some of the most severe floodthe afternoon of February 7, 

quality was affected for 

In February 1996, Northwest Oregon experienced 

ing in recorded history. 

Heavy, warm rain fell on 

above average snowpack in 

the Cascade Range of the Willamette River Basin, resulting 

in 50- to 100-year flood events 

in many area rivers. The 

North Santiam River at 

Mehama crested at nearly 

21⁄2 feet above flood stage on 

1996. Although the water 

level returned to normal 

within a few weeks, the water 

months to come. 

The City of Salem water-treatment facility withdraws water 

from the North Santiam River. Changes in water quality, as 

during floods, affect the facility’s operation. 

The North Santiam River, Oregon, 

Water-Quality Monitoring Network 

U.S. Army Corps of Engineers released 

water from Detroit Lake. This turbid lake 

water flowed downstream, keeping turbidity values at the water-treatment facility 

intakes high until July 1996. The City of 

Salem was forced to temporarily cease 

operations of the facility for 8 days and 

acquire water from reserve sources and 

neighboring communities until an alternate treatment scheme was developed. 

In 1998, a monitoring program was 

initiated to better understand the sources 

and transport of sediment that causes high 

turbidity within the North Santiam River 

Basin. The project is a cooperative effort 

of the City of Salem, the U.S. Geological 

Survey (USGS), the U.S. Forest Service, 

and the U.S. Army Corps of Engineers. In 

anticipation of future events like the 1996 

flooding, the agencies now continuously 

monitor hydrologic and water-quality con- Why Monitor Water Quality?	 Lake was held back to prevent further ditions throughout the basin. The data col- flooding downstream. When the turbid 

The water quality of the North Santiam lected by this program are available online 

waters of the North Santiam tributaries 

River is important to more than 170,000 in real-time and are used by the coopera- flowed into the lake, the larger sand parti- tors for current operational decisions, residents of the Salem, Oregon area that cles settled out of the water. The fine silt ongoing research projects and future basin rely on the river as their primary source of and clay particles, stirred by currents, wind management. drinking water. The river normally runs so and waves, remained suspended. As the clear that the City of Salem is able to use a flood waters downstream receded, the relatively inexpensive and environmentally 

low-impact water-treatment process called 

slow-sand filtration. This process uses sand 

and gravel filters to remove suspended 

organic and inorganic particles in conjunction with natural biological processes to 

remove dissolved organic contaminants. If 

the river turbidity (see inset) is greater than 

10 NTU, these filters can become clogged. 

To keep the facility running smoothly, the 

intake water is tested daily. If the turbidity 

remains consistently above 10 NTU, the 

water intakes are closed. 

During the 1996 flooding, the North 

Santiam River had turbidity values in 

excess of 100 NTU at the water-treatment 

facility intakes. (It is impossible to determine the exact maximum turbidity value 

because there was no continuous waterquality monitoring system in place at the 

time.) Much of the water entering Detroit 

What Is TURBIDITY? 

Turbidity is a measure of the 

“muddiness” of water caused by 

suspended and dissolved material, 

as well as organic matter. The currently accepted numerical measure of turbidity is the nephelometric turbidity unit (NTU). An 

NTU value represents the amount 

of light scattered by particles in 

the water. As the number of suspended particles in the water increases, the intensity of scattered 

light increases, which results in 

higher turbidity values. In this 

photograph, the North Santiam 

River near Detroit has a turbidity 

of approximately 700 NTU. 

U.S. Department of the Interior	 USGS Fact Sheet FS–2004–3069 

U.S. Geological Survey	 December 2004 
 The North Santiam River Basin

1

Includes the area upstream from the station location and contributing subbasins.

2

Includes water temperature, specific conductance, pH, and turbidity.

3

Samples collected manually through June 30, 2004.

4

75 samples from automatic pumping sampler.

Table 1. North Santiam River Basin monitoring stations.

Map number Site name

Subbasin area

(square miles)1

USGS station 

number Station name

Date of water-quality 

probe installation2

Number of suspendedsediment samples3

1 Mehama 655 14183000 North Santiam River at Mehama April 2000 156

2 Little North 112 14182500 Little North Santiam River near Mehama April 2000 150

3 Niagara 453 14181500 North Santiam River at Niagara April 2000 93

4 French 9.9 14179100 French Creek near Detroit June 2001 64

5 Breitenbush 108 14179000 Breitenbush River near Detroit October 1998 131

6 North Santiam 216 14178000 North Santiam River near Detroit October 1998 4

227

7 Blowout 26 14180300 Blowout Creek near Detroit October 1998 158

The North Santiam River Basin 

Study

The North Santiam River Basin is 

located on the western slopes of the Cascade Range in northwestern Oregon, east 

of Salem. The river flows west from 

Mount Jefferson to the Willamette River, 

draining 766 square miles upstream from 

Salem’s water-treatment facility. The 

geology of the central part of the basin is 

dominated by Western Cascade volcanic 

rocks. The steep terrain and older, weathered soils of this area produce many earthflows and landslides that supply sediment 

to the rivers. The central basin is bounded 

on the east by less steep and younger High 

Cascades volcanics and on the west by 

Willamette Valley alluvial lowlands. 

