USGS Professional Paper 1703—Ground-Water Recharge

in the Arid and Semiarid Southwestern United States—

Chapter J

Ephemeral-Stream Channel and Basin-Floor Infiltration 

and Recharge in the Sierra Vista Subwatershed of the 

Upper San Pedro Basin, Southeastern Arizona

By Alissa L. Coes and Donald R. Pool

Abstract

The timing and location of streamflow in the San Pedro 

River are partially dependent on the aerial distribution of 

recharge in the Sierra Vista subwatershed. Previous investigators have assumed that recharge in the subwatershed occurs 

only along the mountain fronts by way of stream-channel 

infiltration near the contact between low-permeability rocks 

of the mountains and the basin fill. Recent studies in other 

alluvial basins of the Southwestern United States, however, 

have shown that significant recharge can occur through the 

sediments of ephemeral stream channels at locations several 

kilometers distant from the mountains. The purpose of this 

study was to characterize the spatial distribution of infiltration 

and subsequent recharge through the ephemeral channels in 

the Sierra Vista subwatershed.

Infiltration fluxes in ephemeral channels and through 

the basin floor of the subwatershed were estimated by using 

several methods. Data collected during the drilling and coring 

of 16 boreholes included physical, thermal, and hydraulic 

properties of sediments; chloride concentrations of sediments; 

and pore-water stable-isotope values and tritium activity. Surface and subsurface sediment temperatures were continuously 

measured at each borehole.

Twelve boreholes were drilled in five ephemeral stream 

channels to estimate infiltration within ephemeral channels. 

Active infiltration was verified to at least 20 meters at 11 of 

the 12 borehole sites on the basis of low sediment-chloride 

concentrations, high soil-water contents, and pore-water tritium activity similar to present-day precipitation. Consolidated 

sediments at the twelfth site prevented core recovery and estimation of infiltration. Analytical and numerical methods were 

applied to determine the surface infiltration flux required to 

produce the observed sediment-temperature fluctuations at six 

sites. Infiltration fluxes were determined for summer ephemeral flow events only because no winter flows were recorded at 

the sites during the monitoring period.

Four boreholes were drilled in the basin floor to estimate 

infiltration in areas between ephemeral channels. Infiltration fluxes through the basin floor ranged from less than 1 

centimeter to 6 centimeters per year. At a site in semiconsolidated to consolidated basin-fill conglomerate, the long-term 

infiltration fluxes were very low (less than 1 centimeter per 

year). Chloride, tritium, and stable-isotope data indicate long 

periods of no net deep downward percolation flux beneath the 

basin floor. At a site in unconsolidated to semiconsolidated 

basin-fill sand and gravel, infiltration fluxes were high (2 to 

6 centimeters per year). Chloride, tritium, and stable-isotope 

data indicate active infiltration to 8 meters, and a decrease in 

infiltration below 8 meters. The change in the infiltration rate 

below 8 meters is controlled by an increase in the silt and clay 

content of the sediment.

Ephemeral-channel recharge for the entire subwatershed 

was estimated by upscaling the calculated infiltration fluxes 

and weighting the fluxes by streamflow duration, evaporation, and transpiration. In contrast to previous assumptions, 

recharge from ephemeral-streamflow infiltration occurs not 

only near the mountain fronts, but also along significant 

lengths of ephemeral channels. Although most of the ephemeral streams in the subwatershed flow less than a few days per 

year, the available streamflow quickly infiltrates past depths 

where it is available for evapotranspiration. This water likely 

stays in the unsaturated zone until it is vertically displaced by 

infiltrated water from subsequent streamflows and eventually 

recharges the regional aquifer. Ephemeral-channel infiltration 

during 2001 and 2002 was estimated to account for about 12 

to 19 percent of the estimated average annual recharge in the 

Sierra Vista subwatershed.

Introduction

An improved understanding of the recharge distribution in the Sierra Vista subwatershed of the Upper San Pedro 

ground-water basin was needed to better estimate the effects 

of ground-water withdrawals on natural discharges from 

the system through base flow and riparian vegetation. The 

interception of ground water that would flow naturally from 

recharge areas to the San Pedro River by pumping could result 

in decreased streamflows in the river. The timing and location 

of the reduced streamflow are dependant on the location of 

the withdrawal wells, the hydraulic properties of the aquifer, 

and the aerial distribution of recharge. Recharge occurring 

downgradient of withdrawal wells is less likely to be cap-
254 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona

tured by withdrawal wells and more likely to discharge to 

the river. Improved understanding of recharge distributions 

will enable local, State, and Federal organizations and agencies to effectively manage available water resources to meet 

water needs in the basin. Toward this goal, the U.S. Geological Survey (USGS), in cooperation with the Bureau of Land 

Management (BLM) and the Upper San Pedro Partnership, 

has collected and analyzed hydrologic information describing 

infiltration and recharge, ground- and surface-water interactions, water-level and ground-water storage trends, and 

geometry and lithology of the aquifer. This report documents 

the results of investigations of recharge by stream-channel 

and basin-floor infiltration, potentially important recharge 

mechanisms in the basin.

The Sierra Vista subwatershed encompasses about 2,460 

square kilometers (km2) in the southern part of the San Pedro 

River Basin in southeastern Arizona (fig. 1) and extends about 

43 km north from the international boundary with Mexico 

to near Fairbank, Ariz. The subwatershed is part of a broad 

alluvial basin and is bounded on the west by the Huachuca 

Mountains and on the east by the Mule Mountains and the 

Tombstone Hills. Elevations of the basin floor vary from about 

1,150 to 1,310 m; mountain elevations range from about 1,520 

to 2,900 m.

The San Pedro River flows northward through the subwatershed (fig. 1). The river and its associated ground-water 

system support a corridor of riparian vegetation that hosts 

several endangered species and is an important habitat for 

American migratory birds. About 64 km of the river and riparian area has been protected by designation as the San Pedro 

Riparian National Conservation Area (SPRNCA; fig. 1), and is 

managed by the BLM.

Sierra Vista, with a population of 37,775 in 2000, is the 

largest city in the subwatershed (U.S. Census Bureau, 2000). 

By 2020, the population of Sierra Vista is projected to be 

52,571 (Arizona Department of Economic Security, 1997), an 

increase of 39 percent. Populations of other cities in the subwatershed in 2000 were 6,090 in Bisbee, 1,751 in Huachuca 

City, and 1,504 in Tombstone (U.S. Census Bureau, 2000).

Ground water is the primary source for municipal, 

domestic, livestock, and irrigation water needs in the subwatershed. As the population has increased, ground-water withdrawals have increased. The magnitude of the effect that these 

increasing withdrawals have on the river and its associated 

riparian vegetation is proportional to the amount and distribution of recharge to the ground-water system. Ground-water 

pumping intercepts part of the natural flow of water through 

the aquifer before the water reaches natural discharge areas. 

Therefore, to better understand and predict the effects of historic, present, and future ground-water withdrawals on natural 

discharge, the spatial and temporal variability of recharge rates 

must be adequately understood.

Previous investigators have assumed that recharge in 

the Sierra Vista subwatershed occurs only near the mountain fronts (Freethey, 1982; Corell and others, 1996; Goode 

and Maddock, 2000). They envisioned recharge occurring 

as stream-channel infiltration near the contact of the lowpermeability rocks of the mountains and the basin fill. Recent 

studies in other alluvial basins of the Southwestern United 

States, however, have shown that significant recharge can 

occur through the sediments of stream channels far from the 

mountains (Blasch and others, 2000; Izbicki and others, 2000; 

Constantz and others, 2003). Direct infiltration of precipitation 

through the floors of alluvial basins in the Southwest has been 

considered negligible because of high evapotranspiration and 

low precipitation. The possibility of significant recharge along 

ephemeral stream channels far from the mountains or through 

direct infiltration on the basin floor places uncertainty on the 

adequacy of previous recharge concepts for use in the development of water-management plans.

Purpose and Scope

This report presents estimates of infiltration and recharge 

through the ephemeral channels and the basin floor of the 

Sierra Vista subwatershed, and documents the data collection and analysis. Data resulted from drilling and coring of 

16 boreholes and included physical, hydraulic, and thermal 

properties of sediment; chloride concentrations of sediment; 

pore-water stable-isotope values and tritium activity; neutronsoil moisture and electromagnetic induction (EMI) logs; and 

continuous sediment-temperature profiles and water levels 

during 2001 and 2002. Unsaturated-zone infiltration processes at six ephemeral-stream channel sites were modeled to 

estimate infiltration and percolation fluxes during and following streamflows.

Land Cover

Major types of land cover include grassland (32.6 percent), desert scrub (28.8 percent), mesquite woodland (13.5 

percent), and urban (5.3 percent; fig. 2; U.S. Environmental Protection Agency, 2003). The remaining 19.8 percent 

includes oak woodlands (15.2 percent) and forest (2.2 percent) 

in and near the mountains and the riparian (0.9 percent) and 

agricultural (0.8 percent) areas near the San Pedro and Babocomari Rivers (U.S. Environmental Protection Agency, 2003). 

Although the urban percentage is small, most of the urban land 

is concentrated in the north-central part of the subwatershed.

The hydrologic influence of each major land-cover type 

on the portion of precipitation that is transported to ephemeral 

stream channels has not been qualified. Some basic assumptions can, however, be inferred. Runoff produced in mesquite 

woodlands and desert scrub areas most likely is a small 

percentage of precipitation because leaves and branches can 

intercept precipitation and the high soil temperatures and low 

soil-moisture contents and potentials result in high soil permeability. Runoff from grasslands likely is a greater percentage 

of precipitation because the lower soil temperatures and higher 

soil-moisture contents result in lower soil permeability than 

that in mesquite woodlands and desert scrub areas. Urban 
Introduction 255

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Figure 1. Map of the Sierra Vista ground-water-recharge study area, southeastern Arizona and northeastern Sonora, Mexico, 

showing the locations of boreholes, temperature sensors, Agricultural Research Service flumes, U.S. Geological Survey 

streamflow-gaging stations, and precipitation stations.
256 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona





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Introduction 257

areas produce the highest percentage of runoff into stream 

channels because of large expanses of impermeable surfaces 

that prevent soil infiltration and engineered drainage infrastructures that concentrate and focus runoff.

Soils

The distribution of soil types in the Sierra Vista subwatershed is dominated by lithic, loamy, and fine paleosoils near the 

mountains, and clayey soils and calcium carbonate soils along 

the lower reaches of the watersheds (fig. 3; U.S. Environmental Protection Agency, 2003). Narrow ribbons of sandy loam 

typically lie along ephemeral-stream channels; sandy, clayey, 

and calcium carbonate soils typically lie between the channels. 

Calcium carbonate soils dominate areas below the mountains 

across much of the eastern part of the subwatershed. A wedge 

of calcium carbonate soils also extends nearly to the mountains in the central part of the study area west of the San Pedro 

River. The southwestern part of the subwatershed is dominated 

by clayey and sandy soils.

Soil types can also have a strong influence on the fraction 

of precipitation that is transported to ephemeral-stream channels. Sandy loam soils likely are the most permeable, enabling 

direct infiltration of precipitation and limiting runoff into 

stream channels. Clayey soils can limit deep infiltration where 

they underlie channels. Soils having secondary calcium carbonate are less permeable and enhance runoff. Shallow lithic 

soils underlain by bedrock or rocky layers promote runoff into 

stream channels and limit infiltration.

Precipitation

The subwatershed climate is arid to semiarid. Precipitation data are available from the Western Regional Climate 

Center (2003) from a station in Tombstone, at an elevation of 

1,384 m, from 1905 to 2002; and from a station in the Huachuca Mountains, at an elevation of 1,692 m, from 1956 to 

2002 (figs. 1 and 4). Historically, July through September are 

the wettest months; precipitation during this period averages 

21 cm at the Tombstone station and 27 cm at the Huachuca 

Mountains station. Precipitation from October through March 

averaged 12 and 23 cm at the Tombstone and Huachuca 

Mountains stations, respectively; and precipitation from April 

through June averaged less than 3 cm at both stations.

Long-term monitoring indicates that annual precipitation rates were above average before about 1940 and during 

the early to mid-1980s and below average from about 1940 

to 1980; and annual precipitation was about average after the 

mid-1980s (Pool and Coes, 1999). Trends in seasonal precipitation, however, are different from trends in annual precipitation. From 1956 to 1997, winter (November–February) precipitation rates increased while wet-season (June 10–October) 

precipitation rates decreased (Pool and Coes, 1999).

Estimates of recharge in this report are biased by precipitation immediately prior to and during the monitoring period. 

Precipitation during the year that preceded the monitoring 

period, 2000, was normal (36 cm) at the Tombstone station, 

but wetter than normal (78 cm) at the Huachuca Mountains 

station (fig. 4). During 2000, the Huachuca Mountain station 

recorded an abnormally wet June and August, and October 

was the wettest month on record (32 cm). Precipitation during the monitoring period, 2001 and 2002, was dominated by 

dry winters and slightly drier than normal summers (fig. 4). 

During July through September of 2001 and 2002, precipitation was below average at the Tombstone station (16 and 17 

cm, respectively) and slightly above average at the Huachuca 

Mountains station (29 cm during both years). Precipitation in 

October through June of 2001 and 2002 was below average at 

both stations.

Surface-Water Drainage System

The San Pedro River, an intermittent stream, drains the 

Sierra Vista subwatershed (fig. 1). Annual and wet-season 

runoff in the San Pedro River have declined since the mid1910s, probably as a result of reduced precipitation duration 

and intensity, increased vegetation, and increased streamflow 

infiltration along ephemeral reaches of the river and its tributary streams (Pool and Coes, 1999). Base flow in the river is 

lowest during the summer, when rates of near-stream groundwater withdrawals by wells and phreatophytes are highest. 

Long-term records indicate that summer base flows have been 

declining since 1937 (Pool and Coes, 1999).

Tributaries of the San Pedro River are ephemeral except 

for the Babocomari River, which is perennial in some areas 

(fig. 5). Flow occurs only in direct response to rainfall or snowmelt, and the amount of flow is generally dependant on the 

spatial distribution and intensity of precipitation and the runoff 

characteristics of the channel and the associated drainage area. 

The temporal distribution of flow in ephemeral-stream channels 

in the arid Southwest generally is the result of monthly, annual, 

and decadal oscillations in precipitation frequency (Redmond 

and Koch, 1991; Webb and Betancourt, 1992).

The majority of tributaries to the San Pedro River originate in the mountains bounding the subwatershed and coalesce 

downstream to form higher-ordered ephemeral-stream 

channels (fig. 5). Tributaries generally have narrow, shallow 

channels close to the mountain fronts that become wide, deep 

channels below a knick point. Channels draining the east side 

of the Huachuca Mountains typically have long and narrow 

drainage areas and few channels coalescing downstream; the 

southern tributaries become wider and less incised towards 

the San Pedro River. Channels draining the western side of the 

Mule Mountains typically have much wider drainage areas and 

multiple channels coalescing downstream.

Ground-Water System

The ground-water system of the Sierra Vista subwatershed has been described by previous investigators (Brown 
258 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona





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and others, 1966; Pool and Coes, 1999); an overview is given 

here. The primary aquifer in the subwatershed is within basin 

fill that overlies crystalline and sedimentary rocks. Secondary 

aquifers comprise stream alluvium beneath the flood plains of 

the San Pedro and Babocomari Rivers, and pre-basin fill and 

limestones that crop out in the mountains and hills surrounding 

the subwatershed. Ground water generally flows from recharge 

areas to discharge areas along the San Pedro and Babocomari 

Rivers. Ground water also discharges from the aquifer through 

ground-water withdrawals, evapotranspiration, springs, and 

ground-water underflow to the north.

Aquifers

The Pantano Formation, a consolidated to semiconsolidated conglomerate, overlies the bedrock in the subwatershed 

and is the oldest of the basin sediments. The formation probably 

is greater than 900 m thick in some areas (Halverson, 1984; 

Gettings and Houser, 1995). The Pantano Formation is a locally 

important water-bearing unit, as it yields water through fractures 

to many wells in the Sierra Vista area (Pool and Coes, 1999).

The basin fill that overlies the Pantano Formation has 

been divided into upper and lower units on the basis of com-
Introduction 259

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positional, textural, and depositional differences. The lower 

unit consists of partially cemented interbedded gravel, sand, 

silt an clay that is often described as conglomerate, and ranges 

in thickness from about 45 to 90 m (Pool and Coes, 1999). 

Permeability of the lower unit varies because of variability in 

sediment size, sorting, and cementation (Brown and others, 

1966). The upper unit consists of poorly cemented gravel, 

sand, silt, and clay (Brown and others, 1966), and is generally less than 120 m thick (Pool and Coes, 1999). The upper 

unit includes a permeable fan-gravel facies near the mountain 

fronts that grades to a poorly permeable silt and clay facies 

with interspersed sand and caliche beds near the basin center 

(Pool and Coes, 1999). Between the city of Sierra Vista and 

the San Pedro River, and between the city of Hereford and 

Highway 90, the upper unit is primarily a saturated confining bed of silt and clay (Pool and Coes, 1999). The upper and 

lower basin-fill units are the major water-yielding units in the 

Sierra Vista subwatershed and constitute the basin-fill aquifer. 

Water levels in the basin-fill aquifer range from less than 1 m 

to as much as 165 m (USGS data).

Terrace deposits of clay, silt, sand, and gravel overlie the 

upper basin fill in most areas. The deposits form a veneer of 

stream alluvium that is thin near the mountain fronts but is as 

much as 15 to 30 m thick in erosional channels that parallel the San Pedro River (Pool and Coes, 1999). Older terrace deposits include lakebed deposits of silt, clay, and marl 

(Haynes, 1968) that are local confining layers where they 

occur near the San Pedro River; erosion has removed most of 

the lakebed deposits along tributaries (Pool and Coes, 1999). 

Younger terrace deposits include stream alluvium along the 

San Pedro River and some of its tributaries (Pool and Coes, 

1999). The older deposits are rarely saturated outside of the 

flood plains of the San Pedro and Babocomari Rivers; the 

younger deposits are saturated in some areas near the San 

Pedro and Babocomari Rivers and along some tributaries near 

the base of the mountains, and are locally important waterbearing units (Pool and Coes, 1999).

Recent stream alluvium lies along the San Pedro and 

Babocomari Rivers. Stream alluvium deposited prior to the 

entrenchment of the San Pedro River consists of clay, silt, and 

fine sand interbedded with coarse sand and gravel, and is as 

much as 6 m deep and 1.5 km wide (Pool and Coes, 1999). 

Stream alluvium deposited after the entrenchment of the San 

Pedro River consists of sand and gravel, and is less than 6 m 
260 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona

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Introduction 261

deep and only about 1 km wide (Pool and Coes, 1999). The 

post-entrenchment stream alluvium is highly permeable; the 

pre-entrenchment stream alluvium is less so (Pool and Coes, 

1999). The pre- and post-entrenchment stream alluvium 

forms a long, narrow, shallow aquifer along the San Pedro 

River that is referred to as the flood-plain aquifer. Water 

levels in the flood-plain aquifer range from less than 1 to as 

much as 6 m below land surface (USGS data), and water levels in this aquifer are a major influence on river discharges 

and show seasonal trends reflecting cycles of surface-water 

runoff and evapotranspiration.

Recharge Mechanisms

Historically, recharge to the basin-fill aquifer in the Sierra 

Vista subwatershed was thought to primarily occur near the 

mountain fronts through ephemeral-stream channel infiltration of runoff from the relatively impermeable rocks of the 

mountains. Previous conceptual models of the ground-water 

flow system included annual recharge rates of 15 to 23 cubic 

hectometers per year (hm3

/yr), all of which was distributed 

within about 1.5 km of the mountains (Freethey, 1982; Corell 

and others, 1996; Goode and Maddock, 2000). Infiltration and 

recharge could, however, be distributed along much greater 

lengths of the channels. Recent studies (Blasch and others, 

2000; Izbicki and others, 2000; Constantz and others, 2003) 

have shown that significant recharge can occur through the 

beds of ephemeral streams far from mountain fronts. In the 

Sierra Vista subwatershed, Corell and others (1996) estimated that infiltration along the length of Greenbush Draw 

contributed about 1.20 hm3/yr of recharge. Goodrich and 

others (2004) estimated that a 6.8-km reach of Walnut Gulch 

contributed about 0.14 to 0.47 hm3 of recharge in 1999 and 

about 0.13 to 0.37 hm3 of recharge in 2000. The occurrence of 

similar rates of recharge along other major ephemeral streams 

would result in significant alterations to the preexisting conceptual model of recharge distributions in the subwatershed. 

Recharge through direct infiltration of precipitation through 

the basin floor is thought to rarely occur because of high evaporation, low precipitation, and water use by desert vegetation 

in the semiarid Southwest (Anderson and others, 1992; Scott 

and others, 2000). Rare basin-floor recharge could, however, 

be a significant source of recharge during extended periods of 

high precipitation and low evapotranspiration.

The occurrence of significant recharge along the lengths of 

ephemeral stream channels or through the basin floor, however, would not result in increased estimates of average annual 

basin-wide recharge rates. Water-budget analysis requires that 

estimates of recharge rates be maintained to balance inflows and 

outflows. The change would simply be in the conceptual model 

of recharge distribution: less concentrated near the mountains 

and more extensive downstream in tributary channels.

Previous recharge estimates for the Sierra Vista subwatershed have generally assumed that recharge rates are constant 

with time. Trends in seasonal and annual precipitation (Pool 

and Coes, 1999), however, likely result in long-term variations 

in recharge rates. Water-chemistry data for the Sierra Vista subwatershed and the adjacent Tucson Basin indicate that a greater 

percentage of precipitation infiltrates during winter streamflow 

than during summer streamflow (Gallaher, 1979; Keith, 1981; 

Pool and Coes, 1999). Rates of summer streamflow have varied 

randomly from year to year, but rates of winter streamflow 

vary over decadal periods with Pacific Ocean climate indicators 

(Cayan and Webb, 1992; Webb and Bentancourt, 1992; Cayan 

and others, 1999; McCabe and Dettinger, 1999).

Ground-Water Flow System

Ground water in the basin-fill aquifer is transmitted from 

recharge areas to discharge areas primarily through the sands 

and gravels of the upper and lower basin-fill units. Near the 

mountain fronts, shallow bedrock and relatively impermeable sediments support perched aquifers. Silt and clay layers 

within the upper and lower basin-fill units on the western side 

of the subwatershed split ground-water flow in the regional 

aquifer into deep and shallow flow systems (Pool and Coes, 

1999). Exceptions to the regional directions of ground-water 

flow exist near the Sierra Vista-Fort Huachuca area, where 

withdrawals have removed ground water from aquifer storage 

and altered pre-development ground-water flow paths (Pool 

and Coes, 1999).

