Hydrogeologic Framework, Groundwater Movement, 

and Water Budget in Tributary Subbasins and Vicinity, 

Lower Skagit River Basin, Skagit and Snohomish 

Counties, Washington

Scientific Investigations Report 2009–5270

Prepared in cooperation with the Skagit County Public Works Department, 

Washington State Department of Ecology, and Skagit County Public Utility District No. 1

U.S. Department of the Interior

U.S. Geological Survey
Cover: Lake Creek which connects Lake McMurray to Big Lake, lower Skagit River basin, 

Washington. Photograph taken May 9, 2006, courtesy of Skagit County Public Works.
Hydrogeologic Framework, Groundwater 

Movement, and Water Budget in 

Tributary Subbasins and Vicinity, 

Lower Skagit River Basin, Skagit and 

Snohomish Counties, Washington

By Mark E. Savoca, Kenneth H. Johnson, Steven S. Sumioka, Theresa D. Olsen, 

Elisabeth T. Fasser, and Raegan L. Huffman

Prepared in cooperation with the Skagit County Public Works Department, 

Washington State Department of Ecology, and Skagit County Public Utility 

District No. 1 

Scientific Investigations Report 2009–5270

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

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

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Suggested citation:

Savoca, M.E., Johnson, K.H., Sumioka, S.S., Olsen, T.D., Fasser, E.T., and Huffman, R.L., 2009, Hydrogeologic 

framework, groundwater movement, and water budget in tributary subbasins and vicinity, lower Skagit River basin, 

Skagit and Snohomish Counties, Washington: U.S. Geological Survey Scientific Investigations Report 2009–5270, 

46 p.
iii

Contents

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

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

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

Description of Study Area ...................................................................................................................2

Methods of Investigation..............................................................................................................................4

Well Inventory and Water-Level Measurements ............................................................................4

Hydrogeology.........................................................................................................................................4

Streamflow.............................................................................................................................................5

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

Geologic Setting....................................................................................................................................5

Geologic Units .......................................................................................................................................6

Hydrogeologic Units.............................................................................................................................8

Hydraulic Conductivity.......................................................................................................................18

Groundwater Movement ............................................................................................................................20

Recharge .............................................................................................................................................20

Groundwater-Flow Directions ..........................................................................................................26

Discharge.............................................................................................................................................32

Groundwater/Surface-Water Interactions.....................................................................................34

Groundwater-Level Fluctuations......................................................................................................34

Water Budget ...............................................................................................................................................40

Summary and Conclusions.........................................................................................................................42

Acknowledgments.......................................................................................................................................43

Selected References ..................................................................................................................................43

Plates

Plate 1. Map showing locations of selected wells, streamflow-gaging stations, and

streamflow-measurement sites, and map showing generalized surficial

geology in tributary subbasins and vicinity, lower Skagit River basin, Washington.

Plate 2. Map and hydrogeologic sections showing surficial hydrogeology,

hydrogeologic units, and locations of selected wells in tributary subbasins

and vicinity, lower Skagit River basin, Washington.
iv

Figures

Figure 1. Map showing location of tributary subbasins and vicinity, lower Skagit River

basin, Washington........................................................................... 3

Figure 2. Map showing extent and thickness of alluvial and recessional outwash aquifer

(Qago) in tributary subbasins and vicinity, lower Skagit River basin, Washington 11

Figure 3. Map showing extent and thickness of till confining unit (Qgt) in tributary

subbasins and vicinity, lower Skagit River basin, Washington ........................ 12

Figure 4. Map showing extent and thickness of advance outwash aquifer (Qga) in

tributary subbasins and vicinity, lower Skagit River basin, Washington ............ 13

Figure 5. Map showing extent and thickness of glaciolacustrine and distal outwash

confining unit (Qgl) in tributary subbasins and vicinity, lower Skagit River

basin, Washington........................................................................... 14

Figure 6. Map showing extent and thickness of inter-glacial alluvial aquifer (Qco) in

tributary subbasins and vicinity, lower Skagit River basin, Washington ............ 15

Figure 7. Map showing extent and thickness of older till confining unit (Qot) in tributary

subbasins and vicinity, lower Skagit River basin, Washington ........................ 16

Figure 8. Map showing extent and thickness of older outwash and alluvial aquifer

(Qooa) in tributary subbasins and vicinity, lower Skagit River basin, Washington 17

Figure 9. Map showing extent of sedimentary aquifer (OEc) and igneous and

metamorphic bedrock unit (EJTP) in tributary subbasins and vicinity, lower

Skagit River basin, Washington............................................................ 19

Figure 10. Map showing average annual precipitation, canopy cover, and impervious

surface across the tributary subbasins and vicinity, lower Skagit River basin, 

Washington, September 2006–August 2008 ............................................. 22

Figure 11. Graph showing precipitation-recharge relations used in this study, lower

Skagit River basin, Washington............................................................ 23

Figure 12. Map showing detail of distribution of impervious surfaces in tributary

subbasins and vicinity, lower Skagit River basin, Washington, September

2006–August 2008 ........................................................................... 24

Figure 13. Map showing distribution of average annual groundwater recharge from

precipitation in tributary subbasins and vicinity, lower Skagit River basin,

Washington, September 2006–August 2008 ............................................. 25

Figure 14. Map showing water-level altitudes and direction of groundwater flow in

alluvial and recessional outwash aquifer (Qago) in tributary subbasins and

vicinity, lower Skagit River basin, Washington, August 2006–September 2008 ...... 27

Figure 15. Map showing water-level altitudes and direction of groundwater flow in

advance outwash aquifer (Qga) in tributary subbasins and vicinity, lower

Skagit River basin, Washington, August 2006–September 2008 ..................... 28

Figure 16. Map showing water-level altitudes and direction of groundwater flow in

inter-glacial alluvial aquifer (Qco) in tributary subbasins and vicinity, lower

Skagit River basin, Washington, August 2006–September 2008 ..................... 29

Figure 17. Map showing water-level altitudes and direction of groundwater flow in older

outwash and alluvial aquifer (Qooa) in tributary subbasins and vicinity, lower

Skagit River basin, Washington, August 2006–September 2008 ..................... 30

Figure 18. Map showing water-level altitudes and direction of groundwater flow in the

sedimentary aquifer (OEc) in tributary subbasins and vicinity, lower Skagit

River basin, Washington, August 2006–September 2008 .............................. 31
v

Figures–Continued

Figure 19. Graph showing mean monthly streamflow (2001–08) for East Fork

Nookachamps Creek at Washington State Department of Ecology

streamflow-gaging station 03G100, lower Skagit River basin, Washington ......... 36

Figure 20. Graph showing daily streamflow for U.S. Geological Survey streamflow-gaging

stations on Nookachamps (12199600), Carpenter (12200684), and Fisher

(12200701) Creeks, lower Skagit River basin, Washington, August 1–15, 2007 ...... 37

Figure 21. Graph showing daily streamflow for U.S. Geological Survey

streamflow-gaging stations on Nookachamps (12199600), Carpenter

(12200684), and Fisher (12200701) Creeks, lower Skagit River basin,

Washington, June 10–25, 2008 ............................................................ 37

Figure 22. Map showing locations of stream sites where streamflow was measured to

determine groundwater discharge and delineate gaining and losing stream

reaches in tributary subbasins and vicinity, lower Skagit River basin,

Washington, August 2007 and June 2008 ................................................ 38

Figure 23. Hydrographs of water levels in well 34N/05E-32P01, stream stage at U.S.

Geological Survey steamflow-gaging station on Nookachamps Creek

(12199600), and precipitation at Sedro-Woolley, lower Skagit River basin,

Washington, April 2007–August 2008...................................................... 39

Figure 24. Hydrographs of water levels in well 33N/04E-28M01, stream stage at U.S.

Geological Survey streamflow-gaging station on Fisher Creek (12200701), and

precipitation at Sedro-Woolley, lower Skagit River basin, Washington, April

2007–August 2008 ........................................................................... 39

Tables

Table 1. Simplified geologic units defined in this study and correlation with previous

investigations .............................................................................. 7

Table 2. Hydrogeologic units defined in this study and correlation with geologic units

defined in this study and previous investigations ....................................... 9

Table 3. Statistical summary of hydraulic conductivity values by hydrogeologic unit in

tributary subbasins and vicinity, lower Skagit River basin, Washington ............ 20

Table 4. Synoptic streamflow measurements used to determine groundwater

discharge and estimates of evaporative loss from lakes in tributary subbasins

and vicinity, lower Skagit River basin, Washington, August 2007 and June

2008 .......................................................................................... 33

Table 5. Synoptic streamflow measurements and estimates of gains and losses in

tributary subbasins, lower Skagit River basin, Washington, August 2007 and

June 2008 .................................................................................... 35

Table 6. Statistical summary of groundwater-level fluctuations and well depth by

hydrogeologic unit in tributary subbasins and vicinity, lower Skagit River basin,

Washington, October 2006 through September 2008.................................... 40

Table 7. Estimated average annual water budget for tributary subbasins, lower 

Skagit River basin, Washington, September 1, 2006, to August 31, 2008 ............ 41
vi

Conversion Factors, Datums, and Acronyms

Conversion Factors

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 0.4047 hectare (ha)

acre 0.004047 square kilometer (km2)

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

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

Flow rate

acre-foot per year (acre-ft/yr) 1,233 cubic meter per year (m3/yr)

foot per day (ft/d) 0.3048 meter per day (m/d)

cubic foot per second (ft3

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

gallon per day (gal/d) 0.003785 cubic meter per day (m3/d)

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

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

°F=(1.8×°C)+32.

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

°C=(°F-32)/1.8.

Datums

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

(NAVD88), referred to in this report as “sea level.”

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD83).

Altitude, as used in this report, refers to distance above or below sea level.

Acronyms

ANUDEM Australian National University Digital Elevation Model

DDMFZ Darington-Devils Mountain Fault Zone

DEM digital elevation model

DNR Washington Department of Natural Resources

Ecology Washington State Department of Ecology

GIS Geographic Information System

GPS Global Positioning System

LiDAR Light Detection and Ranging

NWS National Weather Service

NED National Elevation Dataset

NLVD National Land Cover Database

NWIS USGS National Water Information System

PRISM Parameter-elevation Regressions on Independent Slopes Model

PVC polyvinyl chloride

USGS U.S. Geological Survey
vii

Well-Numbering System

Wells in Washington State are assigned a local well number that identifies each well based on 

its location within a township, range, section, and 40-acre tract. For example, local well number 

33N/04E-02E01 indicates that the well is in township 33 north of the Willamette Base Line, 

and range 4 east of the Willamette Meridian. The numbers immediately following the hyphen 

indicate the section (02) within the township, and the letter following the section (E) gives the 

40-acre tract of the section. The two-digit sequence number (01) following the letter is used to 

distinguish individual wells in the same 40-acre tract. A “D” following the sequence number 

indicates a well that has been deepened. In the plates of this report, wells are identified using 

only the section and 40-acre tract, such as 02E01; the township and range are shown on the 

map borders.

Willamette Meridian

Willamette Base Line

W A S H I N G T O N

Study area

SECTION 02

33N/04E-02E01 ABCD

E F G H

JKLM

N P Q R

R. 4 E.

T.

33

 N.

13456

7 12

18 13

19 24

30 25

31 32 3433 35 36

TOWNSHIP

Diagram showing well numbering system used in Washington.
viii

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Abstract

A study to characterize the groundwater-flow system 

in four tributary subbasins and vicinity of the lower Skagit 

River basin was conducted by the U.S. Geological Survey to 

assist Skagit County and the Washington State Department 

of Ecology in evaluating the effects of potential groundwater 

withdrawals and consumptive use on tributary streamflows.

This report presents information used to characterize the 

groundwater and surface-water flow system in the subbasins, 

and includes descriptions of the geology and hydrogeologic 

framework of the subbasins; groundwater recharge and 

discharge; groundwater levels and flow directions; seasonal 

groundwater-level fluctuations; interactions between aquifers 

and the surface-water system; and a water budget for the 

subbasins.

The study area covers about 247 mi2 along the Skagit 

River and its tributary subbasins (East Fork Nookachamps 

Creek, Nookachamps Creek, Carpenter Creek, and Fisher 

Creek) in southwestern Skagit County and northwestern 

Snohomish County, Washington. The geology of the area 

records a complex history of accretion along the continental 

margin, mountain building, deposition of terrestrial and 

marine sediments, igneous intrusion, and the repeated advance 

and retreat of continental glaciers. A simplified surficial 

geologic map was developed from previous mapping in the 

area, and geologic units were grouped into nine hydrogeologic 

units consisting of aquifers and confining units. A surficial 

hydrogeologic unit map was constructed and, with lithologic 

information from 296 drillers’ logs, was used to produce unit 

extent and thickness maps and four hydrogeologic sections.

Groundwater in unconsolidated aquifers generally flows 

towards the northwest and west in the direction of the Skagit 

River and Puget Sound. This generalized flow pattern is likely 

complicated by the presence of low-permeability confining 

units that separate discontinuous bodies of aquifer material 

and act as local groundwater-flow barriers. Groundwaterflow directions in the sedimentary aquifer likely reflect 

local topographic relief (radial flow from bedrock highs) 

and more regional westward flow from the mountains to 

the Puget Sound. The largest groundwater-level fluctuations 

observed during the monitoring period (October 2006 

through September 2008) occurred in wells completed in the 

sedimentary aquifer, and ranged from about 3 to 27 feet. Water 

levels in wells completed in unconsolidated hydrogeologic 

units exhibited seasonal variations ranging from less than 1 to 

about 10 feet.

Synoptic streamflow measurements made in August 

2007 and June 2008 indicate a total groundwater discharge 

to creeks in the tributary subbasin area of about 13.15 and 

129.6 cubic feet per second (9,520 and 93,830 acre-feet per 

year), respectively. Streamflow measurements illustrate a 

general pattern in which the upper reaches of creeks in the 

study area tended to gain flow from the groundwater system, 

and lower creek reaches tended to lose water. Large inflows 

from tributaries to major creeks in the study area suggest 

the presence of groundwater discharge from upland areas 

underlain by bedrock.

The groundwater system within the subbasins received 

an average (September 1, 2006 to August 31, 2008) of 

about 92,400 acre-feet or about 18 inches of recharge from 

precipitation a year. Most of this recharge (65 percent) 

discharges to creeks, and only about 3 percent is withdrawn 

from wells. The remaining groundwater recharge (32 percent) 

leaves the subbasin groundwater system as discharge to the 

Skagit River and Puget Sound.

Introduction

In Washington State, the availability of water for outof-stream uses must be determined before water can be 

appropriated. This determination is most often made as part 

of an application for a water right; however, certain uses 

are exempted from the water rights permitting system. To 

prevent water withdrawals from impacting other out-of-stream 

Hydrogeologic Framework, Groundwater Movement, 

and Water Budget in Tributary Subbasins and Vicinity, 

Lower Skagit River Basin, Skagit and Snohomish 

Counties, Washington

By Mark E. Savoca, Kenneth H. Johnson, Steven S. Sumioka, Theresa D. Olsen, Elisabeth T. Fasser, and 

Raegan L. Huffman
2 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

and instream uses, Washington State may reserve a specific 

quantity of water in a stream basin for out-of-stream uses 

as part of the regulation establishing minimum instream 

flows (the Instream-Flow Rule). The reservation allows new 

groundwater withdrawals in basins where all available water 

is appropriated. Once the total of new withdrawals equals the 

quantity specified in the reservation, subsequent new uses 

would have to find an alternative source of water, obtain an 

existing water right, or provide compensating mitigation for 

streamflow impacts.

Recent population growth along the Interstate 5 corridor 

near Mount Vernon, Washington, has led to increased water 

use with many new domestic wells serving residents in the 

lower Skagit River basin in areas not served by a regional 

public water system. Planning for future development 

in the lower basin, including the reservation of water for 

new domestic wells, requires identification of areas where 

withdrawals from existing and new wells could adversely 

impact streamflow in the Skagit River or its tributaries. Skagit 

County, as the land-use authority for unincorporated areas 

requires a scientifically credible basis for implementing landuse restrictions to protect instream resources. 

In June 2006, the USGS, in cooperation with Skagit 

County Public Works Department, the Washington State 

Department of Ecology (Ecology), and Skagit County Public 

Utility District No. 1, began a project to characterize the 

groundwater-flow system in the tributary subbasins and 

vicinity of the lower Skagit River basin. A second phase of 

this project will integrate this and other information into a 

numerical flow model to evaluate the effects of potential 

groundwater withdrawals and consumptive use on tributary 

streamflows.

Purpose and Scope

This report presents information used to characterize 

the groundwater-flow system in and around four subbasins 

tributary to the lower Skagit River: East Fork Nookachamps 

Creek, Nookachamps Creek, Carpenter Creek, and Fisher 

Creek. The report describes the hydrogeologic framework 

of the subbasins and vicinity; groundwater recharge and 

discharge; groundwater levels and flow directions; seasonal 

groundwater-level fluctuations; interactions between 

groundwater and the surface-water system; and a water budget 

for the subbasins. 

Description of Study Area

The study area covers about 247 mi2 along the Skagit 

River and its tributary subbasins in southwestern Skagit 

County and northwestern Snohomish County, Washington 

(fig. 1). The Skagit River occupies a large, relatively flat 

alluvial valley that extends across the northern and western 

margins of the study area, and is bounded to the south and 

east by upland and mountainous terrain. The alluvial valley 

primarily is underlain by fluvial sand and gravel deposits 

associated with the present and ancient Skagit River, and 

locally preserved lahar runout deposits originating from 

Glacier Peak, located about 55 mi east-southeast of the study 

area. Upland areas contain laterally discontinuous bodies of 

glacial and interglacial deposits that reflect both terrestrial and 

shallow marine depositional environments. Bedrock consisting 

of a complex assemblage of metamorphic rocks, sedimentary 

units, and igneous rocks underlies the alluvial valley and 

upland areas, and crops out throughout the mountainous 

terrain.

The southwest flowing Skagit River receives 

streamflow from four tributary subbasins that originate 

within the mountainous interior of the study area: East Fork 

Nookachamps Creek, Nookachamps Creek, Carpenter Creek, 

and Fisher Creek. These creeks drain areas of about 37, 28, 

19, and 10 mi2, respectively. The lower reaches of most 

creeks flow year-round, however, intermittent-flow conditions 

are common in middle and upper creek reaches during the 

summer months. Backwater conditions periodically occur 

near the confluence of creeks with the Skagit River. Springs 

are present throughout the study area, and contribute to latesummer baseflow to creeks. Major lakes in the study area 

include Big Lake, Clear Lake, Lake McMurray, Beaver Lake, 

Barney Lake, and Sixteen Lake (fig. 1).

