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North Santiam River Basin Suspended-Sediment and Turbidity Study

Project Summary

Background

The February 1996 flood event in the North Santiam River Basin caused high turbidity that persisted for several months, with peak turbidity levels near 140 Nephelometric Turbidity Units (NTU), and halted operations for 2 weeks at the City of Salem water treatment plant (WTP). The North Santiam River is the primary drinking water source for 155,000 residents of the Salem area. Subsequent high-flow events since 1996 also have caused high persistent turbidity, resulting in approximately 5-10 closures of the WTP intake for up to 48 hours per closure. The Salem WTP uses a slow-sand filtration process that is unable to treat water with turbidity levels greater than 10 NTU. A pretreatment facility was constructed in 1997 to handle high turbidity conditions. Its use requires a significant increase in operating costs. The Oregon Department of Environmental Quality requires water suppliers to provide users with water having an average turbidity at or below 1 NTU, with no exceedance allowed over 5 NTU.

North Santiam River at Niagara (BCLO) during average flow conditions, looking upstream from cableway.

North Santiam River at Niagara during high flow. Gage house on right, Little Sardine Creek enters on left.

Objectives

1. Establish a network of real-time streamflow and water-quality stations to monitor short-term (daily, monthly, storm-to-storm, and seasonal) and long-term (year-to-year and decadal) temporal changes in stream discharge, stream temperature, specific conductance, pH, and turbidity.

2. Estimate suspended-sediment loads for the major subbasins and main-stem North Santiam River using correlations developed between real-time turbidity readings and suspended-sediment concentrations.

3. Identify the relative contribution of turbid water (both short-term and long-term persistent turbidity) from major subbasins and other primary sources to Detroit Lake and the North Santiam River at and above the City of Salem's water intake.

4. Establish an early warning system to monitor high streamflow and turbidity events in the North Santiam River Basin that may affect the operation of the City of Salem's water treatment plant.

5. Define the spatial extent of suspended-sediment loads and turbidity in the North Santiam River Basin relative to geology, forest cover, and topographic features.

Relevance and Benefits

The real-time streamflow and water-quality network designed in this project meets long-term USGS data collection goals and helps minimize loss of life and property by providing data for flood response and emergency management of the Salem WTP. Data from this project will benefit drinking water quality and endangered species recovery in the basin.

Approach

Multiparameter water-quality monitors have been installed and telemetered at six sites, three at inputs to Detroit Lake and three below the lake, and made available in real-time via USGS and U.S. Army Corps of Engineers websites. Daily streamflow, turbidity, water temperature, specific conductance, and pH data will be processed and published for the six sites for the water years 1999-2003. Suspended-sediment samples will be collected at all sites for the water years 1999-2001. Mean daily and annual estimates of suspended-sediment load for all sites will be computed using regression equations derived from the instantaneous turbidity readings and suspended-sediment concentration data. Experiments will be conducted analyzing turbidity changes over time from storm-event or high-flow samples collected concurrently with the fluvial sediment samples. Estimates of relative persistent turbidity from these tests, correlated to specific sediment size classes and settling rates, will be compared for each site and sampling period. The final study results will identify the status and trends of suspended-sediment load and the relative contributions of persistent turbidity from the major subbasins. Hydrologic, landscape, and geomorphic features also will be used to further characterize the subbasins and explain the overall sediment-flux conditions in the North Santiam River Basin.

Reports

WRIR 03-4098. 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 , by Mark A. Uhrich, and Heather M. Bragg

FS 2004-3069. The North Santiam River, Oregon, Water-Quality Monitoring Network, by Heather M. Bragg and Mark A. Uhrich.

SIR 2007-5178. Major Turbidity Events in the North Santiam River Basin, Oregon, Water Years 1999–2004, by Steven Sobieszczyk, Mark A. Uhrich, and Heather M. Bragg.

SIR 2007-5187. Suspended-Sediment Loads and Yields in the North Santiam River Basin, Oregon, Water Years 1999–2004, by Heather M. Bragg, Steven Sobieszczyk, Mark A. Uhrich, and David R. Piatt

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