Post-development discharge from the basin-fill aquifer 

in the Sierra Vista subwatershed occurs primarily as groundwater withdrawals, discharge to the San Pedro and Babocomari Rivers (base flow), and evapotranspiration. Ground-water 

withdrawals in the subwatershed began in about 1940 and 

peaked in the early 1980s at about 18.5 hm3

/yr (Freethey, 

1982; Corell and others, 1996). Withdrawals declined to about 

13.5 hm3/yr by 1991 (Corell and others, 1996). Post-development discharge to streams is about 7.4 hm3

/yr, and post-development evapotranspiration is estimated to be about 7.0 hm3

/yr 

(Freethey, 1982). About 3.7 to 4.9 hm3/yr discharges from the 

subwatershed as underflow through basin fill and stream alluvium in the Fairbank area (Freethey, 1982; Corell and others, 

1996). In addition, a small amount of ground water discharges 

as springs near the San Pedro River.

Pool and Coes (1999) identified four types of long-term 

water-level changes in the Sierra Vista subwatershed. The first 

type is periodic decline and recovery of water levels near the 

mountains related to variations in precipitation and rates of 

recharge. The second is a decline of 0.2 to more than 0.3 m/yr 

in the Sierra Vista-Fort Huachuca area caused by ground-water 

withdrawals. The third is a regional decline of 0.1 to 0.2 m/yr 

during 1940 through the mid-1960s to early 1980s followed by 

a period of no decline or slight recovery. This regional decline 

could be caused by variations in recharge rates or regional 

response to incision of the San Pedro River. The fourth type of 

long-term water-level change is recovery near the San Pedro 

River after the mid-1980s that is probably due to a decrease in 

agricultural ground-water withdrawals.
262 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona

Methods of Investigation

Multiple methods were used to estimate infiltration 

through ephemeral channels and the basin floor in the Sierra 

Vista subwatershed. Information gathered through unsaturated-zone borehole drilling and monitoring was used to better 

describe infiltration through the unsaturated zone. Tritium data 

were used to describe the extent to which water has moved 

through the unsaturated zone since the 1950s. Ratios of the 

stable isotopes of oxygen and hydrogen were used to identify 

evaporative and seasonal signatures of pore water. The distribution of chloride in the subsurface was used to identify active 

or inactive recharge areas, and where possible, was balanced 

to determine infiltration fluxes and water residence times. The 

transport of heat with infiltrating water was used to quantify 

infiltration rates from individual ephemeral streamflow events.

Field and Laboratory Methods

To characterize ephemeral-stream channel and basinfloor recharge in the Sierra Vista subwatershed, 12 tributary 

sites and 4 intertributary sites were chosen for intensive 

unsaturated-zone data collection. At each site, a borehole was 

drilled into the subsurface and sediment cuttings and cores 

were collected. Of the 16 boreholes, 15 were completed with 

casing for subsurface monitoring. Sediment textures were 

described in the field, and sediment-chloride concentrations 

were measured. Sediment cores were measured for hydraulic, 

physical, and thermal properties; pore-water stable-isotopes 

values; and tritium activity. Twelve of the completed boreholes 

were instrumented for continuous monitoring of sediment 

temperature. Ground-water levels of saturated intervals were 

continuously monitored in three of the completed boreholes.

Borehole Site Selection

Tributary and intertributary borehole locations were 

chosen by using a multistep approach. First, the Automated 

Geospatial Watershed Assessment (AGWA) tool (Miller and 

others, 2002), an extension to the Environmental Systems 

Research Institute’s ArcView version 3, was used to delineate 

the drainage basins of the major tributaries of the San Pedro 

River (fig. 5). For each basin, the main channel length, main 

channel slope, total basin area, mean basin elevation, basin 

perimeter, basin length, major land use, and major soil type 

were quantified by using the Xtools and Spatial Analyst extensions to ArcView (table 1). The basins were then divided into 

seven groups on the basis of similar morphometric, land-use, 

and soil-type characteristics (fig. 5). Twelve tributary sites 

were chosen in five drainage basins that represent four of the 

seven groups: four sites in Woodcutters Wash, two sites in 

Miller Canyon Wash, two sites in Greenbush Draw, one site 

in Banning Creek, and three sites in Walnut Gulch. In addition, four intertributary (basin floor) sites were chosen in three 

drainage basins: two sites in Walnut Gulch, one site in Woodcutters Wash, and one site in Carr Canyon.

Borehole Drilling and Completion

Unsaturated-zone boreholes were drilled and completed 

in January 2001 and November – December 2001 (table 2). 

All boreholes were drilled by using the ODEX air-hammer 

method, also known as the under-reamer method (Driscoll, 

1986; Hammermeister and others, 1986). This drilling method 

minimized disturbance of the formation near the borehole, and 

enabled collection of representative cuttings and cores at predetermined intervals. Boreholes were drilled to depths of less 

than 30.0 m and were either 15.2 or 20.3 cm in diameter. At 

each borehole, drill cuttings were collected every 0.3 m, and 

0.6-m-long cores were collected at differing intervals by using 

a 10.2-cm-diameter piston core barrel. The 0.6-m-long core 

barrel was lined with three 15.2-cm-long sleeve liners and two 

7.6-cm-long sleeve liners. Upon core collection, each of the 

liners was immediately capped, taped, plastic wrapped, and 

placed in an aluminum pouch, which was then heat-sealed, 

following the procedure described by Hammermeister and others (1986), to preserve the integrity of each core sample.

Of the 16 boreholes, 15 were completed to enable future 

subsurface monitoring (table 2). Permission was not granted 

from the land owner to complete the borehole at WC2. Each 

borehole was completed with 5.1-cm-diameter schedule-40 

polyvinyl chloride (PVC) pipe. Twelve of the completed 

boreholes were completed with solid-walled PVC, and capped 

at the bottom and top. During drilling, three of the completed boreholes intercepted saturated intervals. These three 

boreholes were completed with solid-walled PVC above the 

saturated interval and a 1.5-m section of slotted PVC spanning 

the unsaturated/saturated interface. The annular space of the 

12 boreholes completed with solid-walled PVC was filled with 

a mixture of cuttings from the boreholes and sand. The annular 

space of the three boreholes completed with slotted PVC was 

filled with gravel in the slotted interval, bentonite above the 

slotted interval, and a mixture of cuttings and sand above the 

bentonite. Surface casing consists of 10.2-cm-diameter schedule-80 PVC pipe from above land surface to 0.9 to 1.5 m depth 

around the 5.1-cm-diameter PVC casing. The uppermost 0.9 

to 1.5 m of annular space was filled with cement. The surface 

casing was capped with a watertight, locking, aluminum cap. 

Completion of the 15 boreholes with PVC casing resulted in 

12 unsaturated-zone monitoring access points and 3 wells. Use 

of the term “borehole” is retained, however, for convenience of 

discussion in this report.

Sediment Analysis

Cuttings—Cuttings from each borehole were visually 

described for grain-size distribution at 0.3-m intervals (fig. 

6). Cuttings from three boreholes were also analyzed in the 

laboratory for particle-size distribution (fig. 6).
Methods of Investigation 263

Table 1. Geomorphic, land-cover, and soil-type characteristics of tributary drainage basins, Sierra Vista ground-water recharge 

study area, Arizona.

[Group numbers refer to figure 5. Abbreviations: km, kilometers; m/km, meters per kilometer; km2, square kilometers; ND, not determined]

Tributary name

1

 Main channel length,

in km

Main channel slope,

in m/km

2

 Total basin 

area,

in km2

Mean basin 

elevation, 

in m

Basin

perimeter,

in km

Basin

length, 

in km

2

 Major land cover,

in percent

2

 Major soil type,

in percent

Group 1

Babocomari River 47.8 7.9 528.0 1,512 187.5 48.2 Grassland (48.3) ND

Group 2

Unnamed Wash 1 15.4 10.9 41.8 1,288 39.2 14.4 Desert scrub (44.1) Loam (27.9)

Graveyard Gulch 14.4 12.3 30.9 1,310 35.1 12.7 Desert scrub (38.3) Loam (49.7)

Escapule Wash 20.7 13.8 50.3 1,370 44.8 19.4 Urban (37.9) Loam (54.8)

Group 3

Woodcutters Wash 23.0 13.9 37.5 1,434 54.7 32.6 Desert scrub (26.7) Loam (34.4)

Garden Canyon Wash 21.7 13.5 86.4 1,651 63.8 33.5 Oak woodland 

(37.0) Loam (17.3)

Ramsey Canyon Wash 17.4 18.1 32.5 1,701 51.5 25.2 Forest (31.0) Clay (22.6)

Carr Canyon Wash 16.8 18.1 57.2 1,590 42.5 23.0 Urban (23.1) Loam (26.9)

Miller Canyon Wash 16.2 20.5 32.8 1,693 48.1 27.9 Forest (25.2) Loam (23.3)

Hunter Canyon Wash 15.5 19.1 24.1 1,478 43.0 23.9 Grassland (38.5) Loam (32.9)

Stump Canyon Wash 14.6 19.5 18.5 1,624 36.3 16.4 Grassland (35.3) Clay (41.5)

Ash Canyon Wash 12.9 23.7 17.5 1,818 37.5 15.6 Oak woodland 

(67.2) Paleosoil (13.3)

Brown-Bob Thompson Wash 9.5 23.3 21.0 1,536 25.7 11.0 Grassland (38.4) Loam (31.9)

Group 4

Lewis Springs Wash 12.1 12.0 13.0 1,300 22.0 12.5 Desert scrub (46.7) Secondary calcium 

carbonate (71.8)

Bakarich-McCool Wash 11.8 12.6 18.5 1,320 28.5 13.2 Desert scrub (52.0) Secondary calcium 

carbonate (58.8)

Three Canyons Wash 6.6 12.7 21.2 1,354 29.1 12.7 Grassland (41.7) Clay (85.0)

Palominas Wash 11.1 19.6 15.4 1,385 23.6 17.2 Desert scrub (47.3) Sandy stream channel (52.3)

Group 5

Greenbush Draw 19.5 8.8 306.3 1,476 81.6 23.9 Grassland (38.6) ND

Group 6

Banning Creek 8.6 15.6 41.3 1,655 47.8 21.2 Desert scrub (46.4) Secondary calcium 

carbonate (11.0)

Unnamed Wash 2 10.1 24.1 19.0 1,436 24.7 13.3 Desert scrub (51.7) Secondary calcium 

carbonate (59.4)

Stagg Ranch Wash 10.5 25.7 21.9 1,456 25.0 10.2 Desert scrub (63.3) Secondary calcium 

carbonate (53.8)

Little Dry Creek 10.6 23.4 19.2 1,466 27.6 13.4 Desert scrub (40.5) Secondary calcium 

carbonate (61.1)

Spring Creek 11.4 22.9 22.6 1,527 33.3 14.6 Desert scrub (43.3) Loam (29.0)

Group 7

Willow Creek 20.9 16.0 130.8 1,531 76.6 23.1 Grassland (40.1) Rocky calcium 

carbonate (29.0)

Walnut Gulch 26.5 12.1 152.1 1,411 86.1 34.1 Desert scrub (57.6) Rocky calcium 

carbonate (35.2)

Government Draw 17.8 7.6 148.4 1,399 80.8 20.5 Desert scrub (65.0) Lithic (26.4)

High Knolls Canyon Wash 18.7 12.5 98.9 1,443 56.5 29.4 Desert scrub (45.2) Lithic (43.6)

1

From the mountain front.

2

U.S. Environmental Protection Agency, 2003.
264 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona

Table 2. Borehole construction and instrumentation, Sierra Vista ground-water-recharge study area, Arizona.

[Abbreviations: km, kilometers; m, meters; cm, centimeters; ", ditto; NA, not applicable; NC, not completed; PVC, slotted polyvinyl chloride; Surface TidbiT: Y, 

yes; N, no]

Borehole 

identifier

Borehole

identification

number

Distance 

downstream 

from 

mountain 

front,

in km

Approximate 

channel 

width,

in m

Construction information Instrumentation information

End drill 

date

Borehole

diameter,

in cm

Borehole

depth,

in m

Casing 

diameter,

in

cm

Casing 

depth,

in m

Opening 

type

Depth to

top of 

opening,

in m

Depth to 

bottom 

of opening,

in m

Transducer 

depth,

in m

Surface 

TidbiT

Down-hole

TidbiT

depths,

in m

Ephemeral-channel boreholes

BC1 (D-22-22)23bbd 3.9 4 01/17/01 20.3 26.3 5.1 26.3 None NA NA NA Y 1.5, 3.0, 4.6, 6.1, 

7.6, 9.1, 12.2

GD1 (D-24-23)06dbd 12.4 14 11/30/01 15.2 19.5 " 19.5 None NA NA NA N 1.5, 3.0, 6.1, 9.1

GD2 (D-24-23)14aba 5.6 2 11/29/01 " 28.2 " 28.2 None NA NA NA Y 1.5, 3.0, 4.6, 6.1, 

7.6, 9.1, 12.2

MC1 (D-22-21)36bad 7.1 4 11/18/01 " 23.0 " 23.0 None NA NA NA Y 1.5, 3.0, 4.6, 6.1, 

9.1

MC2 (D-23-21)bca2 0.0 2 11/20/01 " 16.0 " 16.0 None NA NA NA N 1.5, 3.0, 4.6, 6.1, 

7.6, 9.1, 12.2

WC1 (D-21-21)14dbc1 16.4 10 01/14/01 20.3 9.4 " 9.4 None NA NA NA Y 1.5, 3.0, 4.6, 6.1, 

7.6, 9.1

do. (D-21-21)14dbc2 " " " " " " 8.5 PVC 7.3 8.8 8.8 N NA

WC2 (D-21-21)28bbb 12.3 22 01/12/01 " 12.5 NC NC NC NC NC NA N NA

WC3 (D-21-20)36caa 7.2 8 11/09/01 15.2 22.6 5.1 22.6 None NA NA NA N 1.5, 3.0, 4.6, 6.1, 

7.6, 9.1, 12.2

WC4a (D-22-20)16abc1 0.4 0.5 01/10/01 20.3 12.5 " 12.7 None NA NA NA Y 1.5, 3.0, 4.6, 6.1, 

7.6, 9.1, 12.2

do. (D-22-20)16abc2 " " " " " " 5.3 PVC 3.8 5.3 4.6 N NA

WG1 (D-20-21)01aba 25.6 31 11/11/01 15.2 23.0 " 23.0 None NA NA NA N 1.5, 3.0, 4.6, 6.1, 

9.1

WG2 (D-20-22)01bdc 13.2 13 11/16/01 " 12.2 " 11.4 None NA NA NA N 1.5, 3.0, 4.6

WG3 (D-19-23)33aad 7.2 2 11/15/01 " 12.3 " 12.3 None NA NA NA N NA

Basin-floor boreholes

BF1 (D-22-21)32dad NA NA 12/01/01 15.2 15.8 5.1 15.1 None NA NA NA Y 1.5, 3.0, 4.6, 6.1, 

7.6, 9.1, 12.2

WC4c (D-22-20)16acb NA NA 01/08/01 20.3 12.5 " 12.5 PVC 4.3 5.8 9.1 Y 1.5, 3.0, 4.6, 6.1, 

7.6, 9.1, 12.2

WG4 (D-19-22)36abb NA NA 11/12/01 15.2 13.4 " 13.4 None NA NA NA N NA

WG5 (D-19-23)36dbc NA NA 11/13/01 " 12.3 " 12.3 None NA NA NA N NA
Methods of Investigation 265

Figure 6. Neutron soil-moisture, electrical conductivity, field grain-size, and laboratory grain-size data for boreholes in the Sierra Vista 

ground-water-recharge study area, Arizona and northeastern Sonora, Mexico: A, WC4a; B, WC3; C, WC2; D, WC1; E, MC2; F, MC1; G, 

WG3; H, WG2; I, WG1; J, BC1; K, GD2; L, GD1; M, WG4; N, WG5; O, BF1; P, WC4c.

















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266 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona

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268 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona 
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Methods of Investigation 269

Sediment-chloride concentrations of borehole cuttings 

collected at 0.3-m intervals were determined in the field 

(table 3) (tables 3-13 are placed at the end of this chapter). A 

subsample of cuttings representative of each 0.3-m interval 

was sieved to obtain particles less than 2 mm in diameter. Fifty 

grams of the sieved subsample was mixed well with 50 mL of 

deionized water and allowed to settle. The chloride concentration of the leachate was then measured by using an Orion 

chloride-specific electrode, Model 96-17 (Thermo Electron 

Corporation, 2000). This electrode measures chloride concentrations of 1.8 to 35,500 mg/L with a reproducibility of ±2 percent. The electrode was calibrated in the field at the beginning 

of each set of measurements; calibration was checked every 1 

to 2 hours. Chloride is reported in milligrams of chloride per 

kilogram of soil (mg/kg; MCl, in M/M):

 MC l V 

M Cl samp 

w

s

= , (1)

where

Clsamp = chloride concentration of leachate [M/L3],

Vw = volume of deionized water in leachate [L3]

Ms = mass of sediment in leachate [M].

Cores—Cores were analyzed to determine pore-water stable-isotope values and tritium activity; thermal, physical, and 

hydraulic properties; and particle-size distributions. Pore water 

was extracted and analyzed for the stable isotopes of oxygen 

and hydrogen at the USGS Isotope Fractionation Project Laboratory in Reston, Virginia (table 4). Pore water was extracted 

and analyzed for tritium activity at the USGS Water-Quality 

Laboratory in Menlo Park, Calif. (table 4). The precision of 

individual tritium measurements is a function of the volume of 

water extracted from the core material and ranged from ±0.2 

tritium units (TU) for moist cores to ±5.0 TU for an extremely 

dry core. Thermal properties (heat capacity, thermal conductivity, and thermal diffusivity; all at field soil-water content; 

table 5) were measured at the USGS Hydrologic Research 

Laboratory in Sacramento, Calif., by using a dual-needle, 

line-heat source probe and a ThermoLink measurement system 

(Campbell and others, 1991; Decagon Devices, Inc., 1999).

Core analyses for hydraulic properties (saturated hydraulic conductivity and van Genuchten parameters) and physical properties (bulk density, volumetric soil-water content, 

porosity, and particle density) were completed in a laboratory at the University of Arizona in Tucson, Ariz. (table 6). 

Initially, each core’s weight was measured and its volume 

calculated. Cores were then fully saturated and weighed again. 

Saturated hydraulic conductivity (Ks

, in L/t) was measured by 

the falling-head method (Klute and Dirksen, 1986). Reported 

Ks values are the average of two to five falling-head tests run 

sequentially. Van Genuchten parameters (alpha (α), in 1/L; 

n, dimensionless; residual soil-water content (hR), in L3/L3; 

saturated soil-water content (hS

), in L3/L3) were determined 

from moisture-release data measured by the pressure-step 

outflow method (Gardner, 1956) from about 15 to 15,000 cm 

water pressure. Cores were then oven dried at 105oC for 24 

hours, and weighed a third time. Dry bulk density (b

, in M/L3) 

was determined by dividing the weight of the core after oven 

drying by the calculated volume of the core. Gravimetric field 

soil-water content (hg, in M/M) was calculated as the difference between the initial core weight and the weight of the core 

after oven drying, divided by the weight of the core after oven 

drying. Volumetric field soil-water content (hv, in L3/L3) was 

calculated as the product of the gravimetric soil-water content 

and the bulk density. Porosity (, dimensionless) was assumed 

equal to the saturated soil-water content and was calculated as 

the product of the bulk density and the difference between the 

saturated core weight and the dry core weight, divided by the 

dry core weight. Particle density (p, in M/L3) was calculated 

by (Danielson and Sutherland, 1986):

 ρ 

ρ 

p 

b = 

1 − � , (2)

The Soil, Water, and Plant Analysis Laboratory at the University of Arizona measured particle-size distributions for the cores 

(table 6). Gravel-size fractions (greater than 2 mm) were determined by sieve analysis. Sand-, silt-, and clay-sized fractions were 

determined by hydrometer analysis (Gee and Bauder, 1986).

Borehole Logging

Electromagnetic-induction (EMI) and neutron soilmoisture geophysical borehole tools were used to augment 

subsurface sampling of borehole cuttings and core (fig. 6). EMI 

measures the electrical conductivity of the sediments near the 

borehole by measuring the strength of a secondary magnetic 

field induced in the sediments by a primary electromagnetic 

field. The EMI tool has a variable radius of investigation 

dependent on the frequency of the primary field, the spacing 

between the primary and secondary magnetic coils, and the 

subsurface conductivity. The tool used in this investigation used 

a frequency of about 40 kiloHertz and a coil spacing of 0.5 m. 

At this setting, about 90 percent of the secondary magnetic field 

results from materials within a radius of about 1.3 m from the 

center of the coil spacing (Peterson, 1999). Variations in subsurface electrical conductivity are primarily caused by variations 

in amounts of electrically conductive silt, clay, and dissolved 

ions in water. Electrical conductivity is proportional to silt, clay, 

and soil-water contents. Dry zones with little silt and clay can 

have electrical conductivity values well below 10 millisiemens 

per meter (mS/m), but saturated clay can have values greater 

than 100 mS/m. Variations in electrical conductivity can also be 

related to variations in electrically conductive salts; however, the 

salt contents in most of the boreholes drilled for this investigation were very low and did not likely contribute significantly to 

variations in electrical conductivity.

The neutron tool used in this study contained a 50-millicurie americium-241/beryllium neutron source and detector 
270 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona

to measure variations in the amount of water molecules near 

the borehole. The tool had a radius of investigation of about 60 

to 75 cm. Response of the neutron tool is reported as measured 

neutron counts at the detector; higher neutron counts indicate 

greater amounts of water near the borehole. Neutron counts can 

be converted to soil-water content by using a soil-dependent 

calibration; however, calibration was not attempted for this 

investigation, and the resultant neutron counts from different 

boreholes can only be compared in a relative sense.

