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<br />means and coefficients of variation for each of the 32 parameters results in the computation of <br /> <br />64 different Indicators of Hydrologic Alteration. Approximate confidence limits were also <br /> <br />estimated for the difference between means and coefficients of variation (Tables 3, 4), <br /> <br />respectively, using standard formulae that are approximately valid when distributions are noe <br /> <br />Normal or change (e.g., unequal variances) between time periods (Snedecor & Cochran'I%7; <br /> <br />Stewart-Oaten et al. 1992). <br /> <br />;.':.L:~~,f}l <br /> <br />. \.~}~a <br /> <br /> <br />Roanoke River; North Carolina <br /> <br />~ "lna '- <br />~'" <br /> <br />Daily streamflow measurements (cubic feet persecond, cfs) have been Collected at RoariOr <br /> <br />Rapids on the Roanoke ,River by the USGS since 1913. Dam impacts'onthe Roanoki River:- <br />system began with tbe completion of Philpott Lake on the Smith River (ih tbe upper<l<l'O;~;!A~;t> <br />watershed) in August 1950, followed by completion of Kerr Reservoir on the mainstein tW'l'JO ' <br />0;~,._ .. ~;_._ <br />.--- - .,1,.,;.........".,,- <br />September 1950. In 1955, Roanoke Rapids Lake was built just downstrearnofKerr Reservolf ' <br /> <br /> <br />for "run-of-the-river" hydropower generation purposes. The pre-impact data set has beCn ';j;~rt <br /> <br />. , ~ ....~~f' <br />deftned as 1913-1949.;andthe,poshimpactdata:setcovers 1956-1991. Typical pre- and post.." <br /> <br />dam annual hydrographs are presented in Figure I. <br />The IHA results for the Roanoke River are given in Table 3 and illustrated in Figur~ <br /> <br />,--f~~I <br /> <br />8-11., The relative difference between, means ranged from -73% (annual 1 ~y maximum <br /> <br /> <br />flow) to. 232% (low pulse counts) for the.jndividual attributes, while the average absolute'1$1l <br /> <br /> <br />difference for'the,five groups ranged from 15 % (Group' 1: monthly means) to 88 % (Group' ~ <br /> <br /> <br />, frequency and duration of pulses). For individual attributes, the relative difference between' <br />CVsranged from-60% (mean August flow) to 72%. (mean April flow); the range for th~f~1l' <br /> <br />., <br /> <br />17 <br />