The study area has a temperate marine climate with 

warm, dry summers, and cool, wet winters with snow and 

freezing temperatures common at high altitudes. Temperatures 

are moderated by the Pacific Ocean and Puget Sound, and 

these bodies of water provide an abundant supply of moisture 

for storms that typically approach the area from the west. 

Mean annual precipitation (average annual precipitation for 

the study period September 1, 2006, to August 31, 2008) 

varies across the study area according to distance from the 

Puget Sound and altitude, and ranges from about 30 in. near 

Puget Sound to greater than 120 in. in the mountains to the 

east. Land-surface altitude in the study area ranges from 

about 10 ft in the Skagit River valley to near 4,000 ft in the 

mountainous areas. Normal annual precipitation (average 

annual precipitation for 1971-2000) at Sedro-Woolley is 

46.6 in., and at Mount Vernon is 32.7 in. (National Oceanic 

and Atmospheric Administration, 2007). The distribution 

of precipitation varies throughout the year. Summers (JuneAugust) typically are dry with a normal summer precipitation 

(average “summer” precipitation for 1971–2000) of 6.4 in. 

at Sedro-Woolley and 4.5 in. at Mount Vernon. Winters 

(December–February) are wetter than summers with a 

normal winter precipitation (average “winter” precipitation 

for 1971–2000) of 16.4 in. at Sedro-Woolley and 11.0 in. at 

Mount Vernon. The normal monthly temperature (average 

temperature for selected months for 1971–2000) at these 

locations ranges from about 39 oF in January to about 63 oF in 

August (National Oceanic and Atmospheric Administration, 

2007).
Introduction 3

tac09-9722-0328 Upper Skagit Geo_Fig 01

43210 5 MILES

43210 5 KILOMETERS

Base from U.S. Geological Survey and/or

Washington Division of Geology and Earth Resources

digital data, 1983, 1:100,000

Universal Transverse Mercator projection, Zone 10

Horizontal Datum: North American Datum of 1927 (NAD 27)

Noo kachamps Creek

SNOHOMISH COUNTY

SKAGIT COUNTY

122°20' 122°10'

48°25'

48°20'

R. 3 E. R. 4 E. R. 5 E. R. 6 E.

T.

35

N.

T.

34

N.

T.

33

N.

T.

32

N.

Sk agit Rive r

South Fork Skagit River

Nookachamps Creek

Lake Creek

Carpenter Creek

Lake

Ketchum

Ten

Lake

Devils

Lake

Big

Lake

Sixteen

Lake

Clear

Lake

Lake

McMurray

Beaver

Lake

Barney

Lake

Armstrong

Creek

Pilchuck

Creek

East Fork

Nookachamps Creek

Puget

Sound

Fisher Cr eek

Skagit River

Skagit River

North Fork

Burlington

Mount

Vernon

SedroWoolley

Stanwood

SR

20

SR

20

SR

9

SR

9

SR

534

SR

9

SR

538

SR

536

I

5

I

5

Fisher Creek subbasin

Carpenter Creek subbasin

Nookachamps

Creek subbasin

East Fork Nookachamps Creek subbasin

EXPLANATION

Boundary of tributary 

subbasins

WASHINGTON

Lower Skagit River study area

Tributary subbasins

Figure 1. Location of tributary subbasins and vicinity, lower Skagit River basin, Washington.
4 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

Methods of Investigation

Methods used to compile and analyze information for the 

characterization of the groundwater and surface-water flow 

system in the study area are described in this section. Methods 

used to describe groundwater movement and water budget of 

the study area, are included with the respective sections later 

in this report. 

Well Inventory and Water-Level Measurements

Characterization of the groundwater-flow system relied 

on the analysis of spatially distributed information about 

groundwater levels, and the physical and hydraulic properties 

of the geologic units encountered during well construction. 

This information was obtained through the measurement of 

water levels in wells, and the evaluation of hydrogeologic 

descriptions and well tests from well drillers’ logs. Well 

records were compiled from USGS, Ecology, and Washington 

Department of Natural Resources (DNR) databases to identify 

potential wells to be used in this study. Candidate wells were 

selected for field inventory based on the location and depth 

of the well, and the availability of a driller’s log. The goal 

of the inventory was to obtain an even distribution of wells 

throughout the study area. However, this was not possible 

for the entire study area because of a lack of wells in less 

populated areas. During the field inventory (August through 

October 2006), permission for access was obtained, and 

synoptic water levels were measured in 128 wells (pl. 1). 

Water levels were measured on a monthly basis from October 

2006 through September 2008 in 62 of the inventoried wells 

and 9 new wells constructed for this study (pl. 1). Continuous 

water-level recorders were installed in four of the monthly 

monitoring wells (pl. 1).

Latitude and longitude locations were determined for 

each well using a Global Positioning System (GPS) receiver 

with a horizontal accuracy of one-tenth of a second (about 

10 ft). Light Detection and Ranging (LiDAR) data were 

used to determine the altitude of land surface at each well, 

and for the computation of water-level altitudes. LiDAR 

data were collected and processed by a private vendor 

under contract with the USGS. Vertical accuracy (typically 

±1 ft) was evaluated for internal consistency (repeatability), 

and conformance with independent ground-control points. 

Water level, reported as depth to water below land surface, 

was measured using a calibrated electric tape or graduated 

steel tape, both with accuracy to 0.01 ft. All water-level 

measurements were made by USGS personnel according 

to standardized techniques of the USGS (Drost, 2005). 

New wells were installed using direct-push technology and 

were constructed of 1.5 in. polyvinyl chloride (PVC) pipe, 

and 5 or 10 ft of 0.01- to 0.02-in. slotted PVC screen with 

integrated sand-filter pack. Sediment cores were continuously 

collected as the drive casing was advanced. Non-water 

bearing sediments were encountered at four locations; cores 

were collected, however, wells at these locations were not 

constructed (pl. 1).

The spatial distribution of hydrogeologic data from 

inventoried and newly constructed wells was insufficient 

to fully evaluate the high degree of spatial variability of 

hydrogeologic units in the study area. Therefore, an additional 

168 wells with available drillers’ logs were selected from 

USGS, Ecology, and DNR databases to help refine the 

hydrogeologic framework in areas where data from the 

original set of wells were limited (pl. 1). The approximate 

location of most of the additional wells had been previously 

established by DNR; these and the remaining well locations 

were established using the well address listed on the drillers’ 

log and the Skagit County Assessors tax parcel database. Well 

information collected during the field inventory, monthly 

monitoring network, and construction of the hydrogeologic 

framework were entered into the USGS National Water 

Information System (NWIS) database and published in Fasser 

and Julich (2009). 

Hydrogeology

The surficial geology for the tributary subbasins 

was compiled from previous mapping by Schuster (2000; 

1:100,000), Dragovich and others (2002; 1:24,000), and 

Dragovich and DeOme (2006; 1:24,000). No attempt was 

made to reconcile matching of surficial geologic units across 

map boundaries; however, in some areas, modifications 

were made to unit designations from previous maps based 

on stratigraphic evidence obtained during this investigation, 

primarily drillers’ logs for field located wells. Differences in 

geologic unit nomenclature and map scales were addressed 

through the use of simplified stratigraphy and consistent 

nomenclature that is based on the work of Dragovich and 

others (2002). When possible, geologic units were grouped 

under a single new unit designation based on similarities in 

lithology and stratigraphic position to allow for a simplified 

and consistent representation of geology across the study area. 

This process resulted in the grouping of 62 geologic units from 

previous mapping into 18 geologic units, and the production 

of a simplified surficial geologic map for this study (pl. 1). 

These geologic units were grouped into nine hydrogeologic 

units, consisting of aquifers and confining units, on the basis 

of lithologic (depositional facies, grain size, and sorting) 

and hydrologic (hydraulic conductivity and unit geometry) 

characteristics. A map of the surficial distribution of these 

hydrogeologic units was constructed for this study (pl. 2). The 

hydrogeologic units identified in this report do not in all cases 

correspond to geologic time-stratigraphic deposits.

Hydrogeologic sections and unit extent and thickness 

maps of the tributary subbasin groundwater system were 

constructed based on: (1) the simplified surficial geology, 

(2) geologic and hydrogeologic interpretations, maps, and 

sections from previous investigations, and (3) geologic unit 
Hydrogeologic Framework 5

delineations made by this and previous investigations using 

information collected from 296 wells. Hydrogeologic unit top 

and extent information was used to create digital elevation 

model (DEM) surfaces in a Geographic Information System 

(GIS) database at a 30 ft cell size. The interpolation method 

for creating each hydrogeologic unit surface in GIS was based 

on the Australian National University Digital Elevation Model 

(ANUDEM) procedure developed by Hutchinson (1989), 

using well unit picks and extent maps. Each hydrogeologic 

unit surface was constrained to the National Elevation Dataset 

(NED) 30 ft DEM for land surface where the unit cropped out.

Thickness maps were constructed for each hydrogeologic 

unit using GIS to calculate the difference between the 

altitude of the interpolated top of the unit and the altitude 

of the interpolated top of units underlying it. If part of a 

hydrogeologic unit was interpolated to extend above the top 

of an overlying hydrogeologic unit, then minimum thickness 

values for the overlying unit were used in the calculations 

to adjust the altitude of the top of the underlying unit where 

needed. Unconsolidated hydrogeologic unit thicknesses were 

constrained by bedrock-surface data in areas with limited 

subsurface information. Average minimum thicknesses were 

used to represent occurrences of unconsolidated hydrogeologic 

units overlying bedrock in areas of limited subsurface data.

In developing the hydrogeologic framework, the original 

data interpretations were honored as much as possible. 

The resulting interpolated hydrogeologic unit surfaces, and 

calculated unit thickness, were compared to the original 

map, section, and well interpretations, and adjusted to more 

accurately reflect the original interpretations when necessary. 

The areas where the calculated units are less accurate are in 

areas of (1) data gaps, (2) where the surficial geology changes 

abruptly, and (3) where the well locations are less accurate. 

Streamflow

Characterization of the surface-water flow system in the 

tributary subbasins was facilitated by the installation of three 

USGS streamflow-gaging stations to measure streamflow on 

Nookachamps, Carpenter, and Fisher Creeks; streamflow on 

East Fork Nookachamps Creek was already being measured 

at an Ecology streamflow-gaging station (pl. 1). Two sets of 

synoptic streamflow measurements were made in August 2007 

and June 2008 at 27 sites along the four major creeks and 

their tributaries (pl. 1) to quantify surface water leaving the 

tributary subbasins during low-flow conditions, and to identify 

gaining and losing creek reaches. Streamflow measurements at 

USGS gaging stations and synoptic sites were made by USGS 

personnel, assisted by Skagit County Public Works staff, 

using Price pygmy or AA current velocity meters according 

to standardized techniques of the USGS (Rantz, 1982). 

Streamflow data from the Ecology gaging station on East Fork 

Nookachamps Creek were obtained from the Washington 

State Department of Ecology (2009). The USGS rates the 

accuracy of discharge measurements based on the equipment, 

character of the measurement section, number of observations, 

stability of stage, wind, and the 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, ratings of “fair” indicate the measurements 

are within 8 percent of actual values, and ratings of “poor” 

indicate the measurements are not within 8 percent of actual 

values (assumed to be within 11 percent of actual values for 

this study).

Hydrogeologic Framework

This section describes the geology and hydrogeologic 

framework, which define the physical, lithologic, and 

hydrologic characteristics of the hydrogeologic units that 

compose the groundwater system in the tributary subbasins. 

An understanding of these characteristics is important in 

determining the occurrence, movement, and availability of 

groundwater within the aquifer system, and the exchange of 

water between the aquifer system and surface-water features. 

Geologic Setting

A brief summary of major geologic events in the study 

area is given below, and is based on the work of Hansen and 

Mackin (1949), Easterbrook (1969), Marcus (1981), Johnson 

(1982), Booth (1994), Tabor (1994), Dragovich, and Grisamer 

(1998), Dragovich and others (2002), and Dragovich and 

DeOme (2006). The geology of the study area records a 

complex history of accretion along the continental margin, 

mountain building, deposition of terrestrial and marine 

sediments, igneous intrusion, and the repeated advance and 

retreat of continental glaciers. Bedrock in the study area 

consists of: (1) complex assemblages of faulted and folded 

low-grade metamorphic rocks formed during Late Jurassic 

or Early Cretaceous continental margin subduction; (2) 

sedimentary units deposited in alluvial fan, braided stream, 

and near shore shallow marine settings; and (3) igneous 

intrusive and extrusive rocks that occur as dikes, sills, 

domes, and flows (pyroclastic and lava). Metamorphic rocks 

were likely brought to the surface by Mid-Cretaceous thrust 

faulting and Tertiary displacement along the Darington-Devils 

Mountain Fault Zone (DDMFZ; extends from northwest to 

southeast across the central part of the study area). Tertiary 

vertical or oblique offset along the DDMFZ likely provided 

the topographic relief necessary to produce the alluvial fan and 

braided stream deposits in the sedimentary units. The presence 

of igneous rocks within fault-bounded blocks of the DDMFZ 

suggests that emplacement of these rocks was strongly 

controlled by pre-existing strands of the DDMFZ. Evidence of 

Quaternary displacement along the DDMFZ and other faults 

in the study area has not been widely documented. Dragovich 

and DeOme (2006) offer evidence of Holocene offset along 
6 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

a mile-long portion of the main strand of the DDMFZ 

located north of Lake McMurray. Surficial and subsurface 

interpretations suggest a lack of Quaternary displacement 

along faults else where in the study area (Dragovich and 

others, 2002; Dragovich and DeOme, 2006).

Continental glaciers advanced into Skagit County 

several times during the Pleistocene Epoch. This ice, part of 

the Cordilleran ice sheet, is known as the Puget Lobe. The 

most recent period of glaciation, the Vashon Stade of Fraser 

glaciation, began about 17,000 years ago when the continental 

ice sheet in Canada expanded, and the Puget Lobe advanced 

southward into western Skagit County, eventually covering 

the entire Puget Sound basin before halting and retreating. 

During the Everson Interstade, beginning about 13,500 years 

ago, the climate warmed and the lobe wasted back allowing 

marine waters to enter the Puget Sound basin, which had been 

depressed due to glacial isostatic loading. Marine inundation 

buoyed the retreating ice and produced marine and estuarine 

conditions in the study area. Postglacial filling of the Skagit 

River valley, which had been excavated by subglacial melt 

water, was accomplished through Holocene fluvial, estuarine, 

and deltaic deposition, and volcanic lahar deposits originating 

from Glacier Peak.

Unconsolidated deposits of glacial and interglacial 

origin are present throughout the study area. A typical 

glacial sequence progresses from advance outwash, to till, 

to recessional outwash. Fluvial, lacustrine, bog and marsh 

depositional environments were common during interglacial 

periods. Beneath these unconsolidated deposits of varying 

thickness are bedrock units that are exposed in large parts of 

the glacial upland and within the mountains along the eastern 

margin of the study area. Descriptions of the unconsolidated 

and bedrock units present in the study area are given below.

Geologic Units

The simplified geologic representation of the tributary 

subbasins developed for this study consists of 18 geologic 

units (table 1) that are described below and are shown on the 

surficial geologic map (pl. 1) constructed for this investigation. 

Quaternary (Holocene to latest Pleistocene) nonglacial 

deposits include: 

Alluvium (Qa).—Alluvium consisting of active or 

abandoned channel and overbank deposits associated with the 

present and ancient Skagit River. Channel deposits typically 

are coarse grained and consist of loose sand and gravel. 

Overbank deposits consist mostly of soft to stiff, stratified 

sand, silt, and clay and minor amounts of peat. Floodplain 

splay deposits are composed of sand and gravel and form 

subtle to distinct levees adjacent to or near the present Skagit 

River channels. Alluvial-fan deposits are composed of poorly 

sorted, massive to weakly stratified, soft to stiff, gravel, silt, 

and sand that are mostly of debris-flow or debris-torrent 

origin. Beach deposits consist of loose, moderately to wellsorted sand and gravel along modern shorelines that locally 

include wave-worn shell fragments. Nearshore deposits in 

estuarine or tidal flat environments are composed of loose or 

soft, sand, silt, and clay with various admixtures of organic 

material.

Peat (Qp).—Soft fibrous to woody peat, muck, and 

organic silt accumulated in bogs and swamps of abandoned 

channels, kettles, and shallow oxbow lakes or other 

depressions; commonly poorly stratified to unstratified.

Landslide deposits (Qls).—Landslide deposits

consisting of mostly poorly sorted, unstratified, soft to 

cohesive diamicton composed of boulders, cobbles, and 

gravel in a soft sand, silt, or clay matrix. Mode of origin 

includes slump-earth flows, debris slumps or flows, and rock 

avalanches (talus) and also includes a few alluvial fan and 

thick colluvial deposits.

Lahar runout deposits (Qvl)—Lahar runout deposits 

consisting of loose, well-sorted, massive to normally 

graded, medium to fine grained, volcanic sand. These 

deposits are interpreted by Dragovich and others (2000) as 

hyperconcentrated flood or lahar runout deposits, originating 

from a Glacier Peak eruptive event(s), that followed an 

ancestral channel of the Skagit River, and are preserved in the 

lower Skagit River Valley within the study area.

Quaternary (Pleistocene) glacial and non-glacial deposits 

include: 

Everson glaciomarine drift (Qgdme).—Glaciomarine 

drift deposits consisting of soft (when wet) to stiff (when dry) 

diamicton locally containing vertical jointing or desiccation 

cracks, and lenses or layers of loose outwash sand and gravel. 

Dragovich and others (2002) identified two distinct facies: 

(1) a clast-rich diamicton that is massive or crudely stratified 

and composed of clay, gravel, sand and silt, with abundant 

dropstones, and (2) a silt- and clay-rich deposit that is massive 

or, less commonly, occurs as varved or laminated rhythmites 

and is composed of moderately to well-sorted silt, clay, and 

sand that lacks or contains only rare gravel, cobble, or boulder 

dropstones.

Everson recessional outwash (Qgoe).—Terrestrial to 

marine recessional and deltaic outwash deposits consisting 

of loose sand, gravel, with local concentrations of cobbles, 

boulders, and lenses of silt. Recessional outwash deposits vary 

from non-bedded to subhorizontal beds a few feet thick that 

are crudely defined by variations in cobble, gravel, and sand 

content, and contain sedimentary structures indicative of a 

fluvial braided-channel environment. Deltaic outwash deposits 

are moderately to well-sorted, and beds typically are inches 

to several feet thick. Dragovich and others (2002) identified 

high-amplitude planar foreset beds, indicative of deltaic 

deposition in the study area.

