Groundwater/Surface-Water Interactions in the Tunk, 

Bonaparte, Antoine, and Tonasket Creek Subbasins, 

Okanogan River Basin, North-Central Washington, 2008 

Scientific Investigations Report 2009–5143

Prepared in cooperation with the Okanogan Conservation District and the 

Washington State Department of Ecology

U.S. Department of the Interior

U.S. Geological Survey

Groundwater/Surface-Water Interactions in the 

Tunk, Bonaparte, Antoine, and Tonasket Creek 

Subbasins, Okanaogan River Basin, 

North-Central Washington, 2008 

By S.S. Sumioka and R.S. Dinicola

Prepared in cooperation with the Okanogan Conservation District and the

Washington State Department of Ecology

Scientific Investigations Report 2009–5143

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Sumioka, S.S., and Dinicola, R.S., 2009, Groundwater/surface-water interactions in the Tunk, Bonaparte, Antoine, and 

Tonasket Creek subbasins, Okanogan River basin, north-central Washington, 2008: U.S. Geological Survey Scientific 

Investigations Report 2009–5143, 26 p.
iii

Contents

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

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

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

Previous Water Resources Studies...................................................................................................3

Description of Study Area ...................................................................................................................3

Generalized Hydrogeologic Framework ...........................................................................................5

Streamflow-Gaging Stations and Current and Historical Data.....................................................5

Methods...........................................................................................................................................................8

Streamflow and Water-Level Measurements.........................................................................................11

Groundwater/Surface-Water Interactions..............................................................................................16

General Streamflow Characteristics...............................................................................................16

Streamflow and Hydraulic Gradient ................................................................................................19

Subbasin Hydrogeology.....................................................................................................................20

Data Gaps and Suggestions for Further Study .......................................................................................24

Summary and Conclusions.........................................................................................................................24

Acknowledgments.......................................................................................................................................26

References Cited..........................................................................................................................................26
iv

Tables

Table 1. Location and selected physical characteristics of four study area subbasins,

Washington ................................................................................. 3

Table 2. Extents of different land covers in the four study area subbasins, Washington ... 5

Table 3. Areal extents of generalized surficial geologic units in the four study area

subbasins, Washington ..................................................................... 5

Table 4. Site information and measured streamflows in four study area subbasins,

Washington, June and September 2008 ................................................ 12

Table 5. Measured streamflows and stream and groundwater levels, and calculated

hydraulic gradients and metrics related to groundwater/surface-water

interactions at sites in the four study area subbasins, Washington, June and

September 2008.............................................................................. 14

Figures

Figure 1. Map showing location of Water Resources Inventory Area 49 and the four

study area subbasins, Washington ...................................................... 2

Figure 2. Map showing land cover in the four study area subbasins, Washington ............ 4

Figure 3. Map showing generalized surficial geology of the four study area subbasins,

Washington ................................................................................. 6

Figure 4. Map showing locations of streamflow-gaging stations maintained by the

Washington State Department of Ecology, and historical USGS

streamflow-gaging stations in the four study area subbasins, Washington ......... 7

Figure 5. Map showing potential streamflow measurement sites and flow conditions

observed by USGS during May 2008 reconnaissance in the four study area

subbasins, Washington ..................................................................... 9

Figure 6. Map showing selected sites for measuring streamflows, stream levels, and

shallow groundwater levels beneath streams in the four study area subbasins,

Washington ................................................................................. 10

Figure 7. Graphs showing streamflow and streamflow per unit area in the four study

area subbasins, Washington, June and September 2008 .............................. 17

Figure 8. Graphs showing hydraulic gradients and streamflow for four study area

subbasins, Washington, June and September 2008 .................................... 20

Figure 9. Map showing approximate locations of wells for which driller’s logs were

reviewed in the four study area subbasins, Washington .............................. 22

Figure 10. Graph showing numbers of post-1974 constructed wells with specified ranges

in depth to bedrock in the four study area subbasins, Washington .................. 23
v

Conversion Factors and Datums

Conversion Factors

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

acre 0.4047 hectare (ha)

acre-foot (acre-ft) 1,233 cubic meter (m3)

acre-foot (acre-ft) 0.001233 cubic hectometer (hm3) 

section (640 acres or 1 square 

mile)

259.0 square hectometer (hm2) 

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

cubic foot (ft3) 28.32 cubic decimeter (dm3) 

cubic foot (ft3) 0.02832 cubic meter (m3) 

Flow rate

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

Hydraulic gradient

foot per mile (ft/mi) 0.1894 meter per kilometer (m/km)

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C= (°F-32)/1.8.

Datums

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.
vi

Local and Surface-Water Station Numbers

Wells and other data-collection sites in Washington are assigned so-called local numbers by 

the USGS that identify their location in a township, range, and section, based on the rectangular 

subdivision of public land. For example, well number 37N/28E-34A01 indicates, from left to right, 

the township (37 North), the range (28 East); the 640-acre section (Section 34); and the 40-acre 

quarter-quarter section (A) within that section. A number follows the quarter-quarter section 

designation to indicate the sequence in which the well was inventoried in that quarter-quarter 

section.

Surface-water stations at which streamflows are measured are assigned a number, in 

downstream order, if there are more than one on a stream. A description of this system of 

numbering may be found at http://wdr.water.usgs.gov/wy2007/documentation.html#sitenumber.

6 5 4 3 2 1

7 8 9 10 11 12

18 17 16 15 14 13

19 20 21 22 23 24

30 29 28 27 26 25

31 32 33 34 35 36

37N/28E-34A01

T.

37

N.

R. 28 E. 

Diagram showing local number site identification system 

used in Washington State.
Groundwater/Surface-Water Interactions in Tunk, 

Bonaparte, Antoine, and Tonasket Creek Subbasins, 

Okanogan River Basin, North-Central Washington, 2008

By S.S. Sumioka and R.S. Dinicola

Abstract

An investigation into groundwater/surface-water 

interactions in four tributary subbasins of the Okanogan 

River determined that streamflows and shallow groundwater 

levels beneath the streams varied seasonally and by location. 

Streamflows measured in June 2008 indicated net losses of 

streamflow along 10 of 17 reaches, and hydraulic gradients 

measured between streams and shallow groundwater indicated 

potential recharge of surface water to groundwater at 11 

of 21 measurement sites. In September 2008, net losses of 

streamflow were indicated along 9 of 17 reaches, and potential 

recharge of surface water to groundwater was indicated at 18 

of 21 measurement sites. The greatest losses of streamflow 

occurred near the confluences with the Okanogan River, likely 

due to the presence of thick layers of unconsolidated deposits 

in the flood plain of the Okanogan River.

Based on available geologic information compiled from 

drillers’ logs, a surficial geologic map, and streamflow records, 

the extensive and thick deposits of unconsolidated material 

in the Tunk and Bonaparte Creek subbasins are factors in 

sustaining the almost perennial streamflow in those creeks. 

The less extensive and generally thinner unconsolidated 

deposits in the Tonasket and Antoine subbasins are 

contributing factors to the occasional extended periods of zero 

flow (a dry stream channel) in those creeks.

Even though groundwater withdrawals would affect 

streamflows, relatively low precipitation in the area, along 

with limited groundwater storage capacity and the presence 

of permeable, unconsolidated deposits underlying the stream 

channels, would likely lead to loss of surface water to the 

groundwater system without any withdrawals.

Introduction

In recent years, increasing demands for water for 

domestic, agricultural, recreational, and other uses in 

watersheds of Washington have created concern that 

insufficient water resources remain for fish and other uses. 

The Okanogan River basin includes portions of British 

Columbia, Canada, and Washington. The Similkameen River 

is the largest tributary of the Okanogan River and also drains 

British Columbia and Washington. The drainages of the 

Okanogan and Similkameen Rivers in Washington constitute 

Water Resources Inventory Area (WRIA) 49 (fig. 1), one of 

many watersheds in Washington where local citizens and 

governments have elected to coordinate with Tribes and State 

agencies to develop a watershed management plan, according 

to the guidelines outlined in the Watershed Management Act 

of 1998 (Washington State Engrossed Substitute House Bill 

2514). With leadership from the Okanogan Conservation 

District (OCD), the planning group is working to implement 

a long-range sustainable watershed plan to meet the needs 

of current and future water demands in the basin, while also 

working to protect and improve its natural resources. In this 

report, the Okanogan River basin refers to the mainstem of the 

Okanogan River south of the Canada/United States boundary.

The WRIA 49 planning group needs information 

regarding the interaction of groundwater and surface water 

in the tributaries to the Okanogan River as part of the 

assessment phase. As lead agency for WRIA 49 planning, 

the OCD selected Tunk, Bonaparte, Antoine, and Tonasket 

Creek subbasins, tributaries to the Okanogan River (fig. 1) to 

investigate groundwater/surface-water interactions. The OCD 

requested that the U.S. Geological Survey (USGS) collect and 

evaluate data to better understand those interactions in the 

selected subbasins.
2 Groundwater/Surface-Water Interactions in Four Subbasins, Okanogan River Basin, Washington, 2008

watac09-0389_fig01

Okanogan

River

Similkameen R.

Omak

Disautel

Oroville

Tonasket

Riverside

120°0'W 119°30'W 119°0'W

49°0'N

48°30'N

0 5 10 20 MILES

0 10 20 KILOMETERS 5

EXPLANATION

Water Resource Inventory Area 49—

 Okanogan and Similkameen River basins

Tonasket 

Creek

subbasin

Antoine 

Creek

subbasin

Bonaparte 

Creek

subbasin

Tunk 

Creek

subbasin

Basin delineation from Washington Streamstats,

http://water.usgs.gov/osw/streamstats/Washington.html

Washington

STUDY

AREA

Havillah

Figure 1. Location of Water Resources Inventory Area 49 and the four study area subbasins, 

Washington.

