2006). Water year runs from October 1 to September 30 and is 

denoted by the calendar year in which it ends. Figure 1 shows the location of the Amargosa Desert Research Site.

In addition to these large perennials, a variety of small annuals 

quickly fill the intervening gaps after accumulation of more 

than a few millimeters of precipitation when conditions are 

favorable. At the entrance to the basin, perennial flow supports 

a salt-cedar–willow community along the Amargosa River.

Potential evapotranspiration in the Amargosa Desert 

Basin greatly exceeds precipitation on an annual basis. Nichols (1987) estimated potential evaporation to be 2.5 m yr-1, 

exceeding average annual precipitation by a factor of 23. Daily 

accounting of actual evaporation in conjunction with a waterbalance model showed that deep percolation (precipitation in 

excess of evaporation and soil-moisture replenishment) might 

have occurred beneath non-vegetated surfaces on three separate occasions during 1961-1976, in amounts ranging from 

5 to 26 mm (Nichols, 1987).

Micrometeorological and soil data from the Amargosa 

Desert Research Site clearly show the decisive role of desert vegetation in controlling the near-surface water balance. 

Early work indicated that removal of vegetation for five years 

(1987–1992) reversed the potential gradient for water movement, from upward to downward, in a gradually deepening layer 

(Andraski, 1997). Measured evapotranspiration from native 

vegetation (48 mm) exceeded total precipitation (3.5 mm) by 

a factor of 13.7 in 2002 (Johnson and others, 2007). A net 

decrease in soil moisture during 2002 made up the difference. 

Precipitation data at Beatty show that 2002 was the driest 

year in 64 years of record. Lysimeter data for the same plant 

association on the Nevada Test Site showed that complex 

feedbacks between native vegetation and available moisture 

maintained upward gradients for water movement from 1994 

through 2001 (Scanlon and others, 2005). Due to increased 

plant vigor, upward gradients strengthened rather than weakened in response to the period of El Niño enhanced precipitation during 1997–1998.

Previous Work and Scope

Relatively few studies have examined ground-water 

recharge in the Amargosa Desert Basin. Walker and Eakin 

(1963) provided an early reconnaissance estimate based on 

earlier work in east-central Nevada, where recharge (assumed 

to be equal to ground-water discharge through springs and 

evapotranspiration) in 13 closed basins was correlated with 

precipitation (Maxey and Eakin, 1949; Eakin and Maxey, 

1951; Avon and Durbin, 1994). Walker and Eakin divided the 

greater Amargosa area into precipitation zones. The current 

study area is entirely in the driest precipitation zone (less than 

200 mm), in which recharge was estimated to be zero.
112 Focused Ground-Water Recharge in the Amargosa Desert Basin

        



















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Claassen (1985) examined the geochemical composition of ground water in the west-central part of the basin and 

concluded that recharge was primarily from direct infiltration of overland flow in or near present day stream channels, 

rather than from subsurface inflows from the surrounding 

mountains. Depletion of stable isotopes oxygen-18 and 

deuterium in water indicate that most of the recharge originated as snowmelt. Carbon-14 dates indicate that most of the 

sampled ground water recharged during late Wisconsin to 

early Holocene time, with unadjusted ages ranging from 9 to 

17 thousand years before present.

Osterkamp and others (1994) used a distributed-parameter water-balance approach to estimate recharge arising from 

contemporary streambed infiltration. This approach classified 

the Amargosa River into geomorphically similar reaches and 

assumed that all infiltration became recharge. Between the 

basin entrance near Beatty and outlet near Amargosa Farms, 

channel losses produced a total estimated annual recharge of 

0.5 million cubic meters per year (Mm3 yr-1).

The geographic focus of the current study is the portion of the basin through which the Amargosa River flows. In 

addition, Beatty Wash—the largest tributary upstream of the 

Amargosa Desert—was instrumented near its confluence with 

the Amargosa River, in Oasis Valley (fig. 1). The study also 

considered recharge from irrigation return in the Amargosa 

Farms area near the downstream end of the study reach. The 

primary data for the study are from water-years 1998 through 

2001, which spanned a range of wet to dry conditions (fig. 4). 

In addition to developing recharge estimates, the goal of the 

study was to gain understanding of recharge processes and 

controls, with particular regard to the timing and extent of 

recharge-producing events.

Figure 5. Discharge of the Amargosa River at Beatty, Nev., for water years 1998−2001 (USGS streamflow-gaging station 

10251217). Inset shows detailed record for three stormflow events in July 1999. Under typical (non-storm) conditions, all 

base flow is lost to infiltration and evaporation within a few kilometers of the gage.
Methods 113

( 1975) 

700 

( 1967) 

7,200 

0 

5 

10 

15 

20 

25 

30 

1960 1970 1980 1990 2000 

( 1978) 

1,100 

= water year 

= peak flow ( m 3 /min) 

E x p l anat ion: 

= no f l o w during entire year 

= peak flow < 25 m 3 /min 

= flow minimal or zero 

( 1969) 

27,000 

( 1978) 

1,100 ( 1995) 

2,200 

( 1990 

310 

PEAK STREAMFLOW, IN THOUSANDS 

OF CUBIC METERS PER MINUTE 

YEAR

Methods

This study combined thermal flow detection with 

analyses of vertical profiles of water potential and naturally 

occurring environmental tracers to characterize infiltration 

and recharge within the Amargosa Desert Basin. Sampling 

locations included sites within the channel, irrigated fields, 

and beneath undisturbed native vegetation on the basin floor. 

Direct-current (DC) resistivity imaging, a surface geophysical technique, allowed generalization of results obtained at 

the limited number of sampled sites to areas of the basin with 

similar geomorphology and vegetation. This section briefly 

describes instrumentation, sampling, and data analysis. 

Detailed descriptions appear in cited references.

Streambed-temperature anomalies indicated ephemeral 

flow at instrumented locations (Constantz and others, 2001; 

Stewart, 2003; table 1). Measurement techniques included 

deployment of single-channel temperature loggers at a nominal depth of 0.1 m in channel sediment, nested thermocouples 

near the inlet to the basin and at the Amargosa Desert Research 

Site, and borehole-temperature loggers at two locations in the 

channel (Stonestrom and Blasch, 2003). Streambed-temperature 

measurements were supplemented by peak-flow estimates by 

using slope-conveyance and slope-area techniques (Benson and 

Dalrymple, 1967; Dalrymple and Benson, 1968).

Sediment samples were obtained from boreholes within the 

channel (sites C1 and C2), beneath native vegetation near the 

Amargosa Desert Research Site (ADRS) and Amargosa Farms 

area (sites ADRS and AFNV), and beneath irrigated fields 

(sites AF-A1–AF-C2; table 2; fig. 7). Water potentials for each 

sample were determined with a water-activity meter (Gee and 

others, 1992). Gravimetric water contents were determined by 

oven drying at 105o C (Gardner, 1986). Pore-water chemistry 

was characterized by using methods in Page and others (1982) 

and Sparks (1996). Each oven-dried sample was mixed with an 

equal mass of deionized water and shaken periodically for 

24 hours. Supernatant liquid was filtered and analyzed for 

chloride and nitrate by using ion chromatography. Supernatant 

Figure 6. Annual peak flows, Amargosa River near Beatty, 

Nev., for October 1963 through September 2001. Data for water 

years 1964–1968 and 1991–1995 are from USGS streamflowgaging station 10251218, 3.7 km downstream of station 10251217 

(Amargosa River at Beatty, Nev.; temperature station PS-1). Data 

for water years 1969–1990 are from crest-stage partial-record 

station 10251220 (at PS-2), 5.4 km downstream of the Beatty gage. 