Everson glaciomarine outwash (Qgome).—

Glaciomarine outwash deposits consisting of loose gravel, 

sand, and silt, and occasional silt beds and laminated to varved 

silt-sand couplets. Average grain size is smaller in this unit 

than in terrestrial or deltaic outwash (Qgoe). Interlayering 

with glaciomarine drift indicates submarine deposition for 

most areas mapped as unit Qgome, although it may locally 
Hydrogeologic Framework 7

include terrestrial outwash deposits (Dragovich and others, 

2002). Beach deposits of loose sand and gravel are included in 

this unit and are locally associated with topographic benches 

or subtle wave-cut terraces that reflect temporary beach 

reworking of the substrate during isostatic emergence.

Vashon Till (Qgtv).—Till composed of non-stratified, 

unsorted, dense to very dense diamicton consisting of clay, 

silt, sand, and gravel in various proportions, with scattered 

cobbles and boulders and rare to locally common layers and 

lenses of sand and/or gravel. Vashon till commonly underlies 

glaciomarine drift in the western part of the study area, and 

unconformably overlies bedrock, advance outwash, and less 

commonly, older glacial and non-glacial units.

Vashon advance outwash (Qgav).—Advance outwash 

deposits of moderately to very dense, medium to coarse sand 

and gravel, with local silt and clay interbeds. Advance outwash 

deposits are moderately stratified to stratified, moderately 

to well sorted, thinly to very thickly bedded (subhorizontal 

or cross-stratification), and contain sedimentary structures 

indicative of fluvial deposition. Advance outwash commonly 

is overlain by till along a sharp contact, and conformably 

overlies or is complexly interlayered with older glacial and 

nonglacial units where present.

Glaciolacustrine and distal outwash deposits (Qglv).—

Glaciolacustrine and distal outwash deposits of glacial and (or) 

nonglacial origin, composed of moderately dense to dense, 

well sorted, clay and silt that are very thinly to very thickly 

bedded, and contain varying amounts of sand and gravel, and 

locally contains thick beds of massive, clast-rich diamicton, 

and scattered dropstones. Clay and silt deposits represent 

low-energy lacustrine and distal fluvial facies; diamicton and 

dropstones likely resulted from iceberg melt-out. 

Table 1. Simplified geologic units defined in this study and correlation with previous investigations.

[Definitions of simplified geologic units defined in this study are shown on plate 1]

Period Epoch

Simplified geologic 

units defined in 

this study

Geologic units in 

Schuster (2000) 

1:100,000

Geologic units in 

Dragovich and others 

(2002) 1:24,000

Geologic units in 

Dragovich and DeOme 

(2006) 1:24,000

Quaternary

 Holocene to latest

Pleistocene

Qa Qa Qac

 Qas Qaf Qb Qf 

Qoa Qoas

af Qb Qn Qas Qasl Qaf Qa Qoa

Qp Qp Qm Qp Qp

Qls Qls Qta Qls Qls

Qvl Qvlk Qvl

Pleistocene

Qgdme Qgdme Qgoc Qgdme Qgdmec Qgdmed Qgdme Qgle

Qgoe Qgo Qgog Qgos Qgoe Qgode Qgoge Qgike Qgode Qgose

Qgome QgomQgome Qgome Qgomee

Qgtv Qgt Qgtv Qgtv

Qgav Qga Qgas Qgav Qgav

Qglv Qgat Qglv Qglv

Qco Qco Qco Qco

ot ot ot

oo oo oo

Qcw Qcw Qcw

Tertiary

Oligocene

to Eocene

OEcb OEcb OEnb OEcbs OEcbcg OEcbs OEcbcg

Evr Evr Evr Evr Eib

Ecbc Ecc Ecb Ecc

Jurassic and 

Pennsylvanian

JTP

Jphd Jmvh

 Jshs JTRmte

JMmtt MZuh

 MZmmh

Pigbdt 

Jmvh Juh Juhl Jhmch

Jmvh Juh JTRmct JTRmvt

Pzi
8 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

Olympia nonglacial deposits (Qco).—Olympia 

nonglacial deposits composed of dense to very dense, well 

sorted, sand, gravelly sand, silt, clay, and peat that are very 

thinly to thickly bedded, with minor gravel and cobble gravel, 

and rare diamicton of probable mass-flow origin (Dragovich 

and others, 2002). Organic material (logs or wood fragments) 

is common and differentiates the Olympia from the overlying 

glaciolacustrine and distal outwash deposits. Olympia deposits 

contain sedimentary structures indicative of a meandering 

river environment.

Older till (ot).—Older till consisting of dense to very 

dense diamicton composed of clay, silt, sand, and gravel in 

various proportions, with scattered cobbles and boulders; 

may locally include glaciomarine drift. Dragovich and others 

(2002) do not assign a formal geologic symbol to this unit, 

which indicates the tentative nature of the correlation with 

deposits of the Possession Glaciation (60,000–80,000 yr B.P.). 

Older outwash (oo).—Older outwash consisting of 

glacial or nonglacial deposits composed of sand and gravel 

with varying amounts of silt and clay. Dragovich and others 

(2002) do not assign a formal geologic symbol to this unit, 

which indicates the tentative nature of the correlation with 

deposits of the Possession Glaciation (60,000–80,000 yr B.P.).

Whidbey nonglacial deposits (Qcw).—Whidbey 

nonglacial deposits of sand with interbeds of silt, clay, and 

local gravel lenses; peat and wood are common. Hansen and 

Mackin (1949) interpreted the depositional environment as 

slowly aggrading meandering streams and adjacent flood 

plains.

Tertiary (Oligocene to Eocene) sedimentary and igneous 

rocks include:

Rocks of Bulson Creek (OEcb).—The rocks of Bulson 

Creek consist of a conglomerate and sandstone facies. The 

conglomerate facies is composed of poorly to rarely well 

indurated pebble and cobble conglomerate, and contains lesser 

interbeds of pebbly sandstone, siltstone, and minor diamictite 

(debris flows), and coal. The sandstone facies is composed 

of sandstone with interbeds of pebbly sandstone, siltstone, 

conglomerate, coal, and shale. Marcus (1981) concluded 

that the conglomerate facies was deposited in an alluvial fan 

to braided river environment. Dragovich and others (2002) 

suggest the sandstone facies was deposited in a nearshore or 

shallow marine environment.

Volcanic rocks (Evr).—Rhyolite, andesite, and basalt 

occur as pyroclastic ash flow tuffs, lava flows, domes, dikes, 

sills, and breccias. Lahar deposits (sandstones, siltstones, and 

conglomerates) are locally interbedded with rhyolitic tuffs, 

breccias, and very thin coal beds. Age and field relations 

indicate that andesites are contemporaneous with deposition 

of the Bulson Creek sandstone facies (Dragovich and DeOme, 

2006). 

Chuckanut Formation (Ecbc).—The Chuckanut 

Formation consists of alternating intervals of coarse-grained 

(sandstone and minor conglomerate) and fine-grained 

(mudstone, fine-grained sandstone, and siltstone) deposits. 

These upward-fining cycles have been interpreted to represent 

a river and adjacent flood-plain depositional environment 

(Johnson, 1982).

Jurassic to Pennsylvanian low-grade metamorphic rocks:

Metamorphic rocks (JTP).—Rocks of the HelenaHaystack melange and Trafton sequence are composed 

of complex assemblages of faulted and folded low-grade 

metasediments, metavolcanics, and meta-intrusives, formed 

as a result of continental margin subduction during the Late 

Jurassic or Early Cretaceous. The exhumation of these rocks 

from the subduction zone was likely accomplished by midCretaceous thrust faulting; followed by Tertiary displacement 

along the DDMFZ (Tabor, 1994; Dragovich and others, 2002; 

Dragovich and DeOme, 2006). 

Hydrogeologic Units

The geologic units defined for this study were grouped 

into hydrogeologic units, consisting of aquifers and confining 

units (table 2) on the basis of lithologic (depositional facies, 

grain size, and sorting) and hydrologic (hydraulic conductivity 

and unit geometry) characteristics. The hydrogeologic 

units defined in this study are similar to those defined and 

used by other investigations in areas adjacent to this study 

(Thomas and others, 1997; Dragovich and Grisamer, 1998; 

GeoEngineers, 2003). 

An aquifer is saturated geologic material that is 

sufficiently permeable to yield water in significant quantities 

to a well or spring, whereas a confining unit has low 

permeability that restricts the movement of groundwater and 

limits the usefulness of the unit as a water source. Unconfined 

and confined aquifer conditions are present in the tributary 

subbasins groundwater system. Unconfined or “water-table” 

conditions occur when the upper surface of the saturated zone 

is at atmospheric pressure and is free to rise and decline in 

response to changes in groundwater recharge and discharge. 

The position of the water table is represented by water levels 

in shallow wells. Confined or “artesian” conditions occur 

when an aquifer is overlain by a less permeable confining 

unit and the groundwater is under pressure greater than 

atmospheric pressure. Water in a tightly cased well drilled into 

a confined aquifer will rise to a height corresponding to the 

hydraulic head (the potentiometric surface) of the confined 

groundwater at that location. If the hydraulic head is sufficient 

to raise the water above land surface, the well will flow and 

is called a flowing artesian well. The potentiometric surface 

in a confined aquifer is analogous to the water table in an 

unconfined aquifer. It fluctuates in response to changes in 

recharge and discharge, however, unlike the water table, the 

potentiometric surface is higher in altitude than the top of the 

confined aquifer. 

Glacial deposits generally are heterogeneous, and 

although a glacial aquifer may be composed primarily of 

sand or gravel, it may locally contain varying amounts 

of clay or silt. Conversely, a confining layer composed 

predominantly of silt or clay, may contain local lenses of 

coarse material. These small-scale variations in lithology may 

influence the occurrence and movement of groundwater at 

a scale that is likely too small to be adequately represented 

by the hydrogeologic framework constructed for this 
Hydrogeologic Framework 9

Table 2. Hydrogeologic units defined in this study and correlation with geologic units defined in this study and previous 

investigations.

[Definitions for hydrogeologic units defined in this study are shown on plate 2]

Period Epoch Hydrogeologic units 

defined in this study

Simplified 

geologic units 

defined in 

this study

Geologic units in 

Schuster (2000)

Geologic units in 

Dragovich and 

others (2002)

Geologic units in 

Dragovich and 

DeOme (2006)

Quaternary

Holocene to

Pleistocene

Qago 

Alluvial and recessional 

outwash aquifer 

Qa Qvl Qgome

Qgoe 

Qa Qac Qas Qaf 

Qb Qf Qoa Qoas 

Qvlk Qgom

Qgome Qgo 

Qgog Qgos

af Qb Qn Qas

 Qasl

Qaf Qvl Qgome

Qgomee Qgoe

Qgode

Qa Qoa Qgoge

Qgike

 Qgode 

Qgose

Pleistocene

Qgt

Till confining unit Qls Qgdme

 Qgtv

Qp Qls Qta Qgdme 

Qgoc Qgt

Qm Qp Qls Qgdme

Qgdmec Qgdmed

Qgtv

Qp Qls Qgdme 

Qgle Qgtv

Qga

Advance outwash 

aquifer

Qgav Qga Qgas Qgav Qgav

Qgl

Glaciolacustrine 

and distal outwash 

confining unit

Qglv Qgat Qglv Qglv

Qco

Inter-glacial 

alluvial aquifer

Qco Qco Qco Qco

Qot

Older till 

confining unit

ot ot ot

Qooa

Older outwash and 

alluvial aquifer

oo Qcw Qcw oo Qcw oo

Tertiary

Oligocene to 

 Eocene

OEc

Sedimentary aquifer OEcb

 Ecbc OEcb OEnb Ecc OEcbs OEcbcg Ecb OEcbs OEcbcg Ecc

Tertiary to 

Pennsylvanian 

EJTP

Igneous and 

metamorphic 

bedrock unit

Evr JTP

Jphd Jmvh Jshs

JTRmte

 JMmtt 

MZuh MZmmh

Pigbdt

EvrJmvh Juh Juhl

Jhmch

Evr Eib Jmvh Juh

JTRmct JTRmvt

Pzi

study. Local-scale variability in the distribution of glacial 

depositional facies often results in the formation of spatially 

discontinuous units of varying thickness. Therefore, most units 

are not aerially contiguous throughout the study area, and unit 

thickness may vary considerably over short distances. Glacial 

and older non-glacial deposits are interpreted as largely absent 

within the Skagit River valley to a depth of about 300 ft 

below sea level, likely due to removal by southward flowing 

subglacial melt water, prior to subaerial exposure of the 

glacier bed during ice recession (Booth, 1994; Dragovich and 

others, 1994). This interpretation is supported by the absence 

of glacial and older non-glacial deposits in wells located 

along the Skagit River valley, and similar interpretations 

from previous investigations (Dragovich and Grisamer, 1998; 

GeoEngineers, 2003). Infilling of the Skagit River valley was 

accomplished through the accumulation of Holocene fluvial, 

estuarine, and deltaic deposits, and volcanic lahar deposits 

originating from Glacier Peak. 
10 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

Bog and marsh deposits (Qp) typically are thin (less 

than 10 ft), discontinuous, and have a small areal extent in 

the study area. These deposits likely have little influence on 

the regional hydrologic system and are not designated as a 

hydrogeologic unit in this study. Nine hydrogeologic units 

are recognized in the study area (table 2 and pl. 2) and their 

lithologic and hydrologic characteristics are described below.

Alluvial and recessional outwash aquifer (Qago).—

The alluvial and recessional outwash aquifer is present 

throughout the Skagit River valley (Qa and Qvl, pl. 1) and in 

discontinuous or isolated bodies in glacial upland areas (Qgoe

and Qgome, pl. 1) (fig. 2). The aquifer consists of sand, gravel, 

and cobbles with minor lenses of silt and clay. Thicknesses 

of Qago typically range from 10 to 50 ft in upland areas, and 

from 200 to 450 ft in the Skagit River valley. Groundwater 

in this aquifer is unconfined where it is not fully saturated 

or exposed at land surface, however, confined conditions 

are likely where it is fully saturated and overlain by the till 

confining unit (Qgt).

Till confining unit (Qgt).—The till confining unit is 

present at land surface throughout the glacial upland area 

and as thin, discontinuous bodies in the mountains along the 

eastern margin of the study area (fig. 3). This low-permeability 

unit is composed of marine and terrestrial glacial diamicton 

(Qgdme, and Qgtv) and poorly sorted landslide deposits (Qls). 

The till confining unit consists of various proportions of clay, 

silt, sand, gravel, cobbles, and boulders, with locally occurring 

sand and gravel lenses capable of providing water for domestic 

use. Thicknesses of Qgt vary widely, but generally range from 

10 to 100 ft, and exceed 300 ft in places (fig. 3).

Advance Outwash Aquifer (Qga).—The advance 

outwash aquifer is present in the subsurface throughout 

large parts of the glacial upland (fig. 4). Surface exposures 

of the unit are limited to a few steep slopes and along the 

walls of deeply incised stream valleys. The unit consists 

mostly of sand and gravel with minor amounts of silt, and 

scattered layers of pebble-cobble gravel and local silt and clay 

interbeds. The thickness of Qga typically ranges from 10 to 

100 ft, but exceeds 200 ft in places. In most of the study area, 

groundwater in this aquifer is confined by the overlying till 

confining unit (Qgt), however, unconfined conditions may 

occur locally where it is not fully saturated or is exposed at 

land surface.

Glaciolacustrine and distal outwash confining unit 

(Qgl).—The glaciolacustrine and distal outwash confining 

unit is present in the subsurface throughout much of the 

glacial upland in the northern part of the study area, and in 

discontinuous or isolated bodies in upland areas to the south 

(fig. 5). Surface exposures of the unit are limited to a few 

steep slopes and along the walls of deeply incised stream 

valleys. This low-permeability unit consists of layers of clay 

and silt that contain varying amounts of sand and gravel with 

occasional diamicton and dropstones. The unit commonly 

thickness ranges from 10 to 50 ft; however, thicknesses exceed 

100 ft in places. 

Inter-glacial alluvial aquifer (Qco).—The inter-glacial 

alluvial aquifer is present in the subsurface along the northern 

and western periphery of the glacial upland, and in a few 

isolated bodies in the upland interior (fig. 6). Surface exposures 

of the unit occur along the southern edge of the Skagit River 

valley. The unit consists primarily of sand, gravel, silt, and 

clay, with minor lenses of gravel and cobbles, and commonly 

thickness ranges from 10 to 50 ft; however, thicknesses exceed 

100 ft in places. In most of the study area, the inter-glacial 

alluvial aquifer is overlain by either the glaciolacustrine-distal 

outwash (Qgl) or till (Qgt) confining units, and groundwater 

occurs under confined conditions. Unconfined conditions occur 

in limited areas where the aquifer may not be fully saturated or 

where it is exposed at land surface.

Older till confining unit (Qot).—The presence of the 

older till confining unit in the subsurface along the western 

periphery of the glacial upland (fig. 7) is based on the 

identification of glacial till deposits in 12 wells, and subsurface 

geologic interpretations from Dragovich and others (2002). 

Deposits associated with the older till confining unit were 

not identified in any of the other wells used in this study 

and substantial uncertainty exists about the actual extent 

and thickness of this unit in the remainder of the study area. 

The potential presence of this unit in the subsurface along 

the northern periphery of the glaciated upland was inferred 

based on the units occurrence in the sediments to the south 

(Dragovich and others, 2002), and the need to characterize 

areas of residual sediment thickness between the base of the 

overlying inter-glacial alluvial aquifer and the underlying 

top of bedrock. Limited well data indicate that thicknesses of 

Qot typically range from 10 to 20 ft, and locally exceed 50 ft. 

This low-permeability unit is composed of terrestrial glacial 

diamicton consisting of various proportions of clay, silt, sand, 

and gravel, with scattered cobbles, and boulders.

Older outwash and alluvial aquifer (Qooa).—The 

presence of the older outwash and alluvial aquifer in the 

subsurface along the western periphery of the glacial upland 

(fig. 8) is based on the identification of older outwash and 

alluvial deposits in eight wells, and subsurface geologic 

interpretations from Dragovich and others (2002). Deposits 

associated with the older outwash and alluvial aquifer were 

not identified in any of the other wells used in this study 

and substantial uncertainty exists about the actual extent 

and thickness of this unit in the remainder of the study area. 

The potential presence of this unit in the subsurface along 

the northern periphery of the glaciated upland was inferred 

based on the unit’s occurrence in the sediments to the south 

(Dragovich and others, 2002), and the need to characterize 

areas of residual sediment thickness between the base of the 

overlying older till confining unit and the underlying top of 

bedrock. The unit is composed of glacial (oo) and non-glacial 

(Qcw) alluvial deposits and consists primarily of sand, and 

gravel, with varying amounts of silt and clay. Limited well data 

indicate thicknesses of Qooa typically range from 50 to 100 ft, 

and locally exceed 200 ft (fig. 8). Groundwater in this aquifer 

is confined by the overlying older till confining unit (Qot).
Hydrogeologic Framework 11

tac09-9722-0328 Upper Skagit Geo_Fig 02

122°20' 122°10'

48°25'

48°20'

R.3 E. R.4 E. R.5 E. R.6 E.

