U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2015–5109

Prepared in cooperation with the Tillamook Estuaries Partnership

Water-Quality Conditions and Suspended-Sediment 

Transport in the Wilson and Trask Rivers, 

Northwestern Oregon, Water Years 2012–14
Cover: Photograph showing Wilson River during storm in February 2014. 

Photograph by Steven Sobieszczyk, U.S. Geological Survey.
Water-Quality Conditions and SuspendedSediment Transport in the Wilson and 

Trask Rivers, Northwestern Oregon, 

Water Years 2012–14

By Steven Sobieszczyk, Heather M. Bragg, and Mark A. Uhrich

Prepared in cooperation with the Tillamook Estuaries Partnership 

Scientific Investigations Report 2015-5109

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

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Suggested citation:

Sobieszczyk, Steven, Bragg, H.M., and Uhrich, M.A., 2015, Water-quality conditions and suspended-sediment 

transport in the Wilson and Trask Rivers, northwestern Oregon, water years 2012–14: U.S. Geological Survey 

Scientific Investigations Report 2015-5109, 32 p., http://dx.doi.org/10.3133/sir20155109.

ISSN 2328-0328 (online) 
iii

Contents

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

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

Background ...........................................................................................................................................1

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

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

Wilson River Watershed (USGS Streamgage 14301500).......................................................2

Trask River Watershed (USGS Streamgage 14302480)..........................................................2

Data Collection...............................................................................................................................................4

Instream Monitoring.............................................................................................................................4

Suspended-Sediment Sampling.........................................................................................................4

Quality Assurance and Review ..........................................................................................................4

Data Analysis..................................................................................................................................................5

Model Calibration Dataset ..................................................................................................................5

Suspended-Sediment Concentration Regression Models ............................................................5

Continuous Computation of Suspended-Sediment Concentrations ............................................6

Wilson River Suspended-Sediment Concentration Record .................................................6

Trask River Suspended-Sediment Concentration Record ....................................................6

Suspended-Sediment Load Calculations..........................................................................................7

Water-Quality Conditions and Suspended-Sediment Transport............................................................7

Water Temperature ..............................................................................................................................7

Dissolved Oxygen Concentration.......................................................................................................8

Turbidity ..................................................................................................................................................8

Suspended-Sediment Loads...............................................................................................................8

Historical Streamflow Record ............................................................................................................9

Implications for Stream Conditions for Wilson and Trask Rivers ........................................................11

Water-Quality Status of Wilson and Trask Rivers .........................................................................11

Watershed Characteristics That Influence Sediment Production .............................................11

Trask River Watershed—Integrating Science...............................................................................11

Tillamook Southern Flow Corridor Project......................................................................................12

Summary and Conclusions.........................................................................................................................12

Acknowledgments.......................................................................................................................................12

References Cited..........................................................................................................................................12

Appendix A. Wilson River Suspended-Sediment Concentration Record...........................................15

Appendix B. Trask River Suspended-Sediment Concentration Record..............................................23

Appendix C. Troubleshooting Instream Monitors...................................................................................31
iv

Figures

1. Map showing location of the Wilson and Trask Rivers, northwestern Oregon .................3

2. Graphs showing instantaneous turbidity duration curves for suspended-sediment

samples collected at Wilson River and Trask River streamgage locations,

northwestern Oregon, water years 2012–2014 ........................................................................5

3. Time-series graphs showing 7-day average maximum water temperature for the

Wilson and Trask Rivers, northwestern Oregon, water years 2012–2014...........................7

4. Time-series graph showing dissolved oxygen data for the Wilson and Trask

Rivers, northwestern Oregon, water years 2012–2014...........................................................8

5. Graphs showing daily median turbidity data for the Wilson and Trask Rivers,

Oregon, water years 2012–2014 .................................................................................................9

6. Graphs showing monthly suspended-sediment loads for the Wilson and Trask

Rivers, northwestern Oregon, water years 2012–2014.........................................................10

7. Graphs showing peak annual streamflow for the period of record for the Wilson

and Trask Rivers, northwestern Oregon .................................................................................10

Tables

1. Streamflow and water-quality monitoring information for the Wilson and Trask

Rivers, northwestern Oregon......................................................................................................3

2. Water-quality parameters measured at the Wilson and Trask Rivers,

northwestern Oregon, water years 2012–2014 ........................................................................4

3. Suspended-sediment concentration regression models for the Wilson and Trask

Rivers, northwestern Oregon......................................................................................................6

4. Annual suspended-sediment loads for the Wilson and Trask Rivers, northwestern

Oregon, water years 2012–2014 ................................................................................................9
v

Conversion Factors

Inch/Pound to International System of Units

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2

) 2.590 square kilometer (km2) 

square mile (mi2

) 640 acre

Volume

gallon (gal) 3.785 liter (L) 

cubic foot (ft3

) 0.02832 cubic meter (m3) 

Flow Rate

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3s)

Mass

ton, short (2,000 lb) 0.9072 megagram (Mg) 

ton per day per square mile [(ton/d)/mi2

] 0.3503 megagram per day per square kilometer 

[(Mg/d)/km2

]

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

°F=(1.8×°C)+32.

Supplemental Information

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

25°C).

Suspended-sediment concentrations are reported in milligrams per liter (mg/L). Sediment loads 

are reported in tons.

Turbidity is given in formazin nephelometric units.

Dissolved oxygen is reported in milligrams per liter (mg/L).

A water year is the 12-month period from October 1 through September 30 of the following 

calendar year. The water year is designated by the calendar year in which it ends. For example, 

water year 2008 is the period from October 1, 2007, through September 30, 2008.
vi

Datums

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

(NGVD 29).

Horizontal coordinate information is referenced to Oregon Lambert (HARN) North American 

Datum of 1983 (NAD 83).

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

Abbreviations and Acronyms

BCF bias correction factor

DO dissolved oxygen

EWI equal-width-increment

FNU Formazin Nephelometric Unit

MSPE model standard percent error

NWIS U.S. Geological Survey National Water Information System

OLS ordinary least-squares

PPCC probability plot correlation coefficient

PRESS predicted residual sum of squares

Q streamflow

R2 coefficient of determination

RMSE root mean squared error

SC specific conductance

SSC suspended-sediment concentration

SSL suspended-sediment load

ST stage

TB turbidity

USGS U.S. Geological Survey

VIF variance inflation factor

WT water temperature

WY water year
Water-Quality Conditions and Suspended-Sediment 

Transport in the Wilson and Trask Rivers, 

Northwestern Oregon, Water Years 2012–14

By Steven Sobieszczyk, Heather M. Bragg, and Mark A. Uhrich

Abstract

In October 2011, the U.S. Geological Survey began 

investigating and monitoring water-quality conditions and 

suspended-sediment transport in the Wilson and Trask 

Rivers, northwestern Oregon. Water temperature, specific 

conductance, turbidity, and dissolved oxygen were measured 

every 15–30 minutes in both streams using real-time instream 

water-quality monitors. In conjunction with the monitoring 

effort, suspended-sediment samples were collected and 

analyzed to model the amount of suspended sediment being 

transported by each river. Over the course of the 3-year study, 

which ended in September 2014, nearly 600,000 tons (t) of 

suspended-sediment material entered Tillamook Bay from 

these two tributaries. 

Each year of the study, the Wilson River transported 

between 80,300 and 240,000 t of suspended sediment, while 

the Trask River contributed between 28,200 and 69,900 t. The 

suspended-sediment loads observed during the study were 

relatively small because streamflow conditions were routinely 

lower than normal between October 2011 and September 

2014. Only one storm had a recurrence interval between a 

2- and 5-year event. Every other storm produced streamflows 

equivalent to what would be classified as a 1- or 2-year event. 

Because most sediment moves during high flows, the lack 

of heavy rainfall and elevated streamflows muted any high 

sediment loads.

Along with assessing suspended-sediment transport, 

the U.S. Geological Survey also monitored instream water 

quality. This monitoring was used to track instream conditions 

and relate them to water temperature, dissolved oxygen, 

and sedimentation issues for the Wilson and Trask Rivers. 

Stream temperatures in the Wilson and Trask Rivers exceeded 

the temperature standard for cold-water habitat. Water 

temperatures at both streams exceeded the standard for more 

than 30 percent of the year, as stream temperatures increased 

above the seasonal 13 degrees Celsius (°C) (seasonal 

core cold-water habitat) and 16 °C (salmon and steelhead 

[Oncorhynchus mykiss] spawning) thresholds. Conversely, 

dissolved oxygen concentrations rarely decreased to less than 

the absolute water-quality criterion of 8 milligrams per liter 

for cold-water streams.

Results from this study will provide resource managers 

insight into the seasonality of water-quality conditions and 

the extent of suspended-sediment transport in the Wilson and 

Trask Rivers. The data are useful for establishing a baseline 

and for maintaining best-use land management practices and 

possibly for aiding in prioritization of restoration actions for 

both rivers and their respective watersheds. 

Introduction

Background 

Water-quality impairments in the Tillamook Bay 

watershed (fig. 1) threaten native fish species, such as 

coho salmon (Oncorhynchus kisutch) and cutthroat trout 

(Oncorhynchus clarkii). Recent studies (Tillamook Estuaries 

Partnership, 1999; Oregon Department of Environmental 

Quality, 2001; Demeter Design, 2009; Johnson and Drake, 

2011; Reiter and others, 2013) have identified the primary 

water-related issues for Tillamook Bay and its tributaries as 

(1) warming stream temperatures, (2) increased sedimentation 

and associated point and nonpoint source pollution, such as 

nutrients and toxics, (3) low dissolved oxygen concentrations, 

and (4) altered or modified channels. Each of these conditions 

greatly affects the overall health and quality of aquatic 

habitats. 
2 Water-Quality Conditions and Suspended-Sediment Transport, Wilson and Trask Rivers, Oregon, Water Years 2012–14

Over the last few decades, landscape changes such 

as large forest fires, removal of riparian vegetation, and 

engineered channel modifications have greatly degraded the 

water quality of many of Oregon’s northern coastal streams 

(Oregon Department of Environmental Quality, 2001). These 

degraded conditions have led to increases in fine-sediment 

transport, scouring of stream channels, decreases in suitable 

streambed habitat, and increases in stream temperatures 

resulting from increased exposure to direct sunlight (Demeter 

Design, 2009). High stream temperatures are especially 

problematic in summer and autumn, when above-average 

water temperatures can stress spawning fish populations 

(Oregon Department of Environmental Quality, 2001). 

