Hydrology of the Johnson Creek Basin, Oregon 

Scientific Investigations Report 2009–5123

Prepared in cooperation with the city of Portland, the city of Gresham, the city of Milwaukie, 

Clackamas County’s Water Environment Services, and Multnomah County

U.S. Department of the Interior

U.S. Geological Survey
Cover:

Top: Photograph of Crystal Springs Creek at Reed College, Portland, Oregon, July 6, 2005.

Middle: Photograph of Holgate Lake at Portland, Oregon, March 13, 2006.

Bottom: Photograph of Johnson Creek at Portland, Oregon, December 25, 2006. 

Photographs taken by Karl K. Lee, U.S. Geological Survey.
Hydrology of the Johnson Creek Basin, Oregon

By Karl K. Lee and Daniel T. Snyder

Prepared in cooperation with the city of Portland, the city of Gresham, the 

city of Milwaukie, Clackamas County’s Water Environment Services, and 

Multnomah County 

Scientific Investigations Report 2009–5123

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

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

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, 

natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod

To order this and other USGS information products, visit http://store.usgs.gov

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Lee, K.K., and Snyder, D.T., 2009, Hydrology of the Johnson Creek basin, Oregon: U.S. Geological Survey Scientific 

Investigations Report 2009–5123, 56 p.
iii

Contents

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

Introduction.....................................................................................................................................................2

Hydrologic Setting ................................................................................................................................2

Land Use.................................................................................................................................................4

Previous Investigations........................................................................................................................4

Purpose and Scope ..............................................................................................................................5

Methods...........................................................................................................................................................5

Groundwater..........................................................................................................................................5

Surface Water.......................................................................................................................................8

Water Quality.........................................................................................................................................9

Meteorologic Data................................................................................................................................9

Groundwater Hydrology................................................................................................................................9

Recharge................................................................................................................................................9

Groundwater Discharge ....................................................................................................................10

Springs and Seepage................................................................................................................11

Long-Term Streamflow Data....................................................................................................17

Use of Environmental Tracers to Identify Groundwater Discharge ..................................18

Groundwater Flow Direction.............................................................................................................20

Variation in Groundwater Levels and Storage...............................................................................22

Response of the Groundwater System to Precipitation Extremes ............................................29

High and Low Groundwater Discharge: Crystal Springs Creek.........................................29

Use of Hydrologic Data to Predict Streamflow of 

Crystal Springs Creek .........................................................................................30

Flooding from High Groundwater Level–Holgate Lake........................................................32

Use of Hydrologic Data to Anticipate Flooding from Holgate Lake..........................34

Surface-Water Hydrology ..........................................................................................................................35

Annual Flow .........................................................................................................................................35

Spatial Trends.............................................................................................................................35

Temporal Trends.........................................................................................................................36

Low Flow...............................................................................................................................................36

Spatial Trends.............................................................................................................................37

Temporal Trends.........................................................................................................................38

High Flow..............................................................................................................................................41

Spatial Trends.............................................................................................................................41

Temporal Trends.........................................................................................................................44

Implications for Water Quality...................................................................................................................47

Stream Temperature...........................................................................................................................47

Sediment and Other Contaminants..................................................................................................49

Potential Future Studies..............................................................................................................................50

Summary .......................................................................................................................................................50

Acknowledgments.......................................................................................................................................52

References Cited..........................................................................................................................................52
iv

Figures

Figure 1. Map showing location of the Johnson Creek basin, Oregon........................... 3

Figure 2. Graph showing streamflow measurements of Crystal Springs Creek at Reed

College, measurements and estimates of streamflow at the mouth of Crystal

Springs Creek, and measurements of Errol Spring Creek, Portland, Oregon ...... 11

Figure 3. Graph showing relation between average measured streamflow at the 

mouth of Crystal Springs Creek, Portland, Oregon, and consecutive 7-day 

average low streamflow of Johnson Creek at Milwaukie, Oregon, August to 

October 1989, 1997–2006 .................................................................. 12

Figure 4. Graph showing seepage measurements during low flow in 1988, 1997–2000,

2006, and specific conductance measurements during low flow in 1998, 1999,

and 2006, Johnson Creek, Oregon ......................................................... 15

Figure 5. Graph showing annual, 3-year average, and cumulative departure from 

average precipitation at Portland Airport, Oregon, 1911–2006 ........................ 16

Figure 6. Graph showing gain in consecutive 7-day average low streamflow between

Johnson Creek at Regner Road at Gresham, Oregon, and Johnson Creek at

Sycamore, Oregon, and between Johnson Creek at Sycamore and Johnson

Creek at Milwaukie, Oregon ............................................................... 17

Figure 7. Graph showing temperature at river mile (RM) 7.8, RM 5.5, and RM 3.2, 

Johnson Creek, Oregon..................................................................... 19

Figure 8. Map showing estimated water table elevation, Johnson Creek basin, Oregon...... 21

Figure 9. Hydrographs showing water levels in selected long-term observation wells,

Johnson Creek basin, Oregon ............................................................ 24

Figure 10. Graphs showing water level elevation and depth to water in wells: near 

133rd Avenue and Raymond Street, at Brentwood Park, at Woodstock Park, 

and at Berkeley Park, Portland, Oregon ................................................ 26

Figure 11. Graphs showing precipitation at Portland Airport, Oregon, water level 

elevation in the shallow well at Westmoreland Park and water level of 

Johnson Creek at Milwaukie, Oregon, and water level elevation in the 

deep well at Westmoreland Park, and level of the Willamette River at 

Portland, Oregon ........................................................................... 27

Figure 12. Graph showing relation between water level elevation in wells at Berkeley

Park, and at 32nd Avenue and Steele Street, Portland, Oregon ..................... 31

Figure 13. Graph showing relation between streamflow of Crystal Springs Creek at 

Reed College and mouth of Crystal Springs Creek at Portland, and water 

level elevation in the well at Berkeley Park, Portland, Oregon ........................ 31

Figure 14. Graph showing water level elevation (1999–2006) of Holgate Lake at 

Portland, Oregon, in the well near 133rd Avenue and Raymond Street, in the 

well in the bed of Holgate Lake, in the well adjacent to Holgate Lake, and 

cumulative precipitation (from October to September each year) at Portland 

Airport, Oregon .............................................................................. 33

Plate

Plate 1. Map showing location of groundwater and surface-water sites in the Johnson Creek 

basin, Oregon.
v

Figures—Continued

Figure 15. Graph showing relation between annual rise in water level in a well near 

133rd Avenue and Raymond Street, Portland, Oregon, and cumulative 

precipitation at the Portland Airport, Oregon, from October 1 of each year to 

date of maximum water level in well, water years 1999–2006 ........................ 34

Figure 16. Graph showing cumulative departure from annual mean streamflow of 

Johnson Creek at Sycamore, Oregon, water years 1941–2006, Johnson Creek 

at Milwaukie, Oregon, water years 1990–2006, and annual total precipitation 

at the Portland Airport, Oregon (site number 356751), water years 1941–2006 ...... 37

Figure 17. Graph showing flow duration curves of the upper area of Johnson Creek 

basin at Gresham, Oregon, of the middle basin between Johnson Creek at 

Gresham and Johnson Creek at Sycamore, Oregon, and of the lower basin 

between Johnson Creek at Sycamore and Johnson Creek at Milwaukie, 

Oregon, water years 1999–2006............................................................ 38

Figure 18. Graphs showing consecutive 7-day and 30-day average low streamflow of

Johnson Creek at Sycamore, Oregon, and of Little Sandy River near Bull Run,

Oregon ....................................................................................... 39

Figure 19. Graph showing flow duration curves based on water years 1941–1962 (early),

water years 1963–1984 (middle), and water years 1985–2006 (later), Johnson

Creek at Sycamore, Oregon ............................................................... 40

Figure 20. Graph showing annual peak streamflow of Johnson Creek at Sycamore, and

Johnson Creek at Milwaukie, Oregon ................................................... 43

Figure 21. Graph showing flood frequency curves based on log-Pearson Type III

probability distribution, Johnson Creek at Sycamore, Oregon, water years

1941–2006 and 1990–2006, and Johnson Creek at Milwaukie, Oregon, water

years 1990–2006.............................................................................. 45

Figure 22. Graph showing rating curve in use during water year 2006, and annual peak

stream level and streamflow from water years 1941 to 2006, Johnson Creek at

Sycamore, Oregon........................................................................... 45

Figure 23. Graph showing temperature of streams in the Johnson Creek basin, Oregon,

May to October 2005 ........................................................................ 48

Figure 24. Graph showing estimated temperature of Johnson Creek at Gresham, Oregon,

and Johnson Creek at Milwaukie, Oregon, based on air temperature at the

Portland Airport, Oregon (site number 356751), 1998–2006 ........................... 49

Tables

Table 1. Groundwater and surface-water sites in the Johnson Creek basin, Oregon......... 6

Table 2. Streamflow and specific conductance measurements used in seepage 

analysis, Johnson Creek, Oregon. ......................................................... 14

Table 3. Annual peak streamflow and volume, Johnson Creek, Oregon, water years 

1990–2006 .................................................................................... 42

Table 4. Magnitude and probability of peak streamflow of Johnson Creek, Oregon ......... 44
vi

Conversion Factors, Datums, and Abbreviations

Conversion Factors

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

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)

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

million gallons per day (Mgal/d) 0.04381 cubic meter per sec (m3/s)

Flow rate

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

acre-foot per year (acre-ft/yr) 0.001233 cubic hectometer per year (hm3/yr)

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

cubic foot per second per square 

mile [(ft3/s)/mi2]

 0.01093 cubic meter per second per square 

kilometer [(m3/s)/km2]

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

Hydraulic gradient

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

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

°F=(1.8×°C)+32.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25°C).

Datums

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 1929), or to the North American Vertical Datum of 1988 (NAVD 1988), as indicated in text, 

plate, figures, and tables.

Horizontal coordinate information is referenced to the North American Datum of 1927 

(NAD 1927), or to the North American Datum of 1983 (NAD 1983), as indicated in text, plate, 

figures, and tables.

Elevation, as used in this report, refers to distance above the vertical datum.
vii

Abbreviation Meaning

DEM Digital elevation model

GPS Global Positioning System

NWIS National Water Information System

NWS National Weather Service

OWRD Oregon Water Resources Department

PRISM Precipitation Elevation Regressions on Independent Slopes Model

RM River mile

TMDL Total Maximum Daily Load

UIC Underground injection control

USGS U.S. Geological Survey

UTM Universal Transverse Mercator

WY Water year, the 12-month period from October 1 through September 30, 

and is identified by the calendar year in which it ends

Abbreviations
viii

This page intentionally left blank.
Abstract

The Johnson Creek basin is an important resource in the 

Portland, Oregon, metropolitan area. Johnson Creek forms a 

wildlife and recreational corridor through densely populated 

areas of the cities of Milwaukie, Portland, and Gresham, and 

rural and agricultural areas of Multnomah and Clackamas 

Counties. The basin has changed as a result of agricultural and 

urban development, stream channelization, and construction 

of roads, drains, and other features characteristic of human 

occupation. Flooding of Johnson Creek is a concern for the 

public and for water management officials. The interaction 

of the groundwater and surface-water systems in the Johnson 

Creek basin also is important. The occurrence of flooding 

from high groundwater discharge and from a rising water 

table prompted this study. As the Portland metropolitan 

area continues to grow, human-induced effects on streams 

in the Johnson Creek basin will continue. This report 

provides information on the groundwater and surface-water 

systems over a range of hydrologic conditions, as well as the 

interaction these of systems, and will aid in management of 

water resources in the area. 

High and low flows of Crystal Springs Creek, a 

tributary to Johnson Creek, were explained by streamflow 

and groundwater levels collected for this study, and results 

from previous studies. High flows of Crystal Springs Creek 

began in summer 1996, and did not diminish until 2000. 

Low streamflow of Crystal Springs Creek occurred in 

2005. Flow of Crystal Springs Creek was related to waterlevel fluctuations in a nearby well, enabling prediction of 

streamflow based on groundwater level.

Holgate Lake is an ephemeral lake in Southeast Portland 

that has inundated residential areas several times since the 

1940s. The water-surface elevation of the lake closely tracked 

the elevation of the water table in a nearby well, indicating 

that the occurrence of the lake is an expression of the water 

table. Antecedent conditions of the groundwater level and 

autumn and winter precipitation totals were used to anticipate 

flooding of Holgate Lake.

Several factors affect annual mean flow of Johnson 

Creek. More precipitation falls in the southeastern area of the 

basin because of the topographic setting. Runoff from much 

of the northern and western areas of the basin does not flow 

into Johnson Creek due to permeable deposits, interception by 

combined sewer systems, and by groundwater flow away from 

Johnson Creek. Inflow from Crystal Springs Creek accounts 

for one-half of the increase in streamflow of Johnson Creek 

between the Sycamore and Milwaukie sites.

Low flows of Johnson Creek vary as a result of 

fluctuations in groundwater discharge to the creek, although 

past water uses may have decreased flows. The groundwater 

contributions to streamflow upstream of river mile (RM) 5.5 

are small compared to contributions downstream of this 

point. Comparison of flows to a nearby basin indicates that 

diversions of surface water may have resulted in a 50 percent 

decrease in low flows from about 1955 to 1977.

Runoff from the drainage basin area upstream of the 

Johnson Creek at Sycamore site contributes more to peak 

streamflow and peak volume than the drainage basin area 

between the Sycamore and Milwaukie sites. The average 

increase in annual peak streamflow and annual peak volume 

between the two sites was 11 and 24 percent, respectively. 

Decreased contribution in the lower area of the drainage basin 

is a result of infiltration, interception by drywell and combined 

sewer systems, and temporary overbank storage.

Trends in flow typically associated with increasing urban 

development were absent in Johnson Creek. Annual, low, 

and high flows showed no trend from 1941 to 2006. Much 

of the infrastructure that may affect runoff from agricultural, 

residential, and urban development was in place prior to 

collection of hydrologic data in the basin. Management 

of stormwater in the urban areas by routing runoff from 

impervious surfaces to drywell and combined sewer systems 

may have affected runoff characteristics.

Understanding the distribution of runoff in the Johnson 

Creek basin helps protect water quality. Summer temperature 

of Johnson Creek and tributary streams is affected by 

groundwater discharge and by exposure of the stream to the 

surrounding atmosphere. Although groundwater discharge 

cools the stream in some reaches, other stream reaches with 

relatively shallow, unshaded ponds show warming. High flow 

in Johnson Creek may entrain sediment and sediment-borne 

contaminants. Management of runoff, especially in the eastern 

area of the basin, will maintain and improve the ecological 

health of Johnson Creek. 

Hydrology of the Johnson Creek Basin, Oregon

By Karl K. Lee and Daniel T. Snyder
2 Hydrology of the Johnson Creek Basin, Oregon

Introduction

The Johnson Creek basin is located in northwestern 

Oregon on the eastern side of the Portland metropolitan area in 

Multnomah and Clackamas Counties. Johnson Creek is about 

24 mi long and has a surface-water drainage basin that covers 

an area of 54 mi2. The surface-water drainage basin is defined 

by the surface-water flow divide—a ridge in the land surface 

from which surface water moves away in both directions 

perpendicular to the ridge line. Johnson Creek flows generally 

westward from agricultural areas near Boring, through 

residential and industrial areas in the cities of Gresham 

and Portland, and enters the Willamette River in the city of 

Milwaukie (pl. 1, fig. 1). 

Record rainfall in water years (WY) 1996 and 1997 

resulted in two types of flooding in the Johnson Creek basin. 

Intense rainfall in February and November 1996 led to 

flooding of Johnson Creek. The cumulative effect of 2 years 

of high annual precipitation led to groundwater flooding, 

manifested in high streamflow of Crystal Springs Creek—an 

entirely groundwater fed tributary to Johnson Creek; and an 

elevated water table in the vicinity of Holgate Lake. Although 

the flooding of Johnson Creek lasted on a time scale of 

several days, the groundwater flooding persisted for months 

to years. These flooding events revealed the interaction of 

the groundwater and surface-water systems, and the need for 

better understanding of the hydrology of the Johnson Creek 

basin. 

In addition to better understand specific flooding events, 

information was needed about spatial and temporal trends in 

streamflow, and the interaction of the groundwater system and 

streams in the basin at low flow for the protection of water 

quality. The U.S. Geological Survey (USGS) began a study in 

1997 with the city of Portland. In 2000, the cities of Gresham 

and Milwaukie, and Clackamas County’s Water Environment 

Services joined the cooperative study, followed in 2002 by 

Multnomah County. 

The Johnson Creek basin has a temperate marine climate 

in which winters typically are wet and summers are dry. About 

two-thirds of the annual precipitation is from November 

through March, and less than 10 percent from July through 

September. Most precipitation falls as rain. Although snow 

falls several times each year, accumulation is uncommon and 

usually melts rapidly during subsequent rain storms. Annual 

precipitation in the Johnson Creek basin increases to the 

southeast from about 40 in. at the mouth of the creek to more 

than 60 in. in the upland area of the basin. Average annual 

precipitation (WY 1911–2006) in Portland is about 37 in. 

(Oregon Climate Service, 2007). 

Hydrologic Setting

The Johnson Creek basin is within the southern end of the 

Portland basin, a large topographic and structural depression 

that includes most of the Portland metropolitan area in 

northwestern Oregon and that extends across the Columbia 

River into southwestern Washington. The Johnson Creek 

basin is bounded on the south by the Clackamas River and 

Kellogg Creek basins. A subtle surface-water divide separates 

the Johnson Creek basin from the Sandy River basin to the 

northeast and the basins of the Columbia River and Fairview 

Creek to the north. 

The hydrogeologic setting of much of the Portland 

metropolitan area, including the Johnson Creek basin, is 

summarized in Snyder (2008, p. 8-9). The study area can 

be divided into three areas where geology and soils have 

important effects on groundwater discharge and streamflow: 

1. A group of volcanic buttes that are the western extent of 

Cascade volcanoes arise on the south side of the basin. 

The highest elevation is about 1,100 ft (Trimble, 1963). 

The largest tributary to Johnson Creek in the area is 

Kelley Creek. The greatest component of soils is the 

Cascade silt loam group (U.S. Department of Agriculture 

Natural Resources Conservation Service, 2007). The steep 

slopes and silty soils contribute to low infiltration and 

rapid runoff. 

2. Consolidated sands and gravels underlie the Gresham area 

and the lowlands on the southern side of the creek east 

of I-205, which is Troutdale Formation as identified in 

McFarland and Morgan (1996, p. 9-11) and the “middle 

sedimentary unit” as identified by Conlon and others 

(2005, p. 15). Soils in the area are Powell and Cascade 

silt loams. The runoff characteristics of these soil types 

are similar to those in the area of the buttes, although the 

terrain is less steeply sloped. 

3. The northern side of the basin west of Gresham and 

the southern side of the basin west of I-205 is a distinct 

contrast to the more steeply sloped, less-permeable areas 

to the south and east. Except for isolated volcanic buttes, 

the landscape is relatively flat and has terrace deposits that 

are identified as the “unconsolidated sedimentary aquifer” 

(McFarland and Morgan, 1996, p. 9-10) and the upper 

sedimentary unit (Conlon and others, 2005, p. 9). This 

area of the basin was shaped by Missoula Floods after 

the last ice age, leaving a coarse mix of fluvial deposits 

(Waitt, 1985). Although surface drainage comes from the 

buttes on the northern area of the Johnson Creek basin, 

distinct stream channels from these features generally 

do not extend to Johnson Creek. The topographic setting 

and the highly permeable deposits explains the minimal 

stream-channel development in this area of the Johnson 

Creek basin (Hogenson and Foxworthy, 1965, p. 11). 
Introduction 3

tac09_9711_0344_JohnsonCrk_fig01

CA

SCA

D

E

RA

NGE

RIVER

River

Sandy

Eagle

COLUMBIA

Willamette

Columbia Slough

Rock Cr

McKay Creek

Creek

Creek

Clackamas

River

River

River Fanno

Dairy

Creek

Cr

Johnson

Tualatin

Molalla R

Pudding

R

Vancouver

Lake

Willamette

River

Bull Run River

Little Sandy R

MULTNOMAH

YAMHILL

MARION

WASHINGTON

CLACKAMAS

30 CLARK SKAMANIA

212

219

233

99W

99W

212

224

224

8

43

217 

219 

205

211

211

26

99E

240

99E 14

500

26

26

84

5

205

205

405

5

5

84

B o r i n g H i l l s

T u a l a t i n M o u n t a i n sPortland

Gresham

Vancouver

COLUMBIA

RIVER

GORGE

MilwaukieMilwaukie

Portland

International

Airport

0 2 4 6 8 10 MILES

0 2 4 6 8 10 KILOMETERS

EXPLANATION

Johnson Creek and Little Sandy

River drainage basins 

Extent of plate 1

Land-surface elevation, in feet above 

North American Vertical Datum of 1988

4,000

3,000

2,000

1,000

0

WASHINGTON

OREGON

Portland

Salem

Base modified from U.S. Geological Survey data and other digital sources. Projection: UTM, Zone 10N, North American 

Datum 1983, Scale factor= 0.9996, False easting = 500,000, False northing = 0.

123°00' 122°45' 122°30' 122°15' 122°05'

45°

40'

45°

30'

45°

15'

Figure 1. Location of the Johnson Creek basin, Oregon.
4 Hydrology of the Johnson Creek Basin, Oregon

Except for Crystal Springs Creek and other spring inflows 

in the lower area of the Johnson Creek basin, no known 

perennial tributaries enter Johnson Creek from the north. Soils 

in the area are Multnomah and Latourelle loams, and some 

soils in areas near the creek midbasin are Wapato silt loam. In 

the lower area of the basin, Johnson Creek cuts through the 

terrace deposits as it flows toward the Willamette River. Near 

the confluence with Crystal Springs Creek, Johnson Creek 

enters an area of a former alluvial channel of the Clackamas 

River, the Willamette River, or both (Hogenson and 

Foxworthy, 1965, p. 10-11, 28). The creek turns south in the 

lower 1 mi because of a bedrock outcrop near the confluence 

with the Willamette River. 

Precipitation over the basin follows several pathways 

to groundwater and surface-water systems. In the eastern 

basin, delivery of stormwater to Johnson Creek is expedited 

by drains in agricultural areas, runoff from roads, ditches, 

and other hard surfaces, resulting in a rapid rise in response 

to precipitation. In the lower basin, some runoff is directed to 

the subsurface through drywells and to the sewer system that 

discharges outside the basin, resulting in lessened contribution 

to peak flows from the urban area. Summer flows of Johnson 

Creek are low through much of the basin because of low 

precipitation and, in places, minimal groundwater discharge. 

In some areas, regional groundwater flow paths lead away 

from Johnson Creek and toward nearby large rivers. In the 

lower basin, summer flow of Johnson Creek is sustained by 

groundwater discharge.

About three-fourths of the annual flow of Johnson Creek 

is from November through March, and less than 10 percent 

of the annual flow is in July through September. High-flow 

events typically begin with intense rainfall over 1 to 2 days 

during which prestorm conditions may include saturated soils, 

snow, or both.

Land Use

Land use varies in the Johnson Creek basin, and generally 

follows a gradient from forested, agricultural, and ruralresidential areas in the headwaters to urban and industrial 

areas in the lower basin. Land uses on the southern side of the 

basin include forest, nurseries, and light to dense residential. 

The northern side of the basin within the cities of Gresham 

and Portland is densely populated. Tanner and Lee (2004, p. 4, 

6-7) discuss general land-cover categories for areas upstream 

of several monitoring sites on Johnson Creek.

The Johnson Creek basin, parts of which are in urban, 

suburban, and agricultural settings, has been affected by 

human occupation. Channel simplification, installation 

of storm drains, and paving over surfaces have affected 

the hydrologic character of the stream. In recent years, 

development has resulted in conversion of agricultural and 

light-residential areas to densely urban land uses, particularly 

in the southern and eastern areas of the Johnson Creek basin. 

The stream channel of the lower 11 mi of Johnson Creek was 

altered in a project of the Works Progress Administration 

in the 1930s. The primary purpose was flood control, and 

consisted of limiting the stream to a single, trapezoidal, 

masonry lined channel. Data collection in the basin did not 

begin until after the completion of this project. Although 

a systematic analysis of land use changes through time is 

beyond the scope of this report, the general grid of streets, 

drains, and ditches probably already was established by the 

1940s.

Management of storm runoff in the basin varies 

considerably. As such, the fate of precipitation and subsequent 

runoff and/or groundwater recharge can differ, even within 

the same land-use category. For example, some agricultural 

areas are drained by a network of ditches and subsurface tile 

drains that facilitate rapid delivery of precipitation to the 

stream, whereas runoff from other areas may be managed 

by onsite infiltration through swales and ponds. Likewise, 

in urban areas, runoff can be routed out of the basin entirely 

through a combined sewer system (where sanitary sewage and 

stormwater runoff are combined in a single pipe), directed to 

the stream through storm-drain networks, or directed to onsite 

stormwater drainage systems that are designed to allow for 

the infiltration of stormwater. Stormwater drainage systems 

designed to divert stormwater runoff into the subsurface 

include underground injection control (UIC) systems (for 

example, stormwater injection systems, sumps, and drywells) 

and vegetated swales, pervious pavement, disconnected 

downspouts, and other diversion methods that are designed to 

allow for the infiltration of stormwater.

Previous Investigations

Previous investigations by the USGS in the Johnson 

Creek basin fall in three general categories: groundwater and 

geologic studies, surface-water studies including hydraulic 

and hydrologic modeling, and water-quality investigations. 

Although some results of these studies do not relate directly 

to the analyses in this report, most results contain relevant 

observations on the hydrology of the basin. For example, 

chemical characteristics reported in a water-quality study may 

offer new relevance in understanding the chemical signature of 

groundwater discharge to the stream. 

Previous groundwater studies focused on the Portland 

basin, in which the Johnson Creek basin is located, and 

were the foundation for a regional groundwater flow model 

developed to identify the groundwater flow system and to 

provide a tool for groundwater managers to use in evaluating 

development scenarios. These studies and others are listed 

in Snyder (2008, p. 6, 33-37), a study estimating water-table 

elevation and unsaturated zone thickness throughout much of 

the Portland metropolitan area, including the Johnson Creek 

basin. 
Methods 5

Johnson Creek has been included in several surface-water 

studies, ranging in scope from the Portland metropolitan area 

to statewide. Laenen (1980) provided equations to estimate 

peak flow based on basin characteristics of the Portland 

urban area. Moffatt and others (1990) and Wellman and 

others (1993) provided statistical summaries of daily and 

peak streamflow data for streams throughout Oregon. Lee 

(1995) used dye-tracer methods to determine time of travel 

and dispersion characteristics of Willamette basin streams. 

Laenen and Risley (1997) constructed precipitation-runoff and 

streamflow-routing models of streams in the Willamette basin, 

and Lee and Risley (2002) estimated base flow of streams in 

the Willamette basin. 

Water-quality studies include analyses and interpretation 

of whole-water, filtered, and bed sediment data. Edwards 

(1992), Edwards and Curtiss (1993), and Edwards (1994) 

provided analyses and interpretation, specific to the Johnson 

Creek basin, of physical characteristics (pH, dissolved oxygen, 

alkalinity, and specific conductance), nutrient, trace element, 

manmade organic compound, and sediment data during 

high- and low-flow periods. Johnson Creek was sampled in 

a Willamette River basin study for trace elements, organic 

compounds, and suspended sediment (Anderson and others, 

1996). McCarthy and Gale (1999) used semipermeable 

membrane devices to assess the distribution of organic 

compound in a Columbia basin study. Finally, Tanner and Lee 

(2004) reported on organochlorine pesticides in whole-water 

samples from several locations on Johnson and Kelley Creeks, 

including changes in the relation of suspended sediment to 

pesticides over time. 