T.

35

N.

T.

34

 N.

T.

33

 N.

T.

32

 N.

0 1 2 3 4 5 MILES

43210 5 KILOMETERS

Base from U.S. Geological Survey and/or

Washington Division of Geology and Earth Resources

digital data, 1983, 1:100,000

Universal Transverse Mercator projection, Zone 10

Horizontal Datum: North American Datum of 1927 (NAD 27)

EXPLANATION

Well used to determine extent and

 thickness of aquifer—See plate 1

0 – 50

51 – 100

101 – 200

201 – 300

301 – 450

Extent and thickness of alluvial and recessional Bedrock outcrop

 outwash aquifer (Qago), in feet Boundary of tributary subbasin

Figure 2. Extent and thickness of alluvial and recessional outwash aquifer (Qago) in tributary subbasins and 

vicinity, lower Skagit River basin, Washington.
12 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

tac09-9722-0328 Upper Skagit Geo_Fig 03

122°20' 122°10'

48°25'

48°20'

R.3 E. R.4 E. R.5 E. R.6 E.

T.

35

N.

T.

34

 N.

T.

33

 N.

T.

32

 N.

Base from U.S. Geological Survey and/or

Washington Division of Geology and Earth Resources

digital data, 1983, 1:100,000

Universal Transverse Mercator projection, Zone 10

Horizontal Datum: North American Datum of 1927 (NAD 27)

Well used to determine extent and 

 thickness of confining unit—See plate 1

5 – 50

51 – 100

101 – 200

201 – 300

301 – 541

Extent and thickness of till confining 

 unit (Qgt), in feet

EXPLANATION

Bedrock outcrop

Boundary of tributary subbasin

R.5 E. R.6 E.

0 1 2 3 4 5 MILES

43210 5 KILOMETERS

Figure 3. Extent and thickness of till confining unit (Qgt) in tributary subbasins and vicinity, lower Skagit River 

basin, Washington.
Hydrogeologic Framework 13

tac09-9722-0328 Upper Skagit Geo_Fig 04

122°20' 122°10'

48°25'

48°20'

R.3 E. R.4 E. R.5 E. R.6 E.

T.

35

N.

T.

34

 N.

T.

33

 N.

T.

32

 N.

0 1 2 3 4 5 MILES

43210 5 KILOMETERS

Base from U.S. Geological Survey and/or

Washington Division of Geology and Earth Resources

digital data, 1983, 1:100,000

Universal Transverse Mercator projection, Zone 10

Horizontal Datum: North American Datum of 1927 (NAD 27)

Well used to determine extent and 

 thickness of aquifer—See plate 1

5 – 50

51 – 100

101 – 200

201 – 300

301 – 331

Extent and thickness of advance outwash 

 aquifer (Qga), in feet

EXPLANATION

Bedrock outcrop

Boundary of tributary subbasin

Figure 4. Extent and thickness of advance outwash aquifer (Qga) in tributary subbasins and vicinity, lower 

Skagit River basin, Washington.
14 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

tac09-9722-0328 Upper Skagit Geo_Fig 05

122°20' 122°10'

48°25'

48°20'

R.3 E. R.4 E. R.5 E. R.6 E.

T.

35

N.

T.

34

 N.

T.

33

 N.

T.

32

 N.

0 1 2 3 4 5 MILES

43210 5 KILOMETERS

Base from U.S. Geological Survey and/or

Washington Division of Geology and Earth Resources

digital data, 1983, 1:100,000

Universal Transverse Mercator projection, Zone 10

Horizontal Datum: North American Datum of 1927 (NAD 27)

5 – 50

51 – 100

101 – 200

201 – 239

Extent and thickness of glaciolacustrine and 

 distal outwash confining unit (Qgl), in feet

Well used to determine extent and 

 thickness of confining unit—See plate 1

EXPLANATION

Bedrock outcrop

Boundary of tributary subbasin

Figure 5. Extent and thickness of glaciolacustrine and distal outwash confining unit (Qgl) in tributary subbasins 

and vicinity, lower Skagit River basin, Washington.
Hydrogeologic Framework 15

tac09-9722-0328 Upper Skagit Geo_Fig 06

122°20' 122°10'

48°25'

48°20'

R.3 E. R.4 E. R.5 E. R.6 E.

T.

35

N.

T.

34

 N.

T.

33

 N.

T.

32

 N.

0 1 2 3 4 5 MILES

43210 5 KILOMETERS

Base from U.S. Geological Survey and/or

Washington Division of Geology and Earth Resources

digital data, 1983, 1:100,000

Universal Transverse Mercator projection, Zone 10

Horizontal Datum: North American Datum of 1927 (NAD 27)

5 – 50

51 – 100

101 – 200

201 – 288

Extent and thickness of inter-glacial

 alluvial aquifer (Qco), in feet

EXPLANATION

Well used to determine extent and

 thickness of aquifer—See plate 1

Bedrock outcrop

Boundary of tributary subbasin

Figure 6. Extent and thickness of inter-glacial alluvial aquifer (Qco) in tributary subbasins and vicinity, lower 

Skagit River basin, Washington.
16 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

tac09-9722-0328 Upper Skagit Geo_Fig 07

122°20' 122°10'

48°25'

48°20'

R.3 E. R.4 E. R.5 E. R.6 E.

T.

35

N.

T.

34

 N.

T.

33

 N.

T.

32

 N.

0 1 2 3 4 5 MILES

43210 5 KILOMETERS

Base from U.S. Geological Survey and/or

Washington Division of Geology and Earth Resources

digital data, 1983, 1:100,000

Universal Transverse Mercator projection, Zone 10

Horizontal Datum: North American Datum of 1927 (NAD 27)

Extent and thickness of older

 till confining unit (Qot), in feet

Well used to determine extent and

 thickness of confining unit—See plate 1

5 – 50

51 – 100

101 – 200

EXPLANATION

Bedrock outcrop

Boundary of tributary subbasin

Figure 7. Extent and thickness of older till confining unit (Qot) in tributary subbasins and vicinity, lower Skagit 

River basin, Washington.
Hydrogeologic Framework 17

tac09-9722-0328 Upper Skagit Geo_Fig 08

122°20' 122°10'

48°25'

48°20'

R.3 E. R.4 E. R.5 E. R.6 E.

T.

35

N.

T.

34

 N.

T.

33

 N.

T.

32

 N.

0 1 2 3 4 5 MILES

43210 5 KILOMETERS

Base from U.S. Geological Survey and/or

Washington Division of Geology and Earth Resources

digital data, 1983, 1:100,000

Universal Transverse Mercator projection, Zone 10

Horizontal Datum: North American Datum of 1927 (NAD 27)

EXPLANATION

5 – 50

51 – 100

101 – 200

201 – 269

Extent and thickness of older outwash and 

 alluvial aquifer (Qooa), in feet

Well used to determine extent and

 thickness of aquifer—See plate 1

Bedrock outcrop

Boundary of tributary subbasin

Figure 8. Extent and thickness of older outwash and alluvial aquifer (Qooa) in tributary subbasins and vicinity, 

lower Skagit River basin, Washington.
18 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

Sedimentary aquifer (OEc).—The sedimentary aquifer 

crops out in large parts of the glacial upland and mountains 

in central and southern portions of the study area, and also is 

present in the subsurface throughout this same area (fig. 9). 

The aquifer is largely absent in the mountains along the 

eastern margin of the study area. The unit consists primarily 

of pebble and cobble conglomerate (OEcb), and medium- to 

coarse-grained sandstone (OEcb and Ecbc), with fine-grained 

intervals of mudstone, siltstone, coal, and shale. Groundwater 

in the sedimentary aquifer is unconfined where it crops out; 

however, confined conditions are likely where it is fully 

saturated and overlain by glacial confining units. Fine-grained 

intervals within the aquifer also may produce locally confined 

conditions.

Igneous and metamorphic bedrock unit (EJTP).—The 

igneous and metamorphic bedrock unit crops out along the 

northern margin of the glacial uplands in the mountains along 

the eastern margin of the study area, and within segments of 

the DDMFZ (fig. 9). This low-permeability unit is composed 

of volcanic (Evr) and metamorphic rocks (JTP) and consists 

of rhyolite, andesite, basalt, and complex assemblages of lowgrade metasediments, metavolcanics, and meta-intrusives, and 

is considered to be non-water bearing except in localized areas 

of fracturing.

Hydraulic Conductivity

Hydraulic conductivity is a measure of a material’s 

ability to transmit water, and hydraulic conductivity in 

unconsolidated sediment is dependent on the size, shape, 

distribution, and packing of the particles. Because these 

physical characteristics vary greatly within the glacial deposits 

of the study area, hydraulic conductivity values also are 

highly variable. Estimates of the magnitude and distribution 

of hydraulic conductivity were used to help understand 

groundwater movement and availability in the hydrogeologic 

units.

Horizontal hydraulic conductivity was estimated for the 

hydrogeologic units using drawdown data from drillers’ logs 

that were observed after wells were pumped for a specified 

period. Only data from those wells that had a drillers’ log 

containing discharge rate, time of pumping, drawdown, static 

water level, well-construction data, and lithologic log were 

used.

Two different sets of equations were used to estimate 

hydraulic conductivity, depending on well construction. 

For data from wells with a screened or perforated interval, 

the modified Theis equation (Ferris and others, 1962) was 

first used to estimate transmissivity of the pumped interval. 

Transmissivity is the product of horizontal hydraulic 

conductivity and thickness of the part of the hydrogeologic 

unit supplying water to the well. The modified equation is

2

2.25 , 4

where

drawdown in the well, in feet;

discharge or pumping rate of the well, in cubic

feet per day;

transmissivity of the hydrogeologic unit, in

feet squared per day;

length of time

Q Tt s ln

T r S

s

Q

T

t

π =

=

=

=

= the well was pumped, in days,

radius of the well, in feet; and

storage coefficient, a dimensionless number,

assumed to be 0.0001 for confined units

and 0.1 for unconfined units.

r

S

=

=

(1)

Assumptions for using equation 1 are that aquifers are 

homogeneous, isotropic, and infinite in extent; wells fully 

penetrate the aquifer; flow to the well is horizontal; and water 

is released instantaneously from storage. Additionally, for 

unconfined aquifers, drawdown is assumed to be small in 

relation to the saturated thickness of the aquifer. Although 

many of the assumptions are not precisely met, the field 

conditions in the study area approximate most of the 

assumptions and the calculated hydraulic conductivities are 

likely reasonable estimates.

A computer program was used to solve equation 1 for 

transmissivity (T) using Newton’s iterative method (Carnahan 

and others, 1969). The difference in computed transmissivity 

between using 0.1 and 0.0001 for the storage coefficient was a 

factor of only about 2. Next, the following equation was used 

to calculate horizontal hydraulic conductivity: 

,

where

horizontal hydraulic conductivity of the

geologic material near the well opening,

in feet per day; and

thickness, in feet, approximated using the

length of the open interval as reported in

h

h

T K

b

K

b

=

=

=

the drillers' report.

(2)

The use of the length of a well’s open interval for b may 

overestimate values of Kh because the equations assume that 

all water flows horizontally within a layer of this thickness. 

Although some of the flow will be outside this region, 

the amount can be expected to be small because in most 

sedimentary deposits, vertical flow is inhibited by layering.
Hydrogeologic Framework 19

tac09-9722-0328 Upper Skagit Geo_Fig 09

122°20' 122°10'

48°25'

48°20'

R.3 E. R.4 E. R.5 E. R.6 E.

T.

35

N.

T.

34

 N.

T.

33

 N.

T.

32

 N.

0 1 2 3 4 5 MILES

43210 5 KILOMETERS

Base from U.S. Geological Survey and/or

Washington Division of Geology and Earth Resources

digital data, 1983, 1:100,000

Universal Transverse Mercator projection, Zone 10

Horizontal Datum: North American Datum of 1927 (NAD 27)

Well used to determine extent of sedimentary

 aquifer and igneous and metamorphic 

 bedrock unit—See plate 1

Fault

Sedimentary aquifer (OEc)

Igneous and metamorphic

 bedrock unit (EJTP)

Extent of hydrogeologic bedrock units Bedrock at land surface

EXPLANATION

Boundary of tributary subbasin

Figure 9. Extent of sedimentary aquifer (OEc) and igneous and metamorphic bedrock unit (EJTP) in tributary 

subbasins and vicinity, lower Skagit River basin, Washington.
20 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

For data from wells having only an open end, a second 

equation was used to estimate hydraulic conductivities. Bear 

(1979) provides an equation for hemispherical flow to an 

open-ended well just penetrating a hydrogeologic unit. When 

modified for spherical flow to an open-ended well within a 

unit, the equation becomes 

, 4 h

Q K

π sr = (3)

This equation is based on the assumption that horizontal 

and vertical hydraulic conductivities are equal, which is not 

likely for the deposits in the study area. The result of violating 

this assumption probably is an underestimate of Kh by an 

unknown amount.

Horizontal hydraulic conductivities were calculated for 

those wells with available data, and statistical summaries 

were prepared by hydrogeologic unit (table 3). The values of 

estimated median hydraulic conductivity for the aquifers are 

similar in magnitude to values reported by Freeze and Cherry 

(1979) for similar materials: Qago, 47 ft/d; Qga, 48 ft/d; Qco, 

57 ft/d: Qooa, 26 ft/d; and OEc, 0.27 ft/d (table 3). Estimated 

median hydraulic conductivity for the confining units (Qgt, 

13 ft/d; Qgl, 26 ft/d; Qot, 11 ft/d) and bedrock unit (EJTP, 

0.13 ft/d) are higher than is typical for most of the material 

in these units because the available data for confining units 

usually are from wells that are preferentially open to lenses 

of coarse material, or in the case of bedrock, where fractures 

exist. As a result, the data are biased toward the more 

productive zones in these units and are not representative of 

the entire unit. 

Groundwater Movement 

This section describes the movement of groundwater in 

the aquifer system in the study area, and includes discussions 

of recharge, flow direction, discharge, exchange of water 

between the aquifer system and creeks, and temporal 

fluctuations in groundwater levels. These processes occur 

within the physical domain described by the hydrogeologic 

framework, and are influenced by the hydrogeologic 

characteristics of the aquifer system in which they occur, and 

other factors, including streamflow, and the spatial distribution 

of precipitation and land cover. 

Recharge 

Precipitation is the dominant source of water recharging 

the groundwater system in the study area, and it is reasonable 

to expect variations in recharge to be related to spatial and 

temporal variations in precipitation. However, factors, such 

as the permeability of surficial hydrogeologic units and 

land-cover characteristics, also affect recharge; therefore, the 

relation between precipitation and recharge is likely to vary 

according to hydrogeologic and land-cover characteristics. 

The distribution of recharge from precipitation in the four 

tributary subbasins was estimated by applying precipitationrecharge relations based on regression equations developed 

for areas in Washington State (Bidlake and Payne, 2001) that 

incorporate the effects of surficial hydrogeology and tree 

canopy characteristics. The effects of impervious surfaces 

on the distribution of recharge from precipitation also were 

estimated in the study area.

Hydrogeologic unit Number 

of wells

Hydraulic conductivity (feet per day)

Minimum Median Maximum

Qago Alluvial and recessional outwash aquifer 13 0.04 47 1,322

Qgt Till confining unit 4 6.7 13 89

Qga Advance outwash aquifer 30 2.6 48 722

Qgl Glaciolacustrine and distal outwash confining unit 1 – 126 –

Qco Inter-glacial alluvial aquifer 8 1.4 57 393

Qot Older till confining unit 1 – 111 –

Qooa Older outwash and alluvial aquifer 1 – 126 –

OEc Sedimentary aquifer 16 .05 .27 20

EJTP Igneous and metamorphic bedrock unit 5 .04 .13 40

1

Single measurement values represented as median.

Table 3. Statistical summary of hydraulic conductivity values by hydrogeologic unit in tributary subbasins and 

vicinity, lower Skagit River basin, Washington.

[–. no data]
Groundwater Movement 21

Average annual precipitation totals were calculated 

from daily values for the study period (September 1, 2006, 

to August 31, 2008), obtained from the National Climate 

Data Center, NCDC, (www.ncdc.noaa.gov), for three active 

National Weather Service (NWS) stations near the study 

area: Sedro-Woolley (NWS station 457507), Arlington (NWS 

station 450257), and Anacortes (NWS station 450176). 

These point data were extrapolated across the study area 

based on the spatial distribution of normal precipitation 

(average annual precipitation for 1971–2000) provided by 

the computer program Parameter-elevation Regressions on 

Independent Slopes Model, PRISM, (Daly and others, 1994; 

Oregon State University, 2009). The PRISM model estimates 

the distribution of normal annual precipitation based on a 

statistical method that takes into account altitude and spatial 

variation. 

Normal annual precipitation at each NWS station was 

obtained by sampling the PRISM distribution at the three 

station locations; allowing the PRISM distribution to be scaled 

for extrapolation. The normal precipitation was compared 

to the average annual precipitation for the study period 

(September 1, 2006, to August 31, 2008) at the NWS stations 

and a regression equation was developed for the three points:

Pactual = 4.35 in/yr + 0.911 × Pnormal

This relation was used to estimate the distribution of average 

annual precipitation for the study period throughout the 

study area (fig. 10), based on the PRISM distribution of 

normal precipitation. The tributary subbasins received about 

284,000 acre-ft or about 56 in. of precipitation during an 

average year (September 1, 2006, to August 31, 2008). 

Precipitation during an average year for each subbasin 

was: East Fork Nookachamps Creek, 136,920 acre-ft 

(70 in/yr); Nookachamps Creek, 74,820 acre-ft (49 in/yr); 

Carpenter Creek, 46,610 acre-ft (46 in/yr); and Fisher Creek, 

25,730 acre-ft (47 in/yr).

The effects of surficial hydrogeology on the distribution 

of recharge from precipitation (fig. 11) were estimated based 

on regression equations developed by Bidlake and Payne 

(2001) for soils in western Washington formed on glacial 

outwash and alluvial sediments, and soils formed on glacial 

till and fine-grained sediments. Recharge estimates for aquifer 

units (outwash and alluvium) exposed at land surface in the 

study area were based on the regression equation developed 

for soils formed on glacial outwash and alluvial sediments; 

recharge estimates for confining units (till and lacustrine) 

were based on the regression equation developed for soils 

formed on glacial till and fine-grained sediments. Recharge 

estimates for areas where sedimentary and bedrock units 

are exposed at land surface required the approximation of 

additional precipitation-recharge equations for this study that 

were based on a qualitative comparison of the hydrogeologic 

properties of unconsolidated, sedimentary, and bedrock units. 