Data for water years 1996–2002 are from the Beatty gage. No 

gages were active in water years 1982 and 1986; however, flows 

were zero or small. The channel downstream of 10251220 is dry 

more than 98 percent of the time. The 1969 flood was the largest 

on record, producing a peak flow that exceeded the median 

annual peak flow by more than two orders of magnitude. From 

Stonestrom, Prudic, and others (2004).

concentrations were converted to pore-water concentrations by 

dividing by gravimetric water contents and multiplying by the 

pore-water density (assumed to be 1.00 × 106 gram m-3). Volumetric water contents were obtained by multiplying gravimetric 

water content by bulk densities estimated on the basis of lithologic description. Unsaturated-zone chloride-mass-balance and 

tracer-velocity techniques provided estimates of deep percolation and recharge (Stonestrom, Prudic, and others, 2003). Water 

for stable isotopic analysis was extracted by complete-recovery 

cryodistillation (Prudic and others, 1997).

Surface-based DC-resistivity measurements were made 

in May of 2003 along transects normal to the sedimentary 

depositional fabric in three distinct geomorphologic settings; 

one where the Amargosa channel is incised into the adjacent 

terrace sediments (near PS-4), one where the channel forms 

an actively migrating distributory network (near PS-6E), and 

one on the alluvial surface adjacent to the ADRS. Water years 

2002 and 2003 were dry, producing no flows that extended 

more than a few kilometers into the basin. At each resistivity 

transect, linear arrays of 32 to 80 electrodes were deployed 

with a uniform 2 to 5-m spacing between adjacent electrodes. A 

multiplexing 8-channel resistivity instrument was used to make 

automated resistivity measurements along the line, combining 

sounding and profiling for vertical and horizontal resolution 

(fig. 8; Stonestrom, Abraham, and others, 2003; Abraham and 

Lucius, 2004). Each measurement used four electrodes at a 

time, with geometry varying between inverse-Schlumberger 

and inverse-Wenner configurations (Telford and others, 1990). 

Sodium-chloride solution was used to improve electrical contact 

between electrodes and the extremely dry surface soil. Imposed 

currents ranged from 250 to 400 milliamps. The line was shifted 

incrementally until composite transects consisted of 168 to 232 

electrode positions. Each transect produced vertical arrays of 

3,000 to 4,000 apparent resistivity soundings.

Apparent resistivity soundings were used in a constrained inversion scheme, generating a model distribution of 

subsurface DC resistivities based on the difference between 

measured and predicted apparent resistivities. The inversion 
114 Focused Ground-Water Recharge in the Amargosa Desert Basin

Description Code Latitude1

, 

in degrees

Longitude1, 

in degrees

Altitude2,

in meters

Borehole depth,

in meters

Amargosa channel site 1, at PS-4 C1 36.7981 116.7525 889 14

Amargosa channel site 2, at PS-6E C2 36.7131 116.6764 808 14

ADRS3

, native vegetation ADRS 36.7656 116.6936 847 48

Amargosa farms, native vegetation AFNV 36.5656 116.5261 724 15

Amargosa farms, field 1, hole A AF-1A 36.5647 116.5261 723 12

Amargosa farms, field 1, hole B AF-1B 36.5622 116.5275 722 15

Amargosa farms, field 2, hole A AF-2A 36.5536 116.5264 719 10

Amargosa farms, field 2, hole B AF-2B 36.5497 116.5325 717 10

Amargosa farms, field 3, hole A AF-3A 36.5461 116.4897 717 15

Amargosa farms, field 3, hole B AF-3B 36.5442 116.4917 718 16

1

North latitude and west longitude; North American Datum of 1927.

2

Land surface altitude, National Geodetic Vertical Datum of 1929.

3

Composited data from boreholes at the Amargosa Desert Research Site (see Stonestrom, Prudic, and others, 2004).

Description Code Latitude1

, 

in degrees

Longitude1, 

in degrees

Altitude2, 

in meters

Distance from

basin inlet3

,

in kilometers

Beatty Wash BW 36.9434 116.7190 1049 -8.3

Amargosa River at Beatty (station 10251217) GAGE 36.9106 116.7564 1003 -3.0

Amargosa River near highway 95 bridge PS-1 36.8802 116.7525 966 0.8

Amargosa River near airport road PS-2 36.8678 116.7595 954 2.4

Amargosa River near highway 95 bend PS-3 36.8595 116.7570 942 3.4

Amargosa River near beacon road PS-4 36.7979 116.7555 888 10.6

Unnamed tributary near beacon road PS-4T 36.7932 116.7647 887 NA4

Amargosa River west of ADRS5 PS-5 36.7658 116.7323 859 14.9

Amargosa River near Ashton site, east channel PS-6E 36.7111 116.6772 807 22.9

Amargosa River near Ashton site, west channel PS-6W 36.7066 116.6805 805 22.9

Unnamed tributary near Ashton site PS-6T 36.6887 116.6880 799 NA

Amargosa River near Big Dune PS-7 36.6324 116.6111 749 33.7

1

North latitude and west longitude; North American Datum of 1927.

2

Land surface altitude, National Geodetic Vertical Datum of 1929.

3

Measured from gap in bedrock at entrance to basin, 3.0 km downstream of USGS streamflow-gaging station 10251217 (Amargosa River at 

Beatty, Nev.). Negative value is distance upstream; positive is distance downstream.

4

NA—not applicable.

5

ADRS is the Amargosa Desert Research Site (Andraski and Stonestrom, 1999; http://nevada.usgs.gov/adrs/).

Table 2. Locations of sampled boreholes within the Amargosa Desert study area.

Table 1. Locations of streamflow-gaging station and peak-flow- and temperature-measurement sites, Amargosa Desert 

study area.
Results and Discussion 115

!..ATIVE6EGETATION ".!MARGOSA2IVER#HANNEL

#.)RRIGATED&IELD $.#ORE3AMPLEOF3EDIMENTS

Figure 7. Photographs of unsaturated-zone sediment sampling in the Amargosa Desert study area. A, Native vegetation, 

Amargosa Farms; B, Amargosa River channel; C, irrigated field; D, sediment core from channel.

assumed an exponential distribution of data errors, minimizing an L1-norm of combined data misfits and model stabilization constraints (Abraham and Lucius, 2004). Figure 9 

shows the locations of resistivity transects, unsaturated-zone 

sampling boreholes, and temperature measurement sites.