In October 2011, the U.S. Geological Survey (USGS), in 

cooperation with the Tillamook Estuaries Partnership, began 

investigating and monitoring water-quality conditions and 

suspended-sediment transport in the Wilson and Trask Rivers, 

northwestern Oregon. 

Purpose and Scope

The purpose of this report is to summarize suspendedsediment transport and continuously monitored water-quality 

data for the Wilson (USGS streamgage 14301500) and Trask 

(USGS streamgage 14302480) Rivers. This study addressed 

a deficiency in long-term monitoring of local streams 

by establishing a water-quality and suspended-sediment 

monitoring network for two major tributaries to Tillamook 

Bay. This study provided water-resource managers with 

continuous real-time data of water temperature, specific 

conductance, turbidity, and dissolved oxygen concentrations. 

USGS researchers provided estimates of suspended-sediment 

loads for the two rivers during the 3-year study period 

(October 1, 2011–September 30, 2014; water years 2012–14). 

This study did not address issues of Escherichia coli, fecal 

coliform bacteria, or other contaminants that are common 

water-quality issues in the two streams and in Tillamook Bay. 

Archived data can be accessed through the USGS National 

Water Information System database (U.S. Geological Survey, 

2015a, 2015b).

Along with monitoring instream conditions and providing 

estimates for suspended sediment, specific objectives also 

included:

• Publishing site-specific regression models that estimate 

suspended-sediment concentrations using continuous 

turbidity and (or) streamflow data as surrogates;

• Evaluating stream conditions for water temperature, 

dissolved oxygen, turbidity, and sedimentation; and 

• Evaluating future effects of sediment on potential 

downstream restoration projects, such as the Southern 

Flow Corridor Project (Northwest Hydraulic 

Consultants, 2011).

Description of Study Area

Studies in Tillamook Bay (Oregon Department of 

Environmental Quality, 2001; Mico and Mico, 2009; 

Tillamook Estuaries Partnership, 2010; Johnson and Drake, 

2011) have provided detailed basin setting and ecological 

characterization of the Wilson River watershed (Sullivan and 

others, 2001; Duck Creek Associates, 2008) and the Trask 

River watershed (Follansbee and Stark, 1998; Snyder and 

others, 2003). For this study, the combined drainage area 

for the two monitoring sites accounts for approximately 

60 percent of the total contributing area to Tillamook Bay. 

Typical rainfall for the Wilson and Trask River watersheds is 

about 123 in/yr (Follansbee and Stark, 1998).

Wilson River Watershed (USGS Streamgage 

14301500)

The Wilson River begins in the Coast Range of 

northwestern Oregon, approximately 45 mi west of Tillamook 

Bay (fig. 1). Although the river flows into the bay, the Wilson 

River streamgage is 10.2 mi upstream of the delta (table 1). 

From that monitoring location, the river drains 161 mi2 of 

mostly forested land (about 80 percent of the basin; Risly 

and others, 2008). Terrain in the watershed varies from peak 

elevations of higher than 3,620 ft in the Coast Range to a 

valley floor where elevations are at or just above sea level. 

Most of the watershed is within the Tillamook State Forest. 

In the upper watershed, the Wilson River flows through wide 

gravel-rich areas and through stable confined basalt gorges 

(Jones and others, 2012). Near the streamflow gage along the 

lower parts of the watershed, the Wilson River meanders as a 

wide channel with abundant large gravel bars.

Trask River Watershed (USGS Streamgage 

14302480)

Similar to the Wilson River, the Trask River headwaters 

originate along the Coast Range in the Tillamook State 

Forest. Geographically, the Trask River watershed is the next 

Tillamook Bay tributary south of the Wilson River (fig. 1); 

therefore, they share very similar physiographic and geologic 

settings. For this study, water quality was monitored on the 

Trask River at USGS streamgage 14302480 (table 1). From 

this location, the river drains 156 mi2 of mostly forested land 

(about 78 percent of the basin; Risly and others, 2008). Unlike 

the Wilson River, the Trask River sampling occurred at a 

different location than the monitoring. Suspended-sediment 

samples were collected at the Long Prairie Road Bridge, 

4.0 mi downstream of the streamgage. This sampling site 

was used because there was not a cableway located at the 

streamgaging site (fig. 1).
Introduction 3

tac15-1012_fig 01

Tillamook

Bay

Wilson River

Trask River

101

101

6

Tillamook State

Forest

PACIFIC OCEAN

14302480

14301500

14301500 USGS streamgage

USGS sampling site

Watershed boundary

EXPLANATION

124°00' 123°50' 123°40' 123°30' 123°20'

45°

40'

45°

35'

45°

30'

45°

25'

45°

20'

Base map modified from U.S. Geological Survey digital data, 

various scales. Coordinate reference system: Oregon Lambert 

(HARN). Horizontal datum is North American Datum 1983. 0

0

10 KILOMETERS

5 10 MILES

5

OREGON

Study

area

Tillamook

C

O

A

S

T

R

A

N

G

E

Figure 1. Location of the Wilson and Trask Rivers, northwestern Oregon.

Table 1. Streamflow and water-quality monitoring information for the Wilson and Trask Rivers, northwestern Oregon.

[Parameters: DO, dissolved oxygen concentration; SC, specific conductance; TB, turbidity; WT, water temperature. Abbreviations: USGS, U.S. Geological 

Survey. mi2

, square miles]

USGS

streamgage 

No.

USGS streamgage name

Drainage

basin area

(mi2

)

Water-quality record Streamflow record

Parameters Period of record 

(water year)

Years of

record

Period of record 

(water year)

Years of 

record

14301500 Wilson River near Tillamook 161 DO, SC, TB, WT 2012–2014 3 1915–1916,

1931–present

85

14302480 Trask River above Cedar Creek, 

near Tillamook

156 DO, SC, TB, WT 2012–2014 3 1996–present 18
4 Water-Quality Conditions and Suspended-Sediment Transport, Wilson and Trask Rivers, Oregon, Water Years 2012–14

Data Collection

Data were collected using a combination of instream 

water-quality monitoring and suspended-sediment sampling. 

More details about the sediment collection and processing are 

provided in appendixes A and B.

Instream Monitoring

Water temperature, specific conductance, and turbidity 

data were collected in near-real-time at the Wilson and Trask 

River streamgaging locations between October 2011 and 

September 2014 (water years 2012–14) (table 2). Dissolved 

oxygen concentration also was monitored at both rivers; 

however, it was only measured during the warmer months 

(May–June through October). Water-quality conditions 

were monitored using YSI, Inc. 6920-V2 multiparameter 

instruments. Sensors were checked and calibrated monthly 

using protocols described by Wagner and others (2006). 

Streamflow was computed from stage using USGS protocols 

(Rantz and others, 1982; Sauer and Turnipseed, 2010; 

Turnipseed and Sauer, 2010). At the Wilson River streamgage, 

all parameters were recorded at 15-minute intervals. At the 

Trask River streamgage, parameters were logged at 30-minute 

intervals from October 1, 2011 to May 22, 2012, after which 

the interval was changed to 15 minutes. All data were recorded 

on Sutron Satlink datalogger-transmitters and uploaded to the 

online National Water Information System database every 2 

hours.

Suspended-Sediment Sampling

USGS personnel collected suspended-sediment samples 

during calibration-site visits and during storm-related events. 

An equal-width-increment (EWI) method (Edwards and 

Glysson, 1999; U.S. Geological Survey, 2006) was used to 

collect cross-sectional, depth-integrated samples from a bankoperated cableway at the Wilson River site. EWI samples were 

collected from the Long Prairie Road Bridge downstream of 

the Trask River site. All samples were analyzed at the USGS 

Cascade Volcano Observatory sediment laboratory based on 

procedures described in Guy (1969) for suspended-sediment 

concentration in milligrams per liter (mg/L), and most were 

analyzed for percent silt and clay (fine sediment), as reported 

in percentage of samples finer than 63 μm. 

During the study, 93 EWI samples were collected, 45 

at the Wilson River and 48 at the Trask River. Suspendedsediment samples were collected over nearly the entire range 

of hydrologic conditions for both rivers. Figure 2 shows the 

distribution of sample collection over the range and duration 

of instantaneous turbidity values at each streamgage. Most 

samples were collected during the less-frequent high turbidity 

events. These conditions were targeted for sampling because 

they were indicative of the greatest potential suspendedsediment transport. Only a few samples were collected when 

turbidity was less than 5.0 Formazin Nephelometric Units 

(FNU), when suspended-sediment transport conditions were 

greatly reduced.

Quality Assurance and Review

For quality assurance, sequential replicate sample pairs 

were compared individually to validate the reproducibility 

of the sampling method (Rasmussen and others, 2009). An 

ordinary least-squares (OLS) linear regression analysis was 

completed between the sample pairs at both monitoring sites. 

The OLS regression was useful because it formulated an 

equation that most closely approximated the sampled data. 

The results showed that the suspended-sediment concentration 

values for all sample pairs at both sites were highly correlated 

(coefficient of determination [R2] = 0.98) and close to a 1:1 

relation (slope = 1.01) over a range of 1–1,730 mg/L.

Table 2. Water-quality parameters measured at the Wilson and Trask Rivers, northwestern Oregon, water years 2012–2014.