Average annual precipitation in the area 

ranges from 45 inches in Stayton to over 

200 inches at Mount Jefferson. The basin 

contains the main-stem North Santiam 

River, its major tributaries (Breitenbush 

River, Blowout Creek, French Creek, and 

the Little North Santiam River), and two 

reservoirs (Detroit Lake and Big Cliff 

Lake), formed by the damming of the 

river. The reservoirs are operated by the 

Corps of Engineers for power generation, 

flood control, streamflow management, 

and recreation.

How Is Water Quality of the North 

Santiam River Monitored?

 The USGS operates a network of 

monitoring stations (sites) throughout the 

North Santiam River Basin. Seven sites 

provide water-quality and streamflow 

information (table 1). Three sites are 
located downstream from Detroit Lake 

(map numbers 1–3), and four sites are 

located on streams that flow into the lake 

(map numbers 4–7). Each site has equipment that measures the water level of the 

river and several water-quality parameters. These data are recorded electronically every half-hour. Several times a day, 

the data are uploaded to the USGS Portland office, stored in a database, and made 

available through a Website (http:// 

or.water.usgs.gov/santiam). These provisional data are immediately available to 

the agencies involved in the study, as well 

as to the public. The USGS periodically 

corrects or deletes the raw data according 

to routine field checks of the water-quality 

probes and other calibration or performance issues. The final data are then published in a year-end report. 

Multiparameter Water-Quality 

Probes 

Water-quality probes in the North Santiam River Basin measure specific conductance, pH, water temperature, and turbidity. These physical and chemical 

characteristics are important indicators of 

the overall health of the aquatic system. 

A USGS scientist calibrates a water-quality 

instrument at the Breitenbush monitoring station. 

Specific Conductance 

Specific conductance is the measure of 

the capacity of water to conduct electricity 

at 25 degrees Celsius. A change in conductance signals a change in concentrations of chemical ions in the water. Abrupt 

conductance deviations may result from 

chemical spills or sewage overflows 

entering a stream, lake, or other waterbody. 

A dramatic spike in conductivity appeared in 

the Breitenbush River (map number 5) over 

just a few hours. Periods of regularly occurring spikes such as this may lead to an investigation of possible causes of contamination 

upstream of the monitoring station. 

pH 

pH is the measure of the alkaline or 

acidic properties of water. Proper pH is 

important for the survival and abundance 

of aquatic plant and animal communities, 

as well as for the aesthetic qualities of 

drinking water, such as taste, odor, and 

color. 

Warm, sunny afternoons result in increased 

photosynthetic activity from instream algae 

and rooted aquatic plants. This can be observed in daily variations of pH values at Little 

North Santiam River near Mehama (map number 2). Summer heat and low-flow conditions 

can cause pH to exceed the Oregon standard 

of 8.5. 

Water Temperature 

Optimal water temperature is important for the survival and vitality of fish and 

aquatic insect populations. Changes in 

river temperatures can affect these populations, as well as algal, plant, and 

amphibian species. 

The summer water temperature in the North 

Santiam River at Mehama (map number 1) 

sometimes peaks above 16oC on several 

consecutive days, potentially exceeding the 

Oregon standard, which is calculated by averaging the maximum values of the previous 7 

days. 

Turbidity

 Turbidity is used as a monitoring and 

regulatory parameter in the industrial, 

sanitation, and environmental fields, and 

can be used as a substitute for suspendedsediment concentration. Elevated turbidity reduces the transparency of water due 

to the presence of suspended and dissolved materials. Increases in turbidity 

can reduce biological primary production 

(algal growth), important to the health and 

balance of the aquatic ecosystem, and may 

aid in transporting contaminants attached 

to suspended particles. Turbidity can be 

an indicator of water suitability for fishery, drinking, industrial, and recreational 

uses, and has been used to evaluate the 

effects of mining, dredging, stream-side 

construction, wastewater effluent, logging, road building, and other land use 

activities. 