Purpose and Scope

This report presents the results of streamflows and 

shallow groundwater levels measured beneath streams in the 

Tunk, Bonaparte, Antoine, and Tonasket Creek subbasins 

of the Okanogan River in Washington. Data were collected 

in June and September 2008; a low-flow period when water 

demand is high and water availability is limited. The data were 

used to identify net streamflow gains and losses along reaches 

of the creeks and to determine if groundwater is discharging 

to streams or streamflow is recharging groundwater at 

measurement locations. In addition, those findings are 

evaluated with regard to available information about the 

hydrogeologic framework of the subbasins. Suggestions for 

additional data collection and interpretation that could refine 

the understanding of groundwater/surface-water interactions in 

the subbasins are presented.
Introduction 3

Geologic and hydrogeologic information for the 

subbasins was obtained from previously published reports, 

from surficial geologic maps published by the Washington 

State Department of Natural Resources (2005), and from 

drillers’ logs either on file at the USGS Washington Water 

Science Center or downloaded from the Washington State 

Department of Ecology (WDOE) website (http://apps.ecy.

wa.gov/welllog/textsearch.asp, accessed November 7, 2008).

Previous Water Resources Studies

The water resources for the entire Okanogan River basin 

were described by Walters (1974), based on water-resources 

information compiled from various sources. Using existing 

records of hydrologic conditions (precipitation, streamflow, 

and groundwater levels), Walters (1974) described, to the 

extent possible, the amount of water available, the quality or 

usability of the water, and the frequency of seasonal water 

shortages or surpluses in the Okanogan River basin and in its 

tributary subbasins, including the four subbasins of the present 

study.

Montgomery Water Group, Inc. and others (1995) 

evaluated existing data and presented an initial assessment of 

the availability of groundwater and surface water that WDOE 

could use in making decisions regarding water rights. 

A more detailed study of the Bonaparte Creek subbasin 

(Packard and others, 1983) collected groundwater and surfacewater data to describe the relationship between groundwater 

levels, streamflow, and water levels in several lakes in the 

subbasin. The study also located the groundwater divide 

between the Bonaparte Creek subbasin and the Sanpoil River 

basin to the southeast.

Description of Study Area

The study area consists of four subbasins located on the 

eastern side of the Okanogan River in the Okanogan River 

basin in north-central Washington (fig. 1 and table 1). The 

Okanogan River flows southward from British Columbia, 

Canada, to the Columbia River and drains about 8,300 mi2 in 

the United States and Canada. WRIA 49 encompasses about 

2,100 mi2 within that area, and the four subbasins make up 

about 370 mi2 of the WRIA. The Bonaparte Creek subbasin is 

the largest of the four subbasins (about 160 mi2), and the other 

three subbasins range between about 60 and 70 mi2. Altitudes 

of the WRIA range from about 840 ft at the confluence of the 

Okanogan River and the Columbia River, to about 7,300 ft in 

the uplands to the east of the Okanogan River.

The climate of WRIA 49 is characterized by warm 

summers and cold winters and precipitation typical of 

semi-arid regions. The mean July temperature at Omak, 

Washington, near the Okanogan River, is about 87°F and the 

mean January temperature at Omak is about 17°F (Western 

Regional Climate Center, http://www.wrcc.dri.edu/summary/

climsmwa.html, accessed November 25, 2008). Precipitation 

ranges from about 11 in/yr at Omak to about 16 in/yr 

at Disautel in the highlands east of the Okanogan River 

(fig. 1; National Oceanic and Atmospheric Administration, 

http://www.wrcc.dri.edu/summary/waF.html, accessed 

November 25, 2008).

The predominant land cover in WRIA 49 and the study 

area subbasins include shrub/scrub land, evergreen forests, 

and grassland/pasture/hay (fig. 2). (Land-cover/land-use data 

were obtained from the National Land Cover Database 2001, 

downloaded from the Multi-Resolution Land Characteristics 

Consortium at http://www.mrlc.gov, accessed April 5, 2007). 

Most agricultural lands in WRIA 49 are in the lowlands 

adjacent to the Okanogan River. The major population 

centers also are adjacent to the Okanogan River. Timber 

operations and recreational land uses generally take place in 

areas of evergreen forest in the WRIA. Within the study area 

subbasins, shrub/scrub land cover from about 50 to 60 percent 

of each subbasin, evergreen forest covers from about 33 

to 40 percent of each subbasin, and grassland/pasture/hay 

cover from about 7 to 18 percent of each subbasin (fig. 2

and table 2). Some of the shrub/scrub land is used for stock 

grazing. A residential development is currently (2008) under 

construction in the headwater region of a tributary to Tunk 

Creek.

Table 1. Location and selected physical characteristics of four 

study area subbasins, Washington.

[Location of subbasins are shown in figure 1. Basin characteristics from 

http://streamstats.usgs.gov/wastreamstats/index.asp, accessed November 26, 

2008. Altitudes are given in feet above North American Vertical Datum of 

1988 (NAVD 88). mi2

, square mile; ft, foot]

Subbasin 

name

Location of 

subbasin mouth 

(river miles along 

Okanogan River)

Drainage 

area

(mi2

)

Altitude 

range 

(ft)

Average 

altitude 

(ft)

Tunk Creek 45.0 71.7 860 – 6,050 3,300

Bonaparte Creek 56.7 161 890 – 7,260 3,550

Antoine Creek 61.2 73.4 900 – 7,250 3,440

Tonasket Creek 77.8 60.1 920 – 5,090 3,300
4 Groundwater/Surface-Water Interactions in Four Subbasins, Okanogan River Basin, Washington, 2008

River

Similkameen River

Okanogan

0 84

0 3 6 12 MILES

16 KILOMETERS

Tonasklet 

Creek

subbasin

Bonaparte 

Creek

subbasin

Tunk 

Creek

subbasin

Antoine 

Creek

subbasin

119°30'W 119°15'W 119°0'W

48°45'N

48°30'N

Water Resource Inventory Area 49

EXPLANATION

Shrub/scrub

Generalized land cover

Cultivated crops

Developed, open space

Developed, low to medium intensity

Developed, high intensity

Evergreen forest

Deciduous forest

Grassland/pasture/hay

Wetlands

Barren land

Open water

watac09-0389_fig02

Land cover/use data from Multi-Resolution

Land Characteristics Consortium,

http://www.mrlc/gov

Figure 2. Land cover in the four study area subbasins, Washington.
Introduction 5

These materials are the major sources of groundwater in the 

subbasins, except in those areas where they are thin or are 

composed of clay or till (a compacted mixture of clay, silt, 

sand, and gravel). The Tunk Creek subbasin has the highest 

areal extent (65 percent of the subbasin; fig. 3 and table 3) of 

surficial unconsolidated deposits of the four subbasins. The 

areal extent of unconsolidated deposits in each of the other 

three subbasins is about 50 percent of each subbasin. The 

unconsolidated deposits are underlain by granitic, andesitic, 

and metamorphosed rocks forming the bedrock of the 

Okanogan River basin. Wells that are open in these bedrock 

units generally provide only enough water to satisfy domestic 

uses. A part of the southeastern part of the WRIA is underlain 

by basalts of the Columbia River Basalt Group (Walters, 

1974) that can potentially yield more groundwater, but these 

basalts are not present in the study area subbasins. More 

detailed information concerning unconsolidated deposits in the 

subbasins are presented in section, “Subbasin Hydrogeology.”

Streamflow-Gaging Stations and 

Current and Historical Data

During 2008, the WDOE maintained five streamflowgaging stations in the study area subbasins (fig. 4). Two 

of the gaging stations (Tunk Creek near Riverside, station 

49E080; and Bonaparte Creek near Tonasket, station 49F070) 

transmit 15-minute interval data by telemetry to WDOE, 

where they are published on the WDOE website (https://

fortress.wa.gov/ecy/wrx/wrx/flows/regions/state.asp). Data 

are collected intermittently, the interval between visits ranging 

from biweekly to quarterly, at the remaining three stations 

(Tonasket Creek near Oroville, station 49H080; Antoine Creek 

near mouth, station 49G060; and Bonaparte Creek at Aeneas 

Valley Road, station 49F150), and they also may be found on 

the WDOE website. 

Subbasin Land cover Extent 

(mi2

)

Percentage

 of subbasin

Tunk Shrub/scrub 42.0 58.9

Cultivated crops .076 .11

Developed, open space .015 .02

Developed, low to medium intensity .003 .00

Evergreen forest 23.9 33.4

Deciduous forest .006 .01

Grassland/pasture/hay 5.15 7.22

Wetlands .261 .40

Open water .005 .01

Bonaparte Shrub/scrub 79.5 47.7

Cultivated crops .104 .06

Developed, open space 1.10 .66

Developed, low to medium intensity 1.28 .77

Developed, high intensity .005 .00

Evergreen forest 66.5 39.9

Deciduous forest .004 .00

Grassland/pasture/hay 17.2 10.33

Wetlands .594 .36

Barren land .012 .01

Open water .305 .18

Antoine Shrub/scrub 33.9 46.2

Cultivated crops .486 .66

Developed, open space .459 .63

Developed, low to medium intensity .165 .23

Evergreen forest 27.0 36.8

Deciduous forest .011 .02

Grassland/pasture/hay 10.14 13.8

Wetlands 1.18 1.61

Barren land .000 .00

Open water .026 .04

Tonasket Shrub/scrub 28.9 47.4

Cultivated crops .040 .07

Developed, open space .436 .72

Developed, low to medium intensity .223 .37

Evergreen forest 19.8 32.6

Grassland/pasture/hay 11.0 .1

Wetlands .403 .66

Open water .142 .23

Table 2. Extents of different land covers in the four study area 

subbasins, Washington.