[Units: ft3/s, cubic feet per second; ft, feet; °C, degrees Celsius; μS/cm, microsiemens per centimeter; FNU, Formazin Nephelometric Unit; mg/L, milligrams 

per liter]

Parameter Units Description

Streamflow (Q) ft3

/s Stream velocity over a given area

Stage (ST) ft Height of water based off a known datum

Water temperature (WT) °C

Specific conductance (SC) μS/cm Water, unfiltered, microsiemens per centimeter at 25 °C

Turbidity (TB) FNU Monochrome near infra-red LED light, 780–900 nanometers, detection angle 90 ± 2.5 

degrees 

Dissolved oxygen concentration (DO) mg/L Optical dissolved oxygen concentration
Data Analysis 5

tac15-1012_fig 02

0.1

1

10

100

1,000

0 20 40 60 80 100

Percentage of time exceeded

0 20 40 60 80 100

Percentage of time exceeded

0.1

1

10

100

1,000

Turbidity, in Formazin Nephelometric Units 

A. Wilson River (USGS streamgage 14301500)

B. Trask River (USGS streamgage 14302480)

Suspended-sediment samples

EXPLANATION

Figure 2. Instantaneous turbidity duration curves 

for suspended-sediment samples collected at (A)

Wilson River and (B) Trask River streamgage locations, 

northwestern Oregon, water years 2012–2014.

Data Analysis

Model Calibration Dataset

Each suspended-sediment concentration (SSC) sample 

was assigned a discrete turbidity and streamflow value from 

the continuous water-quality monitoring record (15- or 

30-minute data). For each sample, turbidity was computed as 

an average of the instantaneous sensor readings, beginning 

with the value logged immediately before the start time 

of the sample collection and ending with the value logged 

immediately after the end time. Because EWI samples could 

take as long as an hour to complete, there were usually 3–4 

turbidity readings recorded during the sampling period. The 

streamflow was interpolated between the instantaneous values 

to the mean time of the sample collection (see appendixes A

and B for more detail). 

The collection times for the Trask River EWI samples 

were adjusted to account for the distance between the 

streamgage and the sampling site. The time-of-travel 

correction ranged from 55 to 150 minutes, depending on the 

streamflow at the time of sample collection (see appendix B

for more detail). The time differences were subtracted from 

the actual beginning, mean, and ending sample times before 

assigning discrete turbidity and streamflow values to the 

samples. No obvious outliers were identified in the initial 

graphical analysis of the sample datasets. However, three EWI 

samples collected in November 2011 at the Trask River had 

to be excluded from analysis because the associated turbidity 

values were removed because of sensor fouling. When EWI 

sample pairs were collected, the associated SSC, turbidity, and 

streamflow values of the individual samples were averaged 

over the sampling period and used for the regression analysis. 

As a result, the final model calibration dataset included 25 

sampling events for the Wilson River and 23 for the Trask 

River. Additional information concerning the development of 

the regression models and computation of the continuous SSC 

record is available in appendixes A and B.

Suspended-Sediment Concentration Regression 

Models

Using the final sample datasets, OLS regression 

analyses were completed with the SSC sample data and the 

instream turbidity and streamflow data for both the Wilson 

and Trask Rivers. All calculations were computed with a 

standardized USGS spreadsheet tool designed specifically for 

surrogate regressions for SSC (Rasmussen and Gray, 2014) 

using methods described in Rasmussen and others (2009). 

Turbidity and streamflow were evaluated individually using 

simple linear regressions and together using multiple linear 

regressions. They also were evaluated using log10-transformed 

and untransformed data, as possible independent variables. At 

both sites, turbidity and streamflow were too highly correlated 

to use both parameters, so single linear regressions were 

chosen. 

Several summary statistics recommended by 

Rasmussen and others (2009) were computed to evaluate the 

appropriateness of the regression models (table 3). These 

included the coefficient of determination (R2

), which was 

used to explain variance of predicted versus observed; the 

root mean squared error (RMSE), which was converted to the 

upper and lower model standard percent errors (MSPE); the 

probability plot correlation coefficient (PPCC), which was 

used to indicate improved normality of the residuals by data 

transformations; and the predicted residual sum of squares 

(PRESS), which was used to check the fit of observations 

that were not used in the model. Residual plots for evaluating 

variance, normality, homoscedasticity, and curvature are 

provided in appendixes A and B. 
6 Water-Quality Conditions and Suspended-Sediment Transport, Wilson and Trask Rivers, Oregon, Water Years 2012–14

Table 3. Suspended-sediment concentration regression models for the Wilson and Trask Rivers, northwestern Oregon.

[Regression model equation: SSC, suspended-sediment concentration; TB, turbidity. BCF: bias correction factor. R2: coefficient of determination. MSPE: 

model standard prediction error. PPCC: probability plot correlation coefficient. PRESS: predicted residual sum of squares. USGS, U.S. Geological Survey]

USGS

streamgage 

No.

USGS streamgage name Regression model equation BCF Adjusted

R2

MSPE

(percent) PPCC PRESS

14301500 Wilson River near Tillamook log10SSC = 0.361 + 1.05 log10TB 1.11 0.95 57.2 0.97 1.17

-36.4

14302480 Trask River above Cedar Creek,

near Tillamook

log10SSC = 0.331 + 1.06 log10TB 1.06 0.96 42.6 0.94 0.60

-29.9

The log10-transformed models using turbidity as the 

explanatory variable were chosen for both sites based on 

residual plots, adjusted R2

, MSPE, PPCC, and PRESS 

statistics. The final form of the regression model was:

log10SSC = b + a*log10TB (1)

where 

SSC is suspended-sediment concentration, in 

milligrams per liter; 

TB is turbidity, in Formazin Nephelometric Units; 

and 

a and b are the slope and y-intercept coefficients, 

respectively, obtained by the OLS regression 

analysis. 

The logarithmic transformation and subsequent conversion 

back to original form introduced a known bias, which was 

addressed with a bias correction factor (BCF) as outlined in 

Helsel and Hirsch (2002).

Continuous Computation of SuspendedSediment Concentrations 

A complete SSC record was needed to compute the 

annual suspended-sediment loads (SSL) for the Wilson and 

Trask Rivers. When turbidity values were missing from the 

records, instantaneous SSC values were estimated by different 

methods, depending on streamflow conditions. For the 

simplest method, SSC values were estimated by interpolating 

between the model-computed SSC values immediately before 

and after the missing turbidity data. This method worked well 

for short time periods when streamflow conditions were steady 

or when turbidity was consistently increasing or decreasing. 

For longer periods, or during changing streamflow conditions, 

SSC was estimated by developing an OLS regression model of 

SSC using streamflow, rather than turbidity, as an explanatory 

variable. This method worked best when SSC and streamflow 

were strongly correlated. Prediction intervals were calculated 

for each of the regression models to provide error estimates for 

the continuous SSC. For each computed SSC, the upper and 

lower predictions were calculated at 90-percent confidence 

intervals (appendixes A and B).

Wilson River Suspended-Sediment Concentration Record

For most of the 3-year period, continuous SSC at the 

Wilson River was computed using the log10-transformed 

turbidity regression model and 15-minute turbidity data. 

Simple interpolations were used to estimate 11.0, 6.9, and 

11.5 percent of the annual records for water years 2012–14, 

respectively. Most of these estimates were during lowflow, low-turbidity, and low-sediment transport conditions 

when there were issues with algal biofouling of the optical 

turbidity sensor (appendix C). During water years 2012 and 

2013, several storms produced turbidity values greater than 

the maximum (410 FNU) included in the model calibration 

dataset. Therefore, the computed SSCs were designated 

as “estimated” in the SSC record. These estimated values 

comprised 0.05 and 0.14 percent of the annual records for 

water years 2012 and 2013, respectively.

Trask River Suspended-Sediment Concentration Record

For the Trask River, continuous SSCs were computed 

using a similar log10-transformed turbidity regression model, 

but with both 30- or 15-minute turbidity data. Simple 

interpolations were used to estimate 7.3, 4.3, and 15.8 percent 

of the annual records for water years 2012–14, respectively. 

Similarly, most of these estimates were during low-flow and 

low-turbidity conditions. As with the Wilson River, several 

storms produced turbidity values for the Trask River greater 

than the maximum 170 FNU included in the model calibration 

dataset. For these periods, the computed SSCs were described 

as “estimated,” as well, and comprised 0.02, 0.07, and 0.13 

percent, respectively, of the annual records for water years 

2012–14. Excessive leaf compaction and siltation during a 

storm in November 2011 resulted in the need to remove 12 

days of instream turbidity data. SSC values during this period 

were computed with a separate streamflow OLS regression 

model. The resulting computed SSC values were considered 

“estimated” and comprised 2.2 percent of the annual SSC 

record for water year 2012. 
Water-Quality Conditions and Suspended-Sediment Transport 7

Suspended-Sediment Load Calculations

The computed and estimated SSC values and 

corresponding streamflow data were used to calculate 

continuous SSL for the Wilson and Trask Rivers. The 

instantaneous SSL values were used to calculate daily SSL, 

which were then summed to calculate monthly and annual 

SSL. SSL was calculated as:

SSL = SSC*Q*c (2)

where 

SSL is suspended-sediment load, in pounds per 

second, 

SSC is suspended-sediment concentration, in 

milligrams per liter, 

Q is streamflow, in cubic feet per second, and 

c is the conversion coefficient to convert values to 

pounds per second (equal to 0.00006242). 

The instantaneous SSL values were multiplied by the 

appropriate time interval and summed to compute total daily 

SSL. The monthly and annual SSL values were calculated by 

summing the daily SSL values and converting to tons.

Water-Quality Conditions and 

Suspended-Sediment Transport

Water Temperature

Between water years 2012 and 2014, there were long 

periods when the Wilson and Trask Rivers did not meet the 

water temperature standard (fig. 3) established for coldwater habitat streams in Oregon (Oregon Department of 

Environmental Quality, 2005a, 2005b, 2014). Each year, 

between July and October, stream temperatures increased to 

at least 20 °C in both streams, well above the 7-day average 

maximum temperature criterion of 16 °C for summer seasonal 

periods or the 13 °C criterion for the remainder of the year 

(Oregon Department of Environmental Quality, 2014). High 

stream temperatures were likely exacerbated by the relatively 

low baseflow conditions observed each summer during the 

study period. Each year, 35 percent of the Wilson River 

temperature readings exceeded the established threshold, 

and about 33 percent of Trask River temperature readings 

exceeded the criteria.