Borehole Monitoring

Onset StowAway TidbiT temperature sensors were 

installed in boreholes WC1, WC4a, WC4c, and BC1 in February 2001, and in boreholes WC3, MC1, MC2, BF1, GD1, 

GD2, WG1, and WG2 from January to May 2002. Sensors 

were installed from land surface to a maximum depth of 12.2 

m at intervals of 1.5 to 3.0 m (table 2). Additionally, at most 

boreholes, a sensor was buried about 15 cm below land surface 

next to the borehole surface casing. Temperature was measured 

and recorded every 30 minutes. The TidbiT sensors measure 

temperatures of –5oC to +37oC with an accuracy of ±0.2 oC.

In-Situ Inc. miniTROLL pressure transducers were 

installed in the three boreholes that intercepted saturated 

intervals (WC1, WC4a, and WC4c) during February 2001. 

Depth to water was measured and recorded every 30 minutes.

Precipitation Collection and Analysis

Composite atmospheric deposition samples were collected 

twice a year after the summer (April to October) and winter 

(October to April) rains at the Upper Babocomari River and 

Greenbush Draw streamflow-gaging stations (fig. 1). Sample 

collection began in June 2000 and continued through April 

2003. Samples were analyzed for bulk chloride concentrations, stable-isotope values, and tritium activity (table 7). Bulk 

chloride was determined by ion chromatography at the USGS 

laboratory in San Diego, Calif.. The stable isotopes of oxygen 

and hydrogen were analyzed at the USGS Isotope Fractionation 

Project Laboratory in Reston, Virginia. Tritium activity was 

determined at the Laboratory of Isotope Geochemistry at the 

University of Arizona in Tucson.

Streamflow-Data Collection and Analysis

Knowledge of ephemeral streamflow timing and duration 

in the tributaries was needed to determine the availability of 

water for ephemeral-stream channel infiltration. In this study, 

streamflow availability was estimated by using frequency and 

duration of flow determined by USGS streamflow-gaging 

stations, ARS flumes, and temperature methods. Onset 

StowAway TidbiT temperature sensors were buried about 15 

cm below the surface of streambed sediments at 7 of the 12 

tributary borehole sites (table 2) and at selected channel locations between boreholes (fig. 5). Sediment temperatures were 

logged every 15 to 30 minutes. A rapid drop in temperature of 

more than 0.2oC indicated onset of streamflow; a low-temperature inflection point in the thermograph was interpreted as the 

cessation of streamflow (Constantz and others, 2001; Gungle, 

2003). Durations of individual ephemeral-streamflow events 

ranged from 15 minutes to 48 days (table 8).

Data-Analysis Methods

Infiltration is defined as the flow of water from above 

ground into the unsaturated zone; recharge is defined as the 

flow of water across the regional water table. The rate of infiltration, or infiltration flux, is strongly dependent on the spatial 

and temporal distribution of source water and the hydraulic 

and physical properties of the subsurface sediments. At the 

onset of infiltration, the initial infiltration flux is at its highest and is extremely transient. As infiltration continues over 

time, the infiltration flux decreases to a nearly constant rate 

approaching the effective mean saturated hydraulic conductivity of the subsurface sediments.

Infiltration can lead directly to recharge when the wetting front reaches the regional water table while infiltration is 

still occurring. In the arid and semiarid Southwest, however, 

deep water tables and short infiltration times lead to infiltration ending long before the wetting front crosses the water 

table. In these instances, water that has infiltrated into the 

unsaturated zone can be removed by evapotranspiration or, 

if the water has moved past the root zone, remain in storage 

until it is displaced by water from a subsequent infiltration 

event. Unsaturated-zone water in storage below the root zone 

can continue to redistribute over time. This long-term movement of water, or percolation flux, occurs both vertically, 

by drainage, and horizontally in response to heterogeneity 

or anisotropy of the sediments. Long-term percolation can 

result in recharge.

Unsaturated Hydraulic Properties

Moisture-release curves describe the nonlinear decrease 

in soil-water content at decreasing matric potentials. The van 

Genuchten (1980) algebraic expression relates soil-water content to matric potential by:

(1 ( ) )n m

v p h − E  
 > , (3)

where

hv = volumetric soil-water content [L3/L3],

a = van Genuchten fitting parameter [1/L],

hp = matric potential [L],

n = van Genuchten fitting parameter 

(dimensionless), and

m = van Genuchten fitting parameter equal to 

1–1/n (dimensionless).
Methods of Investigation 271

For this study, the pressures (in cm water) at which soilwater contents were determined are considered equivalent to 

matric potentials.

The RETC (RETention Curve) computer code (van 

Genuchten and others, 1991) was used to fit moisture-release 

curves to the induced-pressure and measured water-content 

data to determine the van Genuchten fitting parameters of α

and n (table 6). All curves were fit so that their coefficients of 

determination (R2) for the regression of the measured values 

versus the fitted values were greater than 0.95. Volumetric 

residual and saturated soil-water contents (hR and hS, in L3/L3) 

were also determined by using the RETC code. 

Unsaturated-Zone Chloride Mass Balance

The mass of chloride (Cl) in the unsaturated zone can be 

used to estimate long-term vertical water movement. Chloride 

is continuously deposited on the land surface by precipitation 

and dry fallout. The high solubility of Cl enables its transport into the subsurface by infiltrating water. Because Cl is 

essentially nonvolatile and Cl uptake by plants is minimal, Cl 

is retained in the sediment when water is removed by evaporation and transpiration. Therefore, an increase in Cl within 

the root zone of the shallow subsurface is proportional to 

the amount of water lost by evapotranspiration (Allison and 

Hughes, 1978). In areas where active infiltration is occurring, 

an increase in Cl in the shallow subsurface will generally 

be absent, and concentrations will be very low through the 

unsaturated zone. In areas where little to no active infiltration 

is occurring, an increase in Cl in the shallow subsurface will 

be present, and concentrations will be relatively high through 

the unsaturated zone.

If the Cl deposition rate on the land surface is known, the 

average travel time of Cl (t

Cl; in t) to a depth in the unsaturated 

zone (z, in L) can be calculated by:

 t

Cl dz

Cl Cl

soil

z

dep

=

∫

0 , (4)

where

Clsoil= chloride mass in the sample interval [M/L3], and

Cldep= chloride deposition rate [M/L2/t].

The above calculations entail several assumptions: (1) 

flow in the unsaturated zone is downward-vertical and piston 

type, (2) bulk precipitation (precipitation plus dry fallout) is 

the only source of Cl and there are no mineral sources of Cl, 

(3) the Cl deposition rate has stayed constant over time, and 

(4) there is no recycling of Cl within the unsaturated zone.

This model of Cl movement predicts that in interdrainage areas with little to no infiltration, Cl concentrations should 

increase through the root zone and then remain constant down 

to the water table. Numerous published chloride profiles, however, show that Cl concentrations commonly decrease below 

the peak concentration in the root zone. Therefore, some of the 

above assumptions may not be valid for all unsaturated-zone 

systems. The decrease in Cl concentrations below the peak has 

been attributed to nonpiston flow (Sharma and Hughes, 1985), 

ground-water dilution (Allison and others, 1985), or nonsteady 

flow as a result of paleoclimatic variations (Phillips and Stone, 

1985; Scanlon, 1991).

For some geomorphic settings, such as ephemeral 

streams, assumption 2 is not valid because streamflow 

provides an additional source of Cl to the subsurface. To 

correctly determine percolation flux below ephemeral 

streams with the Cl mass balance method, the mass of Cl in 

streamflow needs to be included in equation 5. In this study, 

ephemeral streamflow discharges and Cl concentrations were 

not quantified; therefore, the Cl mass method was not used to 

determine percolation fluxes below ephemeral streams.

Chloride deposition rates in the Sierra Vista subwatershed were determined from the composite precipitation 

samples collected for this study (table 7). Annual rates 

ranged from 0.011 to 0.032 mg/cm2

 yr. The average annual 

Cl deposition rate for the subwatershed was determined to be 

0.022 mg/cm2 yr.

Meteoric Tritium

Tritium (3H), a naturally occurring radioactive isotope 

of hydrogen, can be used to estimate the age of subsurface 

water and infiltration fluxes into the subsurface. Large 

quantities of tritium were released to the atmosphere during thermonuclear-weapons testing from 1952 until the 

late 1960s; maximum releases occurred in the early 1960s. 

As a result, the amount of tritium in precipitation sharply 

increased during testing as tritium was introduced into the 

water cycle, and decreased after testing ended. The amount 

of tritium in subsurface water at a given time is a function 

of the amount of tritium in the atmosphere when infiltration 

occurred and the radioactive-decay rate of tritium. If flow in 

the unsaturated zone is assumed to be downward-vertical and 

piston type, the average infiltration flux (qi, in L/T) can be 

estimated by:

 q z

t i v = ∆

∆

θ , (5)

where

z = depth of maximum tritium activity [L],

t = elapsed time between sampling and 

maximum atmospheric tritium activity [t] (38 years for this 

study), and

hv = volumetric soil-water content [L3/L3].

Tritium activity in the composite precipitation samples 

collected during this study ranged from 1.7 to 4.2 tritium units 

(TU) for winter precipitation and 4.6 to 4.8 TU for summer 

precipitation (table 7). Therefore, pore water having a tritium 
272 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona

activity within this range was considered to be recent infiltration. Pore water having an activity of less than 0.5 TU was 

considered to have infiltrated prior to 1952.

Stable Isotopes

The stable-isotope ratios of oxygen (18O/16O) and hydrogen (2

H/1H) can be used to estimate seasonal cycles of infiltration and to determine if pore water has undergone evaporation. 

Ratios determined in this study are reported relative to Vienna 

Standard Mean Ocean Water (VSMOW). Differences from the 

standard are expressed by delta notation (), in per mil. The 

delta notation is computed by:

δ =  −



 



 ×

R R

R

x Std

Std

1 000, , (6)

where

Rx = ratio of isotopes measured in sample, and

RStd = ratio of same isotopes in standard.

The relation between 18O and 2H in precipitation can be represented by the global meteoric water line (Craig, 1961):

δ δ H O = 8 1 + 0 2 18 , (7)

The amount of each isotope in precipitation is dependant on the temperature and source location of the precipitation. Because precipitation temperatures and sources vary 

by season in the Sierra Vista subwatershed, stable-isotope 

values in precipitation show seasonal variation. The 18O for 

the composite precipitation samples collected for this study 

ranged from –5.23 to –8.17 per mil for summer precipitation 

and from –10.37 to –17.71 per mil for winter precipitation 

(table 7). The  2H ranged from –34.0 to –54.7 per mil for 

summer precipitation and from –65.6 to –133.4 per mil for 

winter precipitation (table 7).

Mass differences between 18O and 16O and between 2

H 

and 1H enable isotopic fractionation during phase changes, 

such as evaporation. Water molecules consisting of 16O and 1

H evaporate preferentially, resulting in water enriched in 18O 

and 2H. Lines describing the relation between 18O and 2H in 

enriched water have smaller slopes than the slope of the global 

meteoric water line.

Heat as a Tracer

Sediment-temperature profiles can be used to estimate 

one-dimensional infiltration fluxes in the unsaturated zone 

below the beds of ephemeral-stream channels (Constantz 

and Thomas, 1996; Constantz and others, 2003). Temperatures of streambed surfaces are predominantly influenced by 

heating from solar radiation and ambient air temperatures. 

Beneath dry streambeds, shallow sediment temperatures 

vary diurnally and seasonally in response to downward 

conductive heat transport. Deeper sediment temperatures 

are less affected by diurnal or seasonal air temperatures, and 

therefore do not greatly vary over time. During periods of 

stream-channel infiltration, heat transport into the subsurface 

by advection predominates and transport by conduction is 

considered negligible.

An analytical method (Taniguchi and Sharma, 1990; Constantz and Thomas, 1996) was used as a first approximation to 

calculate infiltration flux (qi, in L/t) from measured sediment 

temperatures at each ephemeral-stream site (table 9):

 q z

t

C

C i

b s

b w

soil

water

= ∆

∆

ρ

ρ

, (8)

where

z = vertical distance between temperature sensors [L],

t = travel time of the temperature perturbation

 between sensors [t],

b

soil = bulk density of sediment [M/L3

],

Cs = heat capacity of the dry sediment [E/L3/T],

b

water = bulk density of water [M/L3

], and

Cw = heat capacity of water [E/L3/T].

Onset of streamflow was determined from streambedtemperature data. The distance between temperature sensors 

was known for each borehole, and the travel time of the 

temperature signal was measured. The b and CS of the 

sediment were determined from cores. For depth intervals 

where more than one property value was available, average 

values were used. The bwater is a constant 1.0 g/cm3, and the 

CW is a constant 4.2 × 106 J/m3 C.

The infiltration flux determined by the use of the analytical method represents the initial, transient infiltration flux. 

This method is only valid for cases where pore-water velocities are high enough such that heat transport by conduction 

is negligible compared with heat transport by advection. The 

high Ks

 values determined for stream-alluvium cores indicate 

that this situation is typical for most of the subsurface sediments beneath ephemeral-stream channels in the Sierra Vista 

subwatershed. The analytical method is also only valid for 

infiltration under nonisothermal, continuous streamflow loss; 

this condition is assumed in the ephemeral-stream channels.

A more comprehensive, rigorous numerical approach was used 

to account for heat transport with water flow in the unsaturated zone. Convective and advective heat transport can be 

expressed by (Kipp, 1987):
Methods of Investigation 273

 v w ( ) 1 s

d C C

dt

 ̈2 + −À = a  ̈

a

 d

dz

K dT

dz

d

dz

C D dT

dz

d

dz

C Tq t v v w h v w w  	 � � �  ̈

a

© ·

1

 ̧  ¥

§

¦  ́

¶

μ 
  	 , (9)

where

hv = volumetric soil-water content [L3/L3],

Kt = thermal conductivity [E/t/L/T],

T = temperature [T], and

Dh = a thermomechanical dispersion tensor [L2/t].

To describe water flow in the unsaturated zone, variably saturated ground-water flow can be expressed by (Richards, 1931):

 

d z t

dt

d

dz

K h z dh z t

dz u p

θ ( , ) ( , ) ( , ) = 



 



 , (10)

where

Ku = unsaturated hydraulic conductivity [L/t],

hp = matric potential [L], and

h = total head [L].

The numerical code VS2DH (Healy and Ronan, 1996) 

and its graphical user interface (Hsieh and others, 2000) were 

used to solve equations (9) and (10) simultaneously.

One-dimensional numerical models were developed 

to represent conceptual fluid flow and heat transfer at each 

ephemeral-stream site (tables 10 and 11). Models were created 

only for sites and times where temperature perturbations were 

detected at depth during streamflow events. Models were not 

created for sites and events where temperature perturbations 

were not detected until after streamflow ended. Similarly, 

simulations were terminated at the end of streamflow because 

at that point, heat transfer is dominated by both water and 

vapor flux, a condition VS2DH cannot simulate.

Sediment properties were determined from core measurements. For depth intervals where more than one property value 

was measured, average values were used in the calculation. 

Thermal conductivities at saturation were estimated on the 

basis of measured thermal conductivities at ambient conditions 

(table 5). All layers were assumed to be isotropic and to have a 

specific storage of zero. Streamflow water temperatures were 

determined from values measured by the surface temperature 

sensors. Upper boundaries were defined as no flow for the 

hour prior to the onset of flow, and then as specified normalflux boundaries during streamflow. Initial sediment temperatures were determined from values measured by temperature 

sensors at depth. Initial hydraulic conditions were estimated 

as soil-water contents. Lower boundaries were defined as 

possible seepage faces. Onset and length of streamflow were 

determined from streambed sediment-temperature data.

The model simulations yielded subsurface sediment 

temperatures due to advective heat transport. In all cases, the 

saturated hydraulic conductivity had to be adjusted to accurately simulate the temperature inflection point identifying 

streamflow arrival time (table 12). The models were calibrated 

by adjusting the specified infiltration flux at the upper boundary to minimize the difference between the calculated and the 

measured sediment temperatures at depth.

The infiltration flux calibrated for the upper boundary 

represents an average value of the initial, transient infiltration 

flux. The model simulations represent infiltration from streamflow events ranging in duration from 1 to 5.5 hours; long-term 

constant infiltration rates were probably not achieved during 

these ephemeral streamflows.

Rates of Ephemeral-Channel Recharge

Recharge deriving from ephemeral streamflow along the 

length of a channel can be estimated by:

 R = − S wq E i V T− d ∫( ) �

�

0

, (11)

where

R = recharge [L3],

S = streamflow duration [t],

w = wetted width of channel [L],

qi = infiltration flux [L/t],

EV = water lost to channel evaporation per channel 

 length [L3/L],

T = water lost to near-channel transpiration per 

 channel length [L3/L], and

l = length of channel containing alluvial 

 sediments [L].

Average annual recharge was determined by dividing 

the calculated recharge rate for the 2001–2002 period by the 

number of years in the time period (2 years for this study). 

The total streamflow duration was determined for the 2-year 

period at each streambed-temperature sensor, ARS flume, and 

USGS streamflow-gaging station (table 8), and an exponential 

best-fit relation between streamflow duration and distance in 

the channel downstream from the mountain front was then 

developed for each channel (fig. 7); only sites having streamflow-duration data for the entire 2001–2002 period were used. 

The width of the channel at each borehole was known (table 

2), and was linearly extrapolated between boreholes. The averaged wetted-channel width during flow events was determined
274 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona



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$)34!.#%&2/--/5.4!).&2/.4).+),/-%4%23

"ANNING#REEKY  En X

'REENBUSH$RAWY  EX

-ILLER#ANYON7ASHY  EnX

7OODCUTTERS7ASHY  EnX

7ALNUT'ULCHY  EnX

 

Figure 7. Regression of streamflow duration to distance from 

the mountain front for 2001 and 2002, Sierra Vista ground-waterrecharge study area, Arizona and northeastern Sonora, Mexico. 

In the equations, y is the duration of streamflow, in hours; x is 

distance from the mountain front, in kilometers; and e is the base 

of the natural log.

to be between 10 and 20 percent of the channel width on the 

basis of the effective wetted channel width along a portion of 

Walnut Gulch as estimated by Goodrich and others (2004). 

An average wetted-channel width of 15 percent of the channel width was used in the calculations. Goodrich and others 

(2004) also estimated channel evaporation losses and nearchannel transpiration losses for 1999 and 2000 along a 6.8-km 

reach of Walnut Gulch. The average losses were scaled so that 

channel evaporation was represented by 3.0 × 10–4 hm3/km/2yr 

and near-channel transpiration was represented by 1.4 × 10–2

hm3/km/2yr. These values were used for all the channels in the 

2001–2002 calculations

Ephemeral-stream channel recharge rates determined 

with equation 11 were compared with rates derived by using 

other independent methods (channel-reach water balance, 

chloride mass balance, ground-water mounding model, and 

microgravity measurements) for a 6.8-km reach of Walnut 

Gulch (Goodrich and others, 2004). The infiltration flux used 

in this comparison was the lowest one calculated for Walnut Gulch by sediment-temperature analysis. As previously 

stated, streamflow events for which infiltration fluxes could 

be determined were all less than 5.5 hours in duration; the 

calculated infiltration fluxes represent an average value of 

the initial, transient infiltration fluxes. The lowest calculated 

infiltration fluxes are assumed to best represent the steadystate infiltration rate. Calculations of recharge for 1999 were 

0.44 hm3

 from the use of equation 11 and 0.14 to 0.47 hm3

from the use of other methods; recharge for 2000 was 0.16 

hm3

 from the use of equation 11 and 0.13 to 0.37 hm3 from 

the use of other methods. These results validate the assumption that the lowest calculated infiltration flux can represent 

the steady-state infiltration flux when determining ephemeral-stream channel recharge.

Ephemeral-Stream Channel Infiltration

Infiltration fluxes during, and percolation fluxes immediately following, streamflow events were determined for sites 

in Woodcutters Wash, Miller Canyon Wash, Walnut Gulch, 

Banning Creek, and Greenbush Draw. Data used in the determination of fluxes included physical, hydraulic, and thermal 

properties of sediment; chloride concentrations of sediment; 

pore-water stable isotope values and tritium activity; neutron 

soil-moisture and EMI logs; and sediment-temperature and 

water-level monitoring. Where possible, fluxes through the 

upper 1.5 to 12.2 m of sediments were estimated.

 Woodcutters Wash

Woodcutters Wash is a northeastward-trending channel 

with headwaters in the Huachuca Mountains. The channel 

is 23.0 km long and has an average slope of 13.9 m/km. The 

channel widens from less than 1 m along the upper reaches 

to more than 20 m along the lower reaches. It is incised less 

than 0.5 m along the upper reaches and 2 m or more along the 

lower reaches. Several knickpoints occur along the lower onehalf of the channel in an area where the stream has cut through 

several layers of clay and caliche.

The channel drains a 37.5-km2 area that ranges in elevation from 1,204 to 2,488 m. Desert scrub and grassland are 

the primary land-cover types in the drainage basin; mesquite 

is dominant along the mountain fronts, and oak woodland is 

dominant in the mountainous areas (fig. 2). About 21 percent 

of the drainage basin, the central part, is urban. The banks of 

Woodcutters Wash have been stabilized in this area.

Soils in the drainage basin vary from loamy near the 

mountains to calcium carbonate and clayey downgradient; 

soils are sandy along the stream channel (fig. 3). Thickness 

of permeable stream alluvium is about 1 m near the mountains, a few centimeters within the city of Sierra Vista, and 

about 3 m in the lower reaches of Woodcutters Wash. The 

stream alluvium is underlain by the compacted clayey gravels of the Pantano Formation near the mountains; the poorly 

sorted sand, silt, and clay of the basin fill in the Sierra Vista 

area; and the low-permeability silt and clay and calcium carbonate of the basin fill along the lower reaches of the wash.

Ephemeral streamflows recorded from 2001 to 2002 in 

Woodcutters Wash ranged in duration from about 15 min to 22 

hr (table 8). Flows in the upper reaches generally were more 

frequent and were of a longer duration than flows in reaches 

downstream (fig. 7). The farthest upstream temperature sensor, 
Ephemeral-Stream Channel Infiltration 275

375010, detected 19 flows, which had an average duration of 6.5 

hr. The farthest downstream temperature sensor, at site WC1, 

detected 18 flows, which had an average duration of 4.0 hr.

Borehole WC4a is the farthest upstream site in Woodcutters Wash and is about 0.4 km from the base of the Huachuca 

Mountains. The site is in a reach about 0.5 m wide and incised 

less than 1 m into terrace deposits, basin fill, and the Pantano 

Formation. The highly permeable sand and gravel stream 

alluvium extends from the land surface to a depth of 3.4 m, 

and the less permeable semiconsolidated conglomerate of the 

Pantano Formation extends from 3.4 to 12.5 m (fig. 6A). Electrical conductivities of the stream alluvium and the Pantano 

Formation ranged from about 10 to 30 mS/m, and from about 

25 mS/m to 45 mS/m, respectively (fig. 6A). A neutron soilmoisture log was not recorded at this site.

