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Physical habitat below a hydropeaking dam : examining progressive downstream change Winterhalt, Lesley Marie

Abstract

This study examines the short-term physical habitat conditions at four sites on the Kananaskis River, Alberta, where a hydropeaking dam was installed in 1955. This dam imposes both the approximate pre-dam minimum flow, and the pre-dam flood (from a small flood year) on a daily basis. The purpose of this study was to examine the extent of daily changes in physical habitat conditions that organisms in the stream would have to endure, and the extent to which these fluctuations might be reduced downstream due to distance from the dam and unregulated tributary influence. Physical habitat conditions monitored over low flow and high flow dam releases were: velocity; depth; bed mobility; ramping rates; and total suspended solids. River2D was used to calculate weighted usable area and potential habitat for Brown Trout (fry, juveniles and adults) and Mountain Whitefish (fry, juveniles and adults) at the low and high flow conditions. Of the factors examined, only ramping rates and total suspended solids showed signs of downstream attenuation. Differences in depth, velocity, weighted usable area, and potential habitat between low flow and high flow dam releases were variable, and showed no downstream pattern. Between low and high flow releases, significant (p = 0.05) changes in depth were observed at all sites, and significant changes (p = 0.05) in velocity were observed at all but the second site. The second site also saw the smallest changes in measures of habitat between low flow and high flow dam releases; however, all other sites saw median differences of 48.1% to 170.9%. Percent differences in habitat between low and high flow dam releases ranged from 2.6% (second downstream site, juvenile Brown Trout) to 193.3% (third downstream site, adult Mountain Whitefish). These habitat changes happen more often than before the dam was installed (many times weekly vs. about once a year during the spring freshet) and they occur more rapidly. Because these changes happen at times of the year that are out of synchronization with the biota of the river, and as these changes are extreme, this implies challenging physical habitat conditions for indigenous stream biota.

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Attribution-NonCommercial-NoDerivs 2.5 Canada

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