Purpose and Scope

This report provides a quantitative description of the 

groundwater and surface-water hydrology of the Johnson 

Creek basin, including information about the interaction of 

the groundwater and surface-water systems, groundwater 

discharge to springs, surface manifestations of the water 

table, and groundwater influence on streamflow and stream 

temperature. This report also includes findings on spatial and 

temporal trends in annual, low, and high streamflow. 

The results build upon previous investigations and longterm data. The previous investigations consist of a USGS 

regional groundwater study on the Portland metropolitan 

area and hydrologic and statistical studies of streamflow 

of Johnson Creek. The description of the groundwater 

system in this report is more general in nature. Conclusions 

of these investigations were derived from hydrogeologic 

mapping, well tests, groundwater level data, streamflow, 

and water-quality data. New data included measurements 

of groundwater level, streamflow, specific conductance, and 

stream temperature. Historic groundwater, streamflow, and 

climate data provided decade-scale context to the dynamics 

of the hydrologic system. New data collection and analyses 

provided explanation of specific hydrologic phenomena, 

particularly related to the interactions of the groundwater and 

surface water systems.

Methods

Hydrologic analyses in the Johnson Creek basin were 

based on data collected at numerous sites. Each groundwater 

and streamflow site has a unique 8 or 15 digit number and 

is associated with a map number that is used throughout 

the report (table 1; pl. 1). Map numbers 1 through 24 are 

groundwater sites and map numbers 25 through 45 are 

surface-water sites. Climate site numbers are assigned by the 

National Weather Service (NWS). 

Groundwater

Groundwater level data were collected and evaluated 

using a monitoring well network consisting of wells measured 

quarterly or more frequently and supplemented by data from 

wells that were equipped with continuous groundwater level 

recorders for this study. Candidate wells were identified 

from previous USGS studies and from the Oregon Water 

Resources Department (OWRD) well database (http://www.

oregon.gov/OWRD/PUBS/ToolsData.shtml). A criterion for 

selection was that the water level in a well should represent 

unconfined or water-table conditions. Priority was given 

to relatively shallow, recently constructed wells that had 

complete location information. Well information, including 

location, construction, and groundwater level measurements, 

was entered into the U.S. Geological Survey National Water 

Information System (NWIS), and is available online at http://

waterdata.usgs.gov/or/nwis/gw using the USGS site number 

(pl. 1; table 1). Groundwater levels relative to a measuring 

point on a well and the elevation of the groundwater relative to 

land surface were established using NGVD 1929 as the landsurface datum. The land-surface elevation at each well was 

determined from a topographic map or from a digital elevation 

model (DEM). The 2-m lateral resolution DEM covering most 

of the Portland metropolitan area was obtained from Metro 

(2002), the regional government agency serving the Portland 

metropolitan area. The vertical resolution of the 2-m DEM 

is reported as about 0.3 ft (Metro, 2002). The land-surface 

elevations for wells used in the study were estimated using the 

2-m DEM and calculated as the median land-surface elevation 

within a 100-ft radius of the reported locations. The buffer 

was used because most locations of wells and springs only are 

known to an accuracy of 100 ft, depending on the method of 

determination. The elevation of some wells additionally was 

determined by leveling from a known point, using methods 

established by Kennedy (1990).
6 Hydrology of the Johnson Creek Basin, Oregon

Table 1. Groundwater and surface-water sites in the Johnson Creek basin, Oregon.

[Map No.: refers to the number on plate 1. USGS site No.: a unique 8 or 15 digit identification number. Additional information on groundwater and surfacewater sites are available from the USGS National Water Information System (NWIS) online at http://waterdata.usgs.gov/or/nwis using the USGS site number. 

OWRD well No.: Oregon Water Resources Department well number. Well reports (logs) documenting the well installation with information describing the 

well location, type of subsurface materials encountered, well depth, construction, and the depth to water are available online at http://www.wrd.state.or.us

using the OWRD well number. Site name and location: All sites in Portland, Oregon, except as noted (name and approximate location). UTM Easting: The 

X-coordinate used to identify the position of a feature based on the distance, in meters, east or west from the central meridian of the UTM zone (UTM zone 10; 

NAD 1927). UTM Northing: The Y-coordinate used to identify the position of a feature based on the distance, in meters, north of the equator (NAD 1927). 

Land-surface elevation: The elevation of the land-surface in feet above NGVD (1929) as determined from a digital elevation model (d) or from a topographic 

map (m). Elevation may differ from previously published values due to new method of determination. Open interval: In a well, the screened part through 

which water enters. If open interval not known, used depth of well (e). Data type (a): PL, periodic water-level measurement; CL, continuous groundwater level 

recorder; PQ, periodic streamflow measurement; CQ, continuous stream level and streamflow recorder; CT, continuous stream temperature recorder; RT, realtime telemetry. Abbreviations: UTM, Universal Transverse Mercator; ft, foot; m, meter; –, not available] 

Map

No.

USGS site No./

OWRD well No. Site name and location

UTM

(m)

Landsurface 

elevation

(ft)

Open interval

depth below land 

surface (ft)

Data

type (a)

Easting Northing From To

Groundwater sites

1 452841122295401/

MULT 2876

159th Ave. and Martins St. 539194 5035974 244 (d) 125 135 PL

2 453056122295801/

MULT 2838

160th Ave. and Taylor St. 539075 5040204 247 (d) 77 85 PL

3 452840122302201/

–

150th Ave. and Foster Rd. 538556 5035928 238 (d) 51 54 PL

4 452840122302202/

–

150th Ave. and Foster Rd. 538555 5035929 238 (d) 14 17 PL

5 452916122305801/

MULT 4693

141st Ave. and Holgate Blvd. 537811 5037029 398 (d) 277 277 PL

6 452842122305801/

MULT 195

134th Ave. and SE Foster Rd. 537801 5036001 243 (d) 38 38 PL

7 452854122305901/

MULT 2886

141st Ave. and Ellis St. 537795 5036366 276 (d) – 110 (e) PL

8 452859122311001/

MULT 4596

139th Ave. and Ellis St. 537557 5036501 271 (d) 79 79 PL

9 452912122312801/

MULT 2881

133rd Ave. and Raymond St. 537147 5036903 229 (d) 50 58 CL, RT

10 452919122313702/

MULT 60838

132nd Ave. and Long St. 536972 5037132 191 (d) 12 23 PL

11 452919122313601/

–

132nd Ave. and Long St. 

(piezometer)

536990 5037130 183 (d) 11 9 PL

12 452858122322801/

MULT 52202

117th Ave. and Harold St. 535856 5036481 202 (d) 48 65 PL

13 452824122325401/

MULT 4279

110th Ave. and Foster Rd. 535311 5035412 214 (d) 96 126 PL

14 452841122330001/

–

Beggars Tick Marsh Park, 

111th Ave. and Foster Rd.

535166 5035926 207 (d) – 6 (e) PL

15 452912122340401/

MULT 50871

Lents Park (deep), 92nd Ave. and 

Raymond St., lower open interval 

533778 5036902 251 (d) 407 437 PL

upper open interval 377 397

16 452921122340401/

MULT 63388

Lents Park (shallow), 92nd Ave. and 

Pardee St.

533774 5037152 261 (d) 107 127 PL

17 452851122350801/

MULT 63293

Mount Scott Park, 74th Ave. and 

Knight St.

532381 5036246 233 (d) 102 122 PL
Methods 7

Map

No.

USGS site No./

OWRD well No. Site name and location

UTM

(m)

Landsurface 

elevation

(ft)

Open interval

depth below land 

surface (ft)

Data

type (a)

Easting Northing From To

Groundwater sites—Continued

18 452725122354301/

CLAC 347

64th Ave. and Johnson Creek Blvd.,

Milwaukie

531607 5033575 149 (d) 130 143 PL

19 452825122355501/

MULT 63294

Brentwood Park, 62nd Ave. and 

Cooper St.

531376 5035423 255 (d) 134 154 CL

20 452859122364701/

MULT 63237

Woodstock Park, 47th Ave. and 

Harold St.

530244 5036480 238 (d) 147 167 CL

21 452822122372001/

MULT 63234

Berkeley Park, 39th Ave. and 

Bybee Blvd.

529538 5035326 194 (d) 102 122 CL

22 452909122375001/

MULT 2784

32nd Ave. and Steele St. 528867 5036780 137 (d) 77 77 PL

23 452827122382401/

MULT 63238

Westmoreland Park (shallow),

 23rd Ave. and Bybee Blvd.

528141 5035465 52 (d) 20 25 CL

24 452827122382402/

MULT 63239

Westmoreland Park (deep),

 23rd Ave. and Bybee Blvd.

528139 5035462 52 (d) 76 96 CL

Surface-water sites

25 452823122240900 Johnson Creek at Palmblad Rd.

 near Gresham

546724 5035448 360 (m) – – PQ

26 14211400 Johnson Creek at Regner Rd. 

at Gresham

545282 5036930 305 (m) – – CQ, CT, RT

27 452944122260000 Johnson Creek at Walters Rd.

 at Gresham

544276 5037910 290 (m) – – PQ

28 452917122275700 Johnson Creek at 190th Ave.

 at Gresham

541707 5037098 260 (m) – – PQ

29 14211499 Kelley Creek at 159th Dr. 539321 5035863 245 (m) – – CQ, CT, RT

30 14211500 Johnson Creek at Sycamore 538559 5035928 228 (m) – – CQ, CT, RT

31 452835122324200 Johnson Creek at Brookside Park 535585 5035749 220 (m) – – PQ

32 452747122344000 Johnson Creek at 82nd Ave. 533012 5034327 190 (m) – – PQ

33 452743122365400 Johnson Creek at 45th Ave. 530068 5034124 80 (m) – – PQ

34 452749122370000 Errol Spring Creek at mouth 529965 5034331 80 (m) – – PQ

35 452750122365300 Storm Drain adjacent to Errol 

Spring Creek

529963 5034356 80 (m) – – PQ

36 452754122374800 Johnson Creek at Berkeley Pl. 528990 5034455 70 (m) – – PQ

37 452740122382700 Johnson Creek at Sherrett St. 528104 5034023 40 (m) – – PQ

38 452856122380000 Crystal Springs Creek at 

Reed College

528656 5036369 70 (m) – – PQ

39 14211542 Crystal Springs Creek at Bybee 

Blvd.

528074 5035472 50 (m) – – CT, PQ

40 14211546 Crystal Springs Creek at mouth 528016 5033990 40 (m) – – CT, PQ

41 14211550 Johnson Creek at Milwaukie 527998 5033126 30 (m) – – CQ, CT, RT

42 14211559 Johnson Creek at mouth

 at Milwaukie

527966 5032226 20 (m) – – PQ

43 452919122313701 Holgate Lake 537000 5037130 190 (d) – – CL, PL

44 14211720 Willamette River 526050 5040330 2 (m) – – CQ, RT

45 14141500 Little Sandy River near Bull Run 564920 5029220 720 (m) – – CQ, RT

Table 1. Groundwater and surface-water sites in the Johnson Creek basin, Oregon.—Continued
8 Hydrology of the Johnson Creek Basin, Oregon

Surface Water

Surface-water data consist of records from continuous 

streamflow sites and individual streamflow measurements 

(pl. 1; table 1). The continuous streamflow sites are: Johnson 

Creek at Regner Road, at Gresham (map number 26), 

beginning in 1998; Johnson Creek at Sycamore (map number 

30), beginning in 1940; Johnson Creek at Milwaukie (map 

number 41), beginning in 1989; and Kelley Creek at 159th 

Drive at Portland (map number 29) beginning in 2000. 

Streamflow records were computed according to methods 

described in Rantz and others (1982). Daily mean streamflow 

and instantaneous peaks are from the U.S. Geological Survey 

National Water Information System (NWIS), and are available 

online at http://waterdata.usgs.gov/or/nwis/sw by using the 

USGS site number to access the information (table 1). 

Several streamflow statistics based on aggregated daily 

mean streamflow values were used to characterize mean 

and low-flow conditions. Thus, daily mean streamflow 

was averaged over an annual time scale to provide an 

indication of annual mean flow conditions. Low streamflow 

was characterized using the annual 7-day and 30-day 

minimum streamflow, which is the average of the lowest 

7 or 30 consecutive daily mean streamflow values during 

a specified time period during each year, respectively. For 

example, the annual 7-day low flow during the months of 

May through October for each year of streamflow record 

would be calculated as the average streamflow of the lowest 

7 consecutive daily mean streamflows during the months 

of May through October only. Base-flow separation, using 

the program PART, partitions daily mean streamflow to 

estimate the base-flow component (Rutledge, 1998). Flowduration curves, which were developed by ranking daily 

mean streamflow over a given time period and calculating 

the percentage of time that a specified daily mean streamflow 

was equaled or exceeded (Searcy, 1959), also were used to 

characterize low streamflow. 

High flows were characterized for streamflow sites 

with more than 10 years of record using annual peak 

streamflow data. Peak streamflow frequency, commonly 

termed flood frequency, indicates the annual exceedance 

probability associated with a particular magnitude of annual 

peak streamflow. For example, an annual peak streamflow 

with a 1-percent exceedance probability represents a large 

flood that has only a 1-percent chance of that streamflow 

being exceeded in any year. The reciprocal of the annual 

exceedance probability is the average recurrence interval of 

a particular annual peak streamflow. Thus, the flood with an 

annual exceedance probability of 1 percent has an average 

recurrence interval of 100 years and commonly is referred to 

as the 100-year flood. Flood frequency data for this study were 

determined by fitting the log Pearson 3 probability distribution 

to the recorded annual peak streamflow values at each site 

having sufficient record using methods described by the U.S. 

Interagency Advisory Committee on Water Data (1982) and 

Flynn and others (2006).

Streamflow measurements were used to determine 

temporal changes in groundwater discharge to springs and 

to identify gains or losses in streamflow from the stream as 

a result of interaction with the groundwater system using 

methods described in Rantz and others (1982). Streamflow 

measurements were made at many locations on Johnson 

Creek and tributary streams. Streamflow measurements at all 

locations described in this report are available online from the 

U.S. Geological Survey National Water Information System 

(NWIS), and are available at http://nwis.waterdata.usgs.gov/

or/nwis/measurements by using the USGS site number. Spring 

discharge was determined by measuring the streamflow in 

the channel formed by the spring. Because springs in the 

Johnson Creek basin typically emerge at multiple locations, 

the streamflow was measured downstream where depth and 

uniformity of flow were sufficient for measurement by a 

current meter. Streamflow generally was measured during 

dry-weather periods to most accurately characterize spring 

discharge.

Seepage measurements are an indirect method of 

quantifying groundwater discharge (gains) or recharge (losses) 

at the streambed. Seepage measurements consist of a series of 

streamflow measurements made at numerous locations along 

a stream reach at nearly the same time. Assuming no tributary 

inflows or streamflow diversions from one location to the next, 

the difference in streamflow at the two locations indicates the 

net gain or loss attributed to interaction with the groundwater 

system. As such, a seepage study is a “snapshot” at a given 

time of the interaction of the stream and the surrounding 

aquifer. Seepage measurements are made during the summer 

low-flow period when streamflow is fairly constant and runoff 

from precipitation is minimal.

As a result of streamflow measurement uncertainty, the 

use of seepage measurements to determine streamflow gains 

and losses may not be reliable when the gains or losses are 

a relatively small percentage of the measured streamflow. 

The accuracy of a streamflow measurement is determined 

by several factors, including uniformity of velocity, channel 

characteristics, and limitations of the meter in use. Most 

streamflow measurements made during this study were rated 

as “good,” meaning they were within 5 percent of the actual 

value. The determination of gains and losses and the effect 

of measurement uncertainty are described in Lee and Risley, 

(2002, p. 22-23).

Spatial and temporal variations in hydrologic data 

were analyzed by using parametric and nonparametric 

methods. Spatial variations generally were analyzed using 

linear regression, a parametric method that relates one 

hydrologic variable to another with a best-fit line (equation). 

The strength of the linear regression relation commonly is 

measured by the R-squared (R2) value. Correlation was used 

to quantify the degree by which two variables are related. 

The strength of the correlation is described by the R value. A 

nonparametric correlation method, Kendall’s tau, was used to 

analyze temporal variations or temporal trends of hydrologic 
Groundwater Hydrology 9

variables (Helsel and Hirsch, 2002). Kendall’s tau is the 

correlation between the ranked values of two variables, and 

was implemented using the S-PLUS® data-analysis software 

(Insightful Corporation, 2005). Values of Kendall’s tau range 

from -1 to +1. The sign of Kendall’s tau indicates whether the 

relation is directly proportional (positive value) or inversely 

proportional (negative value). The magnitude of the deviation 

(either positive or negative), from zero indicates the strength 

of trend. The null hypothesis is that no temporal trend exists. 

The statistical significance of the trend was evaluated by the 

probability (p) that the observed trend happened by chance. 

A p-value of 0.05 indicates a 95-percent probability that the 

observed trend is not a chance occurrence. For this study, 

Kendall’s tau values having p-values less than 0.05 were 

considered significant.

Water Quality

Water-quality results consist of discrete stream samples 

analyzed for specific conductance and data from continuous 

stream-temperature recorders. Temperature data were 

recorded at long-term streamflow sites and at other locations 

for several weeks in conjunction with seepage studies. 

Continuous stream-temperature data collection in the Johnson 

Creek basin began in 1998 (pl. 1; table 1). Daily maximum, 

minimum, and mean stream temperature data are stored in 

the NWIS, and are available online at http://waterdata.usgs.

gov/or/nwis/qw by using the USGS site number to access the 

information. Summer stream temperature was characterized 

using the 7-day average maximum value, a statistic commonly 

used for regulatory purposes. Samples analyzed for specific 

conductance and short-term, continuous temperature data 

collected during the seepage studies were used as a qualitative 

measure of groundwater discharge to the stream. The shortterm temperature data collected in conjunction with the 

seepage studies are not published, but are available from the 

Oregon Water Science Center. Specific conductance (Wilde, 

2005) and stream temperature data (Wagner and others, 2006) 

were collected according to set guidelines.

Meteorologic Data

The NWS site at the Portland Airport (site number 

356751), about 10 mi north of the mouth of Johnson Creek, 

was the primary source of precipitation data. These data were 

provided by the NWS and served to the public by the Oregon 

Climate Service (Oregon Climate Service, 2007). Climate 

data at the Portland Airport began in 1938. These data were 

merged with unadjusted monthly total precipitation data at the 

NWS site in downtown Portland (site number 356761) from 

1911 to 1937 (Oregon Climate Service, 2007). Some data gaps 

were filled with monthly precipitation data from Vancouver, 

Washington (site number 458773), about 10 mi northwest 

of the Portland Airport (National Oceanic and Atmospheric 

Administration, 2007), and Salem, Oregon (site number 

357500), about 50 mi to the south (Oregon Climate Service, 

2007). The precipitation data from Vancouver and Salem 

were adjusted proportionally, based on adjacent periods of 

concurrent data. 

Precipitation data at the fixed location and the spatial 

distribution of precipitation were assessed using the 

Precipitation Elevation Regressions on Independent Slopes 

Model (PRISM) (PRISM Group, 2007). PRISM is a data layer 

of estimated annual precipitation in the State of Oregon in 

800 × 800 m grid cells based on the period from 1971 to 2000. 

Groundwater Hydrology

The elements of the groundwater hydrology of Johnson 

Creek basin include the basic inflow (recharge) and outflow 

(discharge), and the change in storage manifested by 

fluctuations in water levels. Understanding of these elements 

provides a foundation for discussion of the groundwaterrelated events that motivated this study: extremes in 

streamflow of Crystal Springs Creek, the emergence of 

the water table in a low-lying area of the basin (Holgate 

Lake (map number 43)), and spatial and temporal trends in 

groundwater discharge to Johnson Creek. 

Recharge

Recharge to the Johnson Creek basin is through the 

infiltration of precipitation, although in areas of urban 

development, the diversion of stormwater runoff into UIC 

systems and infiltration of effluent from onsite waste-disposal 

(septic) systems are additional sources of recharge. Recharge 

to the Portland basin was estimated using data from the late 

1980s by Snyder and others (1994, p. 30). Within the Johnson 

Creek basin recharge ranged from 0 to 48 in/yr, with a mean of 

about 22 in/yr. Recharge from UIC systems and septic systems 

contributed about 11 and 12 percent of the total, respectively. 

Irrigation-return flow and losing streams also may constitute 

locally important sources of seasonal recharge; however, they 

were not quantified by Snyder and others (1994, p. 3). 

The addition of UIC systems and the removal of septic 

systems since the study by Snyder and others (1994) require 

a recalculation of recharge based on 2008 conditions using 

the methods of Snyder and others (1994). The addition 

of UIC systems increases recharge by routing stormwater 

runoff onsite to the subsurface, whereas stormwater runoff 

was previously routed out of the basin through a combined 

sewer system. Removal of septic systems decreases recharge 

by routing sewage to the sewer system that had previously 

been infiltrated onsite. For this study, it was assumed that 

the pattern of spatial distribution and rates of precipitation 

have not changed much since the study by Snyder and others 

(1994). Although impervious area is expected to increase 
10 Hydrology of the Johnson Creek Basin, Oregon

because of infill development in the urban areas and new 

development in the rural areas, it was beyond the scope of this 

study to evaluate the effect of these changes on the amount of 

recharge from the infiltration of precipitation. Therefore, the 

infiltration of precipitation calculated by Snyder and others 

(1994) was considered to be representative of conditions 

for this study. The number of UIC systems has increased 

substantially and nearly all septic systems in the areas used 

in that analysis have been removed as part of an extensive 

sewer improvement project in central Multnomah County. 

Recharge from septic systems in rural areas of the Johnson 

Creek basin was not quantified by Snyder and others (1994, 

p. 26) or by this analysis because these areas generally are less 

densely populated than the rest of the basin. However, septic 

systems do remain in some unincorporated urbanized areas 

but they are the focus of efforts for decommissioning (Andrew 

Swanson, Clackamas County’s Water Environment Services, 

written commun., 2008). The source of the water supply used 

for septic systems can be either internal or external to the 

Johnson Creek basin; however, for this study, no distinction 

was made regarding the source of water for septic systems. 

Recharge is possible from overbank floodwaters of Johnson 

Creek, particularly in the area just east of I-205. This recharge 

might affect groundwater levels and the quantity of discharge 

at locations in the study area and downgradient of the recharge 

area for short periods of time.

The analysis by Snyder and others (1994, p. 23) 

estimated there were about 3,700 UIC systems owned by 

public agencies in Multnomah County and an undetermined 

number of privately owned UIC systems. Estimates of the 

number of UIC systems in the Portland metropolitan area 

in 2008 include about 11,000 publicly owned and 25,000 to 

35,000 privately owned UIC systems, most are in Multnomah 

County (Snyder, 2008, p. 6-7). The area drained by the newly 

installed, publicly owned UIC systems in the Johnson Creek 

basin is an additional 2,100 acres. These new UIC systems 

are estimated to contribute recharge at a rate of 10.6 in/yr, 

the same mean rate of recharge for areas with UIC systems 

already identified within the Johnson Creek basin (Snyder and 

others, 1994, pl. 1B), for about 1,800 acre-ft/yr of additional 

recharge to the Johnson Creek basin. This additional recharge 

represents a 22-percent increase in recharge from UIC systems 

to the Johnson Creek basin since the analysis by Snyder and 

others (1994), which estimated recharge from UIC systems to 

be about 8,100 acre-ft. 

The recharge from areas with septic systems within 

the Johnson Creek basin identified by Snyder and others 

(1994, pl. 1C) totaled about 7,400 acre-ft/yr. The installation 

of sanitary sewer systems in these areas has resulted in the 

decommissioning of nearly all these septic systems. For this 

calculation, the quantity of recharge previously attributed to 

septic systems has been diverted to the sewer systems and no 

longer contributes to recharge in the Johnson Creek basin. 

The 2008 annual recharge for the Johnson Creek basin is 

equal to the recharge estimate of 66,600 acre-ft as reported by 

Snyder and others (1994), supplemented by 1,800 acre-ft of 

recharge from new UIC systems, and reduced by 7,400 acre-ft 

because of the decommissioning of septic systems resulting in 

an estimated annual recharge of 61,000 acre-ft for 2008 in the 

Johnson Creek basin. The change in recharge resulting from 

the 2008 configuration of UIC systems and septic systems 

by about 5,600 acre-ft/yr represents about an 8-percent 

reduction since the analysis by Snyder and others (1994) to 

the Johnson Creek basin. This change in recharge was almost 

entirely within the intervening drainage basin area between the 

Milwaukie and Sycamore sites. The recharge to the drainage 

basin area upstream of the Sycamore site is unchanged from 

the analysis of Snyder and others (1994) and was estimated at 

34,500 acre-ft/yr. These estimates of recharge assume that the 

infiltration of precipitation is identical to that of the previous 

analysis by Snyder and others (1994) and does not take into 

consideration the substantial but unknown amount of recharge 

contributed from privately owned UIC systems or from the 

installation of new septic systems outside areas where sanitary 

sewers are available. These changes to recharge may result in 

changes in the discharge to rivers, streams, and springs or may 

be reflected in changes in groundwater levels. 

Groundwater Discharge

Groundwater in the Johnson Creek basin discharges to 

springs, to the stream by leakage through the streambed, to 

wells, by evapotranspiration, and by subsurface flow to other 

basins. The existence of streamflow during the late summer, 

a period of little or no precipitation, indicates groundwater 

discharge. Groundwater withdrawals by wells are mostly 

restricted to the eastern area of the basin, where wells are used 

for domestic supply and for irrigation (Collins and Broad, 

1993). Municipal sewage is not discharged to Johnson Creek. 

Evapotranspiration is not a major source of groundwater 

discharge because the depth to groundwater typically exceeds 

plant root depth. Evapotranspiration losses probably are 

greatest in areas of shallow groundwater adjacent to Johnson 

Creek and in wetland areas just east of I-205 at Beggars Tick 

Marsh (pl. 1). 

Groundwater discharge, which contributes to flow of 

Crystal Springs and Johnson Creeks, was estimated in several 

ways: (1) using measurements of springs (and predominantly 

spring-fed streams) available since the 1970s, (2) using 

seepage measurements made along Johnson Creek from 

1988 to 2006, (3) comparing streamflow in Johnson Creek 

at the streamflow sites during the low-flow period from 

1989 to 2006, (4) comparing base-flow separation results for 

different time periods at the Johnson Creek streamflow sites, 

and (5) assessing qualitatively the groundwater discharge to 

Johnson Creek using environmental tracers (chemical and 

thermal characteristics of the stream).
Groundwater Hydrology 11

Springs and Seepage

Johnson Creek is a perennial stream, where flow is 

sustained during the dry summer and autumn by groundwater 

discharge. Groundwater discharge occurs as springs, where 

a distinct flow emanates from an area, typically as a small 

stream forming a tributary to Johnson Creek, or as seepage 

through the streambed. Seepage may be visible if it discharges 

along the banks above stream level. Relative to streamflow, 

springs and seepage studied in this report are groundwater 

contributions to the stream. Most spring and seepage 

discharge to Johnson Creek is downstream of RM 5.5. The 

predominance of springs and seepage in the lower basin 

results in relatively high summer flow compared to the flow 

upstream of RM 5.5. 

Crystal Spring (fig. 1) is the largest spring in the 

Johnson Creek basin, and, as referred to in this report, 

consists of several complexes of springs that discharge to 

Crystal Springs Creek. The individual spring locations are 

described in McFarland and Morgan (1996, p. 8, p. 24-27) 

and in McCarthy and Anderson (1990, p. 31). Crystal 

Springs Creek is about 2.5 mi long, flows westward from 

the Reed College campus, southward through a golf course, 

Westmoreland Park, and residential areas, entering Johnson 

Creek at RM 1.0. Crystal Springs Creek provides most of 

the summer streamflow of Johnson Creek downstream of 

RM 1.0. Spring flow originates in two general areas. The 

upper spring complex is on the Reed College campus, where 

flow emanates from the bluffs surrounding a lake and wetland 

area. The lower spring complex is about 1 mi from the mouth 

of the creek, where flow emanates at several locations from 

the bluffs to the east, flowing into a constructed pond, and then 

into the main channel of Crystal Springs Creek. 

