The modification of guide or rule curves to water storage in reservoirs can be used as an
operational technique to enhance water quality. By modifying the hydraulic residence time of the
reservoir, inflows can be routed quickly through the reservoir or retained. This allows the reservoir to
retain high quality water for later release or retain poor quality water for treatment by in-reservoir
processes to modify its quality.
A numerical water quality model can be used to evaluate changes in the operational guide or
rule curve. Although few examples of guide curve changes have been published, some referenced
examples indicate positive benefits to this technique. Table 4.4.1 summarizes the guide curve change
Summary of Guide Curve Change
Nutrient and sediment loading, turbidity, and poor water quality inflows.
Adjust scheduled reservoir pool-up to change residence time and minimize
Mode of action
the effects of poor water quality inflows.
Highly effective on small- to medium-sized reservoirs.
Possible loss of fish and wildlife habitat and/or access to wetlands or
spawning areas during critical hydrologic events.
Access to recreation areas may be limited.
Aesthetics, shoreline erosion, and aquatic weed control affected.
Risk as to being able to fill the reservoir to summer levels in the season
Small- to medium-sized reservoirs, where volume change will significantly
affect the residence time.