The sudden increase in turbidity at Blowout 

Creek (map number 7) reached the sensor’s 

maximum value (about 1,350 NTU) in just minutes, gradually dropping after remaining for 

2 hours at the sensor limit. A site visit and inspection of the area upstream of the station 

revealed that a washed-out road and related 

debris flow resulted in sediment transport, 

causing increased turbidity (see photograph

at the end of the report).
Suspended-Sediment Samples 

At each of the seven monitoring sites, 

the USGS collects water samples that are 

analyzed for suspended-sediment concentration. The USGS adheres to strict quality-assurance and quality-control protocols to assure the reliability of the 

resulting data. The sampling procedure 

requires that water be collected across the 

entire cross-section of the river, ensuring a 

representative sample. The samples are 

collected in one of three ways: (1) Sites 

where the river is typically over 3 feet 

deep have a suspended cableway across 

the river from which samples are collected. (2) Other sites can be sampled 

from a bridge. (3) Smaller streams and 

rivers at low-flow conditions can sometimes be sampled by wading. Each of 

these sampling methods has equipment 

designed specifically for the task, including different size and weight samplers, 

cranes, and reels. Samples are collected at 

each site on a regular basis and during 

high-turbidity events. It is particularly 

important to collect samples during 

intense precipitation periods that produce 

high streamflows, since this is when most 

of the sediment is transported downstream. 

Automatic Pumping Samples 

When time or personnel constraints 

make it impossible to sample all seven 

sites during a high-turbidity event, at night 

or on weekends, automatic samplers are 

useful. These devices are programmed to 

automatically collect suspended-sediment 

samples under certain conditions. The 

sampler is positioned on the river bank 

along with flexible tubing deployed from 

the sampler into the water. When the turbidity reaches a certain value, the sampler 

pumps water into bottles stored within it. 

Unlike manually collected samples, these 

“point” samples (samples collected at a 

single point) do not necessarily provide a 

sediment and water mixture representative of the river cross-section. A correlation must be developed between the crosssectional samples and point samples by 

collecting both types at the same time 

during a variety of flow conditions. Once 

this correlation is established, the point 

samples can be used to estimate the suspended-sediment concentration of the 

river cross section. 

Capturing the Unexpected 

On October 21, 2003, the automatic sampler deployed at the North Santiam River near Detroit station was triggered to begin sampling 

by a sharp rise in turbidity. The turbid water entered the North Santiam River from Pamelia Creek, 11 miles upstream from the monitoring 

station (photo at left). The sediment plume moved quickly downstream. The automatic sampler collected 24 samples over the 16-hour 

event. Peak turbidity in these samples exceeded 5,000 NTU (center samples in photograph at right). About 4 hours after the peak, a USGS 

technician arrived at the site and manually collected a sample, which showed a sharp decrease to 560 NTU. Typically, stream turbidity 

increases during periods of storm runoff; however, this turbidity event was not associated with rainfall. Glacial melt and related landslide 

activity on Mount Jefferson were the most likely cause. 
Persistent-Turbidity Samples 

Another important aspect of the water 

quality is “persistent turbidity.” This term 

refers to material that remains in suspension for a long period of time. Fine silt and 

clay particles settle through the water 

more slowly than larger sand particles. A 

higher percentage of fine material results 

in more persistent turbidity. Samples are 

collected at the monitoring sites during 

high-turbidity events for persistent-turbidity analysis. In the USGS laboratory, the 

turbidity of these samples is measured at 

regular time intervals. As the sediment 

settles, the turbidity near the surface of 

the water sample decreases. The rate of 

the decrease depends on the amount of 

fine material in the sample. These data 

help to determine the proportion of clays 

and silts that enter the stream network 

from each of the monitored watersheds 

upstream from Detroit Lake. 

Persistent-turbidity lab analysis begins with a 

well-mixed sample of water and sediment. 

Subsamples are collected [at a specific depth 

from the sample water surface] after approximately 0, 2, 4, 8 and 24 hours of settling time. 

The turbidity values of these subsamples are 

then plotted to determine the decrease of turbidity over time. Cylinders A through E demonstrate the results of a typical persistentturbidity experiment. The graph (top) shows 

the actual results of the analysis. Notice how 

the turbidity decreases over the 24-hour period of settling (cylinder A to cylinder E). 

Detroit Lake Samples 

To better understand the processes of 

sediment transport through Detroit Lake, 

the USGS collected lake samples regularly at three locations from April 2002 to 

October 2003. Samples were collected 

throughout the water column and analyzed for suspended-sediment concentration and persistent turbidity using the 

same methods as for the samples from the 

rivers. The resulting data allow researchers to model the movement of sediment 

through the lake. 