Results and Discussion 

Streamflow Characteristics

The volume of water passing the USGS streamflowgaging station at Beatty, Nev. (10251217; “Beatty gage” 

hereafter) during the four-year study period was 3.03 million 

cubic meters (Mm3), averaging 0.76 Mm3 per year (table 3; 

fig. 5). Even though precipitation during the study period was 

greater than the long-term average—25 percent greater at the 

ADRS, for example—the streamflow represents only a small 

fraction (less than 4 percent on an average annual basis) of 

historic maximum ground-water withdrawals in the Amargosa 

Farms area. Ranking the daily average flows, a sharp inflection point separates base flow from storm runoff at about 2.5 

cubic meters per minute (m3

 min-1). Base flow dominates the 

record in terms of duration and volume. About 95 percent 

(1389 of 1461) of daily average flows were less than 2.5 m3

min-1. From a volume standpoint, roughly three quarters of the 

discharge at the Beatty gage during the four-year period—2.26 

Mm3

 of 3.03 Mm3—was base flow. The dominance of base 

flow into the Amargosa Desert Basin contrasts sharply with 

the dominance of storm flow in the Abo Arroyo portion of the 

middle Rio Grande Basin (chapter D, this volume), reflecting 

weaker monsoonal influences, higher aridity, and the relatively 

permeable rocks and sediments of the Amargosa headwaters 

compared to the Abo Arroyo headwaters. 
116 Focused Ground-Water Recharge in the Amargosa Desert Basin

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Figure 8. Direct-current resistivity imaging in the Amargosa Desert study area. A, Transect near Amargosa Desert 

Research Site (ADRS; Andraski and Stonestrom, 1999); B, transect across Amargosa River channel (arrow points to 

person in channel); C, electrode (stainless steel stake); with wetted sediment around electrode to decrease contact 

resistance; D, multiplexing resistivity meter; E, sequence of measurements.
Results and Discussion 117

  

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Figure 9. Detailed locations of temperature sites, resistivity transects, and unsaturated-zone 

boreholes in the Amargosa Desert study area. Temperature-measurement sites are denoted by 

PS-number (table 1). ADRS and AFNV denote boreholes in undisturbed native vegetation at the 

Amargosa Desert Research Site and in the Amargosa Farms area (table 2). Additional boreholes in 

irrigated fields south and southeast of AFNV (not shown) are listed in table 2. Resistivity transects are 

denoted by blue lines near probe sites PS-4, PS-6, and borehole ADRS. Blue square (GAGE) denotes the 

USGS streamflow-gaging station at Beatty, Nev. (10251217). Figure 1 shows the study-area location with 

latitudes and longitudes.
118 Focused Ground-Water Recharge in the Amargosa Desert Basin

Water 

year1

Median daily 

average flow,

in cubic meters 

per minute

Maximum daily 

average flow,

in cubic meters 

per minute

Minimum daily 

average flow,

in cubic meters 

per minute

Total 

volume2

, 

in millions 

of cubic 

meters

Storm-flow 

volume2

,

in millions 

of cubic 

meters

Base-flow 

volume2

,

in millions of 

cubic meters

Base-flow 

volume,

in percentage of total 

volume

19983 1.1 37 0.42 0.88 0.36 0.52 59

19993 1.2 19 0.41 0.69 0.08 0.61 89

20003 1.0 13 0.46 0.73 0.17 0.56 77

20014 0.9 20 0.55 0.74 0.17 0.56 77

Four-year study period

1998–

2001 1.1 37 0.41 3.0 0.78 2.3 74

1

Water year is October 1 through September 30 and denoted by calendar year in which it ends.

2

Values rounded for reporting purposes. Calculations used unrounded numbers.

3

Water-year statistics derived from daily means obtained at http://waterdata.usgs.gov/nwis; accessed January 3, 2007.

4

Statistics derived from daily means of 15-minute data.

Table 3. Amargosa River flow at Beatty, Nev. (USGS streamflow-gaging station 10251217) for water years 1998–2001. 

Summary daily statistics and total storm-flow versus base-flow volumes.

The strongest El Niño of the modern instrumental record 

(post 1981) produced increased precipitation during the first 

year of the study period (Curtis and Adler, 2000; Vecchi and 

others, 2006). Rainfall at the ADRS in water year 1998 was 

238 mm, more than twice the long-term average (Johnson and 

others, 2002). February was the wettest month, accounting for 

about 42 percent of annual precipitation. Frontal systems moving through the region resulted in several flows into the Amargosa Desert Basin, with peak flows at the Beatty gage larger 

than 20 m3 min-1 on two occasions by mid month, February 

4, 1998 (36 m3 min-1) and February 15, 1998 (44 m3 min-1). 

These storms were followed by a large, slow-moving system 

that produced widespread flooding on February 23–24. The 

largest flow of the study period, about 150 m3 min–1, occurred 

on February 23 (fig. 5).

Other large runoff events occurred in July 1999, August 

2000, and July 2001 (fig. 5). Of these, only the July 1999 

flows traversed more than a few kilometers into the Amargosa 

Desert Basin. The July 1999 flows stemmed from a stationary 

region of high-pressure that started building over the fourcorners region early in the month. Associated anticylonic 

circulation transported subtropical moisture from the Gulf 

of California into the Amargosa area. Flashy runoff from 

convective storms was recorded by the Beatty gage on July 9, 

13, and 14 (fig. 5).

Site visits following large storms established the extent 

and peak rates of flow. Table 4 shows estimated peak flows 

for storms during the study period that produced peak flows 

at the Beatty gage exceeding 80 m3 min-1. Peak-flow estimates 

were made by using the slope-area method, where the energy 

gradient was determined by detailed surveying of high-water 

marks, and the slope-conveyance method, where the gradient 

is approximated by the channel slope. Whereas slope-area estimates are more accurate, they too are uncertain (Jarrett, 1987). 

In both cases the largest errors are systematic, making relative 

changes instructive.

An actively used road to a mining operation crosses 

the channel near PS-2, 2.4 kilometers from the entrance to 

the basin (fig. 9). The unpaved road lacked culverts and was 

regraded following flow events that extended into the basin 

past the road. The February 1998 flows readily breached a low 

roadbed, judging from high-water marks upstream and downstream of the road. The first of the July 1999 flows breached a 

higher roadbed, which acted as a temporary dam. Thus, peak 

flows of the July 1999 event downstream of PS-1 were artificially increased by the sudden release of ponded water.

Streamflow passing through the Beatty gage is generally 

lost to seepage within a few kilometers of entering the Amargosa Desert Basin. The storm-generated flow of February 

23-24, 1998 passed through the entire basin, extending from 

the Nevada Test Site to Death Valley (Tanko and Glancy, 2001). 