[mi2, square mile]

Generalized Hydrogeologic Framework

Unconsolidated deposits, Pleistocene-aged continental 

drift (table 3) consisting of clay, silt, sand, and gravel 

generally are the predominant surficial geologic material in 

the study area. These materials, deposited by the Okanogan 

Lobe of the Cordilleran ice sheet when it receded following 

the last, large-scale glaciations in the area (Montgomery Water 

Group, Inc. and others, 1995), are thickest (in places, several 

hundreds of feet thick) in the stream valleys. In the upland 

areas, however, thicknesses may be only a few tens of feet. 

Table 3. Areal extents of generalized surficial geologic units in 

the four study area subbasins, Washington. 

[mi2, square mile]

Subbasin Unit name Extent

(mi2

)

Percentage of 

subbasin

Tunk Unconsolidated deposits 48 66

Bedrock units 24 34

Bonaparte Unconsolidated deposits 84 51

Bedrock units 81 49

Antoine Unconsolidated deposits 37 51

Bedrock units 36 49

Tonasket Unconsolidated deposits 29 48

Bedrock units 31 52
6 Groundwater/Surface-Water Interactions in Four Subbasins, Okanogan River Basin, Washington, 2008

watac09-0389_fig03

River

Similkameen River

Okanogan

0 84

0 3 6 12 MILES

16 KILOMETERS

Tonasklet 

Creek

subbasin

Bonaparte 

Creek

subbasin

Tunk 

Creek

subbasin

Antoine 

Creek

subbasin

119°30'W 119°15'W 119°0'W

48°45'N

48°30'N Water Resource Inventory Area 49

EXPLANATION

Bedrock

Generalized surficial geology

Unconsolidated deposits

Geologic data from Washington Division of Geology and Earth Resources

Open File Report 2005-3

Figure 3. Generalized surficial geology of the four study area subbasins, Washington.
Introduction 7

River

Similkameen River

Okanogan

0 84

0 3 6 12 MILES

16 KILOMETERS

Tonasklet 

Creek

subbasin

Bonaparte 

Creek

subbasin

Tunk 

Creek

subbasin

Antoine 

Creek

subbasin

119°30'W 119°15'W 119°0'W

48°45'N

48°30'N

12444490

12439300

49F150

49G060

49F070

49E080

49H080

Omak

Oroville

Tonasket

Riverside "

"

"

"

Water Resource Inventory Area 49

12444490

49H080

EXPLANATION

Washington Department of 

 Ecology streamflow-gaging

 station and number

Discontinued USGS streamflow- 

 gaging station and number

watac09-0389_fig04

Figure 4. Locations of streamflow-gaging stations maintained by the Washington State Department of Ecology, and historical 

USGS streamflow-gaging stations in the four study area subbasins, Washington.
8 Groundwater/Surface-Water Interactions in Four Subbasins, Okanogan River Basin, Washington, 2008

In addition, in the past, the USGS operated two 

continuous-record streamflow-gaging stations in two of the 

study area subbasins (Tonasket Creek at Oroville, station 

12439300; and Bonaparte Creek near Wauconda, station 

12444490; fig. 4). Streamflow data for these stations can be 

accessed at http://waterdata.usgs.gov/wa/nwis/dv. For this 

investigation, instantaneous streamflow measurements were 

made at all WDOE and USGS gaging stations except for two 

in the Bonaparte Creek subbasin (WDOE station 49F150 and 

USGS station 12444490), where no access was possible. 

The gaging station operated by WDOE on Tunk Creek 

(station 49E080) is about 1.3 mi from the mouth of Tunk 

Creek and has been operating since August 2002. The annual 

mean streamflow at the gaging station for water years 2003–07 

ranged from an estimated 2 to 7.5 ft3/s, and the lowest daily 

mean streamflows (during July, August, or September) ranged 

from 0.02 to 0.2 ft3/s. Tunk Creek was never dry at this gaging 

station. 

The WDOE station on Bonaparte Creek (station 49F070) 

is near the mouth of Bonaparte Creek and has been operating 

since September 2002. The annual mean streamflow at 

the gaging station for water years 2003–07 ranged from 

an estimated 3.4 to 8.2 ft3/s, and the lowest daily mean 

streamflows (during July, August, or September) ranged from 

0.0 to 0.3 ft3/s.

The WDOE stations located near the mouths of Antoine 

Creek (station 49G060) and Tonasket Creek (station 49H080) 

and on Bonaparte Creek near Aeneas Valley (station 49F150) 

have been operating since 2002; however, measurements for 

the Bonaparte Creek gaging station after April 2008 are not 

listed on the website. Zero flow has been reported at least once 

during the period of record for each of these gaging stations. 

The lowest flows occur during the summer and early autumn.

The USGS operated continuous-record streamflowgaging stations (stream levels recorded every 15 minutes) 

during 1967–73 on Bonaparte Creek in the central part of the 

subbasin (station 12444490) and during 1967–91 on Tonasket 

Creek (station 12439300). The lowest daily mean streamflow 

in Bonaparte Creek was 0.1 ft3/s, and zero flow was recorded 

in Tonasket Creek for many days during the summer and 

winter.

Methods

Potential sites for streamflow measurements and 

temporary piezometer installations were identified during 

a reconnaissance field trip in May 2008. Flow conditions 

were recorded for streams and their tributaries, as well as 

accessibility to the streams. About 70 sites were visited in the 

four study area subbasins and flowing water was observed 

at about 75 percent of the sites (fig. 5). Sites that were 

likely to be flowing in late summer and that were accessible 

for measurement, were chosen for later visits (June and 

September) to measure stream levels and shallow groundwater 

levels beneath streams for the purpose of calculating hydraulic 

gradients (fig. 6).

Measurements of streamflows were made during two 

field trips in June and September 2008. Streamflows were 

measured at selected stream sites with an Acoustic Doppler 

Velocity (ADV) meter in accordance with the surface-water 

quality-assurance plan for the USGS Washington Water 

Science Center (Kresch and Tomlinson, 2004). At a few 

sites in September (site 8 on Tunk Creek and sites 33 and 

36 on Bonaparte Creek; fig. 5), flows were low enough that 

with slight channel modifications, a portable flume was used 

to measure streamflow depth, which was then converted 

to streamflow. At site 54 on Tonasket Creek, a volumetric 

streamflow measurement was made in September. Measured 

streamflow at the beginning and end of a reach were compared 

and sites where streamflow was greater than the next upstream 

site and sites where streamflow was less than the next 

upstream site were identified.

Measurements of stream levels and shallow groundwater 

levels beneath streams also were made during two field trips in 

June and September 2008. Shallow groundwater levels were 

measured using an electronic tape in temporary piezometers 

installed about 5-ft deep beneath the streambeds in accordance 

with the groundwater quality-assurance plan for the USGS 

Washington Water Science Center (Drost, 2005). Stream levels 

were measured concurrently relative to the top of the same 

piezometers. The piezometers consisted of small-diameter 

pipes with holes drilled near one end that were driven into 

the streambed near the streamflow-measuring section on the 

streams. The difference in water levels in the piezometer and 

the stream is a measure of the head difference, in feet, between 

groundwater and surface water. Dividing that head difference 

by the length of pipe beneath the streambed, in feet, gave 

a value for the hydraulic gradient at that point, in feet per 

foot. A positive hydraulic gradient indicates the potential for 

groundwater discharge to the stream, and a negative hydraulic 

gradient indicates a potential for streamflow recharge to the 

shallow groundwater system. A zero gradient indicates no net 

potential flow between surface water and groundwater.

The USGS rates the accuracy of streamflow 

measurements based on the equipment, character of the 

measurement section, number of observation verticals, 

stability of stage, wind and accuracy of depth, and velocity 

measurements (Rantz, 1982, p. 179). Accuracy ratings of 

“good” indicate that the measurements are within 5 percent of 

actual values and “fair” indicate the measurements are within 

8 percent of actual values. All streamflow measurements were 

rated “good” or “fair.” Water levels measured in the shallow 

wells and streams using an electronic tape are assumed 

to be within 0.01 ft of actual values based on replicate 

measurements.
Methods 9

River

Similkameen River

Okanogan

0 84

0 3 6 12 MILES

16 KILOMETERS

5

7 9

6

4

3

8

2

1

24

67

72

58

26

10

32

65

64

28

63

53

37

61

60

30

62

59

57

56

55

52

51 50

48

43

42

41

40

39

35

31 29

27

25

21 22

20

19 18

17

16

15

14

13

12

11

71

45

38

70

54

49

47

46

69

68

34

33

36

66

23

44

EXPLANATION

Dry

Water Resouces Inventory Area 49

Flowing

Channel not found

Standing water

Potential streamflow measurement site 

 and number and flow condition

5

watac09-0389_fig05

Tonasklet 

Creek

subbasin

Bonaparte 

Creek

subbasin

Tunk 

Creek

subbasin

Antoine 

Creek

subbasin

119°30'W 119°15'W 119°0'W

48°45'N

48°30'N

Figure 5. Potential streamflow measurement sites and flow conditions observed by USGS during May 2008 reconnaissance 

in the four study area subbasins, Washington.
10 Groundwater/Surface-Water Interactions in Four Subbasins, Okanogan River Basin, Washington, 2008

Figure 6. Selected sites for measuring streamflows, stream levels, and shallow groundwater levels beneath streams in the 

four study area subbasins, Washington.