Recharge characteristics of the sedimentary aquifer were 

estimated to be less than unconsolidated aquifers and greater 

than unconsolidated confining units, and a precipitationrecharge relation was selected for the sedimentary aquifer that 

plots mid-way between these unconsolidated units (fig. 11). 

Recharge characteristics of the bedrock unit were estimated 

to be less than the unconsolidated confining units, and a 

precipitation-recharge relation was selected for the bedrock 

unit that represents one-half the recharge of the unconsolidated 

confining units.

The effect of evaporative loss associated with the 

interception of precipitation by tree canopy on recharge from 

precipitation (fig. 11) was estimated for unconsolidated and 

bedrock aquifers using equations from Bidlake and Payne 

(2001), and tree canopy distribution data obtained from the 

National Land Cover Database, NLCD (2001). Interception 

loss was applied to areas with more than 50 percent tree 

canopy (fig. 10). Urban centers in the study area manage storm 

water by discharging runoff to rivers or streams rather than 

by infiltrating to groundwater, therefore, recharge within city 

limits was reduced according to the percentage of impervious 

surface (figs. 10 and 12) derived from the National Land 

Cover Database (2001). No direct recharge from precipitation 

was assumed for areas covered by lakes.

GIS techniques were used to combine the data coverages 

described above, and calculate the distribution of groundwater 

recharge from precipitation at a 1,000 ft cell size in the four 

tributary subbasins (fig. 13). Recharge rates range from less 

than1 in/yr in urban areas underlain by impervious surfaces to 

about 46 in/yr in mountainous terrain underlain by till deposits 

with less than 50 percent tree canopy along the eastern 

margin of East Fork Nookachamps Creek subbasin where 

precipitation locally exceeds 120 in/yr. Summing the recharge 

areas shown in figure 13 indicates that the groundwater system 

within the subbasins receives about 92,400 acre-ft or about 

18 in. of recharge from precipitation during an average year 

(September 1, 2006, to August 31, 2008). The calculated 

recharge from precipitation during an average year for each 

subbasin was: East Fork Nookachamps Creek, 41,060 acre-ft 

(21 in/yr); Nookachamps Creek, 23,840 acre-ft (16 in/yr); 

Carpenter Creek, 17,200 acre-ft (17 in/yr); and Fisher Creek, 

10,300 acre-ft (19 in/yr). 

Precipitation-recharge relations developed by Bidlake 

and Payne (2001) included only annual precipitation as much 

as 60 in/yr, whereas, areas along the eastern boundary of the 

tributary subbasins locally receive greater than 120 in/yr. 

To estimate recharge for areas receiving between 60 and 

120 in. of annual precipitation, regression equation lines were 

extended using a constant slope from 60 to 120 in/yr. The 

upper limits of the precipitation-recharge relation are poorly 

understood and a reduction in the efficiency of groundwater 

recharge from precipitation likely takes place at some point, 

resulting in the potential for over estimation of recharge 

(William Bidlake, U.S. Geological Survey, oral commun., 

2009).

In addition to groundwater recharge from precipitation, 

groundwater recharge from creeks also occurs in the 

study area along losing creek reaches. The total amount 

of groundwater recharge from creeks was not quantified, 

but this total is reflected in the computation of the total net 

groundwater discharge to creeks used in the water budget.
22 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

tac09-9722-0328 Upper Skagit Geo_Fig 10

43210 5 MILES

43210 5 KILOMETERS

Base from U.S. Geological Survey and/or

Washington Division of Geology and Earth Resources

digital data, 1983, 1:100,000

Universal Transverse Mercator projection, Zone 10

Horizontal Datum: North American Datum of 1927 (NAD 27)

SNOHOMISH COUNTY

SKAGIT COUNTY

Skagit River

South Fork Skagit River

Nookachamps Creek

Lake Creek

Carpenter Cre e k

Lake

Ketchum

Ten

Lake

Devils

Lake

Big

Lake

Sixteen

Lake

Clear

Lake

Lake

McMurray

Beaver

Lake

Armstrong 

Creek

Pilchuck

Creek

East Fork

Nook achamps

Creek

Skagit

Bay

Fischer Creek

Skagit River

Skagit River

No rth

Fork

Walker Creek

Turner

Creek

Mundt Creek

Nookachamps Creek

Johnson Creek

Sandy Cre ek

Barney

Lake

Bulson Creek

Carpenter Creek

Burlington

Mount

Vernon

SedroWoolley

Stanwood

40

80

80

100

120

60

80

60

60

EXPLANATION

Less than 50 percent

More than 50 percent

Represents all percentages.

 See figure 12 for detail

Line of equal average annual precipitation.

 Interval is 20 inches

60

Canopy cover, in percent Impervious surface

Boundary of tributary subbasin

See figure 12 for detail

48°25'

122°20' 122°10'

48°20'

R. 3 E. R. 4 E. R. 5 E. R. 6 E.

T.

35

N.

T.

34

N.

T.

33

N.

T.

32

N.

Figure 10. Average annual precipitation, canopy cover, and impervious surface across the tributary subbasins 

and vicinity, lower Skagit River basin, Washington, September 2006–August 2008.
Hydrogeologic Framework 23

tac09-9722-0328 Upper Skagit Geo_Fig 11

0

20

40

60

80

100

120

0 20 40 60 80 100 120 140

PRECIPITATION, IN INCHES PER YEAR

RECHARGE, IN INCHES PER YEAR

Unconsolidated aquifers (Qago, Qga, Qco, and Qooa)

With trees

Sedimentary aquifer (OEc)

With trees

Unconsolidated confining units (Qgt, Qgl, and Qot)

Igneous and metamorphic bedrock unit (EJTP)

Recharge as a function of surficial hydrogeology

Without trees

Without trees

Figure 11. Precipitation-recharge relations used in this study, lower Skagit River basin, 

Washington.
24 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

tac09-9722-0328 Upper Skagit Geo_Fig 12

0 1 2 3 4 MILES

3210 4 KILOMETERS

Base from U.S. Geological Survey and/or

Washington Division of Geology and Earth Resources

digital data, 1983, 1:100,000

Universal Transverse Mercator projection, Zone 10

Horizontal Datum: North American Datum of 1927 (NAD 27)

Skag it

River

Nookachamps

Creek

Big

Lake

Clear

Lake

Beaver

Lake East

Fork

Nook achamps

Creek

Skagit

River

Skagit River

Nort h

Fork

Turner

Creek

Nook achamps

Cree

Barney k

Lake

Burlington

Mount

Vernon

SedroWoolley

I

5

I

5

SR

20

SR

20 SR

9

SR

9

SR

538

SR

536

60

40

48°25' 80

122°20' 122°10'

R. 3 E. R. 4 E. R. 5 E.

T.

34

N.

T.

35

N.

T.

33

N.

EXPLANATION

Less than 50 percent

More than 50 percent

Less than 20 percent

21 – 40

41 – 60

61 – 80

More than 80 percent

Canopy cover, in percent Impervious surface, in percent Line of equal average annual

 precipitation. Interval

 is 20 inches

60

Boundary of tributary subbasin

Figure 12. Detail of distribution of impervious surfaces in tributary subbasins and vicinity, lower Skagit River basin, 

Washington, September 2006–August 2008.
Hydrogeologic Framework 25

tac09-9722-0328 Upper Skagit Geo_Fig 13

43210 5 MILES

43210 5 KILOMETERS

Base from U.S. Geological Survey and/or

Washington Division of Geology and Earth Resources

digital data, 1983, 1:100,000

Universal Transverse Mercator projection, Zone 10

Horizontal Datum: North American Datum of 1927 (NAD 27)

SNOHOMISH COUNTY

SKAGIT COUNTY

Skagit River

South Fork Skagit River

Nookachamps Creek

Lake Creek

Carpenter Cre e k

Lake

Ketchum

Ten

Lake

Devils

Lake

Big

Lake

Sixteen

Lake

Clear

Lake

Lake

McMurray

Beaver

Lake

Pilchuck

Creek

East Fork

Nook achamps

Creek

Skagit

Bay

Fisher Cr eek

Skagit River

Skagit River

No rth

Fork

Walker Creek

Turner

Creek

Mundt Creek

Nookachamps Creek

Johnson Creek

Sandy Cre ek

Barney

Lake

Bulson Creek

Carpenter Creek

Stanwood

Mount

Vernon

Burlington

SedroWoolley

48°25'

122°20' 122°10'

48°20'

R. 3 E. R. 4 E. R. 5 E. R. 6 E.

T.

35

N.

T.

34

N.

T.

33

N.

T.

32

N.

EXPLANATION

Average annual groundwater recharge,

 in inches per year

0 – 11.50

11.51 – 19.50

19.51 – 26.50

26.51 – 30.50

30.51 – 46.36

Boundary of tributary subbasin

Figure 13. Distribution of average annual groundwater recharge from precipitation in tributary subbasins and 

vicinity, lower Skagit River basin, Washington, September 2006–August 2008.
26 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

Groundwater-Flow Directions

The direction of horizontal groundwater flow can be 

inferred from contour maps of water-level altitudes. The 

direction of groundwater flow generally is from areas of 

recharge to areas of discharge in the direction of decreasing 

water-level altitudes and perpendicular to the water-level 

altitude contours. Groundwater levels measured monthly 

(October 2006 through September 2008) were used to infer 

direction of groundwater flow in study area aquifers (figs. 14

through 18). The mean water-level value for October 2006 

through September 2008 was used to represent the waterlevel altitude at monitoring wells measured monthly for this 

analysis. Synoptic groundwater levels measured during the 

field inventory (August through October 2006) were used only 

in areas where monthly water-level data were not available, 

and in places field inventory values do not correlate well with 

water-level altitude contours based on monthly data. Waterlevel contours for most aquifer units are based on limited 

water-level data, and are subject to some uncertainty. Waterlevel contours were not drawn for the alluvial and recessional 

outwash aquifer (Qago) because of the discontinuous nature 

of the unit within the tributary subbasins. Water-level contours 

also were not drawn for large parts of the advance outwash 

(Qga), inter-glacial alluvial (Qco), and older outwash and 

alluvial (Qooa) aquifers due to limited water-level data for 

these units. 

Groundwater flow in the Qago aquifer likely follows 

the land-surface gradient, with water generally moving in a 

northwesterly direction from high-altitude areas in the upper 

portions of the tributary subbasins towards the Skagit River 

and Puget Sound (fig. 14). This generalized flow pattern 

is likely complicated by the presence of large areas of low 

permeability glacial till (Qgt) that separate discontinuous 

bodies of Qago and act as local groundwater-flow barriers. 

In the southern part of the study area, groundwater flow 

in the advance outwash aquifer (Qga) is towards the west in 

the direction of the Skagit River and Puget Sound (fig. 15). 

North to northwestward groundwater flows beneath major 

tributary river valleys, and localized radial flow are inferred 

from widely spaced water-level data in central and northern 

parts of the area. 

Groundwater flow in the inter-glacial alluvial (Qco) and 

older outwash and alluvial (Qooa) aquifers is towards the west 

in the direction of the Skagit River and Puget Sound in the 

southern part of the study area (figs. 16 and 17, respectively). 

Widely spaced water-level data in the northern part of the 

area suggest a northwestward and southeastward direction of 

groundwater flow in the inter-glacial alluvial aquifer (Qco). 

Directions of groundwater flow in the sedimentary 

aquifer (OEc) likely reflect both local and regional flow 

patterns (fig. 18). Recharge to the sedimentary aquifer (OEc) 

aquifer preferentially occurs in mountainous areas where the 

unit is exposed at land surface (figs. 9 and 13). Water-level 

altitudes in these areas reflect local topographic relief (fig. 18) 

and suggest radial flow from bedrock highs down beneath the 

surrounding unconsolidated sediments. Westward groundwater 

flow in the sedimentary aquifer (OEc) occurs along the 

mountain front in the eastern part of the study area, and is 

coincident with a regional westward decrease in land-surface 

altitude from the mountains to the Puget Sound.

Vertical gradients and flow in the groundwater system 

are difficult to determine because extents and thicknesses 

of hydrogeologic units vary considerably throughout the 

study area, the presence of confining units within and 

between aquifers is highly variable, and water-level data for 

comparison between adjacent units are widely spaced. Waterlevel altitude differences between the advance outwash (Qga) 

and inter-glacial alluvial (Qco) aquifers in the southwestern 

part of the study area, where sufficient contoured data were 

available to make a comparison, suggest downward vertical 

flow (figs. 15 and 16). 

The potential for upward groundwater movement, 

indicated by the presence of flowing wells, was observed at 

several locations within the aquifer units. Confining clays 

within the alluvial and recessional outwash aquifer (Qago) 

likely produce intermittent flowing conditions observed at 

two wells along the eastern margin of the Skagit River valley 

(fig. 14). Upward flow in the advance outwash (Qga) aquifer is 

suggested by the presence of three continuously flowing wells 

near Big Lake, and two intermittent flowing wells located 

along the mountain front (fig. 15). Confined groundwater 

conditions are attributed to the presence of overlying till 

deposits (Qtv) at both of these locations. A continuously 

flowing well completed in the older outwash and alluvial 

aquifer (Qooa) indicates the potential for upward flow in 

the southwestern part of the study area (fig. 17), and upward 

flow in the sedimentary aquifer (OEc) is indicated by an 

intermittent flowing well adjacent to Lake McMurray (fig. 18).
Groundwater Movement 27

tac09-9722-0328 Upper Skagit Geo_Fig 14

122°20' 122°10'

48°25'

48°20'

R.3 E. R.4 E. R.5 E. R.6 E.

T.

35

N.

T.

34

 N.

T.

33

 N.

T.

32

 N.

0 1 2 3 4 5 MILES

43210 5 KILOMETERS

Base from U.S. Geological Survey and/or

Washington Division of Geology and Earth Resources

digital data, 1983, 1:100,000

Universal Transverse Mercator projection, Zone 10

Horizontal Datum: North American Datum of 1927 (NAD 27)

Alluvial and recessional outwash aquifer (Qago)

Inferred direction of groundwater flow 05G02

233 Boundary of tributary subbasin

EXPLANATION

Well used to measure water-level altitudes on a monthly basis—

 The mean water-level altitude for October 2006 through September 2008 

 was used to represent the water-level altitude at each of the wells monitored 

 on a monthly basis. Numbers are well No. (top) and water-level altitude (bottom)

F Flowing well

Field inventory well used to measure synoptic water-level altitudes—

 Synoptic water-level altitude for August through October 2006 was used only in 

 areas where monthly water-level data were not available. Numbers are well No. (top)

 and water-level altitude (bottom)

Sk agit River

South Fork Skagit River

Nookachamps Creek

Lake Creek

Carpenter

Creek Lake

Ketchum

Ten

Lake

Devils

Lake

Big

Lake

Sixteen

Lake

Clear

Lake

Lake

McMurray

Beaver

Lake

Pilchuck

Creek

East Fork

Nookachamps Creek

Skagit

Bay

 Fisher

Creek

Skagit River

Skagit River

North Fork

Walker Creek

Turner

Creek

Mundt Creek

Noo kachamps Creek

Johnson Creek

Sandy Cre ek

Barney

Lake

Bulson Creek

Carpenter

Cr eek

35D01

01A02

11C01

17D01

05M01

06B01

20E01

08D01

6

08D01

Measurement location and water-level altitude, in feet above North 

 American Vertical Datum of 1988 (NAVD 88)

 

7

7

220

6

29

36

28

15

08A01

11Q01

23A01

23R01

20N01

34E01

04C01

04F01

08R01

17D01

20F01

20J01 26B01

05G02

05G01

57

88

39

32 F

11 F

65

713

202

132

221

125

197

233

227

293

Figure 14. Water-level altitudes and direction of groundwater flow in alluvial and recessional outwash aquifer 

(Qago) in tributary subbasins and vicinity, lower Skagit River basin, Washington, August 2006–September 2008.
28 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

tac09-9722-0328 Upper Skagit Geo_Fig 15

122°20' 122°10'

48°25'

48°20'

R.3 E. R.4 E. R.5 E. R.6 E.

T.

35

N.

T.

34

 N.

T.

33

 N.

T.

32

 N.

0 1 2 3 4 5 MILES

43210 5 KILOMETERS

Advance outwash aquifer (Qga)

04N01

253

Inferred direction of groundwater flow

EXPLANATION

Boundary of tributary subbasin

Flowing well

Field inventory well used to measure synoptic water-level altitudes—

 Synoptic water-level altitude for August through October 2006 was used only in 

 areas where monthly water-level data were not available. Numbers are well No. (top)

 and water-level altitude (bottom)

Well used to measure water-level altitudes on a monthly basis—

 The mean water-level altitude for October 2006 through September 2008 

 was used to represent the water-level altitude at each of the wells monitored 

 on a monthly basis. Numbers are well No. (top) and water-level altitude (bottom)

Measurement location and water-level altitude, in feet above North 

 American Vertical Datum of 1988 (NAVD 88)

 

F

Base from U.S. Geological Survey and/or

Washington Division of Geology and Earth Resources

digital data, 1983, 1:100,000

Universal Transverse Mercator projection, Zone 10

Horizontal Datum: North American Datum of 1927 (NAD 27)

Approximate water-level contour—Shows altitude of 

 water level in advance outwash aquifer, October 

 2006–September 2008. Contour interval, 100 feet. 

 Datum is North American Vertical Datum of 1988 

 (NAVD 88)

04N01

253

107

05Q02

28K02

28K01

20Q01

34L02

05Q03

32L01

04N01

14J01

14R01 23A02

01A01

07B01

09R01

23N02

25Q01

25J01

29Q01

31D02

05Q02

8

49

-9

83

86

88

140

166

204

115

237

254

300

233

105

236

331

107

156

18A01

13M01

19M01

19K01

23N01 25B01

36M01

05C01

17J01

21N01

30D01 29B01

29J01

33F01

34L01

04H01

98

123

241

176 F

208 160

120 F

234 F

110

-14

235

106

84

279

 329 

275

18A01

148 F

06D01

118 F

Sk agit River

South Fork Skagit River

Nookachamps Creek

Lake Creek

Carpenter Cree k

Lake

Ketchum

Ten

Lake

Devils

Lake

Big

Lake

Sixteen

Lake

Clear

Lake

Lake

McMurray

Beaver

Lake

Armstrong

Creek

Pilchuck

Creek

East

Fork

No okachamps Creek

Skagit

Bay

Fisher

Cr eek

Skagit River

Skagit River

North Fork

Walker Creek

Turner

Creek

Mundt Creek

Noo kachamps Creek

Johnson Creek

Sandy Cre ek

Barney

Lake

Bulson Creek

Carpenter Creek

200

100

300

100

05Q02

Figure 15. Water-level altitudes and direction of groundwater flow in advance outwash aquifer (Qga) in 

tributary subbasins and vicinity, lower Skagit River basin, Washington, August 2006–September 2008.
Groundwater Movement 29

tac09-9722-0328 Upper Skagit Geo_Fig 16

122°20' 122°10'

48°25'

48°20'

R.3 E. R.4 E. R.5 E. R.6 E.