The peak flow rate was estimated to be 156 m3

 min-1 at Beatty 

(90 cubic feet per second) and 36 m3 min-1 at Big Dune (20 

cubic feet per second). These estimates indicate that 120 m3

min–1 of flow were lost along the reach, if lateral inflows were 

negligible. Assuming a uniform loss rate, the average loss rate 

was about 3.4 m3 min-1 per kilometer. This suggests that a flow 

event with a peak rate of at least 44 m3 min-1 at the Beatty gage 

would reach channel site C1, the instrumented borehole at PS-4, 

and similarly 85 m3 min-1 would reach channel site C2, the 

instrumented borehole at PS-6E. Site C1 and C2, respectively, 

are 13.6 and 25.9 km downstream of the Beatty gage.
Results and Discussion 119

[<, less than; ~, approximately]

Brief description and site

code1

February 23–24,

1998

July 13,

1999

August 30,

2000

July 7,

2001

Estimated peak streamflow, in cubic meters per minute2

Beatty Wash (BW) 39 (51) 0 0 204

Beatty gage (GAGE2

) 143 (153) 143 126 88

Highway 95 bridge (PS-1) 117 51 minor 3

Airport road (PS-2) 65 204 ~03 <0.2

Bend (PS-3) 56 119 ~03 —4

Beacon road (C1) 39 76 0 —4

Beacon tributary (PS-4T) 0 ~03 ~03 —4

West of ADRS (PS-5) 53 51 ~03 —4

Ashton east branch (C2) 39 8 ~03 0

Ashton weat branch (PS-6W) 24 17 ~03 0

Ashton tributary (PS-6T) 0 0 0 0

Big Dune (PS-7) 16 (34) 2 0 0

1

Tables 1 and 2 give site locations.

2

Sites not at USGS streamflow-gaging station 10251217—Amargosa River at Beatty, Nev. (GAGE) were estimated by slope-conveyance 

method. Slope-area estimates, where available, are in parentheses.

3

Peak flow too small to measure (approximately zero)—evidence of sheet flow or segmented flow and local ponding only.

4

Site not visited, but presumed to have had no flow.

Table 4. Estimates of peak flow in the Amargosa River and its main tributaries in the Amargosa Desert study area for 

major runoff events during water years 1998–2001.

To characterize the frequency of flows capable of reaching C1 and C2, data from stream-gaging stations at Beatty 

(including historic partial-record crest-stage stations listed 

in the caption to fig. 6) were compiled for the 37-year period 

of record. Flow events with a peak discharge greater than 

44 m3

 min-1 occurred on at least 26 occasions (Stonestrom, 

Prudic, and others, 2003). Flows with peaks greater than 85 

m3 min-1 occurred on at least 16 occasions. Not all flows were 

documented, as only annual peak discharges were recorded in 

most years. The largest flow on record occurred on February 

24, 1969 (fig. 6). This flood peaked at about 27,000 m3 min-1, 

surpassing other flows by a factor of 3.8 (Moosburner, 1978).

Flow durations were characterized with data from the 

Beatty gage, where stage was recorded every 15 minutes 

from August 1993 to April 1995 and from January 1996 to 

October 2001. Flow was divided into 4 categories: 0 to 6 m3

min-1, greater than 6 to 44 m3 min-1, greater than 44 to 85 m3

min-1, and greater than 85 m3 min-1. Flow at the Beatty gage 

was less than 6 m3 min-1 about 99 percent of the time. Flows 

greater than 44 m3

 min-1 occurred only about 0.13 percent of 

the time. Flows greater than 85 m3 min-1 occurred only about 

0.04 percent of the time. Assuming no lateral inflow from 

tributary channels, and a uniform loss rate, the estimated 

total duration of flow at C1 is about 11 hr yr-1 at C1 and 3.5 

hr yr-1 at C2. Average seepage losses during flow events, 

assuming an average channel width of three meters, is about 

1.1 millimeters per minute, or 68 millimeters per hour. Multiplying this rate by 11 hours yields an annual infiltration 

rate of about 0.75 m yr-1 at C1. Similarly, multiplying by 3.5 

hr yields an annual infiltration rate of about 0.24 m yr-1 at 

C2 (table 5). These estimates are approximate and do not consider possible additions from tributaries or direct runoff from 

the basin floor. They also do not consider antecedent conditions and variations in channel width. Nevertheless, the data 

indicate that seepage losses occur throughout the study reach.

Thermal Detection of Streamflow and Infiltration

Streambed thermal anomalies provided detailed information on the extent and duration of flows. Figure 10 shows 

precipitation, streamflow, and example thermographs for the 
120 Focused Ground-Water Recharge in the Amargosa Desert Basin

[m/yr, cubic meters of water per square meter of land surface per year; g/m2 yr, grams per square meter of land surface per year; g/m3, grams 

per cubic meter of pore water; m3

/m3, cubic meter of pore water per cubic meter of bulk sediment]

Borehole 

code1

Infiltration-flux 

density2,

in m/yr

Chloridemass flux 

across land 

surface2

,

in g/m2 yr

Interval 

used for 

calculation,

in meters

Recharge,

in percentage of 

infiltration

Chloride 

concentration in 

interval,

in g/m3

Recharge-flux 

density from 

chloride massbalance,

in m/yr

Average 

water 

content in 

interval,

in m3/m3

Estimated 

time to 

reach water 

table3,

in years

Rechargeflux density 

from tracervelocity2

,

in m/yr

Amargosa River channel (ephemeral flow, normally dry)

C1 0.75 11 1.1–14.4 12 121 0.09 0.21 225 NA4

C2 0.24 4 1.6–9.5 15 97 0.04 0.18 470 0.07

Undisturbed native vegetation (interfluvial surfaces)

ADRS 0.11 0.06 —5 — — — — — —

AFNV 0.11 0.06 — — — — — — —

Field 1 (7.7–year old irrigated field, used continuously)

AF-1A 2.1 14 1.5–5.9 6 116 0.12 0.21 60 0.196

AF-1B 2.1 14 1.2–14.0 10 69 0.21 0.20 34 0.306

Field 2 (irrigated field, used intermittently since the 1960s)

AF-2A 2.1 14 0.8–9.8 22 30 0.47 0.16 12 0.177

AF-2B 2.1 14 1.2–9.7 9 71 0.20 0.16 30 0.137

Field 3 (irrigated field, used continuously since the 1960s)

AF-3A 2.8 19 0.8–9.9 14 48 0.44 0.17 14 NA4

AF-3B 2.8 19 0.8–16.0 17 42 0.50 0.22 15 NA4

1

See table 2 and figure 9 for locations. 

2

Surface fluxes and chloride concentrations from Stonestrom, Prudic, and others (2003).

3

Water table is about 35 meters deep beneath the Amargosa farms (AF) sites and 100 meters deep beneath the Amargosa River channel (C1 and C2) sites. 

Travel times assume one-dimensional vertical flow.

4

NA, not available. 

5

—, not applicable.

6

From velocity of chloride peak.

7

From velocity of nitrate peak.

Table 5. Infiltration- and recharge-flux densities as estimated from pore-water concentrations of chloride and nitrate in contrasting 

hydrologic settings, Amargosa Desert study area.
Results and Discussion 121

February 23–24, 1998 flow event. Comparisons of the channel 

thermographs with control thermographs outside the active 

channel at PS-1, PS-5, and PS-6E allowed non-flow events to 

be differentiated from flow events, even for low-flow conditions (fig. 11; Constantz and others, 2001).