River

Similkameen River

Okanogan

0 84

0 3 6 12 MILES

16 KILOMETERS

EXPLANATION

Groundwater and surface-

 water measurement site 

 and number

46

8

2

1

67

72

58

35

71

45 44

38 70

54

49

47

46

69

68 33

36

66

23

watac09-0389_fig06

Tonasket 

Creek

subbasin

Bonaparte 

Creek

subbasin

Tunk 

Creek

subbasin

Antoine 

Creek

subbasin

119°30'W 119°15'W 119°0'W

48°45'N

48°30'N
Streamflow and Water-Level Measurements 11

Streamflow and Water-Level 

Measurements

About 70 sites were visited in the four study area 

subbasins in May 2008 and flowing water was observed 

at about 75 percent of the sites (fig. 5). During this May 

reconnaissance, estimated streamflows ranged from less than 

1 to about 10 ft3/s. Streamflow was measured at 21 sites in 

June and September 2008 and ranged from dry and 7.05 ft3/s 

(table 4). Location information and calculated streamflow 

per unit area for each measurement site also are presented in 

table 4. One site measured in September was not accessible 

in June, one site measured in June was flooded by backwater 

(likely from a beaver dam) in September, and four sites were 

dry. Streamflows also are available on-line at the USGS 

National Water Information System http://waterdata.usgs.gov/

wa/nwis/measurements.

The streamflow measurements are presented again with 

coincident hydraulic gradient related measurements for June 

and September 2008 (table 5). Additional metrics related 

to groundwater/surface-water interactions were calculated, 

including:

• net differences in streamflow between sequential sites,

• net differences in streamflow per river mile between 

sequential sites,

• identification of the reach between sequential sites as 

gaining or losing, where gaining sites had net increased 

streamflow downstream and losing sites had net 

decreased streamflow, and

• vertical hydraulic gradients beneath the streambed.

The measurements have some limitations that need to 

be considered when evaluating groundwater/surface-water 

interaction. First, the two sets of measurements were made 

several months apart and represent conditions existing at 

the specific times only, although the measurements within 

each set were all made within a few days. Atypical activities 

occurring during a measurement, such as exceptionally high, 

short-term pumping from a near-stream well would result in 

atypical measurements for the time of year. Furthermore, gains 

or losses of streamflow, as described in this report, refer to 

the cumulative or net gain or loss in streamflow between two 

measurement sites. It was beyond the scope of this study to 

locate and measure the potentially numerous small tributaries 

and surface-water diversions and returns in the subbasins, so 

the reported losses and gains in streamflow may be due to 

processes other than groundwater/surface-water interactions. 

For example, unmeasured surface-water diversions along a 

reach identified as losing could potentially be large enough to 

mask or reduce streamflow gains from groundwater discharge, 

and unmeasured tributaries and return flows could mask or 

reduce streamflow losses along a reach identified as gaining. 

In addition, there could be many localized areas of streamflow 

losses to and gains from groundwater within a reach that 

overall had a net gain or loss of streamflow. Regardless of 

these limitations, some general patterns appear in the data 

that provide useful insight into groundwater/surface-water 

interactions in the study area.
12 Groundwater/Surface-Water Interactions in Four Subbasins, Okanogan River Basin, Washington, 2008 Table 4. Site information and measured streamflows in four study area subbasins, Washington, June and September 2008. [Latitude and longitude are referenced to North American Datum of 1983 (NAD83). USGS, U.S. Geological Survey; mi2, square mile; ft3/s, cubic foot per second; (ft3/s)/mi2, cubic foot per second per square mile; –, no data] Map No. (see fig. 6) Site name USGS site No. Drainage area (mi2

)

River 

mile Latitude Longitude Local No. Measurement date Streamflow (ft3/s) Streamflow per unit area [ft3/s)/mi2

]

Tunk Creek subbasin

23 Tunk Creek at Keystone Road, near Barker 12445400 71.7 0.39 48 33 44.6 119 28 44.4 35N/27E-04E 06-16-08 3.75 0.052

09-16-08 .09 .0013

1 Tunk Creek at Tunk Creek Road, near Barker 12445390 70 1.71 48 33 22.4 119 27 34.6 35N/27E-04R 06-17-08 4.10 .059

09-18-08 .18 .0026

2 Tunk Creek at Knox Road, near Synarep 12445200 58.6 5.72 48 32 30.7 119 23 43.5 35N/27E-12R 06-17-08 3.97 .068

09-18-08 .29 .0049

66 Tunk Creek at Ed Figlenski Road, near Synarep 12445190 33.4 7.75 48 31 44.2 119 21 37.3 35N/28E-17L 06-17-08 3.90 .12

09-18-08 .36 .011

72 Tunk Creek at Soriano’s, near Synarep 12445150 19.1 10.68 48 30 54.5 119 19 07.4 35N/28E-22L 09-18-08 .3 .016

8 Tunk Creek at Clough Homestead Road, near Synarep 12445100 15.6 12.37 48 30 05.8 119 17 53.1 35N/28E-26L 06-17-08 3.46 .22

09-18-08 .079 .0051

Bonaparte Creek subbasin

36 Bonaparte Creek at Tonasket 12444550 161 0.35 48 42 05.7 119 26 32.8 37N/27E-16P 06-17-08 3.24 0.020

09-19-08 .13 .0008

33 Bonaparte Creek below Bannon Creek, near Tonasket 12444530 140 5.24 48 40 19.7 119 21 28.4 37N/28E-30N 06-18-08 2.99 .021

09-16-08 .022 .0002

35 Bonaparte Creek above Bannon Creek, near Tonasket 12444510 131 8.46 48 39 13.0 119 17 58.5 36N/28E-02D 06-18-08 3.97 .030

67 Bonaparte Creek below Peony Creek, near Wauconda 12444488 109 14.23 48 39 23.9 119 11 58.0 37N/29E-32P 06-18-08 4.41 .040

09-16-08 1.69 .0155

68 Bonaparte Creek below Little Bonaparte Creek, near Wauconda 12444475 57.2 18.14 48 40 46.7 119 08 17.2 37N/29E-26D 06-18-08 5.92 .10

09-16-08 .15 .0026

69 Bonaparte Creek above Little Bonaparte Creek, near Wauconda 12444440 44.7 21 48 42 23.3 119 06 27.2 37N/29E-13G 06-18-08 6.65 .15

09-16-08 .54 .012
Streamflow and Water-Level Measurements

13

Map 

No.

(see fig. 6)

Site name USGS site No. Drainage area (mi2) River mile Latitude Longitude Local No. Measurement date Streamflow (ft3/s) Streamflow per unit area [ft3/s)/mi2]

Antoine Creek subbasin

45 Antoine Creek at U.S. Highway 97, near Ellisford 12444290 73.4 0.23 48 45 33.2 119 24 32.9 38N/27E-27R 06-20-08 0.69 0.009

09-19-08 .23 .0031

71 Antoine Creek at Whiskey Creek Road, near Ellisford 12444225 54.5 4.29 48 45 05.6 119 20 36.0 38N/38E-31H 06-20-08 .56 .010

09-17-08 dry –

44 Antoine Creek at Antoine Breaks Road, near Ellisford 12444220 52.8 5.11 48 45 38.7 119 20 00.5 38N/28E-29L 06-20-08 6.38 .12

09-17-08 1.6 .030

38 Antoine Creek at Mt Hull Road, near Havillah 12444175 19.3 13.78 48 49 43.0 119 14 02.5 38N/28E-01A 06-19-08 6.56 .34

09-17-08 .44 .023

70 Antoine Creek near Havillah 12444150 19.1 14.36 48 49 35.9 119 13 21.6 38N/29E-06C 06-19-08 7.05 .37

09-17-08 .58 .030

Tonasket Creek subbasin

46 Tonasket Creek at Oroville 12439300 60.1 0.73 48 56 36.2 119 24 47.7 40N/27E-27A 06-19-08 0.44 0.007

09-17-08 dry –

47 Tonasket Creek at Chesaw Road, near MP3 near Oroville 12439280 58.2 2.39 48 56 57.6 119 22 53.2 40N/27E-24M 06-19-08 .64 .011

09-17-08 dry –

49 Tonasket Creek at West Corral Road, near Oroville 12439260 42.3 5.26 48 56 32.0 119 19 27.8 40N/28E-29A 06-19-08 .79 .019

09-17-08 .01 .00024

54 Tonasket Creek at Forest Service Road 3525, near Oroville 12439240 32.2 7.95 48 55 17.5 119 16 47.1 40N/28E-34J 06-19-08 .36 .011

09-17-08 .006 .00019

58 Tonasket Creek above Dry Creek, near Oroville 12439180 6.46 10.43 48 54 12.7 119 14 31.3 39N/28E-01Q 06-19-08 dry –

09-17-08 dry –

Table 4. Site information and measured stream discharges in four study area subbasins, Washington, June and September 2008.—Continued[Latitude and longitude are referenced to North American Datum of 1983 (NAD83). USGS, U.S. Geological Survey; mi2, square mile; ft3/s, cubic foot per second; (ft3/s)/mi2, cubic foot per second per square mile; 

–, no data]
14 Groundwater/Surface-Water Interactions in Four Subbasins, Okanogan River Basin, Washington, 2008 Table 5. Measured streamflows and stream and groundwater levels, and calculated hydraulic gradients and metrics related to groundwater/ surface-water interactions at sites in the four study area subbasins, Washington, June and September 2008. 

[Hydraulic gradient: A positive gradient indicates the potential for groundwater discharge to the stream. The reverse, a negative hydraulic gradient, indicates the potential for streamflow recharge to the groundwater system. mi2, square mile; ft3/s, cubic foot per second; (ft3/s)/mi, cubic foot per second per mile; ft btp, feet below top of 

piezometer; ft/ft, foot per foot; –, no data; na, not applicable]

Map 

No.

(see fig. 6)

Drainage 

area

(mi2

)

River 

mile

Measurement 

date

Streamflow

(ft3/s)

Net 

difference in 

streamflow

 (ft3/s)

Net difference in 

streamflow per 

river mile

 [(ft3/s)/mi]

Gaining 

or losing 

reach?