A. Wilson River (USGS streamgage 14301500)

B. Trask River (USGS streamgage 14302480)

ODEQ criterion

ODEQ criterion

0

5

10

15

20

25

7-day average maximum temperature, in degrees Celsius

0

5

10

15

20

25

O DN J F M M J A J F M M J J A S O DN A J F M M J J A S A

2011 2012 2013 2014

J A S O DN

O DN J F M M J A J F M M J J A S O DN A J F M M J J A S A

2011 2012 2013 2014

J A S O DN

Figure 3. 7-day average maximum water temperature for the Wilson and Trask Rivers, northwestern Oregon, water years 

2012–2014. ODEQ Criterion line corresponds to Oregon Department of Environmental Quality water temperature criterion for 

seasonal core cold-water habitat (13 °C) and salmon and steelhead spawning (16 °C) designated streams. Shaded areas 

represent times when ODEQ Criterion was not met.
8 Water-Quality Conditions and Suspended-Sediment Transport, Wilson and Trask Rivers, Oregon, Water Years 2012–14

Dissolved Oxygen Concentration

Dissolved oxygen concentrations in the Wilson and 

Trask Rivers (fig. 4) consistently met the minimum 8.0 mg/L 

criterion for cold-water habitat streams in Oregon (Oregon 

Department of Environmental Quality, 2005a, 2005b, 2014). 

Dissolved oxygen concentrations in the Trask River never 

decreased to less than the 8.0 mg/L criterion. Dissolved 

oxygen concentrations in the Wilson River remained greater 

than the threshold for all but a small fraction of time in the 

summer of 2014, when a few isolated readings decreased to 

7.9 and 7.8 mg/L. There were 16 days with instantaneous 

readings less than 8.0 mg/L. Concentrations decreased to less 

than the criterion for less than 1 hour on 8 of those days. The 

longest period of concentrations less than 8.0 mg/L was on 

July 20, 2014, when readings did not meet the established 

criterion for about 6 hours.

Turbidity

Turbidity is an important water-quality indicator of 

sediment issues and can act as a surrogate for fine sediment 

transport (Bragg and Uhrich, 2010). The current Oregon 

Department of Environmental Quality standard for turbidity 

indicates that “turbidity causing activities” should not increase 

downstream turbidity by more than 10 percent (Oregon 

Department of Environmental Quality, 2014). However, it 

does not detail criteria for baseline stream conditions using 

turbidity as a water-quality impairment metric. 

The turbidity record for the Wilson and Trask Rivers for 

water years 2012–14 demonstrates periods of intermittently 

turbid water and increased suspended-sediment transport 

(fig. 5). However, given the previous history of flooding 

(National Weather Service, 2014) and the potential for future 

flooding, the turbidity observed during the study was likely 

low compared to each river’s potential. Between the two 

rivers, the Wilson River was consistently more turbid than 

the Trask River during storms, largely because of the higher 

streamflow conditions. During the study period, the highest 

daily median turbidity at both sites was recorded in water year 

2012 (fig. 5).

Suspended-Sediment Loads

Daily, monthly, and annual SSL were computed for each 

monitored watershed. Mean annual streamflows also were 

referenced to provide context for the annual SSL values. An 

estimated 597,000 t of suspended sediment entered Tillamook 

Bay during water years 2012–14. For both the Wilson and 

Trask Rivers, annual SSL was highest during water year 2012 

(240,000 and 69,900 t, respectively; table 4). Mean annual 

streamflow also was highest during water year 2012. At the 

Wilson River streamgage, most of the annual SSL in water 

year 2012 occurred from November 2011 to January 2012 

(65 percent of the total annual SSL), but the highest single 

month was March 2012 (34 percent; fig. 6). Similarly, for the 

Trask River, the SSL in November 2011 through January 2012 

comprised 58 percent and March 2012 comprised 36 percent 

of the annual SSL in water year 2012.

About one-half the annual SSL was produced in water 

year 2013 compared to water year 2012 for both rivers. Mean 

streamflow also was lower for the Wilson and Trask Rivers in 

water year 2013 compared to the previous year, as well. The 

only significant autumn or winter storm during water year 

2013 occurred in November 2012, although there were several 

smaller storms in December 2012 that added to the annual 

SSL. November and December 2012 accounted for 70 percent 

of the annual SSL at the Wilson River and 73 percent at the 

Trask River. A late summer/early autumn storm in September 

2013 contributed to the annual SSL at the end of water year 

2013.

Not

deployed

Not

deployed

Not

deployed

ODEQ criterion

O DN J F M M J A J F M M J J A S O DN A J F M M J J A S A

2011 2012 2013 2014

J A S O DN

6

7

8

9

10

12

13

11

14

Dissolved oxygen,

in milligrams per liter

Wilson River

Trask River

EXPLANATION

Figure 4. Dissolved oxygen data for the Wilson and Trask Rivers, northwestern Oregon, water years 2012–2014. ODEQ 

Criterion line corresponds to Oregon Department of Environmental Quality dissolved oxygen criterion for cold-water streams 

based on 30-day mean minimum daily concentration (8.0 milligrams per liter).
Water-Quality Conditions and Suspended-Sediment Transport 9

tac15-1012_fig 05

A. Wilson River (USGS streamgage 114301500)

B. Trask River (USGS streamgage 114302480)

O DN J F M M J A J F M M J J A S O DN A J F M M J J A S A

2011 2012 2013 2014

J A S O DN

O DN J F M M J A J F M M J J A S O DN A J F M M J J A S A

2011 2012 2013 2014

J A S O DN

Median daily turbidity, in Formazin Nephelometric Units 

0

50

100

150

200

250

300

350

400

Date

0

50

100

150

200

250

300

350

400

Figure 5. Daily median turbidity data for the Wilson and Trask Rivers, Oregon, water years 2012–2014.

Table 4. Annual suspended-sediment loads for the Wilson and Trask Rivers, northwestern Oregon, 

water years 2012–2014.

[USGS, U.S. Geological Survey; WY, water year]

USGS

station No. USGS station name Annual suspended-sediment load (tons)

WY2012 WY2013 WY2014

14301500 Wilson River near Tillamook 240,000 129,000 80,300

14302480 Trask River above Cedar Creek, near Tillamook 69,900 28,200 49,700

Annual SSL for the Wilson River was lower in water 

year 2014 than for the two prior water years. There were 

no significant autumn or winter storms, so only the minor 

storms in February and March supplied any sizable amount 

of sediment to the annual SSL (combined 67 percent). At 

the Trask River, annual SSL for water year 2014 ranked 

between the other two water years. The storms in December 

2013 contributed more to the annual SSL at the Trask River 

than at the Wilson River (30 and 17 percent, respectively). 

SSL in February (32 percent) and March (25 percent) were 

comparable at the Trask River. Both locations had their lowest 

mean annual streamflow during water year 2014.

Historical Streamflow Record

During the study, weather conditions were calm and peak 

annual streamflows were minimal compared to prior years. 

Between the autumn of 2011 and the autumn of 2014, peak 

streamflows in neither the Wilson nor Trask Rivers exceeded 

a 5-year recurrence interval, and the Trask River streamflow 

never exceeded a 2-year event (fig. 7). Because heavy rainfall 

and high streamflow are required to transport large sediment 

loads, the SSL calculated for this study did not represent the 

full sediment transport capacity by either system. Therefore, 

the regression models developed for this study better reflect 
10 Water-Quality Conditions and Suspended-Sediment Transport, Wilson and Trask Rivers, Oregon, Water Years 2012–14

tac15-1012_fig06

Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept.

2012

2013

2014

Wilson River

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

Suspended-sediment load, in tons

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

Suspended-sediment load, in tons

EXPLANATION Trask River

Figure 6. Monthly suspended-sediment loads for the Wilson and Trask Rivers, northwestern Oregon, water years 

2012–2014.

A. Wilson River (USGS streamgage 14301500)

B. Trask River (USGS streamgage 14302480)

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

Streamflow, in cubic feet per second

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

1915 1932 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015

2-year

5-year

25-year

50-year

2-year

5-year

25-year

50-year

Recurrence

interval

Recurrence

interval

Data

gap

Study

period

Study

period

Data

gap

Figure 7. Peak annual streamflow for the period of record for the (A) Wilson and (B) Trask Rivers, northwestern 

Oregon. Shaded area corresponds to 3-year study period. Dashed lines indicate streamflow recurrence intervals for 

2-year, 5-year, 25-year, and 50-year type events (Cooper, 2005).
Implications for Stream Conditions for Wilson and Trask Rivers 11

the lower range and magnitude of potential SSL in the Wilson 

and Trask Rivers. Given the consistency of the streamflow 

conditions during the study, the models presented do provide 

a strong baseline for SSL transported by a typical storm in a 

given year. To retain validity, the regression models should 

be revisited every few years to ensure that discrete sediment 

sources, such as landslides or changing channel conditions, 

have not altered the previously observed sediment transport 

conditions.

Implications for Stream Conditions for 

Wilson and Trask Rivers

Water-Quality Status of Wilson and Trask Rivers

The Oregon Department of Environmental Quality 

(2012) has listed segments of the Wilson and Trask Rivers 

for a variety of constituent impairments, including water 

temperature, dissolved oxygen, E. coli, fecal coliform, and 

other toxics and pollutants. Between water years 2012–14, 

the USGS continuously monitored water temperature, 

specific conductance, turbidity, and dissolved oxygen in the 

Wilson and Trask Rivers. Both rivers showed periods when 

established criterion were not met for water temperature. 

For example, water temperature routinely exceeded the 

temperature threshold each summer and remained so for the 

months leading into the autumn. Temperature in the Wilson 

and Trask Rivers exceeded the cold-water-habitat temperature 

criterion for about one-third of the year. Both streams did 

maintain compliance with the dissolved oxygen standard, as 

neither showed prolonged periods of low dissolved oxygen. 

However, summer conditions in both streams were near 

the dissolved oxygen threshold set by the State, including a 

brief period of slightly less than the 8.0 mg/L criterion for 

the Wilson River for parts of a few days in summer 2014. 

