Summary of Inflow Routing
Inflows with undesirable water quality
Mode of action
Selective withdrawal of the inflow
Dependent on lake size, distance of inflow to
outlet works, and strength of density difference
between inflow and reservoir.
Days to months
Technique less effective without selective
Requires density difference between the inflow
and the reservoir (the greater the better).
May pass the quality problem on to the river
downstream or a downstream reservoir.
Minimal to none (operating changes and perhaps
lost hydropower generation revenue).
Works best with reservoirs with selective
Applicability to reservoirs
withdrawal; however, the use of other outlet
works is possible
the reservoir, withdrawing undesirable water, or diluting poor-quality release flow with higher quality
water. For example, during the stratification season, the quality of hypolimnetic release water may
degrade because of significant low dissolved oxygen or concentrations of iron, manganese, and
hydrogen sulfide. Releases from the epilimnion through a spillway gate (selective withdrawal) will dilute
the poor quality release. Reaeration of releases through a flood control gate may significantly increase
oxygen for dilution with the poor quality water.
188.8.131.52 Design Criteria
This operational technique has been used at a number of projects to enhance the release quality
during the stratification season. However, the evaluation of the technique has been based on tests in the
field. A general procedure for evaluating this technique for the potential to improve-reservoir or release
water quality is given below.