Stream 

water level

(ft btp)

Groundwater 

level

(ft btp)

Hydraulic 

gradient

(ft/ft)

Tunk Creek subbasin

June 2008

23 71.7 0.39 06-16-08 3.75 -0.35 -0.27 losing 2.99 5.05 -0.82

1 70 1.71 06-17-08 4.10 .13 .03 gaining 3.64 3.95 -.172 58.6 5.72 06-17-08 3.97 .07 .03 gaining 3.69 3.48 .12

66 33.4 7.75 06-17-08 3.90 .44 .10 gaining 2.46 2.33 .04

72 19.1 10.68 06-17-08 – – – – – – –

8 15.6 12.37 06-17-08 3.46 na na na 2.97 2.85 .04

September 2008

23 71.7 0.39 09-16-08 0.09 -0.09 -0.068 losing 2.5 3.98 -0.74

1 70 1.71 09-18-08 .18 -.11 -.027 losing 3.78 3.89 -.06

2 58.6 5.72 09-18-08 .29 -.07 -.034 losing 3.26 3.3 -.01

66 33.4 7.75 09-18-08 .36 .06 .020 gaining 3.37 3.43 -.03

72 19.1 10.68 09-18-08 .30 .221 .13 gaining 1.9 1.84 .02

8 15.6 12.37 09-18-08 .079 na na na 2.96 2.89 .02

Bonaparte Creek subbasin

June 2008

36 161 0.35 06-17-08 3.24 0.25 0.05 gaining 3.97 4.53 -0.28

33 140 5.24 06-18-08 2.99 -.98 -.30 losing 3.11 3.83 -.33

35 131 8.46 06-18-08 3.97 -.44 -.08 losing 1.86 1.67 .05

67 109 14.23 06-18-08 4.41 -1.51 -.39 losing 2.00 2.00 .0068 57.2 18.14 06-18-08 5.92 -.73 -.26 losing 2.36 2.30 .0269 44.7 21 06-18-08 6.65 3.08 2.97 .01

September 2008

36 161 0.35 09-19-08 0.13 -0.09 -0.018 losing 3.66 3.86 -0.09

33 140 5.24 09-16-08 .022 – – – 2.84 3.83 -.35

35 131 8.46 09-19-08 – – – losing – – –67 109 14.23 09-16-08 1.69 1.54 .39 gaining 3.14 3.22 -.07

68 57.2 18.14 09-16-08 .15 -.39 -.14 losing 2.01 2.08 -.02

69 44.7 21 09-16-08 .54 na na na 3.78 3.79 -.002
Streamflow and Water-Level Measurements

15

Map 

No.

(see fig. 6)

Drainage 

area

(mi2)

River 

mile

Measurement 

date

Streamflow

(ft3/s)

Net 

difference in 

streamflow

 (ft3/s)

Net difference in 

streamflow per 

river mile

 [(ft3/s)/mi]

Gaining 

or losing 

reach?

Stream 

water level

(ft btp)

Groundwater 

level

(ft btp)

Hydraulic 

gradient

(ft/ft)

Antoine Creek subbasin

June 2008

45 73.4 0.23 06-20-08 0.69 0.13 0.03 gaining 3.16 5.05 -0.80

71 54.5 4.29 06-20-08 .56 -5.82 -7.10 losing 2.04 1.95 .02

44 52.8 5.11 06-20-08 6.38 -.18 -.02 losing 3.00 3.00 .00

38 19.3 13.78 06-19-08 6.56 -.49 -.84 losing 1.98 2.08 -.03

70 19.1 14.36 06-19-08 7.05 na na na 2.29 2.33 -.01

September 2008

45 73.4 0.23 09-19-08 0.23 0.23 0.06 gaining 3.75 3.84 -0.04

71 54.5 4.29 09-17-08 0 -1.6 -2.0 losing – – <0

44 52.8 5.11 09-17-08 1.6 1.16 .13 gaining 2.56 2.6 -.02

38 19.3 13.78 09-17-08 .44 -.14 -.24 losing 2.4 2.54 -.04

70 19.1 14.36 09-17-08 .58 na na na 2.68 2.59 .03

Tonasket Creek subbasin

June 2008

46 60.1 0.73 06-19-08 0.44 -0.2 -0.12 losing 3.49 5.05 -0.72

47 58.2 2.39 06-19-08 .64 -.15 -.05 losing 2.48 5.65 -.9249 42.3 5.26 06-19-08 .79 .43 .16 gaining 2.75 2.75 .0054 32.2 7.95 06-19-08 .36 .36 .15 gaining 2.41 2.93 -.0758 6.46 10.43 06-19-08 0 na na na – – <0

September 2008

46 60.1 0.73 09-17-08 0 0 0 neutral – – <0

47 58.2 2.39 09-17-08 0 -.01 -.0035 losing – – <049 42.3 5.26 09-17-08 .01 .004 .0015 gaining 3.13 3.25 -0.1254 32.2 7.95 09-17-08 .006 .006 .0024 gaining 2.01 2.16 -.15

58 6.46 10.43 09-17-08 0 na na na – – <0

Table 5. Measured stream discharges and stream and ground-water levels, and calculated hydraulic gradients at sites in the four study area subbasins, Washington, June and September 2008.—Continued[Hydraulic gradient: A positive gradient indicates the potential for groundwater discharge to the stream. The reverse, a negative hydraulic gradient, indicates the potential for streamflow recharge to the groundwater system. mi2, square mile; ft3/s, cubic foot per second; (ft3/s)/mi, cubic foot per second per mile; ft btp, feet below top of 

piezometer; ft/ft, foot per foot; –, no data; na, not applicable]
16 Groundwater/Surface-Water Interactions in Four Subbasins, Okanogan River Basin, Washington, 2008

Groundwater/Surface-Water 

Interactions

Groundwater/surface-water interactions generally were 

characterized for the study area subbasins based on changes in 

measured streamflows between June and September, net gains 

and losses of streamflow along the lengths of the streams, 

and hydraulic gradients between surface water and shallow 

groundwater at measurement sites. Streamflows and hydraulic 

gradients represent groundwater/surface-water interactions 

at different spatial scales. A measured net gain or loss of 

streamflow is a cumulative value for an entire reach that spans 

between two measurement points. In contrast, a positive 

(potential upward flow) or negative (potential downward 

flow) hydraulic gradient represents conditions at a specific 

point at the beginning or end of a reach. Thus, it is possible 

to identify seemingly conflicting conditions such as a losing 

reach that is bounded at one of both ends with sites that have 

positive hydraulic gradients. Such data indicate that the losing 

areas of the reach are located somewhere between the two 

measurement points. The interactions were further evaluated 

with regard to available information on the hydrogeologic 

framework of the subbasins and the distribution of known 

existing wells.

General Streamflow Characteristics

The most obvious difference between the June and 

September streamflow measurements (table 4) is that there 

was substantially less streamflow in all subbasins during 

September 2008 than in June 2008. Beyond that, streamflow in 

each of the subbasins had unique characteristics.

Tunk Creek subbasin.—Measured streamflow changed 

very little along the length of Tunk Creek during June and 

September, although the September streamflows were about 

an order of magnitude smaller than the June streamflows 

(table 4 and fig. 7A). As is typical for drainage basins with 

moderate topographic relief, the June streamflow per unit area 

decreased in a downstream direction, which is likely a result 

of more precipitation-driven runoff and groundwater recharge 

in the high-altitude areas of the Tunk Creek subbasin. During 

September, however, streamflow per unit area at the uppermost 

measurement site (site 8, RM 12.37) was about the same as at 

a mid-basin measurement site (site 2). That change was likely 

a result of either limited groundwater storage capacity and 

streamflow to the stream in the upper basin with presumably 

thinner unconsolidated deposits, or possibly relatively greater 

consumptive use of water in the upper basin. Given that the 

unconsolidated deposits in Tunk Creek generally are less than 

100-ft thick and have relatively low permeability (Walters, 

1974), the upper basin likely does have limited groundwater 

storage capacity and discharge to the stream. The streamflows 

measured by USGS in June and September 2008 at site 1 

in Tunk Creek were consistent with the 2003–07 June and 

September streamflows from WDOE streamflow-gaging 

station 49E080, Tunk Creek near Riverside, which is adjacent 

to site 1.

Bonaparte Creek subbasin.—In contrast to Tunk 

Creek, measured June streamflow in Bonaparte Creek 

decreased consistently from the uppermost to the lowermost 

measurements sites (table 4 and fig. 7B). The September 

streamflows were substantially smaller than those measured 

in June, although changes in streamflow along the length 

of the creek were quite variable. Similar to Tunk Creek, the 

June streamflow per unit area decreased in a downstream 

direction, although the amount of streamflow per unit area was 

only about one-half that measured in Tunk Creek. Assuming 

similar amounts of precipitation for Tunk and Bonaparte 

Creek subbasins, these data indicate that in Bonaparte 

Creek, more runoff either goes into groundwater storage or 

is used consumptively (lost to evapotranspiration). Given 

the potentially large volume of groundwater storage in the 

mid-basin parts of Bonaparte Creek subbasin (the Aeneas 

Valley area located to the southeast of site 67, fig. 6) and 

a correspondingly large amount of groundwater pumping 

(Walters, 1974), there appears to be substantial consumptive 

use of groundwater in the Bonaparte Creek subbasin.

