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<br />28 <br /> <br />Daylight may raise air temperature above freezing and combine with <br />radiation from the sun to break up anchor ice. Inorganic and organic <br />debris frozen to the anchor ice may be carried along wIth the current. <br />Significant, scouring of the streambed and streambank c~m occur as the <br />anchb1f' :t~e"jlDd atfached debris are carried ,along with the current. <br /> <br />Impounded streams subjected to IIlinimum flow releasles below dam,s <br />maxilllize development of frazil and llnchor ice when there are clear skies, <br />high radiiition,' below freezing air temperatures and a lack of insulating <br />snow cover. Sudden and heavy water release'9 for power generation during <br />the IIlOrning cause the anchor ice to float ~.ay with itSI adhering bottom <br />sediments. The result is excessive scour, IlDd a deposi,tion of the <br />suspended load onto pools and gravel bars. <br /> <br />Coldwater and Warmwat.!r Streams <br /> <br />The separation of coldwater and warmwa1:er streams on the basis of <br />water temperature is a commonly accepted practice. Differences in altitude <br />and geographic location strongly influence the presence and extent of <br />warmwater and coldwater stream ecosystems. Temperature is the single most <br />important and dolllinant characteristic that determines whether a ste,eam is <br />considered warmwater or coldwater. In a biological sense, warswater <br />streams have been defined as those "in which the temperature becomes high <br />enough, at least part of the year, to curtai,l the growth, reproduction, and <br />survival of, s{lllllOnids (trout) and in which the native fishes are those that <br />thrive at these highe~ temperatures" (Funk 1970). Historically, th,~ <br />dividing line between warmwater and coldwater streams was generally <br />considered to be 20-21 C (Embody 1921), although trout streams have been <br />separatecifrom wa1'1lllater streams at 24 C (Ricker 1934). Whereas coldwater <br />...--..j <br />streams_.y J,'ange, from 0 C to about 20. C, W8.rmwater streams are considered <br />to rang~, fJ'9m29 C" to about 34 C at northern latitudes and to about 36 C at <br />southern'latitudes (Tarzwell 1957). <br /> <br />Although there is a wealth of studies that have de"lt with coldwater <br />and warmwater streams separately, there is a paucity of information that <br />compares and contrasts cold and warm systems (Winger 19111)" Therefore, it <br />lIIlly be best at this time to separate them on the basis ,~f a mean annual <br />temperature of less than 20 C or greater than 20 C and of whether they <br />support a ,_cold, or warm adapted flora and flluna; that is" organisms l:hat are <br />r~~Ericted to or show a thermal preference for specific warm or cold water <br />tellp,rature c,?nditions. ,It should be understood that cc)ldwater strE!ams may <br />or may 'not, be, ice covered on a seasonal basis and that "armwater <br />streams,l1kew1ie,'uy or may not be seasonally ice covered. Likewise, as <br />linear, cOJ.lUnuull8" .treams ..y be wholly coldlwater, whoJLly var...atez', or <br />partly cofdWater and partly warmwater separated by a tnnsition zone. Irr <br />some cases the transition zones may be as long or longer than the cold and <br />warm temperature zones (Backiel 1964) or the transition from coldwater to <br />warmwater conditions may be fairly abrupt as in some Ontario trout streams <br />(Ricker 1934). In either case the transition from the c:ooler upstream <br />