T.

35

N.

T.

34

 N.

T.

33

 N.

T.

32

 N.

100

200

300

0 1 2 3 4 5 MILES

43210 5 KILOMETERS

Base from U.S. Geological Survey and/or

Washington Division of Geology and Earth Resources

digital data, 1983, 1:100,000

Universal Transverse Mercator projection, Zone 10

Horizontal Datum: North American Datum of 1927 (NAD 27)

R.3 E. R.4 E.

Inter-glacial alluvial aquifer (Qco)

28M01

108

Inferred direction of groundwater flow

Boundary of tributary subbasins

EXPLANATION

Approximate water-level contour—Shows altitude of water 

 level in inter-glacial alluvial aquifer, October 2006–September 2008. 

 Contour interval, 100 feet. Datum is North American 

 Vertical Datum of 1988 (NAVD 88) 32D02

81

Sk agit River

South Fork Skagit River

Nookachamps Creek

Lake Creek

Carpenter Cree k

Lake

Ketchum

Ten

Lake

Devils

Lake

Big

Lake

Sixteen

Lake

Clear

Lake

Lake

McMurray

Beaver

Lake

Armstrong

Creek

Pilchuck

Creek

Skagit

Bay

 Fisher Creek

Skagit River

Skagit River

North Fork

Walker Creek

Turner

Creek

Mundt Creek

Noo kachamps Creek

Johnson Creek

Sandy Cre ek

Barney

Lake

Bulson Creek

Carpenter Creek

East

Fork

Nooka champs

Creek

15C01

26M01

05C02

20B01

23N01

32D02

-8

34

81

217

232

336

Field inventory well used to measure synoptic water-level altitudes—

 Synoptic water-level altitude for August through October 2006 was used only in 

 areas where monthly water-level data were not available. Numbers are well No. (top)

 and water-level altitude (bottom)

Well used to measure water-level altitudes on a monthly basis—

 The mean water-level altitude for October 2006 through September 2008 

 was used to represent the water-level altitude at each of the wells monitored 

 on a monthly basis. Numbers are well No. (top) and water-level altitude (bottom)

Measurement location and water-level altitude, in feet above North 

 American Vertical Datum of 1988 (NAVD 88)

 

26L01

26R01

28M01 27E01

108

216

190

307

Figure 16. Water-level altitudes and direction of groundwater flow in inter-glacial alluvial aquifer (Qco) in 

tributary subbasins and vicinity, lower Skagit River basin, Washington, August 2006–September 2008.
30 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

tac09-9722-0328 Upper Skagit Geo_Fig 17

122°20' 122°10'

48°25'

48°20'

R.3 E. R.4 E. R.5 E. R.6 E.

T.

35

N.

T.

34

 N.

T.

33

 N.

T.

32

 N.

50

100

100

0 1 2 3 4 5 MILES

43210 5 KILOMETERS

Older outwash and alluvial aquifer (Qooa)

04N04

147

33G01

33G01

110

Inferred direction of groundwater flow

Boundary of tributary subbasin

EXPLANATION

Approximate water-level contour—Shows altitude of water level in 

 older outwash and alluvial aquifer, October 2006–

 September 2008. Contour interval, 50 feet. Datum is 

 North American Vertical Datum of 1988 (NAVD 88)

Base from U.S. Geological Survey and/or

Washington Division of Geology and Earth Resources

digital data, 1983, 1:100,000

Universal Transverse Mercator projection, Zone 10

Horizontal Datum: North American Datum of 1927 (NAD 27)

Field inventory well used to measure synoptic water-level altitudes—

 Synoptic water-level altitude for August through October 2006 was used only in 

 areas where monthly water-level data were not available. Numbers are well No. (top)

 and water-level altitude (bottom)

Well used to measure water-level altitudes on a monthly basis—

 The mean water-level altitude for October 2006 through September 2008 

 was used to represent the water-level altitude at each of the wells monitored 

 on a monthly basis. Numbers are well No. (top) and water-level altitude (bottom)

Flowing well

Measurement location and water-level altitude, in feet above North 

 American Vertical Datum of 1988 (NAVD 88)

 

F

Sk agit River

South Fork Skagit River

Nookachamps Creek

Lake Creek

Carpenter Cree k

Lake

Ketchum

Ten

Lake

Devils

Lake

Big

Lake

Sixteen

Lake

Clear

Lake

Lake

McMurray

Beaver

Lake

Armstrong

Creek

Pilchuck

Creek

East Fork

Nookachamps

Creek

Skagit

Bay

Fisher

Cr eek

Skagit River

Skagit River

North Fork

Walker Creek

Turner

Creek

Mundt Creek

Noo kachamps Creek

Johnson Creek

Sandy Cre ek

Barney

Lake

Bulson Creek

Carpenter Creek

31A01

33A01

04N04

14

120

147

28G01

32D01

73 F

118

110

Figure 17. Water-level altitudes and direction of groundwater flow in older outwash and alluvial aquifer (Qooa) 

in tributary subbasins and vicinity, lower Skagit River basin, Washington, August 2006–September 2008.
Groundwater Movement 31

tac09-9722-0328 Upper Skagit Geo_Fig 18

122°20' 122°10'

48°25'

48°20'

R.3 E. R.4 E. R.5 E. R.6 E.

T.

35

N.

T.

34

 N.

T.

33

 N.

T.

32

 N.

200

300

300

400

100

500

600

700

200 300

200

200

400

300

300

400

300

500

0 1 2 3 4 5 MILES

43210 5 KILOMETERS

Base from U.S. Geological Survey and/or

Washington Division of Geology and Earth Resources

digital data, 1983, 1:100,000

Universal Transverse Mercator projection, Zone 10

Horizontal Datum: North American Datum of 1927 (NAD 27)

Sedimentary aquifer (OEc) 03G01

380

03A01

295

Inferred direction of groundwater flow

Boundary of tributary subbasin

EXPLANATION

Flowing well

Field inventory well used to measure synoptic water-level altitudes—

 Synoptic water-level altitude for August through October 2006 was used only in 

 areas where monthly water-level data were not available. Numbers are well No. (top)

 and water-level altitude (bottom)

Well used to measure water-level altitudes on a monthly basis—

 The mean water-level altitude for October 2006 through September 2008 

 was used to represent the water-level altitude at each of the wells monitored 

 on a monthly basis. Numbers are well No. (top) and water-level altitude (bottom)

Measurement location and water-level altitude, in feet above North 

 American Vertical Datum of 1988 (NAVD 88)

 

F

Approximate water-level contour—Shows altitude of water level in 

 sedimentary aquifer, October 2006– September 2008. 

 Contour interval, 50 feet. Datum is North American 

 Vertical Datum of 1988 (NAVD 88)

Sk agit River

South Fork Skagit River

Nookachamps Creek

Lake Creek

Carpenter Cree k

Lake

Ketchum

Ten

Lake

Devils

Lake

Big

Lake

Sixteen

Lake

Clear

Lake

Lake

McMurray

Beaver

Lake

Armstrong

Creek

Pilchuck

Creek

East Fork

Nook achamps

Creek

Skagit

Bay

Fisher Cr eek

Skagit River

Skagit River

North Fork

Walker

Creek

Turner

Creek

Mundt Creek

Noo kachamps Creek

Johnson Creek

Sandy Cre ek

Barney

Lake

Bulson Creek

Carpenter Creek

02E01

02B01

17J02

23Q01

34R01

03R01

03A01

639

563

462

303

338

295

275

28K01

30J01

32P01

04C01

01G01

02M02

02M01

16E01

21H01

27A01

30C01

26A01

27F01

27M01

31B01

34K01

34P01

03G01

02L01

17J01D1

55

353

218

445

95

752

856

263

39 F

156

293

243

457

177

248 F 

351

279

380

605

325

35D01

Figure 18. Water-level altitudes and direction of groundwater flow in the sedimentary aquifer (OEc) in tributary 

subbasins and vicinity, lower Skagit River basin, Washington, August 2006–September 2008.
32 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

Discharge

Groundwater in the study area discharges as seepage to 

streams, lakes, springs, and marshes; as evapotranspiration of 

shallow groundwater; as submarine seepage to Puget Sound; 

and as withdrawals from wells. Groundwater discharge 

sustains the late-summer and early-fall streamflow (baseflow) 

of creeks in the study area. Estimates of groundwater 

discharge to creeks in the tributary subbasins were based on 

synoptic streamflow measurements made in August 2007 and 

June 2008 at seven locations (table 4 and pl. 1); a streamflow 

measurement for Carpenter Creek obtained from Pitz and 

Garrigues (2000); and estimates of evaporative loss from lakes 

within measured reaches (National Oceanic and Atmospheric 

Administration, 1982). Estimates of daily evaporative loss 

from lakes were used to account for losses in baseflow 

during synoptic streamflow measurements (August 2007 and 

June 2008). These estimates were based on maps of annual 

evaporation for shallow lakes near the study area (National 

Oceanic and Atmospheric Administration, 1982). Maps were 

developed using data from Class A pan evaporation stations 

and other spatially distributed meteorological data for 1956–

70. The accuracy of the maps is a function of the number of 

nearby data stations and their proximity to the area of interest; 

the closest stations are located in the southern Puget Sound 

area. Estimates of annual evaporation assume long-term 

thermal stability of lake water. Daily values of evaporation 

were estimated using the average monthly percentage of 

annual evaporation derived from Class A pan evaporation data 

(National Oceanic and Atmospheric Administration, 1982) for 

1956–70.

Precipitation totals at Sedro-Woolley for June, July, 

and August 2007 were 2.48, 1.31, and 1.24 in., respectively 

(Western Regional Climate Center, 2008). The normal 

(average annual precipitation for the period 1971-2000) 

precipitation at Sedro-Woolley for these months is 2.85, 

1.77, and 1.62 in. (National Oceanic and Atmospheric 

Administration, 2007). Precipitation totals at Sedro-Woolley 

for April, May, and June 2008 were 4.40, 2.97, and 3.13 in., 

respectively (Western Regional Climate Center, 2008). The 

normal precipitation (average precipitation for selected months 

for the period 1971–2000) at Sedro-Woolley for these months 

is 3.76, 3.03, and 2.85 in. (National Oceanic and Atmospheric 

Administration, 2007). 

Groundwater discharge estimates represent flow from 

contributing areas upstream of the synoptic streamflowmeasurement sites (57.7 mi2 ) and do not include contributing 

areas in downstream parts of the subbasins (36.6 mi2). A total 

net of about 13.15 ft3/s (9,520 acre-ft/yr) of groundwater 

discharged to creeks measured during August 2007, and 

approximately 129.6 ft3/s (93,830 acre-ft/yr) of groundwater 

discharged to creeks measured during June 2008 (table 4). 

These data reflect seasonal variability in groundwater 

discharge to creeks, however, much of the likely annual 

variation in discharge (dryer and wetter conditions) is not 

represented by these data. Many small streams were not 

measured, but they may collectively receive a significant 

quantity of groundwater discharge at times throughout the 

year. The time averaged (mean of the 2007 and 2008 discharge 

measurements) area weighted groundwater discharge for the 

entire tributary subbasin area was estimated to be 83.43 ft3/s 

(60,400 acre-ft/yr). This value includes area-weighted 

estimates of groundwater discharge for portions of subbasins 

that were downstream of synoptic measurement sites. 

Area weighting values (measured discharge divided by the 

contributing area upstream of the measurement site) were 

derived for each of the tributary subbasins to better represent 

spatial variation in groundwater discharge characteristics. 

The use of a time averaged groundwater discharge estimate 

to compute the area weighted groundwater discharge in the 

study area may not accurately represent the total annual 

variation in discharge, and likely introduces some error into 

this calculation. The time averaged (period of record for each 

streamflow-gaging station), area-weighted streamflow for the 

entire tributary subbasin area was estimated to be 221.8 ft3/s 

(160,600 acre-ft/yr).

Groundwater withdrawals from wells in the tributary 

subbasins in 2008 were an estimated 2,200 acre-ft. This 

quantity represents gross withdrawals (public-water supply, 

domestic use, and crop irrigation) and does not reflect 

the quantity of water returned to the groundwater system 

through septic tanks or through irrigation-return flows to 

shallow aquifers. Public supply and domestic groundwater 

withdrawals were estimated using a typical water-use rate of 

228 gal/d per connection. The typical use rate was estimated 

by multiplying a per-capita water-use rate of 84 gal/d (Lane, 

2009) by an estimate of 2.71 people per connection (U.S. 

Census Bureau, 2000). The number of connections within the 

tributary subbasins area was estimated using the Skagit and 

Snohomish Counties assessor database, and the Washington 

State Department of Health database (Skagit County, 2008; 

Snohomish County, 2008; Washington State Department of 

Health, 2008). Crop irrigation withdrawals were estimated by 

multiplying crop specific application rates by the number of 

acres under production within the tributary subbasins for each 

crop type, and then accounting for irrigation method efficiency 

(U.S. Department of Agriculture, 2007; Washington State 

Department of Agriculture, 2008).
Groundwater Movement 33

Table 4. Synoptic streamflow measurements used to determine groundwater discharge and estimates 

of evaporative loss from lakes in tributary subbasins and vicinity, lower Skagit River basin, Washington, 

August 2007 and June 2008.

[Measurement site: Site locations are shown in figure 22. Accuracy rating of U.S. Geological Survey measurements: F, fair; 

P, poor; estimated values are rated poor. ft3/s, cubic feet per second]

Measurement site Site No. Date discharge 

measured

Discharge

(ft3

/s) 

Accuracy 

rating

East Fork Nookachamps Creek subbasin

Inflow to Beaver Lake 12200022 08-07-07

06-19-08

0.19

3.11

F

F

Turner Creek 12200015 08-07-07

06-18-08

0.50

2.48

F

F

East Fork Nookachamps Creek 12200010 08-07-07

06-19-08

4.58

66.1

F

F

Nookachamps Creek subbasin

Nookachamps Creek 12199600 08-09-07

06-19-08

0.76

33.1

F

F

Carpenter Creek subbasin

Carpenter Creek 12200696 09-21-00

06-19-08

 12.22

 12.4

F

F

Fisher Creek subbasin

Fisher Creek 12200701 08-07-07

06-05-08

0.49

 6.38

P

F

Tributary to Fisher Creek 1220070140 08-07-07

06-18-08

 2

0.01 22.00

P

P

Evaporative loss from lakes

Evaporative loss from Big Lake August 2007 

June 2008

3

3.15

3

2.85

Evaporative loss from Lake McMurray August 2007 

June 2008

3

0.97

3

0.88

Evaporative loss from Sixteen Lake August 2007 

June 2008

3

0.28

3

0.25

Total net measured streamflow August 2007 

June 2008

13.15

129.6

1

 Streamflow measured on September 21, 2000; accuracy rating assumed to be fair (Pitz and Garrigues, 2000); backwater 

conditions observed by U.S. Geological Survey on August 8, 2007.

2

 Estimated by U.S. Geological Survey.

3

 Calculated daily evaporative loss derived from National Oceanic and Atmospheric Administration (1982) annual values.
34 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

Groundwater/Surface-Water Interactions

Characterization of the exchange of water between the 

groundwater system and creeks in the study area was based on 

synoptic streamflow measurements made in August 2007 and 

June 2008 at 27 creek locations and an Ecology streamflowgaging station on East Fork Nookachamps Creek (table 5 and 

pl. 1); streamflow data for Carpenter Creek from Pitz and 

Garrigues (2000); and estimates of evaporative loss from lakes 

(National Oceanic and Atmospheric Administration, 1982). 

This information was used to identify stream reaches that 

either gain flow from or lose flow to the shallow groundwater 

system. August 2007 streamflow measurements were made 

during the low-flow season, usually July–August (fig. 19), 

to capture baseflow conditions. June 2008 measurements 

were made to document the exchange of water between the 

groundwater system and creeks at a higher baseflow condition 

with larger groundwater contributions. Streamflow during the 

August 2007 measurement period remained fairly constant at 

the Carpenter Creek and Fisher Creek gaging stations and was 

steadily decreasing at the Nookachamps Creek gaging station 

(fig. 20). Steadily decreasing streamflow in the study area was 

observed during the June 2008 measurement period (fig. 21). 

The results of the synoptic streamflow measurements 

are presented in table 5. Most measurements were rated 

“fair,” however, 17 measurements were rated “poor” 

due to suboptimal flow conditions (low velocity, shallow 

depth, and aquatic vegetation), or the necessity to estimate 

streamflow values (lack of access to stream). Inflow (table 5) 

to a measurement site is the sum of streamflows measured 

upstream of the measurement site (fig. 22). For example: the 

August 2007 inflow to the Walker Creek measurement site 

(12199890), 1.04 ft3/s, is the sum of the streamflows measured 

at the upstream Walker Creek site (12199860), 0.98 ft3/s, and 

the Tributary to Walker Creek site (12199870), 0.06 ft3/s. 

Inflow is used to compute the difference between streamflow 

upstream of the site and at the site. The sign of the difference 

in streamflow (positive or negative value) indicates a gaining 

or losing creek reach. 

Uncertainties associated with potential measurement 

error were too large at a few locations to make defensible 

conclusions regarding the delineation of gaining or losing 

creek reaches and those values are identified in italic font 

(table 5). Error-adjusted minimum and maximum values 

of measured streamflows were used to evaluate potential 

measurement error. Minimum and maximum values were 

computed by applying the measurement rating to the 

streamflow value; a “fair” measurement rating applies an error 

adjustment of ± 8 percent, and a “poor” rating applies an error 

adjustment of ±10 percent. For example: the August 2007 

error-adjusted minimum and maximum values for inflow to 

Walker Creek (12199890), 0.95 and 1.13 ft3/s, respectively, 

and the error-adjusted minimum and maximum values for flow 

at Walker Creek (12199890), 0.99 and 1.17 ft3/s, respectively, 

result in a gain or loss uncertainty range (cumulative 

measurement error) of -0.14–0.22 ft3/s. The uncertainty range 

was computed by subtracting the error-adjusted maximum 

value for inflow to Walker Creek (1.13 ft3/s) from the erroradjusted minimum value for flow at Walker Creek (0.99 ft3/s) 

to determine the lower uncertainty value (0.99 ft3/s – 

1.13 ft3/s = -0.14 ft3/s). The upper uncertainty value was 

computed by subtracting the error-adjusted minimum value 

for inflow to Walker Creek from the error-adjusted maximum 

value for flow at Walker Creek (1.17 ft3/s – 0.95 ft3/s = 

0.22 ft3/s). The uncertainty range suggests the possibility of 

either a gaining or losing creek reach, and does not support 

the delineation of a gaining reach indicated by the unadjusted 

value of 0.04 ft3/s. Conclusions regarding delineation of 

gaining or losing creek reaches were able to be made at most 

locations (table 5). For example: the June 2008 error-adjusted 

minimum and maximum values for inflow to Walker Creek 

(12199890), 12.4 and 13.8 ft3/s, respectively, and the erroradjusted minimum and maximum values for flow at Walker 

Creek (12199890), 15.5 and 18.1 ft3/s, respectively, result in a 

gain or loss uncertainty range (cumulative measurement error) 

of 1.7 to 5.7 ft3/s, and supports the delineation of a gaining 

reach indicated by the unadjusted value of 3.33 ft3/s.