Figures 12 and 13 show typical thermographs for drychannel and flowing conditions, repectively. In Beatty Wash, 

just upstream of its confluence with the Amargosa River, flow 

began at about 10:00 a.m. on February 23 and ended 17 hours 

later. The duration was extended by snowmelt from higher 

elevations (Tanko and Glancy, 1999). The initiation of flow 

is indicated by the change from a diurnally varying temperature to a nearly constant temperature. The cessation of flow is 

indicated by reappearance of the diurnal signal. Flow exhumed 

the temperature logger, increasing the diurnal range. Twelve 

hours after arriving at Beatty Wash, flow arrived at the PS-1 

site, 9.1 kilometers downstream. Flow at PS-1 lasted about 8 

hours. Flow arrived at PS-6E at about 3:00 a.m. on February 

24, 31.2 kilometers downstream from Beatty Wash, and lasted 

about 3 hours.

Flows in February 1998 occurred during long periods 

of overcast skies, reducing the magnitude of thermal signals. 

Summer flows were marked by larger signals. Figure 14 shows 

thermographs indicating the July 1999 flows. The contrast 

between ambient streambed temperatures and ephemeral 

streamflow averages about 10°C. Flows are more easily identified in summer than in winter, because of greater contrasts 

between the temperature of streamflow and channel sediments 

prior to flow.

Brief periods of flow near the basin inlet also were indicated by thermocouple-nest data corresponding to the JanuaryFebruary 2001 flow events. Times of peak flows as recorded 

by the Beatty gage (fig. 5) are indicated by arrows (fig. 15). 

Downward advection of heat by infiltrating water compressed 

the ambient range in temperatures and carried diurnal fluctuations deep into the profile. The thermal anomalies from brief 

periods of ephemeral flow appear as perturbations on the 

seasonal turnover of the temperature gradient (fig. 15).

Nearly all of the thermal records are for dry-channel conditions, but even these show systematic variations consistent 

with the relative frequency of flow. Average channel temperatures increased with distance from the basin inlet. The increase 

is greater than the 0.0098°C per meter of altitude decrease 

expected on the basis of weather-station data, suggesting 

cooling from greater quantities of infiltration and evaporation 

closer to the basin inlet. Deep temperature profiles support this 

suggestion. Annual temperature envelopes at the two channel 

locations (C1 and C2) and at the ADRS (between C1 and C2) 

show that the highest temperatures are outside the channel, 

where deep percolation and evaporated streamflow amounts 

are negligible. The coolest conditions are at the upstream 

channel location, where streamflow is most frequent and deep 

percolation amounts highest (fig. 16). The temperature difference between upstream and downstream locations is about 

20 percent greater than can be accounted by the difference in 

elevation. The difference between the warmest temperatures, 

at the ADRS, and coolest temperatures, at the downstream 

channel site, is opposite that expected from altitude. 

The difference in annual volume of infiltrated water 

between upstream and downstream channel locations is about 

1.5 m3

 per meter of channel length. Assuming reasonable 

values for sediment density (2.0 × 106 gram m-3) and heat 

capacity (2.2 × 106 joule m–3 °C-1) at ambient water content, 

and given the large latent heat of evaporation (2.27 × 109

joule m-3), the cooling power of infiltrated water is more than 

sufficient to account for the difference in temperatures. If half 

of the infiltrated volume later evaporated, channel sediment 

3 meters wide (the width of the active channel) by 20 meters 

deep would cool about 13°C per year if all heat came from 

cooling of the sediment. Depth and degrees of cooling are 

inversely proportional. The actual cooling is far less than this 

because of heat exchange with surrounding sediments. Nevertheless, average temperatures reflect differences consistent 

with infiltration and recharge regimes.

Recharge Estimates from Potential and 

Environmental-Tracer Profiles

Profiles of water potential, water content, and solute 

concentrations beneath irrigated fields, undisturbed native 

vegetation, and the normally dry channel of the Amargosa 

River also reflect the contrast in recharge regimes. Examples 

of water-potential profiles beneath the channel, native vegetation, and irrigated fields are shown in figure 17. Water 

potentials generally are low beneath native vegetation, with 

potentials lower (more negative) than –5 megapascals (MPa) 

in most of the profile. The profile beneath native vegetation 

in the Amargosa Farms area is similar to the profile beneath 

native vegetation at the ADRS, where calculated deeppercolation fluxes are zero to slightly upward (Walvoord and 

others, 2004). Gradients of temperature, water potential, and 

stable isotopes beneath undisturbed native vegetation at the 

ADRS indicate a net upward flow of heat and water throughout the profile (Stonestrom and others, 1999). Models of heat 

and water movement indicate that these profiles are not in 

equilibrium with current climatic conditions—instead, they 

are slowly drying in response to the change from pluvial to 

arid conditions that occurred in the late Pleistocene (Walvoord and others, 2004).

In contrast, to the profiles beneath native vegetation, 

water potentials beneath irrigated fields and the Amargosa 

River channel indicate net downward movement of water, 

with potentials close to zero in most of the profile (fig. 17). 

Water potentials are more variable beneath a more recently 

converted field than beneath fields converted in the 1960s, 

reflecting the shorter duration of irrigation return flow. High, 

nearly uniform water potentials beneath the older fields and 

channel sites indicate long-established deep percolation in 

which the sediments have water potentials associated with 

approximately steady-state downward flow (Stonestrom, 

Prudic, and others, 2003).
122 Focused Ground-Water Recharge in the Amargosa Desert Basin

0 

150 

100 

50 

0 

5 

10 

15 

20 

25 

30 

0 

5 

10 

15 

20 

25 

30 

0 

5 

10 

15 

20 

25 

30 

0 

5 

10 

15 

20 

25 

30 

0 

5 

10 

15 

20 

25 

30 

35 

0 

5 

10 

15 

20 

25 

30 

1/8 1/15 1/22 1/29 2/5 2/12 2/19 2/26 3/5 3/12 3/19 

1/8 1/15 1/22 1/29 2/5 2/12 2/19 2/26 3/5 3/12 3/19 

1/8 1/15 1/22 1/29 2/5 2/12 2/19 2/26 3/5 3/12 3/19 

1/8 1/15 1/22 1/29 2/5 2/12 2/19 2/26 3/5 3/12 3/19 

1/8 1/15 1/22 1/29 2/5 2/12 2/19 2/26 3/5 3/12 3/19 

1/8 1/15 1/22 1/29 2/5 2/12 2/19 2/26 3/5 3/12 3/19 

1/8 1/15 1/22 1/29 2/5 2/12 2/19 2/26 3/5 3/12 3/19 

STREAMBED TEMPERATURE, IN DEGREES CELSIUS 

FLOW, IN CUBIC 

METERS PER MINUTE 

DATE 

PRECIPITATION, IN 

MILLIMETERS 

STREAMBED TEMPERATURE AT: 

BW 

STREAMFLOW AT 

BEATTY GAGE 

PRECIPITATION AT BEATTY 

PS-1 

PS-6E 

PS-6W 

PS-3 

Figure 10. Precipitation and streamflow at Beatty, Nev., and streambed temperatures at selected sites in Beatty Wash (BW) and the 