Physical and hydraulic properties were determined for 

two core samples from WC4a collected at depths of 2.1 and 

11.3 m (table 6). For the stream alluvium and the Pantano 

Formation, measured saturated hydraulic conductivity was 6.4 

× 10–2 and 4.2 × 10–4 cm/s, respectively; porosity was 0.43 and 

0.33 cm3/cm3, respectively; and soil-water content was 0.09 

and 0.07 cm3/cm3, respectively.

When borehole WC4a was drilled in in January 2001, a 

saturated interval was penetrated above the Pantano Formation at a depth of 2.0 to 3.4 m (fig. 8A). Sediment-chloride 

concentrations were lower than 8 mg/kg in the stream 

alluvium and generally lower than 3 mg/kg in the Pantano 

Formation (fig. 9A). Tritium activity in the stream alluvium 

pore water was similar to activity in present-day precipitation (between 3.4 and 3.7 TU; fig. 9A). Tritium activity was 

10.1 TU in the upper 1.7 m of the Pantano Formation and 

was between 1 and 2 TU from a depth of 6.6 to 11.1 m. This 

pattern indicates that recent precipitation has likely infiltrated 

through the stream alluvium to the Pantano Formation. Water 

is infiltrating into the semiconsolidated, unsaturated Pantano 

Formation slowly, at a rate of about 0.9 cm/yr (assuming an 

average volumetric soil-water content of 0.20 cm3/cm3). Pore 

water within the Pantano Formation was depleted in heavy 

isotopes, similar to winter precipitation (fig. 10). This could 

indicate that the Pantano Formation receives infiltration 

primarily during winter streamflows or that the existing pore 

water was derived from infiltration received when the climate 

was cooler than at present.

Temperature methods detected only one summer flow 

event (30 minutes in duration) at WC4a between January 

2001 and April 2002 (table 8). Water levels in the saturated 

zone, however, rose at least six times during the summer of 

2001 (fig. 8A). The lack of sediment-temperature signals 

may be caused by a retention basin about 260 m upstream 

from the borehole. Water-level recovery was likely the result 

of infiltration at the retention basin and subsequent downgradient subflow above the contact between the Pantano Formation and the stream alluvium. A recharge flux could not be 

calculated from the detected flow event because the water 

level began to rise before the onset of temperature-detected 

flow in the channel.

Borehole WC3 is about 7.2 km downstream from the 

mountain front. This site is within the city limits of Sierra 

Vista, just downstream from an area where the banks and 

streambed of Woodcutters Wash have been stabilized. The 

site is in a reach about 8 m wide and incised 1.8 to 3.0 m into 

terrace deposits and basin fill. Stream alluvium in the channel 

bed is only a few centimeters thick. The poorly sorted sand, 

silt, and clay of the upper basin fill extends from the land 

surface to a depth of 22.6 m (fig. 6B). The silt and clay content 

of the upper basin fill is generally 30 to 60 percent. Electrical conductivity of the sediments ranged from about 25 to 60 

mS/m (fig. 6B). Neutron soil-moisture counts ranged from 

6,000 to 9,000 in the borehole (fig. 6B).

Physical and hydraulic properties were determined 

for five core samples from WC3 collected at depths of 0.9, 

1.5, 8.2, 13.7, and 19.8 m (table 6). The measured saturated 

hydraulic conductivity of the basin fill ranged from 1.7 × 10–4

to 9.9 × 10–3 cm/s. Porosity ranged from 0.33 and 0.40 cm3

/

cm3, and soil-water content ranged from 0.11 to 0.19 cm3/cm3.

Sediment-chloride concentrations ranged from 3 to 70 

mg/kg from the surface to 4.9 m, and were below 4 mg/kg 

from 5.2 to 22.6 m (fig. 9B). Stable-isotope data indicate that 

the high chloride concentrations near the surface are not the 

result of chloride accumulation due to evapotranspiration; 

stable-isotope values in pore water at 0.2 m had evaporative 

signatures, but the values at 0.8 m and below did not (fig. 10). 

The high chloride concentrations in the shallow part of the 

unsaturated zone are probably indicative of chloride concentrations in runoff from Sierra Vista. Pore-water tritium activity 

values from the surface to 16.6 m were similar to those of 

present-day precipitation (between 1.0 and 6.3 TU; fig. 9B). 

The tritium activity at 19.7 m was 0.4 TU. Five flow events 

were detected at WC3 between January 2002 and December 

2002 (table 8). There were no sediment-temperature perturbations, however, at 1.5 m and below during or after flow events.

The temperature data indicate that the infiltration flux at 

WC3 is too low to perturb the sediment-temperature profile 

during and after individual flow events. Tritium data indicate 

an infiltration rate of about 4.1 cm/yr (assuming an average 

volumetric soil-water content of 0.15 cm3

/cm3). Stable-isotope 

values in pore water were between the ranges for summer 

and winter precipitation, indicating that infiltration may have 

occurred during both summer and winter streamflow events in 

the past (fig. 10).

Borehole WC2 is about 12.3 km downstream from the 

mountain front. The site is in a 22-m wide channel reach that 

is incised about 1.8 m into terrace deposits and basin fill. The 

channel bed is floored with only a veneer of stream alluvium 

and is underlain by less permeable, poorly sorted sand, silt, 

and clay of the basin fill (fig. 6C). The silt and clay content of 

the basin fill is generally 50 to 80 percent. Geophysical borehole logs were not recorded in this borehole.

Physical and hydraulic properties were determined for 

five core samples from WC2 collected at depths of 2.1, 3.7, 

6.7, 8.2, and 9.8 m (table 6). The measured saturated hydraulic 

conductivity of the basin fill ranged from 9.8 × 10–6 to 2.2 × 
276 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona %#!&253$.!,7/,%"32%4%-.),%6%,2%4!7











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Figure 8. Water levels and streamflow durations from temperature sensors, Woodcutters Wash boreholes: A, WC4a; B, WC1.

10–2 cm/s. Porosity of the basin fill ranged from 0.34 to 0.52 

cm3/cm3. The soil-water content of the basin fill ranged from 

0.15 to 0.47 cm3/cm3.

Sediment-chloride concentrations to 12.5 m were low 

(less than 7 mg/kg), and tritium activity to 11.1 m was comparable to that of present-day precipitation (between 3.9 and 

5.7 TU), indicating that recent infiltration has occurred to at 

least 11.1 m (fig. 9C). Pore-water stable-isotope values at 2.0 

m had a slight evaporative signature and indicate infiltration 

of both summer and winter streamflow (fig. 10). This borehole was not completed with a casing; therefore, sedimenttemperature data are not available and infiltration fluxes could 

not be determined.

Borehole WC1 is at the SPRNCA boundary 16.4 km 

downstream from the Huachuca Mountains. The site is in a 

reach 10-m wide and incised several meters into the basin fill. 

The highly permeable stream alluvium, consisting of sand and 

gravel, extends from land surface to 3.7 m; basin fill, consisting of silt and clay, extends from 3.7 to 9.1 m; and basin fill, 

consisting of sand, extends from 9.1 to 9.4 m (fig. 6D). The 

basin fill includes a large amount of calcium carbonate from 

3.7 to 5.2 m, and a slightly sandy zone from 6.4 to 7.0 m. 

Electrical conductivity of the sediments was about 10 mS/m 

within the stream alluvium and 60 to 100 mS/m within the 

basin fill (fig. 6D). The higher electrical conductivity in the 

basin fill is likely due to both higher soil-water content and a 

higher silt and clay content than the stream alluvium.

During drilling in January 2001, the borehole penetrated 

saturated sediments at 7.5 m. Water levels were highly variable during the monitoring period, from 6.6 to 8.3 m below 

the land surface, and rose as much as 0.5 m in 2 days following a single flow event (fig. 8B). Neutron soil-moisture counts 

ranged from 5,000 to 7,000 in the stream alluvium and 7,000 

to nearly 20,000 in the basin fill (fig. 6D). The highest counts 

correspond to saturated or near-saturated sediments.

Physical and hydraulic properties were determined for 

four core samples from WC1 collected at depths of 0.3, 2.1, 

3.7, and 6.7 m (table 6). The measured saturated hydraulic 

conductivity of the stream alluvium ranged from 3.6 × 10–2 to 

7.2 × 10–2 cm/s, and that of the basin fill ranged from 2.1 × 10–6

to 3.2 × 10–3 cm/s. Porosity of the stream alluvium ranged from 

0.37 to 0.46 cm3/cm3; porosity of the basin fill was not determined. Soil-water contents of the stream alluvium ranged from 

0.07 to 0.13 cm3/cm3, and the soil-water content at one depth 

in the basin fill was 0.37 cm3/cm3. Sediment-chloride concentrations to 8.8 m were low (less than 6 mg/kg) and tritium 

activity values to 8.1 m were between 3.9 and 7.2 TU (fig. 9D), 

indicating that recent infiltration has occurred to at least 9.1 m. 

Stable-isotope values in pore water were between the isotope 

ratio ranges for summer and winter precipitation, indicating 

that infiltration prior to drilling may have occurred during both 

summer and winter streamflow events (fig. 10). An evaporative 

signature is not evident in the stable-isotope data.

Eighteen flow events occurred at WC1 between January 

2001 and December 2002 (table 8). During four events, temperature perturbations were detected at 1.5 and 3.0 m, but not 

below 3.0 m (table 9). The water level in the saturated zone, 

however, rose sharply following each event, indicating that 

the infiltrating streamflow is recharging the saturated zone. 

The lack of temperature variation below 3.0 m, coupled with 

the substantial water-level response, supports the occurrence 

of recharge from nearby areas but not directly through the silt 

and clay at the site. The water-level response may represent a 

confined response in sandy stringers within the silt and clay 

that are hydraulically connected to upstream areas where 

infiltration occurs.

Infiltration fluxes to 3.0 m below the land surface during 

flow events ranged from 1.3 to 1.5 m/hr (fig. 11 and tables 9 

and 11). Percolation fluxes to 3.0 m after flow events ranged 

from 0.4 to 1.5 m/hr (table 9).
Ephemeral-Stream Channel Infiltration 277

D N A L WO L E B HT P E D 

S R E T E M NI ,E C A F R U S 

0 

5 

A

0 

CHLORIDE, IN MILLIGRAMS PER KILOGRAM

Pantano Formation 

(semiconsolidated) 

Saturated interval 

Saturated interval 

25 50 75 

0 2 4 6 

TRITIUM, IN TRITIUM UNITS TRITIUM, IN TRITIUM UNITS

8 10 12 

10 

15 

25 

S R E T E M NI ,E C A F R U S DN A L WO L E B HT P E D 

0 

5 

0 

CHLORIDE, IN MILLIGRAMS PER KILOGRAM

25 50 75 

0 2 4 6 8 10 12 

10 

15 

20 

B 

D N A L WO L E B HT P E D 

S R E T E M NI ,E C A F R U S 

0 

5 

C 

0 

CHLORIDE, IN MILLIGRAMS PER KILOGRAM

25 50 75 

0 2 4 6 

TRITIUM, IN TRITIUM UNITS

8 10 12 

10 

15 

D N A L WO L E B HT P E D 

S R E T E M NI ,E C A F R U S 

0 

5 

D

0 

CHLORIDE, IN MILLIGRAMS PER KILOGRAM

25 50 75 

0 2 4 6 

TRITIUM, IN TRITIUM UNITS

8 10 12 

10 

NOTE: Tritium values include standard 

 error of estimate bars 

Figure 9. Sediment-chloride and pore-water tritium data, Woodcutters Wash boreholes: A, WC4a; B, WC3; C, WC2; D, WC1.

Miller Canyon Wash

Miller Canyon Wash is a northeastward-trending channel with headwaters in the Huachuca Mountains. The channel 

is 16.2 km long and has an average slope of 20.5 m/km. The 

channel widens from less than 1 m along the upper reaches 

to more than 4 m along the lower reaches. It is incised less 

than 1 m along the upper reaches and 1 m or more along the 

lower reaches. The channel drains a 32.8-km2 area that ranges 

in elevation from 1,252 to 2,859 m. Desert scrub, grassland, 

and mesquite are the primary land-cover types in the drainage 

basin; oak woodland and forest are dominant in the mountainous areas (fig. 2). About 15 percent of the basin, along the 

mountain front, is urban. The urban areas, however, generally 

have less paved areas than the urban areas in the Woodcutters 

Wash drainage basin.

Soils in the drainage basin vary from loamy and fine 

paleosoils below the mountains to clayey downgradient; soils 

are sandy along the stream channel (fig. 3). The permeable 

stream alluvium ranges in thickness from a few centimeters 

near the mountains to a few meters in the lower reaches. The 

stream alluvium is underlain by low permeability basin fill that 

has variable amounts of clay, silt, sand, and gravel.

Ephemeral streamflows recorded in 2001–2002 ranged in 

duration from about 30 min to 19.8 hr (table 8). Flows in the 

upper reaches were less frequent but generally were of longer 

duration than those farther downstream (fig. 7). The farthest 

upstream site, temperature sensor 377806, detected four flows, 
278 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona

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18 

28 

26 

24 

20 

22 

13:00 

JULY 7, 2001 

13:30 14:00 14:30 15:00 15:30 16:00 16:30 17:00 17:30 

Streamflow 

R E P M E T A , E R U T 

duration 

S U I S L E C SE E R G E D NI 

EXPLANATION

DEPTH AND SOURCE OF TEMPERATURE DATA 

0 METER, MEASURED 

1.5 METERS, MEASURED 

3.0 METERS, MEASURED 

4.6 METERS, MEASURED 

1.5 METERS, VS2DH MODEL 

3.0 METERS, VS2DH MODEL 

Figure 10. Stable-isotope data for pore water collected from Woodcutters 

Wash boreholes and for precipitation.

Figure 11. Streamflow duration and sediment temperatures from sensors and from VS2DH model output, Woodcutters 

Wash borehole WC1, July 7, 2001.

which had an average duration of 9.1 min. The farthest downstream site, temperature sensor 374919, detected six flows, 

which had an average duration of 2.8 hr.

Borehole MC2 is at the contact between the crystalline 

rocks of the Huachuca Mountains and the basin fill. The site 

is in a reach about 2 m wide and incised less than 1 m into the 

basin fill. The borehole penetrated a layer of predominantly 

poorly sorted gravel and sand of the basin fill from the land 

surface to 15.8 m that included a layer of silt and clay from 

6.4 to 7.6 m (fig. 6E). Electrical conductivity of the sediments 

at MC2 ranged from about 20 to 40 mS/m (fig. 6E). Borehole 

MC1 is at the SPRNCA boundary 7.1 km downstream from 

the mountain front. The site is in a reach about 4 m wide 

and incised several meters into the basin fill. The borehole 

penetrated poorly sorted sand, silt, and clay of the basin fill 

from the land surface to 25.0 m (fig. 6F). Electrical conductivity of the sediments ranged from about 20 to 100 mS/m (fig. 

6F). Neutron soil-moisture counts ranged from about 7,000 to 

11,000 for MC2 (fig. 6E); a neutron soil-moisture log was not 

completed in MC1.

Physical and hydraulic properties of the basin fill were 

determined for three core samples from MC2 collected at 

depths of 1.8, 7.0, and 10.1 m; and for four core samples from 

MC1 collected at depths of 0.9, 4.0, 8.5, and 19.2 m (table 6). 

The measured saturated hydraulic conductivity ranged from 

1.7 × 10–2 to 3.2 × 10–6 cm/s at MC2 and from 9.3 × 10–3 to 1.8 

× 10–6 cm/s at MC1. Porosities ranged from 0.36 to 0.42 cm3/

cm3 at MC2 and from 0.36 to 0.39 cm3/cm3 at MC1. Soil-water 

contents ranged from 0.18 to 0.30 cm3/cm3 at MC2 and from 

0.28 to 0.31 cm3/cm3 at MC1.
Ephemeral-Stream Channel Infiltration 279

Sediment-chloride concentrations were lower than 5 mg/

kg in the upper 15.8 m of MC2 and in the upper 21.9 m of 

MC1. Tritium activity in the upper 9.9 m of MC2 and in the 

upper 22.1 m of MC1 were comparable to activity in presentday precipitation (1.9 to 7.8 TU; fig. 12).Recent infiltration 

has occurred to at least 9.9 m at MC2 and 22.1 m at MC1. 

Stable-isotope values for the pore water at both sites indicated 

that infiltration occurred during summer and winter; pore water 

below 0.2 m did not show evaporative signatures (fig. 13).

One, 18-hour, streamflow event was detected between 

January 2002 and December 2002 at MC2; streamflow was 

not detected between April 2002 and December 2002 at MC1 

(table 8). There were no sediment-temperature perturbations 

at or below 1.5 m during or after flow events at MC2. The 

temperature data suggest that the infiltration flux at MC2 is 

too low to perturb the sediment-temperature profile during 

and after individual events. Because of a lack of data, infiltration fluxes could not be calculated from sediment-temperature 

profiles at either site.

Walnut Gulch

Walnut Gulch is a westward-trending channel with 

headwaters in the Tombstone Hills and the Mule and Dragoon 

Mountains. The main channel is about 26.5 km long and has 

an average slope of 12.1 m/km. The channel widens from less 

than 2 m along the upper reaches to more than 40 m along 

the lower reaches. It is incised less than 1 m along the upper 

reaches and 4 m or more along the lower reaches. The channel 

drains a 152.1-km2 area that ranges in elevation from 1,164 

TRITIUM, IN TRITIUM UNITS TRITIUM, IN TRITIUM UNITS

25 

S R E T E M NI ,E C A F R U S DN A L WO L E B HT P E D 

0 

5 

0 

CHLORIDE, IN MILLIGRAMS PER KILOGRAM

25 50 75 

0 2 4 6 8 10 12 

10 

15 

20 

B

S R E T E M NI ,E C A F R U S DN A L WO L E B HT P E D 

0 

5 

0 

CHLORIDE, IN MILLIGRAMS PER KILOGRAM

25 50 75 

0 2 4 6 8 10 12 

10 

15 

20 

NOTE: Tritium values include standard 

 error of estimate bars 

A 

to 1,939 m. Desert scrub, grassland, and mesquite are the primary land-cover types in the drainage basin (fig. 2). Approximately 3 percent of the Walnut Gulch drainage basin, near the 

northern extent of the Tombstone Hills, is urbanized.

Soils in the drainage basin range from clayey near 

the mountains to secondarily developed calcium carbonate 

downgradient; soils are sandy along the stream channel. The 

permeable stream alluvium ranges in thickness from about 

1 m near the mountains to 15 m in the lower reaches of the 

channel. The stream alluvium is underlain by low-permeability consolidated to semiconsolidated conglomerate of the 

lower basin fill near the mountains and by upper basin fill in 

the lower reaches of the channel.

The ARS has monitored ephemeral streamflows in Walnut Gulch since the 1950s by using a series of flumes. Ephemeral streamflows recorded in 2001–2002 at flumes 1, 6, and 

11 ranged in duration from 12 min to 82.2 hr (table 8). Flows 

generally were more frequent and of longer duration near the 

mountain front than in areas downstream (fig. 7). The farthest 

upstream site, flume 11, had 12 flows, which had an average 

duration of 11.1 hr. The farthest downstream site, flume 1, had 

eight flows, which had an average duration of 3.2 hr.

Borehole WG3 is just upstream from flume 11 and is 7.2 

km downstream from the mountain front. The site is in a reach 

about 2 m wide and incised less than 1 m into the basin fill. 

The borehole penetrated unconsolidated stream alluvium of 

sand and gravel to 1.8 m, and semiconsolidated conglomerate 

of the lower basin fill from 1.8 to 13.1 m (fig. 6G). The electrical conductivity of the conglomerate was about 5 to 10 mS/m 

(fig. 6G). A neutron soil-moisture log was not recorded in this 

Figure 12. Sediment-chloride and pore-water tritium data, Miller Canyon Wash boreholes: A, MC2; B, MC1.
280 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona

borehole. The high degree of induration of the conglomerate 

and basalt prevented the collection of cores below 1.8 m, and 

physical and hydraulic properties were not determined for the 

stream alluvium above 1.8 m.

Sediment-chloride concentrations were less than 4 mg/kg 

in the upper 1.8 m, and tritium activity in the upper 0.8 m was 

comparable to activity for present-day precipitation (6.5 to 8.5 

TU; fig. 14A), indicating that recent infiltration has occurred to 

at least 0.8 m. Although the primary porosity of the semiconsolidated conglomerate is small, infiltration can occur through 

secondary fractures. The stable-isotope values of the pore 

water at 0.2 and 0.8 m had a strong evaporative signature (fig. 

15). Sediment temperatures were not monitored at this site, 

and therefore, infiltration fluxes were not calculated.

Borehole WG2 is just upstream from flume 6 and is 13.2 

km downstream from the mountain front. The site is in a reach 

about 13 m wide and incised several meters into the basin fill. 

The borehole penetrated unconsolidated stream alluvium of 

sand and gravel to 3.7 m, semiconsolidated conglomerate of 

the lower basin fill from 3.7 to 11.6 m, and basalt from 11.6 

to 12.2 m (fig. 6H). Electrical conductivity of the sediments 

was less than 5 mS/m in the stream alluvium and from 10 to 

15 mS/m in the conglomerate (fig. 6H). Neutron soil-moisture 

counts in the borehole ranged from about 6,000 to 10,000. As 

at WG3, the high degree of induration of the conglomerate 

and basalt prevented the collection of cores below 3.7 m, and 

physical and hydraulic properties were not determined for the 

stream alluvium above 3.7 m.

Sediment-chloride concentrations in the upper 3.4 m 

were less than the detection limit of 1.80 mg/kg, and tritium 

activity in the upper 2.3 m was comparable to values for 

present-day precipitation (4.7 to 6.7 TU; fig. 14B), indicating that recent infiltration has occurred to at least 2.3 m. The 

stable-isotope values for the pore water at 0.5 and 0.8 m had 

a strong evaporative signature; however, the pore water at 2.3 

m did not (fig. 15). Although the primary porosity of the consolidated conglomerate is small, infiltration can occur through 

secondary fractures.

Seven flow events occurred at flume 6 between May 2002 

and December 2002 (table 8). Borehole WG2 was damaged 

Figure 13. Stable-isotope data for pore water 

collected from Miller Canyon Wash boreholes and 

for precipitation.