An increase in the height of the water surface of Crystal 

Springs Creek, noted by local residents beginning in July 

1997, prompted inquiry by the city of Portland (Chestnut, 

1997). Streamflow measurements were made at three 

locations: (1) on the Reed College campus at RM 1.8 (map 

number 38), (2) at RM 1.0 (map number 39), and (3) at the 

mouth of the creek (map number 40) (pl. 1). The streamflow 

measurements characterized the peak in 1997, tracked a 

multiyear recession, and by 2001 the streamflow had receded 

to the rate observed a decade earlier (fig. 2).

1987 1989 1991 1993 1995 1997 1999 2001 2003 2005

0

5

10

15

20

25

0

0.5

1

1.5

2

2.5

 Map number refers to table 1

STREAMFLOW OF CRYSTAL SPRINGS CREEK, IN CUBIC FEET PER SECOND

STREAMFLOW OF ERROL SPRING CREEK, IN CUBIC FEET PER SECOND

CALENDAR YEAR

Crystal Springs Creek at Reed College (map number 38)

Crystal Springs Creek at mouth (map number 40)

Crystal Springs Creek at mouth, estimated

Errol Spring Creek at mouth (map number 34)

Figure 2. Streamflow measurements of Crystal Springs Creek at Reed College, measurements and estimates of 

streamflow at the mouth of Crystal Springs Creek, and measurements of Errol Spring Creek, Portland, Oregon.
12 Hydrology of the Johnson Creek Basin, Oregon

Measurements of streamflow of Crystal Springs Creek 

in the Reed College area began in 1988 when the combined 

discharge of several distinct springs was 1.6 ft3/s (McFarland 

and Morgan, 1996, p. 26). In this study, discharge of the 

springs, determined by streamflow measurements of Crystal 

Springs Creek in the Reed College area, ranged from a 

maximum of 6.3 ft3/s in September 1997 to a minimum of 

0.16 ft3/s in September 2005 (fig. 2). Two measurements in 

1999 indicated greater streamflow; however, surface runoff 

or release of water from a beaver dam may have temporarily 

increased the flow of Crystal Springs Creek. Streamflow 

measurements made in 2001, 2003, and 2004 indicated that 

the flow was about 1 ft3/s. The low streamflow observed in 

2005 was followed by an increase to 1.31 ft3/s in 2006. 

Streamflow measurements made prior to 1997 

(primarily during the summer and autumn) at or near the 

mouth of Crystal Springs Creek indicate that the collective 

discharge of the springs was between 10.5 and 14.8 ft3/s. 

Concurrent streamflow measurements in 1997 and 1998 

at RM 1.0 and at the mouth of the creek indicate that the 

difference in streamflow usually is within the range of 

measurement uncertainty, so data from either site can be 

used for comparison. The earliest known streamflow of 

Crystal Springs Creek was 12.4 ft3/s in 1872, when the City 

of Portland was considering the feasibility of tapping Crystal 

Springs Creek as a source for public water supply (McFarland 

and Morgan, 1996, p. 26). The high streamflow of Crystal 

Springs Creek, as measured in 1997, seems to have begun 

the previous year. Although Crystal Springs Creek was not 

measured in 1996, streamflow was inferred from streamflow 

of Johnson Creek at Milwaukie (map number 41) by using 

the relation of late summer streamflow of Crystal Springs 

Creek to that of Johnson Creek at Milwaukie (fig. 3). The 

streamflow measurements of Crystal Springs Creek used for 

this analysis were made during the period from August to 

October 1989 and August to October of every year from 1997 

to 2006. These streamflows were related to the annual 7-day 

minimum streamflow of Johnson Creek at Milwaukie for the 

same period. Based on this relation, the streamflow of Crystal 

Springs Creek in late summer 1996 was estimated to be 19.5 

ft3/s, close to that measured in July 1997. 

The streamflow of Crystal Springs Creek at the 

mouth (map number 40) decreased from 1997 to 2001, 

decreased less rapidly from 2002 to 2005, and similar to the 

upper spring area, increased slightly in 2006 (fig. 2). The 

streamflow reached 20.1 ft3/s in September 1997, which is 

about 60 percent greater than measured or estimated values 

between 1987 and 1995. Although the maximum streamflow 

is in December 1999, this high flow probably was a result of 

surface runoff or beaver activity. Streamflow in July 2005 

was 9.2 ft3/s, lower than any previous measurement of Crystal 

Springs Creek. 

Errol Spring, a complex of individual springs, emanates 

from a bluff about 0.3 mi from Johnson Creek and forms what 

is known locally as Errol Spring Creek (map number 34) 

(pl. 1). Errol Spring Creek passes through a wetland and enters 

Johnson Creek at RM 3.1.

5

10

15

20

25

STREAMFLOW OF JOHNSON CREEK, IN CUBIC FEET PER SECOND

STREAMFLOW OF CRYSTAL SPRINGS CREEK, IN CUBIC FEET PER SECOND

5 10 15 20 25 30

Relation: CSM = (JCM * 0.642) + 2.97

n = 11, R 2 = 0.97 

[Crystal Springs Creek at mouth (CSM, map number 40)

Johnson Creek at Milwaukie (JCM, map number 41)

Map number refers to table 1]

Figure 3. Relation between average measured streamflow at the mouth of Crystal Springs Creek, Portland, Oregon, and 

consecutive 7-day average low streamflow of Johnson Creek at Milwaukie, Oregon, August to October 1989, 1997–2006.
Groundwater Hydrology 13

Another spring discharges to Johnson Creek through a 

pipe (map number 35) a few feet downstream of the mouth 

of Errol Spring Creek. This spring emanates from the bluffs 

near Errol Spring and flows under industrial properties nearby, 

incorporating street drainage along its length, and is piped to 

Johnson Creek. Measurements of this spring were made in late 

summer of 1988, 1999, 2000, and 2006, and indicated fairly 

similar discharge to Errol Spring Creek. 

Errol Spring Creek was measured in August and 

September 1988 when the streamflow was 0.56 and 0.39 ft3/s, 

respectively (fig. 2). Errol Spring Creek was first measured for 

this study in 1998 when the streamflow was 0.97 ft3/s, or about 

twice the streamflow measured a decade before. Streamflow of 

Errol Spring Creek remained relatively high in 1999 and 2000. 

Measurements from 2001 to 2004 indicated a steep decrease 

compared to streamflow observed in 1998 to 2000. Flow 

decreased to 0.19 ft3/s in 2005 and increased to 0.37 ft3/s in 

2006. The general pattern of fluctuation in streamflow of Errol 

Spring Creek from 1988 to 2006 was similar to that of Crystal 

Springs Creek. 

Numerous springs emanate from bluffs along the 

southern side of Johnson Creek between RM 3.2 (map number 

33) and RM 2.2 (map number 36). These springs have not 

been measured directly by the USGS; however, streamflow 

measurements made on Johnson Creek at RM 3.2 and 2.2 

in 1988, 1998, 1999, 2000, and 2006 indicate groundwater 

inflows (including Errol Spring) of between 0.73 and 2.40 ft3/s 

(table 2). 

Several springs discharge near the mouth of Johnson 

Creek in Milwaukie. Spring Creek enters Johnson Creek at 

RM 0.4. The streamflow of Spring Creek was 1.2 ft3/s in 1988 

(McFarland and Morgan, 1996, p. 57). Another spring once 

used to fill a public swimming pool in downtown Milwaukie 

is piped to Johnson Creek at RM 0.1. Collectively, the 

discharge of springs to Johnson Creek between the Milwaukie 

streamflow site (map number 41) and the mouth of the creek 

(map number 42) was 4.3 ft3/s in 1988 and 4.1 ft3/s in 2006.

Comparison of the decrease in flow of springs in the 

high-flow years of 1996–99 to the low flows of 2005 indicates 

that streamflow of Crystal Springs Creek in the Reed College 

area and Errol Spring Creek decreased much more rapidly 

than Crystal Springs Creek at the mouth. By 2005, the flow 

of Crystal Springs Creek in the Reed College area was about 

3 percent of the peak streamflow, and Errol Spring Creek 

decreased to about 20 percent of that observed in 1998. 

Streamflow of Crystal Springs Creek at the mouth decreased 

to 50 percent of the peak, indicating that the saturated 

thickness of the groundwater contributing area to the upper 

Crystal Springs and Errol Spring Creeks is much less than 

that of the lower Crystal Springs Creek because of the higher 

topographic position of the upper Crystal Springs and Errol 

Spring Creeks. Therefore, changes in the water-table elevation 

have a proportionately larger effect on groundwater discharge 

to upper Crystal Springs Creek and Errol Spring Creek relative 

to the groundwater discharge contributing to lower Crystal 

Springs Creek. The springs contributing streamflow to the 

lower area of Crystal Springs Creek additionally may be 

the result of regional groundwater flow, which may be less 

sensitive to short-term climatic variation. 

Seepage is the exchange between groundwater and 

surface water at the streambed forming the boundary between 

a stream and an aquifer system. Rates and locations of seepage 

to and from Johnson Creek were determined by evaluating 

the difference (gain or loss) in measured streamflow between 

measurement locations. Although some recharge to the system 

is from losing reaches of Johnson Creek, most of reaches are 

gaining, receiving discharge from the groundwater system. 

Seepage measurements were made each summer from 1997 

through 2000 and in 2006 as part of this study and compared 

to seepage measurements made in 1988 (fig. 4, table 2). 

Precipitation in water years when seepage measurements 

were made varied widely (fig. 5). Although the average (WY 

1911–2006) precipitation at the Portland Airport is about 

37 in., precipitation was several inches less than average in 

WY 1988 and 2000, and several inches more than average in 

WY 1998, 1999, and 2006 (Oregon Climate Service, 2007). 

Precipitation in WY 1997 was the highest since recordkeeping 

began in 1911, and was about 21 in. more than average.

The individual measurements and general conditions 

for quantifying gains and losses to the stream were good 

overall; however, the measurements for the 2006 study 

caused considerable uncertainty because of multiple beaver 

dams between RM 17.2 and 1.2. The inability to measure the 

streamflow at several of the sites measured previously because 

of ponded conditions and the buildup and subsequent wash-out 

of these dams raised uncertainty about the stability of flows 

during the 2006 study.

The Johnson Creek basin was divided into three reaches 

for this analysis based on seepage characteristics. The upper 

reach extends from RM 17.2 to 10.2 (pl. 1). The slope of the 

stream in the upper reach is 20 ft/mi and the elevation of the 

channel decreases from 370 to 228 ft. The drainage basin area 

increases by 14.3 mi2 in this reach (Tanner and Lee, 2004, 

p. 7). Much of the surface-water contributing area (the area 

in a drainage basin that contributes water to streamflow) of 

this reach consists of Troutdale Formation gravels and steeply 

sloped volcanic buttes. These materials are less permeable 

than the deposits north and west of this reach. The middle 

reach is from RM 10.2 to 5.5 (pl. 1). The slope of the stream 

channel in the middle reach is 8 ft/mi and the elevation 

decreases from 228 to 190 ft, as a result the stream channel 

of the middle reach is less steep than the upstream reach. The 

drainage basin area increases by 17.6 mi2 in this reach. 
14

Hydrology of the Johnson Creek Basin, Oregon

Table 2. Streamflow and specific conductance measurements used in seepage analysis, Johnson Creek, Oregon. [Map numbers are shown in table 1. Streamflow: (a) from rating curve; (b) measured at RM 2.4; (c) from rating curve at Johnson Creek at Milwaukie, Oregon (map number 41), less flow of Crystal Springs Creek (map number 40); (d) sum of streamflow measurements at map number 37 and map number 40. Abbreviations: ft3/s: cubic foot per second, μS/cm: microsiemens per centimeter at 25 degrees Celsius, 

RM: river mile]

Map

No.

Site name

Johnson Creek 

at:

River 

mile

September 

1988

September 

1997 August 1998 August 1999 September 1999 August 2000 October 2006

Streamflow 

(ft3/s)

Streamflow 

(ft3/s)

Streamflow 

(ft3/s)

Specific 

conductance 

(μS/cm)

Streamflow 

(ft3/s)

Specific 

conductance 

(μS/cm)

Streamflow 

(ft3/s)

Specific 

conductance 

(μS/cm)

Streamflow 

(ft3/s)

Streamflow 

(ft3/s)

Specific 

conductance 

(μS/cm)

25 Palmblad Road 17.2 0.08 – 0.81 123 0.86 137 – – 0.49 0.59 12926 Regner Road 15.8 – – 1.02 137 1.02 139 – – .72 (a) 1.49 140

27 Walters Road 14.5 .42 – 1.36 145 1.24 148 – – .70 – –28 190th Avenue 12.6 .47 – 1.83 147 1.62 139 – – 1.16 – –30 Sycamore 10.2 .64 (a) 5.2 (a) 2.52 152 2.25 146 1.96 (a) 152 1.77 (a) 2.41 152

31 Brookside Park 7.8 .74 2.38 149 – – 1.87 152 1.46 – –

32 82nd Avenue 5.5 .92 4.8 2.43 151 – – 2.02 140 1.31 2.46 143

33 45th Avenue 3.2 1.35 6.1 3.56 200 – – 3.50 206 2.36 2.62 175

36 Berkeley Place 2.2 3.45 (b) – 5.53 226 – – 5.90 228 3.99 3.35 194

37 Sherrett Street 1.2 2.91 9.9 (c) 5.69 222 – – 5.55 226 3.55 3.54 192

41 Milwaukie 0.7 13.4 (d) 31.0 (a) 21.8 218 – – 22.0 (a) – 17.0 14.0 195

Summary: Seepage values in bold are greater than the measurement uncertaintyUpper 

reach

RM 17.2 to 

RM 10.2

0.56 – 1.71 1.39 – 1.28 1.82

Middle 

reach

RM 10.2 to 

RM 5.5

.28 -0.4 -0.09 – 0.06 -.46 .05

Lower 

reach

RM 5.5 to 

RM 0.7

12.5 26.2 19.4 – 20.0 15.7 11.5
Groundwater Hydrology 15

The contributing area to the middle reach on the southern side 

is similar to that of the upstream reach, except at the lower end 

of the reach, which is flat and composed of unconsolidated 

sediments. The contributing area on the northern side of the 

creek is relatively flat and consists of permeable Pleistocene 

flood deposits. The lower reach extends from RM 5.5 to 0.7 

(pl. 1). The channel slope (35 ft/mi) is greater than that of 

both reaches upstream. Elevation decreases from 190 to 24 ft. 

The drainage basin area in this reach increases by 8.8 mi2. 

The stream channel in this reach intersects a relatively large 

thickness of unconsolidated sediments of the terrace deposits, 

contributing to increased seepage. This reach includes Errol 

Spring and Crystal Springs Creeks and numerous other spring 

inflows. 

Seepage measurements in the upper reach indicated 

relatively small gains during each study (fig. 4, table 2). All 

gains in the upper reach were greater than the measurement 

uncertainty of 5 percent. Streamflow in this reach was not 

measured in 1997. During the September 1988 seepage run, 

the flow at the upstream end of this reach was only 0.08 ft3/s. 

Because the drainage basin size upstream of this location is 

12.5 mi2, this relatively low streamflow is an indication of 

minimal groundwater contribution to streamflow. The least 

gain in streamflow along this reach was in 1988 (0.56 ft3/s). 

The greatest gain was in 2006 (1.82 ft3/s). The gains decreased 

from 1998 (1.71 ft3/s) to 2000 (1.28 ft3/s), but were still more 

than twice the gains recorded in 1988. 

tac09_9711_0344_JohnsonCrk_fig04

UPPER REACH

MIDDLE REACH

LOWER REACH

16 14 12 10 8 6 4 2 0

25 26 27 28 30 31 32 33 36 37 41

18

0

5

10

15

20

25

30

35

0

50

100

150

200

250

300

350

MAP NUMBER

JOHNSON CREEK RIVER MILE

STREAMFLOW, IN CUBIC FEET PER SECOND

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER AT 25 DEGREES CELSIUS

Inflow from 

Crystal Springs

Creek

Streamflow

 September 1988

 September 1997

 August 1998

 August/September 1999

 August 2000

 October 2006

 August 1998

 August/September 1999

 October 2006

25 Map number refers to table 1

Specific conductance

Figure 4. Seepage measurements during low flow in 1988, 1997–2000, 2006, and specific conductance measurements 

during low flow in 1998, 1999, and 2006, Johnson Creek, Oregon.
16

Hydrology of the Johnson Creek Basin, Oregon

tac09_9711_0344_JohnsonCrk_fig05

1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

6050403020

500-50

WATER YEAR

TOTAL WATER-YEAR PRECIPITATION, IN INCHES

CUMULATIVE DEPARTURE FROM AVERAGE, IN INCHES

3-year average precipitationAnnual precipitation

EXPLANATION

Cumulative departure from average precipitation

Portland Airport (site number 356751) 

Figure 5. Annual, 3-year average, and cumulative departure from average precipitation at Portland Airport, Oregon, 1911–2006.
Groundwater Hydrology 17

Seepage measurements in the middle reach indicated 

slight gains and losses; however, in 4 of the 6 years that 

measurements were made, the gains or losses were less 

than the measurement uncertainty. The only gain that was 

greater than the measurement uncertainty was in 1988 when 

streamflow gained 0.28 ft3/s. The only loss greater than 

the measurement uncertainty was in 2000 when the flow 

decreased by 0.46 ft3/s. These gains and losses are small 

considering the reach length and substantial increase in 

drainage basin area. 

Gains in flow in the lower reach were much greater than 

in either of the two reaches upstream. The lower reach is 

characterized by diffuse seepage to the stream and by distinct 

spring inflows, the largest of which is Crystal Springs Creek. 

The least gain was in 2006 (11.5 ft3/s). The greatest gain was 

in 1997 (16.2 ft3/s), and gains generally decreased from 1997 

to 2006. All gains in streamflow in this reach were greater than 

the measurement uncertainty. Streamflow in the lower reach 

indicated gains at each subsequent measurement location, 

except in some years between RM 2.2 and 1.2 (fig. 4). Losses 

between RM 2.2 and 1.2 may be attributed to recharge to 

groundwater through the streambed, as the stream gradient 

decreases and the stream channel intersects permeable 

deposits near the confluence with Crystal Springs Creek. 

In summary, spring-flow and seepage measurements 

indicate that groundwater discharge to Johnson Creek is 

low in the upper and middle reaches, and high in the lower 

reach. In 1998, when spring flow (fig. 2) and seepage (fig. 4, 

table 2) were high, streamflow of Johnson Creek in the 11.7 mi 

(encompassing an increase in drainage basin size of 31.9 mi2) 

from RM 17.2 to 5.5 increased only 1.62 ft3/s. In contrast, 

in the relatively short (4.8 mi) distance and small (8.8 mi2) 

increase in drainage basin size from RM 5.5 to 0.7, even in 

1988, a relatively dry year, the stream gained 12.5 ft3/s. 

Long-Term Streamflow Data

Long-term records of daily streamflow were used to 

quantify groundwater discharge to the stream in two ways. 

First, analyses were made of differences in low flows of 

Johnson Creek each year at the Gresham, Sycamore, and 

Milwaukie streamflow sites (map numbers 26, 30, and 41, 

respectively). Second, base-flow separation techniques were 

used to estimate the groundwater discharge component of 

streamflow at the Sycamore and Milwaukie sites. Comparison 

of the recharge and groundwater discharge derived from baseflow separation provides insight into the spatial distribution of 

groundwater discharge in the Johnson Creek basin.

Similar to the results of seepage measurements, analysis 

of low-flow data at the streamflow sites indicates differences 

attributable to groundwater discharge. Although the seepage 

measurements provided detailed spatial definition of 

groundwater discharge to the creek in specific reaches, and 

only during the years the seepage measurements were made, 

analyses of low flows from the streamflow sites provided a 

year-by-year indication of seepage to the stream. 

The difference in low flow is shown in fig. 6 between 

the Gresham and Sycamore sites (from 1998 to 2006), and 

between the Sycamore and Milwaukie sites (from 1989 to 

2006). At each site, the minimum flow is during late summer. 

1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

0

5

10

15

20

25

30

GAIN IN STREAMFLOW, IN CUBIC FEET PER SECOND

Map number refers to table 1

Between Johnson Creek at Regner Road, 

at Gresham (map number 26) and 

Johnson Creek at Sycamore (map 

number 30), 1998–2006 

Between Johnson Creek at Sycamore

 and Johnson Creek at Milwaukie

 (map number 41), 1989–2006

CALENDAR YEAR

Figure 6. Gain in consecutive 7-day average low streamflow between Johnson Creek at Regner Road at Gresham, 

Oregon, and Johnson Creek at Sycamore, Oregon, and between Johnson Creek at Sycamore and Johnson Creek at 

Milwaukie, Oregon.
18 Hydrology of the Johnson Creek Basin, Oregon

The analysis was based on the same 7-day period at each site 

each year and was indexed to the days of minimum streamflow 

at the Sycamore site. For example, the 7-day low streamflow 

in 2005 at the Sycamore site was from September 21 to 27, 

and was compared to the 7-day streamflow for those days 

at the Gresham and Milwaukie sites. Although the annual 

7-day minimum streamflow at the Gresham and Milwaukie 

sites may not coincide with that of the Sycamore site, 

differences in streamflow between the common period and 

the annual 7-day low flow at each site were usually within the 

uncertainty associated with the streamflow records. For each 

year, the 7-day flow from the upstream site was subtracted 

from that of the downstream site, resulting in the gain during 

the low-flow time of each year. The relatively large (about 

1 ft3/s) groundwater discharge from Gresham to Sycamore in 

1998 through 2000 was followed by a decrease to less than 

0.4 ft3/s beginning in 2001. In 2003, the stream lost about 

0.3 ft3/s. Although only an indication of a loss, considering 

measurement uncertainties, the net groundwater discharge to 

this area of Johnson Creek during the summer of 2003 could 

be characterized as near zero. From 1989 to 2006, gains in 

flow from groundwater discharge to Johnson Creek between 

the Sycamore and Milwaukie sites were greater, ranging 

from 8.5 to 25.9 ft3/s. As discussed previously, most of the 

groundwater discharge is downstream of RM 5.5 and Crystal 

Springs is the largest contributor. The average summer gain 

in flow for 1996–99 was 22.4 ft3/s, compared to the 1989–95 

average of 14.8 ft3/s and the 2000–2006 average of 12.2 ft3/s. 

Use of low-flow data provides a minimum estimate of seasonal 

groundwater discharge to Johnson Creek. Groundwater 

discharge during the remainder of the year is higher because of 

increased infiltration of precipitation (recharge) and resulting 

increases in discharge to the stream from the surrounding 

aquifer. 

For years when seepage measurements were made (1997 

to 2000, and 2006), differences in streamflow measured at 

the Gresham, Sycamore, and Milwaukie sites were similar to 

differences in streamflow derived by comparison of 7-day low 

flows. The seepage measurements were made at low flow, but 

not necessarily at the lowest flow of the year. For this reason, 

groundwater discharge from seepage was usually slightly 

greater than determined from the 7-day low flows. 

Several inherent factors contribute to uncertainty in 

estimation of seepage to the stream from groundwater 

discharge using the low-flow data. Streamflow is computed 

using a lookup table, also known as a “stage-discharge rating.” 

(“Stage” is the stream level relative to an arbitrary datum.) 

At low flow, small changes in stream level result in relatively 

large changes in flow. Although streamflow measurements 

define the stage-discharge relation at a streamflow site, the 

relation can be imprecise and is affected by impermanent 

factors such as leaves, algae growth, and beaver dams. 

Similar to methods used in compiling seepage measurements, 

subtracting one small number from another also introduces 

uncertainty. Other factors that were not quantified include 

differences in evapotranspiration losses and possible water 

withdrawals. The lowest 7-day flow of the year at a given site 

additionally was not necessarily at the same time at all three 

sites because of the recession characteristics and differences in 

response to small rainfall events during the summer.

Base-flow separation also was used to quantify 

groundwater discharge to Johnson Creek, and to provide 

comparison between recharge estimates. This analysis is 

made using multidecade-scale, average streamflow values, 

and draws a comparison to long-term average recharge. 

Although recharge and discharge vary from year to year, these 

relatively short-term variations are dampened by the decadescale analysis. Snyder and others (1994) estimated recharge 

for the period from 1949 to 1983. The streamflow records at 

the Sycamore site begin in WY 1941, and at the Milwaukie 

site in WY 1989. The base-flow component of streamflow at 

the Sycamore site was calculated for the period covered by 

the Snyder and others (1994) analysis, the period of record 

at the Sycamore site, and from WY 1990 to 2006, the period 

of concurrent record at the Milwaukie site. The difference in 

the average groundwater discharge between these periods was 

less than 10 percent. For comparison, the concurrent period of 

record of the Sycamore and Milwaukie sites (WY 1990–2006) 

was selected. 

The average base-flow component of streamflow from 

WY 1990 to 2006 at the Sycamore site was about 20,500 

acre-ft/yr and about 35,500 acre-ft/yr at the Milwaukie site. At 

each site, groundwater discharge (the base-flow component of 

streamflow) represents about 60 percent of estimated recharge. 

The remaining 14,000 acre-ft of recharge at the Sycamore 

site is assumed to leave the drainage basin upstream of the 

site by groundwater flow paths leading toward other points of 

discharge either downstream of the site or outside the Johnson 

Creek basin. The remaining 25,300 acre-ft at the Milwaukie 

site likely discharges to areas outside of the Johnson Creek 

basin. Possible discharge of water that recharges to the 

Johnson Creek basin to areas outside of the basin is discussed 

further in the section “Groundwater Flow Direction.”

Use of Environmental Tracers to Identify 

Groundwater Discharge

A qualitative assessment of seepage was based on 

observations of specific conductance and continuous records 

of stream temperature. In this context, specific conductance 

and temperature were used as tracers to identify the presence 

of groundwater discharge in a given stream reach, providing 

independent confirmation of trends identified by flow 

measurements (Winter and others, 1998; Stonestrom and 

Constanz, 2003). 

The specific conductance of groundwater typically is 

higher than surface runoff because of prolonged contact with 

and dissolution of minerals in the subsurface environment. For 

example, the specific conductance of Johnson Creek during 
Groundwater Hydrology 19

high flows is usually less than 100 μS/cm compared to specific 

conductance values of greater than 200 μS/cm in Crystal 

Springs Creek, a groundwater fed stream (Edwards, 1992, 

p. 28). Increasing specific conductance from one measurement 

location to the next downstream generally is an indicator of 

groundwater discharge to the stream. 

Specific conductance measurements were made at 

most locations during the 1998, 1999, and 2006 seepage 

studies. Specific conductance generally increased less than 

30 μS/cm from RM 17.2 to the lower end of the middle reach 

(RM 5.5) (fig. 4, table 2). In contrast, specific conductance 

increased more than 50 μS/cm between RM 5.5 and 2.2. 

These results were consistent with the small gains in flow 

observed upstream of RM 5.5 and the much greater gains 

between RM 5.5 and 2.2. The absence of change in specific 

conductance from RM 2.2 to 1.2 is consistent with the 

absence of gain in streamflow indicated by the streamflow 

measurements. A large gain in streamflow is observed without 

a large increase in specific conductance between RM 1.2 and 

0.7 because the gain is a result of inflow from Crystal Springs 

Creek, and at low flow, the specific conductance of Johnson 

Creek is similar to that of Crystal Springs Creek. 