Amargosa River channel, January 8 through March 17, 1998. Site locations are shown on figure 9.
Results and Discussion 123

15 

20 

25 

30 

35 

40 

1999/07/01 1999/07/08 1999/07/15 1999/07/22 

15 

20 

25 

30 

35 

40 

1999/07/01 1999/07/08 1999/07/15 1999/07/22 

-8 

-6 

-4 

-2 

0 

2 

4 

6 

8 

1999/07/01 1999/07/08 1999/07/15 1999/07/22 

Tributary streambed temperature 

Control temperature 

Streambed − control Period of inferred flow 

DATE

TEMPERATURE DIFFERENCE, 

IN DEGREES CELSIUS 

CONTROL TEMPERATURE, 

IN DEGREES CELSIUS 

STREAMBED TEMPERATURE, 

IN DEGREES CELSIUS 

Figure 11. Timing of sheet flow in an unnamed minor tributary to the Amargosa River (site PS-6T, figure 9) is indicated by a 

drop in the streambed temperature as compared to the control temperature. Temperatures higher than the upper limit of the 

temperature logger are truncated at 38oC.
124 Focused Ground-Water Recharge in the Amargosa Desert Basin 342%!-"%$4%-0%2!452%).$%'2%%3#%,3)53 342%!-"%$4%-0%2!452%).$%'2%%3#%,3)53 342%!-"%$4%-0%2!452%).$%'2%%3#%,3)53































       

       

       

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Figure 12. Example streambed temperatures during dry conditions, Amargosa 

Desert study area, January 22 through 28, 1998. Site locations are shown on figure 9.
Results and Discussion 125

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Figure 13. Example streambed temperatures during period with ephemeral 

flow, Amargosa Desert study area, February 21 through 25, 1998. Arrows 

indicate thermal anomalies interpreted as initiation and cessation of flow. Site 

locations are shown on figure 9.
126 Focused Ground-Water Recharge in the Amargosa Desert Basin

   













   













   













   













   













   













   













   









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Figure 14. Amargosa River streamflow at Beatty, Nev., and streambed temperatures downstream, July 1 through 21, 

1999. Temperatures higher than the upper limit of the temperature logger are truncated at 38oC. Figure 9 shows site 

locations.
Results and Discussion 127

      



























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Figure 15. Channel temperatures at six depths near PS-2, 2.4 kilometers from the basin inlet, Amargosa Desert study 

area, November 2000 through March 2001. Arrows show times of peak flow at Beatty (fig. 5). Gap in record is due to loss 

of power to data logger.

Figure 16. Annual 

temperature envelopes 

beneath channel site C1 

and C2, 10.6 and 22.9 km 

downstream from the 

Amargosa Desert Basin 

inlet, and beneath native 

vegetation at the Amargosa 

Desert Research Site 

(ADRS), halfway between C1 

and C2. Figure 9 shows site 

locations.
128 Focused Ground-Water Recharge in the Amargosa Desert Basin






















  
  
  
  
  
  
 
 
 
  

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Chloride and nitrate profiles at all undisturbed nativevegetation sites are similar, with large increases in concentration (bulges) just below the root zone (fig. 18). Bulges in the 

concentrations of atmospherically derived salts are common 

beneath desert plants (Phillips, 1994; Tyler and others, 1996; 

Hartsough and others, 2001). Initiation of chloride accumulation dates back to the major change in climate from the cool 

and wet (pluvial) conditions prevailing during the late Pleistocene to the arid-thermic conditions prevailing today (Walvoord 

and others, 2004). Increasing aridity led to the succession of 

xerophytes efficient at scavenging moisture, resulting in accumulation of atmospherically deposited salts just beneath the 

root zone (Walvoord, Plummer, and others, 2002; Walvoord, 

Phillips, and others, 2002). The change from pluvial to dry 

conditions in the Amargosa Desert Basin may have started as 

early as 20,000 years ago on the basis of vegetation changes in 

the area (Spaulding, 1985), paleoclimate modeling (Spaulding 

Figure 17. Unsaturated-zone water potential profiles beneath 

native vegetation and irrigated fields in the Amargosa Farms area, 

and the normally dry Amargosa River channel. Storms wetted 

surface sediments prior to sampling in February 2001, producing 

near-zero water potentials at shallow depths at all sites. Water 

potentials beneath the Amargosa River channel (C1 and C1, 

triangles) and older fields (2 and 3, circles and diamonds) are 

close to zero throughout the profile. Water potentials beneath the 

new field (open squares) are near zero but more variable than 

beneath the older field. From Stonestrom and others (2004).

and Graumlich, 1986), and an abrupt decline in ground-water 

level recorded at Devils Hole (fig. 1; Szabo et al., 1994). 

Assuming that the profiles beneath field 1 were initially 

like those beneath undisturbed native vegetation, chloride 

peaks at depths of about 9 and 13 m demonstrate that deep 

percolation from irrigation return flow is moving previously 

accumulated chloride downward from just below the root 

zone (fig. 18A). Eight years of irrigation is insufficient to flush 

accumulated salts from the sampled profile completely. Subroot-zone nitrate profiles are similar to the chloride profiles, 

reinforcing this conclusion (fig. 18B).

Chloride concentrations beneath the root zone of field 2 

are uniformly low, indicating that deeply percolating irrigation 

water has flushed the presumed preexisting bulge completely 

from the measured profile (fig. 18A). Sub-root-zone nitrate 

concentrations are much lower than chloride concentrations 

at most depths, except for one interval in each profile where 

nitrate concentrations are consistently at least twice the chloride concentrations. These well-defined nitrate peaks occur in 

the 6.9–8.3-m interval at one borehole and in the 8.3–9.8-m 

interval at the other (fig. 18B). The peaks most likely represent 

heavy application of liquid fertilizer in 1992, when the field 

was returned to production.

Profiles of chloride and nitrate beneath the Amargosa 

River channel are similar to those beneath the irrigated fields 

in that they lack salt accumulations near land surface 

(fig 18). Chloride and nitrate concentrations at the upstream 

site are low throughout the profile at all depths greater than 1 

m. Concentrations at the downstream site rise sharply in the 

10 to 14-m depth interval. This abrupt rise suggests downward 

displacement of a previously formed salt bulge, similar to the 

downward-advected bulge at field 1.

The active channel at C2 appears to have moved to its 

current position during the record flood of 1969 (fig. 6). 

Aerial photographs taken before 1969 show the channel at 

C2 about 0.5 kilometer east of its present location and the 

channel at C1 in its present location. Photos taken after 1969 

show the channel in its present location at both sites. As 

at field 1, the duration of deep percolation at C2 has been 

insufficient to move previously accumulated salts completely 

from the sampled profile.

General Patterns of Deep Percolation and 

Ground-Water Recharge

The slope of the relation between cumulative chloride 

and cumulative water represents a depth-integrated pore-water 

chloride concentration. A linear relation that passes through 

the origin is consistent with the hypothesis that chloride fluxes 

at depth are in approximate equilibrium with time-averaged 

fluxes across the land surface, in accordance with the assumptions of the chloride mass-balance method (Stonestrom, Prudic 

and others, 2003).