Sampling for other water-quality impairments, such as E. coli

and nutrients, was beyond the scope of this project.

Along with monitoring water-quality conditions, the 

USGS sampled and modeled suspended-sediment transport. 

Sedimentation was identified as one of the greatest basin-wide 

concerns for Tillamook Bay and has been a focal point for 

monitoring and management in the past (Tillamook Estuaries 

Partnership, 1999; Johnson and Drake, 2011). Although many 

North Coast rivers are considered as being in good condition, 

some water-quality constituents like biochemical oxygen 

demand (BOD) and phosphorus have shown a downward trend 

in recent years (Johnson and Drake, 2011). During this study, 

normal to less than normal precipitation limited the amount 

of erosion and subsequent suspended-sediment transport 

throughout the area. The annual transported totals were likely 

only a fraction of the material that would be transported during 

prolonged high streamflow or flooding conditions.

Watershed Characteristics That Influence 

Sediment Production

Historically, sedimentation issues have influenced much 

of the resource planning and land management practices in the 

Tillamook Bay area (Duck Creek Associates, 2008; Johnson 

and Drake, 2011). As such, there is a continuing desire to 

better understand sediment sources and transport. Currently, 

there are no defined criteria because there is a lack of sufficient 

sediment data (Oregon Department of Environmental Quality, 

2012). Data from this study can be used to supplement 

previous datasets from the State. 

Sediment affects many things, including fish populations, 

water-quality impairment, contaminant transport, efficacy of 

restoration projects, and shipping and navigation. Previous 

studies (Duck Creek Associates, 2008) have demonstrated 

that undisturbed soil erosion in the Wilson and Trask River 

watersheds does not produce excessive sedimentation because 

native soils are sufficiently permeable. However, issues arise 

when soils become compacted or when drainage from roads 

augments sediment production. Thus, potential processes for 

increased sediment production in the Tillamook Bay watershed 

would include runoff from logging roads, storm-driven debris 

flows, erosion of freshly harvested timber plots, and other 

disruptive land use and development practices (Follansbee and 

Stark, 1998; Komar and others, 2004; Duck Creek Associates, 

2008; Arismendi and others, 2013; Hatten and others, 2013). 

Therefore, any effort to impede excessive sedimentation and 

limit sediment transport relates directly to the reduction of soil 

disruptions in the Wilson and Trask River watersheds.

Trask River Watershed—Integrating Science

The Trask River watershed is heavily studied because 

resource agencies, universities, and timber companies are 

interested in how the basin is managed. In any area where 

landscape disturbance may occur, such as with active logging, 

there is always a potential for impacts to stream health. Recent 

studies (Arismendi and others, 2013) have begun to analyze 

what impact forest practices have on turbidity, SSC, and 

SSL. Early results indicate a possible increase in turbidity 

and SSC from roads used to access the new timber areas. In 

addition to assessing sediment, other studies like Reiter and 

others (2013) have explored the effect canopy shading and 

other thermal processes have on stream temperatures and 

how conditions may change because of changing climate or 

continued landscape alterations. Linking upstream landscape 

activity and water quality to lower watershed conditions would 

be a valuable next step for integrating science and better 

understanding stream functions in the Trask River.
12 Water-Quality Conditions and Suspended-Sediment Transport, Wilson and Trask Rivers, Oregon, Water Years 2012–14

Tillamook Southern Flow Corridor Project

One aspect of ecosystem health that benefits from stream 

monitoring is local restoration projects. At the confluence 

of the Wilson and Trask Rivers near Tillamook Bay, there is 

a proposed plan to reduce flood damage and restore habitat 

along the Tillamook Southern Flow Corridor (Federal 

Emergency Management Agency, 2014). The current proposal 

has undergone an environmental impact assessment and five 

restoration alternatives have been proposed for the area. The 

favored alternative focuses on the removal of 7–10 mi of 

levees to allow flood waters to flow across the project area, 

restoring 526 acres of mostly farmland back to tidal wetlands 

(Northwest Hydraulic Consultants, 2011). Monitoring SSL 

on the Wilson and Trask Rivers can help planners determine 

how much new material will enter the project area, when it 

will be entering, and how it might affect fluvial and tidal flow 

dynamics of the restored area. Long-term data collection also 

helps identify any temporal trends in water temperature or 

dissolved oxygen, components necessary for maintaining a 

healthy aquatic habitat. 

Summary and Conclusions

The U.S. Geological Survey (USGS) investigated and 

monitored water-quality conditions and suspended-sediment 

transport in the Wilson and Trask Rivers, northwestern 

Oregon. The study established a water-quality and suspendedsediment monitoring network for the two rivers, which are 

major tributaries to Tillamook Bay. The purpose of the study 

was to provide water-resource managers with continuous 

real-time water temperature, specific conductance, turbidity, 

and dissolved oxygen data for the Wilson and Trask Rivers. In 

addition, USGS researchers provided estimates of suspendedsediment loads for the two rivers during a 3-year study period 

(October 2011–September 2014; water years 2012–14).

Four main conclusions can be drawn from this USGS 

monitoring and modeling effort for the Wilson and Trask 

Rivers:

1. During years when conditions were typical (no drought 

or flooding), water temperature did not meet established 

criterion for cold-water habitat. These conditions will 

likely be exacerbated during drought years or during 

months with periods of prolonged hot weather.

2. During the study, dissolved oxygen generally met the 

criterion for migrating or spawning salmonids. Given 

the standard set by the State of Oregon, there were very 

few instances during the study when dissolved oxygen 

concentrations decreased to less than the established 

threshold. 

3. Suspended-sediment transport likely remains an issue to 

fish populations, restoration efforts, and even navigation; 

however, given the average rainfall observed during the 

study, low streamflow conditions did not mobilize and 

transport significant amounts of sediment to Tillamook 

Bay. Nonetheless, baseline characterization did provide 

context for expected suspended-sediment loads in a 

given year. 

4. Instream monitoring provides data to assist land and 

resource managers make informed decisions. For 

example in this study, water temperature was shown to 

still be a potential concern for spawning and migrating 

fish. As restoration efforts continue in the Wilson and 

Trask Rivers, monitoring can be instrumental in the 

management of stream temperature and sedimentation.

Acknowledgments

We thank York Johnson from the Tillamook Estuaries 

Partnership and Oregon Department of Environmental Quality 

and members of the Oregon Watershed Enhancement Board 

for their vision, support, and funding for this research. We 

thank Chauncey Anderson (U.S. Geological Survey) for his 

guidance and oversight. We thank U.S. Geological Survey 

employees Amy Brooks, Cassandra Smith, Mary Janet, 

Stewart Rounds, Jami Goldman, John Williams, and David 

Piatt for their assistance and resources that helped keep 

everything running smoothly. Lastly, we thank Leo Adams for 

his responsiveness and tireless efforts in helping to keep the 

Trask River water-quality monitor up and running.

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Techniques and Methods, book 3, chap A8, 87 p., http://

pubs.usgs.goc/tm/tm3-a8/.

U.S. Geological Survey, 2006, Collection of water samples 

(ver. 2.0): U.S. Geological Survey Techniques of WaterResources Investigations, book 9, chap. A4, September 

2006, accessed December 2014, at http://pubs.water.usgs.

gov/twri9A4/.

U.S. Geological Survey, 2015a, National Water Information 

System Web Interface—Wilson River near Tillamook, 

Oregon: accessed June 10, 2015, at http://waterdata.usgs.

gov/or/nwis/inventory/?site_no=14301500&agency_

cd=USGS.

U.S. Geological Survey, 2015b, National Water Information 

System Web Interface—Trask River above Cedar Creek, 

near Tillamook, Oregon: accessed June 10, 2015, at 

http://waterdata.usgs.gov/or/nwis/inventory/?site_

no=14302480&agency_cd=USGS.

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.

YSI, 2013, Anti-fouling C-Spray protective probe solution: 

Website accessed February 2015, at http://www.ysi.com/

accessoriesdetail.php?Anti-fouling-C-Spray-ProtectiveProbe-Solution-129.
Appendix A 15

Appendix A. Wilson River Suspended-Sediment Concentration Record

Model Calibration Dataset

Suspended-sediment concentration (SSC) 

samples were collected using U.S. Geological 

Survey (USGS) protocols and were stored online in 

the National Water Information System database. 

Samples were collected over nearly the entire range 

of turbidity and streamflow conditions for the 3 

years analyzed (water years 2012–14). The ordinary 

least-squares regression model was based on 25 

equal-width-increment (EWI) sampling events where 

concurrent instream turbidity and streamflow data 

were available. The model inputs were either the 

event averages of multiple sample sets (EWI-A and 

EWI-B) or from single samples (EWI, table A1).

Methods for Assigning Turbidity and 

Streamflow

To assign turbidity values to discrete SSC 

samples, continuous (15-minute) instream turbidity 

data were averaged over the period of EWI sample 

collection. Turbidity values were averaged starting 

with the data value immediately before the start 

of the EWI collection period and ending with the 

data value immediately after the end of the EWI 

collection period. Streamflow values were timeweighted between the two 15-minute data values 

before and after the mean time of the SSC sample. 

For mean samples times collected on a 15-minute 

mark, single unit values of streamflow were used 

(table A1). 

Model Development

All regression analyses were done with the 

“Turbidity Sediment Spreadsheet” using the methods 

described in Rasmussen and others (2009). Turbidity 

and streamflow were evaluated separately and 

together, log10-transformed and untransformed, as 

possible surrogates. Turbidity and streamflow were 

too highly correlated to one another (high variance 

inflation factor; VIF = 13) to use both parameters. 

The log10-transformed turbidity model was chosen 

on the basis of residual plots, adjusted coefficient 

of determination, model standard percent error, 

probability plot correlation coefficient, and prediction error sum of 

squares statistics. Residual plots for evaluating variance, normality, 

homoscedasticity, and curvature are provided (fig. A1). For the 

log10-transformed model, computed SSC values were multiplied by a 

retransformation bias correction factor. 

