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<br />groups was 26% (Group 4: frequency and duration of pulses) to 41 % (Group 3: timing of
<br />
<br />extreme events).
<br />
<br />The results of the IRA analysis for the Roanoke reflect the effects of Kerr Reservoir '
<br />
<br />operations for the purposes of flood control and hydroelectric power generation at Kerr
<br />
<br />..-....,'7
<br />
<br />Reservoir, and Roanoke Rapids Lake. An obvious impact of flood control operations-on'tl(e
<br />
<br />Roanoke is the virtual elimination of high-magnitude flooding (Figure 8). Floods ine~"
<br />';,/~i~,~5~}~~t '.
<br />8500 cms (cubic meters per.second;.approx..equaLto30,OOO cubic feet per second) occurredin..
<br />, ': ~~o~~~~f~
<br />only five of the post-dam years, whereas floods greater than this size occurred in every-..~.o.?':';"
<br />
<br />dam year. Multi-day maxima are likewise affected by the flood control operations (Tab~"
<br />
<br />','-or.
<br />
<br />, The, Plllsingbehavior of the Roanoke River has been severely impacted, as bOth.~';.
<br />. "v,,~~,'_'\:
<br />~;!,"'.-'
<br />and especially !owPl1lses (Fig. 9) now occur with substantially greater frequency. 'I'IICi' '~;fJ':
<br />
<br />
<br />.'-',-',
<br />average duration of pulses is, on the other hand, much shorter in the post-dam period.'TI&'ii; . .'
<br />. ,'~:~~:.:,
<br />''''''a byproduct of hydropower generation, wherein water is stored in the reservoir until sufmliiiii""'>O"
<br />
<br />
<br />head is attai,ned to efficiently generate power, then rapidly released through the dam turbInes?'
<br />
<br />
<br />The effect on the hydrologic.regimejs.to.createA.greaterfrequency of high and low pul_1Htr
<br />
<br />lesser duration (Group 4), and also increase the number of hydrograph rises and falls(Gm~.,.
<br />
<br />5). ' ",,' ~.:i,7~,:."'
<br />, .1. _.,. ~',-;:."_'
<br />
<br />
<br />.The,/lIagpitude .and timing of the. ann~tm~mum .have, changed, with a shift friiml,,,,.,':L
<br />"-' ~.~---,. ,-, ; , .:;-,_,~~~~:~:~,::-i-
<br />higher, fall season to lower, mid-winter annual lows (Figure 10). This.probably resulrs;r~:::;'f"':
<br />. ",.0' ~."."
<br /><, ~ ' -i~~~~(~~:;f?, c, .
<br />attempts to capture winter flows for later spring and summer use in hydropower generatiomI!lli "
<br />
<br />
<br />Somewh.atsurprisingly, the average hydrogJ;apb rise rate. (Group 5; see.Fig. l1Pf~,...,
<br />t . "i~-':;'~-2J': .
<br />Roanoke. is red~ from the pre-dam p~riod. Typ~cally, areas downstream of hydropowelZV".;'J. , ' .-,
<br />
<br />- "_i.~~" ~ -",
<br />
<br />18
<br />
<br />
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