The synoptic streamflow data (table 5) illustrate a general 

pattern in which the upper reaches of creeks in the study area 

tended to gain flow from the groundwater system, and lower 

creek reaches tended to lose flow (fig. 22). Substantial inflows 

from tributaries to major creeks in the study area suggest 

the presence of groundwater discharge from upland areas 

underlain by bedrock. Pitz and Garrigues (2000) noted that 

discharge to tributaries of Carpenter Creek are likely derived 

in large part from groundwater fracture flow within upland 

bedrock areas during low-flow conditions. Groundwater 

discharge from permeable clastic units (OEc) also is a likely 

contributor to baseflow in upland areas.

Groundwater-Level Fluctuations

Groundwater levels fluctuate over time, both seasonally 

and long term, in response to changing rates of recharge to 

and discharge from the groundwater system. When recharge 

exceeds discharge, the amount of water stored in an aquifer 

increases and water levels rise; when discharge exceeds 

recharge, groundwater storage decreases and water levels 

decline. Groundwater levels also may respond to changes 

in nearby stream stage. When stream stage exceeds nearby 

groundwater levels, streamflow may recharge the aquifer, 

causing a rise in groundwater levels; when groundwater levels 

exceed nearby stream stage, discharge from the aquifer to 

the stream may occur, resulting in a decline in groundwater 

levels. Seasonal changes in groundwater levels that follow a 

typical pattern for shallow wells in western Washington were 

observed in many tributary subbasin wells (Fasser and Julich, 

2009). Water levels rise from October through March, when 

precipitation and river stage are high, and decline from April 

through September, when precipitation and river stage are 

lower (figs. 23 and 24). 
Groundwater Movement 35

Table 5. Synoptic streamflow measurements and estimates of gains and losses in tributary subbasins, lower Skagit River basin, 

Washington, August 2007 and June 2008.

[Measurement site: Site locations are shown in figure 22. Inflow is the sum of streamflows measured upstream of the measurement site. Accuracy rating of the 

U.S. Geological Survey measurements: F, fair; P, poor; estimated values also are rated poor. Gain or Loss: Uncertainties associated with potential measurement 

error were too large at a few locations to make defensible conclusions regarding the delineation of gaining or losing creek reaches and those values are identified 

in italic. ft3/s, cubic feet per second]

Measurement site Site No. Date discharge 

measured

Discharge

 (ft3

/s) 

Accuracy 

rating

Inflow

(ft3/s)

Gain or loss 

(ft3/s)

East Fork Nookachamps Creek subbasin

Walker Creek 12199860 08-08-07

06-17-08

0.98

12.8

F

F

Tributary to Walker Creek 12199870 08-08-07

06-17-08

.06

.67

P

P

Walker Creek 12199890 08-08-07

06-18-08

1.08

16.8

F

F

1.04

13.47

0.04

3.33

East Fork Nookachamps Creek 12199900 08-07-07

06-19-08

4.29

51.4

F

F

East Fork Nookachamps Creek 03G100 08-07-07

06-19-08

 15.10 163.8

4.29

51.4

.81

12.4

Mundt Creek 12200005 08-06-07

06-18-08

1.09

11.1

F

P

East Fork Nookachamps Creek 12200010 08-07-07

06-19-08

4.58

66.1

F

F

6.19

74.9

-1.61

-8.8

Turner Creek 12200015 08-07-07

06-18-08

.50

2.48

F

F

Inflow to Beaver Lake 12200022 08-07-07

06-19-08

.19

3.11

F

F

Nookachamps Creek subbasin

Lake Creek 12199300 08-06-07

06-17-08

0.47

9.35

F

F

Lake Creek 12199400 08-07-07

06-17-08

1.13

19.2

F

F

.47

9.35

.66

9.85

Nookachamps Creek 1219949950 08-09-07

06-19-08

.60 F 2

3.75

 32.2 F 2

35.0

F

F

1.13

19.2

2.62

15.8

West Tributary to Nookachamps Creek 12199540 08-07-07

06-18-08

 0.46

1.88

P

P

East Tributary to Nookachamps Creek 12199560 08-09-07

06-18-08

.07

.39

P

P

Nookachamps Creek 12199600 08-09-07

06-19-08

.76

33.1

F

F

1.13

34.47

-.37

-1.37

Carpenter Creek subbasin

Carpenter Creek 12200682 08-09-07

06-16-08

0.08

3.71

P

F

Carpenter Creek 12200684 08-09-07

06-16-08

.22

5.29

P

F

0.08

3.71

0.14

1.58

Carpenter Creek 12200685 08-09-07

06-16-08

.41

8.89

F

F

.22

5.29

.19

3.60

Sandy Creek 12200686 07-23-07

06-16-08

.14

2.24

P

F

Johnson Creek 12200688 08-09-07

06-16-08

.01

1.68

F

F
36 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

Measurement site Site No. Date discharge 

measured

Discharge

 (ft3

/s) 

Accuracy 

rating

Inflow

(ft3/s)

Gain or loss 

(ft3/s)

Carpenter Creek subbasin—Continued

Bulson Creek 12200692 08-08-07

06-17-08

0.41

5.13

F

F

Tributary to Bulson Creek 12200694 08-08-07

06-17-08

.49

2.21

P

F

Carpenter Creek 12200696 09-21-00

06-19-08

 3 2.22

 12.4 F

1.46

20.15

0.76

-7.75

Fisher Creek subbasin

Fisher Creek 12200698 08-08-07

06-18-08

 4 0.01 41.50

P

P

Fisher Creek 12200699 08-07-07

06-18-08

 .00

5.80 F

4 0.01

4

1.50

-0.01

4.30

Fisher Creek 12200701 08-09-07

06-05-08

.49

6.38

P

F

.00

5.80

.49

.58

Tributary to Fisher Creek 1220070120 08-07-07

06-18-08

 .00

 41.00 P

Tributary to Fisher Creek 1220070140 08-07-07

06-18-08

4 .01 4 2.00

P

P

1

 Daily mean streamflow at Ecology streamflow-gaging station; accuracy rating assumed to be fair.

2

 Includes measured streamflow plus evaporative loss from Big Lake (table 4).

3

 Streamflow measured on September 20, 2000, accuracy rating assumed to be fair (Pitz and Garrigues, 2000); backwater conditions observed by the U.S. 

Geological Survey on August 8, 2007.

4

 Estimated by U.S. Geological Survey.

Table 5. Synoptic streamflow measurements and estimates of gains and losses in tributary subbasins, lower Skagit River basin, 

Washington, August 2007 and June 2008.—Continued

[Measurement site: Site locations are shown in figure 23. Inflow is the sum of streamflows measured upstream of the measurement site. Accuracy rating of the 

U.S. Geological Survey measurements: F, fair; P, poor; estimated values also are rated poor. Gain or Loss: Uncertainties associated with potential measurement 

error were too large at a few locations to make defensible conclusions regarding the delineation of gaining or losing creek reaches and those values are identified 

in italic. ft3/s, cubic feet per second]

Mean monthly streamflow (2001–08)

East Fork Nookachamps Creek

Gaging Station No. 03G100

0

20

40

60

80

100

120

140

OCT NOV DEC JAN FEB MAR APR MAY JUNE JULY AUG SEPT

MEAN MONTHLY STREAMFLOW, 

IN CUBIC FEET PER SECOND

Figure 19. Mean monthly streamflow (2001–08) for East Fork Nookachamps Creek at 

Washington State Department of Ecology streamflow-gaging station 03G100, lower Skagit 

River basin, Washington.
Groundwater Movement 37

wa19_0386_Fig20

11 14

AUGUST 2007

1 2 3 4 5 6 7 8 9 10 12 13 15

0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

2.0

DISCHARGE, IN CUBIC FEET PER SECOND

Carpenter Creek (12200684)

Nookachamps Creek (12199600)

Fisher Creek (12200701)

August 2007

synoptic streamflow

measurement period

EXPLANATION

20 23

JUNE 2008

10 11 12 13 14 15 16 17 18 19 21 22 24 25

0

20

10

40

60

80

30

50

70

90

100

DISCHARGE, IN CUBIC FEET PER SECOND

Carpenter Creek (12200684)

Nookachamps Creek (12199600)

Fisher Creek (12200701)

EXPLANATION

June 2008

synoptic streamflow

measurement period

Figure 20. Daily streamflow for U.S. Geological Survey streamflow-gaging stations on Nookachamps 

(12199600), Carpenter (12200684), and Fisher (12200701) Creeks, lower Skagit River basin, Washington, 

August 1–15, 2007.

Figure 21. Daily streamflow for U.S. Geological Survey streamflow-gaging stations on Nookachamps 

(12199600), Carpenter (12200684), and Fisher (12200701) Creeks, lower Skagit River basin, Washington, June 

10–25, 2008.
38 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

Figure 22. Locations of stream sites where streamflow was measured to determine groundwater discharge 

and delineate gaining and losing stream reaches in tributary subbasins and vicinity, lower Skagit River basin, 

Washington, August 2007 and June 2008.

tac09-9722-0328 Upper Skagit Geo_Fig 22

122°20' 122°10'

48°25'

48°20'

R.3 E. R.4 E. R.5 E. R.6 E.

T.

35

N.

T.

34

 N.

T.

33

 N.

T.

32

 N.

0 1 2 3 4 5 MILES

43210 5 KILOMETERS

EXPLANATION Streamflow-gaging stations

Ecology

U.S. Geological Survey

Synoptic streamflow site—Discharge 

 in cubic feet per second

August 2007

June 2008

12200701

12200005

03G100

 1.09

11.1

Boundary of tributary subbasin

Base from U.S. Geological Survey and/or

Washington Division of Geology and Earth Resources

digital data, 1983, 1:100,000

Universal Transverse Mercator projection, Zone 10

Horizontal Datum: North American Datum of 1927 (NAD 27)

03G100 12199600

12200684

12200701

12200686

12200698

12200699

12200022

12200015

12200005

12200010

12199560 12199900

12199540

12200694

12200692

12199860

12199890

12199300

12199400

12200696

12200682

12200685

12200688

1220070120 1220070140

1219949950

12199870

 0.98

12.8

 0.08

3.71

0.47

9.35

 0.06

0.67

0.07

0.39

 0.76

33.1

0.22

5.29

0.49

6.38

0.46

1.88 1.08

16.8

 4.29

51.4

 1.09

11.1

 4.58

66.1

0.50

2.48

0.19

3.11

 5.10

63.8

 1.13

19.2

1.14

2.24 0.41

8.89

0.01

1.68

0.49

2.21 2.22

12.4

0.01

2.00 0.00

1.00

 0.60 3.75

32.2 35.0

0.41

5.13

0.00

5.80

0.01

1.50

Sk agit River

South Fork Skagit River

Nookachamps Creek

Lake Creek

Carpenter Cree k

Lake

Ketchum

Ten

Lake

Devils

Lake

Big

Lake

Sixteen

Lake

Clear

Lake

Lake

McMurray

Beaver

Lake

Armstrong

Creek

Pilchuck

Creek

East Fork

Nook achamps

Creek

Skagit

Bay

Fisher

Cr eek

Skagit River

Skagit River

North Fork

Walker Creek

Turner

Creek

Mundt Creek

Noo kachamp Creek

Johnson Creek

Sandy Cre ek

Barney

Lake

Bulson Creek

Carpenter Creek
Groundwater Movement 39

tac09-9722-0386_Fig 23

9

8

7

6

5

4

3

2

1

0

GROUNDWATER LEVEL, IN FEET BELOW LAND SURFACE

PRECIPITATION, IN INCHES

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

STREAM GAGE HEIGHT, IN FEET

APR

2008

FEBJANDECNOV

2007

MAY JULYJUNE AUG SEPT OCT APRMAR MAY JULYJUNE AUG

0

1

2

3

4

5

6

7

8

9

Nookachamps Creek Gaging Station No 12199600

Monthly precipitation at Sedro-Woolley

Well No 34N/05E-32P01

172.0

171.6

171.2

170.8

170.4

170.0

169.6

169.2

168.8

168.4

GROUNDWATER LEVEL, IN FEET BELOW LAND SURFACE

PRECIPITATION, IN INCHES

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

STREAM GAGE HEIGHT, IN FEET

APR

2008

FEBJANDECNOV

2007

MAY JULYJUNE AUG SEPT OCT APRMAR MAY JULYJUNE AUG

0

1

2

3

4

5

6

7

8

9

Fisher Creek Gaging Station No 12200701

Monthly precipitation at Sedro-Woolley

Well No 33N/04E-28M01

Figure 23. Water levels in well 34N/05E-32P01, stream stage at U.S. Geological Survey steamflowgaging station on Nookachamps Creek (12199600), and precipitation at Sedro-Woolley, lower Skagit 

River basin, Washington, April 2007–August 2008.

Figure 24. Water levels in well 33N/04E-28M01, stream stage at U.S. Geological Survey streamflowgaging station on Fisher Creek (12200701), and precipitation at Sedro-Woolley, lower Skagit River basin, 

Washington, April 2007–August 2008.
40 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

The timing and magnitude of seasonal groundwaterlevel fluctuations in an aquifer system are related to the 

hydraulic characteristics of aquifer materials and adjacent 

confining units, the presence of unconfined or confined aquifer 

conditions, the depth to groundwater, and the depth of the 

well and screened intervals being measured. Water levels in 

deep wells typically respond to changes in recharge more 

slowly and with less magnitude than water levels in shallow 

wells, because deep wells are usually farther from the source 

of recharge, and variability is dampened. The largest waterlevel fluctuations observed during the monitoring period 

(October 2006 through September 2008) occurred in wells 

completed in the sedimentary aquifer (OEc), and ranged from 

about 3 to 27 ft (table 6). These unexpectedly large waterlevel fluctuations in relatively deep sedimentary aquifer wells 

may be attributed to several factors including the presence of 

water-bearing fractures (high conductivity and low storage) 

within local outcrop areas receiving precipitation recharge, 

and the relatively lower storage capacity of cemented 

sediments compared to sands and gravels (Freeze and Cherry, 

1979; Fetter, 1988). Water levels in wells completed in 

the unconsolidated hydrogeologic units exhibited seasonal 

variations ranging from less than 1 to about 10 ft.

Water Budget

On a long-term basis, a hydrologic system is usually in 

a state of dynamic equilibrium; that is, inflow to the system 

equals outflow from the system, and there is little or no change 

in the amount of water stored within the system. An estimated 

water budget for average precipitation during the study 

period (September 1, 2006, to August 31, 2008) in the four 

tributary subbasin area, as well as each individual subbasin, 

is presented in table 7. The methods used to estimate values 

of precipitation, groundwater recharge, and groundwater 

discharge to creeks are described in previous sections of this 

report. Surface runoff, including shallow subsurface flow, was 

computed as a residual; that is, it represents the quantity that 

remains after groundwater discharge to creeks is subtracted 

from total streamflow. The value for evapotranspiration also is 

a residual and was computed as the quantity that remains after 

surface runoff plus groundwater recharge is subtracted from 

precipitation. Precipitation during the study period (September 

1, 2006, to August 31, 2008) averaged an estimated 56 

in/yr over the tributary subbasins. Approximately one-third 

(33 percent) of precipitation enters the groundwater system in 

the subbasins as groundwater recharge. Most of this recharge 

(65 percent) discharges to creeks, and only about 3 percent is 

withdrawn from wells. The remaining groundwater recharge 

(32 percent) leaves the subbasin groundwater system as 

discharge to the Skagit River and Puget Sound.

Table 6. Statistical summary of groundwater-level fluctuations and well depth by hydrogeologic unit in tributary subbasins and vicinity, 

lower Skagit River basin, Washington, October 2006 through September 2008.

[–, no data]

Hydrogeologic unit Number 

of wells

Water-level fluctuation 

(feet)

Well depth 

(feet below land surface)

Minimum Median Maximum Minimum Median Maximum

Qago Alluvial and recessional outwash aquifer 7 2.72 5.96 7.37 17 35 58

Qgt Till confining unit 5 1.65 5.82 6.78 10 20 35

Qga Advance outwash aquifer 13 0.52 4.09 10.23 40 80 152

Qgl Glaciolacustrine and distal outwash confining unit 2 1.25 4.34 7.42 25 103 180

Qco Inter-glacial alluvial aquifer 4 0.96 1.69 2.57 126 268 366

Qot Older till confining unit 0 – – – – – –

Qooa Older outwash and alluvial aquifer 2 3.00 3.21 3.42 240 248 256

OEc Sedimentary aquifer 12 3.28 10.51 27.49 15 241 500

EJTP Igneous and metamorphic bedrock unit 2 1.50 5.75 10.00 124 252 380
Groundwater Movement 41

Water-budget component

Quantity

Percent Inches 

per year

Acre-feet 

per year

All subbasins

Precipitation

Fate of precipitation

Surface runoff 20 100,200 35

Evapotranspiration 18 91,400 32

Groundwater recharge 18 92,400 33

Total precipitation 56 284,000 100

Fate of recharge

Discharge to creeks 12 60,400 65

Other natural discharge 6 29,800 32

Withdrawals from wells <1 2,200 3

Total recharge 18 92,400 100

East Fork Nookachamps Creek subbasin 

Precipitation

Fate of precipitation

Surface runoff 27 52,960 39

Evapotranspiration 22 42,900 31

Groundwater recharge 21 41,060 30

Total precipitation 70 136,920 100

Fate of recharge

Discharge to creeks 18 34,740 85

Other natural discharge 3 6,300 15

Withdrawals from wells <1 20 <1

Total recharge 21 41,060 100

Nookachamps Creek subbasin

Precipitation

Fate of precipitation

Surface runoff 16 24,870 33

Evapotranspiration 17 26,110 35

Groundwater recharge 16 23,840 32

Total precipitation 49 74,820 100

Fate of recharge

Discharge to creeks 11 16,610 70

Other natural discharge 5 7,020 30

Withdrawals from wells <1 210 <1

Total recharge 16 23,840 100

Water-budget component

Quantity

Percent Inches 

per year

Acre-feet 

per year

 Carpenter Creek subbasin

Precipitation

Fate of precipitation

Surface runoff 18 17,720 38

Evapotranspiration 11 11,690 25

Groundwater recharge 17 17,200 37

Total precipitation 46 46,610 100

Fate of recharge

Discharge to creeks 5 5,480 32

Other natural discharge 10 9,880 57

Withdrawals from wells 2 1,840 11

Total recharge 17 17,200 100

Fisher Creek subbasin

Precipitation

Fate of precipitation

Surface runoff 8 4,610 18

Evapotranspiration 20 10,820 42

Groundwater recharge 19 10,300 40

Total precipitation 47 25,730 100

Fate of recharge

Discharge to creeks 7 3,590 35

Other natural discharge 12 6,580 64

Withdrawals from wells <1 130 1

Total recharge 19 10,300 100

Table 7. Estimated average annual water budget for tributary subbasins, lower Skagit River basin, Washington, September 1, 2006, to 

August 31, 2008.

