Modeling water quality in the Tualatin River, Oregon, 1991-1997

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Title Modeling water quality in the Tualatin River, Oregon, 1991-1997
Creator Rounds, Stewart A.; Wood, Tamara M.
Subject Water quality; Water temperature; Hydraulics; Trace elements in water; Organic compounds
Spatial Coverage Portland (Or.); Oregon
Description The calibration of a model of flow, temperature, and water quality in the Tualatin River, Oregon, originally calibrated for the summers of 1991 through 1993, was extended to the summers of 1991 through 1997. The model is now calibrated for a total period of 42 months during the May through October periods of 7 hydrologically distinct years. Based on a modified version of the U.S. Army Corps of Engineers model CE-QUAL-W2, this model provides a good fit to the measured data for streamflow, water temperature, and water quality constituents such as chloride, ammonia, nitrate, total phosphorus, orthophosphate, phytoplankton, and dissolved oxygen. In particular, the model simulates ammonia concentrations and the effects of instream ammonia nitrification very well, which is critical to ongoing efforts to revise ammonia regulations for the Tualatin River. In addition, the model simulates the timing, duration, and relative size of algal blooms with sufficient accuracy to provide important insights for regulators and managers of this river. Efforts to limit the size of algal blooms through phosphorus control measures are apparent in the model simulations, which show this limitation on algal growth. Such measures are largely responsible for avoiding violations of the State of Oregon maximum pH standard of 8.5 in recent years, but they have not yet reduced algal biomass levels below the State of Oregon nuisance phytoplankton growth guideline of 15 mg/L chlorophyll-a. Most of the dynamics of the instream dissolved oxygen concentrations are captured by the model. About half of the error in the simulated dissolved oxygen concentrations is directly attributable to error in the size of the simulated phytoplankton population. To achieve greater accuracy in simulating dissolved oxygen, therefore, it will be necessary to increase accuracy in the simulation of Tualatin River phytoplankton. Future efforts may include the introduction of multiple algal groups in the model. This model of the Tualatin River continues to be used as a quantitative tool to aid in the management of this important resource.
Publisher U.S. Geological Survey
Contributors Unified Sewerage Agency of Washington County, Oregon
Date 2001
Type Text
Format application/pdf
Digitization Specifications pdf file copied from USGS website ( ). Uploaded into CONTENTdm version 3.7.
Source Rounds, Stewart A. and Wood, Tamara M., Modeling water quality in the Tualatin River, Oregon, 1991-1997, Portland, Oregon: U.S. Geological Survey Water-Resources Investigations Report 01-4041, p60
Language eng
Rights Management Public Domain, Courtesy of the USGS
Holding Institution University of Utah
Metadata Cataloger Seung Hoon Yoo; Kristin Willmore
ARK ark:/87278/s6xs5t9p
Setname wwdl_er
Date Created 2004-12-01
Date Modified 2005-10-13
ID 1145752
Reference URL