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sometime after mid-July 2002, however, and therefore only 

sediment temperatures from the flow on July 19, 2002, can be 

used to determine infiltration fluxes at this site. During this 

flow, a temperature perturbation was detected at a depth of 3.0 

m (table 9). The temperature sensor at 1.5 m malfunctioned 

during this time and all data were lost. The calculated infiltration fluxes to 3.0 m during flow ranged from 0.4 to 1.0 m/hr 

(fig. 16A and tables 9 and 11).

Borehole WG1 is just upstream from flume 1 and 25.6 

km downstream from the mountain front. The site is in a reach 

about 31 m wide and incised several meters into the basin fill. 

The borehole penetrated stream alluvium of sand and gravel in 

the upper 14.5 m underlain by basin fill that is 20 to 55 percent 

silt and clay (fig. 6I). Electrical conductivity of the sediments 

ranged from less than 20 mS/m within the stream alluvium to 

25 to 65 mS/m within the basin fill (fig. 6I). A neutron soilmoisture log was not recorded in this borehole.

Physical and hydraulic properties were determined for 

four core samples from WG1 collected at depth of 3.0, 3.7, 

13.4, and 22.6 m (table 6). The data indicate little variation 

of properties between the stream alluvium and the upper 

basin fill. The measured saturated hydraulic conductivity of 

the cores ranged from 2.0 × 10–2 to 4.6 × 10–2 cm/s; porosity ranged from 0.35 to 0.47 cm3

/cm3; and soil-water content 

ranged from 0.10 to 0.25 cm3/cm3.

Sediment-chloride concentrations in the upper 22.3 m 

were less than 3 mg/kg, and tritium activity in the upper 22.4 

m was comparable to present-day precipitation (2.9 to 4.5 TU; 

fig. 14C), indicating that recent infiltration has occurred to at 

least 22.4 m. Stable-isotope values at 2.9 m had a slight evaporative signature (fig. 15) and also indicated that water in the 

unsaturated zone infiltrated during both summer and winter 

streamflow events.

Three flow events occurred at flume 1 between April 

2002 and December 2002 (table 8). All were during the summer and had durations from 12 min to about 10 hr. During 

each event, sediment-temperature perturbations in WG1 were 

detected at 1.5, 3.0, and 4.6 m (table 9). Temperature perturbations were detected at 6.1 m after the end of each flow event 

(table 9), but no perturbations were detected below 6.1 m.

Calculated infiltration fluxes to 4.6 m below 

the land surface during flow events ranged from 

0.4 to 2.1 m/hr (figs. 15B and 15C and tables 9 and 

11). Percolation fluxes to 6.1 m after flow ended 

ranged from 0.1 to 1.0 m/hr (table 9).

Banning Creek

Banning Creek is a westward-trending channel 

with headwaters in the Mule Mountains. The channel is 8.6 km long and has an average slope of 15.6 

m/km. The creek drains a 41.3-km2

 area that ranges 
Ephemeral-Stream Channel Infiltration 281

AD N A L WO L E B HT P E D 

S R E T E M NI ,E C A F R U S 

0 

5 

0 

CHLORIDE, IN MILLIGRAMS PER KILOGRAM

25 50 75 

0 2 4 6 

TRITIUM, IN TRITIUM UNITS 

8 10 12 

10 

NOTE: Tritium values include standard 

 error of estimate bars 

TRITIUM, IN TRITIUM UNITS 

25 

S R E T E M NI ,E C A F R U S DN A L WO L E B HT P E D 

0 

5 

0 

CHLORIDE, IN MILLIGRAMS PER KILOGRAM

25 50 75 

0 2 4 6 8 10 12 

10 

15 

20 

C D N A L WO L E B HT P E D 

S R E T E M NI ,E C A F R U S 

0 

5 

0 

CHLORIDE, IN MILLIGRAMS PER KILOGRAM

25 50 75 

0 2 4 6 

TRITIUM, IN TRITIUM UNITS 

8 10 12 

10 

B 

Figure 14. Sediment-chloride and pore-water tritium data, 

Walnut Gulch boreholes: A, WG3; B, WG2; C, WG1.

in elevation from 1,257 to 2,217 m. Desert scrub, grassland, 

and mesquite are the primary land-cover types in the drainage 

basin; oak woodland dominates the mountainous areas (fig. 2). 

Less than 1 percent of the basin is urbanized land.

Soils in the drainage basin vary from lithic rock near 

the mountains to calcium carbonate downgradient; soils 

are sandy along the stream channel (fig. 3). The permeable 

stream alluvium ranges in thickness from less than 1 m near 

the mountains to more than 7 m in the lower reaches of the 

creek. The stream alluvium is underlain by limestone in the 

upper reaches and unconsolidated basin fill of clay, silt, sand, 

and gravel in the lower reaches.

Ephemeral streamflows recorded during 2001–2002 

ranged in duration from 1 hr to 48 days (table 8). Flows in the 

upper reaches were not more frequent but were of a longer 

duration than flows farther downstream (fig. 7). The farthest 

upstream streamflow-gaging station, 09470700, and temperature sensor, 377822, detected two flows in 2001 to 2002. 

The flows had an average duration of 42.9 days. The farthest 

downstream temperature sensor, at site BC1, detected eight 

flows, which had with an average duration of 4.6 hr.

Borehole BC1 is 3.9 km downstream from the crystalline rocks of the Mule Mountains. The channel at the site is 

about 4 m wide and is incised several meters into the basin fill. 

The borehole penetrated unconsolidated stream alluvium of 

clay, silt, sand, and gravel from the land surface to 6.4 m (fig. 

6J). Basin fill, which includes greater amounts of clay and 

silt than the stream alluvium, was penetrated from 6.4 to 25.9 

m. Electrical conductivity ranged from 10 to 50 mS/m in the 

stream alluvium and from 10 to 70 mS/m in the basin fill (fig. 

6J). Neutron soil-moisture counts ranged from 6,000 to 10,000 

in the borehole (fig. 6J).

Physical and hydraulic properties were determined for 

six core samples from BC1 collected at depths of 2.1, 5.2, 

8.2, 14.3, 15.8, and 20.4 m (table 6). The measured saturated 

hydraulic conductivity ranged from 9.6–3 to 1.2–1 cm/s for the 

stream alluvium and from 4.1–7 to 8.9–3 cm/s for the basin fill. 

Porosity of the two units ranged from 0.25 to 0.43 cm3/cm3, 

and soil-water content ranged from 0.08 to 0.29 cm3/cm3.

Sediment-chloride concentrations in the upper 25.9 m 

were less than 12 mg/kg, and tritium activity in the upper 

23.3 m were comparable to values for present-day precipitation (3.2 to 6.7 TU; fig. 17), indicating that recent infiltration 

has occurred to at least 23.3 m. Stable-isotope values for pore 

water were between bulk precipitation ranges for summer and 

winter (fig. 18), indicating that infiltration occurs during summer and winter streamflow events.

Eight flow events occurred at BC1 between January 2001 

and December 2002 (table 8). During seven of the events, 

temperature perturbations were detected at 1.5 and 3.0 m; 

temperature perturbations were also detected at 4.6 and 6.1 m 

after the end of each event (table 9).

Calculated infiltration fluxes to 3.0 m during flow events 

ranged from 0.4 to 2.8 m/hr (fig. 19 and tables 9 and 11). 

Percolation fluxes to 6.1 m after flow ended ranged from 0.7 

to 2.8 m/hr (tables 9 and 11).
282 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona

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Figure 15. Stable-isotope data for pore water 

collected from Walnut Gulch boreholes and for 

precipitation.

Greenbush Draw

Greenbush Draw is a northwestward-trending channel with headwaters in the Mule Mountains and in parts of 

Mexico. The main channel is 19.5 km long and has an average 

slope of 8.8 m/km. The channel widens from less than 2 m 

along the upper reaches to more than 14 m along the lower 

reaches of the draw. It is incised 2 m or more along the lower 

reaches. The draw drains a 306.3-km2 area that ranges in 

elevation from 1,280 to 2,258 m. Grassland, mesquite, and 

desert scrub are the primary land-cover types in the drainage 

basin (fig. 2). About 4 percent of the basin is urbanized land.

Soils in the drainage basin are primarily sandy along the 

stream channels and clayey and calcium carbonate elsewhere 

(fig. 3). Secondary calcium carbonate soils dominate the 

lower downgradient areas to the north of Greenbush Draw, 

and clayey soils dominate the downgradient areas to the south 

of Greenbush Draw. The stream alluvium ranges in thickness 

from 2 m or less in the upper reaches to 10 m along the lower 

reaches. The stream alluvium is underlain by unconsolidated 

to semiconsolidated upper basin fill that includes interbedded 

sand, gravel, silt, and clay.

Ephemeral streamflows recorded during 2001–2002 

ranged in duration from 30 min to 19 hr (table 8). Flows in 

the upper reaches of Greenbush Draw were not more frequent 

or of a longer duration than flows at sites farther downstream 

(fig. 7). The farthest upstream temperature sensor, 377815, 

detected five flows in 2001 and 2002, which had an average 

duration of 7.5 hr. The farthest downstream temperature sensor, 377820, detected six flows, which had an average duration 

of 10.0 hr.

Borehole GD2 is 5.6 km downstream from the limestone 

and crystalline rocks of the mountains. The channel at the site 

is about 2 m wide and is incised less than 1 m into the basin 

fill. The borehole penetrated unconsolidated stream alluvium of clay, silt, sand, and gravel from the surface to 2.0 m 

and basin fill from 2.0 to 25.0 m (fig. 6K). The basin fill has 

greater percentages of clay and silt than the stream alluvium. 

Electrical conductivity of the sediments ranged from 10 to 

70 mS/m in the stream alluvium and from 10 to 100 mS/m in 

the basin fill (fig. 6K). Thin saturated intervals (less than 1.2 

m in thickness) were penetrated at depths of 8.2, 12.8, and 

24.1 m during drilling. A neutron log was not recorded in this 

borehole.

Physical and hydraulic properties were determined for 

three core samples from GD2 collected at depths of 2.4, 5.3, 

and 13.1 m (table 6). All the cores were from basin fill. The 

saturated hydraulic conductivity ranged from 5.9 × 10–3 to 5.3 

× 10–2 cm/s. Porosity ranged from 0.41 to 0.53 cm3/cm3, and 

soil-water content ranged from 0.14 to 0.44 cm3/cm3.

Sediment chloride concentrations in the upper 25.0 m 

were less than 3 mg/kg, and tritium activity in the upper 19.1 

m were similar to values for present-day precipitation (3.5 

to 4.3 TU; fig. 20A), indicating that recent infiltration has 

occurred to at least 19.1 m. Stable-isotope values for pore 

water were between ranges for summer and winter precipitation (fig. 21), indicating that infiltration occurs during summer 

and winter streamflow events.

Three flow events occurred at GD2 between January 

2002 and December 2002 (table 8). During two of the events, 

temperature perturbations were detected at 1.5 m; temperature 

perturbations were detected at 3.0, 6.1, 9.1, and 12.2 m after 

flow ended (table 9). Infiltration fluxes to 1.5 m during flow 

ranged from 0.7 to 0.9 m/hr. Percolation fluxes after flow 

ended ranged from 0.3 to 1.8 m/hr.

Borehole GD1 is 12.4 km downstream from the limestone 

and crystalline rocks of the mountains. The channel at the site 

is about 14 m wide and is incised several meters into the basin 

fill. The borehole penetrated unconsolidated stream alluvium 

of clay, silt, sand, and gravel from the land surface to 10.0 m 

and basin fill from 10.0 to 19.5 m (fig. 6L). The basin fill has 

a greater percentage of clay and silt than the stream alluvium 

and includes a large amount of calcium carbonate from 10.1 to 

10.4 m. Electrical conductivity of the sediments ranged from 

10 to 20 mS/m in the stream alluvium and from 15 to 100 

mS/m in the basin fill (fig. 6L). Neutron counts did not vary 

greatly (7,000 to 12,000) in the borehole (fig. 6L).

Physical and hydraulic properties were determined 

for four core samples from GD1 collected at depths of 4.0, 

7.0, and 13.1 m (table 6). The measured saturated hydraulic 

conductivity ranged from 4.6 × 10–3 to 1.4 × 10–2

cm/s for the stream alluvium and was 6.8 × 10–8

cm/s for the basin fill. Porosity was determined 

only for one core, from the stream alluvium, and 

was 0.27 cm3/cm3. Soil-water content was determined only for the stream alluvium, and ranged 

from 0.11 to 0.15 cm3/cm3.

Sediment-chloride concentrations in the 

upper 18.9 m were less than the detection limit of 

1.80 mg/kg, and tritium activity in the upper 19.1 

m was similar to values for present-day precipita-
Ephemeral-Stream Channel Infiltration 283

20 

R E P M E T A S U I S L E C SE E R G E D NI ,E R U T 

28 

30 

26 

22 

24 

14:00 

AUGUST 4, 2002 

15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 12:00 

Streamflow duration 

Streamflow duration 

Streamflow duration 

18 

R E P M E T A S U I S L E C SE E R G E D NI ,E R U T 

28 

30 

26 

24 

20 

22 

21:30 

JULY 26–27, 2002 

20:00 22:00 23:00 24:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 

16 

R E P M E T A S U I S L E C SE E R G E D NI ,E R U T 

26 

28 

30 

24 

22 

18 

20 

JULY 19, 2002 

13:00 14:00 15:00 16:00 17:00 18:00 19:00 

A 

B

C 

EXPLANATION

DEPTH AND SOURCE OF TEMPERATURE DATA 

0 METER, MEASURED 

1.5 METERS, MEASURED 

3.0 METERS, MEASURED 

4.6 METERS, MEASURED 

6.1 METERS, MEASURED 

1.5 METERS, VS2DH MODEL 

3.0 METERS, VS2DH MODEL 

4.6 METERS , VS2DH MODEL 

Figure 16. Streamflow durations and sediment temperatures from sensors and from VS2DH model output, Walnut Gulch 

boreholes: A, WG2, July 19, 2002; B, WG1, July 26–27, 2002; C, WG1, August 4, 2002.
284 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona

tion (3.3 to 4.6 TU; fig. 20B), indicating that recent infiltration 

has occurred to at least 19.1 m. Stable-isotope values for pore 

water at 0.5 m had strong evaporative signatures; the remaining values were between bulk precipitation ranges for summer 

and winter (fig. 21), indicating that infiltration occurs during 

summer and winter streamflow events.

One flow event was detected at GD1 between May 2002 

and December 2002 (table 8). Temperature perturbations, at 

depths of 1.5, 3.0, 6.1, and 9.1 m, were detected only after 

flow ended (table 9). Percolation fluxes to 9.1 m after flow 

ended ranged from 0.1 to 0.8 m/hr (table 9).

Basin-Floor Infiltration

Infiltration fluxes were determined for basin-floor sites in 

the Walnut Gulch, Carr Canyon Wash, and Woodcutters Wash 

drainage basins. Data used in the determination of infiltration 

fluxes included physical and hydraulic properties of sediments, chloride concentrations of sediments, and pore-water 

stable-isotope values and tritium activity. Where possible, 

infiltration fluxes through the upper 4.0 to 9.8 m of sediments 

were estimated.

Borehole WG4 is within the Walnut Gulch drainage 

basin on a hilltop in the ARS Lucky Hills research station. 

Mesquite woodland is the primary land-cover type at the 

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data, Banning Creek borehole BC1.

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Banning Creek borehole BC1 and for precipitation.

site (fig. 2). Basin fill penetrated by the borehole consists of 

semiconsolidated to unconsolidated sand and gravel from the 

surface to 3.4 m, consolidated clay and silt from 3.4 to 5.5 m, 

semiconsolidated to unconsolidated sand and gravel from 5.5 

to 9.8 m, and semiconsolidated to consolidated clay, silt, and 

sand from 9.8 to 13.4 m (fig. 6M). Electrical conductivity of 

the sediments ranged from 0 to 30 mS/m (fig. 6M). A neutron 

soil-moisture log was not recorded in this borehole.

Physical and hydraulic properties were determined for 

two core samples collected at depths of 4.3 and 13.4 m in the 

borehole (table 6). Saturated hydraulic conductivity was 1.3 × 

10–2 and 1.7 × 10–2 cm/s. Porosity was 0.48 and 0.50 cm3/cm3, 

and soil-water content was 0.10 and 0.19 cm3/cm3.

Sediment-chloride concentrations increased sharply to 

226 mg/kg from 1.5 to 2.1 m as a result of evapotranspirative enrichment (fig. 22A). Concentrations then decreased 

sharply to 34 mg/kg from 2.4 to 3.4 m, probably as a result 

of no downward water movement or preferential transport 

past the root zone. Below 3.4 m, the chloride concentration 

ranged from 3 to 90 mg/kg. Chloride below 2.1 m was likely 

emplaced by infiltration during a wetter period.

Tritium activity of the pore water indicates that water has 

infiltrated to at least 7.5 m since 1952 (fig. 22A). No anthropogenic tritium was detected at 13.3 m. The location of the 

tritium peak at 2.0 m indicates an infiltration flux of about 1.0 

cm/yr (assuming an average volumetric soil-water content of 

0.19 cm3

/cm3) to 2.0 m. The chloride data indicate that about 

694 years is required for water to infiltrate to this depth, at 

a flux of about 0.2 cm/yr (fig. 22B). Deeper penetration of 

tritium relative to that of chloride was previously identified in 

desert soils; possible explanations have included the downward movement of tritium in the vapor phase (Phillips and 

others, 1988; Scanlon, 1991) and the downward preferential 

flow of tritium through cracks and macropores (Izbicki and 

others, 2000).

Pore-water stable-isotope values to 13.3 m plot along an 

evaporative trend line that has a slope of 2.5 (fig. 23). The point 

of intersection between the evaporative trend line and the meteoric water line indicates that historical infiltration at WG4 was 
Basin-Floor Infilration 285



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Figure 19. Streamflow durations and sediment temperatures from sensors and from VS2DH model output, Banning Creek 

borehole BC1: A, July 20, 2001; B, July 25, 2001; C, August 1, 2001.
286 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona

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Figure 20. Sediment-chloride and pore-water tritium data, 

Greenbush Draw boreholes: A, GD2; B, GD1.

isotopically similar to recent winter precipitation. The chloride, 

tritium, and stable-isotope data indicate that little to no recent 

infiltration has occurred past shallow depths at site WG4.

Borehole WG5 is also within the Walnut Gulch drainage 

basin. The borehole is on a hilltop within the ARS Kendall 

research station. Grassland is the primary land-cover type at 

the site (fig. 2). The borehole penetrated consolidated basinfill conglomerate from the surface to 12.2 m (fig. 6N). The 

electrical conductivity ranged from 10 to 20 mS/m (fig. 6N). 

A neutron soil-moisture log was not recorded in this borehole. 

The degree of consolidation of the sediments precluded collection of complete cores; therefore, physical and hydraulic 

properties of the conglomerate were not determined.

Sediment-chloride concentrations were not measured at 

this site. Stable-isotope values of pore water at 0.2 m showed 

a slight evaporative signature, but were not as enriched as at 

similar depths at other basin-floor sites (fig. 23). The tritium 

activity of pore water at 0.2 m was 0.4 TU. These isotopic data 

indicate that recent infiltration at this site has not extended 

past shallow depths.

Borehole BF1 is within the Carr Canyon drainage basin 

on a flat area of the basin floor between the Carr Canyon 

and Ramsey Canyon Washes. Vegetation at the site is sparse 

and the primary land-cover types are mesquite woodland 

and grassland (fig. 2). The borehole penetrated two primary 

lithologic layers within the basin fill: unconsolidated sand and 

gravel from the surface to about 8 m; and semiconsolidated 

clay, silt, sand, and gravel from 8 m to 15.8 m (fig. 6O). The 

electrical conductivity of the sediments were about 15 to 25 

mS/m from the surface to 11 m, and about 30 to 60 mS/m 

from 11 to 15.8 m. The higher values below 11 m are indicative of a higher soil-water content or higher silt and clay 

content below 11 m (fig. 6O). A neutron soil-moisture log was 

not recorded in this borehole.

Physical and hydraulic properties were determined for 

seven core samples from BF1 collected at depths of 0.3, 4.0, 

5.5, 7.0, 8.5, 10.1, and 13.1 m (table 6). Saturated hydraulic 

conductivity at 0.3 and 7.0 m was 2.1 × 10–2 and 1.4 × 10–2

cm/s, respectively. Porosity was 0.39 and 0.35 cm3/cm3, 

and soil-water content was less than 0.02 cm3

/cm3 and 0.11 

cm3/cm3, respectively. The silt and clay content of the cores 

from 0.3 to 7.0 m was less than 15 percent. The silt and clay 

content at 8.5 m, however, was 30.7 percent. The saturated 

hydraulic conductivity of this core was 5.1 × 10–3 cm/s, the 

porosity was 0.45 cm3/cm3, and the soil-water content was 

0.26 cm3/cm3. The silt and clay content from 10.1 and 31.1 m 

was less than 15 percent.

Sediment-chloride concentrations were less than 5 mg/

kg from the surface to 5.8 m (fig. 24A) and were between 10 

and 32 mg/kg from 6.1 to 14.3 m. Below 14.3 m, concentrations were less than 10 mg/kg. This chloride profile is not 

typical for desert soils in that the chloride peak is not near 

the land surface; is broad, extending almost 8 m; and has a 

low concentration.

Tritium activity of the pore water indicates that water has 

infiltrated to at least 5.3 m, and possibly to 10.2 m, since 1952 
Basin-Floor Infilration 287

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Figure 21. Stable-isotope data for pore water collected from Greenbush 

Draw boreholes and for precipitation.

Figure 22. Walnut Gulch borehole WG4: A, Sediment-chloride and pore-water tritium data; B, Residence time and infiltration flux, 

calculated from chloride data.

Figure 23. Stable-isotope data for pore water collected from Walnut Gulch 

basin-floor boreholes WG4 andWG5 and for precipitation.
288 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona





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Figure 24. Carr Canyon borehole BF1: A, Sediment-chloride and pore-water tritium data; B, Residence time and infiltration flux, 

calculated from chloride data.

(fig. 24A). An infiltration flux could not be calculated by using 

the tritium data because there is not a clear depth of maximum 

tritium activity. The presence of tritium to 5.3 m, however, 

corresponds well with the chloride profile, which indicates that 

about 75 years is required for water to infiltrate to this depth.