Stream temperature is another indicator of presence or 

absence of groundwater discharge. Seepage measurements 

are usually made during the summer, when air temperature is 

higher than the stream temperature. Groundwater discharge 

to the stream is cooler than either the stream temperature 

or the summer air temperature. During the summer, the 

temperature of Johnson Creek fluctuates on a diurnal cycle, 

warming several degrees during the day and cooling at 

night. In contrast, groundwater temperature is much cooler 

and fluctuates little. For example, the temperature of two 

springs (spring identification numbers 12 and 15 as shown in 

McCarthy and Anderson, 1990, table 2) in the Crystal Springs 

area was a constant 12.6°C from May to August 2000, despite 

seasonably warm air temperatures.

Groundwater discharge is identified by an overall cooling 

of the stream in the summer and moderation of the magnitude 

of the diurnal fluctuation in temperature. In the absence of 

groundwater discharge to the stream in a given reach, the 

diurnal pattern of stream temperature is repeated at subsequent 

locations downstream, generally warming because of 

increased exposure of the stream to the warm air and to solar 

radiation along many of the reaches. Groundwater discharge 

to the stream is identified by comparing the temperature at the 

upstream and downstream end of a given reach. 

Temperature recorders were installed in the stream 

at each streamflow location during the seepage studies of 

1998 and 2000 for several days before and after the day 

of streamflow measurements. An example of the stream 

temperature is shown in figure 7 at three locations on Johnson 

Creek in 2000, and the results shown are similar to those of 

1998. The stream temperature was fairly similar between 

RM 7.8 and 5.5, indicating negligible groundwater discharge 

to the stream, and substantiated by seepage measurement, 

which indicated little change in streamflow (fig. 4, table 2). In 

contrast, streamflow increased from RM 5.5 to 3.2 and was 

accompanied by an overall decrease in stream temperature. 

20

0:00 6:00 12:00 18:00 0:00 6:00 12:00 18:00 0:00 6:00 12:00 18:00 0:00 6:00 12:00 18:00 0:00

21 22 23

AUGUST 2000

12

14

16

18

20

22

24

26

 Map number refers to table 1

TEMPERATURE, IN DEGREES CELSIUS

RM 7.8 (map number 31)

RM 5.5 (map number 32)

RM 3.2 (map number 33)

Figure 7. Temperature at river mile (RM) 7.8, RM 5.5, and RM 3.2, Johnson Creek, Oregon.
20 Hydrology of the Johnson Creek Basin, Oregon

Groundwater Flow Direction

An understanding of groundwater flow direction is useful 

in evaluating the source areas (referred to as the contributing 

areas) for features that may receive groundwater discharge 

such as streams, lakes, wetlands, springs, and wells. If the 

location and extent of the contributing areas for discharge 

features is identified then information can be provided about 

how natural and man-made changes in climate, water use, or 

land use, for example, can influence the quantity and quality 

of water that may discharge. Therefore, knowledge of the 

direction of groundwater flow can be used to improve our 

understanding of the hydrology of the Johnson Creek basin, 

which will facilitate effective management of the water 

resources.

The direction of groundwater flow in an aquifer is 

dependent on the hydraulic head, an indicator of the total 

energy available to move groundwater through an aquifer 

(Taylor, and Alley, 2002, p. 3). Hydraulic head differs from the 

water level which describes the position of the groundwater 

surface usually relative to some datum such as sea level. For 

the water table, the hydraulic head is equal to the water-level 

elevation. For a vertical position in the water column below 

the water table or under confined conditions, the hydraulic 

head is the sum of the elevation of the position and fluid 

pressure at that point (the contribution to the hydraulic head 

from kinetic energy as a result of flow typically is assumed to 

be negligible) (Freeze and Cherry, 1979, p. 18-22, 39; Taylor, 

and Alley, 2002, p. 3). The hydraulic head at some point in an 

aquifer, such as a narrow open interval for a well, typically 

is measured as the height (water level) to which a column 

of water will stand above some datum. Groundwater flows 

from areas of high hydraulic head to areas of low hydraulic 

head. The direction of groundwater flow is used to identify 

the presence of a groundwater flow divide (a ridge in the 

groundwater surface from which groundwater moves away in 

both directions perpendicular to the ridge line), which is useful 

in inferring the extent of contributing areas to groundwaterdischarge features such as streams and springs. However, 

groundwater moves in complex, three dimensional patterns 

that change with time and consist of vertical and horizontal 

components of flow (Franke and others, 1998, p. 12). 

Water-level maps are useful in determining the approximate 

horizontal direction of groundwater flow but should be used 

with caution and the knowledge that a vertical component of 

flow also is present and that the direction of lateral flow may 

vary with depth below the water surface.

Groundwater flow directions in the Johnson Creek basin 

were inferred from water-level maps determined directly 

from measurement of groundwater elevations (McFarland and 

Morgan, 1996) and groundwater flow modeling that simulates 

the physical properties of the groundwater flow system and 

the stresses applied to the system to calculate hydraulic heads 

(Morgan and McFarland, 1996). A USGS study of the depth 

to groundwater and configuration of the water table in the 

Portland metropolitan area by Snyder (2008) resulted in a map 

of the estimated water-table elevation. The water-table map 

utilized much of the groundwater data collected as part of this 

study and can be used to infer the direction of groundwater 

flow on a local scale (Snyder, 2008, p. 5). The results of the 

analysis by Snyder (2008, p. 28, pl. 2) (see fig. 8) and analyses 

by McFarland and Morgan (1996, pls. 2-3) and Morgan and 

McFarland (1996, pls. 3-4) indicate that in many areas of the 

Johnson Creek basin, the direction of groundwater flow is 

not toward Johnson Creek, but instead is out of the drainage 

basin towards the Sandy, Columbia, or Willamette Rivers. 

Upstream of about RM 21, the direction of groundwater 

flow in the Johnson Creek basin generally is northward to 

the Sandy River. Between RM 21 and 15, the direction of 

groundwater flow is towards Johnson Creek. Between RM 15 

and 3, groundwater flow may be towards Johnson Creek in the 

immediate vicinity of the creek. However, between RM 15 and 

3, groundwater may flow north to the Columbia River in the 

eastern reach, with flow becoming more westerly towards the 

Willamette River in the western part of this area. Downstream 

of RM 3, in the lower part of the Johnson Creek drainage 

basin, the direction of groundwater flow at the water table 

is more consistently toward Johnson Creek, indicating local 

groundwater discharge.

The greater relative streamflow observed in the lower 

reaches of the Johnson Creek basin compared to the upper 

and middle reaches is likely explained by discharge from 

intermediate and regional groundwater flow systems in these 

areas. The general direction of shallow and intermediate 

depth groundwater flow in the middle and eastern areas of the 

Johnson Creek basin (containing the middle and upper reaches 

of Johnson Creek) generally is toward the Columbia River 

north or northwest, away from Johnson Creek (fig. 8; 

McFarland and Morgan, 1996, pls. 2-3; Snyder, 2008, pl. 2). 

Vertical hydraulic gradients between the water table and the 

underlying hydrogeologic unit and between the water table 

and deeper hydrogeologic units as simulated by Morgan and 

McFarland (1996, p. 32-35) additionally indicate downward 

movement of water throughout most of the eastern area of 

the Johnson Creek basin. In the middle areas of the basin, 

the vertical gradients are mixed. In the western area of the 

Johnson Creek basin, the general direction of shallow and 

intermediate depth groundwater flow is northwest changing to 

west towards the Willamette River and the mouth of Johnson 

Creek in the westernmost area of the basin. Vertical hydraulic 

gradients in the westernmost area of the basin indicate upward 

gradients that may denote the discharge of intermediate and 

regional groundwater flow to the lower reaches of Johnson 

Creek, tributaries and springs in the area, or to the Willamette 

River.
Groundwater Hydrology 21

Figure 8. Estimated water table elevation, Johnson Creek basin, Oregon.

Columbia Slough

RIVER

C

OLUMBIA

RIVER

RIVER

SANDY

WILLAMETTE

Butler Cr

Kelly

Creek

Kelley Creek

Mitchell

r C

Johnson Creek

North Fork

Kellogg

Creek

Deep Creek

CLACKAMAS

RIVER

Holgate

Lake

r CrpSl atsyr C

Lake

Oswego

30

43

43

212

212

224

99E

99E

205

405

5

5

5

84

205

211

26

26

224

30

26

500

500

500

600

900

500

300

300

200

100

100

600

300

300

400

100

200 200

100

600

600

600

300

300

300

300

700

100

500

200

100

200

400

300

300

200

100

600

100

100

100

200

200

100

500

300

600

500

200

400

500

400

200

200

100

200

600

600

600

300

300

200

300

200

300

400

400

300

500

400

100

800

700

700

600

700

500

400

400

300

300

200

400

600

600

500

400

300

600

600

400

300

300

500

500 500

500

500

400

500

600

400

400

400

100

300

200

200

300400

500

200

100

200

200

300

300

400

500

700

200

100

200

300

200

100

100

100

400

600

400

300

600

600

Oatfield

Hill

Aemisegger

Hill

Sunshine

Valley

Chamberlain

Hill

Beggars

Tick

Marsh

Mt

Tabor

Kelly

Butte

Powell

Butte

Mt

Scott

Mt

Talbert

Rocky

Butte

Government Island Reed Island

MULTNOMAH

CLACKAMAS

OREGON WASHINGTON

Kelso

Barton

Boring

Orient

Damascus

Cottrell

Sellwood

Rockwood Portland

Parkrose

Milwaukie

Pleasant

Valley

Troutdale

HappyValley

Gresham

Clackamas

Corbett

122°16' 122°18' 122°20' 122°22' 122°24' 122°26' 122°28' 122°30' 122°32' 122°34'

122°36' 122°38' 122°40'

45°

34'

45°

32'

45°

30'

45°

28'

45°

26'

45°

24'

0 1 2 3 4 5 MILES

0 1 2 3 4 5 KILOMETERS

Modified from Snyder (2008, plate 2). Base modified from U.S. Geological Survey data and other digital sources. Projection: UTM, Zone 10N, North American Datum 1983, Scale factor= 0.9996, False easting = 500,000, False northing = 0.

EXPLANATION

Water-table elevation index 

contour—Interval is 100 feet

Estimated water-table elevation—

in feet above North American Vertical Datum of 1988 

Johnson Creek basin boundary

1,00050011

400
22 Hydrology of the Johnson Creek Basin, Oregon

The apparent absence of groundwater discharge to some 

reaches of Johnson Creek is further indicated by a particletracking analysis (the simulation of hypothetical particles 

of water through the groundwater flow system using the 

results of a groundwater flow model) by Hinkle and Snyder 

(1997). The results of Hinkle and Snyder (1997) indicate that 

groundwater that recharges in areas of the Boring Hills flows 

vertically down and north beneath Johnson Creek through the 

regional groundwater flow system and likely discharges to the 

Columbia River (Hinkle and Snyder, 1997, p. 20 and pl. 1 A, 

B, and C). 

These observations and analyses indicate that the surfacewater divides delineating the Johnson Creek drainage basin 

are not necessarily coincident with groundwater divides 

particularly along the northern boundary of the basin. The 

surface-water divides along the southern boundary of the 

basin generally are coincident with the groundwater divides 

with possible exceptions in the vicinity of Happy and 

Pleasant Valleys, where areas of the valleys may be within 

the groundwater contributing area of the Johnson Creek 

basin although they are within the surface-water basins for 

Mt. Scott and Rock Creeks, respectively. As a result, recharge 

to the groundwater system within some areas of the Johnson 

Creek surface-water drainage basin may not discharge 

to Johnson Creek and instead may flow and discharge to 

regional groundwater discharge areas such as the Columbia 

and Willamette Rivers. Discharge of groundwater to areas 

outside the Johnson Creek basin appears to be more prevalent 

in the eastern and northern areas of the basin. This conclusion 

is further supported by the observations based on seepage 

measurements and streamflow data that indicate relatively 

small gains to Johnson Creek in the upper and middle basin 

compared to the lower basin.

Variation in Groundwater Levels and Storage

Understanding the factors that affect the location, 

timing, and magnitude of variations in groundwater levels 

and storage will aid managers in development of guidelines 

and regulations to protect the groundwater and surface-water 

resources of the Johnson Creek basin. Water-level fluctuations 

in wells represent variations in groundwater storage and are 

a result of many factors, including aquifer properties, the 

rates of recharge or discharge, the direction and magnitude 

of groundwater flow, and the construction of the well. In the 

Johnson Creek basin, the fluctuation of groundwater levels 

and storage is of particular concern because of the influence of 

these factors on the magnitude and timing of spring discharge, 

streamflow, and the surface expression of the water table in 

low-lying areas. 

Changes in the rates of recharge or discharge cause 

changes in groundwater storage, which are represented by 

water-table fluctuations. The water table rises because of 

increased groundwater storage when the rate of recharge 

exceeds the rate of discharge and declines when these 

conditions are reversed (Veeger and Johnston, 1996, p. 28). 

The water table rises in response to increased groundwater 

storage that can result from recharge because of precipitation, 

losing streams, stormwater runoff into UIC systems, 

infiltration from septic systems and excess irrigation, or 

increased inflow of groundwater from adjacent areas. The 

water table declines in response to decreased groundwater 

storage that can result from discharge to gaining streams, 

springs, pumpage, evapotranspiration, or the outflow of 

groundwater to adjacent areas. In the Portland area, the 

quantity and timing of precipitation typically exerts the 

greatest influence on water-level fluctuations, and because 

of the seasonal nature of precipitation, a seasonal response 

in water-table level results (Snyder, 2008, p. 24-25, 29-30). 

Groundwater levels rise following precipitation of sufficient 

intensity and duration to exceed evapotranspiration and 

soil moisture deficits and the residual infiltration results in 

recharge. Water levels decline as groundwater is removed 

from storage during periods when discharge to rivers, streams, 

springs, pumping wells or evapotranspiration, is greater than 

recharge. Time scales for water-table fluctuations range from 

hours (in the response to high intensity precipitation events or 

changes in stream level) to years or decades (in response to 

long-term changes in climate or land-use practices). 

Well construction also can influence water-level 

fluctuations in wells. The well depth, the open-interval length 

and its proximity to the water table, and if the well is open to 

a water-table (unconfined) aquifer or confined aquifer can all 

contribute to water-level fluctuations in wells.

Changes in groundwater storage indicated by fluctuations 

in groundwater levels are of special interest in two areas 

within the Johnson Creek basin: (1) the groundwater 

contributing area to Crystal Springs (which provides the flow 

to Crystal Springs Creek (map number 40) that consequently 

provides most of the late summer flow to Johnson Creek 

downstream of the confluence with Crystal Springs Creek), 

and (2) the vicinity of Holgate Lake (map number 43) that is 

subject to flooding when groundwater levels exceed landsurface elevation in low-lying areas. 

The surface-water contributing area to Crystal Springs 

Creek is insufficient to supply the observed discharge based 

on estimates of groundwater recharge (Dames & Moore, 

1998, p. 59). The groundwater contributing area for the flow 

to Crystal Springs, which supplies most of the discharge 

to Crystal Springs Creek, may extend to areas well beyond 

the surface-water contributing area of the Crystal Springs 

Creek basin perhaps as far east as Powell Butte according to 

observations of regional and local groundwater flow directions 

(McFarland and Morgan, 1996, pls. 2-3; Snyder, 2008, 

pl. 2). However, an accurate delineation of the groundwater 

contributing area for Crystal Springs will require the use of 

an updated three-dimensional groundwater flow model with 

sufficient discretization and data to adequately represent the 

springs and gaining and losing reaches of Johnson Creek. The 

change in groundwater storage in this area may have a direct 

relation to the timing and quantity of streamflow of Crystal 

Springs Creek.
Groundwater Hydrology 23

Analysis of the groundwater flow system was focused 

on the area extending from Powell Butte westward which 

includes the areas of Crystal Springs Creek and Holgate Lake, 

two concerns to the community. A monitoring network of 

wells was established in 1998 to increase understanding of 

the groundwater flow system in the area. Initially, the wells 

were measured monthly, changing to bimonthly in 2000, and 

to quarterly beginning in 2005. Hydrographs from these wells 

were used to analyze the spatial and temporal variations in 

groundwater levels in the western area of the Johnson Creek 

basin (fig. 9; pl. 1; table 1). In 1998 a continuous waterlevel recorder with real-time telemetry was installed near 

Holgate Lake (map number 9). In 2001, the city of Portland 

completed construction of seven monitoring wells between 

I-205 and Westmoreland Park. Continuous water-level 

recorders were installed in five of these wells (map numbers 

19, 20, 21, 23, and 24). The records from the continuous 

water-level recorders at Holgate Lake and between I-205 and 

Westmoreland Park provide the most detailed information on 

the magnitude and timing of groundwater fluctuations in the 

area west of Powell Butte (figs. 10 and 11). This information 

was used to evaluate how groundwater storage changes from 

day to day, season to season, or year to year in response to 

precipitation events, seasonal variations, or long-term trends, 

respectively. 

Water levels in the four easternmost wells with 

continuous water-level recorders (fig. 10) fluctuated in 

response to precipitation (fig. 11). The general pattern of 

water level in these four wells is a sinusoidal fluctuation that 

varies seasonally. From east to west, the magnitude of the 

response is increasingly attenuated and the time between 

precipitation and the corresponding rise in water level is 

increased. The annual water-level fluctuation (fig. 10) ranges 

from as much as 10 ft in the easternmost well (map number 

9) to less than a foot in the westernmost well of this group 

(map number 21). In a given year, the water level in the 

easternmost well responds quickly to the autumn rains, rising 

rapidly following distinct rainy periods, and usually peaks in 

March or April, coincident with the end of the rainy period 

and the beginning of substantial uptake of water by plants 

and evaporation. The rise in water levels illustrated by this 

set of the four easternmost wells with continuous recorders 

is increasingly muted and delayed with distance westward 

(from east to west: map numbers 9, 19, 20, and 21), such that 

the response from autumn rains in the westernmost well of 

these wells does not usually begin until March or April of 

the following year, a 6-month difference. In 2001 and 2005, 

precipitation was decreased or fell later than normal (fig. 11) 

and seems to have contributed less to groundwater recharge 

due to decreased infiltration or uptake by soil moisture storage 

and evapotranspiration compared to other years as indicated 

by a lower than normal rise in the groundwater level at the 

easternmost well (map number 9), and little or no increase 

in groundwater levels in the other wells shown in figure 10, 

until the following season’s recharge from precipitation. 

The increase in the attenuation and delay of the rise in the 

level of groundwater in response to the autumn and winter 

precipitation in an east-to-west direction may be attributed to 

the characteristics of the unsaturated zone, such as thickness 

and composition. The unsaturated zone thickness is one of 

the factors affecting the travel time of precipitation from 

the land surface to the water table and greater thickness 

contributes to longer and more diverse travel times. The 

median daily thickness of the unsaturated zone is about 

44 ft in the easternmost well, and is about 120, 131, and 

100 ft in the other three wells from east to west, respectively 

(fig. 10). Unsaturated zone travel time also is a function of 

several factors, including the composition of the unsaturated 

zone including rock type, particle size/texture (clay, silt, 

sand, and gravel), sorting, consolidation, cementation, 

homogeneity, and moisture content. The unsaturated zone 

materials consist primarily of unconsolidated deposits from 

the Missoula Floods. These deposits tend to be finer grained 

to the west as distance increases from the western end of the 

Columbia River Gorge (Trimble, 1963, p. 63; Hogenson and 

Foxworthy, 1965, p. 26). However, these materials can be 

variable and discontinuous vertically and laterally (Trimble, 

1963, p. 58–62). The presence of poorly sorted finer grained 

materials may further increase the time and diversity of travel 

times through the unsaturated zone. Differences in effective 

porosity of these materials also could result in differences 

in the magnitude of the response to precipitation events, 

such that greater effective porosity results in greater storage 

available within the aquifer and a smaller change in the watertable position resulting from a change in a given volume of 

water when compared to an aquifer with a lesser effective 

porosity (Snyder, 2008, p. 24-25, 29-30). 

Alternatively or additionally, there may be a groundwater 

wave (hydraulic pulse) in the saturated zone moving from east 

to west when recharge enters the groundwater flow system 

and moves laterally. A groundwater wave is defined as “a 

high in the water table that moves laterally, with a wavelike 

motion, away from a place where a substantial quantity of 

water has been added to the saturated zone within a brief 

period” (Wilson and Moore, 2003, p. 97). A groundwater 

wave originating in the area on the west side of Powell Butte 

and moving westward could explain the pattern of water-level 

fluctuations in the wells from Powell Butte extending west to 

the area just east of Westmoreland Park. The pattern displays 

increased attenuation and delay of the rise in the level of 

groundwater as distance increases from the source area. A 

groundwater wave is an expression of a hydraulic (pressure) 

pulse that can move more rapidly through an aquifer when 

compared to the actual movement of groundwater, which 

would be expected to be much slower. The existence of a 

groundwater wave may be resolved by further analysis of 

existing or new groundwater level data in this area.
24 Hydrology of the Johnson Creek Basin, Oregon

tac09_9711_0344_JohnsonCrk_fig09a

1998 1999 2000 2001 2002 2003 2004 2005 2006

1998 1999 2000 2001 2002 2003 2004 2005 2006

1998 1999 2000 2001 2002 2003 2004 2005 2006

1998 1999 2000 2001 2002 2003 2004 2005 2006

1998 1999 2000 2001 2002 2003 2004 2005 2006

1998 1999 2000 2001 2002 2003 2004 2005 2006

1998 1999 2000 2001 2002 2003 2004 2005 2006

1998 1999 2000 2001 2002 2003 2004 2005 2006

70

75

80

85

90 47

50

55

60

65

67 135

140

145

150

155 78

80

85

90

95

98

90

95

100

105

110 84

85

90

95

100

104 163

165

170

175

180

183 78

80

85

90

95

98

100

105

110

115

120 118

120

125

130

135

138 135

140

145

150

155 96

100

105

110

115

116

125

130

135

140

145 110

115

120

125

130 197

200

205

210

215

217 -10

-5

0

5

10

ELEVATION, IN FEET ABOVE NGVD 1929

ELEVATION, IN FEET ABOVE NGVD 1929

DEPTH TO WATER, IN FEET BELOW LAND SURFACE

DEPTH TO WATER, IN FEET BELOW LAND SURFACE

CALENDAR YEAR CALENDAR YEAR

MAP NUMBER 22 MAP NUMBER 17

MAP NUMBER 21

MAP NUMBER 20

MAP NUMBER 19

MAP NUMBER 16

MAP NUMBER 15

MAP NUMBER 14

Measurement Measurement

Measurement

Measurement

Measurement

Water level below bottom of well

 (dry), map number 14 only

Daily mean

Measurement

Daily mean

Measurement

Daily mean

Measurement

Figure 9. Water levels in selected long-term observation wells, Johnson Creek basin, Oregon. Map numbers refer to table 1.
Groundwater Hydrology 25

tac09_9711_0344_JohnsonCrk_fig09a ELEVATION, IN FEET ABOVE NGVD 1929

ELEVATION, IN FEET ABOVE NGVD 1929

DEPTH TO WATER, IN FEET BELOW LAND SURFACE

DEPTH TO WATER, IN FEET BELOW LAND SURFACE

175

180

185

190

195 7

10

15

20

25

27 220

225

230

235

240 -2

0

5

10

15

18

179

180

185

190

195

199 30

35

40

45

50

MAP NUMBER 9

205

210

215

220

225 13

15

20

25

30

33

180

185

190

195

200 198

200

205

210

215

218

MAP NUMBER 5

220

225

230

235

240 4

5

10

15

20

24

203

205

210

215

220

223 48

50

55

60

65

68

MAP NUMBER 8

178

180

185

190

195

198 49

50

55

60

65

69

MAP NUMBER 4

MAP NUMBER 3

MAP NUMBER 1

MAP NUMBER 2

1998 1999 2000 2001 2002 2003 2004 2005 2006

1998 1999 2000 2001 2002 2003 2004 2005 2006

1998 1999 2000 2001 2002 2003 2004 2005 2006

1998 1999 2000 2001 2002 2003 2004 2005 2006

1998 1999 2000 2001 2002 2003 2004 2005 2006

1998 1999 2000 2001 2002 2003 2004 2005 2006

1998 1999 2000 2001 2002 2003 2004 2005 2006

1998 1999 2000 2001 2002 2003 2004 2005 2006

MAP NUMBER 12 Measurement Measurement

Measurement

Measurement

Measurement Measurement

Measurement

Daily mean

Measurement

CALENDAR YEAR CALENDAR YEAR

Figure 9.—Continued
26 Hydrology of the Johnson Creek Basin, Oregon

tac09_9711_0344_JohnsonCrk_fig10

179

180

185

190

194 35

40

45

50

128

130

135

140

143 112

115

120

125

127

100

105

110

115 123

125

130

135

138

2001

F A J A O D F A J A O D F A J A O D F A J A O D F A J A O D F A J A O D

2002 2003 2004 2005 2006

90

95

100

105 89

90

95

100

104

ELEVATION, IN FEET ABOVE NGVD 1929

DEPTH TO WATER, IN FEET BELOW LAND SURFACE

Map number refers to table 1

Well near 133rd Avenue and Raymond Street (map number 9)

Well at Brentwood Park (map number 19)

Well at Woodstock Park (map number 20)

Well at Berkeley Park (map number 21)

Daily mean

Measurement

CALENDAR YEAR

Figure 10. Water level elevation and depth to water in wells: near 133rd Avenue and Raymond Street, at Brentwood Park, 

at Woodstock Park, and at Berkeley Park, Portland, Oregon. Map numbers refer to table 1..
Groundwater Hydrology 27

tac09_9711_0344_JohnsonCrk_fig11

F A J A O D F A J A O D F A J A O D F A J A O D F A J A O D F A J A O D

0

5

10

15

45

46

47

48

49

50

51

52

53

54

55

23

24

25

26

27

28

29

30

2001 2002 2003 2004 2005 2006

39

40

41

42

43

44

45

46

47

48

49

0

5

10

15

20

25

PRECIPITATION, IN INCHES ELEVATION, IN FEET ABOVE NGVD 1929

JOHNSON CREEK STREAM LEVEL, IN FEET ABOVE NGVD 1929

ELEVATION, IN FEET ABOVE NGVD 1929 

WILLAMETTE RIVER STREAM LEVEL, IN FEET

A. Portland Airport (site number 356751)

B.

C.

CALENDAR YEAR

Monthly total precipitation

Westmoreland Park shallow well (map number 23)

 Daily mean

 Measurement

Johnson Creek at Milwaukie (map number 41)

Daily mean

Westmoreland Park deep well (map number 24) 

 Daily mean

 Measurement

Willamette River at Portland (map number 44)

 Daily mean

Figure 11. Precipitation at (A) Portland Airport, Oregon, (B) water level elevation in the shallow well at Westmoreland Park 

and water level of Johnson Creek at Milwaukie, Oregon, and (C) water level elevation in the deep well at Westmoreland 

Park, and level of the Willamette River at Portland, Oregon. (Willamette River stream level is set to an arbitrary gage datum. 

Map numbers refer to table 1.)
28 Hydrology of the Johnson Creek Basin, Oregon

Understanding of the pattern of water-level fluctuations 

in the two Westmoreland Park wells is needed to assess 

the possibility of a relation of groundwater levels in this 

area to the level and streamflow of Crystal Springs Creek 

in the Westmoreland Park area. The patterns of water-level 

fluctuations in the two wells in Westmoreland Park (a shallow 

well (map number 23), and a deeper well (map number 24); 

fig. 11) are fairly similar, but differ greatly when compared to 

the four continuous-recorder wells toward the east (fig. 10). 

The different trends in water levels are a result of two factors. 

First, the Westmoreland wells are completed in permeable 

deposits of a former stream channel that could be either of the 

Clackamas River or of the Willamette River (Hogenson and 

Foxworthy, 1965, p. 10-11, 28). The channel facies deposits 

consist of interlayered silts, sands, and gravels, which in some 

places are locally covered by bog or pond sediments (Beeson 

and others, 1989). These deposits may exert a strong influence 

on the response of water levels within the groundwater system. 