Almost all of the profiles beneath the irrigated fields and 

channel sites show evidence of approximately steady-state 
Results and Discussion 129





















   

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,)4%2/&0/2%7!4%2

.)42!4%#/.#%.42!4)/.).-),,)'2!-30%2

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Figure 18. Profiles of anion concentrations in pore water beneath native vegetation, irrigated fields, and the Amargosa River 

channel, in the Amargosa Desert study area. A, chloride-concentration profiles; B, nitrate-concentration profiles. The ADRS is the 

Amargosa Desert Research Site (fig. 9). From Stonestrom and others (2004).

deep percolation, that is, simple linear relations that extrapolate towards the origin (fig. 19). Deviations in slope near the 

origin reflect the effects of unfiltered variations in surface 

forcing from meteorological conditions in the immediate past. 

The new field and the downstream channel site show concave 

upward departures from linearity at depth. As already discussed, these reflect previously formed shallow salt accumulations moving downward through the profile due to the recent 

onset of deep percolation.

In contrast to the sites indicating steady deep percolation, relations between cumulative chloride and cumulative 

water content beneath native vegetation are characterized by 

steep segments at shallow depths (close to the origin) that do 

not extrapolate through the origin, followed by sharp inflections to relatively low slopes beneath the root zone (far from 

the origin; fig. 19). These patterns indicate a lack of chloride 

throughput due to lack of water movement between the bottom 

of the root zone and the water table. The non-linear relations 

show that chloride fluxes at depth are not in equilibrium with 

fluxes across the land surface, violating a key assumption of 

the chloride mass-balance approach (Scanlon, 2000).

Multiyear observations at the ADRS indicate that precipitation on areas of undisturbed native vegetation penetrates to 

depths of less than one meter before returning to the atmosphere (Fischer, 1992; Andraski, 1997). Isotopic data from the 

ADRS (Stonestrom and others, 1999) and the Nevada Test Site 

(Tyler and others, 1996) support the conclusion of negligible 

recharging fluxes under current climatic conditions and rule 

out dilution of deep pore water by preferential flow of recent 

infiltration. Instead, low chloride concentrations in pore water 

beneath shallow chloride and nitrate bulges represent relict 

recharge from pluvial periods. Modeling studies of coupled 

heat and water movement indicate that the net movement of 

water (liquid plus vapor) is upwards in an increasingly deep 

region beneath the root zone under current climatic conditions 

(Walvoord and others, 2004). 

Estimates of Recharging Fluxes Beneath 

Irrigated Fields

Table 5 shows chloride mass-balance estimates of 

recharging fluxes beneath irrigated fields. The table includes 

the depth intervals and average pore-water chloride concentrations corresponding to the linear portions of the cumulativewater versus cumulative-chloride curve for which the chloride 

mass-balance method applies (fig. 19).

The chloride-mass balance estimates of deep percolation for field 1 are 0.12 and 0.21 m yr-1. Downward displacement of the salt bulge following onset of irrigation in field 1 
130 Focused Ground-Water Recharge in the Amargosa Desert Basin















       

.ATIVE

VEGETATION

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"

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Figure 19. Cumulative mass of chloride versus cumulative 

volume of water beneath undisturbed native vegetation, irrigated 

fields, and the Amargosa River channel, in the Amargosa 

Desert study area. Slopes of the curves represent pore-water 

concentrations of chloride, which are inversely proportional 

to recharge rates for steady-state conditions (linear relations). 

AF-3B is in the interior of the field; 3A is on the perimeter. Dashed 

arrows indicate time trajectories of profile evolution under current 

climatic and land-use conditions. The ADRS is the Amargosa 

Desert Research Site (fig. 9). From Stonestrom and others (2004).

provides a largely independent estimate of deep percolation. 

Assuming that the center of mass of the chloride moved from 

about 1.8 m (the observed depth under native vegetation) to 

8.9 and 13 m in 7.7 years, the macroscopic velocities of the 

bulge are 0.9 and 1.5 m yr–1, respectively. Multiplying by the 

average water content gives deep-percolation estimates of 0.19 

and 0.30 m yr–1 (table 5). These rates are about 50 percent 

higher than the chloride mass-balance estimates, reflecting the 

uncertainty of the estimates (Stonestrom, Prudic and others, 

2003). Similar variations in deep-percolation rates characterized a sandy agricultural field in a semiarid region in the western Murray Basin, South Australia (Cook and others, 1989).

The chloride mass-balance estimates of deep percolation for field 2 are 0.20 and 0.47 m yr-1. Travel-time estimates 

based on the nitrate peak are 0.13 and 0.17 m yr-1 (table 5). 

These estimates are based on the assumption that the deep 

nitrate peaks represent surface application of liquid fertilizer 

in 1992, when field 2 went back into production after being 

fallow for nine years. The lower nitrate-based values suggest retardation of nitrate relative to chloride in the root zone 

(Smith, Doyle, and others, 1997). Chloride mass-balance 

estimates of deep percolation beneath field 3 are 0.44 and 0.50 

m yr-1 (table 5). The percentage of irrigation water returning 

to the water table is simply the ratio of chloride concentration in irrigation water to that in deep pore water. The average 

estimated percentage of return flow is 8 percent for field 1, 15 

percent for field 2, and 16 percent for field 3. Differences correlated with cultivation histories. Field 3 had the highest rates 

of irrigation and the highest percentage of return flow.

The depth to ground water beneath the irrigated fields 

is about 35 m (Kilroy, 1991). Assuming vertical, one-dimensional flow, the estimated time for irrigation return flow to 

reach the water table is 12–30 years beneath fields 2 and 3, 

and 34–60 years beneath field 1 (table 5). This pattern is consistent with asymptotically decreasing divergence of infiltrating water through time following the onset of irrigation in an 

initially dry profile (Philip, 1983).

Estimates of Recharging Fluxes Beneath the 

Amargosa River Channel

Chloride mass-balance estimates of deep percolation for the upstream-channel site (C1) used the entire 

profile below 1.1 m, the depth below which the cumulative chloride-cumulative pore water relationship indicated 

approximately steady conditions (table 5). Estimates for the 

downstream site excluded concentrations deeper than 9.5 

m. Elevated chloride beneath this depth evidently represents 

a near-surface accumulation that began moving downward 

when the active channel shifted to its current location, as 

indicated by aerial photographs. Chloride mass-balance 

deep-percolation rates were 0.09 m yr-1 at the upstream site 

and 0.04 m yr-1 at the downstream site. These rates exceed 

estimated sub-root zone liquid and vapor fluxes at the 

ADRS by several orders of magnitude (Walvoord and others, 2004). Thus, virtually all deep percolation beneath the 

channel becomes ground-water recharge.