[<. less than]
42 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

Summary and Conclusions

Recent population growth along the Interstate 5 corridor 

near Mount Vernon, Washington, has led to increased water 

use, with many new domestic wells serving residents in the 

lower Skagit River basin in areas not served by a regional 

public-water system. Planning for future development 

in the lower basin, including the reservation of water for 

new domestic wells, requires identification of areas where 

withdrawals from existing and new wells could adversely 

impact streamflow in the Skagit River or its tributaries. A 

study to characterize the groundwater/surface-water flow 

system in four tributary subbasins of the lower Skagit River 

was conducted by the U.S. Geological Survey to assist Skagit 

County and the Washington State Department of Ecology in 

evaluating the effects of potential groundwater withdrawals 

and consumptive use on tributary streamflows. 

The study area covers about 247 square miles along the 

Skagit River and its tributary subbasins in southwestern Skagit 

County and northwestern Snohomish County, Washington. 

The Skagit River occupies a large, relatively flat alluvial 

valley that is bounded to the south and east by upland and 

mountainous terrain. The alluvial valley primarily is underlain 

by fluvial sand and gravel deposits, and locally preserved lahar 

runout deposits. Upland areas contain laterally discontinuous 

bodies of glacial (till and outwash) and interglacial (fluvial 

and lacustrine) deposits of varying thickness that reflect both 

terrestrial and shallow marine depositional environments. 

Bedrock consisting of metamorphic rocks, sedimentary units, 

and igneous rocks underlies the alluvial valley and upland 

areas, and crops out throughout the mountainous terrain. The 

southwest flowing Skagit River receives streamflow from 

four tributary subbasins (East Fork Nookachamps Creek, 

Nookachamps Creek, Carpenter Creek, and Fisher Creek) that 

originate within the mountainous interior of the study area. 

The lower reaches of most creeks flow year-round, however, 

intermittent flow conditions are common in middle and upper 

creek reaches during the summer months.

A simplified surficial geologic map was compiled 

from previous mapping in the area, and geologic units were 

differentiated into nine hydrogeologic units: Alluvial and 

recessional outwash aquifer (Qago), Till confining unit (Qgt), 

Advance outwash aquifer (Qga), Glaciolacustrine and distal 

outwash confining unit (Qgl), Inter-glacial alluvial aquifer 

(Qco), Older till confining unit (Qot), Older outwash and 

alluvial aquifer (Qooa), Sedimentary aquifer (OEc), and 

Igneous and metamorphic bedrock unit (EJTP). A surficial 

hydrogeologic unit map was constructed and used with 

drillers’ logs from 296 wells to produce four hydrogeologic 

sections, and unit extent and thickness maps.

Unconsolidated aquifers (Qago, Qga, Qco, and Qooa) 

typically consist of moderately to well-sorted alluvial and 

glacial outwash deposits of sand, gravel, and cobbles, with 

minor lenses of silt and clay. These units typically occur as 

discontinuous or isolated bodies, and are of highly variable 

thickness. Unconfined conditions exist in areas where aquifer 

units are present at land surface; however, much of the 

study area is mantled by glacial till, and confined aquifer 

conditions are common. Estimated hydraulic conductivity 

for the aquifers ranged from 0.27 ft/d (OEc) to 57 ft/d (Qco). 

Groundwater in the unconsolidated aquifers generally flows 

towards the northwest and west in the direction of the Skagit 

River and Puget Sound. This generalized flow pattern is likely 

complicated by the presence of low permeability confining 

units that separate discontinuous bodies of aquifer material 

and act as local groundwater flow barriers. Water-level altitude 

differences between the advance outwash (Qga) and interglacial alluvial (Qco) aquifers in the southwestern part of the 

study area suggest downward vertical flow. The potential for 

upward groundwater movement, indicated by the presence of 

flowing wells, was observed at several locations within the 

aquifer units. 

Unconsolidated confining units (Qgt, Qgl, and Qot) 

typically consist of poorly sorted glacial till, glaciolacustrine, 

and landslide deposits of clay, silt, sand, gravel, cobbles, 

and boulders, with locally occurring sand and gravel lenses 

capable of providing water for domestic use. Estimated 

hydraulic conductivity for the confining units ranged from 

0.13 ft/d (EJTP) to 26 ft/d (Qgl). The Vashon Till (Qgt) is 

present throughout much of the study area; other confining 

units are more limited in extent. 

The sedimentary aquifer (OEc) is present in large parts 

of the glacial upland and mountains in central and southern 

parts of the study area and consists primarily of conglomerate 

and sandstone with fine-grained intervals. Confined conditions 

are likely where the aquifer is fully saturated and overlain 

by glacial confining units; fine-grained intervals within 

the aquifer also may produce locally confined conditions. 

Groundwater flow directions in the sedimentary aquifer likely 

reflect local topographic relief (radial flow from bedrock 

highs) and more regional westward flow from the mountains 

to the Puget Sound.

The igneous and metamorphic bedrock unit (EJTP) is 

present along the northern margin of the glacial uplands in 

the mountains along the eastern margin of the study area, 

and within segments of the Darington-Devils Mountain Fault 

Zone. This low-permeability unit is composed of volcanic 

and metamorphic rocks and consists of rhyolite, andesite, 

basalt, and complex assemblages of low-grade metasediments, 

metavolcanics, and meta-intrusives, and is considered to be 

non-water bearing except in localized areas of fracturing.
Selected References 43

The largest groundwater level fluctuations observed 

during the monitoring period (October 2006 through 

September 2008) occurred in wells completed in the 

sedimentary aquifer, and ranged from about 3 to 27 feet. Water 

levels in wells completed in unconsolidated hydrogeologic 

units exhibited seasonal variations ranging from less than 1 to 

about 10 feet. Synoptic streamflow measurements made in 

August 2007 and June 2008 indicate groundwater discharge 

to creeks in the subbasins ranged from about 13.15 to 

129.6 cubic feet per second (9,520 to 93,830 acre-feet per 

year), respectively. Streamflow measurements illustrate a 

general pattern in which the upper reaches of creeks in the 

study area tended to gain flow from the groundwater system, 

and lower creek reaches tended to lose water. Significant 

inflows from tributaries to major creeks in the study area 

suggest the presence of groundwater discharge from upland 

areas underlain by bedrock. 

The groundwater system within the subbasins received 

an average (September 1, 2006, to August 31, 2008) of 

about 92,400 acre-feet or about 18 inches of recharge from 

precipitation a year. Most of this recharge (65 percent) 

discharges to creeks, and only about 3 percent is withdrawn 

from wells. The remaining groundwater recharge (32 percent) 

leaves the subbasin groundwater system as discharge to the 

Skagit River and Puget Sound.

Acknowledgments

The authors wish to thank the many well owners in the 

study area who provided access to their wells during this 

study, and special thanks go to the property owners who 

allowed observation wells to be installed on their property. Joe 

Dragovich and other staff of the Washington State Department 

of Natural Resources generously provided interpretive 

data that was crucial to the subsurface identification and 

delineation of geologic units, and the development of the 

hydrogeologic framework presented in this report. The authors 

gratefully acknowledge this significant contribution. The 

authors also wish to thank Skagit County and the Washington 

State Department of Ecology for providing assistance in the 

compilation of well information.

Selected References 

Bear, Jacob, 1979, Hydraulics of groundwater: New York, 

McGraw-Hill, 569 p.

Bidlake, W.R., and Payne, K.L., 2001, Estimating recharge to 

ground water from precipitation at Naval Submarine Base 

Bangor and Vicinity, Kitsap County, Washington: U.S. 

Geological Survey Water- Resources Investigations Report 

01-4110, 33 p.

Booth, D.B., 1994, Glaciofluvial infilling and scour of the 

Puget Lowland, Washington, during ice-sheet glaciation: 

Geology, v. 22, no. 8, p. 695-698.

Carnahan, B., Luther, H.A., and Wilkes, J.O., 1969, Applied 

numerical methods: New York, John Wiley and Sons, Inc., 

604 p.

Daly, Christopher, Neilson, R.P., and Phillips, D.L., 1994, A 

statistical-topographic model for mapping climatological 

precipitation over mountainous terrain: Journal of Applied 

Meteorology, v. 33, no. 2, p. 140–158.

Dethier, D.P., Whetten, J.T., and Carroll, P.R., 1980, 

Preliminary geologic map of the Clear Lake SE quadrangle, 

Skagit County, Washington: U.S. Geological Survey OpenFile Report 80-303, 11 p., 2 plates.

Dethier, D.P., and Whetten, J.T., 1980, Preliminary geologic 

map of the Clear Lake SW quadrangle, Skagit and 

Snohomish Counties, Washington: U.S. Geological Survey 

Open-File Report 80-825, 11 p., 2 plates.

Dethier, D.P., and Whetten, J.T., 1981, Preliminary geologic 

map of the Mount Vernon 7.5-minute quadrangle, Skagit 

County, Washington: U.S. Geological Survey Open-File 

Report 81-105, 10 p., 1 plate, scale 1:24,000.

Dragovich, J.D., and DeOme, A.J., 2006, Geologic map of the 

McMurray 7.5-minute quadrangle, Skagit and Snohomish 

Counties, Washington: Washington Division of Geology 

and Earth Resources Geologic Map GM-61, 18 p., 1 sheet, 

scale 1:24,000.

Dragovich, J.D., Gilbertson, L.A., Norman, D.K., Anderson, 

Garth, and Petro, G.T., 2002, Geologic map of the Utsalady 

and Conway 7.5-minute quadrangles, Skagit, Snohomish, 

and Island Counties, Washington: Washington Division of 

Geology and Earth Resources Open-File Report 2002-5, 

34 p., 2 sheets, scale 1:24,000.

Dragovich, J.D., and Grisamer, C.L., 1998, Quaternary 

stratigraphy, cross sections, and general geohydrologic 

potential of the Bow and Alger 7.5-minute quadrangles, 

western Skagit County, Washington: Washington Division 

of Geology and Earth Resources Open File Report 98-8, 

30 p., 6 plates.

Dragovich, J.D., Pringle, P.T., and Walsh, T.J., 1994, Extent 

and geometry of the Mid-Holocene Osceola Mudflow in the 

Puget Lowland—Implications for Holocene sedimentation 

and paleogeography: Washington State Department of 

Natural Resources, Washington Geology, v. 22, no. 3, 

p. 3-26.
44 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

Dragovich, J.D., Troost, M.L., Norman, D.K., Anderson, 

Garth, Cass, Jason, Gilbertson, L.A., and McKay, D.T., 

Jr., 2000, Geologic map of the Anacortes South and 

La Conner 7.5-minute quadrangles, Skagit and Island 

Counties, Washington: Washington Division of Geology 

and Earth Resources Open File Report 2000-6, 4 sheets, 

scale 1:24,000.

Drost, B.W., 2005, Quality-assurance plan for ground-water 

activities, U.S. Geological Survey, Washington Water 

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

05-1126, 27 p. http://pubs.usgs.gov/of/2005/1126/.

Easterbrook, D.J., 1969, Pleistocene chronology of the Puget 

Lowland and San Juan Islands, Washington: Geological 

Society of America Bulletin, v. 80, no. 11, p. 2273-2286.

Fasser, E.T., and Julich, R.J., 2009, Hydrographs showing 

ground-water level changes for selected wells in the Lower 

Skagit River basin, Washington: U.S. Geological Survey 

Data Series 441.

Ferris, J.G., Knowles, D.B., Brown, R.H., and Stallman, R.W., 

1962, Theory of aquifer tests: U.S. Geological Survey 

Water-Supply Paper 1536-E, 174 p.

Fetter, C.W., 1988, Applied hydrogeology: Columbus, OH, 

Merrill Publishing Company, 592 p.

Freeze, R.A., and Cherry, J.A., 1979, Groundwater: 

Englewood Cliffs, NJ, Prentice-Hall, 604 p.

GeoEngineers, 1996, Geologic/hydrogeologic services, water 

resources plan, Skagit County, Washington: File no. 2402-

006-73/121196, 389 p., 4 plates.

GeoEngineers, 2003, Lower and upper Skagit watershed 

plan Samish River sub-basin, ground water hydrology 

evaluation: File no. 7291-001-00-1180, 175 p.

Hansen, H.P., and Mackin, J.H., 1949, A pre-Wisconsin forest 

succession in the Puget Lowland, Washington: American 

Journal of Science, v. 247, no. 12, p. 833-855.

Hutchinson, M.F., 1989, A new method for gridding elevation 

and streamlining data with automated removal of pits: 

Journal of Hydrology, v. 106, p. 211-232.

Johnson, S.Y., 1982, Stratigraphy, sedimentology, and tectonic 

setting of the Eocene Chuckanut Formation, northwest 

Washington: University of Washington Ph.D thesis, 221 p., 

4 plates.

Lane, R.C., 2009, Estimated water use in Washington, 

2005: U.S. Geological Survey Scientific Investigations 

Report 2009–5128, 30 p.

Marcus, K.L., 1981, The rocks of Bulson Creek–EoceneOligocene sedimentation and tectonics in the Lake 

McMurray area, Washington: Western Washington 

University M.S. thesis, 84 p., 1 plate.

National Land Cover Database, 2001: accessed May, 2009, 

http://www.mrlc.gov/multizone_download.php?zone=1.

National Oceanic and Atmospheric Administration, 1982, 

Evaporation atlas for the contiguous 48 United States: 

NOAA Technical Report NWS 33, 27 p., 4 plates.

National Oceanic and Atmospheric Administration, 2007, 

Climatological data, annual summary, Washington, 2007: 

Asheville, North Carolina, National Climatic Data Center, 

v.111, no. 13, 30 p.

Oregon State University, 2009, PRISM Products: accessed 

May, 2009 at http://www.prism.oregonstate.edu.

Pessl, Fred, Jr., Dethier, D.P., Booth, D.B., and Minard, J.P., 

1989, Surficial geologic map of the Port Townsend 30- by 

60-minute quadrangle, Puget Sound region, Washington: 

U.S. Geological Survey Miscellaneous Investigations 

Series Map I-1198-F, 1 sheet, scale 1:100,000, with 13 p. 

text.

Pitz, C.F., and Garrigues, R.S., 2000, Summary of streamflow 

conditions, September 2000, Fisher Creek and Carpenter 

Creek Basin: Washington State Department of Ecology 

Publication no. 00-03-049, 44 p.

Rantz, S.E., 1982, Measurement and computation of 

streamflow, volume 1—Measurement of stage and 

discharge: U.S. Geological Survey Water-Supply Paper 

2175, 284 p.

Schuster, J.E., 2000, 1:100,000-scale digital geology of 

Washington State: Washington Division of Geology and 

Earth Resources: Digital Coverage.

Skagit County Assessor, 2008, domestic connections: 

accessed March, 2008, at http://www.skagitcounty.net/

Common/Asp/Default.asp?d=GIS&c=General&p=Digital/

main.htm.

Snohomish County Assessor, 2008, domestic connections: 

accessed April 2008, at http://www1.co.snohomish.wa.us/

Departments/PDS/Divisions/LR_Planning/Information/

Maps/mapsgisdata.htm.
Selected References 45

Tabor, R.W., 1994, Late Mesozoic and possible Early Tertiary 

accretion in western Washington State–The HelenaHaystack mélange and the Darrington-Devils Mountain 

fault zone: Geological Society of America Bulletin, v. 106, 

no. 2, p. 217-232, 1 plate.

Thomas, B.E., Wilkinson, J.M., and Embrey, S.S., 1997, The 

ground-water system and ground-water quality in western 

Snohomish County, Washington: U.S Geological Survey 

Water-Resources Investigations Report 96-4312, 218 p., 

9 plates.

U.S. Census Bureau, 2000: accessed April, 2008, at http://

www.census.gov/census2000/states/wa.html.

U.S. Department of Agriculture Natural Resources 

Conservation Service, 2007, crop irrigation rates and 

methods: accessed March, 2009, at http://www.wa.nrcs.

usda.gov/technical/ENG/irrigation_guide/index.html.

Washington State Department of Agriculture, 2008, crop 

location maps: accessed January, 2009 at http://agr.wa.gov/

PESTFERT/NatResources/AgLandUse.aspx.

Washington State Department of Ecology, 2009, river and 

stream flow monitoring: accessed February, 2009, at http://

www.ecy.wa.gov/programs/eap/flow/shu_main.html.

Washington State Department of Health, 2008, Public supply 

connections: accessed March, 2008, at http://www4.doh.

wa.gov/sentryinternet/Intro.aspx

Western Regional Climate Center, 2008: accessed November, 

2009, at http://www.wrcc.dri.edu/cgi-bin/cliMONtpre.

pl?wa7507

Whetten, J.T., Carroll, P.I., Gower, H.D., Brown, E.H., and 

Pessl, Fred, Jr., 1988, Bedrock geologic map of the Port 

Townsend 30- by 60-minute quadrangle, Puget Sound 

region, Washington: U.S. Geological Survey Miscellaneous 

Investigations Series Map I-1198-G, 1 sheet, scale 

1:100,000. 

Whetten, J.T., Dethier, D.P., and Carroll, P.R., 1979, 

Preliminary geologic map of the Clear Lake NE quadrangle, 

Skagit County, Washington: U.S. Geological Survey OpenFile Report 79-1468, 10 p., 2 plates.

Whetten, J.T., Dethier, D.P., and Carroll, P.R., 1980, 

Preliminary geologic map of the Clear Lake NW 

quadrangle, Skagit County, Washington: U.S. Geological 

Survey Open-File Re port 80-247, 12 p., 2 plates.
46 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

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Savoca and others— Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington —Scientific Investigations Report 2009–5270