Antoine Creek subbasin.— Measured streamflows and 

calculated streamflows per unit area during June in Antoine 

Creek at and upstream of RM 5.11 were substantially larger 

than comparable streamflows in the other subbasins (table 4, 

fig. 7C). In contrast, June streamflows at the two measurement 

sites downstream of RM 5.11 in Antoine Creek were 

substantially smaller than streamflows in the lower reaches 

of Bonaparte and Tunk Creeks. The substantial decrease 

in June streamflow occurred downstream of a long canyon 

and upstream of an intensively irrigated area, about 4 mi 

upstream of the mouth of Antoine Creek. The agricultural 

area is irrigated with groundwater (Walters, 1974). There 

are a number of very productive irrigation wells in the area 

between Antoine and Siwash Creeks near the Okanogan River 

(Walters, 1974). It is possible that groundwater pumping was 

at least partly responsible for the rapid decrease in Antoine 

Creek streamflow during June. However, the largest decrease 

in streamflow was measured at site 71 (RM 4.29; fig. 6) that is 

upstream of the irrigated area and at the mouth of the canyon 

where unconsolidated deposits are likely of limited thickness. 

Thus, a surface-water diversion for irrigation may be a more 

likely explanation for the decreased June streamflow.
Groundwater/Surface-Water Interactions 17

watac09-0389_fig07AB

A. Tunk Creek

STREAMFLOW, IN CUBIC FEET PER SECOND

STREAMFLOW PER UNIT AREA,IN CUBIC FEET PER SECOND PER SQUARE MILE

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.00

0 2 4 6 8 10 12 14

0 5 10 15 20 25

B. Bonaparte Creek 

7

6

5

4

3

2

1

0

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.00

RIVER MILES UPSTREAM OF MOUTH

Streamflow

 June 2008

 September 2008

EXPLANATION

Streamflow per unit area

 June 2008

 September 2008

Figure 7. Streamflow and streamflow per unit area in the four study area subbasins, Washington, June and 

September 2008.

Tonasket Creek subbasin.—Measured streamflows and 

calculated streamflow per unit area in Tonasket Creek were 

substantially less than those in the other subbasins (fig. 7D). 

Even in June, the uppermost measurement site in Tonasket 

Creek was dry, and the largest value of streamflow per 

unit area [0.019 (ft3/s)/mi2] was only about one-eighth of 

the largest value for the other three subbasins. The highest 

altitudes in Tonasket Creek subbasin are 1,000 to 2,000-ft 

lower than altitudes in the other subbasins (table 1), so 

precipitation in Tonasket Creek subbasin may be slightly 

less, but that cannot account for the substantial difference in 

streamflow per unit area during June and September. These 

data indicate that in Tonasket Creek, there is very limited 

groundwater recharge from winter/spring runoff and generally 

little groundwater discharge and storage. Additionally, data 

are consistent with the hypothesis of exceptionally large 

consumptive use of groundwater and (or) surface water in 

the subbasin. Because there are not an exceptional number 

of wells in the subbasin and there does not appear to be an 

appreciable volume of groundwater storage (Walters, 1974), 

naturally limited groundwater resources in the subbasin are 

indicated. The instantaneous streamflows measured by USGS 

in June and September 2008 at the lowermost site in Tonasket 

Creek (0.44 and 0 ft3/s) were lower than the average monthly 

June and September streamflows reported for 1967–79 for the 

discontinued USGS streamflow-gaging station at the same 

location (2.5 and 1.0 ft3/s). However, the range of average 

daily streamflows during June and September for 1967–79 at 

the discontinued USGS streamflow-gaging station was 0.0 to 

greater than 10 ft3/s, and the 2008 measurements fall within 

that range.
18 Groundwater/Surface-Water Interactions in Four Subbasins, Okanogan River Basin, Washington, 2008

watac09-0389_fig07CD

0.00 

0.05 

0.10 

0.15 

0.20 

0.25 

0.30 

0.35 

0.40 

0

1

2

3

4

5

6

7

8

0 2 4 6 8 10 12 14 16 

C. Antoine Creek 

STREAMFLOW, IN CUBIC FEET PER SECOND

STREAMFLOW PER UNIT AREA, IN CUBIC FEET PER SECOND PER SQUARE MILE

0.00 

0.05 

0.10 

0.15 

0.20 

0.25 

0.30 

0.35 

0.40 

0.0 

0.1 

0.2 

0.3 

0.4 

0.5 

0.6 

0.7 

0.8 

0.9 

0 2 4 6 8 10 12 

D. Tonasket Creek 

RIVER MILES UPSTREAM OF MOUTH

Figure 7.—Continued.
Groundwater/Surface-Water Interactions 19

Streamflow and Hydraulic Gradient

Changes in measured streamflow between sites indicated 

net gains or losses along the reach of stream between the sites 

that were at least in part due to groundwater discharge to the 

stream or streamflow recharge to groundwater. The direction 

of the hydraulic gradient at a measurement site indicated 

groundwater discharge to surface water (positive gradients) or 

surface-water recharge to groundwater (negative gradients) at 

that specific point, which corresponds to either end of a reach.

During June 2008, 10 of 17 reaches were identified 

as losing, and 11 of 21 measurement sites had negative 

hydraulic gradients (table 5, fig. 8). During September 

2008, 9 of 17 reaches were identified as losing, and 18 of 21 

measurement sites had negative hydraulic gradients. All four 

streams appeared to lose water to the groundwater system 

as they neared the Okanogan River. The most substantial 

losses were for Antoine Creek, as previously discussed. It is 

likely that regardless of groundwater pumping, streamflow 

losses would occur as the streams flow across the relatively 

permeable floodplain deposits of the Okanogan River. 

The losses possibly are exacerbated by pumping from the 

relatively abundant wells along the Okanogan River, but 

measured streamflow data alone cannot determine the effects 

of pumping. Overall, there was good correspondence between 

losing reaches and negative hydraulic gradients at the sites 

at the ends of the reaches. The only neutral reach (lack of a 

gain or loss in streamflow) identified was in lower Tonasket 

Creek in September when both measurement sites (sites 46 

and 47) were dry. This does not necessarily indicate a lack 

of groundwater and surface-water interaction, but rather the 

cumulative gains and losses between measurement sites equal 

to 0.0 ft3/s.

In June, hydraulic gradients in Tunk and Bonaparte 

Creeks at upstream sites (sites 66 and 2 on Tunk Creek, and 

sites 69 and 68 on Bonaparte Creek) were positive, indicating 

groundwater was flowing into the stream at these sites. The 

hydraulic gradient at site 35 on Bonaparte Creek (RM 8.46) 

also was positive. Hydraulic gradients at other sites on the two 

creeks were less than or equal to zero. The hydraulic gradient 

at site 71 (RM 4.29) on Antoine Creek was positive in June. 

All other sites on Antoine Creek exhibited negative hydraulic 

gradients and were near zero, or slightly less than zero, 

indicating no or little water movement between the stream and 

the groundwater system. All streams had negative hydraulic 

gradients at the sites near their mouths. In September, most 

sites had negative hydraulic gradients, the exceptions being 

a few upper basin sites. It is not possible to quantify the 

hydraulic gradient at sites with zero flow, but it is known 

that the gradient is negative. Thus, zero flows at the two 

downstream-most sites on Tonasket Creek (sites 46 and 47, 

fig. 6) indicate negative hydraulic gradients.

In Tunk Creek during June (fig. 8A), groundwater 

discharged to the creek at the upstream sites and streamflow 

was lost from the creek at the downstream sites. Tunk Creek 

flows through a thick layer of unconsolidated deposits from 

about RM 12.37 (site 8) to slightly upstream of RM 5.72 

(site 2), and the stream gained water from these sediments 

in June and lost water to these sediments during September. 

Downstream of RM 5.72 (site 2), the unconsolidated deposits 

thin and the creek flows through an area where bedrock is 

near or at land surface. Near RM 1.71 (site 1), unconsolidated 

deposits again forms the near-surface geologic material and 

the creek lost water from that point to its mouth during June 

and September.

Hydraulic gradients measured in Bonaparte Creek were 

similar in June and September (fig. 8B). Site 33 (RM 5.24), 

downstream of the ‘bedrock sill segment’ defined by Packard 

and others (1983) had a relatively large negative hydraulic 

gradient in June and September. Site 33 is located in a losing 

reach (Packard and others, 1983). Downstream of site 33, the 

gradient was less steep but still negative. 

Antoine Creek lost water between the two most 

upstream measurement sites (sites 70 and 38, fig. 6; RM 

14.36 and 13.78, fig. 8C) during June and September. Based 

on drillers’ logs, the thickness of unconsolidated deposits 

in this part of the subbasin appears to be as much as about 

200 ft. About 10 river miles downstream, after the creek 

emerges from the narrow, bedrock canyon, the gradients were 

slightly less negative (sites 44 and 45, fig. 6). In June, the 

gradient was zero at site 44 (RM 5.11), positive about 0.8 mi 

downstream (site 71 at RM 4.29), then strongly negative near 

the mouth of the creek (site 46 at RM 0.73). The positive 

to neutral hydraulic gradients, combined with the large loss 

of streamflow at RM. 4.29, indicates that a surface-water 

diversion may be the cause of the decreased streamflow.

The uppermost site on Tonasket Creek (site 58, fig. 6; 

RM 10.43, fig. 8D) was observed flowing only during the May 

reconnaissance (it was dry in June and September), and the 

number of measurement sites on Tonasket Creek with zero 

flow increased from one to three between June and September. 

The next two downstream sites on Tonasket Creek (site 54 

at RM 7.95 and site 49 at RM 5.26) had negative or neutral 

hydraulic gradients in June and September (fig. 8D). At the 

downstream sites (site 47 at RM 2.39 and site 46 at RM 0.73) 

in June, the hydraulic gradients were more negative, and in 

September both sites had zero flow. Considering the surficial 

geology of the subbasin, it is possible there are reaches of 

the creek that are gaining. Between sites 49 and 54, bedrock 

approaches land surface or may be exposed, which could 

lead to groundwater moving upward and entering the creek. 

