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20 <br />Each of the selected water years was then sub-divided into hydro-periods <br />considered to be hydrologically and biologically distinct. The base flow period was <br />delineated as October 1 through March 31. A runoff period was defined from April 1 <br />through June 30, and a recession period from July 1 through September 30. Flow <br />duration statistics (Dunne and Leopold 1978), were then calculated for each water year <br />type and hydro-period. From a biological perspective, razorback sucker spawn on the <br />ascending limb of the runoff hydrograph, and young fish are transported downstream <br />during runoff and recession. Sediment transport and channel dynamics are also most <br />significant during these two hydro-periods. The base flow period represents a long <br />interval of low flows encompassing the winter months, when young fish may be <br />concentrated among the numerous predators that occur in this system. <br />Temperature data collection <br />Continuous-recording temperature data loggers were installed during March 2000 <br />at the Green River site and April 2000 at the Yampa River site. Four temperature <br />recorders were placed in the spawning channel at the Green River site and two each in the <br />Green River upstream from the Yampa confluence, the Yampa River upstream from the <br />Green confluence and in the Green River about 2 km downstream from the Yampa <br />confluence. At each site temperature recorders were installed on both sides of the <br />channel and hourly water temperatures were recorded. Temperature recorders were <br />retrieved in August 2000. Hourly temperatures were reduced to daily means for each <br />temperature recorder. Daily mean water temperatures for each recorder were used to <br />calculate a mean daily temperature for each site.