Impact evaluation of Maple Hill dam microhydro facility on downstream trout movement

Publication Date



Report prepared for the Ontario Ministry of Natural Resources


trout, smolt, downstream migration, migration, salmon, upstream, entrainment, intake, bubble curtain, curtain, canal, fish movement, upstream migration, weir, plunge pool, pool


Smolts require access to the fishway (i.e., the fishway must be open and operational) during their downstream migration. In our professional opinion, the fishway should remain open to allow downstream passage of smolts in July/August, particularly as water temperature decreases in the autumn. It is beneficial to close the fishway to prevent accumulation of debris very early in the spring; however, the fishway should be opened as soon as possible each year, and remain open for as long as possible (i.e., until December). The benefits of providing downstream passage of fish around the micro-hydro facility may outweigh costs of preventing salmon access to areas upstream from the Maple Hill dam. Entrainment of smolts and other smaller fishes, as well as delay of larger downstream migrating fishes at the turbine intakes can be minimized through the use of a bubble curtain in the power canal. This curtain can be operated during periods of known downstream fish movement (summer and fall) and not operated during periods when fish are expected to use the fishway for upstream migration (i.e., early spring). Alternatively, a bubble curtain can be positioned on an angle from the fishway exit across the power canal and operated throughout the year. The flashboards at the dam reduce the depth of water flowing over the crest to less than 2 cm in some places. Based on our professional opinion, the most environmentally beneficial operating protocol would include a notch in the dam crest (deeper than the current narrow weir section) and installation of an adequate plunge pool, so that the power canal can be closed off completely to facilitate downstream movement of fish over the Maple Hill dam during periods of known downstream migration (i.e., July/August when river levels are low).

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