Second, proximity to Johnson Creek and the Willamette River 

indicates that changes in the hydraulic head of these streams 

(as represented by their surface-water elevations) may be 

transmitted through the permeable channel facies deposits 

and affect water levels in the Westmoreland Park wells as 

indicated from the hydrograph characteristics for the two wells 

(see discussion below). Water levels in the two Westmoreland 

Park wells are relatively close to land surface, where depth 

to water from 2001 to 2006 was about 3 to 12 ft below land 

surface. 

The water level in both Westmoreland Park wells rises 

quickly in response to precipitation, and also rises and declines 

on an annual cycle (fig. 11). Following the end of a given 

precipitation event, the water level in these wells declines 

rapidly. This rapid decline in water level in the Westmoreland 

Park wells is unlike the wells to the east, where the effect of 

precipitation typically is cumulative within a given year, and 

water levels begin to decline slowly in response to decreased 

precipitation intensity and groundwater flow towards 

discharge areas (fig. 10). Of the two wells in Westmoreland 

Park, the shallow well (map number 23) responds slightly 

more quickly, and the rise generally is of greater magnitude 

than the deep well (map number 24). Response time of both 

wells to precipitation is within 1 to several days. Most of the 

water-level rise associated with a typical several-day winter 

storm with 2 to 3 in. of rainfall is often about 2 ft in the 

shallow well and about 1 ft in the deep well. The short-term 

rise and decline in water level because of discrete rainfall 

events is superimposed on an annual, relatively steep rise in 

water level in autumn and winter and an attenuated recession 

during the spring and summer periods. Water levels in these 

two adjacent wells at Westmoreland Park were compared 

to precipitation at the Portland Airport (NWS site number 

356751) (Oregon Climate Service, 2007). Weekly precipitation 

totals show a moderate correlation with the weekly change 

in groundwater levels at the shallow and deep well, with a 

correlation coefficient (R) of 0.60 and 0.65, respectively. 

Although rises in water level in both wells are on a severalday time scale, these rises are followed by declines on the 

same time scale. These declines in water level may account for 

the relative weakness in this correlation. Water levels in these 

wells show stronger correlations with stream levels in Johnson 

Creek and the Willamette River. The hydrographs of the two 

Westmoreland Park wells bear a striking similarity to the 

river-level hydrographs of Johnson Creek and the Willamette 

River (fig. 11) —similar shape and distinct storm and annual 

sinusoidal responses. Daily water levels in the shallow well 

(map number 23) are closely correlated (R = 0.85) to the 

daily mean stream level at the Johnson Creek at Milwaukie 

site (map number 41), and are at least in part affected by 

tidally induced fluctuations of the Willamette River. Although 

the well is about 1.5 mi north of the Johnson Creek stream 

monitoring site, the closest approach is only about 0.7 mi 

north of Johnson Creek. There seems to be a subsurface 

hydraulic connection between the shallow well and Johnson 

Creek because the lag time between a change in stream level 

and a corresponding change in the water level at the well 

is less than 1 day as determined using a cross-correlation 

analysis. At about RM 2.0, where Johnson Creek flows out of 

an incised canyon, the streambed consists of recent alluvial 

deposits that overlie the channel facies deposits at the mouth 

of the canyon (Beeson and others, 1989). At this location, the 

elevation of Johnson Creek is several feet above the elevation 

of the water table in the low-lying drainage basin of Crystal 

Springs Creek. Changes in stage in Johnson Creek likely are 

transmitted through the shallow, semi-confined channel facies 

deposits, to the Westmoreland Park wells. Potential recharge to 

the aquifer from Johnson Creek has been indicated by seepage 

measurements, which often indicate small losses along this 

reach to just upstream of the confluence with Crystal Springs 

Creek (fig. 4, table 2). 

Backwater from tidal fluctuations of the Willamette 

River, about 0.8 mi to the west, also affects the water level in 

the shallow Westmoreland Park well. Backwater is the effect 

on the water-surface elevation at a given stream location from 

fluctuations of a downstream water body. The Willamette 

River fluctuations of several feet per day (as observed at the 

site in downtown Portland (map number 44) about 3 river 

miles downstream) are transmitted to the shallow well through 

permeable channel deposits, resulting in a fluctuation of a few 

hundredths of a foot, daily and sometimes twice daily.

The daily mean water level in the deep well (map number 

24) at Westmoreland Park also exhibits a strong correlation 

with the daily mean level of the Willamette River. The lag 

times in response to changes in level of the Willamette River 

and subsequent changes in the water level in the deep well 

at Westmoreland Park are short, perhaps less than 1 day as 

determined through cross-correlation. This strong correlation 

(R = 0.81) and short lag time may be the result of a hydraulic 

connection between the Willamette River and the channel 

facies deposits within the former river channel that extend to 

the Willamette River and to which the deep well is open. As 
Groundwater Hydrology 29

indicated above, a minor relation is apparent in the connection 

of tidal fluctuation in the Willamette River to the shallow 

well in Westmoreland Park. The deep well responds more 

reliably to the twice-daily tidal fluctuations, where two highs 

and two lows during many days affect the water level in 

this well. Similar to the shallow well, the amplitude of these 

fluctuations is several hundredths of a foot. The difference in 

the tidal effect observed in the shallow and deep wells may 

be attributed to a coarsening of subsurface materials at depth. 

The driller’s logs of these two wells indicated a silty layer 

about 20 ft below land surface near the open interval of the 

shallow well, which may inhibit movement of water from the 

otherwise coarse alluvial deposits to the shallow well. 

The tidal influence and backwater from the Columbia 

River affect the Willamette River and these fluctuations also 

affect the water level in the Westmoreland Park deep well 

(fig. 11). Although the high-flow period of the Willamette 

River (and associated high stream level) usually is in winter, 

the spring melt in the headwaters of the Columbia River basin 

(several hundred miles to the northeast) in May and June of 

each year raises the Columbia River in the Portland area, 

backing water up in the Willamette River in the Portland area. 

The backwater creates a “hump” in the otherwise (usually) 

smooth recession of the Willamette River at Portland (map 

number 44). This rise is not associated with precipitation 

in the area and provides clear differentiation between 

precipitation and river-level induced changes in water level 

in the Westmoreland Park deep well. Evaporative losses 

additionally are high during late spring and effectively reduce 

recharge from precipitation in the May–June time period. 

The backwater effect is not the same each year, and depends 

primarily on the magnitude and duration of high flow of the 

Columbia River. For example, the presence of backwater was 

almost nonexistent in 2001, when May and June flows of the 

Columbia River were at a near-record low, but was present in 

2006, an average flow year for the Columbia River. 

Response of the Groundwater System to 

Precipitation Extremes 

The response of the groundwater system to extended 

periods of either unusually high or low precipitation is 

manifested by changes in groundwater levels and discharge to

rivers, streams, and springs. The period of study, 1997–2006, 

encompassed relative extremes in annual precipitation 

which were accompanied by changes in groundwater levels, 

streamflow, and spring discharge. The analysis of data 

collected during this period enabled the development of 

relations to forecast the effect of these precipitation extremes 

on groundwater levels and the resulting effect on surface-water 

features. These relations can be used to anticipate changes in 

discharge of spring-fed streams or to estimate the expected 

inundation of low-lying areas as a result of groundwater levels 

rising above land surface.

High and Low Groundwater Discharge: Crystal 

Springs Creek

Crystal Springs Creek receives flow from several 

springs, flows in a channel through park and residential areas 

of Southeast Portland, and enters Johnson Creek at RM 1.0. 

Historically, increased discharge of these springs has raised 

concerns about the stream level and potential flooding of areas 

adjacent to Crystal Springs Creek. Flooding was reported in 

park and residential areas adjacent to the creek in July 1997 

(Chestnut, 1997). In 2005, low flow of Crystal Springs Creek 

in the Reed College area prompted concern about fish survival 

under these conditions. 

The channel of Crystal Springs Creek has been 

modified. Although the creek is a natural feature, the mostly 

predevelopment landscape, as mapped by the General Land 

Office in 1852, consisted of a distinct stream channel in the 

upper area near the present location of Reed College campus, 

tributaries corresponding to the location of several springs in 

2008, and an extensive wetland area covering much of what 

is now Westmoreland Park (University of Oregon, 2006). 

The wetland narrowed to a single stream channel near the 

confluence with Johnson Creek. The creek was channelized 

through much of its length in 1936 during construction 

of Westmoreland Park. The present configuration is an 

approximately 10-ft-wide natural bottom, concrete-walled 

channel, where the creek flows nearly bankfull year-round. 

The stream channel opens into a pond in Westmoreland Park 

and narrows again toward the mouth of the creek.

 Flooding along Crystal Springs Creek was first noticed in 

the summer of 1997 (Chestnut, 1997; Dillin, 1997). The creek 

overtopped the banks and flowed into park and recreational 

areas, onto streets, and into basements of creekside properties. 

The cause of the flooding was increased discharge from 

springs and decreased capacity of the channel. Reductions in 

the channel capacity between 1996 and 1997 probably was a 

factor because the streamflow of Crystal Springs Creek was 

nearly as high in 1996 when no flooding was reported as it was 

in 1997 when flooding was reported (fig. 2). An assessment of 

the channel capacity, specifically the effect of aquatic growth 

or sediment in the stream channel was beyond the scope of 

this study. Removal of aquatic weeds in August 1997 (when 

the streamflow was still relatively high) lowered the level of 

Crystal Springs Creek in the Westmoreland Park area by about 

1.5 ft, which caused a near-bankfull rather than an overbank 

condition (Sellwood Bee, 1997). 

The cumulative impact of consecutive years of higherthan-average precipitation and the resulting increase in 

groundwater discharge was the primary factor contributing 

to the high flow of Crystal Springs Creek. Precipitation 

records indicate that Crystal Springs Creek probably did not 

have an increased streamflow such as recorded from 1996 to 

1999 since the channel was modified in 1936, and possibly 

not since 1911. The near-record precipitation in WY 1996 
30 Hydrology of the Johnson Creek Basin, Oregon

(54.7 in.) was followed by the highest annual precipitation 

on record in WY 1997 of 58.7 in. (Oregon Climate Service, 

2007) (fig. 5) The 3-year moving average annual precipitation 

depicts the unprecedented surge in groundwater recharge and 

subsequent discharge, and the multiyear recession observed 

in the late 1990s. The 3-year moving average precipitation 

in WY 1997, 1998, and 1999 was several inches greater than 

any year after recordkeeping began. By WY 2000, the 3-year 

moving average annual precipitation was close to the longterm average, and flow on Crystal Springs Creek had receded 

as well.

The elevated level of Crystal Springs Creek in the 

Westmoreland Park area probably is not associated with the 

rise of local groundwater levels and instead is the result of 

increased discharge of the numerous springs upstream of 

the Westmoreland area. Comparison of the hydrographs for 

the shallow and deep wells at Westmoreland Park (fig. 11) 

indicates a consistent downward gradient (where the head 

in the deeper well is less than the head in the shallow well) 

in this area. The absence of fluctuation in level of Crystal 

Springs Creek in the Westmoreland Park area (compared to 

1 to 3 ft fluctuations in the shallow water table) and concurrent 

measurements along Crystal Springs Creek that showed 

little gain or loss indicates an absence of connection with the 

aquifer. A survey of measuring point elevations for the wells 

and along Crystal Springs Creek would help determine if the 

stream lies above the water table and is therefore disconnected 

from the groundwater system.

Low flow of Crystal Springs Creek in the Reed College 

area (map number 38) in July 2005 prompted curtailment 

of irrigation withdrawals. The low flow in this area was 

confirmed by streamflow measurements made in July, 

September, and October 2005 (fig. 2). The average of the three 

measurements made in 2005 was about 0.3 ft3/s, less than 

one-third of the flow measured in the previous 3 years, and 

less than 5 percent of the highest flow measured in 1997. The 

likely cause of decreased spring discharge was a decline in 

water levels and therefore groundwater storage of the aquifer 

upgradient of the springs. The monitoring well at Berkeley 

Park (map number 21), 0.8 mi southeast of the streamflow 

measurement location at Reed College, indicated there was 

little or no recharge in 2005, in contrast to previous years 

(2002 through 2004) that indicated an annual fluctuation in 

response to precipitation (fig. 10). Although 2005 was not a 

particularly dry year, precipitation came late in the season. In 

this condition, recharge for a given amount of precipitation 

may be less because of increased losses to evapotranspiration 

and soil moisture storage.

Use of Hydrologic Data to Predict Streamflow of 

Crystal Springs Creek

Because flow in Crystal Springs Creek is predominantly 

from the springs, and the spring flow is related to groundwater 

levels, flow of Crystal Springs Creek can be predicted using 

groundwater levels. The high flows of Crystal Springs Creek 

from 1996 to 1999 were the result of the prolonged effect 

of consecutive years of high precipitation in 1996 and 1997. 

Precipitation in 2005 was decreased or fell later (fig. 11), 

contributing little to groundwater recharge, which may have 

led to unusually low flows that summer. The groundwater 

level in the terrace just east of the headwaters of Crystal 

Springs Creek, represented by the Berkeley Park well (map 

number 21), fluctuates in response to precipitation (recharge), 

which is reflected in the subsequent discharge to the creek 

from the springs. 

The Berkeley Park well has a continuous water-level 

recorder providing a useful data record for comparison with 

the streamflow of Crystal Springs Creek. However, in order 

to describe the relation between the streamflow of Crystal 

Springs Creek and groundwater levels, an intermediate step 

was required to estimate what the groundwater level was in 

the Berkeley Park area before the well was drilled in 2001. 

The water level in the Berkeley Park well relates closely to a 

well nearby that has a longer record of periodic measurements 

(map number 22) (pl. 1; fig. 9; table 1). Concurrent water-level 

measurements at these two wells from 2001 to 2006 were used 

in a regression to estimate the water level at the Berkeley Park 

well from October 1998 through August 2000, the period prior 

to the installation of the well (fig. 12). The extent of the data 

and the linear regression is scaled in fig. 12 to show the extent 

of extrapolation. Further data collection at higher water levels 

than those collected during the period of study may provide a 

better understanding of this relation. 

The flow of Crystal Springs Creek at the Reed College 

site and at the mouth of the creek can be predicted based on 

groundwater levels at the Berkeley Park well (fig. 13). The 

relation of water level in the Berkeley Park well and flow of 

Crystal Springs Creek is valid over the range of concurrent 

water-level measurements and estimates, and streamflow 

measurements. The water level in the well ranged from 

92.3 to 103.9 ft. The streamflow of Crystal Springs Creek 

encompassed by this relation was from 0.2 to 5.9 ft3/s and 

from 9.2 to 19.1 ft3/s for the locations at Reed College and at 

the mouth of the creek, respectively.
Groundwater Hydrology 31

tac09_9711_0344_JohnsonCrk_fig12

90

92

94

96

98

100

102

104

106

WATER-LEVEL ELEVATION, MAP NUMBER 22, IN FEET ABOVE NGVD 1929

WATER-LEVEL ELEVATION, MAP NUMBER 21, IN FEET ABOVE NGVD 1929

74 75 76 77 78

Map number refers to table 1

R 2 = 0.97

Berkeley Park, 39th Avenue, and Bybee Boulevard (map number 21)

32nd Avenue and Steele Street (map number 22)

Figure 12. Relation between water level elevation in wells at Berkeley Park, and at 32nd Avenue and Steele Street, 

Portland, Oregon.

90 95 100 105

0

5

10

15

20

WATER-LEVEL ELEVATION IN WELL AT BERKELEY PARK (MAP NUMBER 21), IN FEET ABOVE NGVD 1929

STREAMFLOW, IN CUBIC FEET PER SECOND

Map number refers to table 1

Crystal Springs Creek at Reed College (map number 38)

Crystal Springs Creek at mouth (map number 40)

Relation: CSR = (BERK * 0.466) – 42.90

n = 23, R 2 = 0.97

Relation: CSM = (BERK * 0.800) – 64.57

n = 26, R 2 = 0.94

Figure 13. Relation between streamflow of Crystal Springs Creek at Reed College and mouth of Crystal Springs Creek at 

Portland, and water level elevation in the well at Berkeley Park, Portland, Oregon.
32 Hydrology of the Johnson Creek Basin, Oregon

As discussed previously, groundwater level in the area 

of the Crystal Springs Creek basin in Westmoreland Park is 

affected by the stream level of Johnson Creek and Willamette 

River. Although the summer stream level of Johnson Creek 

varies little from year to year, the Willamette River was 

particularly high in the summer of 1997, which was coincident 

with the high flow of Crystal Springs Creek. Because the wells 

in Westmoreland Park were not drilled until 2001, the relation 

of nearby river levels to groundwater level and streamflow 

in 1997 could not be explored. During June 1997, the stream 

level of the Willamette River was about 16 ft, about 6 ft higher 

than during the same period from 1998 to 2006. Previous 

discussion referred to an absence of connection between 

Crystal Springs Creek in the Westmoreland Park area and the 

shallow aquifer. Continued monitoring of nearby stream levels 

and groundwater levels in wells in Westmoreland Park may 

provide further indications of stream–aquifer relations in this 

area. 

Flooding from High Groundwater Level–Holgate 

Lake

Holgate Lake (map number 43) is an ephemeral lake in 

Southeast Portland near 136th Avenue and Holgate Boulevard 

(pl. 1). The origin of the lake and recurrent flooding and 

damage to nearby properties has been the subject of concern 

for local residents and municipal officials, prompting 

focused study in this area. Although the history of residential 

development of this area is uncertain, the first homes were 

probably built in the early 20th century. Until then, land 

use was primarily small farms. The lake is in a topographic 

depression in a residential area, and has flooded residences 

numerous times over the past several decades. Based on the 

present configuration of streets and residential development 

in the area, flooding begins whenever the lake level exceeds 

about 191 ft. Analysis of nearby groundwater level data and 

precipitation data has led to the conclusion that the occurrence 

of the lake is the result of groundwater flooding. Groundwater 

flooding begins in low-lying areas whenever the water 

table rises above the land surface (Jones and others, 2000). 

Precipitation and groundwater level data may be used to 

anticipate the extent of flooding in the low-lying area that has 

been designated as “Holgate Lake.”

The first record of flooding in the area now known as 

Holgate Lake was in March 1949, indicating the lake had risen 

6 ft in 1 week, flooding several homes on the south side of 

the lake. The water-surface elevation of the lake was inferred 

from a photograph, indicating an elevation of between 190 

and 195 ft. The cause was attributed to seepage from the 

surrounding slopes. The water level observed in 1949 was the 

highest since about 1943 (Gresham Outlook, 1949). 

The next reports of flooding were in 1969. The elevation 

of the lake was about 199 ft, covered an area of about 50 acres 

(although the present interpretation of the flooded area is about 

30 acres), and the western extent of the lake was near 128th 

Avenue. These observations were made in January 1969 and 

included a groundwater level measurement and reference to 

the land-surface elevation at a well near 122nd Avenue and 

Holgate Boulevard. The emergence of the lake was attributed 

to a rise in the water table (William S. Bartholomew, State of 

Oregon, written commun., 1969). A local newspaper attributed 

the flooding to unusually high water table and springs, 

following the heaviest precipitation since 1881. Flooding was 

reported by residents in 1943, 1948, 1956, and 1964 (Gresham 

Outlook, 1969). 

Flooding from Holgate Lake began again in February 

1996, lasting at least a month. The city of Portland pumped 

about 5 Mgal/d for a month from the lake to the sewer system, 

resulting in no decrease of the lake level. Flooding began 

again in December 1996, lasting at least until February 1997 

(Oregonian, 1997). An aerial photograph of Holgate Lake in 

January 1997 was used to estimate the elevation of the lake 

at 195 ft (Jennifer Antak, city of Portland, written commun., 

2008).

Observations of the level of Holgate Lake by the USGS 

began in February 1999 and a water-level recorder was 

installed in March of that year (fig. 14). The recorder operated 

through 2000 and periodic water-level observations were 

made until May 2006. Except for the absence of the lake in 

2001 and 2005, the typical pattern observed during the period 

of study was emergence of the lake in early winter each year 

and a return to a dry lakebed by midsummer.

The maximum lake level observed from WY 1999 to 

2006 was 192.3 ft on March 5, 1999, corresponding to a depth 

of about 9 ft at the deepest part of the lake. The lake again 

extended over the street on its south side. The surface area 

of the lake was 1.2 acres on April 13, 1999 when the lake 

level was 190.3 ft (about 2 ft lower than the maximum level 

observed the previous month). The lake perimeter was defined 

using a Global Positioning System (GPS), and then mapping 

software was used to calculate the area. At the time of 

maximum level on March 5, 1999, the lake area was estimated 

to be about 3 acres. 

Groundwater level monitoring near Holgate Lake began 

in July 1998 (fig. 14). The primary observation well (map 

number 9) is about 0.2 mi southeast of the lake (table 1). A 

recorder (with telephone telemetry) provided real-time waterlevel data. In 1999, a hand-driven piezometer (map number 

11) was temporarily placed in the lake bed to monitor the 

water level beneath the lake (fig. 14). In April 2000, a well 

was drilled on the western side of the lake (map number 10), 

replacing the piezometer, which was inaccessible much of 

each year.
Groundwater Hydrology 33

Figure 14.

Water level elevation (1999–2006) of Holgate Lake at Portland, Oregon, in the well near 133rd Avenue and Raymond Street, in the well in the bed of Holgate 

Lake, in the well adjacent to Holgate Lake, and cumulative precipitation (from October to September each year) at Portland Airport, Oregon.

tac09_9711_0344_JohnsonCrk_fig14

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

195190185180175

7550250

ELEVATION, IN FEET ABOVE NGVD 1929

CUMULATIVE PRECIPITATION, IN INCHES

Holgate Lake (map number 43)Well near 133rd Avenue and Raymond Street (map number 9)  Daily meanWell in the bed of Holgate Lake (map number 11)Well adjacent to Holgate Lake (map number 10)Holgate Lake bed, approximatelyCumulatiive daily precipitation at Portland Airport

 Map number refers to table 1
34 Hydrology of the Johnson Creek Basin, Oregon

The fluctuation of water level in the primary observation 

well closely matches that of Holgate Lake (fig. 14). The lake 

level and the groundwater level in the wells in and on the 

western side of the lake agree closely. When water levels 

rise each winter, the lake level and groundwater level are 

similar. When groundwater and lake levels decline in spring 

and summer, the lake level declines more rapidly than the 

level in the primary observation well. By early winter, prior 

to the beginning of the recharge period, the groundwater level 

beneath the lakebed can be as much as 2 ft lower than at the 

primary observation well. 

Use of Hydrologic Data to Anticipate Flooding from 

Holgate Lake

 Observations dating back to 1949 indicated that the 

cause of flooding of Holgate Lake was closely related to the 

water level in the shallow aquifer near the lake. This study 

confirms this hypothesis by comparison of lake level to 

water levels in nearby wells. The maximum level of Holgate 

Lake corresponds closely to the maximum groundwater 

level in the observation well (map number 9) nearby, and the 

groundwater level generally follows trends in cumulative 

precipitation each year (fig. 14). The primary observation well, 

equipped with telemetry, provides the water-table elevation 

to the public through the world-wide web at http://waterdata.

usgs.gov/nwis/dv/?site_no=452912122312801&agency_

cd=USGS&referred_module=sw. The groundwater data from 

this well and precipitation data can be used in a general way 

to anticipate the emergence of the lake and the potential for 

flooding. Heavy precipitation, particularly in the autumn and 

early winter, leads to a rapid rise in groundwater levels, which 

in turn leads to emergence of Holgate Lake. Precipitation 

after about March and into the summer has less effect than 

early season precipitation, probably because of the increased 

evaporation, uptake by vegetation, and soil-moisture storage. 

For example, in WY 2001 and 2005, less than 20 in. of 

precipitation fell between October and March, resulting in no 

emergence of Holgate Lake. In 2005, substantial precipitation 

came later in the spring and summer, totaling about 30 in. 

for the water year; however, losses, probably because of 

evapotranspiration and soil-moisture uptake, reduced recharge 

to the shallow aquifer and resulted in no emergence of the 

lake.

The water level of Holgate Lake corresponds to 

precipitation amounts and timing, when, after satisfying a soilmoisture storage threshold, groundwater level rises several 

feet for each foot of precipitation (figs. 14 and 15). The annual 

groundwater level rise from WY 1999 to 2006 ranged from 

1.8 ft (2001) to 9.6 ft (2003). Although the net rise observed 

in 2003 (but no flooding) was greater than observed in 1999 

(and flooding present), the antecedent groundwater level 

prior to the autumn rainy period was 4.6 ft higher in 1999 

than in 2003. The higher antecedent groundwater level and 

higher precipitation in 1999 than in 2003 contributed to the 

1999 flooding. Although no lake-level measurements were 

made at the beginning of WY 1999, the groundwater level 

at the site of the lake likely was near the lakebed, based on 

the assumption of relatively high groundwater levels in the 

area in the years following the high precipitation of 1996 and 

0

1

2

3

4

5

6

7

8

9

10

11

12

Relation: annual rise = (precipitation * 0.392) – 4.18

 n = 8, R 2 = 0.63

WATER LEVEL RISE IN WELL NEAR 133RD AVENUE AND 

RAYMOND STREET (MAP NUMBER 9), IN FEET

PRECIPITATION AT PORTLAND AIRPORT (SITE NUMBER 356751), IN INCHES

2001

2005

2000

2004 2006

2002

2003

1999

15 20 25 30 35 40

Figure 15. Relation between annual rise in water level in a well near 133rd Avenue and Raymond Street, Portland, Oregon, 

and cumulative precipitation at the Portland Airport, Oregon, from October 1 of each year to date of maximum water level in 

well, water years 1999–2006.
Surface-Water Hydrology 35

1997. As indicated by the scatter of data points in figure 15, 

the response of groundwater level to precipitation is not 

predictable with certainty. The uncertainty may be a result 

of other factors not easily measured, including antecedent 

soil moisture, variations in porosity of the unsaturated zone 

at different depths, evapotranspiration, air temperature, 

precipitation timing and intensity, and basin-scale groundwater 

flow. Despite these uncertainties, the relation of water-level 

rise to precipitation may be useful to local residents and 

municipal agencies to assess flooding risks in the Holgate 

Lake area.

Surface-Water Hydrology

The following section is a discussion of the surface-water 

hydrology of the Johnson Creek basin as it relates to trends 

in annual flow, low flow, and high flow. Analyses of trends 

include comparisons of streamflow data on Johnson Creek 

and data from a streamflow measurement site in a nearby, 

undeveloped basin to ascertain the effects of development 

on streamflow. The Little Sandy River (map number 45) is 

not affected by regulation, and the long period of continuous 

streamflow record allows long-term comparison of the period 

of record of Johnson Creek at Sycamore (map number 30), 

where streamflow data collection began in 1940. The two 

basins additionally are similar in size, shape, and orientation 

and are only about 20 mi apart. Land cover in the Little Sandy 

River basin primarily is forest, and periodic logging over the 

past century or more. However, hydrologic change because 

of land use and other human intervention generally has been 

less in the Little Sandy River basin than in the Johnson Creek 

basin. 

Differences in both low and high flows are discussed in 

the sections below. The key differences are likely because of 

differences in elevation and precipitation. The elevation of 

the Little Sandy River basin is from about 700 to 4,300 ft, 

compared to 50 to 1,100 ft in the Johnson Creek basin. These 

differences result in lower temperature, more snow, and a 

more attenuated summer flow recession in the Little Sandy 

River compared to Johnson Creek. Average precipitation in the 

Little Sandy basin is 106 in./yr compared to 59 in./yr for the 

Johnson Creek basin at the Sycamore site, based on PRISM 

data from 1971 to 2000 (PRISM Group, 2007). In all, these 

differences result in more than triple the flow per unit area of 

the Little Sandy River compared to Johnson Creek.