Model Information

The model used for the Wilson River is represented as:

log10SSC = 0.361 + 1.05 log10TB (A1)

–See equation 1 and table 3

–Number of measurements = 25

–Standard error (SE) = 0.20

–Upper model standard percent error (MSPE) = +57.2 percent

–Lower model standard percent error (MSPE) = -36.4 percent

–Adjusted coefficient of determination (Adj R2) = 0.95

–Probability plot correlation coefficient (PPCC) = 0.97

–Prediction error sum-of-squares (PRESS) = 1.17

–Duan bias correction factor (BCF) = 1.11

Suspended-Sediment Concentration Record

SSC time-series data were computed from the 15-minute turbidity 

data. During short periods of missing or deleted turbidity data, the SSC 

unit values were estimated by interpolating between the computed SSC 

values. The daily mean SSC estimated dates were:

Nov. 22, 2011 Jan. 3–5, 2012 Mar. 16, 2013 Jan. 22, 2014

Nov. 26–28, 2011 Mar. 12–13, 2012 June 5–6, 2013 Mar. 14, 2014

Dec. 24–25, 2011 Mar. 21–23, 2012 June 20–25, 2013 May 23–29, 2014

Apr. 25, 2012 July 14, 2013 June 12–July 10, 2014

May 16–17, 2012 July 17, 2014

June 26, 2012 Aug. 5–11, 2014

July 2–3, 2012 Aug. 24–26, 2014

July 5, 2012

July 7, 2012

July 17–24, 2012

Aug. 19, 2012

Nov. 3–5, 2012

Nov. 19, 2012

Mar. 2–3, 2012

Summary statistics for the regression model dataset and the 

continuous turbidity and SSC records are provided in table A2. The 

continuous SSC data and 90-percent prediction intervals are shown in 

figures A2–A4.
16 Water-Quality Conditions and Suspended-Sediment Transport, Wilson and Trask Rivers, Oregon, Water Years 2012–14

Table A1. Suspended-sediment sample and model calibration data for the Wilson River, northwestern Oregon.

[Sample type/set: EWI is a single sample; EWI-A/B/C are consecutive samples and are averaged into an event average. Abbreviations: EWI, equal-widthincrement; FNU, Formazin Nephelometric Unit; ft3

/s, cubic feet per second; mg/L, millligrams per liter; μm, micrometers]

Date and time

(local Pacific time)

Sample

type/set

Turbidity

(FNU)

Streamflow

(ft3

/s)

Suspendedsediment 

concentration

(mg/L)

Sediment 

finer than

63 μm

(percent)

Record No.

11-14-2011 10:55 EWI-A 2.1 556 2 – 1200045

11:02 EWI event average 2.1 556 2 – 1201907

11:10 EWI-B 2.1 556 2 – 1200046

11-22-2011 15:48 EWI 380 16,300 966 73 1200030

11-29-2011 13:10 EWI 5.4 1,860 8 79 1200065

12-07-2011 16:20 EWI 1.4 715 2 – 1200090

01-19-2012 13:35 EWI-A 68 9,070 618 20 1200136

14:05 EWI-B 71 9,360 446 30 1200137

14:08 EWI event average 71 9,440 527 27 1201908

14:45 EWI-C 75 9,900 516 32 1200140

01-24-2012 16:43 EWI 26 5,200 115 38 1200149

01-25-2012 11:00 EWI-A 76 9,630 245 52 1200152

11:09 EWI event average 74 9,560 260 48 1200153

11:18 EWI-B 72 9,500 276 45 1200153

02-06-2012 16:05 EWI 0.7 1,140 4 50 1200205

03-15-2012 12:50 EWI-A 350 18,500 1,530 56 1201909

13:05 EWI event average 370 18,600 1,630 55 1200225

13:20 EWI-B 390 18,700 1,730 54 1201910

13:47 EWI-A 390 18,800 1,690 54 1201911

14:01 EWI event average 380 18,800 1,680 54 1200231

14:14 EWI-B 380 18,700 1,660 54 1201912

18:14 EWI 280 17,500 1,090 51 1200235

03-16-2012 10:58 EWI 130 9,980 359 59 1200240

05-23-2012 15:50 EWI-A 1 1,170 4 – 1200333

16:06 EWI event average 1 1,160 4 – 1201913

16:22 EWI-B 1 1,160 3 – 1200334

10-29-2012 11:55 EWI-A 69 7,740 216 48 1300124

12:20 EWI event average 66 7,520 220 46 1300127

12:35 EWI-B 64 7,390 225 43 1300125

12:55 EWI-C 63 7,200 223 44 1300126

10-30-2012 12:35 EWI-A 17 3,880 46 39 1301527
Appendix A 17

Table A1. Suspended-sediment sample and model calibration data for the Wilson River, northwestern Oregon.—Continued

Date and time

(local Pacific time)

Sample

type/set

Turbidity

(FNU)

Streamflow

(ft3

/s)

Suspendedsediment 

concentration

(mg/L)

Sediment 

finer than

63 μm

(percent)

Record No.

12:55 EWI event average 17 3,960 44 42 1300134

13:15 EWI-B 17 4,040 42 44 1301528

10-31-2012 11:51 EWI-A 27 5,400 60 52 1300141

12:08 EWI event average 27 5,400 60 52 1301529

12:25 EWI-B 27 5,400 60 – 1300143

11-19-2012 12:59 EWI-A 380 18,400 929 65 1300063

13:26 EWI Event Average 375 18,800 950 70 1301530

13:53 EWI-B 370 19,200 971 74 1301531

14:35 EWI-A 410 19,700 1,030 77 1300072

14:42 EWI event average 410 19,800 1,060 76 1301532

14:50 EWI-B 410 19,900 1,100 74 1300074

11-20-2012 13:24 EWI-A 150 8,920 295 76 1300085

13:29 EWI event average 150 8,900 295 76 1301533

13:34 EWI-B 150 8,890 295 75 1300087

11-21-2012 12:14 EWI-A 50 5,470 106 66 1300101

12:22 EWI event average 50 5,450 110 62 1301534

12:31 EWI-B 50 5,430 114 58 1300102

12-05-2012 10:35 EWI-A 51 6,600 110 58 1300184

10:46 EWI event average 50 6,580 110 56 1301535

10:55 EWI-B 48 6,570 110 55 1300186

09-29-2013 10:24 EWI-A 53 6,550 127 59 1301536

10:38 EWI event average 54 6,620 126 57 1300854

10:59 EWI-B 54 6,690 124 55 1301537

11-19-2013 09:52 EWI-A 80 6,840 180 60 1400037

10:06 EWI event average 80 6,830 185 58 1400040

10:20 EWI-B 79 6,820 190 55 1400042

12-02-2013 14:05 EWI-A 72 7,130 156 62 1400077

14:19 EWI event average 71 7,040 150 66 1400775

14:34 EWI-B 70 6,950 143 69 1400080

02-12-2014 11:03 EWI-A 130 10,100 333 66 1400254

11:19 EWI event average 130 9,790 322 65 1400776

11:35 EWI-B 130 9,480 312 64 1400255
18 Water-Quality Conditions and Suspended-Sediment Transport, Wilson and Trask Rivers, Oregon, Water Years 2012–14

Table A2. Summary statistics for model calibration and continuous turbidity and suspended-sediment concentration for the 

Wilson River, northwestern Oregon.

[Continuous data: SSC, suspended-sediment concentration; WY, water year. Abbreviations: FNU, Formazin Nephelometric Unit; mg/L, millligrams per liter]

Summary 

statistic

Model calibration data

(number of sampling 

events = 25)

Continuous data (15-minute interval)

WY2012 WY2013 WY2014

Turbidity

(FNU)

SSC 

(mg/L)

Turbidity

(FNU)

SSC

(mg/L)

Turbidity

(FNU)

SSC

(mg/L)

Turbidity

(FNU)

SSC

(mg/L)

Minimum 1 2 0 0 0.2 0.5 0.1 0.2

Maximum 410 1,680 600 2,110 540 1,890 250 843

Median 128 411 0.6 1.5 1.1 2.8 1 2.5

Mean 71 185 8.2 25.7 5.6 16.9 4.6 13.7

R2 = 0.95

Turbidity, in Formazin Nephelometric Units 

Suspended-sediment concentration (SSC), in milligrams per liter

Regression computed SSC

Regression computed SSC

Residual log (SSC)

Normal quantiles

Residual log(SSC)

SSC, in milligrams per liter

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

1 10 100 1,000 10,000

1

10

100

1,000

10,000

1 10 100 1,000 10,000

-0.6

-0.4

-0.2

0.0

0.2

0.4

-3 -2 -1 0 1 2 3

0.1

1

10

100

1,000

10,000

0 1 10 100 1,000

EXPLANATION

Samples

Power (log)

Upper and lower 

90-percent

prediction 

interval

Figure A1. Ordinary least-squares regression model plots for the Wilson River, northwestern Oregon. 
Appendix A 19

tac15-1012_fig A2 tac15-1012_fig A3

log10SSC = 0.361 + 1.05 log10TB

log10SSC = 0.361 + 1.05 log10TB

2011 2012

October November December January February March

2012

April May June July August September

Suspended-sediment concentration (SSC),

in milligrams per liter

0.1

1

10

100

1,000

10,000

Suspended-sediment concentration (SSC),

in milligrams per liter

0.1

1

10

100

1,000

10,000

Upper and lower 90-percent

prediction interval

Samples

Time-series estimates

EXPLANATION

A

B

Figure A2. Suspended-sediment concentration (SSC) data, 90-percent prediction intervals, and sample data at the Wilson 

River, northwestern Oregon, October 2011–March 2012 and April–September 2012.
20 Water-Quality Conditions and Suspended-Sediment Transport, Wilson and Trask Rivers, Oregon, Water Years 2012–14

tac15-1012_fig A3

log10SSC = 0.361 + 1.05 log10TB

2013

April May June July August September

log10SSC = 0.361 + 1.05 log10TB

0.1

1

10

100

1,000

10,000

Suspended-sediment concentration (SSC),

in milligrams per liter

0.1

1

10

100

1,000

10,000

A

B

Suspended-sediment concentration (SSC),

in milligrams per liter

Upper and lower 90-percent

prediction interval

Samples

Time-series estimates

EXPLANATION

2012 2013

October November December January February March

Figure A3. Suspended-sediment concentration (SSC) data, 90-percent prediction intervals, and sample data at the Wilson 