Pore-water stable-isotope values show strong evaporative 

enrichment at 0.5 m and a slight evaporative enrichment from 

3.8 to 13.0 m; values plot along an evaporative trend line that 

has a slope of 2.0 (fig. 25). The point of intersection between 

the evaporative trend line and the meteoric water line indicates 

that historical infiltration at BF1 was isotopically similar to 

recent winter precipitation.

The chloride, tritium, and stable-isotope data indicate 

that infiltration occurs at a rate of about 6 cm/yr through the 

more permeable upper zone of sediments to a depth of about 

8 m. Infiltration is much slower through the less permeable 

sediments at depths of 8 to 15.8 m. Infiltration through the 

upper sediments maintains a low chloride content and high 

tritium activity. The water that infiltrates the upper permeable sediments slowly infiltrates and transports chloride to the 

deeper zone. The chloride content in the deep zone is enriched 

through transport of water to the atmosphere by plant roots.

Borehole WC4c is within the Woodcutters Wash drainage 

basin. The borehole is about 150 m south of borehole WC4a 

on an area of the basin floor that slopes northward towards 

Woodcutters Wash (fig. 26). Grassland is the primary landcover type at the site (fig. 2). The borehole penetrated terrace deposits of mostly unconsolidated sand and gravel from 

the surface to 5.8 m; basin fill of clay, silt, sand, and gravel 

from 5.8 to 7.6 m; and a semiconsolidated conglomerate, the 

Pantano Formation, from 7.6 to 12.5 m (fig. 6P). Electrical 

conductivity of the terrace and basin fill ranged from less than 

10 to 50 mS/m, and the electrical conductivity of the Pantano 

Formation ranged from 50 to 75 mS/m (fig. 6P). A neutron 

soil-moisture log was not recorded in this borehole.

Physical and hydraulic properties were determined for 

five core samples from WC4c collected from depths of 1.1, 

2.4, 3.8, 9.9, and 11.3 m (table 6). The saturated hydraulic 

conductivity ranged from 5.1 × 10–3 to 1.5 × 10–2 cm/s for the 

terrace deposits and from 7.2 × 10–6 to 1.9 × 10–5 cm/s for 

the Pantano Formation. Porosity ranged from 0.33 to 0.40 

cm3/cm3 for both units. Soil-water content ranged from 0.07 

to 0.15 cm3/cm3 for the terrace deposits and was 0.24 in the 

Pantano Formation.

During drilling in January 2001, the borehole intersected 

a saturated interval within the terrace deposits and basin fill 

above the Pantano Formation at 4.7 m (fig. 27). Sedimentchloride concentrations were 17 mg/kg at 1.5 m and generally were less than 6 mg/kg below 2.7 m (fig. 28A). Tritium 

activity of 2.6 to 7.0 TU in pore water to 3.7 m indicated that 

recent water is present in the unsaturated zone above the saturated interval (fig. 28A). The chloride data, however, indicate 

that about 150 years is required for water to infiltrate to the 

saturated interval, at a flux of about 3 cm/yr (fig. 28B). Similar 

to conditions at site WC4a, the saturated interval at WC4c is 

probably controlled by infiltration from an upgradient retention basin and subsequent downgradient subflow above the 

contact of the Pantano Formation with terrace and basin fill.

Pore-water tritium activity indicates that the perched 

water is infiltrating into the semiconsolidated Pantano Formation very slowly, at about 0.4 cm/yr (assuming an average 

soil-water content of 0.07 cm3

/cm3). This flux is comparable to 
Basin-Floor Infilration 289

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Figure 25. Stable-isotope data for pore water 

collected from basin-floor boreholes BF1 and WC4c 

and for precipitation.

Figure 26. Generalized hydrogeologic section in the area of Woodcutters Wash boreholes WC4a and WC4c.

Figure 27. Water level in Woodcutters Wash borehole WC4c.
290 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona $.!,7/,%"(40%$ 32%4%-.)%#!&253





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the percolation flux for the Pantano Formation at WC4a of 0.3 

cm/yr. Pore-water stable-isotope values above the water table 

and within the Pantano Formation did not have an evaporative 

signature, but rather fell within the range of values for winter 

precipitation (fig. 25). This indicates that infiltration at WC4c 

could be dominated by winter precipitation.

Subwatershed Ephemeral-Stream 

Channel and Basin-Floor Recharge

Average annual recharge during 2001–2002 was estimated for the Sierra Vista subwatershed by upscaling the 

infiltration fluxes determined for the basin-floor and ephemeral-stream channel sites. This recharge estimate does not 

include mountain-front recharge; this study did not monitor 

streamflow or infiltration near the contact between the hard 

rock of the mountains and the basin fill. Precipitation during 

the period of study was slightly below average and primarily 

occurred during July through September (fig. 4). As a result, 

the calculated annual recharge represents recharge under drierthan-normal conditions.

At the basin-floor sites in the Walnut Gulch drainage 

basin, the long-term infiltration fluxes were very low (less 

than 1 cm/yr). Chloride, tritium, and stable-isotope data 

indicate long periods of no net deep downward percolation 

flux beneath the basin floor. Previous investigators have shown 

that infiltration of precipitation through the basin floor and 

past the root zone may not be significant in arid areas of the 

Southwestern United States that have thick unsaturated zones 

(Phillips, 1994; Walvoord and others, 2002). Additionally, 

Scott and others (2000) reported that moisture fronts in the 

unsaturated zone at WG4 and WG5 reach a maximum depth 

of only 0.5 m in the summer and only 1.3 m in the winter. The 

chloride, tritium, and stable-isotope data, coupled with the 

work done by previous investigators, support the conclusion 

that recharge through the basin floor area is negligible. Infiltration rates could also be negligible in other areas of the basin 

floor that have soil and vegetation that are similar to those at 

WG4 and WG5.

Infiltration fluxes were higher at the basin-floor site in 

the Carr Canyon Wash drainage basin (2 to 6 cm/yr) than at 

other basin-floor sites. Chloride, tritium, and stable-isotope 

data indicate active infiltration to 8 m and a decrease in infiltration below 8 m. The change in the infiltration rate below 8 

m is controlled by an increase in the silt and clay content of 

the soil. Relatively high infiltration rates could occur in other 

areas of the basin floor that have soil and vegetation that are 

similar to those at BF1. The depth that infiltrating water moves 

through the unsaturated zone, and whether the infiltrating 

water will ultimately become recharge, however, are strongly 

dependant on the silt and clay content of limiting soil horizons 

in the unsaturated zone.

Recharge through ephemeral-stream channels is strongly 

influenced by the thickness and hydraulic properties of stream 

alluvium and the permeability of the underlying basin fill. 

Steamflow infiltration readily occurs through the highly 

permeable stream alluvium and the unconsolidated basin fill 

that do not have thick intervals of silt and clay. Infiltration is 

limited by shallow low-permeability layers, such as bedrock, 

silt and clay, caliche, or consolidated basin fill. Where the contact between unconsolidated sediments and low-permeability 

layers is deeper than the depth of root penetration, streamflow 

infiltrates to depths at which water is probably not removed by 

evapotranspiration. This water will remain in storage within 

the unsaturated zone until it is vertically displaced by subseFigure 28. Woodcutters Wash borehole WC4c: A, Sediment-chloride and pore-water tritium data; B, Residence time and infiltration 

flux, calculated from chloride data.
Subwatershed Ephemeral-Stream Channel and Basin-Floor Recharge 291







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Figure 29. Approximate distribution of annual ephemeral-stream channel recharge, 2001–2002, Sierra Vista subwatershed, Arizona.
292 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona #)"5#.)%'2!(#%2 32!%92%032%4%-/4#%(







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quent infiltration and eventually recharges the regional aquifer. 

Where the contact between unconsolidated sediments and 

low-permeability layers is shallow, however, aquifer recharge 

may be minimal because the infiltrated water is available for 

upward transport by evapotranspiration. Water not lost by 

evapotranspiration likely flows laterally above the contact until 

it encounters the limit of the low-permeability layer, reaches 

permeable fractures, or recharges the aquifer where the water 

table intersects the top of the low-permeability layer.

Infiltration fluxes at the ephemeral-stream channel sites 

were very high (0.4 to 2.8 m/hr) during streamflow events. 

Percolation fluxes were also high (0.1 to 2.8 m/hr) immediately following streamflow events. Chloride data indicate 

that in areas where low-permeability layers are absent in 

the shallow subsurface, infiltrated water moves past depths 

where it is available for evapotranspiration, resulting in a net 

downward water flux. Tritium data indicate that water that 

has infiltrated since 1952 is reaching depths of more than 20 

m. We assume that the net water flux below 20 m continues 

to be downward and that infiltrated streamflow ultimately 

recharges the regional aquifer. Stable-isotope data indicate 

that both summer and winter streamflows contribute to 

ephemeral-channel recharge.

Subwatershed recharge during 2001–2002 from ephemeral-stream channel infiltration was estimated by upscaling 

the calculated infiltration fluxes to the area covered by each 

ephemeral-stream channel in the watershed and weighting 

the fluxes by streamflow duration, evaporation, and transpiration for the 2-year period, per equation 11 (table 12 and fig. 

29). Recharge estimates were not derived for channels in the 

Figure 30. Examples of sensitivity analysis results, Greenbush Draw, 2001–2002.
Summary and Conclusion 293

Babocomari River drainage basin (group 1) because the river 

is perennial over much of its length and, therefore, use of the 

infiltration parameters derived for the ephemeral channels is 

not appropriate.

The infiltration flux used in equation 11 was the lowest flux calculated for each channel by sediment-temperature 

analysis. The calculated infiltration fluxes represent average 

values of the initial transient infiltration fluxes during each 

ephemeral-flow event. Consequently, we assume that the lowest calculated infiltration flux best represents the steady-state 

infiltration flux when determining ephemeral-stream channel recharge. This assumption was validated by comparing 

ephemeral-stream channel recharge rates determined by use of 

equation 11 with rates determined by using other independent 

methods (channel-reach water balance, chloride mass balance, 

ground-water mounding model, and microgravity measurements) for a 6.8-km reach of Walnut Gulch (Goodrich and 

others, 2004).

Groups 3, 5, 6, and 7 contain ephemeral-stream channels for which infiltration fluxes were determined. We assume 

that these infiltration fluxes are the same in other ephemeral 

channels within each group. The infiltration flux determined 

for Woodcutters Wash was also used for channels in groups 

2 and 4, which did not contain instrumented borehole sites. 

Infiltration fluxes for periods of streamflow were not calculated for Greenbush Draw; therefore, the average percolation 

flux for periods after cessation of streamflow was used in the 

Greenbush Draw calculation. Channel segments in Woodcutters Wash and Walnut Gulch underlain at shallow depths by 

the low-permeability sediments of the lower basin fill were 

not included in the recharge calculations; it was assumed that 

similar conditions exist in Escapule Wash, because of its location relative to Woodcutters Wash, and Government Draw and 

High Knolls Canyon Wash, because of their locations relative 

to Walnut Gulch (fig. 29).

The streamflow durations measured in Woodcutters Wash 

during 2001–2002 were greater than those measured in Miller 

Canyon Wash (table 8 and fig. 7); the longer durations are 

assumed to be related to the corresponding higher percentage of urban land cover in the drainage basin. Therefore, the 

streamflow-duration and wetted-channel-width regressions 

determined for Woodcutters Wash were also used for Escapule 

and Carr Canyon Washes, whose drainage basins have similar 

amounts of urban land cover as that in Woodcutters Wash 

and, therefore, likely have similar runoff characteristics. The 

streamflow-duration and wetted-channel-width regressions 

determined for Miller Canyon Wash were used for the remaining channels in groups 2, 3, and 4.

The estimated annual recharge derived from ephemeralstream channel infiltration during 2001–2002 is 2.95 hm3

/

yr. This rate is slightly lower than average recharge rates of 

3.4 to 9.7 hm3 determined by Goodrich and others (2004) for 

1999–2000. The rate calculated during this study is lower 

probably because fewer streamflow events occurred during the 

2001–2002 monitoring period than during 1999–2000. At the 

Tombstone and Huachuca Mountains stations, precipitation 

during 2001–2002 averaged 36.4 cm/yr, whereas precipitation 

during 1999–2000 averaged 47.4 cm/yr.

This calculated ephemeral-stream channel recharge rate 

is about 12 to 19 percent of previous total recharge estimates 

for the Sierra Vista subwatershed of 15 to 23 hm3/yr (Freethey, 

1982; Corell and others, 1996; Goode and Maddock, 2000), 

indicating that ephemeral-stream channel recharge is a significant component of total recharge. These previous investigators have assumed that recharge occurred only within about 

1.5 km of the mountains; however, the borehole data clearly 

indicated that when streamflow is available, a significant 

portion of recharge is distributed along the entire lengths of 

ephemeral-stream channels (fig. 29). During this study, most 

of the streamflow, and therefore most of the recharge, occurred 

during the summer; however, stable-isotope data from most of 

the ephemeral-stream channel boreholes indicate infiltration 

from past summer and winter streamflow events.

Sensitivity Analysis

A sensitivity analysis was done to quantify bounds on 

the calculated ephemeral-stream channel recharge rates by 

independently varying the recharge calculation parameters 

in equation 11 within reasonable limits and recalculating 

recharge over the length of each channel (table 13). Channel 

evaporation and near-channel transpiration were increased and 

decreased by 100 percent. Streamflow duration was increased 

and decreased by 50 percent. The wetted channel width was 

increased to 100 percent, and decreased to 10 percent, of 

the total channel width. Calculated infiltration fluxes were 

increased by 100 percent and decreased by 50 percent.

Recharge rates were most sensitive to the wetted channel 

width (fig. 30 and table 13) — average annual recharge for 

the subwatershed increased by 937 percent with the assumption that 100 percent of the channel widths are wetted during streamflow events. Although there is a high degree of 

uncertainty associated with the wetted channel width value, 

the assumption that the total channel width is wetted during 

streamflow is most likely not valid. Recharge was less sensitive to other parameters (fig. 30 and table 13). The highest and 

lowest annual recharge rates determined through the sensitivity analysis (excluding the rate determined for 100 percent 

wetted channel width) produce bounds of +4.84 hm3

/yr and 

–1.79 hm3/yr on annual ephemeral-stream channel recharge 

for 2001–2002.

Summary and Conclusions

As part of a project to better understand the hydrologic 

system in the Sierra Vista subwatershed, infiltration and 

recharge fluxes through the subwatershed’s ephemeral channels and basin floor were investigated. Data used in this study 

include information resulting from the drilling and coring 

of 16 boreholes: 12 within ephemeral channels and 4 on the 
294 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona

basin floor. The collected data includes physical, hydraulic, 

and thermal properties of sediment; chloride concentrations of 

sediment; pore-water stable-isotope values and tritium activity; neutron soil-moisture and EMI logs; continuous sedimenttemperature profiles; and continuous water levels.

Infiltration fluxes through the basin floor were 0.2 to 6 cm/

yr. At the basin-floor sites in the Walnut Gulch drainage basin, 

long-term infiltration fluxes were very low (less than 1 cm/yr). 

Chloride, tritium, and stable-isotope data indicate long periods 

of no net deep downward percolation flux beneath the basin 

floor. The sediment-chloride profiles coupled with previous 

studies in the arid Southwestern United States indicate that 

water infiltrated through the basin floor does not move downward past the root zone for long periods of time. Infiltration 

rates could also be negligible in other areas of the basin floor 

that have soil and vegetation similar to those at WG4 and WG5.

Infiltration fluxes in the Carr Canyon drainage basin (2 to 

6 cm/yr) were higher than at other basin-floor sites. Chloride, 

tritium, and stable-isotope data indicate active infiltration to 

8 m, and a decrease in infiltration below 8 m. The change in 

the infiltration rate below 8 m is controlled by an increase in 

the silt and clay content of the sediment. At this site, the depth 

that infiltrating water moves through the unsaturated zone and 

whether the infiltrating water will ultimately become recharge 

are strongly dependant on the silt and clay content of limiting 

soil horizons in the unsaturated zone. Relatively high infiltration rates could occur in other areas of the basin-floor that 

have soil and vegetation similar to those at BF1, but detailed 

subsurface soil data are necessary to determine if infiltrated 

water will become recharge.

Infiltration through ephemeral-stream channels in the 

Sierra Vista subwatershed is rapid, occurs to depths of at least 

20 m, and occurs from the edge of the mountain front to as far 

as 25.6 km downstream. During streamflow events, infiltration 

fluxes ranged from 0.4 to 2.8 m/hr. After streamflow ended, 

percolation fluxes ranged from 0.1 to 2.8 m/hr. In areas where 

low-permeability layers are absent in the shallow subsurface, 

infiltrated water moves past depths where it is available for 

evapotranspiration, resulting in a net downward flux. This 

deep downward water flux is assumed to ultimately recharge 

the regional aquifer.

Recharge from ephemeral-stream channel infiltration is 

highly dependant on the thickness and hydraulic properties of 

the stream alluvium, the permeability of the sediments underlying the stream alluvium, the streambed geomorphology, the 

runoff characteristics of the contributing drainage basin, and the 

availability of streamflow. Ephemeral-stream channel recharge 

for the entire Sierra Vista subwatershed was estimated by 

upscaling the calculated infiltration fluxes to the area covered 

by each ephemeral-stream channel and weighting the fluxes 

by streamflow duration, evaporation, and transpiration. The 

resulting average annual recharge during 2001–2002 is 2.95 

hm3

/yr. Analysis indicates that the calculated recharge rates are 

most sensitive to wetted channel width and are less sensitive to 

the other parameters of evaporation, transpiration, streamflow 

duration, and infiltration flux. The upper and lower bounds for 

the annual recharge estimate determined from the sensitivity 

analysis are +4.84 hm3/yr and –1.79 hm3/yr, respectively.

 The calculated annual ephemeral-stream channel 

recharge rate indicates that ephemeral-stream channel infiltration is a significant contributor to total recharge in the subwatershed. When streamflow is available, recharge is significant 

along the entire length of the ephemeral-stream channels. In 

addition, ephemeral-stream channel recharge occurs during 

both summer and winter streamflow events.

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Sharma, M.L., and Hughes, M.W., 1985, Groundwater 

recharge estimation using chloride, deuterium and oxygen-18 profiles in the deep coastal sands of western Australia: Journal of Hydrology, v. 81, p. 93−109.

Taniguchi, M., and Sharma, M.L., 1990, Solute and heat 

transport experiments for estimating recharge rate: Journal 

of Hydrology, v. 119, pp. 57–96.

Thermo Electron Corporation, 2000, Orion chloride electrode 

instruction manual: Waltham, Mass., Thermo Electron 

Corporation, 39 p.

U.S. Census Bureau, 2000, Census 2000 summary file 

1, http://factfinder.census.gov/servlet/GCTTable?ds_

name=DEC_2000_SF1_U&geo_id=04000US04&_box_

head_nbr=GCT-PH1&format=ST-7, last accessed February 

21, 2003.

U.S. Environmental Protection Agency, 2003, Upper San 

Pedro Watershed geodata, http://www.epa.gov/esd/land-sci/

html2/HTML/PAGES/sanpedro_uspws.htm, last accessed 

June 1, 2003.

van Genuchten, M.T., 1980, A closed-form equation for predicting the hydraulic conductivity of unsaturated soil: Soil 

Science Society of America Journal, v. 44, p. 892−898.

van Genuchten, M.T., Leij, F.J., and Yates, S.R., 1991, The 

RETC code for quantifying the hydraulic functions of 

unsaturated soils: U.S. Salinity Laboratory, 85 p.

Walvoord, M.A., Phillips, F.M., Tyler, S.W., and Hartsough, 

P.C., 2002, Deep arid system hydrodynamics 2. Application to paleohydrologic reconstruction using vadose zone 

profiles from the northern Mojave Desert: Water Resources 

Research, v. 38, no. 12, p.

Webb, R.H., and Betancourt, J.L., 1992, Climatic variability 

and flood frequency of the Santa Cruz River, Pima County, 

Arizona: U.S. Geological Survey Water-Supply Paper 

2379, 40 p.

Western Regional Climate Center, 2003, Arizona Climate 

summaries, http://www.wrcc.dri.edu/summary/climsmaz.

html, last accessed June 1, 2003.
 

Tables 3–13 
298 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona

Table 3. Sediment-chloride concentrations, Sierra Vista ground-water recharge study area, Arizona.

