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<br />dams experience steeper hydrograph rises due to rapid releases of water from the reservoir <br /> <br />during peaking power generation. However, the apparent reduction in rise rates on the <br /> <br />Roanoke is probably due to the fact that flow releases seldom exceed 20,000 cfs (566 cms), <br /> <br />which corresponds to turbine capacity limits; in the pre-dam period, flows commonly rose' <br /> <br />more than 40,000 cfs in a single day during rainstorms. <br /> <br />Changes in the variability of the 32 IHA parameters are also quite evident (Table'~o:,:;; <br /> <br />Figs. 8-11). In general,variabilityhasbeenreducedcin the summer and winter monthly '/lld <br /> <br />means, in the extreme low water conditions, in the timing of the annual highs and lows, iIlt <br /> <br />high and low pulse durations, and in the frequency and rate of hydrograph ris~ and fallS"!,' ttii <br /> <br />the other hand; increased coefficients of variation are indicated in the springtime monthty~' 'e(J , <br /> <br />-"Y~u' <br /> <br />means and in long duration (e.g., 30- and 9O-day) high flow magnitudes. <br /> <br />, .~.:;, ~1" ~,~;<';~l:~~:~:--" <br />__,...-...."i9:~,,"<.:..>-___ <br />. '_P -'<;:.;~-J:./': <br /> <br />Dam alterations to the Roanoke flow regime have been blamed for the drastic redua1&'a;' .' <br />of striped bass populations (Zincone & Rulifson 1991). Higher average streamflows in tIk h~-" <br /> <br />spring months (May-June) have been associated with less successful rates of juvenile bass ; ~!~ <br /> <br />recruitment. Aquatic"invertebrates~inhabiting;,the littoral zone along the river's edge maybe;:)- <br /> <br />severely impacted by the greater frequency of hydro graph pulses, rises and falls. Rapidly\! 1.,1. <br /> <br /> <br />reversing cycles of wetting and drying have been shown to decimate littoral zone benthiC' fatiiUi. <br />- , ~ ""' " <br /> <br />unable to migrate with the shifting river edge (Walker et al. 1992; Armitage 1984). TIIis-;iiii-;~' <br /> <br />i ". <br /> <br />be substantially reducing the availability of prey for the Roanoke's fishes. <br /> <br />,.,,,,,'l:;-~ <br /> <br />Altered flood patterns may lead to significant alterations in the composition and <br /> <br />structure of the- Roanoke's bottomland hardwood forest by changing the magnitude and'l!$! , <br /> <br />duration of floods (Lea 1991; Richter 1993b). The different plant species and floodplain.ftlrest <br /> <br />19 <br />