Very few drillers’ logs were available for this area to confirm 

this interpretation. Downstream of site 49 to the mouth, the 

creek channel is underlain by unconsolidated deposits, with 

thicknesses greater than 150 ft in some places, that would be 

expected to coincide with negative hydraulic gradients and 

streamflow losses to groundwater.
20 Groundwater/Surface-Water Interactions in Four Subbasins, Okanogan River Basin, Washington, 2008

watac09-0389_fig8AB

A. Tunk Creek

HYDRAULIC GRADIENT, IN FEET PER FOOT

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.00

0 2 4 6 8 10 12 14

1.0

0.0

-1.0

Streamflow

 June 2008

 September 2008

EXPLANATION

Hydraulc gradient

 June 2008

 September 2008

0 5 10 15 20 25

B. Bonaparte Creek 

RIVER MILES UPSTREAM OF MOUTH

1.0

0.0

-1.0

STREAMFLOW, IN CUBIC FEET PER SECOND

7

6

5

4

3

2

1

0

Figure 8. Hydraulic gradients and streamflow for four study area subbasins, Washington, June and September 2008

Subbasin Hydrogeology

A summary evaluation of subbasin hydrogeology was 

completed by compiling information from available well 

logs and recent surficial geologic maps and comparing it to 

previously published descriptions (Walters, 1974) to refine 

understanding of hydrogeologic features. The logs are not an 

ideal source of information largely because different drillers’ 

describe subsurface materials differently, and because there 

is inherent uncertainty in the driller-provided well locations 

on the well logs that are, in most cases, accurate to a 40-acre 

quarter-quarter section (the well-log information was not field 

checked by USGS). In spite of these limitations, logs were of 

value because the vast majority of the 1,041 logs reviewed 

were for wells constructed after the Walters (1974) report was 

published.
Groundwater/Surface-Water Interactions 21

watac09-0389_fig8CD

0 2 4 6 8 10 12 14

RIVER MILES UPSTREAM OF MOUTH

HYDRAULIC GRADIENT, IN FEET PER FOOT

1.0

0.0

-1.0

STREAMFLOW, IN CUBIC FEET PER SECOND

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

1.0

0.0

-1.0

C. Antoine Creek 

8

7

6

5

4

3

2

1

0

0 2 4 6 8 10 12 14 16

D. Tonasket Creek

June gradient

September gradient

June streamflow

September streamflow

Figure 8.—Continued.

There is a substantially greater extent of unconsolidated 

surficial deposits in the study area subbasins, shown by the 

2005 maps (Washington Department of Natural Resources, 

2005; fig. 3) compared to plate 1 in Walters (1974). However, 

the distribution of wells in study area subbasins for which 

drillers’ logs were reviewed (fig. 9) generally coincides with 

the extent of quaternary alluvium and terrace deposits mapped 

by Walters (1974). The Washington Department of Natural 

Resources (2005) maps likely include significant areas of 

mapped unconsolidated deposits that are unsaturated or very 

thin, so the expanded surficial extents of unconsolidated 

deposits do not likely reflect newly found expanded 

groundwater storage.

Wells constructed in study area subbasins after 1974 

were compiled according to depth to bedrock (fig. 10) for 

comparison to information presented by Walters (1974). 

Depth to bedrock is essentially equivalent to thickness of 

unconsolidated deposits. Overall, the Bonaparte Creek 

subbasin stands out as having about three times more wells 

in total and wells deeper than 99 ft compared to the other 

subbasins. This is indicative of Bonaparte Creek subbasin 

having the most ample groundwater resources. This is 

consistent with Walters’ estimates of groundwater storage 

in the Siwash-Bonaparte-Chewiliken subarea of 200,000 

acre-ft, in the Tunk-Omak subarea of 60,000 acre-ft and in the 

Tonasket-Antoine subarea of 70,000 acre-ft. Tonasket Creek 

subbasin has the fewest and the shallowest wells, which is 

indicative of having the most limited groundwater resources. 

This is consistent with the extremely low streamflow per unit 

area values calculated from streamflows measured in June and 

September 2008, that are in turn indicative of naturally limited 

groundwater storage and streamflow needed to sustain summer 

low flows.
22 Groundwater/Surface-Water Interactions in Four Subbasins, Okanogan River Basin, Washington, 2008

River

Similkameen River

Okanogan

0 84

0 3 6 12 MILES

16 KILOMETERS

Tonasklet 

Creek

subbasin

Bonaparte 

Creek

subbasin

Tunk 

Creek

subbasin

Antoine 

Creek

subbasin

119°30'W 119°15'W 119°0'W

48°45'N

48°30'N

Water Resource Inventory Area 49

Approximate locations of wells

EXPLANATION

watac09-0389_fig09

Figure 9. Approximate locations of wells for which driller’s logs were reviewed in the four study area subbasins, 

Washington.
Groundwater/Surface-Water Interactions 23

One conclusion from the Initial Watershed Assessment 

(Montgomery Water Group, Inc. and others, 1995) was that 

some locations in the study area may have deep confined 

aquifers within unconsolidated deposits that may not be in 

connection with nearby surface water. Most drillers’ logs 

showing well depths greater than 100 ft indicate multiple 

potential confining layers, such as blue or gray clays or 

various cemented units, but evaluating the continuity and 

hydraulic characteristics of confining layers was beyond the 

scope of this investigation. 

About 66 percent of the Tunk Creek subbasin is mantled 

with unconsolidated deposits, the highest percentage of the 

four study area subbasins. The relatively high percentage of 

unconsolidated deposits in the subbasin is consistent with the 

relatively constant streamflow measured along the length of 

the creek in June and September 2008. This is because the 

extensive deposits can store groundwater along most of the 

length of the Tunk Creek mainstem. Because nearly one-half 

of the drillers’ logs for wells in the subbasin indicate sediment 

thicknesses of less than 100 ft, there is a high potential for 

groundwater withdrawals to affect groundwater discharge to 

streams.

About one-half of the Bonaparte Creek subbasin is 

mantled with unconsolidated deposits, and depths to bedrock 

may exceed 300 ft especially near the center of the subbasin 

following the course of the Bonaparte Creek streambed. 

Most well logs with depths to bedrock greater than 300 ft for 

the Bonaparte Creek subbasin were located in the lowlands 

immediately adjacent to the Okanogan River and are not 

typical of unconsolidated deposits farther upstream in the 

subbasin. 

About one-half of the Antoine Creek subbasin is mantled 

with unconsolidated deposits. Most of these deposits are in 

the upper basin, although about 16 percent lies within about 

5 river miles of the mouth of the creek (fig. 3). Drillers’ logs 

indicate that the unconsolidated deposits in this lower part of 

the subbasin may be relatively thin, about 100 ft thick or less. 

Measured streamflows abruptly decreased by a substantial 

amount in this lower part of the subbasin. Antoine Creek flows 

through a deep and narrow canyon upstream of this location; 

the downstream end of which is about 5.5 mi from the mouth 

of the creek. The canyon is about 4.6 mi long and about 

150–200 ft deep. Based on the available logs, the thickest 

layer of unconsolidated deposits exist around the town of 

Havillah, Washington, near RM 14. Thicknesses exceed 200 ft 

in this area. 

Again, about one-half of the surface is mantled with 

unconsolidated deposits in the Tonasket Creek subbasin, 

and most of those deposits are in the northern and eastern 

parts of the subbasin. Surface and near-surface bedrock 

is in the southwestern part of the subbasin. Based on 

information contained in the drillers’ logs, the thickest layer 

of unconsolidated deposits, exceeding 300 ft, is between 2 and 

5 mi from the mouth of the creek. Thicknesses in most other 

areas of the subbasin range from a few feet to greater than 

100 ft.

Figure 10. Numbers of post-1974 constructed wells with specified ranges in depth to bedrock in 

the four study area subbasins, Washington.

watac09-0389_fig 10

0

50

100

150

200

250

Tunk Bonaparte Antoine Tonasket

NUMBER OF WELLS WITH SPECIFIED

DEPTH TO BEDROCK, IN FEET 

SUBBASIN

Depth ranges, in feet

500–599

400–499

300–399

200–299

100–199

50–99
24 Groundwater/Surface-Water Interactions in Four Subbasins, Okanogan River Basin, Washington, 2008

Data Gaps and Suggestions for 

Further Study

Low summer streamflows that have a high potential 

for being impacted by groundwater withdrawals appear to 

indicate that groundwater storage may be limited in most 

parts of the study area subbasins. However, given the limited 

precipitation and groundwater storage capacity, together with 

permeable unconsolidated deposits along most of their lengths, 

the creeks measured during this investigation also would 

likely lose summer streamflow to groundwater over much of 

their lengths even without groundwater withdrawals. These 

conditions make it difficult to parse out the specific effects 

of groundwater pumping on streamflow without intensive 

measurements and evaluations.

Given those difficulties, it would be expedient to select 

more limited, high-interest areas where detailed quantitative 

assessments of groundwater/surface-water interactions 

would be of most use. The USGS Bonaparte Creek study 

(Packard and others, 1983) is a reasonable starting point 

for what a detailed quantitative assessment of groundwater/

surface-water interactions would include. In addition, it 

would be informative to field-locate surface-water diversions 

and pumping wells with estimates or measurements of 

the diversion and pumpage amounts, and to use pressure 

transducers and recorders in selected near-stream wells to 

measure pumping-induced changes in water levels.

Characterizing possible deep, confined aquifers within 

unconsolidated deposits that may not be in connection with 

nearby surface water also would require investigation that 

again would benefit by focusing on a few limited, high-interest 

areas. As previously described, most drillers’ logs showing 

well depths greater than 100 ft indicate multiple potential 

confining layers, such as blue or gray clays or various 

cemented units. However, the presence of such layers alone 

is not indicative of an unconnected deep aquifer. It seems 

unlikely that a deep, confined, unconnected aquifer exists in 

the relatively limited unconsolidated deposits of the subbasins. 