[cm, centimeters; mg/kg, milligrams chloride per kilograms sediment; m, meters; —, below the 1.8 mg/kg detection limit; blank cell, no data]

Depth 

to top of 

15.2 cm 

interval,

in m

Chloride, in mg/kg

Basin-floor boreholes Ephemeral-channel boreholes

BF1 WC4c WG4 BC1 GD1 GD2 MC1 MC2 WC1 WC2 WC3 WC4a WG1 WG2 WG3

0.3 3.1 3.0 

0.6 — 2.8 — — 

0.9 3.3 6.1 — — — 1.9 9.9 

1.2 2.4 5.2 42.2 — — — — — 7.9 3.5 —

1.5 3.3 17.1 130.0 — — — — — — 3.3 8.5 3.6 — —

1.8 — 222.0 — — — — — — 6.5 27.3 4.6 — 3.8

2.1 2.0 11.1 226.0 — — — 2.1 — — — 9.1 7.5 — 

2.4 — 8.1 168.0 1.8 — — — — — — 8.9 5.1 

2.7 — 8.2 73.6 2.4 — — — — 5.0 2.2 9.3 7.3 — 

3.0 1.9 3.8 54.6 — — — — — — — 36.9 3.9 — — 

3.4 2.5 2.4 34.2 — — — — — — 3.6 32.6 — — 

3.7 2.1 2.5 90.3 — — — — — — — 73.1 — 2.6 

4.0 — 2.4 77.5 — — — — 3.7 — — 7.8 — — 

4.3 — 3.3 66.1 1.9 — — — — — — 3.0 — — 

4.6 — 2.8 54.8 2.7 — — — — — — 2.7 — — 

4.9 1.8 3.2 50.3 2.8 — — — — — — 24.2 — — 

5.2 2.3 61.7 3.4 — — — — — — — 2.0 — 

5.5 3.9 2.4 33.2 3.0 — — — — — — 1.9 — 

5.8 4.8 3.0 15.0 3.2 — 2.6 — — — — — — — 

6.1 10.1 6.0 20.0 2.9 — — — — — — — — — 

6.4 16.4 4.4 9.1 2.5 — — 2.6 — — — — — — 

6.7 15.8 2.5 7.3 2.0 — — — — — — — — — 

7.0 21.2 4.8 6.7 — — — — — — — — — 

7.3 22.1 4.4 7.7 — — — — — — — — — 

7.7 27.7 — 20.1 — — — — — — — — — — 

7.9 22.8 — 21.1 — — — — — — — — — — 

8.2 29.3 — 22.6 — — — — — — — 3.3 — — 

8.5 24.2 2.7 23.4 — — — — — — — — 

8.8 25.2 3.2 34.3 — — — — — — — — — — 

9.1 20.2 — 40.7 — — — — — — — — 

9.4 15.0 — 32.5 — — — — — — — — — 

9.8 21.7 — 16.1 — — — — — — — — 

10.1 30.4 — 18.8 — — — — — — — 

10.4 21.2 — 22.7 — — — — — — — — 

10.7 19.3 — 3.2 3.2 — — — — 2.9 2.0 2.1 

11.0 23.8 — 4.3 — — — — 1.8 — 2.9 — — 

11.3 28.1 — 5.8 2.8 — — — 1.9 — 2.2 2.3 — 

11.6 32.1 — 5.6 2.5 — — — — — 2.7 2.1 — 

11.9 26.4 — 4.3 5.2 — — — 3.9 — 4.1 — — 

12.2 22.6 — 4.3 8.4 — — — 2.3 — — — 

12.5 23.5 — 4.1 5.1 — — — 1.9 — — — — 

12.8 20.4 3.7 5.9 — — — 4.2 — — 

13.1 17.1 3.6 3.5 — — 3.4 — — 

13.4 11.8 3.2 — — 3.2 — — 

13.7 10.7 5.1 — — — — — 

14.0 14.3 4.1 — — — — — 

14.3 15.5 3.2 — — — 1.9 — — 

14.6 9.9 2.6 — — — — — — 

14.9 7.1 2.3 — — — — — — 

15.2 7.1 5.2 — — — 1.9 — — 

15.5 6.0 3.6 — — — — — — 

15.8 5.5 2.7 — — — — — — 

16.2 3.6 — — — — — 

16.5 2.4 — — — — — 

16.8 2.5 — — — — — 

17.1 — — — — — 

17.4 4.9 — — — — — 

17.7 6.6 — — — — — 
Tables 3–13 299

Table 3. Sediment-chloride concentrations, Sierra Vista ground-water recharge study area, Arizona.—Continued

[cm, centimeters; mg/kg, milligrams chloride per kilograms sediment; m, meters; —, below the 1.8 mg/kg detection limit; blank cell, no data]

Depth 

to top of 

15.2 cm 

interval,

in m

Chloride, in mg/kg

Basin-floor boreholes Ephemeral-channel boreholes

BF1 WC4c WG4 BC1 GD1 GD2 MC1 MC2 WC1 WC2 WC3 WC4a WG1 WG2 WG3

18.0 4.5 — — — — — 

18.3 8.1 — — — — — 

18.6 10.5 — — — — — 

18.9 11.1 — — — — — 

19.2 11.9 — — — — 

19.5 9.6 — — — — 

19.8 8.2 — — — — 

20.1 2.4 — — — — 

20.4 — — — — — 

20.7 — — — — — 

21.0 2.5 — — — — 

21.3 2.0 — — — — 

21.6 3.1 — — — — 

21.9 6.8 — — — — 

22.3 9.4 — — — 

22.6 4.8 — — 

22.9 5.0 — 

23.2 7.2 — 

23.5 6.2 — 

23.8 3.5 — 

24.1 4.5 — 

24.4 3.1 — 

24.7 5.1 — 

25.0 3.5 — 

25.3 4.5 

25.6 3.7 

25.9 3.3 

16 METERS)

BELOW

(NO DATA
300 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona

Table 4. Stable-isotope and tritium data for pore water, Sierra Vista ground-water recharge study area, Arizona.

[Abbreviations: cm, centimeters; m, meters; δD, delta dueterium; δ18O, delta oxygen-18; ‰, per mil; TU, tritium units; —, no data]

Depth to top 

of 15.2-cm 

interval,

in m

δD,

in ‰

δ18O,

in ‰

3

H,

in TU

3

H

error,

in TU

Depth to top 

of 15.2-cm 

interval,

in m

δD,

in ‰

δ18O,

in ‰

3

H,

in TU

3

H

error,

in TU

Ephemeral-channel boreholes Ephemeral-channel boreholes—Continued

BC1 WC1—Continued

2.0 -63.5 -9.50 3.8 0.2 5.0 -61.7 -8.80 4.4 0.2

3.5 -64.0 -9.22 3.3 .2 6.6 -57.8 -8.40 4.6 .2

5.0 -60.8 -8.80 3.2 .6 8.1 -57.8 -8.30 3.9 .2

6.6 -61.8 -8.96 3.8 .6 WC2

8.1 -60.8 -9.23 4.8 .3 2.0 -59.2 -6.29 3.9 .7

9.6 -60.0 -8.52 4.4 .3 3.5 -60.0 -7.70 5.4 .6

11.1 -63.4 -9.25 4.1 .3 5.0 -59.5 -7.70 5.0 .6

12.6 -60.0 -8.81 4.5 .7 6.6 -46.8 -6.70 4.6 .6

14.2 -63.8 -9.24 3.4 .3 8.1 -50.5 -6.90 5.7 .6

15.7 -63.6 -9.00 3.9 .3 9.6 -50.0 -6.80 4.3 .5

17.2 -59.5 -8.51 6.7 .9 11.1 -63.8 -8.43 3.9 .3

20.3 -57.0 -8.30 3.6 .6 WC3

23.3 -60.0 -8.65 4.5 .9 .2 -36.1 -1.36 6.3 .5

GD1 0.8 -48.8 -5.83 4.5 .4

0.5 -60.0 -.41 4.0 5.0 1.4 -48.6 -6.10 5.0 .4

.8 -65.6 -9.64 3.7 .4 2.9 -55.9 -7.05 3.8 .3

5.3 -64.7 -9.67 4.0 .3 8.1 -52.2 -6.90 5.5 .3

6.9 -65.1 -9.41 3.3 .3 10.5 -49.4 -6.75 5.4 .5

8.4 -64.4 -9.18 4.6 .6 13.6 -59.9 -7.84 2.6 .3

9.9 -62.0 -9.09 4.3 .3 16.6 -62.5 -8.26 1.0 .6

19.1 -65.6 -9.68 4.1 .3 19.7 -62.1 -8.04 0.4 .3

GD2 WC4a

2.3 -55.5 -8.32 3.5 .3 .8 -63.0 -7.70 3.7 .7

3.8 -58.4 -8.57 3.7 .2 2.1 -59.0 -7.38 3.4 1.1

5.5 -59.3 -8.24 4.1 .3 3.6 -64.6 -8.82 5.0 .4

6.9 -62.0 -8.89 4.3 .3 5.1 -60.0 -8.20 10.1 .7

8.4 -64.5 -9.02 3.9 .3 6.6 -66.0 -8.90 1.6 .5

9.9 -67.9 -9.34 3.8 .3 8.2 -63.0 -8.30 1.0 .4

13.0 -63.5 -8.83 4.0 .4 9.6 -73.0 -9.90 1.6 .5

16.0 -63.7 -9.02 4.3 .3 11.1 -68.8 -9.55 1.0 .4

19.1 -67.0 -9.03 3.8 .4 WG1

MC1 2.9 -50.9 -6.94 2.9 1.2

.2 -39.4 -1.25 7.8 .6 3.5 -67.7 -9.60 3.6 .7

1.1 -59.8 -8.59 4.2 .3 7.5 -64.7 -9.14 3.9 .4

2.3 -59.5 -8.44 4.7 .3 8.7 -62.0 -9.06 4.5 .4

3.8 -65.8 -9.07 4.2 .3 10.2 -63.3 -9.24 4.4 .4

5.3 -69.3 -9.23 4.1 .3 13.3 -52.3 -7.60 3.9 .8

6.9 -63.1 -8.96 4.0 .3 16.3 -55.5 -8.10 3.7 .4

8.4 -64.9 -8.94 4.4 .3 19.4 -54.6 -8.14 4.2 .3

9.9 -64.9 -9.10 4.0 .3 22.4 -59.6 -8.66 5.7 .5

13.0 -72.5 -10.09 3.7 .2 WG2

16.0 -66.0 -9.00 3.6 .3 .5 -29.9 -2.80 5.6 1.1

19.1 -64.9 -8.81 4.1 .4 .8 -28.5 -3.72 6.7 .6

22.1 -84.6 -11.77 3.3 .3 2.3 -55.3 -8.38 4.7 .3

MC2 WG3

.2 -65.1 -5.28 — — .2 -32.0 3.27 8.5 2.4

1.7 -64.7 -9.14 1.9 .5 .8 -29.1 3.32 6.5 1.5

6.9 -71.3 -9.93 3.8 .3 Basin-floor boreholes

9.9 -69.1 -9.71 5.9 .4 BF1

WC1 .5 -45.8 -.60 6.4 .9

.2 -63.5 -7.70 7.2 .8 3.8 -62.2 -7.82 6.4 .9

2.0 -78.7 -11.60 5.9 .5 5.3 -59.5 -7.34 2.5 .6

3.5 -57.1 -8.02 4.3 .3 6.9 -57.2 -7.03 .8 .6
Tables 3–13 301

Table 4. Stable-isotope and tritium data for pore water, Sierra 

Vista ground-water recharge study area, Arizona.—Continued

[Abbreviations: cm, centimeters; m, meters; δD, delta dueterium; δ18O, delta 

oxygen-18;‰, per mil; TU, tritium units; —, no data]

Depth to top 

of 15.2-cm 

interval,

in m

δD,

in ‰

δ18O,

in ‰

3

H,

in TU

3

H

error,

in TU

Basin-floor boreholes—Continued

BF1—Continued

8.4 -59.8 -7.11 0.8 0.5

10.2 -58.0 -7.18 .6 .4

13.0 -56.5 -7.04 .3 .2

WC4c

.2 -67.0 -9.20 4.1 .7

.8 -75.5 -10.37 2.6 .8

1.7 -68.0 -9.40 4.6 1.0

2.3 -68.4 -8.99 7.0 2.0

3.7 -77.0 -9.60 4.9 1.4

5.2 -64.4 -8.07 3.7 .4

6.7 -59.8 -7.74 5.6 .3

8.2 -63.0 -8.56 11.4 .4

9.8 -63.0 -8.68 10.4 .4

11.3 -71.0 -9.40 .3 .3

WG4

.5 -44.1 -0.32 6.3 .7

1.1 -42.5 -0.94 9.1 .9

2.0 -52.2 -2.82 10.2 1.2

4.1 -53.8 -3.91 8.2 .4

7.5 -43.1 -3.37 4.0 2.4

13.3 -55.9 -5.23 .4 .6

WG5

.2 -60.0 -6.12 .4 .4
302 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona

Table 5. Thermal properties of sediment, Sierra Vista ground-water recharge study area, Arizona.

[Abbreviations: cm, centimeters; m, meters; MJ, megajoules; J/m3· ̊C, joules per cubic meter degree Celsius; J/s·m· ̊C, joules per second meter degree Celsius; 

—, no data] 

Depth to top 

of 15.2-cm 

interval,

in m

Field water 

content,

in cm3

/cm3

Volumetric 

specific heat, 

field water 

content,

in MJ/m3  ̊C

Thermal conductivity, field water 

content,

in J/s m  ̊C

Depth to top 

of 15.2-cm 

interval,

in m

Field water 

content,

in cm3

/cm3

Volumetric 

specific heat, 

field water 

content,

in MJ/m3  ̊C

Thermal conductivity, field water 

content,

in J/s m  ̊C

Ephemeral-channel boreholes Ephemeral-channel boreholes—Continued

BC1 WC4a—Continued

2.3 0.20 2.06 2.25 8.4 — 3.33 2.32

3.8 — 2.24 2.03 9.9 — 1.94 .90

5.3 .09 1.94 2.87 11.4 .20 1.43 1.91

6.9 — 1.68 2.32 WG1

8.4 — 3.93 2.30 2.7 0.25 1.63 0.86

9.9 — 2.78 4.11 10.1 — 1.41 .93

11.4 — 3.46 2.11 19.2 — 2.40 1.55

14.5 .27 2.15 2.59 WG2

16.0 .29 1.07 1.76 2.1 — 1.23 .80

17.5 — 2.54 1.50 WG3

20.6 .08 2.32 2.61 .6 — 1.15 .27

23.6 — 1.34 1.74 Basin-floor boreholes

GD1 BF1

6.7 .11 1.74 1.56 6.7 .11 2.47 1.73

18.9 — 2.42 1.63 12.8 — 2.42 1.45

GD2 WC4c

2.1 .44 2.54 1.66 .5 — 1.22 .56

9.8 — 2.30 1.63 1.1 .09 1.25 .53

18.9 — 2.58 .77 2.0 — 1.48 .69

MC1 2.6 .07 9.70 .42

0 — 1.34 1.09 4.0 .15 1.55 .67

8.2 .28 3.01 1.99 5.5 — 2.67 1.49

18.9 — 2.76 1.54 7.0 — 3.20 2.31

MC2 8.5 — 2.42 2.05

6.7 .30 1.90 2.08 10.1 — 2.00 1.89

WC1 11.6 .24 1.44 1.12

.5 .13 1.37 .95 WG4

2.3 .07 1.11 .60 0 — 1.49 .31

3.8 — 5.08 1.32 13.1 .10 1.33 .89

5.3 — 4.41 1.22 WG5

6.9 .37 3.41 2.00 0 .10 1.24 .34

8.4 — 2.60 1.57

WC2

2.3 .15 1.34 1.20

3.8 .33 1.75 1.00

5.3 — 2.71 1.93

6.9 .47 2.79 1.33

8.4 .40 1.27 1.50

9.9 .18 2.22 1.50

11.4 — 3.02 1.63

WC3

0 — 2.72 1.35

10.4 — 1.23 1.03

WC4a

1.1 — 1.71 1.38

2.4 .25 1.36 .79

3.9 — 1.63 1.64

5.4 — 2.98 1.66

6.9 — 3.25 2.94
Tables 3–13 303

Table 6. Physical and hydraulic properties of sediments, Sierra Vista ground-water recharge study area, Arizona.

[Abbreviations: cm, centimeters; m, meters; %, percent; g/cm3, grams per cubic centimeter; m3/m3, cubic meter per cubic meter; cm/s, centimeters per second; e, 

base-10 exponent (1.2e–1 = 1.2 × 10–1, for example); —, no data]

Depth 

to top of 

7.6-cm 

interval,

in m

Gravel,

in %

Sand,

in %

Silt,

in %

Clay,

in %

Bulk 

density,

in g/cm3

Particle 

density,

in g/cm3

Porosity,

in

m3/m3

Field 

water 

content,

in

m3

/m3

Saturated 

hydraulic 

conductivity,

in cm/s

van Genuchten parameters

α,

in cm–1

n

(dimensionless)

m

 (= 1-1/n)

Residual 

water 

content,

in m3/m3

Saturated

water

content,

in m3/m3

R2

Ephemeral-channel boreholes

BC1

2.1 63.7 22.6 8.9 4.8 1.85 2.81 0.34 0.20 9.6e-3 0.145 1.86 0.46 0.19 0.34 0.99

5.2 79.7 16.2 2.6 1.5 1.82 2.65 .31 .09 1.2e-1 .122 2.01 .50 .11 .31 1.00

8.2 — — — — — — — — 4.1e-7 — — — — — —

14.3 70.8 19.9 7.4 1.9 1.82 3.00 .39 .27 1.7e-6 .138 1.45 .31 .07 .39 1.00

15.8 35.3 37.8 23.5 3.4 1.63 2.88 .43 .29 3.3e-5 .009 1.62 .38 .16 .42 1.00

20.4 77.7 19.5 1.9 .9 2.02 2.70 .25 .08 8.9e-3 .145 1.96 .49 .08 .25 1.00

GD1

4.0 47.6 48.3 2.2 1.9 1.82 2.49 .27 .15 1.4e-2 .145 2.19 .54 .11 .26 .95

7.0 46.1 47.6 2.8 3.5 1.89 — — .11 4.6e-3 .145 1.29 .23 .06 .36 1.00

13.1 19.4 38.9 27.3 14.4 — — — — 6.8e-8 — — — — — —

GD2

2.4 2.7 66.1 21.9 9.3 1.47 3.11 .53 .44 5.9e-3 .067 1.11 .10 .20 .50 .99

5.3 50.7 33.0 4.2 12.1 1.44 2.60 .45 .14 5.3e-2 .145 2.54 .61 .18 .44 .97

13.1 70.9 12.5 4.2 12.4 1.57 2.64 .41 .27 1.6e-2 .145 2.40 .58 .25 .40 .97

MC1

0.9 4.2 60.1 22.9 12.8 1.84 2.87 .36 — 9.3e-3 .145 1.20 .17 .11 .36 .99

4.0 18.9 44.6 19.1 17.4 1.84 2.91 .37 .31 3.5e-6 .005 1.33 .25 .12 .35 .95

8.5 4.2 57.6 25.3 12.9 1.78 2.92 .39 .28 1.3e-3 .005 1.21 .17 .12 .39 .95

19.2 4.5 31.5 32.1 31.9 — — — — 1.8e-6 — — — — — —

MC2

1.8 36.4 42.7 12.2 8.7 1.37 2.35 .42 .18 3.3e-3 .066 1.22 .19 .08 .41 .99

7.0 3.7 63.7 21.0 11.6 1.87 2.92 .36 .30 3.2e-6 .013 1.37 .27 .16 .36 .95

10.1 73.0 19.0 4.9 3.1 1.60 2.76 .42 .22 1.7e-2 .136 1.33 .25 .14 .42 .97

WC1

0.3 25.6 72.5 <.7 1.9 1.49 2.74 .46 .13 7.2e-2 .145 2.44 .59 .05 .45 .98

2.1 53.0 43.5 1.0 2.5 1.84 2.90 .37 .07 3.6e-2 .145 2.32 .57 .07 .36 .97

3.7 45.1 36.1 13.0 5.8 — — — — 3.2e-3 .006 1.23 .19 .28 .54 1.00

6.7 61.1 20.8 12.1 6.0 1.69 — — .37 2.1e-6 .008 1.59 .37 .22 .52 .98

WC2

2.1 34.7 61.8 .2 3.3 1.71 2.64 .35 .15 6.3e-3 .145 2.56 .61 .07 .35 .97

3.7 22.0 39.5 22.7 15.8 1.64 3.18 .48 .33 2.2e-2 .106 1.25 .20 .22 .48 .96

6.7 59.0 14.5 12.7 13.8 1.43 2.95 .52 .47 5.0e-4 .028 1.15 .13 .20 .52 .95

8.2 27.4 30.1 30.7 11.8 1.52 2.92 .48 .40 9.8e-6 .014 1.41 .29 .21 .47 .95

9.8 15.9 76.1 3.7 4.3 1.65 2.48 .34 .18 3.0e-3 .068 1.51 .34 .10 .32 .97

WC3

0.9 38.7 45.3 4.8 11.2 1.64 2.48 .34 .11 8.5e-3 .1451 2.03 .51 .13 .34 1.00

1.5 — — — — — — — — 1.7e-4 — — — — — —

8.2 92.4 5.0 1.7 .9 1.75 2.60 .33 .21 2.3e-3 .043 1.36 .27 .08 .32 .97

13.7 20.7 62.4 9.8 7.1 1.64 2.71 .39 .11 9.9e-3 .162 1.53 .35 .10 .39 1.00

19.8 11.3 58.9 22.6 7.2 1.72 2.88 .40 .19 5.8e-3 .068 1.37 .27 .13 .39 .98

WC4a

2.1 78.7 15.9 1.9 3.5 1.81 3.16 .43 .25 6.4e-2 .1451 2.03 .51 .15 .42 .99

11.3 48.5 32.7 11.7 7.1 1.80 2.69 .33 .20 4.2e-4 .049 1.48 .32 .22 .33 1.00

WG1

3.0 68.5 27.9 1.4 2.2 1.68 2.97 .43 .25 2.0e-2 .146 1.39 .28 .05 .43 1.00

3.7 72.8 24.0 1.6 1.6 1.84 2.81 .35 .13 4.6e-2 .145 1.51 .34 .04 .34 .98

13.4 43.9 52.9 .7 2.5 1.37 2.58 .47 .10 4.0e-2 .145 1.98 .50 .07 .47 .99

22.6 66.0 27.8 5.7 .5 1.59 2.66 .40 .19 2.0e-2 .145 1.29 .23 .05 .39 .97
304 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona

Table 6. Physical and hydraulic properties of sediments, Sierra Vista ground-water recharge study area, Arizona.—Continued

[Abbreviations: cm, centimeters; m, meters; %, percent; g/cm3, grams per cubic centimeter; m3/m3, cubic meter per cubic meter; cm/s, centimeters per second; e, 

base-10 exponent (1.2e–1 = 1.2 × 10–1, for example); —, no data]

Depth 

to top of 

7.6-cm 

interval,

in m

Gravel,

in %

Sand,

in %

Silt,

in %

Clay,

in %

Bulk 

density,

in g/cm3

Particle 

density,

in g/cm3

Porosity,

in

m3/m3

Field 

water 

content,

in

m3

/m3

Saturated 

hydraulic 

conductivity,

in cm/s

van Genuchten parameters

α,

in cm–1

n

(dimensionless)

m

 (= 1-1/n)

Residual 

water 

content,

in m3/m3

Saturated

water

content,

in m3/m3

R2

Basin-floor boreholes

BF1

0.3 41.7 43.3 7.0 8.0 1.52 2.51 0.39 <.02 2.1e-2 0.076 2.11 0.53 0.09 0.40 1.00

4.0 68.0 25.8 2.5 3.7 — — — — — — — — — — —

5.5 76.5 16.5 1.7 5.3 — — — — — — — — — — —

7.0 64.1 28.5 3.1 4.3 1.77 2.72 .35 .11 1.4e-2 .137 1.72 .42 .14 .35 .99

8.5 34.8 34.5 21.0 9.7 1.60 2.92 .45 .26 5.1e-3 .073 1.28 .22 .18 .46 .95

10.1 77.0 18.5 2.4 2.1 — — — — — — — — — — —

13.1 60.7 24.6 7.7 7.0 — — — — — — — — — — —

WC4c

1.1 41.1 54.4 1.0 3.5 1.70 2.54 .33 .09 1.5e-2 .166 1.58 .37 .03 .33 .98

2.4 51.6 43.9 1.7 2.8 1.69 2.57 .34 .07 5.1e-3 .145 1.81 .45 .05 .34 .99

3.8 23.9 68.5 2.1 5.5 1.66 2.76 .40 .15 1.5e-3 .071 1.89 .47 .06 .40 1.00

9.9 68.3 19.1 9.3 3.3 — — — — 1.9e-5 .025 3.89 .74 .27 .40 .99

11.3 56.6 31.0 9.6 2.8 1.83 2.87 .36 .24 7.2e-6 .021 2.09 .52 .27 .36 .97

WG4

4.3 47.6 26.0 17.2 9.2 1.24 2.38 .48 .19 1.3e-2 .122 1.21 .17 .15 .48 1.00

13.4 36.3 37.2 18.6 7.9 1.30 2.61 .50 .10 1.7e-2 .077 1.63 .39 .17 .47 .96

WG5

0.3 34.0 47.2 15.6 3.2 1.41 2.71 .48 .10 1.5e-2 .126 1.40 .29 .10 .48 .98
Tables 3–13 305

Table 7. Isotope and chloride data for composite precipitation, Sierra Vista ground-water recharge study area, Arizona.

