Upper Chehalis River Pollutant Capacity and Load Allocations

by Paul J. Pickett, (M.ASCE),

Document Type: Proceeding Paper

Part of: North American Water and Environment Congress & Destructive Water


Dry season water quality was evaluated in the Upper Chehalis River in western Washington state, focusing on low dissolved oxygen (DO), and using the Total Maximum Daily Load (TMDL) process. In particular, the Centralia Reach is characterized by low velocities, high temperatures, thermal stratification, and low DO. Both point and nonpoint pollutant sources, as well as natural conditions, contribute to poor water quality conditions. The study used field surveys and computer modeling to evaluate pollutant loading. Under critical conditions with existing sources at maximum levels, DO criteria were exceeded. Natural background DO levels (in the absence of human-caused sources) were also found to fall below criteria over much of the Upper Chehalls River. To remain within the pollutant loading capacity of the Upper Chehalis River, point sources near the Centralia Reach will have to restrict or eliminate their discharges during the dry season, and nonpoint sources must be reduced to background levels. Coordinated watershed management with the involvement of basin residents is necessary for successful implementation of the TMDL.

Subject Headings: Water pollution | Water quality | Load bearing capacity | Dissolved oxygen | Computer models | Rivers and streams | Load factors | Washington | United States

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