A USGS scientist collects water samples from 

Detroit Lake for water-quality analysis. 

Who Uses the Water-Quality Data? 

City of Salem

 The USGS water-quality monitoring 

network serves as an early warning 

system for Salem’s water-treatment facility. During storms, water managers can 

monitor the major tributaries of the North 

Santiam River for changes in streamflow 

and turbidity. The ability to anticipate the 

arrival of excessively turbid water allows 

water-treatment facility operators to close 

water intakes before damage occurs to the 

sand filters. When the turbidity returns to 

10 NTU or less, the intakes are reopened, 

and water can once again enter the filtration system. During periods of prolonged 

high turbidity, water is diverted to a pretreatment facility, where chemical pretreatment removes the turbidity-causing 

material before the water enters the sand 

filters. This diversion is no longer necessary once the monitors show that turbidity 

values have stabilized below 10 NTU. 

Thus, the monitoring network allows the 

City of Salem to better manage the watertreatment facility and to provide clean 

water to its customers. 

U.S. Geological Survey 

The sediment-concentration and other 

water-quality data collected from Detroit 

Lake are being used by USGS researchers 

in a water-quality model of the lake to further the understanding of the overall water 

quality in the North Santiam River Basin. 

The model utilizes data from the continuous-monitoring sites on the tributaries in 

conjunction with the lake data. Streamflow, water quality, and environmental 

factors are used to describe sediment 

transport and thermal structure within the 

lake. This model provides information to 

the agencies involved in this study, as well 

as to those studying water quality farther 

downstream in the Willamette Valley. 

U.S. Army Corps of Engineers 

The Corps of Engineers relies on 

streamflow data from the stream-gaging 

network to manage the water budget of the 

basin. Accurate water volume input and 

output values allow them to plan for flood 

control, flow augmentation, power generation, and recreation. Data from the sampling program will assist the Corps in estimating sedimentation rates in Detroit 

Lake. 

Local Governments, Industry, and the 

Public 

Communities, municipalities, industry, 

and the general public use the data to 

make informed decisions about water use, 

fishing, and other recreational activities. 

Land Managers 

Turbidity sensors allow the estimation 

of real-time sediment concentrations at 

each of the monitored sites. The sediment 

data can be used to calculate the quantity 

of suspended material being transported 

downstream past each monitoring station 

and to identify the source of the sediment. 

Knowing which subbasins produce the 

most turbidity-causing material can aid 

in the understanding of processes related 

to glacial activity, landslides, and earthflows, and thus in the management of land 

use, such as streamside construction, 

timber harvesting, and road building. 
Heavy rain in December 2001 triggered a road 

failure on a tributary of Blowout Creek. The resulting debris flow caused increased turbidity at the 

monitoring station for several days.

 Working together, the City of Salem, 

USGS, land managers, and local agencies 

have developed a water-quality monitoring 

network that benefits a large segment of 

Oregon’s population. The cooperative relationship has helped foster an environment 

that balances drinking-water needs, land use 

and forest activities, and recreation with the 

maintenance of a healthy ecosystem in the 

North Santiam River Basin. 

By Heather M. Bragg and Mark A. Uhrich 

Where can I learn more? 

City of Salem Drinking Water Program 

555 Liberty SE 

Salem, OR 97301 

http://cityofsalem.net/~swater/ 

North Santiam River Turbidity Study Website 

http://or.water.usgs.gov/santiam 

Detroit Lake, January 29, 2004, looking westward from near where the Breitenbush River enters 

the lake. Note the turbid water entering the main body of the lake after more than 3 inches of rain 

fell over a 3-day period. 

Report: Monitoring Instream Turbidity to Estimate 

Continuous Suspended-Sediment Loads and Yields 

and Clay-Water Volumes in the Upper North Santiam

 River Basin, Oregon, 1998–2000 

http://pubs.water.usgs.gov/wri034098 

U.S. Army Corps of Engineers 

Portland District 

P.O. Box 2946 

Portland, OR 97208 

http://www.nwd-wc.usace.army.mil/nwp/ 

(Use the “dataquery” button to obtain data 

for the Willamette River Basin.) 

Willamette National Forest 

Detroit Ranger District 

HC73, Box 320 

Mill City, OR 97360 

http://www.fs.fed.us/r6/willamette/ 

U.S. Geological Survey 

10615 SE Cherry Blossom Drive 

Portland, OR 97216 

http://or.water.usgs.gov/ 

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