[Abbreviations: cm, centimeters; mg/cm2/yr, milligrams per square centimeter per year; ‰, per mil; TU, tritium units; —, no data]

Begin collection

date

End

collection

date

Precipitation

amount,

in cm

Chloride deposition rate,

in mg/cm2/yr

Delta deuterium,

in ‰

Delta

oxygen-18,

in ‰

Tritium,

in TU

Tritium error,

in TU

Upper Babocomari site

07/27/00 10/17/00 25.7 0.021 -34.0 -5.72 — —

10/17/00 04/11/01 19.1 .011 -73.6 -10.97 3.3 0.4

04/11/01 10/11/01 26.4 .013 -38.7 -5.31 4.7 .3

10/11/01 04/25/02 5.3 .004 -90.7 -12.80 3.3 .3

04/25/02 10/17/02 24.1 .010 -54.7 -8.17 4.8 .3

10/17/02 04/23/03 — — -80.1 -11.47 4.2 .3

Greenbush Draw site

07/26/00 10/18/00 27.2 .011 -38.5 -6.05 — —

10/18/00 04/11/01 15.5 .017 -65.6 -10.41 3.2 .3

04/11/01 10/11/01 14.5 .010 -46.5 -6.12 4.6 .3

10/11/01 04/25/02 4.3 .001 -133.4 -17.71 2.6 .3

04/25/02 10/17/02 15.0 .012 -34.2 -5.23 4.8 .3

10/17/02 04/21/03 — — -68.8 -10.37 1.7 .3
306 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona

Table 8. Streamflow durations at streambed-temperature sensors, Agricultural Research Service flumes, and U.S. Geological Survey 

streamflow-gaging stations; and distance of duration-measurement locations from the mountain front, Sierra Vista ground-water 

recharge study area, Arizona.

[Abbreviations: hr, hours; km, kilometers; —, no data; header numbers are streamgaging-station identifiers; values in parentheses are distance from the mountain 

front in kilometers]

Streamflow 

starting

Streamflow duration, in hr Streamflow 

starting

Streamflow duration, in hr

Greenbush Woodcutters Wash 

377815

(1.8 km)

GD2

(5.6 km)

374866

(11.3 km)

GD12

(12.4 km)

377820

(18.5 km)

WC4a2

(0.4 km)

375010

(3.1 km)

WC32

(7.2 km)

377793

(8.0 km)

WC1

(16.4 km)

01/09/01 1.0 0.0 0 — 0 04/05/01 0 0 — 13 0

04/06/01 7.5 0 0 — 0 04/06/01 0 .5 — 0 3.0

07/09/01 0 2.0 0 — 0 06/19/01 0 16 — 12.5 0

07/10/01 0 3.0 0 — 0 06/25/01 0 0 — 2.0 .3

07/13/01 0 .5 12 — 0 07/05/01 0 13 — 0 0

07/17/01 0 0 15 — 0 07/07/01 0 22 — 1.5 .5

07/18/01 0 0 .8 — 2.5 07/09/01 0 5.0 — 1.3 0

07/21/01 0 13 0 — 5.3 07/16/01 0 0 — 0 .8

07/24/01 0 2.3 0 — 0 07/24/01 0 5.0 — 0 0

07/25/01 0 6.0 0 — 0 07/25/01 0 7.5 — 0 0

07/28/01 0 0 1.8 — 16 07/28/01 0 13 — 2.8 .3

08/05/01 0 16 1.0 — 0 08/01/01 0 1.0 — 0 0

08/11/01 0 3.3 0 — 0 08/05/01 0 2.0 — 0 0

08/12/01 0 5.3 0 — 0 08/11/01 0 7.5 — 0 0

08/13/01 0 7.0 .8 — 0 08/13/01 .5 6.5 — 0 14

09/12/01 0 0 0 — 16 08/14/01 0 1.5 — 0 0

07/14/02 0 0 0 0 1.5 08/16/01 0 2.0 — 0 0

07/21/02 17 0 0 0 0 08/17/01 0 8.5 — 0 4.5

08/01/02 0 2.0 .5 0 0 08/29/01 0 5.5 — 0 12

08/02/02 0 0 0 1.0 0 09/12/01 0 6.5 — 0 0

08/03/02 0 .8 0 0 0 07/08/02 0 1.0 2.5 .8 12

08/18/02 0 0 0 0 19 07/16/02 0 .5 1.5 1.0 .5

08/29/02 0 0 0 0 0 07/18/02 0 0 0 0 .8

09/09/02 7.0 0 0 0 0 07/26/02 0 0 0 0 2.0

09/10/02 0 1.3 0 0 0 08/03/02 0 0 2.0 0 0

Total 37.5 62.5 94.4 1 60.3 08/08/02 0 0 0 0 1.8

Streamflow 

starting

Miller Canyon Wash 08/16/02 0 0 0 0 .8

377806

(0.0 km)

MC21

(0.0 km)

377797

(3.9 km)

MC11

(7.1 km)

374919

(10.9 km)

08/19/02 0 0 1.0 1.0 .8

09/08/02 0 0 0 0 15

04/06/01 0 — 6.0 — 0 09/09/02 0 0 0 0 3.3

06/25/01 0 — 2.0 — 0 10/07/02 0 0 1.5 2.5 1.0

07/18/01 0 — 2.3 — 0 Total 0.5 124.5 8.5 38.4 73.4

07/28/01 .5 — 3.5 — 0 Streamflow 

starting

Banning Creek

08/01/01 0 — 1.8 — 0 094707001

(0.0 km)

3778222

(0.0 km)

BC1

08/05/01 15 — 3.0 — 1.5 (3.9 km)

08/16/01 .8 — 0 — 3.5 07/15/01 1,152 — 0.0

08/17/01 0 — 0 — 2.5 07/20/01 0 — 1.5

10/03/01 0 — 0 — 2.5 07/22/01 0 — 11.

07/16/02 20 18 0 0 0 07/25/01 0 — 1.0

07/25/02 0 0 0 0 2.3 08/01/01 0 — 1.5

08/19/02 0 0 1.0 0 0 10/03/01 0 — 2.3

09/03/02 0 0 2.0 0 0 08/03/02 — 909 13.

09/09/02 0 0 1.3 0 4.5 08/04/02 — 0 1.0

09/10/02 0 0 3.5 0 0 08/05/02 — 0 5.8

Total 36.3 18 26.4 0 16.8 Total 1,152 909 37.1

1

 Data not used in analysis of streamflow duration versus distance from the mountain front.

2

 Streamflow-gaging station 09470700 and temperature sensor 377822 are at the same location. 
Tables 3–13 307

Table 8.—Continued.

Stream-

flow 

starting

Streamflow duration, in hr

Walnut Gulch

3

Flume 11

(7.2 km)

Flume 6

(13.2 km)

Flume 1

(25.6 km)

01/06/0100 .7

01/13/01 3800

01/16/01 8200

07/07/01 1.200

07/13/01 .500

08/11/01 1.700

08/13/01 .80 2.6

08/14/0100 2.9

08/17/0100 .4

09/14/0100 3.4

07/08/02 1.200

07/16/020 .50

07/19/02 1.2 2.80

07/26/020 1.3 10

08/01/02 .6 5.00

08/04/02 3.0 6.0 5.0

08/06/02 1.000

09/08/00200 .2

09/09/020 3.50

09/11/02 1.3 1.00

Total 132.5 20.1 25.2

3

 Provisional data provided by the U.S. Depart-

ment of Agriculture, Agricultural Research Service, 

Southwest Watershed Research Center.
308 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona

Table 9. Stream parameters used in the infiltration-flux analytical method, Sierra Vista ground-water recharge study area, Arizona.

[Abbreviations: m, meters; h, hour; g/cm3, grams per cubic centimeter; MJ/m3  ̊C, megajoules per cubic meter degree Celsius; m/hr, meters per hour; 

", ditto; —, not calculated]

Date of 

flow event

Upper measuring point,

in m

Lower measuring point,

in m

Travel time,

in hr

Bulk density,

in g/cm3

Heat capacity, 

dry soil,

in MJ/m3 °C

Calculated 

transient flux,

in m/h

Flux type

BC1 (borehole identifier)

07/20/01 0.0 1.5 1.0 1.84 2.08 1.4 Infiltration

1.5 3.0 0 " " — —

3.0 4.6 .5 " " 2.8 Percolation

4.6 6.1 2.0 " " .7 Percolation

07/22/01 0 1.5 .5 " " 2.8 Infiltration

1.5 3.0 .5 " " 2.8 Infiltration

3.0 4.6 1.5 " " .9 Percolation

4.6 6.1 1.0 " " 1.4 Percolation

07/25/01 0 1.5 1.0 " " 1.4 Infiltration

1.5 3.0 0 " " — —

3.0 4.6 1.0 " " 1.4 Percolation

4.6 6.1 1.5 " " .9 Percolation

08/01/01 0 1.5 1.0 " " 1.4 Infiltration

1.5 3.0 0 " " — —

3.0 4.6 1.0 " " 1.4 Percolation

4.6 6.1 1.0 " " 1.4 Percolation

10/03/01 0 1.5 1.0 " " 1.4 Percolation

1.5 3.0 0 " " — —

3.0 4.6 .5 " " 2.8 Percolation

4.6 6.1 1.5 " " .9 Percolation

08/03/02 0 1.5 1.0 " " 1.4 Percolation

1.5 3.0 0 " " — —

3.0 4.6 1.0 " " 1.4 Percolation

4.6 6.1 1.5 " " .9 Percolation

08/04/02 0 1.5 1.0 " " 1.4 Percolation

1.5 3.0 0 " " — —

3.0 4.6 1.0 " " 1.4 Percolation

4.6 6.1 .5 " " 2.8 Percolation

GD1

08/02/02 0 1.5 1.5 1.86 1.74 .8 Percolation

1.5 3.0 0 " " — —

3.0 6.1 3.5 " " .7 Percolation

6.1 9.1 17.5 " " .1 Percolation

GD2

08/01/02 0 1.5 1.5 1.46 2.54 .9 Percolation

1.5 3.0 1.5 " " .9 Percolation

3.0 6.1 5.0 " " .5 Percolation

09/10/02 0 1.5 2.0 " " .7 Percolation

1.5 3.0 2.5 " " .5 Percolation

3.0 6.1 1.5 " " 1.8 Percolation

6.1 9.1 1.5 " " 1.8 Percolation

9.1 12.2 10 " " .3 Percolation

WC1

07/07/01 0 1.5 .5 1.67 1.24 1.5 Infiltration

1.5 3.0 .5 " " 1.5 Infiltration

07/16/01 0 1.5 .5 " " 1.5 Percolation

1.5 3.0 .5 " " 1.5 Percolation

07/28/01 0 1.5 .5 " " 1.5 Percolation

1.5 3.0 .5 " " 1.5 Percolation

07/16/02 0 1.5 2.0 " " .4 Percolation

1.5 3.0 2.0 " " .4 Percolation

WG1

07/26/02 0 1.5 1.0 1.76 1.63 1.0 Infiltration

1.5 3.0 .5 " " 2.1 Infiltration

3.0 4.6 .5 " " 2.1 Infiltration

4.6 6.1 5.5 " " .2 Percolation

08/04/02 0 1.5 1.0 " " 1.0 Infiltration

1.5 3.0 0 " " — —

3.0 4.6 0 " " — —

4.6 6.1 7.4 " " .1 Percolation

09/08/02 0 1.5 1.0 " " 1.0 Percolation

WG2

07/19/02 0 3.0 1.5 1.761 1.23 1.0 Infiltration

1

 Estimated on the basis of the value for borehole WG1.
Tables 3–13 309

Table 11. Initial and boundary conditions for the VS2DH numerical simulations, Sierra Vista ground-water recharge 

study area, Arizona.

[Abbreviations: m, meters; °C, degrees Celsius; cm3/cm3, cubic centimeter per cubic centimeter; m/hr, meters per hour; —, no data]

Borehole 

identifier

Simulation

date

Initial sediment temperature, in °C 1

 Initial water

content,

in cm3/cm3

Transport boundary condition

0.0 m 1.5 m 3.0 m 4.6 m 6.1 m Inlet temperature,

in °C

2 Flux into domain,

in m/hr

BC1 07/20/01 29.5 23.7 19.6 — — 0.15 24.0 0.5

07/25/01 37.3 24.1 20.9 — — .25 22.0 .4

08/01/01 25.0 24.6 21.9 — — .25 20.0 .4

WC1 07/07/01 26.2 25.0 21.0 — — .07 24.0 1.3

WG1 07/26/02 28.7 25.9 23.4 21.5 — .10 25.0 .5

08/04/02 26.8 25.7 24.2 22.6 — .20 25.0 .4

WG2 07/19/02 28.2 — 18.0 — — .15 21.0 .4

1

 Estimated from soil-water content at time of sampling.

2

 Determined through calibration.

Table 10. Sediment properties used for the VS2DH numerical simulations, Sierra Vista ground-water recharge study area, Arizona.

[Abbreviations: m, meters; cm/s, centimeters per second; cm3/cm3, cubic centimeters per cubic centimeters; W/m °C, watts per meter degree Celsius; J/m3·°C, 

joules per cubic meter degree Celsius; e, base-10 exponentiation (9.6e–3 = 9.6 × 10–3, for example)]

Borehole

identifier

Depth to top 

of domain,

in m

Depth to 

bottom of 

domain,

in m

Saturated hydraulic 

conductivity, in cm/s Porosity,

in cm3

/cm3

Residual 

water,

in cm3/cm3

α,

in cm–1

n

(dimensionless)

Thermal conductivity, in W/m °C Heat capacity, dry soil,

in MJ/m3 Initial Adjusted °C

Saturation water 

content1

Residual

water

content

BC1 0.0 3.0 9.6e-3 1.5e-2 0.34 0.10 0.145 1.9 2.5 2.1 2.08

WC1 0 3.0 5.4e-2 4.0e-2 .42 .03 .145 2.4 2.0 .8 1.24

WG1 0 4.6 3.3e-2 3.5e-2 .39 .05 .145 1.4 2.5 .9 1.63

WG2 0 3.0 (2)3.3e-2 3.5e-2 (2).39 (2).05 (2).145 (2)1.4 2.5 .8 1.23

1

 Estimated from thermal conductivity at field water content.

2

 Estimated on the basis of values for borehole WG1.
310 Infiltration and Recharge in the Upper San Pedro Basin, Southeastern Arizona

Table 12. Estimated annual ephemeral-stream channel recharge, 2001 and 2002, Sierra Vista ground-water recharge study area, Arizona.

[Group numbers refer to figure 5. Abbreviations: hm3/km/2yr, cubic hectometers per kilometer per 2-year period; hr/2yr, hours per 2-year period; m, meters; m/

hr, meters per hour; km, kilometer; hm3/2yr, cubic hectometers per 2-year period; x, distance from mountain front, in kilometers; e, base of the natural logarithm; 

", ditto; <, less than]

Tributary name

Channel 

evaporation,

in hm3/km/2yr

Near-channel

transpiration,

in hm3/km/2yr

Stream-flow 

duration vs. 

distance from 

mountain front,

in hr/2yr

Wetted channel 

width vs. distance 

from mountain 

front,

in m

Infiltration 

flux,

in m/hr

Channel 

length in 

alluvium,

in km

Ephemeral

channel

recharge,

in hm3

/2yr

Group 2

Unnamed Wash 1 3.0·10–4 1.4·10–2 35.5·e–0.07x 0.15·(0.2x+2.0) 1.3 15.4 0.01

Graveyard Gulch " " " " " 14.4 .01

Escapule Wash " " 89.9·e–0.03x 0.15·(0.9x+1.9) " 18.5 1.16

Group 3

Woodcutters Wash " " " " " 18.5 1.16

Garden Canyon Wash " " 35.5·e–0.07x 0.15·(0.2x+2.0) " 21.7 .01

Ramsey Canyon Wash " " " " " 17.4 .01

Carr Canyon Wash " " 89.9·e–0.03x 0.15·(0.9x+1.9) " 16.8 .88

Miller Canyon Wash " " 35.5·e–0.07x 0.15·(0.2x+2.0) " 16.2 .01

Hunter Canyon Wash " " " " " 15.5 .01

Stump Canyon Wash " " " " " 14.6 .01

Ash Canyon Wash " " " " " 12.9 .01

Brown-Bob Thompson Wash " " " " " 9.5 .01

Group 4

Lewis Springs Wash " " " " " 12.1 .01

Bakarich-McCool Wash " " " " " 11.8 .01

Three Canyons Wash " " " " " 6.6 <.01

Palominas Wash " " " " " 11.1 .01

Group 5

Greenbush Draw " " 40.2·e0.01x 0.15(1.8x–8.2) 0.8 19.5 .9

Group 6

Banning Creek " " 2060.8·e–1.1x 0.15(0.8x+0.9) .4 8.6 .15

Unnamed Wash 2 " " " " " 10.6 .15

Stagg Ranch Wash " " " " " 10.1 .15

Little Dry Creek " " " " " 10.5 .15

Spring Creek " " " " " 11.4 .15

Group 7

Willow Creek " " 126.6·e–0.07x 0.15·(1.6x–8.5) " 7.7 .23

Walnut Gulch " " " " " 7.7 .23

Government Draw " " " " " 7.7 .23

High Knolls Canyon Wash " " " " " 7.7 .23

Total ephemeral-stream channel recharge, 2001 and 2002 , in hm3

/2 yr 5.89

Average annual ephemeral-stream channel recharge, in hm3

/yr 2.95
Tables 3–13 311

Table 13. Sensitivity of estimated annual ephemeral-stream channel recharge to calculation parameters, 2001 and 2002, Sierra Vista 

ground-water recharge study area, Arizona.

[Group numbers refer to figure 5. Abbreviations: hm3/2yr, cubic hectometers per 2-year period; %, magnitude of change, in percentage of base value; <, less than]

Tributary name

Resulting recharge for 2001–2002, in hm3/2yr, after indicated change

Channel evaporation,

in %

Near-channel

transpiration,

in %

Stream-flow duration,

in %

Wetted channel 

width,

in %

Infiltration flux,

in %

+100 -100 +100 -100 +50 -50 100 10 +100 -50

Group 2

Unnamed Wash 1 <0.01 0.01 <0.01 0.23 0.12 <0.01 1.34 <0.01 0.24 <0.01

Graveyard Gulch <.01 0.01 <0.01 0.22 0.12 <0.01 1.27 <0.01 0.23 <0.01

Escapule Wash .15 1.16 1.06 1.26 1.79 0.53 8.30 0.74 2.42 0.53

Group 3

Woodcutters Wash 1.15 1.16 1.06 1.26 1.79 .53 8.30 .74 2.42 .53

Garden Canyon Wash <.01 .01 <.01 .31 .15 <.01 1.79 <.01 .31 <.01

Ramsey Canyon Wash <.01 .01 <.01 .26 .14 <.01 1.52 <.01 .27 <.01

Carr Canyon Wash .87 .88 .80 .95 1.35 .40 6.29 .56 1.83 .40

Miller Canyon Wash <.01 .01 <.01 .24 .13 <.01 1.40 <.01 .25 <.01

Hunter Canyon Wash <.01 .01 <.01 .23 .12 <.01 1.34 <.01 .24 <.01

Stump Canyon Wash <.01 .01 <.01 .22 .12 <.01 1.27 <.01 .23 <.01

Ash Canyon Wash <.01 .01 <.01 .20 .11 <.01 1.14 <.01 .21 <.01

Brown-Bob Thompson Wash <.01 .01 <.01 .15 .08 <.01 .87 <.01 .16 <.01

Group 4

Lewis Springs Wash <.01 .01 <.01 .19 .10 <.01 1.08 <.01 .19 <.01

Bakarich-McCool Wash <.01 .01 <.01 .19 .10 <.01 1.08 <.01 .19 <.01

Three Canyons Wash <.01 <.01 <.01 .10 .05 <.01 .59 <.01 .11 <.01

Palominas Wash <.01 .01 <.01 .17 .09 <.01 1.01 <.01 .18 <.01

Group 5

Greenbush Draw .90 .90 .72 1.11 1.45 .36 7.15 .54 2.00 .36

Group 6

Banning Creek .15 .15 .10 .21 .25 .05 1.32 .08 .35 .05

Unnamed Wash 2 .15 .15 .10 .21 .25 .05 1.32 .08 .35 .05

Stagg Ranch Wash .15 .15 .10 .21 .25 .05 1.32 .08 .35 .05

Little Dry Creek .15 .15 .10 .21 .25 .05 1.32 .08 .35 .05

Spring Creek .15 .15 .10 .21 .25 .05 1.32 .08 .35 .05

Group 7

Willow Creek .23 .24 .12 .35 .41 .06 2.21 .12 .58 .06

Walnut Gulch .23 .24 .12 .35 .41 .06 2.21 .12 .58 .06

Government Draw .23 .24 .12 .35 .41 .06 2.21 .12 .58 .06

High Knolls Canyon Wash .23 .24 .12 .35 .41 .06 2.21 .12 .58 .06

Total recharge, 2001–2002 5.74 5.93 4.62 9.74 10.70 2.31 61.18 3.46 15.55 2.31

Average annual recharge 2.87 2.97 2.31 4.87 5.35 1.16 30.59 1.73 7.78 1.16

Change, in percentage −2.7 .7 −21.7 65.1 81.4 −60.7 937 −41.4 164 −60.7