That is because the underlying and surrounding bedrock 

generally is of low permeability, so recharge to a deep aquifer 

with any appreciable groundwater resource would have to 

originate from the overlying sediments, and streamflow from a 

deep aquifer would need to be through the overlying sediments 

in different locations. By definition, the deep aquifer would 

thus be in connection with nearby surface water. It would 

be possible to better characterize the nature and timing 

of groundwater/surface-water interactions, such as when 

pumping groundwater at a given time may affect streamflow. 

A numerical groundwater-flow model would greatly assist in 

the evaluation, as was done for WRIA 59 in Stevens County 

(Kahle and others, 2003). Such a characterization would 

require more intensive evaluations of the hydrogeologic 

framework of the unconsolidated deposits and their hydraulic 

properties. It is unlikely that there are enough existing wells to 

definitely characterize any deep confined aquifers, so drilling 

of new monitoring wells would be required. Geophysical 

logging methods could be used to further characterize the 

lithology at those locations. Again, it would likely be difficult 

to parse out the specific effects on streamflow of groundwater 

pumping from a deep, confined aquifer compared to the 

existing pumping from shallower unconfined aquifers, even 

with new monitoring wells. 

Summary and Conclusions

The Okanogan Conservation District (OCD) is the lead 

agency of a group of local government agencies and citizens 

undertaking the planning and implementation of a long-range 

watershed plan for the Okanogan River basin in northcentral Washington. The plan will be used to meet the needs 

of current and future water demands in the basin while also 

working to protect and improve its natural resources. Part of 

the planning phase includes an assessment of the groundwater/

surface-water interactions in tributaries to the Okanogan River. 

The OCD selected four subbasins tributary to the Okanogan 

River (Tunk, Bonaparte, Antoine, and Tonasket Creeks) and 

requested that the U.S. Geological Survey (USGS) collect and 

evaluate data to better understand groundwater/surface-water 

interactions in those subbasins.

The objective of this study was to describe the 

groundwater/surface-water interactions in unconsolidated 

deposits in the tributary subbasins. Fieldwork included 

streamflow measurements and shallow groundwater level 

measurements beneath the streams in the subbasins. In 

addition, geologic and hydrogeologic information for the 

subbasins was obtained from previously published reports, 

surficial geologic maps produced by the Washington State 

Department of Natural Resources (WDNR), and from drillers’ 

logs on file at the USGS Washington Water Science Center 

or downloaded from the Washington State Department of 

Ecology database of drillers’ logs.

Granitic, andesitic, and metamorphosed rock underlie 

most of the Okanogan River basin. Wells open in these 

bedrock units generally provide only enough water to satisfy 

domestic uses. The Okanogan Lobe of the Cordilleran ice 

sheet overrode the bedrock units and as the ice sheet receded, 

it deposited layers of clay, silt, sand, and gravel in the river 

and stream valleys. These unconsolidated deposits represent 

the primary sources of groundwater.

The extent of unconsolidated deposits near or at land 

surface ranges from 48 to 66 percent of the subbasins. Drillers’ 

logs suggest that the thickness of these materials ranges from 

less than 20 feet in the upland areas to several hundreds of feet 

in the river and stream valleys.
Summary and Conclusions 25

About 70 stream sites in the four subbasins were visited 

during a reconnaissance trip to the study area in May 2008. 

Flowing water was observed at about 75 percent of the sites. 

Estimated streamflows at the sites during May ranged from 

less than 1 to about 10 ft3/s. A subset of these sites was 

selected for streamflow and groundwater level measurements.

Streamflow was measured at 21 sites in June and 

September 2008. Shallow groundwater levels were measured 

at the same time as the streamflow measurements, using a 

small-diameter piezometer temporarily installed during the site 

visit. Measurements of the water level in the piezometer and 

the distance from the top of the piezometer to the stage of the 

stream were used to compute the hydraulic gradient between 

surface water and groundwater at that point.

Streamflows in June in all streams were higher than 

in September. Streamflow per unit area was calculated for 

each measurement site. For Tunk Creek, the streamflow 

per unit area decreased in a downstream direction in June. 

In September, streamflow per unit area at the uppermost 

measurement site was less than at mid-basin sites. This 

is likely due to limited groundwater storage capacity and 

subsequent streamflow to the stream resulting in less water 

entering the stream later in the year. An alternative is greater 

consumptive use in the upper basin, but given that the 

thickness of unconsolidated deposits is limited, limited storage 

capacity is the most likely explanation. The mid-basin portion 

of Bonaparte Creek has the potential to store large quantities 

of groundwater, given the thickness of unconsolidated 

deposits. In contrast to the Tunk Creek subbasin, however, 

there may be significant consumptive use of water in 

the Bonaparte Creek subbasin that leads to a decrease in 

streamflow.

Streamflow in Antoine Creek downstream of the mouth 

of a narrow canyon at about river mile (RM) 4.29 was lower 

than upstream of that point and also was lower than the 

streamflow per unit area at comparable locations on Tunk 

and Bonaparte Creeks. A possible explanation is that land use 

downstream of RM 5.11 appears to be intensively irrigated. 

Water for irrigation may be from wells or directly from 

Antoine Creek. In either case, streamflow in Antoine Creek 

would be affected.

Streamflows per unit area in Tonasket Creek were the 

smallest of the four subbasins. Data indicate that there is little 

groundwater recharge, even from winter/spring runoff, and 

generally little groundwater storage.

During June 2008, 10 of 17 reaches were identified as 

losing, and 11 of 21 measurement sites had negative hydraulic 

gradients. During September 2008, 9 of 17 reaches were 

identified as losing, and 18 of 21 measurement sites had 

negative hydraulic gradients. All four streams appeared to lose 

water to the groundwater system as they neared the Okanogan 

River, with Antoine Creek exhibiting the greatest losses. 

Streamflow losses probably occur as the streams flow across 

the relatively thick and permeable floodplain deposits of the 

Okanogan River.

In June, positive or neutral hydraulic gradients at 

upstream sites for all four streams indicated that either 

groundwater was discharging to these reaches or there was no 

net water movement into or out of the stream. All streams had 

negative hydraulic gradients near the mouths. In September, 

most sites had negative hydraulic gradients, except for a few 

upper-basin sites.

An evaluation of WDNR geologic maps indicates the 

extent of unconsolidated deposits in the four subbasins is 

greater than previously reported. However, an evaluation of 

drillers’ logs with respect to location and lithology indicate 

general agreement with the previously reported extent 

map. The WDNR maps likely include significant areas of 

unsaturated or very thin unconsolidated deposits that may 

not have been classified as unconsolidated in the previously 

reported extent map.

Interpretation of drillers’ logs to obtain depth-to-bedrock 

provided an estimate of the thickness of unconsolidated 

deposits. The Bonaparte Creek subbasin generally had the 

most and deepest wells, which is indicative of the subbasin 

having larger groundwater resources than the other subbasins. 

The Tonasket Creek subbasin had the fewest and shallowest 

wells, indicating more limited groundwater resources. Due to 

uncertainties in well locations listed on the drillers’ logs and 

the inconsistent naming of geologic materials on the logs, the 

existence of deep, confined aquifers in the unconsolidated 

deposits could not be evaluated.

The presence of extensive and (or) thick layers of 

unconsolidated deposits is consistent with relatively constant 

streamflow in the creek, as in the Tunk Creek subbasin. Areas 

of less extensive or thinner layers of unconsolidated deposits 

may lead to decreases in streamflow, as in lower Antoine 

Creek subbasin.

Groundwater resources appear to be limited in most parts 

of the subbasins, which results in low summer streamflows, 

with a high potential to be affected by groundwater 

withdrawals from nearby, shallow wells. However, given the 

low precipitation, the limited groundwater storage capacity, 

and the permeable unconsolidated deposits underlying the 

stream channels, the creeks also would likely lose water to 

the groundwater system without any withdrawals. To better 

evaluate the specific effects of groundwater pumping on 

streamflow, additional studies would be helpful that are limited 

in areal extent and more focused on quantitative assessments 

of those effects.

To determine if deep, confined aquifers exist within 

unconsolidated deposits, an intensive effort, restricted to a 

limited geographic area would be required. Currently available 

data (drillers’ logs) are not sufficient to confirm the presence 

of deep, confined aquifers.
26 Groundwater/Surface-Water Interactions in Four Subbasins, Okanogan River Basin, Washington, 2008

Acknowledgments

Bob Clark, of the Okanogan Conservation District, and 

Rusty Post, of the Washington State Department of Ecology, 

provided valuable guidance on developing the scope of work 

and work plan for this investigation. Appreciation is expressed 

to landowners who gave permission to measure streamflow in 

creeks that crossed their properties and measure water levels 

in their wells.

References Cited

Drost, B.W., 2005, Quality-assurance plan for groundwater activities, U.S. Geological Survey, Washington 

Water Science Center: U.S. Geological Survey Open-File 

Report 2005-1126, 27 p. (Available on-line at http://pubs.

usgs.gov/of/2005/1126)

Kahle, S.C., Longpré, C.I., Smith, R.R., Sumioka, S.S., 

Watkins, A.M., and Kresch, D.L., 2003, Water resources of 

the groundwater system in the unconsolidated deposits of 

the Colville River Watershed, Stevens County, Washington: 

U.S. Geological Survey Water-Resources Investigations 

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Publishing support provided by the U.S. Geological Survey

Publishing Network, Tacoma Publishing Service Center

For more information concerning the research in this report, contact the

 Director, Washington Water Science Center 

U.S. Geological Survey, 934 Broadway — Suite 300

Tacoma, Washington 98402

http://wa.water.usgs.gov
Sumioka and Dinicola—Groundwater/Surface-Water Interactions in Four Subbasins, Okanogan River Basin, Washington, 2008—Scientific Investigations Report 2009–5143