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Ecology / Army Corps of Engineers Spokane River Water Quality Modeling

The Spokane River and Long Lake exhibit depressed dissolved oxygen (DO) levels during low flow in the summer months. Most of the river violates the Washington State water quality standards for DO, and some segments are listed on the 1998 Clean Water Act (CWA) 303(d) list of impaired water bodies. In addition The Spokane River and Long Lake are also listed on the 303(d) list for PCBs, chromium, and temperature. Studies and clean up efforts will be scheduled for these problems in the future.

The Department of Ecology has contracted with the Corps of Engineers to develop a water-quality computer model for the Spokane River and Long Lake using data obtained from recent and past studies. This model will be used to predict water quality changes in response to varying river flow and types, quantity, and locations of wastewater discharges. The model and its predictions will be used in a future public process to establish the total maximum daily load (TMDL) of pollutants that can be discharged to the river.

The Army Corps of Engineers are developing a 2D longitudinal / vertical, laterally averaged, hydrodynamic water quality model in support of TMDLs for the Spokane River. Ecology will be providing the Corps with groundwater inflows to and outflows from the river based on spreadsheet calculations that compare flow records in a downstream direction from the Post Falls Gage to the Long Lake outlet. Differences in flows between successive gaging stations in a downstream direction (including significant discharge to or withdrawals from the river by industry) represent a loss to or gain from the aquifer. The spreadsheet model is based primarily on 1991-1992 water year data. The model will be capable of predicting how water quality in the Spokane River will be impacted by groundwater and watershed changes only if the flows and concentrations entering and leaving the model resulting from these changes can be provided as input to the model. The model output predicts water surface elevations, velocities, temperatures and water quality for up to 21 constituents. The model is UNIX & PC compatible.

Project Information:

Project Contact:

Elaine Snouwaert at (509) 329-3503 or for TDD 711 or 1-800-833-6388.

Contact: Reanette Boese, Spokane County Water Resources