North Santiam River Basin Turbidity and Suspended-Sediment Study

Current Research

Suspended-sediment sampling

In addition to instream water-quality data, suspended-sediment samples are collected at each of the monitoring stations (excluding Geren Island) over a range of hydrologic conditions. Samples are collected by hand or by automatic pumping sampler. All samples are analyzed at the USGS Cascades Volcano Observatory sediment laboratory. Standard processing includes suspended-sediment concentrations (reported in milligrams per liter [mg/L]), and the fraction of sample sediment smaller than sand-sized particles (reported in percent finer than 62 micrometers). If sufficient sediment is available from the sample, additional analysis are performed to determine complete grain-size distribution [excerpt, USGS SIR 2007-5187].

USGS personnel deploying cable car from A-frame during winter storm sampling.

Storm sampling at North Santiam River below Boulder Creek near Detroit, OR (14178000) during November 2006 storm.

Streamflow studies at Geren Island

Work involves the establishment and operation of a streamflow gaging station, discharge measurements, and rating curve development for five miscellaneous sites. Additional work includes synoptic discharge measurements in and around Geren Island and technical assistance to the City of Salem. These sites were first measured in 2005 with another set of measurements made in June 2006. Three total discharge measurements were made at each of the five sites during the summer.

Aerial view of settling ponds at Geren Island.

North channel of North Santiam River at Geren Island.

Temperature modeling of Big Cliff Reservoir

Big Cliff Reservoir is the small re-regulating reservoir downstream of Detroit Dam. Although Big Cliff Reservoir is only 2.8 miles long, the dam is 191 feet high and a considerable amount of heat exchange can occur as water traverses this reach. There are existing USGS models of the North Santiam River and Detroit Lake; construction and calibration of a Big Cliff Reservoir model is in progress. Together, the USGS models of Detroit Lake, Big Cliff Reservoir and the North Santiam River will allow simulation of the effect of changes in dam operation at Detroit Dam on downstream water temperatures.

Debris flow activity on Mount Jefferson

On November 6, 2006, a rocky debris flow surged off the western slopes of Mount Jefferson into the drainage basins of Milk and Pamelia Creeks in Oregon. This debris flow was not a singular event, but rather a series of surges of both debris and flooding throughout the day. The event began during a severe storm that brought warm temperatures and heavy rainfall to the Pacific Northwest. Precipitation measurements near Mount Jefferson at Marion Forks and Santiam Junction showed that more than 16.1 centimeters of precipitation fell the week leading up to the event, including an additional 20.1 centimeters falling during the 2 days afterward. The flooding associated with the debris flow sent an estimated 15,500 to 21,000 metric tons, or 9,800 to 13,000 cubic meters, of suspended sediment downstream, increasing turbidity in the North Santiam River above Detroit Lake to an estimated 35,000 to 55,000 Formazin Nephelometric Units. The debris flow started small as rock and ice calved off an upper valley snowfield, but added volume as it eroded weakly consolidated deposits from previous debris flows, pyroclastic flows, and glacial moraines. Mud run-up markings on trees indicated that the flood stage of this event reached depths of at least 2.4 meters. Velocity calculations indicate that different surges of debris flow and flooding reached 3.9 meters per second. The debris flow reworked and deposited material ranging in size from sand to coarse boulders over a 0.1 square kilometer area, while flooding and scouring as much as 0.45 square kilometers. Based on cross-sectional transect measurements recreating pre-event topography and other field measurements, the total volume of the deposit ranged from 100,000 to 240,000 cubic meters [excerpt, USGS SIR 2008-5204].

Newly deposited material (light gray) in the Milk Creek drainage basin, Mount Jefferson debris flow, Oregon (Photograph by Robert Ross, Linn Benton Community College, 2007)

Tree damage caused by the Mount Jefferson debris flow, Oregon, November 6, 2006.

Landslide mapping and sediment transport in the Little North Santiam Basin

The North Santiam River serves as the primary source of drinking water for the city of Salem and the surrounding community. One of the greatest threats to the quality of drinking water is turbidity, or the cloudiness of water caused by the influx of sediment into streams. The stream that concerns the City of Salem most is the Little North Santiam River, an unmitigated tributary that drains 112 square miles and flows into the mainstem North Santiam River less than 7 miles upstream of the water treatment facility. As part of a cooperative agreement between the City of Salem and the U.S. Geological Survey (USGS), the USGS monitors water-quality and investigates potential sources of sediment in the basin. Previous studies suggest that features such as landslides are often responsible for supplying large quantities of sediment in short periods of time. In affiliation with the USGS, I will characterize this relation between landslides and sedimentation by generating an erosion susceptibility model. This model will use a Geographic Information System (GIS) to simulate the interaction of multiple parameters, including soil type, precipitation, vegetation cover, and slope characteristics, and how they influence erosion in the Little North Santiam Basin [excerpt, Thesis Proposal, Steven Sobieszczyk, Portland State University].

Downed trees and other damage atop landslide along east bank of Evans Creek.

Evans Creek entering (from left) into the Little North Santiam River during January 2006 storm.

Additional sediment source monitoring

Two sediment source sites have been operated throughout water year 2008 at Evans Creek and Cliff Creek, collecting water temperature, specific conductance, and turbidity. Stream level data was added to both creeks. Streamflow measurements also were collected at both sites to develop rough discharge rathings.

Currently on hold.

XRD analysis of soil samples, in conjunction with Portland State University

The total number of XRD samples submitted to Portland State University (PSU) for all analyses is 52. The total number of earthflow and landslide samples processed to date for XRD at PSU and sediment size breakdown at USGS Cascade Volcano Observatory Sediment Lab is 40, with 12 remaining. The entire set of 52 samples has been processed for clay settling and sediment size analysis. Final report will evaulate the persistent turbidity sources in the North Santiam River Basin and will include clay settling, clay mineralogy, sediment-size analysis from all 52 earthflow, landslide, and fluvial samples.

Currently on hold.