Annual Flow

The factors controlling streamflow of Johnson Creek on 

an annual time scale are the distribution of precipitation and 

groundwater discharge and routing of runoff from the natural 

and human-modified landscape. More rain falls in the southern 

and eastern areas of the basin, coincident with increases in 

elevation. Precipitation, once on the landscape, can follow 

several pathways, where it can be delivered rapidly to the 

stream, or where it may enter the groundwater flow system 

as recharge and eventually discharge to the stream or out of 

the basin. Alterations in the form of roads, ditches, drywells, 

municipal sewer systems, and agriculture have an effect on the 

distribution of runoff; however, many of these changes may 

have predated collection of streamflow data in the Johnson 

Creek basin.

Spatial Trends

Spatial trends in annual flow were analyzed using 

streamflow and precipitation data from WY 1999 to 2006. 

The streamflow data used in this analysis are from Johnson 

Creek at Gresham (map number 26), Sycamore (in Portland) 

(map number 30), and Milwaukie (map number 41), and 

from measured flows of Crystal Springs Creek (map number 

40). Comparisons were made of the flow at each site, of 

the inferred inflow between sites, and of flows compared 

to precipitation. Streamflow per unit area is greatest in the 

eastern area of the basin upstream of the Gresham site. This 

pattern of runoff is a result of three factors: (1) precipitation 

is greater in the upland areas because of the topography; 

(2) the less permeable, fine-grained soils and the relatively 

steep topography of the upland areas favor rapid runoff to the 

stream; (3) part of precipitation enters the combined sewer 

system in the western, more urban areas of the basin. Although 

Johnson Creek downstream of the Gresham site receives 

less runoff than would be expected in per unit area, focused 

groundwater discharge in some areas yields relatively high 

base flow. This high base flow is evident in Crystal Springs 

Creek, which features large flows compared to its relatively 

small surface-water contributing area.

Although spatial comparison of streamflow in per-unitarea generally is useful, this measurement poses challenges 

because of the coupled nature of the groundwater and 

surface-water flow systems, and human causes. Streamflow 

at a given location on Johnson Creek is the result of surface 

runoff and the net discharge from the groundwater flow 

system. The surface-water contributing area is a relatively 

static feature based on the topography. In an urban setting, 

the flow divides defining the contributing area can be altered 

by the configuration of street drains and other development. 

The groundwater contributing area, although it loosely 

mimics the topography, also is affected by groundwater flow 

direction (which varies with depth), and the hydraulic head 

in aquifers. Human-caused alterations additionally are in the 

“plumbing” of the drainage basin, such as expedited delivery 

of precipitation to the stream in agricultural areas by tile drains 

(reducing potential groundwater recharge), diversion of storm 

runoff to drywells in urban areas (reducing surface runoff to 

the stream), and diversion of storm runoff to the combined 

sewer system that discharges out of the basin.
36 Hydrology of the Johnson Creek Basin, Oregon

Annual mean streamflow increased from the Gresham 

to the Sycamore to the Milwaukie sites based on streamflow 

records from WY 1999 to 2006. The average streamflow 

of Johnson Creek from Gresham to Sycamore increased 

by 54 percent (from 28.7 to 44.2 ft3/s), and an additional 

53 percent (to 67.8 ft3/s) from Sycamore to Milwaukie. About 

one-half of the increase in streamflow between the Sycamore 

and Milwaukie sites is from Crystal Springs Creek. 

The streamflow in the three areas of the Johnson Creek 

basin was represented in per-unit-area. Streamflow in the 

upper basin is represented by the Gresham site. Streamflow in 

the middle basin is represented by the difference in streamflow 

between the Gresham and Sycamore sites. The lower basin 

is represented by the difference in streamflow between 

the Sycamore and Milwaukie sites. Dividing the average 

streamflow by the drainage basin area to derive a streamflow 

per-unit-area value enables comparison of different size areas 

of the drainage basin, and expression of streamflow per unit 

area in inches enables comparison to precipitation. The upper 

basin contributes more streamflow to Johnson Creek in per 

unit area than does either the middle or lower basins. The 

average streamflow (WY 1999–2006) of the upper basin was 

25.3 in. compared to 18.5 and 12.1 in. in the middle and lower 

basin, respectively. 

Estimates were made of precipitation falling on each 

area of the Johnson Creek basin to relate precipitation 

to streamflow in the area. Precipitation was estimated 

by determining the ratio between the PRISM-derived 

precipitation at the Portland Airport and of the upper, middle, 

and lower areas of the basin (PRISM Group, 2007). These 

ratios were applied to the measured precipitation at the 

Portland Airport from WY 1999 to 2006 (Oregon Climate 

Service, 2007). Streamflow as a fraction of precipitation 

decreases from 45 percent in the upper basin to 37 and 

28 percent in the middle and lower basin, respectively. 

The differences in the delivery of precipitation to the 

stream are a result of geomorphic settings and human causes. 

The upper area of the basin consists of moderate to steep 

terrain and fine sediments. These factors favor runoff from 

the land surface. A dense network of roads, ditches, and farm 

fields generally direct runoff away from the land surface and 

toward tributaries or the mainstem Johnson Creek. Compared 

to the upper basin, the lower basin generally is lower relief. 

Stream channel development, particularly on the north side 

of the basin is minimal because of the low relief and coarsegrained permeable Missoula Flood deposits. The present 

and predevelopment landscape feature minimal stream 

channel development. This area was shaped by deposits from 

catastrophic Columbia River floods, leaving a relatively flat 

and highly permeable landscape. Maps made by the General 

Land Office between 1852 and 1855 provided detailed 

descriptions of natural-resource features, and indicated 

few streams in the northern area of the basin (University 

of Oregon, 2006). Although the lower area of the Johnson 

Creek basin primarily is a dense urban grid, runoff from 

streets, rooftops, and other impervious surfaces to the creek is 

curtailed through interception by the combined sewer system 

and drywells. The middle basin integrates features of the 

upper and lower basins, representing a mix of upper-basin and 

lower-basin characteristics, resulting in moderated streamflow 

relative to precipitation.

Temporal Trends

Temporal trends in annual flow in the Johnson Creek 

basin were identified through analysis of streamflow and 

precipitation data. The 66 years of record (WY 1941–2006) at 

the Sycamore site (map number 30) indicate long-term trends 

that are a response primarily to variation in precipitation. 

The cumulative departure from annual mean values is shown 

in fig. 16 for the periods of record of streamflow of Johnson 

Creek at Sycamore and at Milwaukie (map number 41), and 

of annual total precipitation at the Portland Airport. Annual 

mean streamflow of Johnson Creek at Sycamore, from WY 

1941 to 2006 ranged from 15.6 ft3/s (WY 1977) to 91.7 ft3/s 

(WY 1997). Decade-scale dry cycles (such as from 1956 to 

1967 and from 1984 to 1994) were accompanied by decreased 

annual mean streamflow. The relatively short period of record 

for Johnson Creek at Milwaukie tracks the end of a dry cycle 

in about WY 1994, follows the relatively wet years of WY 

1995–1999, and again includes a drying trend from WY 2000 

to 2005. 

Temporal trends were tested in streamflow of Johnson 

Creek at Sycamore as a fraction of precipitation from 

WY 1941 to 2006 using the Kendall’s tau correlation statistic. 

In this way, although precipitation varied over time, trends in 

the delivery of that precipitation to the stream on an annual 

scale were assessed. The null hypothesis is that the ratio of 

annual streamflow to precipitation is constant over time. A plot 

of the ratio of annual mean streamflow to precipitation over 

time indicated no visual trend and was substantiated by the 

Kendall tau value of -0.083 (a slight decreasing trend), and a 

p-value of 0.32, indicating that this trend was not statistically 

significant. The generally close relation of annual mean 

streamflow of Johnson Creek at Sycamore from WY 1941 to 

2006 compared to annual total precipitation indicates that little 

has changed on an annual scale in the response of streamflow 

to precipitation.

Low Flow

Analyses of low streamflow, in terms of spatial and 

temporal variability, are needed to understand the effects 

of past land-use practices and the potential effects of future 

activities. Low streamflow and warm stream temperature has 

the potential to negatively impact the beneficial uses of the 

stream by wildlife and people. 
Surface-Water Hydrology 37

Factors that control the low-flow regime of Johnson 

Creek include the general topographic and geologic setting, 

land use, groundwater flow direction and discharge, climate, 

and water use. The low flow period typically is in the late 

summer. In this report, discussion of the groundwater flow 

system preceded discussion of streamflow, and in particular, 

low flow, because groundwater is the primary source of 

streamflow during the dry summer period. An understanding 

of low flow was derived in part from analysis of seepage 

measurements and low-flow characteristics at the streamflow 

sites on Johnson Creek. This analysis adds to the previous 

discussion, including analysis of streamflow data on Johnson 

Creek since 1940, and possible human-induced changes that 

may have exacerbated low flows in some years. The data 

used for this analysis are daily mean streamflow of Johnson 

Creek and Little Sandy River, streamflow measurements, and 

precipitation. 

Spatial Trends

Low flow varies considerably across the Johnson Creek 

basin because of differences in groundwater discharge. 

Although precipitation is the initial source of streamflow, 

rainfall during the summer is minimal. The minimal rain in 

summer mostly is intercepted by the dry soils. Because of 

relatively high temperatures and active plant growth, water on 

the land surface and the vegetated canopy rapidly evaporates 

or transpires. Flow-duration curves were used in the analysis 

of spatial trends in low flow. High flows are exceeded only 

a small fraction of the time, whereas low flows are exceeded 

most of the time. Differences in the lower end of the flowduration curve indicate differences in flow characteristics 

related to the presence or absence of groundwater discharge to 

the stream.

Flow-duration analyses were based on daily mean 

streamflow from WY 1999 to 2006 at the streamflow sites in 

Gresham, Sycamore, and Milwaukie (map numbers 26, 30, 

and 41). The flow-duration curves representing the intervening 

areas were determined by subtracting the daily mean flow 

at the upstream site from that of the downstream site, which 

yielded the daily mean contribution of flow from the upper, 

middle, and lower areas of the basin. The flow associated 

with the percentage of time that was equaled or exceeded 

was divided by the size of the drainage basin area, which 

resulted in flow duration per square mile. Although the curves 

represent the range of flow duration, the focus of this analysis 

is the low-flow part (right side) of the flow-duration curve 

when a given flow is exceeded most of the time during the 

extreme low flow period.

The flow-duration curves shown in figure 17 illustrate 

the low flow characteristics in the three areas of the Johnson 

Creek basin. Notable characteristics of the low-flow end of 

the flow duration curves are the relative similarity of the 

curves for upper and middle areas of the basin and the distinct 

contrast with the curve for the lower area of the basin. The 

low-flow segment of the flow duration curves for the upper 

Figure 16. Cumulative departure from annual mean streamflow of Johnson Creek at Sycamore, Oregon, water years 

1941–2006, Johnson Creek at Milwaukie, Oregon, water years 1990–2006, and annual total precipitation at the Portland 

Airport, Oregon (site number 356751), water years 1941–2006.

tac09_9711_0344_JohnsonCrk_fig16

-40

-20

0

20

40

60

Johnson Creek at Sycamore (map number 30)

Johnson Creek at Milwaukie (map number 41)

Precipitation

 Map number refers to table 1

WATER YEAR

CUMULATIVE DEPARTURE FROM ANNUAL MEAN STREAMFLOW AND 

ANNUAL TOTAL PRECIPITATION, IN INCHES

1940 1950 1960 1970 1980 1990 2000 2010
38 Hydrology of the Johnson Creek Basin, Oregon

and middle areas of the basin are typical of streams that 

receive little groundwater discharge and that have rapidly 

decreasing streamflow during seasons of low precipitation. 

The lower basin, in contrast, features a sustained flow, 

particularly at flow duration greater than 60 percent, which 

is a result of groundwater discharge through springs in the 

lower area of the Johnson Creek basin. Although the broad, 

relatively low-relief northern area of the basin downstream 

of Sycamore contributes minimal flow, spring and seepage 

discharge to Johnson Creek downstream of RM 5.5 sustains 

summer flows. For example, at 90 percent flow duration, 

although the streamflow of the upper and middle areas of the 

basin is about 0.07 (ft3/s)/mi2, streamflow in the lower area of 

the basin is 0.4 (ft3/s)/mi2. 

Temporal Trends

Temporal treads in low flow in the Johnson Creek basin 

from WY 1941 to 2006 were determined from analysis of daily 

mean streamflow data. These analyses include comparison 

of annual 7-day and 30-day minimum streamflow each year, 

comparison of flow-duration characteristics and base-flow 

separation. Although summer and annual precipitation have 

an effect on minimum flows each year, water use may have a 

greater effect during some years. A water-use assessment was 

not part of the study, so the effect of water use was inferred 

from the absence of correlation between low flow of Johnson 

Creek and low flow of Little Sandy River. 

Annual 7-day and 30-day minimum streamflow statistics 

were computed for sites on Johnson Creek and on Little Sandy 

River. Most of the low flows of Johnson Creek extended past 

the water-year boundary (September 30 of each year), so the 

period of analysis for annual minimum flow was the low-flow 

season from May through October of each calendar year. The 

annual 7-day minimum flow of Johnson Creek at Sycamore 

(map number 30), from 1941 to 2006 ranged from about 

0.1 to 2 ft3/s, and the annual 30-day minimum flow ranged 

from about 0.2 to 3 ft3/s (fig. 18). Sustained high annual 

precipitation, characterized by the 3-year moving average 

precipitation from WY 1997 to 1999 (fig. 5) and resulting 

groundwater discharge to Johnson Creek, was the apparent 

cause of consistently elevated minimum flows during those 

years. Other years of particularly high (or low) 7-day or 

30-day minimum flows did not appear to be as closely related 

to extremes in annual precipitation.

0.01

0.02

0.05

0.1

0.2

0.5

1

2

5

10

20

30

PERCENTAGE OF TIME INDICATED STREAMFLOW WAS EQUALED OR EXCEEDED

STREAMFLOW, IN CUBIC FEET PER SECOND PER SQUARE MILE

1 2 5 10 15 20 30 40 50 60 70 80 85 90 95 98 99

Johnson Creek at Gresham (map number 26)

Map number refers to table 1

Between Johnson Creek at Gresham

and Johnson Creek at Sycamore (map number 30)

Between Johnson Creek at Sycamore and

Johnson Creek at Milwaukie (map number 41)

Figure 17. Flow duration curves of the upper area of Johnson Creek basin at Gresham, Oregon, of the middle basin 

between Johnson Creek at Gresham and Johnson Creek at Sycamore, Oregon, and of the lower basin between Johnson 

Creek at Sycamore and Johnson Creek at Milwaukie, Oregon, water years 1999–2006.
Surface-Water Hydrology 39

During the period from 1955 to 1977, the annual 7-day 

and 30-day minimum flows of Johnson Creek at Sycamore 

each year were, on average, about one-half the long-term 

mean values for annual 7-day and 30-day minimum flows. 

These sustained low flows occurred despite some large 

values of annual precipitation (1956 and 1974) and a general 

increasing trend in annual total precipitation from about 

1948 through 1956 and again from about 1969 through 1976 

(fig. 5). Annual 7-day and 30-day low flows of Little Sandy 

River (map number 45) did not indicate decreased summer 

flows during this period and actually were slightly greater 

compared to the period from 1941 to 2006. A potential cause 

for the particularly low streamflow of Johnson Creek during 

the 1955 through 1977 period is increased water use either 

from instream pumping or groundwater withdrawal that 

captured groundwater that would otherwise have discharged 

to the creek. The close relation of the 7-day and 30-day 

minimum flows shows a long-lasting decrease in summer 

Figure 18. Consecutive 7-day and 30-day average low streamflow of Johnson Creek at Sycamore, Oregon, and of Little 

Sandy River near Bull Run, Oregon.

0

1

2

3

4

0

10

20

30

40

50

Johnson Creek at Sycamore

(map number 30)

Little Sandy River near Bull Run

(map number 45)

STREAMFLOW, IN CUBIC FEET PER SECOND

1940 1950 1960 1970 1980 1990 2000 2007

1940 1950 1960 1970 1980 1990 2000 2007

7-day low

30-day low

 Map number refers to table 1

CALENDAR YEAR
40 Hydrology of the Johnson Creek Basin, Oregon

flows of Johnson Creek during this period. After 1977, the 

7-day and 30-day low flows generally increased in Johnson 

Creek indicating perhaps that the period of increased water use 

had ended.

Temporal trends in low flows also were assessed using 

flow-duration analyses. The period of record of Johnson 

Creek at Sycamore (map number 30) was divided into three 

segments of 22 years each, thus providing flow duration for 

the WY 1941–1962 (early), WY 1963–1984 (middle), and 

WY 1985–2006 (later) periods (fig. 19). The result of the flow 

duration analysis is consistent with that of annual minimum 

flows. The lower part (right side, low flow) of each duration 

curve is the focus for this analysis. Low flows, for example at 

90 percent flow duration, during the early period were greater 

than in the middle period. The cause for this difference in 

low flows is likely the extreme low flows in the summers 

of 1955–77 (representing much of the middle period) as 

identified in the annual 7-day and 30-day minimum flow 

analyses (fig. 18). The later period indicates the greatest low 

flows of the three periods analyzed. A comparison of the 

extremes represented by the middle period and later period 

flow-duration curves shows that daily mean flow 90 percent of 

the time has increased from 0.9 to 1.7 ft3/s.

The base-flow component of streamflow may be affected 

by changes in the drainage basin over time. Changes typically 

associated with urbanization may reduce base flow because 

of reduced infiltration and diversion of storm runoff into the 

sewer system. The base-flow component of streamflow for 

Johnson Creek at Sycamore for the period from 1941 to 2006 

was determined using the program PART (Rutledge, 1998). 

Base flow ranged from about 45 to 70 percent of total flow. 

A trend test using Kendall’s tau indicated a slight decreasing 

trend in percent base flow (a tau of -0.14); however, the 

p-value was 0.09, indicating that the trend was not significant 

at the 0.05 level. The test was done on Little Sandy River for 

the same time period and also indicated no trend. 

Trends identified in the low flow of Johnson Creek may 

relate to water use but are not necessarily associated with landuse changes characteristic of urbanization. The cumulative 

impact of urban development upstream from the Sycamore 

site from 1941 to 2006 has not affected the magnitude of low 

flows based on the overall absence of trend observed in the 

7-day and 30-day low flow from 1941 to 2006, and the baseflow component of streamflow. This does not mean that the 

present low-flow condition is the same as prior to development 

in the basin, because much of the infrastructure was already 

in place prior to the beginning of streamflow data collection. 

These data do indicate, however, that changes in land use may 

have had less effect on low flow than water use, which may 

have had an increase around 1955 and subsequently decreased 

around 1977. As land uses change, primarily from agricultural 

and natural areas to a dense urban grid, particularly in upland 

areas, continued streamflow data collection and analyses are 

needed to document hydrologic response in the low-flow 

regime of Johnson Creek. 

Figure 19. Flow duration curves based on water years 1941–1962 (early), water years 1963–1984 (middle), and water years 

1985–2006 (later), Johnson Creek at Sycamore, Oregon.

1

2

5

PERCENTAGE OF TIME INDICATED STREAMFLOW WAS EQUALED OR EXCEEDED

STREAMFLOW AT JOHNSON CREEK AT SYCAMORE (MAP NUMBER 30), 

IN CUBIC FEET PER SECOND

1 2 5 10 15 20 30 40 50 60 70 80 85 90 95 98 99

0.2

0.5

10

20

50

100

200

500

700

1941–62

1963–84

1985–2006
Surface-Water Hydrology 41

High Flow

Flooding of Johnson Creek likely was a concern when 

people began to inhabit areas near the creek. Prevention of 

flood damage was the primary incentive for the large-scale 

channel modification project that resulted in the present 

configuration of the lower 11 mi of the creek. Johnson Creek 

floods as a result of intense rainfall, usually over a several 

day period, and sometimes melting snow adds to the flood. In 

contrast to annual and low flow on Johnson Creek, where the 

magnitude of flow is in part controlled by the groundwater 

system, the presence of high flow mostly is a response to 

runoff from the land surface. The degree of flooding typically 

is determined by precipitation intensity and antecedent soil 

moisture. Other factors that can contribute to spatial and 

temporal variability in high flow events are temperature, 

topography, soil type, vegetation, channel configuration, the 

network of roads, ditches, storm drains, sewer systems, and 

impervious surfaces. Changes in the frequency of flooding, 

particularly related to changes in land uses in the basin 

have been a topic of discussion for decades. The record of 

streamflow of Johnson Creek at Sycamore (map number 30) 

are relatively long, dating back to WY 1941. The Johnson 

Creek streamflow record at Sycamore and the shorter-term 

records at Milwaukie (map number 41; since WY 1990) and at 

Gresham (map number 26; since WY 1999) provide data for 

comparison and assessment of temporal trends in high flow 

across the basin.

Spatial and temporal trends in high flow of Johnson 

Creek were evaluated based on annual peak flow and daily 

mean flow. Stream level during high-flow conditions is often 

of primary interest. Flow is computed at each streamflow 

site and the stream level is related to a peak streamflow 

using a stage-discharge rating. Changes as a result of scour 

and fill in the stream channel, and natural and constructed 

features in and near the stream can affect the level at a given 

streamflow. Flood-frequency statistics were computed for the 

Johnson Creek at Sycamore and at Milwaukie sites. Daily 

mean streamflows were used for flow duration analysis at the 

Gresham, Sycamore, and Milwaukie sites, and comparisons of 

the fraction of days in a year that are greater than the annual 

mean streamflow were made at the Sycamore and Milwaukie 

sites. 

Spatial Trends

Analyses of spatial trends in high flow in the Johnson 

Creek basin include comparison of peak flows and volumes, 

flood frequency, flow duration, and the fraction of daily mean 

flows that are greater than the annual mean streamflow. Better 

understanding derived from comparison of peak flows is 

compared to previous studies of the area. 

The annual peak streamflow at the Milwaukie site can 

be either greater or less than at Sycamore, contrary to what 

may be expected because of a two-fold increase in basin area 

(table 3, fig. 20). The annual peak usually is on the same 

day, and only in WY 2001 (an extremely dry year) was the 

peak of the year at each site the result of a different storm. 

The difference in annual peak streamflow varied widely. The 

annual peak streamflow at the Milwaukie site was between 

24 percent less (WY 1997) and 53 percent more (WY 2005) 

than at the Sycamore site. The average increase in peak flow 

from the Sycamore site to the Milwaukie site, based on peaks 

from WY 1990 to 2006, is 11 percent. The difference in peaks 

after WY 1997 may have increased (table 3); however, the 

record of concurrent peaks is lacking. Uncertainties in the 

stage-discharge rating at the Milwaukie site (because of the 

relatively short period of record compared to the Sycamore 

site) additionally may affect the computation of peak flow. 

The peak flow at each site is a function of the spatial and 

temporal distribution of precipitation and runoff characteristics 

of each area of the Johnson Creek basin. The timing and 

magnitude of precipitation (and subsequent runoff) in the area 

of the basin between the Sycamore and Milwaukie sites is not 

the same as for the area of the basin upstream of the Sycamore 

site because of the general east-west orientation of the basin; 

the tracking of storms, most of which is from west to east; 

and the generally greater precipitation in the areas of the 

basin at higher elevations. Depending on rainfall patterns and 

intensity, the response in flow at the Milwaukie site may be a 

single (and potentially larger) peak, an attenuated response, or 

peaks separated by several hours. Peaks at the Milwaukie site 

additionally may be attenuated by interception of precipitation 

in the relatively flat, permeable deposits on the northern side 

of the basin, and by interception by drywells and combined 

sewer systems. 

The relation of peak streamflow to stream level is 

fairly consistent at Johnson Creek at Milwaukie; however, 

the level of the Willamette River in the Portland area can 

cause backwater conditions in the lower area of Johnson 

Creek, extending an undetermined distance upstream of 

the Milwaukie site. Backwater from the Willamette River 

seems to affect Johnson Creek at the Milwaukie site when 

the level of the Willamette River exceeds about 22 ft, which 

is recorded twice after records at the Milwaukie site began 

in WY 1990. On February 8, 1996, at the time of the peak 

level at the Milwaukie site, the level of the Willamette River 

at Portland (map number 44) was about 22 ft. Although the 

flow of Johnson Creek decreased following the peak, because 

of the relatively large size of the Willamette River basin, the 

Willamette River at Portland continued to rise, peaking at 

about 27.7 ft on February 9. This rise of the Willamette River 

resulted in a rise in stream level of Johnson Creek of about 
42 Hydrology of the Johnson Creek Basin, Oregon

4 ft, despite decreasing streamflow of Johnson Creek. The 

backwater condition at the Milwaukie site lasted for several 

days resulting in the flooding of nearby properties. More 

backwater at Johnson Creek at Milwaukie was recorded in 

January 1997 when the Willamette River at Portland peaked at 

about 23 ft causing backwater at the Milwaukie site for about 

2 days.

Although peak volume increases between the Sycamore 

and Milwaukie sites, the increases are not proportional to 

the increase in the size of the drainage basin area between 

the two sites. The peak volume each year was defined as the 

cumulative daily mean streamflow during the 6-day period 

surrounding the annual peak (table 3). The 6-day period was 

selected by visual inspection of the instantaneous streamflow 

hydrograph, beginning the day of increase in flow and 

extending several days past the day of peak flow. Antecedent 

flow was not taken into account in this analysis because it was 

relatively low (compared to the peak flow) and fairly similar 

at the two sites. The average increase in annual peak volume 

between the Sycamore and Milwaukie sites from 1990 to 

2006 was 24 percent, and ranged from 7 to 40 percent. Factors 

contributing to the relatively small increase in runoff volume 

between the Sycamore and Milwaukie sites may be the 

increased infiltration through the permeable surficial deposits, 

capture of runoff from the urban area between the two sites, 

and subsequent transport of storm runoff either to drywells or 

to the combined sewer system.

Flood frequency statistics for Johnson Creek at 

Milwaukie based on annual peaks from 1990 to 2006 were 

compared to those for Johnson Creek at Sycamore for 

the same period (fig. 21, table 4). This analysis indicates 

that streamflows for recurrence intervals greater than 

about 10 years are greater at the Sycamore site than at the 

downstream site. The smaller values at the Milwaukie site 

may indicate that peak flows at the upstream site that are 

in excess of the channel capacity are temporarily stored on 

the floodplain and do not contribute to the peak flows at the 

Milwaukie site. Flood-frequency statistics for Johnson Creek 

Table 3. Annual peak streamflow and volume, Johnson Creek, Oregon, water years 1990–2006.

