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