Assuming that the chloride bulge at C2 moved downward from 1.8 to 14.4 m in the 32 years between the flood 

of 1969 and sampling in 2001, the macroscopic velocity is 

0.39 m yr–1. The travel-time estimate of deep percolation is 

the product of the macroscopic velocity times the volumetric 

water content of 0.18, or 0.07 m yr-1 (table 5). This value is 

in approximate agreement with the chloride mass-balance 

rate of 0.04 m yr-1.

The percentage of channel infiltration that becomes deep 

percolation is about 12 percent for the upstream site and about 

15 percent for the downstream site (table 5). Multiplying by 

the average annual streamflow volume of 3.0 Mm3

 yr-1 (table 

3), the amount of ground-water recharge from channel infiltration is about 0.4 Mm3

 yr-1. 

Depth to ground water beneath the Amargosa River 

west of the ADRS was 103 m in 1985 (W.D. Nichols, USGS, 
Summary and Conclusions 131

Carson City, Nev., unpub. data, 1985). Assuming the water 

table is about 100 m below the riverbed, channel infiltration 

takes approximately 225 years to reach the aquifer at C1 and 

470 years at C2. These estimates are minimum times because 

the effects of lateral flow are not taken into account. While 

uncertainties in estimated recharge rates are considerable, the 

approximate agreement between travel-velocity estimates and 

chloride mass-balance estimates supports the general magnitude 

of the results.

Areal Generalization by Direct-Current 

Resistivity Imaging

The unsaturated-zone profiles considered above indicate 

that ground-water recharge is localized beneath the main 

channel of the Amargosa River and beneath irrigated fields, 

with little present-day recharge beneath native vegetation. 

These borehole-based results can be regionalized by remote 

sensing by using geomorphologic, pedologic, and vegetational mapping. To bridge the scales between remote sensing 

and borehole-profile analysis, the current study employed 

DC-resistivity imaging.

Numerical inversions of automated Schlumberger-array 

soundings assumed lateral homogeneity normal to the vertical slices being imaged, producing solution sets of resistivity 

values at several thousand points within each modeled cross 

section. Imaged sections were about 30 to 80 m deep and 

1 kilometer wide. Root-mean square errors between apparent 

resistivities in the model inversions and field-measured apparent resistivities were about 10 percent (Stonestrom, Abraham, 

and others, 2003; Abraham and Lucius, 2004).

On the basis of core data from cased boreholes, inverted 

resistivity () values denoted three categories of alluvium: 

(1) low water-content coarse gravel and highly desiccated 

surface material, with ρ greater than 200 Ohm-meters (Ω-m), 

(2) vertical regions of moist alluvium in areas of active 

recharge, with ρ less than 20 Ω-m, and (3) other low to 

low-medium water-content alluvium in areas without active 

recharge, with intermediate values of ρ (fig. 20). The cross 

section beneath native vegetation near the ADRS reveals 

laterally extensive gravel layers that provide preferential 

pathways for gas transport but that are impeding layers for 

downward movement of water through the unsaturated zone 

(Mayers and others, 2005).

The DC-resistivity images indicate focusing of active 

recharge beneath the Amargosa River channel. At the incised 

channel location upstream (C1), vertically elongated, lowresistivity regions indicating relatively moist sediments span 

the half-kilometer width of the channel (fig. 20A). A finger 

of low-resistivity sediment lies beneath the present low-flow 

channel. Pronounced low-resistivity regions are also found 

beneath the migrating reaches of the channel at the downstream site (C2; fig. 20B). The ADRS transect and extrachannel portions of channel transects (fig. 20C) suggest that 

little recharge occurs throughout most of the basin floor.

Summary and Conclusions

The current study characterized streamflow and groundwater recharge in the sparsely populated Amargosa Desert Basin 

of Nye County, Nev. High frequency streamflow and channeltemperature data indicated patterns of ephemeral streamflow 

during a 4-year period (water years 1998 through 2001). The 

period included the largest El Niño of the modern instrumental 

period, which enhanced precipitation, and two years of belowaverage precipitation.

The channel of the Amargosa River is dry more than 

98 percent of the time beyond a few kilometers downstream 

from the basin inlet, where perennial flow supports riparian 

vegetation. Base flow accounted for about three quarters of the 

3.0 million cubic meters (Mm3) of discharge at the Beatty gage 

during the 4-year study period. The average annual flow, 0.76 M 

m3 per year, was small relative to historic ground-water withdrawals for irrigation.

Streambed temperature anomalies indicated the duration 

and extent of storm-generated ephemeral flow into the basin. 

Only two flows traversed the entire reach of the Amargosa 

River during the 4-year study period. Durations and amount of 

flow declined rapidly down channel due to infiltration losses. 

Channel temperatures increased as infiltration and evaporation 

amounts decreased. Temperatures were warmest at the ADRS 

site, which received no flow, and lowest at the upstream channel 

site that received the most flow.

 Unsaturated-zone profiles of water potential and environmental tracers indicate sharply contrasting recharge regimes 

beneath native vegetation, irrigated fields, and the normally dry 

channel of the Amargosa River. Recharge is negligible beneath 

undisturbed native vegetation covering most of the Amargosa 

Desert floor, where water-potential profiles indicate upward 

flow and atmospherically deposited salts have been accumulating more or less continuously since the end of the Pleistocene. 

Accumulation of salts has formed pronounced bulges just below 

the root zone.

Near-zero water potentials and low salt concentrations 

beneath irrigated fields and the Amargosa River channel 

indicate active deep percolation and ground-water recharge. 

Transit times of recharge beneath the channel are on the 

order of centuries. Transit times of irrigation-return flow are 

on the order of decades. Velocities of displaced chloride and 

nitrate bulges beneath a migrated channel and a newly irrigated agricultural field provide largely independent estimates 

of recharging fluxes that are in approximate agreement with 

chloride mass-balance estimates.

Chloride mass-balance calculations indicate that 12 to 

15 percent of infiltrated channel water becomes recharge. 

The bulk of infiltrated water returns to the atmosphere. The 

associated evaporation cools the channel and reduces the 

amount of water available for ground-water recharge. The 

estimated amount of ground-water recharge from channel 

infiltration is about 0.4 Mm3 yr-1.

DC-resistivity imaging proved useful for extrapolating 

borehole-based values of ground-water recharge. Resistivity 
132 Focused Ground-Water Recharge in the Amargosa Desert Basin

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Figure 20. Direct-current resistivity transects in the Amargosa Desert study area. A, transect across the Amargosa River channel 

at site C1, 10.6 km from the basin inlet; B, transect across the Amargosa River channel at site C2, 22.9 km from the basin inlet, and; C, 

transect at the Amargosa Desert Research Site (ADRS). Figure 9 shows site locations.
References Cited 133

images of unsaturated-zone sediment clearly show focusing of 

recharge beneath the normally dry Amargosa River channel. 

Low-resistivities correspond to high water contents associated 

with active recharge from ephemeral streamflow. High-resistivities indicate coarse gravel layers and low water potentials, 

corresponding to regions without active ground-water recharge 

under current climatic conditions. Infiltration losses from the 

Amargosa River channel produce small amounts of recharge 

along the basin floor of the Amargosa Desert. 

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