[Map numbers are shown in table 1. Percentage change and period of analysis: (a) not computed due to different storm event; (b) one or more daily mean 

streamflow estimated. Abbreviations: ft3/s, cubic foot per second; mi2, square mile]

Water 

year

Johnson Creek at 

Sycamore

(map number 30),

drainage basin area

26.8 mi2

Johnson Creek at 

Milwaukie

(map number 41),

drainage basin area

53.2 mi2

Percentage of change 

in annual peak 

streamflow from 

Johnson Creek at 

Sycamore to Johnson 

Creek at Milwaukie

Period of analysis for 

volume computation

Percentage of change 

in volume over annual 

peak storm event (6 

days) from Johnson 

Creek at Sycamore 

to Johnson Creek at 

Date Milwaukie

Peak 

streamflow

(ft3

/s)

Date

Peak 

streamflow

(ft3/s)

1990 01-10-90 860 01-10-90 892 4 Jan. 6–11, 1990 16

1991 02-20-91 1,130 02-20-91 1,030 -9 Feb. 20–25, 1991 7

1992 12-06-91 1,120 12-06-91 1,010 -10 Dec. 5–10, 1991 14

1993 12-10-92 825 12-10-92 799 -3 Dec. 8–13, 1992 16

1994 02-24-94 1,600 02-24-94 1,730 8 Feb. 23–28, 1994 32

1995 11-01-94 1,300 11-01-94 1,400 8 Oct. 31–Nov. 5, 1994 24

1996 02-07-96 2,350 02-08-96 2,170 -8 Feb. 5–10, 1996 19 (b)

1997 11-19-96 2,550 11-19-96 1,940 -24 Nov. 18–23, 1996 16 (b)

1998 01-14-98 854 01-14-98 1,030 21 Jan. 12–17, 1998 23 (b)

1999 12-28-98 950 12-28-98 1,140 20 Dec. 27, 1998–Jan. 01, 1999 25

2000 11-26-99 664 11-26-99 840 27 Nov. 24–29, 1999 30

2001 10-01-00 258 03-28-01 278 (a) (a) (a)

2002 01-25-02 632 01-25-02 782 24 Jan. 24–29, 2002 29

2003 01-31-03 1,820 01-31-03 1,670 -8 Jan. 29–Feb. 3, 2003 25

2004 12-13-03 1,140 12-14-03 1,530 34 Dec. 13–18, 2003 40

2005 03-27-05 447 03-27-05 682 53 Mar. 26–31, 2005 38

2006 12-30-05 1,150 12-30-05 1,540 34 Dec. 27, 2005–Jan. 1, 2006 32
Surface-Water Hydrology 43

tac09_9711_0344_JohnsonCrk_fig20

200

300

400

500

600

800

1,000

2,000

3,000

WATER YEAR

STREAMFLOW, IN CUBIC FEET PER SECOND

1940 1950 1960 1970 1980 1990 2000 2008

Johnson Creek at Sycamore (map number 30) 

 1941–62

 1963–84

 1985–2006

Johnson Creek at Milwaukie (map number 41) 

 1990–2006

 Map number refers to table 1

EXPLANATION

EARLY PERIOD MIDDLE PERIOD LATER PERIOD

Peak streamflow by water years

Figure 20. Annual peak streamflow of Johnson Creek at Sycamore, and Johnson Creek at Milwaukie, Oregon.

at the Sycamore site for the entire 1941–2006 period of record 

also are shown in figure 21 and table 4. Flood-frequency 

statistics generally are more reliable for longer periods of 

record, but the differences between the 1990–2006 period and 

the 1941–2006 period are slight for this site. 

Similar to analyses of low-flow duration statistics, the 

high-flow part of the duration curve indicates differences in 

flow-duration characteristics of the upper, middle, and lower 

areas of the basin. At a flow duration of 5 percent (where 

daily mean streamflow is equaled or exceeded 5 percent of 

the time), as shown in figure 17, the area of the drainage 

basin upstream of the Gresham site contributes 8 (ft3/s)/mi2, 

compared to 5 (ft3/s)/mi2 between the Gresham and Sycamore 

sites and 2 (ft3/s)/mi2 between the Sycamore and Milwaukie 

sites. When the contribution to high flow of the upper, middle, 

and lower areas of the basin are compared, differences 

generally are a result of decreased precipitation, gentler slopes, 

more permeable soils, and greater interception by drywells and 

combined sewer systems toward the west. 

An assessment based on daily mean streamflow at the 

Sycamore and Milwaukie sites from 1990 to 2006 was made 

of the “flashiness” of the stream, which is the tendency of 

the streamflow to rise from a base-flow condition rapidly 

and decline rapidly. The indicator statistic is the percentage 

of days in a year where the daily mean streamflow is greater 

than the mean streamflow in that year. In a basin with rapid, 

short-duration, or “flashy” runoff, a smaller percentage of days 

exceed the mean streamflow for the year when compared to 

a basin in which streamflow rises and declines more slowly. 

Konrad and Booth (2002) and Chang (2006) showed that this 

statistic was an indicator of urbanization, affecting streams 

in Washington and in the Portland, Oregon, area (including 

Johnson Creek). The consequence of rapid changes in flow 

on a stream may be degradation of the stream channel, 

erosion, and disruption of biota in the stream. The mean flow 

of Johnson Creek at the Sycamore and Milwaukie sites was 

exceeded an average of 29 percent of the time. The same 

analysis was made of Little Sandy River (map number 45), 

where the mean streamflow was exceeded an average of 

34 percent during the same period. These results are consistent 

with previous studies that showed the mean streamflow was 

exceeded a smaller fraction of the time in urban streams than 

in rural streams (Konrad and Booth, 2002). The similarity of 

this statistic at the Sycamore and Milwaukie sites primarily is 

because of the absence of storm-induced rapid runoff in the 

lower area of the basin. 
44 Hydrology of the Johnson Creek Basin, Oregon

Water 

years

Recurrence 

interval 

(years)

Annual 

exceedance 

probability 

(percent)

Peak 

streamflow 

(ft3

/s)

Johnson Creek at Sycamore (map number 30)

(systematic n = 66; historical n = 0; weighted skew = 0.448)

1941–2006 1.25 80 717

2 50 1,150

5 20 1,750

10 10 2,140

25 4 2,590

50 2 2,920

100 1 3,220

Johnson Creek at Sycamore (map number 30)

(systematic n = 17; historical n = 0, weighted skew = 0.095)

1990–2006 1.25 80 693

2 50 1,040

5 20 1,580

10 10 1,970

25 4 2,510

50 2 2,930

100 1 3,380

Johnson Creek at Milwaukie (map number 41)

(systematic n = 17; historical n = 0; weighted skew = 0.104)

1990–2006 1.25 80 840

2 50 1,140

5 20 1,570

10 10 1,860

25 4 2,240

50 2 2,530

100 1 2,820

Table 4. Magnitude and probability of peak streamflow of 

Johnson Creek, Oregon.

[Map numbers are shown in table 1. Abbreviations: ft3/s, cubic foot per 

second; n, number of years]

The relatively small change in flood-frequency of 

Johnson Creek at the Sycamore and Milwaukie sites, 

especially the decrease in flood flows for recurrence intervals 

greater than about 10 years, is not consistent with predictions 

of flood frequency from methods currently used in Oregon. 

Although the available flood prediction equations developed 

for use in Oregon (Cooper, 2005) are applicable only to rural 

streams in western Oregon and thus may not be reliable for 

urbanized basins such as the Johnson Creek basin, equations 

for use on urbanized streams in the Portland area were 

developed by Laenen (1980). Laenen’s prediction equations, 

which included data from the Sycamore site on Johnson 

Creek, used basin drainage area and a basin-storage term as 

explanatory variables. The form of the prediction equations 

indicated that flood flows for a given recurrence interval 

increase with increasing size of the drainage basin area, but 

that flood flows for a given recurrence interval decrease with 

increasing basin storage. Results from the prediction equations 

developed by Laenen (1980) are particularly sensitive to 

estimated values of basin storage and basin storage is difficult 

to determine and perhaps not directly related to factors that 

may be affecting flood runoff in the lower area of the basin, 

such as increased storm runoff interception. Based on the 

available data and definitions provided by Laenen (1980), 

basin storage at the downstream Milwaukie site was not much 

different than basin storage at the upstream Sycamore location. 

Application of the prediction equations, using equal values 

for basin storage but considerably larger drainage basin size at 

Milwaukie than at Sycamore, yielded peak-flow estimates for 

the Milwaukie site that were about twice as large as those from 

the log Pearson 3 analysis of the measured peak streamflow. 

As a result, the Laenen (1980) equations do not reliably 

account for the factors that affect flood-frequency statistics on 

Johnson Creek, although they may be reliable for prediction 

purposes on other urbanized streams in the Portland area.

Temporal Trends

Streamflow and water level at the Sycamore site (map 

number 30) were used in the analyses of temporal trends in 

high flow of Johnson Creek. High flows were characterized in 

terms of annual peaks, flow duration, and the fraction of daily 

mean flows that are greater than the annual mean streamflow.

 A Kendall’s tau test applied to the 66-year record of 

annual peak flows (fig. 20) indicated an absence of a temporal 

trend in annual peaks; the value of tau was -0.03 and the 

p-value was 0.70. Although the basin has changed much 

between 1941 and 2006, those changes have not led to a trend 

toward higher or lower peak flows.

Because a concern during flooding is the stream level 

rather than streamflow, an analysis was made of the trend in 

annual peak stream level associated with each annual peak 

streamflow at the Sycamore site from WY 1941 to 2006. The 

stage-discharge rating curve in use in WY 2006 is shown in 

figure 22; points represent the annual peak stream level and

streamflow in the early (WY 1941–62), middle (WY 1963–

84), and later (WY 1985–2006) periods. Most peaks from the 

later period plot along this curve. Many peaks in the early 

and middle periods plot to the right of the curve (greater 

streamflow for a given stream level), indicating, in general, 

that the capacity of the stream channel to carry high flow was 

greater in the early and middle periods than in the later period. 

The change in the relation of stream level to streamflow 

is from about 700 to 1,500 ft3/s, and amounts to a 1-ft 

aggradation (filling) of the stream channel. At streamflow 

less than about 700 ft3/s, the peak stream level relative to 

streamflow is more variable than at higher flow, which is a 
Surface-Water Hydrology 45

tac09_9711_0344_JohnsonCrk_fig21

500

600

800

1,000

2,000

3,000

4,000

5,000

2 5 10 25 50

RECURRENCE INTERVAL, IN YEARS

ANNUAL PEAK STREAMFLOW, IN CUBIC FEET PER SECOND

1.11 1.25 1.5 100

 Map number refers to table 1

Johnson Creek at Sycamore (map number 30)

Water years 1941–2006

 Water years 1990–2006

Johnson Creek at Milwaukie (map number 41)

Water years 1990–2006

Figure 21. Flood frequency curves based on log-Pearson Type III probability distribution, Johnson Creek at Sycamore, 

Oregon, water years 1941–2006 and 1990–2006, and Johnson Creek at Milwaukie, Oregon, water years 1990–2006.

Rating curve

 1941–62 (early period)

 1963–84 (middle period)

 1985–2006 (later period)

Johnson Creek at Sycamore (map number 30)

Annual peak stream level by water years

4

5

6

7

8

9

12

14

10

16

STREAMFLOW, IN CUBIC FEET PER SECOND

STREAM LEVEL, IN FEET

 Map number refers to table 1

200 300 400 500 600 800 1,000 2,000 3,000

Figure 22. Rating curve in use during water year 2006, and annual peak stream level and streamflow from water years 1941 

to 2006, Johnson Creek at Sycamore, Oregon.
46 Hydrology of the Johnson Creek Basin, Oregon

result of the impermanence of vegetation, large wood, and 

other objects in the stream channel. Streamflow greater than 

about 1,500 ft3/s exceeds the capacity of the trapezoidal 

channel and spills into the overbank area. At this stream level, 

the stage-discharge rating changes little over time because of 

the general consistency of the shape and slope of the terrain 

near the streamflow site. This analysis shows that the stream 

channel gradually was filled in, but relative to the range of 

stream level (about 15 ft) and the time period (66 years), 

the 1 ft of fill is small. When flows are greater than about 

2,000 ft3/s, corresponding to a recurrence interval of 10 years 

and more, the relation of stream level to streamflow has not 

changed measurably. This analysis is valid for the Sycamore 

site only. Other changes to the stream channel elsewhere in 

the basin may have altered the relation of stream level to 

streamflow.

The capacity of a stream channel can change naturally 

over time and may or may not be a result of human activity. 

Aside from the initial construction of the stream channel in 

the 1930s (prior to the beginning of streamflow record at the 

Sycamore site), the largest single change seems to be in 1968 

when much of the channel of Johnson Creek was cleared of 

brush and debris. County work crews cleared the channel in 

August of that year and extensive clearing along the creek 

was reported in an article (Johnson Creek Watershed Council, 

2006) citing memories of a once young man employed along 

with “hundreds of Portland boys for the summer” (of 1968), 

using “two-man saws, axes, brush hooks, etc. ... in an effort to 

stop the annual flooding.” The result of this clearing lasted for 

several years afterward; now the channel has refilled from an 

accumulation of vegetation and debris. 

Flow duration was used to evaluate trends in high flow 

of Johnson Creek and indicated little change from WY 1941 

to 2006 in the percentage of time a given daily mean flow was 

exceeded. The period of daily flow record was divided into 

three equal-length periods: WY 1941–62 (early), WY 1963–84 

(middle), and WY 1985–2006 (later) (fig. 19). Flow at a flow 

duration of 5 percent differed by less than 20 percent between 

the early, middle, and later periods. 

The measure of “flashiness” of the stream was assessed 

over time by comparing the percentage of days in a given 

year that the daily mean streamflow was greater than the 

annual mean streamflow for that year. The period of record 

at the Sycamore site was again divided into the same early, 

middle, and later periods defined previously. The annual 

mean streamflow in the early and later periods was exceeded 

29 percent of the time, but the annual mean streamflow in the 

middle period was exceeded 26 percent of the time. Temporal 

trends in “flashiness” were assessed using Kendall’s tau

correlation coefficient. For the period from WY 1941 to 2006, 

the Kendall tau value was 0.04; however, the trend was not 

statistically significant as the p-value was 0.65.

The assessment of “flashiness” of Johnson Creek 

used daily mean (in contrast to instantaneous) streamflow. 

Comparison of the rate of rise and decline during storms using 

instantaneous streamflow may produce inaccurate results 

because of changes in stream-level monitoring instruments 

at Johnson Creek at Sycamore. From 1940 to 1997, the 

stream-level sensor consisted of a stilling well with a floatdriven recorder (Rantz and others, 1982, p. 50). Because the 

stream-level recorder was inundated during high flows many 

times and the pipe (actually an 8-in. handmade stone culvert) 

that relayed the stream level to the stilling well occasionally 

clogged with silt, the hydrograph recorded a delayed response 

on the rising and falling limb of the hydrograph. The condition 

of the pipe could only be detected during periodic visits, so 

many delayed responses may have gone unnoticed. As a result, 

although the daily mean and peak streamflow may be accurate, 

the rate of rise and decline of the stream level may not be. In 

December 1997, the stilling well was replaced with a pressure 

sensor (Rantz and others, 1982, p. 52) that was much less 

subject to fouling and tracked the fluctuations in stream level 

more accurately. Comparison of the potentially erroneous 

delayed-response hydrograph from earlier times to a later 

response may lead to an incorrect conclusion about the rate of 

rise of the stream.
Implications for Water Quality 47

Implications for Water Quality

Although the objective of this report is to describe the 

physical hydrology of the Johnson Creek basin in terms of 

how water moves in space and time, findings also relate to 

water quality. Stream temperature responds to air temperature 

and to groundwater discharge to the stream. These results will 

help watershed managers design and assess the effectiveness 

of measures to reduce summer stream temperature. A previous 

study indicated a positive relation of organochlorine pesticides 

to suspended sediment in the stream (Tanner and Lee, 2004). 

Although this study did not involve collection of sediment 

or contaminant data, analyses provide insight into high flows 

that typically entrain sediment (and potentially contaminants) 

in Johnson Creek. An understanding of controlling factors 

of stream temperature during low flow and runoff response 

during high flow may help in the decisions made to maintain 

and improve water quality in the basin. 

Stream Temperature

Fluctuations in the temperature of Johnson Creek and 

tributaries are a result of human and natural causes. Low 

summer stream temperature supports more native fish life, 

whereas warm temperatures may be harmful to many aquatic 

organisms, raising concern regarding survival of native 

fish and other wildlife. A return to a stream temperature 

regime closer to the predevelopment condition would likely 

encourage a more native aquatic species composition. 

The effects of human modification in a stream basin 

generally cause increases in stream temperature compared 

to a predevelopment condition. Soil compaction decreases 

infiltration, which decreases groundwater discharge to the 

creek. Urban development may direct runoff to a combined 

sewer system, which also decreases groundwater discharge. 

Removal of vegetative cover and installation of ponds 

increases direct sunlight to the stream. Water withdrawals 

for irrigation decrease stream velocity and depth, increasing 

warming from the atmosphere. 

The Total Maximum Daily Load (TMDL) allocation 

for temperature of Johnson Creek was set in 2006; it 

provided goals for reduction of summer stream temperature 

by increasing nearstream shading (Oregon Department 

of Environmental Quality, 2006). Because of the large 

geographic scale of the TMDL and lack of information 

on groundwater discharge to Johnson Creek, the effect of 

groundwater discharge on stream temperature was not fully 

explored. This study reports summer stream temperature 

decreases in areas of groundwater discharge to the stream and 

increases in open-water areas.

Groundwater inflow to Johnson Creek was identified by 

seepage measurements (fig. 4). A similar stream temperature 

is shown in figure 7 between RM 7.8 and 5.5, where little 

groundwater enters the stream. In contrast, groundwater 

discharge between RM 5.5 and 3.2 contributed to a decrease in 

the temperature of Johnson Creek of about 2–3°C.

Stream temperature can increase in ponded and openwater areas. Although the flow of Crystal Springs Creek 

originates as cool groundwater discharge, this stream warms 

because of exposure to relatively large and shallow open-water 

areas. Summer warming between the site at Bybee Boulevard 

(map number 39) and the site at the mouth of Crystal Springs 

Creek (map number 40) is a result of the configuration of 

the stream channel in Westmoreland Park where the stream 

flows through a shallow pond. The 7-day moving average 

of the daily maximum stream temperature in 2005 is shown 

in figure 23. Warming of Crystal Springs Creek between the 

Bybee site and the site at the mouth of the creek is about 2°C. 

The thermal effect of tributary inflows to Johnson Creek 

depends largely on the relative volume of flow. Although 

summer temperature of Kelley Creek (map number 29) is 

low compared to Johnson Creek (fig. 23), streamflow also 

is low compared to Johnson Creek. Kelley Creek, entering 

Johnson Creek between the Gresham (map number 26) and 

Sycamore (map number 30) sites, probably has little effect 

on stream temperature at the Sycamore site. In contrast, 

Crystal Springs Creek contributes most of summer streamflow 

of Johnson Creek at Milwaukie (map number 41) (fig. 4). 

Summer temperature of Crystal Springs Creek at the mouth 

(map number 40) usually exceed that of Johnson Creek 

at Milwaukie (fig. 23). Much of the 1–2°C increase in the 

temperature of Johnson Creek between the Sycamore and 

Milwaukie sites is attributed to inflow from Crystal Springs 

Creek. 

Summer temperature of Johnson Creek is largely 

controlled by air temperature. Comparison of stream 

temperature to air temperature during the warm-weather 

period (from May to October) of each year provides a 

reliable relation. A regression relation was developed for 

each year. The 7-day moving average of the average of the 

daily maximum and minimum air temperature at the Portland 

Airport (Oregon Climate Service, 2007) was compared to 

the 7-day average of the maximum stream temperature at 

the Gresham and Milwaukie sites. This relation was fairly 

consistent within each year at each site. The period of record 

at the Gresham site was from 1999 to 2006, and the average r2

value for each year was 0.89. The record at the Milwaukie site 

began in 1998, and the average r2 value was 0.90.
48 Hydrology of the Johnson Creek Basin, Oregon

Figure 23. Temperature of streams in the Johnson Creek basin, Oregon, May to October 2005.

2005

MAY JUNE JULY AUGUST SEPTEMBER OCTOBER

30

28262422201816141210

7-DAY AVERAGE OF DAILY MAXIMUM STREAM TEMPERATURE, IN DEGREES CELSIUS

Johnson Creek at Gresham (map number 26)Kelley Creek (map number 29)Johnson Creek at Sycamore (map number 30)Crystal Springs Creek at Bybee Boulevard (map number 39)Crystal Springs Creek at mouth (map number 40)Johnson Creek at Milwaukie (map number 41)

 Map number refers to table 1
Implications for Water Quality 49

Although the relation of air temperature to stream 

temperature was fairly consistent from year to year at the 

Gresham site, the relation at the Milwaukie site was more 

variable. Estimated stream temperatures resulting from an 

average air temperature of 22°C are shown in figure 24. At 

the Gresham site, the predicted stream temperature at that air 

temperature varied by less than 1°C from 1999 to 2006. At 

the Milwaukie site, a shift from the 1998 to 1999 period to 

the 2000–2006 period indicated warmer stream temperature 

for a given air temperature. The shift is attributed to the large 

decrease in groundwater discharge and subsequent reduction 

in flow of Crystal Springs Creek. The streamflow of Crystal 

Springs Creek in 1998 and 1999 was about 17 ft3/s (fig. 2). 

Streamflow of Crystal Springs Creek ranged from about 10 

to 14 ft3/s from 2000 to 2006. This decrease in streamflow 

resulted in decreased stream velocity, and overall, greater 

warming in open-water areas of Crystal Springs Creek, 

resulting in warming of Johnson Creek at the Milwaukie 

site for a given air temperature. The summer temperature 

of Johnson Creek at the Milwaukie site at an average air 

temperature of 22°C increased by about 1.5°C in the 2000–

2006 period compared to the 1998–99 period.

The thermal effect of groundwater discharge and openwater areas on stream temperature may provide insight into 

meeting stream-temperature standards, informing landuse decisions, and focusing restoration efforts. Land-use 

decisions that foster increased infiltration (and subsequent 

groundwater discharge), limit instream withdrawals, and 

increase nearstream shading may improve the summer 

temperature regime in Johnson Creek. Restoration efforts 

focused on elimination of instream ponds and increases 

in tree canopy particularly in areas of highest summer 

flows may lead to decreased summer stream temperature. 

Continued monitoring of groundwater levels, of streamflow, 

of temperature, and tracking the many restoration activities 

underway in the Johnson Creek basin may provide insight 

into the effectiveness of measures taken to achieve stream 

temperature goals.

Sediment and Other Contaminants

The area of the Johnson Creek basin upstream of the 

Sycamore site contributes more streamflow per-unit-area than 

the area below this site, where peak flow and volume was 

large relative to peak streamflow and volume as measured 

at the Milwaukie site, considering the increase in drainage 

basin size. Sediment can be a water-quality concern causing 

problems for fish and other wildlife. Tanner and Lee (2004) 

showed a relation between organochlorine pesticides and 

suspended sediment in Johnson Creek. A higher concentration 

of pesticides per unit of sediment was measured in the 

area of the basin upstream of the Palmblad Road site (map 

number 25) compared to the area of the basin upstream of the 

Sycamore (map number 30) and Milwaukie (map number 41) 

sites. These results show the importance of managing runoff 

and minimizing entrainment of sediment in Johnson Creek, 

particularly in the upper basin.

Land-use activities are part of development in 

urban, agricultural, and previously undisturbed settings 

in the Johnson Creek basin. Understanding the transfer of 

precipitation on the landscape to streamflow, and the sources 

and fate of sediment and other contaminants in the basin will 

aid jurisdictions in making land-use decisions for protection of 

water quality.

19

20

21

22

23

24

1998 1999 2000 2001 2002 2003 2004 2005 2006 1998 1999 2000 2001 2002 2003 2004 2005 2006

JOHNSON CREEK AT GRESHAM, OREGON (MAP NUMBER 26) JOHNSON CREEK AT MILWAUKIE, OREGON (MAP NUMBER 41)

ESTIMATED STREAM TEMPERATURE RESULTING 

FROM AVERAGE OF DAILY MAXIMUM AND MINIMUM 

AIR TEMPERATURE OF 22 DEGREES CELSIUS

CALENDAR YEAR CALENDAR YEAR

Figure 24. Estimated temperature of Johnson Creek at Gresham, Oregon, and Johnson Creek at Milwaukie, Oregon, based 

on air temperature at the Portland Airport, Oregon (site number 356751), 1998–2006. Map numbers refer to table 1.
50 Hydrology of the Johnson Creek Basin, Oregon

Potential Future Studies

This study provides a basis for potential future 

investigation to enhance our knowledge of the Johnson Creek 

basin hydrologic system and of the possible effects of land-use 

changes in the basin. For example, further studies to examine 

the groundwater flow system could provide information about 

contributing areas and an insight into the relation between 

springs and streams within the Johnson Creek basin and 

throughout the Portland metropolitan area. The installation of 

a broader network of monitoring wells and development of 

a fine grid flow model are two efforts that would be of use in 

gaining a better understanding of the area. Installation of more 

wells distributed throughout the basin and adjacent areas, 

with data collection on a decade time-scale would provide the 

data necessary for increased understanding of groundwater 

flow and of groundwater interaction with Johnson Creek and 

tributary streams. And the fine-grid flow model could provide 

a finer discretization than was previously possible with the 

coarse-grid regional model made in the 1990s (Morgan and 

McFarland, 1996).

Identification of groundwater contributing areas of 

features such as Crystal Springs Creek and Holgate Lake 

would allow for better determination of causes for variations 

in streamflow and water levels and provide for greater 

opportunities for resource protection. Specific to Crystal 

Springs Creek, further investigation into trends in water levels 

in wells could lead to better understanding of fluctuations 

in streamflow. Better understanding of the connection of the 

aquifer in the Westmoreland Park area to Crystal Springs 

Creek, Johnson Creek, and the Willamette River, could 

provide insight into water-level fluctuations in this area. A 

more detailed analysis of water levels, streamflow, and an 

elevation survey of the key components in the Westmoreland 

Park area, including springs, wells, and the creek, also would 

contribute to an understanding of water level fluctuations.

The groundwater flow system in the volcanic buttes 

on the southern side of the Johnson Creek basin is not well 

understood. Dense urban development of this area could lead 

to negative effects on the hydrology of this area of the basin. 

Refinements in knowledge of the groundwater flow system 

and understanding of water uses in the basin could provide 

guidance to managers on the effects of present and future 

water withdrawals, and on the effects of land-use changes on 

base flows of the creeks in this area of the basin.

In the surface-water realm, future study could provide 

understanding of runoff characteristics of upland areas, 

particularly on the southern side of the basin, and especially 

relative to future urban expansion. Analysis of the impact of 

“green” development, where stormwater is infiltrated onsite, 

could be compared in a paired-basin study to assess the 

effectiveness of these measures on flood frequency. From a 

historical perspective, analyses could be made of the impact of 

past land-use practices, such as stormwater-disposal methods, 

on stream response.

Numerous nearstream restoration projects have been 

completed in the Johnson Creek basin, and more are planned 

in the coming decades. Several projects involve returning 

the constructed trapezoidal stream channel to a more natural 

configuration. The effect of these projects on moderation of 

high flows and augmentation of groundwater recharge through 

use of overbank and backwater areas has not been determined. 

Continued flow monitoring could yield understanding of 

possible changes in peak streamflow and peak volume. 

Additional time-of-travel (dye-tracer) studies could provide 

insight into the effectiveness of the restored features in terms 

of the timing and dispersive characteristics of the stream.

High stream temperature and sediment (and sedimenttransported contaminants) are problems for water quality 

in the Johnson Creek basin. Future studies could provide 

understanding of the effect of measures to reduce thermal 

loading, such as revegetation, removal of instream ponds, 

and securing instream water rights. Channel-modification 

measures underway in 2008 may have an effect on 

the transport and deposition of sediment in the basin. 

Understanding of the effect of these changes on sediment 

transport processes may help guide future restoration work in 

the Johnson Creek basin.

Summary 

Hydrologic responses to greater than average 

precipitation in the Johnson Creek basin in water years 

(WY) 1996-1997 resulted in the flooding of Johnson Creek, 

elevated groundwater levels, and, over the following several 

years, increased groundwater discharge to springs. Although 

the precipitation during distinct storm events resulted in a 

rise and fall of streamflow on the scale of hours to days, the 

back-to-back high annual precipitation in WY 1996-1997 

led to a response of the groundwater system that lasted for 

months to years. This study was prompted by inquiry into the 

causes of floods from increased spring discharge and from an 

elevated water table, and by a need to better understand spatial 

and temporal trends in annual, low, and high streamflow 

of Johnson Creek. The U.S. Geological Survey began the 

cooperative study in 1997 with the city of Portland. In 2000 

the cities of Gresham and Milwaukie and Clackamas County 

Water Environment Services joined the cooperative study, 

followed in 2002 by Multnomah County.
Summary 51

New information was collected for this study, and was 

analyzed in context with previous studies as well as longterm hydrologic data. New data consisted of a network of 

groundwater level measurements (including continuous 

water-level records), numerous streamflow measurements, and 

continuous records of streamflow and stream temperature. 

