Use of Multiple Unequally-Sized Turbines to Reduce Flow Fluctuations Below Hydroelectric Dams

Publication Date



ISBN 0-913235-37-7

Publication Title

Proceedings of the Symposium on Small Hydropower and Fisheries

Start Page


End Page



Olson FW;White RG;Hamre RH;

Publication Place

Bethesda, MD


American Fisheries Society


By incorporating multiple turbines of varying sizes into project designs, hydroelectric developers can reduce the large fluctuations in flow typically associated with the storage and release mode of operation. This system has been used twice in Maryland - at the Gilpin Falls project in Cecil County, and at Brighton Dam on the Patuxent River - to reduce large flow fluctuations that would have occurred had the developers' original designs been used. The results were: (1) 70- and 17-fold daily flow fluctuations were reduced to 3-fold fluctuations, (2) the minimum flow was increased, (3) power generation was increased, and (4) the developers lost very little revenue. Multiple turbine designs are effective because a choice of turbines or turbine combinations enables the developer to spread the release of peaking flows over the entire period when peak buy-back rates are in effect. With a single turbines, the same volume of water is released over a shorter time period, resulting in greater fluctuations in flow. Additionally, with a single large turbine, no generation occurs during periods of minimum flow, giving developers a strong incentive to keep this flow as low as possible. With a multiple-turbine design, the smallest turbine can be use during periods of minimum flow, and the revenue lost by releasing additional water during off-peak periods can be partially or totally offset by producing power with water that would otherwise have been replaced without generation.

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