Abstract
The network of dams throughout the Columbia River Basin (CRB) are managed for
irrigation, hydropower production, flood control, navigation, and fish passage that frequently
result in both voluntary and involuntary spillway releases. The entrainment of air in spillway
releases and the subsequent exchange of atmospheric gasses into solution during passage through
the stilling basin cause elevated levels of total dissolved gas (TDG) saturation.
Physical processes that affect TDG exchange at hydropower facilities have been
characterized throughout the CRB in site-specific studies and at real-time water quality
monitoring stations. These data have been used to develop predictive models of TDG exchange
which are site specific and account for the fate of spillway and powerhouse flows in the tailrace
channel and resultant transport and exchange in route to the downstream dam.
Currently, there exists a need to summarize the findings from operational and structural
TDG abatement programs conducted throughout the CRB and for the development of a
generalized prediction model that pools data collected at multiple projects with similar structural
attributes. A generalized TDG exchange model can be tuned to specific projects and coupled
with water regulation models to allow for the formulation of optimal water regulation schedules
subject to water quality constraints for TDG supersaturation.
It is proposed to develop a methodology for predicting TDG levels downstream of
hydropower facilities with similar structural properties as a function of a set of variables that
affect TDG exchange; such as tailwater depth, spill discharge and pattern, project head, and
entrainment of powerhouse releases.