River, northwestern Oregon, October 2012–March 2013 and April–September 2013.
Appendix A 21

tac15-1012_fig A4

log10SSC = 0.361 + 1.05 log10TB

2014

2013 2014

April May June July August September

A

B

log10SSC = 0.361 + 1.05 log10TB

Suspended-sediment concentration (SSC),

in milligrams per liter

0.1

1

10

100

1,000

10,000

Suspended-sediment concentration (SSC),

in milligrams per liter

0.1

1

10

100

1,000

10,000

Upper and lower 90-percent

prediction interval

Samples

Time-series estimates

EXPLANATION

October November December January February March

Figure A4. Suspended-sediment concentration (SSC) data, 90-percent prediction intervals, and sample data at the Wilson 

River, northwestern Oregon, October 2012–March 2013 and April–September 2013.
22 Water-Quality Conditions and Suspended-Sediment Transport, Wilson and Trask Rivers, Oregon, Water Years 2012–14

This page intentionally left blank.
Appendix B 23

Appendix B. Trask River Suspended-Sediment Concentration Record

Model Calibration Dataset

All suspended-sediment concentration (SSC) samples 

were collected using USGS protocols and are stored in the 

U.S. Geological Survey National Water Information System 

database. Samples were collected over nearly the entire 

range of turbidity and streamflow conditions for the 3 years 

analyzed (water years 2012–14). The ordinary least-squares 

regression model was based on 23 equal-width-increment 

(EWI) sampling events where concurrent instream turbidity 

and streamflow data were available. The model inputs were 

either the event averages of multiple sample sets (EWI-A and 

EWI-B) or from single samples (EWI, table B1).

Time-of-Travel Correction

The location of the water-quality monitor and streamgage 

was about 4 river miles (21,120 ft) upstream of the sampling 

location on the Long Prairie Road Bridge. To account for this 

difference, all suspended-sediment sample times were adjusted 

for time-of-travel. The computation used the mean velocity of 

all streamflow measurements from water years 2008–2014 and 

two high-streamflow measurements from water years 1998 

and 1999 (47 measurements total). The time-of-travel during 

the streamflow measurements was computed using:

1.3*

d

v t

c = (B1)

where 

t is time-of-travel (hr), 

d is the distance (ft),

v is the mean velocity (ft/s), and 

c is a conversion constant to convert seconds to 

hours (equal to 3,600 s/hr). 

The discrete measured streamflow and associated timeof-travel values were plotted and a power function trend 

line was fit to the data. The resulting equation was used to 

determine the time-of-travel correction for each suspendedsediment sample based on the streamflow at the actual mean 

sample time:

0.294 t Q 14* − = (B2)

where 

t is time-of-travel (hr), and 

Q is streamflow (ft3/s). 

The time-of-travel adjustment was subtracted from the actual 

mean sample times for each sample for assigning streamflow 

values. Adjusted begin and end sample times also were 

used for computing average turbidity values for the samples 

(table B1).

Methods for Assigning Turbidity and Streamflow

To assign turbidity values to discrete SSC samples, 

continuous (30- or 15-minute) instream turbidity data were 

averaged over the period of EWI sample collection. Turbidity 

values were averaged starting with the data value immediately 

before the start time (adjusted for time-of-travel) of the EWI 

and ending with the data value immediately after the end time 

(adjusted for time-of-travel) of the EWI. Streamflow values 

were time-weighted between the two 30- or 15-minute data 

values before and after the mean time (adjusted for time-oftravel) of the SSC sample. For mean samples times on a 30- or 

15-minute mark, single unit values of streamflow were used 

(table B2).

Model Development

Regression analyses were done with the “Turbidity 

Sediment Spreadsheet” using the methods described in the 

Rasmussen and others (2009). Turbidity and streamflow were 

evaluated separately and together, log10-transformed and 

untransformed, as possible surrogates. The log10-transformed 

turbidity model was chosen on the basis of residual plots, 

adjusted coefficient of determination, model standard percent 

error, probability plot correlation coefficient, and prediction 

error sum of squares statistics. Residual plots for evaluating 

variance, normality, homoscedasticity, and curvature are 

provided in figure B1. For the log10-transformed model, 

computed SSC values were multiplied by a retransformation 

bias correction factor.
24 Water-Quality Conditions and Suspended-Sediment Transport, Wilson and Trask Rivers, Oregon, Water Years 2012–14

Model Information

The model used for the Trask River site is 

represented as:

log10SSC = 0.331 + 1.06 log10TB (B3)

–See equation 1 and table 3

–Number of measurements = 23

–Standard error (SE) = 0.15

–Upper model standard percent error (MSPE) = +42.6 percent

–Lower model standard percent error (MSPE) = -29.9 percent

–Adjusted coefficient of determination (Adj R2

) = 0.96

–Probability plot correlation coefficient (PPCC) = 0.94

–Prediction error sum-of-squares (PRESS) = 0.60

–Duan bias correction factor (BCF) = 1.06

Suspended-Sediment Content Record

SSC time-series data were computed from the 

15-minute turbidity data. During short periods of 

missing or deleted turbidity data, the SSC unit values 

were estimated by interpolating between the computed 

SSC values. 

The daily mean SSC estimated dates were:

Nov. 17–28, 2011 May 11–16, 2012 Apr. 28–29, 2013 Jan. 13–14, 2014

Dec. 4–7, 2011 May 24–26, 2012 May 15, 2013 Feb. 6–7, 2014

July 3, 2012 May 20, 2013 Feb. 12–15, 2014

July 14–23, 2012 June 5–7, 2013 Feb. 17–19, 2014

Oct. 24, 2012 June 23–27, 2013 Feb. 22–25, 2014

Oct. 29, 2012 Oct. 4, 2013 Mar. 14–16, 2014

Nov. 1–4, 2012 Oct. 8, 2013 May 23–27, 2014

Nov. 19–21, 2012 Oct. 24–30, 2013 May 30–July 1, 2014

Nov. 26–29, 2012 Nov. 19, 2013 Aug. 3–5, 2014

Nov. 22–23, 2013

Dec. 2, 2013

Dec. 6, 2013

Dec. 9, 2013

Dec. 19, 2013

Summary statistics for the regression model dataset and the 

continuous turbidity and SSC records are provided in table B2. The 

continuous SSC data and 90-percent prediction intervals are shown 

in figures B2–B4.

Table B1. Suspended-sediment sample and model calibration data for the Trask River, northwestern Oregon.

[Sample type/set: EWI is a single sample; EWI-A/B/C are consecutive samples and are averaged into an event average. Abbreviations: EWI, equal-widthincrement; FNU, Formazin Nephelometric Unit; ft3

/s, cubic feet per second; mg/L, millligrams per liter; μm, micrometers]

Date and time

(local Pacific time)

Date and time

(time-of-travel

adjusted)

Sample

type/set

Turbidity

(FNU)

Streamflow

(ft3

/s)

Suspendedsediment 

concentration

(mg/L)

Sediment 

finer than

63 μm

(percent)

Record No.

11-14-2011 13:15 11-14-2011 10:44 EWI-A 1.6 342 3 – 1200066

13:27 11-14-2011 10:57 EWI event average 1.6 342 3 – 1201914

13:40 11-14-2011 11:09 EWI-B 1.5 342 2 – 1200067

11-29-2011 10:18 11-29-2011 08:37 EWI 4 1,390 10 50 1200069

12-07-2011 13:55 12-07-2011 11:49 EWI 1.2 651 3 – 1200103

01-19-2012 11:22 01-19-2012 10:19 EWI-A 61 6,010 474 29 1200158

11:35 01-19-2012 10:38 EWI event average 66 6,160 368 45 1200160

12:00 01-19-2012 10:57 EWI-B 71 6,330 261 60 1200161

16:05 01-19-2012 15:06 EWI-A 150 8,740 410 62 1200162

16:17 01-19-2012 15:19 EWI event average 150 8,750 413 65 1200163

16:30 01-19-2012 15:32 EWI-B 150 8,770 416 67 1200164

01-24-2012 15:30 01-24-2012 14:16 EWI-A 16 3,760 74 37 1200165

15:37 01-24-2012 14:25 EWI event average 16 3,810 71 39 1200166

15:47 01-24-2012 14:34 EWI-B 16 3,850 67 40 1200167

01-25-2012 08:42 01-25-2012 07:38 EWI-A 71 6,840 177 72 1200168

08:55 01-25-2012 07:52 EWI event average 70 6,820 180 70 1200169

09:09 01-25-2012 08:05 EWI-B 69 6,790 182 67 1200170

02-07-2012 13:01 02-07-2012 11:07 EWI 1.4 882 5 33 1200206
Appendix B 25

Table B1. Suspended-sediment sample and model calibration data for the Trask River, northwestern Oregon.—Continued

Date and time

(local Pacific time)

Date and time

(time-of-travel

adjusted)

Sample

type/set

Turbidity

(FNU)

Streamflow

(ft3

/s)

Suspendedsediment 

concentration

(mg/L)

Sediment 

finer than

63 μm

(percent)

Record No.