The average annual total precipitation from WY 1911 to 

2006 was about 37 in./yr. Precipitation WY 1996 was 54.7 in., 

followed by a record 58.7 in. in WY 1997. The 3-year moving 

average annual precipitation in WY 1997, WY 1998, and WY 

1999 was the greatest since recordkeeping began. The large 

inflow (recharge) led to a large outflow (discharge) from the 

groundwater system to surrounding streams.

 Results from water-table mapping and from a regional 

groundwater flow model of the Portland basin from previous 

USGS studies indicate that groundwater and surface-water 

flow divides are not necessarily coincident for the Johnson 

Creek basin, implying that in some areas of the Johnson Creek 

basin water that recharges the groundwater system flows out 

of the basin and discharges to major rivers such as the Sandy, 

Columbia, or Willamette Rivers. The greater relative discharge 

observed in the lower reaches of the Johnson Creek basin 

compared to the upper and middle reaches may be caused by 

groundwater flow out of the basin in the upper and middle 

reaches resulting in relatively low base flows in Johnson 

Creek compared to what might be expected from precipitation 

amounts in the basin.

Groundwater levels in wells open to the surficial aquifer 

in the Johnson Creek basin fluctuate generally in a sinusoidal 

annual pattern in which water levels rise in response to autumn 

and winter rains and decline during the relatively dry and 

warm spring and summer seasons. Toward the west, waterlevel fluctuations are damped in magnitude and delayed in 

time relative to precipitation. In the western area of the basin, 

water levels in the Westmoreland Park area wells, which are 

open to a former alluvial channel of either the Clackamas or 

Willamette Rivers, or both, respond quickly to precipitation 

and to the levels of the Willamette River and Johnson Creek. 

Flooding of Crystal Springs Creek, first recorded in 1997, 

was caused by elevated groundwater levels and associated 

increase in groundwater discharge to the springs and the 

creek. Comparisons made between streamflow of Johnson 

Creek at Milwaukie and streamflow of Crystal Springs Creek 

indicated that the high flows of Crystal Springs Creek began 

in 1996. Comparison of streamflow and precipitation (annual 

and 3-year moving average) indicated that the relatively high 

flows of Crystal Springs Creek from 1996 to 1999 probably 

had not occurred since the channel modifications were made in 

1936 during construction of Westmoreland Park, and possibly 

not since precipitation records began in 1911. A relation was 

developed between the groundwater level in a well near the 

springs and streamflow of Crystal Springs Creek in the Reed 

College area and at the mouth of the creek, enabling prediction 

of high and low streamflow of Crystal Springs Creek based on 

groundwater level.’

The appearance of Holgate Lake and occasional flooding 

in the surrounding area was the result of the shallow water 

table. Flooding was related to high precipitation years. 

Groundwater monitoring that began in 1998 and lake-level 

monitoring that began in 1999 indicated that the lake levels 

were similar in height to groundwater levels in a nearby well 

and followed the same pattern of rise and fall. A relation was 

developed providing some capability to anticipate flooding 

from Holgate Lake based on early season (autumn to winter) 

precipitation and antecedent groundwater levels. 

Annual, low, and high streamflows were analyzed 

spatially and temporally using daily mean and annual peak 

flows of Johnson Creek, and where applicable, of a nearby 

basin. On an annual basis, streamflow varies across the 

basin according to several factors. Precipitation is greater 

in the higher elevation area of the basin. Depending on the 

direction of groundwater flow and variations in groundwater 

flow direction at depth, recharge within the surface-water 

contributing area of the Johnson Creek basin may discharge 

to Johnson Creek or may discharge to rivers outside of the 

basin. Some runoff is intercepted by the combined sewer 

system and is routed out of the basin. Runoff per unit area 

was greatest in the upper basin, where the average (from WY 

1999 to 2006) was 25.3 in., compared to 18.5 and 12.1 in. in 

the middle and lower basin, respectively. Similarly, runoff as 

a fraction of precipitation also decreased, where 45, 37, and 

28 percent of precipitation resulted in runoff from the upper, 

middle, and lower areas of the basin, respectively. About half 

of the increase in annual mean streamflow from the middle to 

the lower area of the basin during this period was from Crystal 

Springs Creek. 

Low flows varied from year to year, primarily caused 

by fluctuations in groundwater discharge to Johnson 

Creek, although low flows were apparently affected by 

an unidentified water use between 1955 and 1977 as well. 

Seepage measurements indicated minimal gains in streamflow 

upstream of RM 5.5 and increased gains toward the mouth 

of Johnson Creek. Streamflow records indicated minimal 

increases in low flow between the Gresham and Sycamore 

sites from 1998 to 2006. Most of the increase in low flows 

between the Sycamore and Milwaukie sites is attributable 

to Crystal Springs Creek. Low flows may be exacerbated by 

minimal groundwater discharge to the stream in the upper and 

middle areas of the basin, where Johnson Creek captures little 

groundwater flow. In these areas, groundwater flow leaving 

the drainage basin is inferred from water-table mapping and 

previous modeling results. A comparison of low flows of 

Johnson Creek at Sycamore from 1941 to 2006 to low flows of 

the Little Sandy River indicated that water withdrawals from 

Johnson Creek during the low-flow period from 1955 to 1977 

may have been the cause of a 50 percent decrease in summer 

flows during this period.

High flows result from runoff from the land surface and 

depend on precipitation volume and intensity. Although the 

magnitude of high flows masks groundwater discharge to the 

stream during rainy periods, interception by the combined 
52 Hydrology of the Johnson Creek Basin, Oregon

sewer system, UIC systems, and a permeable landscape 

moderates high flows in the lower area of the Johnson Creek 

basin. The difference in high flow of Johnson Creek at the 

Sycamore and Milwaukie sites, in terms of the magnitude 

of peak streamflow and volume of storm runoff, is relatively 

small considering the increase in drainage basin size.

Temporal trends in flow typically associated with 

increasing urban development generally were absent 

in Johnson Creek. Annual flow as a fraction of annual 

precipitation, low flow (with the exception of unusually 

low flows from 1955 to 1977), annual peak flows, and the 

percentage of days in a given year when the daily mean 

streamflow is greater than the annual mean streamflow, 

exhibited no trend from 1941 to 2006. The absence of 

a temporal trend does not mean that the hydrology of 

the Johnson Creek basin has been unaffected by human 

occupation because much of the agricultural, residential, 

and urban development including the extensive channelmodification of the lower 11 mi of Johnson Creek predated 

data collection in the basin. Because of the management of 

stormwater in urban areas, most urbanization additionally was 

not associated with simple piping of stormwater to the creek. 

Drywells and other UIC systems have been in use for decades, 

taking advantage of the infiltration capacity of permeable 

subsurface deposits in the urban areas. Continued development 

of innovative onsite methods of stormwater disposal, 

particularly in upland areas, may lead to decreased peak flows 

and enhanced recharge to the groundwater system.

Summer temperature of streams in the Johnson Creek 

basin is affected by the cooling effects of groundwater 

discharge and by warming from ponded and open-water 

areas. Although the source of water for Crystal Springs Creek 

is spring flow, warming due to instream constructed ponds 

results in a temperature in Crystal Springs Creek which is 

greater than that in Johnson Creek. Because Crystal Springs 

Creek accounts for most of the flow in Johnson Creek 

downstream from its confluence, it warms Johnson Creek 

during summertime. 

High flow of Johnson Creek may entrain sediment and 

sediment-borne contaminants. Several factors indicate that 

sediment yield of the basin may be sensitive to conditions in 

the upper area of the basin. These factors include generally 

higher precipitation, greater slopes, a dense network of roads 

and ditches associated with agricultural and rural residential 

land uses, and a relative abundance of sources of sediment and 

sediment-borne contaminants compared to the relatively low 

relief, urban areas of the lower basin.

Continued study of the Johnson Creek basin will provide 

insight into the response of the hydrology to land-use changes. 

In particular, runoff from newly acquired areas for urban 

development in the upper area of the basin may be particularly 

sensitive to changes in land use.

Acknowledgments

The authors wish to thank cooperating agencies and 

their staff including Maggie Skenderian and Frank Wildensee 

(city of Portland), Carrie Pak (formerly of city of Gresham), 

Lynne Kennedy and Torrey Lindbo (city of Gresham), the 

late George MacGregor (city of Milwaukie), Ela Whelan 

(formerly of Clackamas County), Andrew Swanson and John 

Nagy (Clackamas County’s Water Environment Services), 

and Kim Peoples (Multnomah County). Special thanks go to 

Mark Liebe (city of Portland) for inspiration and excellent 

insight regarding groundwater flow in the basin, and to Ivy 

Francis (formerly of the city of Portland) for the original 

request for assistance in 1997. Land owners throughout the 

basin provided access to properties for data collection during 

the study. Tiffany Jacklin and Melanie North (USGS) provided 

data base support. USGS personnel, beginning in the early 

1940s provided the basic (and essential) data used in the 

interpretations developed in this report. 

References Cited

Anderson, C.W., Rinella, F.A., and Rounds, S.A., 1996, 

Occurrence of selected trace elements and organic 

compounds and their relation to land use in the Willamette 

River basin, Oregon, 1992-94: U.S. Geological Survey 

Water-Resources Investigations Report 96-4234, 68 p., 

accessed May 28, 2008, at http://pubs.er.usgs.gov/usgspubs/

wri/wri964234

Beeson, M.H., Tolan, T.L., and Madin, I.P., 1989, Geologic 

map of the Lake Oswego quadrangle, Clackamas, 

Multnomah, and Washington Counties, Oregon: Oregon 

Department of Geology and Mineral Industries Map 

GMS-59, 1 sheet, scale 1:24,000, accessed May 28, 2008, 

at http://www.oregongeology.com/sub/publications/GMS/

gms059.pdf

Chang, Heejun, 2006, Comparative streamflow characteristics 

in urbanizing basins in the Portland Metropolitan Area, 

Oregon, USA: Hydrological Processes, v. 21, no. 2, 

p. 211-222, accessed October 31, 2008, at http://dx.doi.

org/10.1002/hyp.6233

Chestnut, C.R., 1997, Summer Flooding from Crystal Springs 

Creek Bedevils Westmoreland: Oregonian, July 24, 1997.

Collins, C.A., and Broad, T.M., 1993, Estimated average 

annual ground-water pumpage in the Portland basin, Oregon 

and Washington, 1987-1988: U.S. Geological Survey 

Water-Resources Investigations Report 91-4018, 26 p., 

accessed May 28, 2008, at http://pubs.er.usgs.gov/pubs/wri/

wri914018
References Cited 53

Conlon, T.D., Wozniak, K.C., Woodcock, Douglas, Herrera, 

N.B., Fisher, B.J., Morgan, D.S., Lee, K.K., and Hinkle, 

S.R., 2005, Ground-water hydrology of the Willamette 

basin, Oregon: U.S. Geological Survey Scientific 

Investigations Report 2005-5168, 83 p., 1 pl., accessed May 

28, 2008, at http://pubs.er.usgs.gov/pubs/sir/sir20055168

Cooper, R.M., 2005, Estimation of peak discharges for rural, 

unregulated streams in western Oregon: U.S. Geological 

Survey Scientific-Investigations Report 2005-5116, 134 

p., accessed May 28, 2008, at http://pubs.er.usgs.gov/

usgspubs/sir/sir20055116

Dames and Moore, 1998, Draft Final Crystal Springs 

watershed assessment—Prepared for the City of Portland 

Bureau of Environmental Services: Portland, Oregon, June, 

1998, 75 p., plus appendixes.

Dillin, J.F., Jr., 1997, Citizens Seek Solutions to Crystal 

Springs Creek Flooding: Sellwood Bee, September 1997.

Edwards, T.K., 1992, Water quality and flow data for the 

Johnson Creek basin, Oregon, April 1988 to January 

1990: U.S. Geological Survey Open-File Report 92-73, 

29 p., accessed May 29, 2008, at http://pubs.er.usgs.gov/

usgspubs/ofr/ofr9273

Edwards, T.K., 1994, Assessment of surface-water quality 

and water-quality control alternatives, Johnson Creek 

basin, Oregon: U.S. Geological Survey Water-Resources 

Investigations Report 93-4090, 50 p., accessed May 29, 

2008, at http://pubs.er.usgs.gov/usgspubs/wri/wri934090

Edwards, T.K., and Curtiss, D.A., 1993, Preliminary 

evaluation of water-quality conditions of Johnson Creek, 

Oregon: U.S. Geological Survey Water-Resources 

Investigations Report 92-4136, 15 p., accessed May 29, 

2008, at http://pubs.er.usgs.gov/usgspubs/wri/wri924136

Flynn, K.M., Kirby, W.H., and Hummel, P.R., 2006, User’s 

manual for program PeakFQ annual flood-frequency 

analysis using Bulletin 17B guidelines: U.S. Geological 

Survey Techniques and Methods 4B4, 42 p., accessed 

May 29, 2008, at http://pubs.er.usgs.gov/usgspubs/tm/

tm4B4

Franke, O.L., Reilly, T.E., Pollock, D.W., and LaBaugh, J.W., 

1998, Estimating areas contributing recharge to wells—

Lessons from previous studies: U.S. Geological Survey 

Circular 1174, 14 p., accessed October 30, 2008, at http://

pubs.er.usgs.gov/usgspubs/cir/cir1174

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

Englewood Cliffs, N.J., Prentice-Hall, 604 p.

Gresham Outlook, 1949, Gilbert Homes Covered by 

Temporary Lake: Gresham Outlook, March 3, 1949, 

photograph and caption, p. 1. 

Gresham Outlook, 1969, S.E. Long Street Residents Seeking 

Help from County: Gresham Outlook, February 6, 1969, 

p. 3.

Helsel, D.R., and Hirsch, R.M., 2002, Statistical methods 

in water resources: U.S. Geological Survey Techniques 

of Water-Resources Investigations, book 4, Hydrologic 

Analysis and Interpretation, chap. A3, 523 p., accessed 

May 29, 2008, at http://pubs.er.usgs.gov/pubs/twri/

twri04A3

Hinkle, S.R., and Snyder, D.T., 1997, Comparison of 

chlorofluorocarbon-age dating with particle-tracking results 

of a regional ground-water flow model of the Portland 

basin, Oregon and Washington: U.S. Geological Survey 

Water-Supply Paper 2483, 47 p., accessed May 29, 2008, at 

http://pubs.er.usgs.gov/pubs/wsp/wsp2483

Hogenson, G.M., and Foxworthy, B.L., 1965, Ground water 

in the East Portland area, Oregon: U.S. Geological Survey 

Water Supply Paper 1793, 78 p., accessed May 29, 2008, at 

http://pubs.er.usgs.gov/pubs/wsp/wsp1793

Insightful Corporation, 2005, S-PLUS® 7.0.6, Release for 

Windows, December 2005, accessed October 28, 2008, at 

http://www.insightful.com/support/doc_splus_win.asp

Johnson Creek Watershed Council, 2006, Within your reach: 

JCWC Newsletter, v. XIV, no. 2, p. 7.

Jones, M.A., Jones, J.L., and Olsen, T.D., 2000, Groundwater flooding in glacial terrain of southern Puget Sound, 

Washington: U.S. Geological Survey Fact Sheet FS-111-00, 

5 p., accessed May 29, 2008, at http://pubs.er.usgs.gov/

usgspubs/fs/fs11100

Kennedy, E.J., 1990, Levels at streamflow gaging stations: 

U.S. Geological Survey Techniques of Water-Resources 

Investigations, book 3, Applications of Hydraulics, chap. 

A19, 26 p., accessed May 29, 2008, at http://pubs.er.usgs.

gov/usgspubs/twri/twri03A19

Konrad, C.P., and Booth, D.B., 2002, Hydrologic trends 

associated with urban development for selected streams 

in the Puget Sound basin, Western Washington: U.S. 

Geological Survey Water-Resources Investigations 

Report 02-4040, 40 p., accessed May 29, 2008, at http://

pubs.usgs.gov/wri/wri024040/

 Laenen, Antonius, 1980, Storm runoff as related to 

urbanization in the Portland, Oregon-Vancouver, 

Washington area: U.S. Geological Survey Open-File 

Report 80-689, 71 p., accessed May 29, 2008, at http://

pubs.er.usgs.gov/usgspubs/ofr/ofr80689
54 Hydrology of the Johnson Creek Basin, Oregon

Laenen, Antonius, and Risley, J.C., 1997, Precipitation-runoff 

and streamflow-routing models for the Willamette River 

basin, Oregon: U.S. Geological Survey Water-Resources 

Investigations Report 95-4284, 197 p., accessed May 29, 

2008, at http://pubs.er.usgs.gov/usgspubs/wri/wri954284

Lee, K.K., 1995, Stream velocity and dispersion 

characteristics determined by dye-tracer studies on selected 

stream reaches in the Willamette River basin, Oregon: 

U.S. Geological Survey Water-Resources Investigations 

Report 95-4078, 39 p., accessed May 29, 2008, at http://

pubs.er.usgs.gov/usgspubs/wri/wri954078

Lee, K.K., and Risley, J.C., 2002, Estimates of ground-water 

recharge, base flow, and stream reach gains and losses in the 

Willamette basin, Oregon: U.S. Geological Survey WaterResources Investigations Report 01-4215, 52 p., accessed 

May 29, 2008, at http://pubs.er.usgs.gov/usgspubs/wri/

wri014215

McCarthy, K.A., and Anderson, D.B., 1990, Ground-water 

data for the Portland basin, Oregon and Washington: 

U.S. Geological Survey Open-File Report 90-126, 56 p., 

accessed May 29, 2008, at http://pubs.er.usgs.gov/pubs/ofr/

ofr90126

McCarthy, K.A., and Gale, R.W., 1999, Investigation of the 

distribution of organochlorine and polycyclic aromatic 

hydrocarbon compounds in the lower Columbia River using 

semipermeable membrane devices: U.S. Geological Survey 

Water-Resources Investigations Report 99-4051, 136 p., 

accessed May 29, 2008, at http://pubs.er.usgs.gov/usgspubs/

wri/wri994051

McFarland, W.D., and Morgan, D.S., 1996, Description of the 

ground-water flow system in the Portland basin, Oregon 

and Washington: U.S. Geological Survey Water Supply 

Paper 2470-A, 58 p., accessed May 29, 2008, at http://pubs.

er.usgs.gov/pubs/wsp/wsp2470A 

Metro, 2002, Digital elevation model—Portland, Oregon: 

Metro Data Resource Center, metadata accessed April 10, 

2009, at http://rlismetadata.oregonmetro.gov/display.

cfm?Meta_layer_id=1956&Db_type=rlis

Moffatt, R.L., Wellman, R.E., and Gordon, J.M., 1990, 

Statistical summaries of streamflow data in Oregon—

Volume 1, Monthly and annual streamflow, and flowduration values: U.S. Geological Survey Open-File 

Report 90-118, 413 p., accessed May 29, 2008, at http://

pubs.er.usgs.gov/usgspubs/ofr/ofr90118

Morgan, D.S., and McFarland, W.D., 1996, Simulation 

analysis of the ground-water flow system in the Portland 

basin, Oregon and Washington: U.S. Geological Survey 

Water Supply Paper 2470–B, 83 p., accessed May 29, 2008, 

at http://pubs.er.usgs.gov/pubs/wsp/wsp2470B

Oregon Climate Service, 2007, Climate data: Corvallis, Oreg., 

Oregon State University, accessed May 11, 2007, at http://

www.coas.oregonstate.edu/OCS/

Oregon Department of Environmental Quality, 2006, 

Willamette basin TMDL—Chapter 5, Lower Willamette 

subbasin: Portland, Oreg., Oregon Department of 

Environmental Quality, accessed January 4, 2008, at http://

www.deq.state.or.us/wq/tmdls/docs/willamettebasin/

willamette/chpt5lowerwill.pdf

Oregon Water Resources Department (OWRD), 2008, 

Well database: Salem, Oreg., Oregon Water Resources 

Department, accessed March 24, 2009, at http://www.

oregon.gov/OWRD/PUBS/ToolsData.shtml

Oregonian, 1997, Anger Overflows near Pesky Lake: 

Oregonian, February 3, 1997.

PRISM Group, 2007, Oregon State University, accessed 

April 10, 2009, at http://prism.oregonstate.edu/products/

viewer.phtml?file=/pub/prism/us_30s/grids/ppt/Normals/

us_ppt_1971_2000.14.gz&year=1971_2000&vartype=ppt

&month=14&status=final

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

of streamflow. Volume 1. Measurement of stage and 

discharge. Volume 2. Computation of discharge.: U.S. 

Geological Survey Water Supply Paper 2175, 631 p., 

accessed May 29, 2008, at http://pubs.usgs.gov/wsp/

wsp2175/

Rutledge, A.T., 1998, Computer programs for describing the 

recession of ground-water discharge and for estimating 

mean ground-water recharge and discharge from 

streamflow data—Update: U.S. Geological Survey WaterResources Investigations Report 98-4148, 43 p., accessed 

May 29, 2008, at http://pubs.usgs.gov/wri/wri984148

Searcy, J.K., 1959, Flow-duration curves—Manual of 

hydrology, Part 2, Low-flow techniques: U.S. Geological 

Survey Water-Supply Paper 1542-A, 33 p., accessed 

May 29, 2008, at http://pubs.er.usgs.gov/usgspubs/wsp/

wsp1542A

Sellwood Bee, 1997, Neighbors Pitch in and Pull Weeds in 

Crystal Springs Creek: Oregonian, October 1997, p. 1.

Snyder, D.T., 2008, Estimated depth to ground water and 

configuration of the water table in the Portland, Oregon 

area: U.S. Geological Survey Scientific Investigations 

Report 2008-5059, 40 p., accessed August 25, 2008, at, 

http://pubs.usgs.gov/pubs/sir/2008/5059
References Cited 55

Snyder, D.T., Morgan, D.S., and McGrath, T.S., 1994, 

Estimation of ground-water recharge from precipitation, 

runoff into drywells, and on-site waste-disposal systems 

within the Portland basin, Oregon and Washington: U.S. 

Geological Survey Water-Resources Investigations Report 

92-4010, 34 p., accessed May 29, 2008, at http://pubs.

er.usgs.gov/pubs/wri/wri924010

Stonestrom, D.A., and Constantz, Jim, eds., 2003, Heat 

as a tool for studying the movement of ground water 

near streams: U.S. Geological Survey Circular 1260, 96 

p., accessed May 29, 2008, at http://pubs.er.usgs.gov/

usgspubs/cir/cir1260

Tanner, D.Q., and Lee, K.K., 2004, Organochlorine pesticides 

in the Johnson Creek basin, Oregon, 1988-2002: U.S. 

Geological Survey Scientific Investigations Report 2004-

5061, 42 p., accessed May 29, 2008, at http://pubs.er.usgs.

gov/usgspubs/sir/sir20045061

Taylor, C.J., and Alley, W.M., 2002, Ground-water-level 

monitoring and the importance of long-term water-level 

data: U.S. Geological Survey Circular 1217, 68 p., accessed 

October 27, 2008, at http://pubs.er.usgs.gov/usgspubs/cir/

cir1217

Trimble, D.E., 1963, Geology of Portland, Oregon and 

adjacent areas–A study of Tertiary and Quaternary deposits, 

lateritic weathering profiles, and of Quaternary history 

of part of the Pacific Northwest: U.S. Geological Survey 

Bulletin 1119, 119 p., accessed October 28, 2008, at http://

pubs.er.usgs.gov/usgspubs/b/b1119

U.S. Department of Agriculture Natural Resources 

Conservation Service, 2007, Oregon soil survey data—

Soil survey for Multnomah and Clackamas Counties: 

Washington, D.C., U.S. Department of Agriculture, 

accessed June 20, 2007, at http://www.or.nrcs.usda.gov/

pnw_soil/or_data.html

U.S. Geological Survey, [2009], Ground-water data for 

Oregon: Washington, D.C., U.S. Geological Survey, 

accessed March 24, 2009, at http://waterdata.usgs.gov/or/

nwis/gw

U.S. Interagency Advisory Committee on Water Data, 

1982, Guidelines for determining flood flow frequency: 

U.S. Geological Survey, Bulletin 17B, 183 p., accessed 

May 29, 2008, at http://water.usgs.gov/osw/bulletin17b/

bulletin_17B.html

U.S. National Oceanic and Atmospheric Administration, 

2007, Monthly climate data: Reno, Nev., Western Regional 

Climate Center, accessed May 29, 2008, at http://www.

wrcc.dri.edu/cgi-bin/cliMAIN.pl?wavanc

University of Oregon, 2006, General Land Office MapsDigital Copies of the Cadastral Survey Maps for Oregon, 

digital images of Township (T) 1 North (N) Range (R) 2 

East (E) (1852), T. 1 N. R. 3 E. (1855), T. 1 South (S) R. 

1 E. (1852), T. 1 S. R. 2 E. (1854), T. 1 S. R. 3 E. (1855): 

Eugene, Oreg., University of Oregon, accessed November 

2, 2006, at http://libweb.uoregon.edu/map/GIS/Data/

Oregon/GLO/Quadrant_4.htm#1s

Veeger, A.I., and Johnston, H.E., 1996, Hydrogeology and 

water resources of Block Island, Rhode Island, with a 

section on Geology, by B.D. Stone and L.A. Sirkin: U.S. 

Geological Survey Water-Resources Investigations Report 

94-4096, 76 p., accessed October 28, 2008, at http://pubs.

er.usgs.gov/usgspubs/wri/wri944096

Wagner, R.J., Boulger, R.W., Jr., Oblinger, C.J., and Smith, 

B.A., 2006, Guidelines and standard procedures for 

continuous water-quality monitors—Station operation, 

record computation, and data reporting: U.S. Geological 

Survey Techniques and Methods 1-D3, 51 p., accessed May 

11, 2007, at http://pubs.usgs.gov/tm/2006/tm1D3/

Waitt, R.B., Jr., 1985, Case for periodic, colossal jökulhlaups 

from Pleistocene glacial Lake Missoula: Geological Society 

of America Bulletin, v. 96, no. 10, p. 1271–1286, accessed 

May 29, 2008, at http://vulcan.wr.usgs.gov/Glossary/

Glaciers/IceSheets/Waitt85GSA/framework.html

Wellman, R.E., Gordon, J.M., and Moffatt, R.L., 1993, 

Statistical summaries of streamflow data in Oregon—

Volume 2, Annual low and high flow, and instantaneous 

peak flow: U.S. Geological Survey Open-File Report 93-63, 

406 p., accessed May 29, 2008, at http://pubs.er.usgs.gov/

usgspubs/ofr/ofr9363

Wilde, F.D., ed., 2005, Field measurements: U.S. Geological 

Survey Techniques of Water-Resources Investigations, book 

9, chap. A6, accessed May 29, 2008, at http://pubs.water.

usgs.gov/twri9A6/

Wilson, W.E., and Moore, J.E., eds., 2003, Glossary of 

hydrology: Falls Church, Va., American Geological 

Institute, 248 p.

Winter, T.C., Harvey, J.W., Franke, O.L., and Alley, W.M., 

1998, Ground water and surface water—A single resource: 

U.S. Geological Survey Circular 1139, 79 p., accessed May 

29, 2008, at http://pubs.er.usgs.gov/usgspubs/cir/cir1139
56 Hydrology of the Johnson Creek Basin, Oregon

This page intentionally left blank.
Publishing support provided by the U.S. Geological Survey

Publishing Network, Tacoma Publishing Service Center

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

 Director, Oregon Water Science Center

U.S. Geological Survey

2130 SW 5th Avenue

Portland, Oregon 97201

http://or.water.usgs.gov
2

Report Title

 Lee and Snyder— Hydrology of the Johnson Creek Basin, Oregon—Scientific Investigations Report 2009–5123