03-15-2012 15:59 03-15-2012 15:03 EWI-A 170 10,400 463 64 1200243

16:08 03-15-2012 15:13 EWI event average 170 10,400 448 68 1200244

16:17 03-15-2012 15:23 EWI-B 170 10,500 433 71 1200245

16:40 03-15-2012 15:44 EWI-A 170 10,300 417 72 1200246

16:50 03-15-2012 15:54 EWI event average 170 10,200 415 70 1200247

17:01 03-15-2012 16:05 EWI-B 170 10,200 412 67 1200248

03-16-2012 09:10 03-16-2012 08:06 EWI-A 71 6,860 195 65 1200249

09:25 03-16-2012 08:21 EWI event average 70 6,780 191 67 1200250

09:40 03-16-2012 08:36 EWI-B 69 6,700 186 69 1200251

05-23-2012 10:31 05-23-2012 08:37 EWI-A 4.3 904 3 – 1200335

10:42 05-23-2012 08:48 EWI event average 4.4 905 4 – 1201915

10:53 05-23-2012 08:59 EWI-B 4.4 909 5 – 1200336

10-29-2012 14:40 10-29-2012 13:27 EWI-A 27 4,270 58 69 1300144

15:15 10-29-2012 14:01 EWI event average 25 4,200 58 69 1301544

15:20 10-29-2012 14:06 EWI-B 25 4,180 54 67 1300145

15:45 10-29-2012 14:30 EWI-C 24 4,100 62 70 1300146

10-30-2012 15:06 10-30-2012 13:48 EWI-A 8.3 3,100 21 67 1300147

15:20 10-30-2012 14:02 EWI event average 8.6 3,140 21 68 1301545

15:35 10-30-2012 14:17 EWI-B 8.9 3,160 21 68 1300148

10-31-2012 09:33 10-31-2012 08:17 EWI-A 8.7 3,360 17 73 1300149

09:47 10-31-2012 08:31 EWI event average 8.8 3,370 18 73 1301546

10:02 10-31-2012 08:45 EWI-B 8.9 3,400 18 72 1300150

11-19-2012 10:17 11-19-2012 09:16 EWI-A 74 7,260 217 76 1300089

10:31 11-19-2012 09:31 EWI event average 74 7,330 202 77 1301547

10:45 11-19-2012 09:45 EWI-B 75 7,450 186 78 1300090

11-20-2012 11:09 11-20-2012 10:04 EWI-A 62 6,460 242 38 1300091

11:26 11-20-2012 10:21 EWI event average 62 6,460 233 41 1301548

11:43 11-20-2012 10:38 EWI-B 61 6,330 223 43 1300092

11-21-2012 10:29 11-21-2012 09:17 EWI-A 21 4,360 47 67 1300104

10:42 11-21-2012 09:30 EWI event average 20 4,350 52 60 1301549

10:55 11-21-2012 09:43 EWI-B 20 4,360 57 52 1300105

12-05-2012 08:25 12-05-2012 07:17 EWI-A 23 5,300 54 64 1300189

08:49 12-05-2012 07:41 EWI event average 22 5,250 52 67 1301550

09:14 12-05-2012 08:05 EWI-B 22 5,240 49 70 1300190

09-29-2013 12:50 09-29-2013 11:31 EWI-A 11 3,210 19 71 1300870

13:00 09-29-2013 11:46 EWI event average 10 3,220 21 68 1300872

13:20 09-29-2013 12:01 EWI-B 9.7 3,230 22 65 1300873

11-19-2013 11:39 11-19-2013 10:23 EWI-A 28 3,610 50 75 1400048

11:50 11-19-2013 10:35 EWI event average 27 3,630 61 64 1400050

12:02 11-19-2013 10:47 EWI-B 26 3,630 72 52 1400051

12-02-2013 11:30 12-02-2013 10:29 EWI-A 150 7,880 317 83 1400083

12:03 12-02-2013 11:02 EWI event average 150 7,800 302 84 1400780

12:05 12-02-2013 11:03 EWI-B 150 7,780 303 84 1400084

12:35 12-02-2013 11:33 EWI-C 140 7,630 287 84 1400085

02-12-2014 14:24 02-12-2014 13:14 EWI-A 53 4,940 274 33 1400259

14:34 02-12-2014 13:24 EWI event average 53 4,880 242 43 1400781

14:45 02-12-2014 13:35 EWI-B 53 4,850 151 52 1400260
26 Water-Quality Conditions and Suspended-Sediment Transport, Wilson and Trask Rivers, Oregon, Water Years 2012–14

Table B2. Summary statistics for model calibration and continuous turbidity and suspended-sediment concentration for the 

Trask River, northwestern Oregon.

[Continuous data: SSC, suspended-sediment concentration; WY, water year. Abbreviations: FNU, Formazin Nephelometric Unit; mg/L, millligrams per liter]

Summary 

statistic

Model calibration data

(number of sampling 

events = 23)

Continuous data (15-minute interval)

WY2012 WY2013 WY2014

Turbidity

(FNU)

SSC 

(mg/L)

Turbidity

(FNU)

SSC

(mg/L)

Turbidity

(FNU)

SSC

(mg/L)

Turbidity

(FNU)

SSC

(mg/L)

Minimum 1 3 0 0 0 0 0 0

Maximum 170 448 180 558 302 966 342 1,100

Median 52 147 1.2 3 1 2.3 1 2.3

Mean 25 61 4.7 14.1 2.8 7.4 4 11

Turbidity, in Formazin Nephelometric Units

Suspended-sediment concentration (SSC), in milligrams per liter

Regression computed SSC

Regression computed SSC

Residual log (SSC)

Normal quantiles

Residual log(SSC)

SSC, in milligrams per liter

-3 -2 -1 0 1 2 3

1 10 100 1,000

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

1 10 100 1,000

1

10

100

1,000

1 10 100 1,000

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

10

100

1,000

R2 = 0.96

1

EXPLANATION

Samples

Power (log)

Upper and lower 

90-percent

prediction 

interval

Figure B1. Ordinary least-squares regression model plots for the Trask River, northwestern Oregon. 
Appendix B 27

tac15-1012_fig B2

2011 2012

October November December January February March April May

2012

May June July August September

log10SSC = 0.331 + 1.06 log10TB

log10SSC = 0.331 + 1.06 log10TB

log10SSC = 0.331 + 1.06 log10TB

A

B

C

Suspended-sediment concentration (SSC), in milligrams per liter

0.1

November 2011 December

13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1 2 1

10

100

1,000

1,000

0.1

1

10

100

1

10

100

1,000

Upper and lower 90-percent

prediction interval

Samples

Time-series estimates

EXPLANATION

Figure B2. Suspended-sediment concentration (SSC) data, 90-percent prediction intervals, and sample data at the Trask 

River, northwestern Oregon, October 1, 2011–May 22, 2012, November 18–28, 2011, and May 22–September 30, 2012.
28 Water-Quality Conditions and Suspended-Sediment Transport, Wilson and Trask Rivers, Oregon, Water Years 2012–14

tac15-1012_fig B3

log10SSC = 0.331 + 1.06 log10TB

April May June July August September

log10SSC = 0.331 + 1.06 log10TB

Suspended-sediment concentration (SSC),

in milligrams per liter

0.1

1

10

100

1,000

B

0.1

1

10

100

1,000

10,000

2012 2013

October November December January February March

A

Suspended-sediment concentration (SSC),

in milligrams per liter

Upper and lower 90-percent

prediction interval

Samples

Time-series estimates

EXPLANATION

2013

Figure B3. Suspended-sediment concentration (SSC) data, 90-percent prediction intervals, and sample data at the Trask 

River, northwestern Oregon, October 2012–March 2013 and April–September 2013.
Appendix B 29

tac15-1012_fig B4

log10SSC = 0.331 + 1.06 log10TB

2014

April May June July August September

log10SSC = 0.331 + 1.06 log10TB

2013 2014

October November December January February March

A

Suspended-sediment concentration (SSC),

in milligrams per liter

0.1

1

10

100

1,000

B

Suspended-sediment concentration (SSC),

in milligrams per liter

0.1

1

10

100

1,000

10,000

Upper and lower 90-percent

prediction interval

Samples

Time-series estimates

EXPLANATION

Figure B4. Suspended-sediment concentration (SSC) data, 90-percent prediction intervals, and sample data at the Trask 

River, northwestern Oregon, October 2013–March 2014 and April–September 2014.
30 Water-Quality Conditions and Suspended-Sediment Transport, Wilson and Trask Rivers, Oregon, Water Years 2012–14

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Appendix C 31

During deployment, instrument sensors at both stations 

occasionally experienced temporary periods of data that did 

not meet established calibration specifications (Wagner and 

others, 2006). Measures were taken to minimize common 

problems of sensor deployment in high gradient mountain 

streams, including seasonal issues such as clogging by leaf 

litter (fig. C1) or accumulated fine sediment, biofouling, or 

sensor calibration drift.

During autumn, additional site visits were made by U.S. 

Geological Survey staff and volunteers to clean leaves and 

sediment buildup from the deployment pipes and instruments. 

Other chemical and mechanical solutions also were tested. 

Appendix C. Troubleshooting Instream Monitors

One of the simpler solutions was to increase the wiping 

interval for the optical sensors (turbidity and dissolved 

oxygen). This helped, but it did not eliminate the issues 

entirely. A non-toxic, anti-fouling nanopolymer C-spray (YSI, 

2013) was used successfully for reducing the summer algal 

fouling issues, albeit for the short term (about 7–10 days). The 

most successful solution was the deployment of an aquarium 

pump attached to the instrument (fig. C2). The pump supplied 

a repetitive jet of water for 1 minute every 2 hours to clean 

the optical turbidity sensors. This worked extremely well, 

especially from July to October 2014.

Figure C1. Siltation and leaf compaction clogging the pipe and 

instrumentation at the Trask River site, northwestern Oregon. 

Photograph by Mark Uhrich, U.S. Geological Survey, November 

2012. 
32 Water-Quality Conditions and Suspended-Sediment Transport, Wilson and Trask Rivers, Oregon, Water Years 2012–14

tac15-1012_fig c2

Aquarium pump

Pump intake Pump tubing

Spray opening

Figure C2. Aquarium pump installed on water-quality monitoring instrumentation at Trask River site, northwestern Oregon. The 

pump successfully eliminated bio-fouling issues during low-streamflow summer months. Photograph by Heather Bragg, U.S. 

Geological Survey, August 2014. 
Publishing support provided by the U.S. Geological Survey

 Science 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
Sobieszczyk and others—Water-Quality Conditions in the Wilson and Trask Rivers, Northwestern Oregon—Scientific Investigations Report 2015–5109

ISSN 2328-0328 (online)

http://dx.doi.org/10.3133/sir20155109