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I I I I I I I I I I I I I I I I I I I marked and released into the same run of capture. This process was continued over the entire reach. The entire study site was sampled for the second time on July 18 and 19. Block nets were not used on the third and fourth samples made on July 20 and July 27. Summer flows are regulated by releases from McPhee dam and flows generally vary between 65 and 80 cfs. Habitat Mauuim! Glohal Positioning Systems and Sonar In 2000, bathymetric surveys of the channel were taken at four sites using the Global Positioning Systems (GPS) and sonar technology. This technique, described in detail in the 2000 progress report (Anderson and Stewart 2000), is performed from a moving boat and gathers a large amount of bathymetry data in a short amount oftime. The GPS system used in this study was a Javad Oddessy Ll/L2 RTK GPS with Glonass and Multi-path reduction options turned on. This system has a published vertical accuracy of 15mm +/- 1.5 mm. The sonar unit used was an ODOM Hyrographic Systems, Hydrotrac - Single Frequency, Portable Survey Sounder. This unit used a 200kHZ frequency with a published accuracy of lcm +/- 1% of depth and an output resolution of lcm. The sonar unit pings and logs 20 depth readings per second and the GPS logs one position per second. The GPS system output a NMEA GGA string at a rate of 1HZ while the sonar output text strings indicating depth at a rate of 10HZ. Data from these instruments was sent to a laptop computer and recorded using the COMLOG software from ODOM Hydrographic. Because the GPS and Sonar data were received at different rates, all data entries collected by the COMLOG software were time-tagged to the millisecond using the computer's clock. The depth readings immediately before and after the GPS reading were interpolated by the computer clock time (nearest millisecond) to produce the XYZ coordinates used to map bed topography of the river channel. 13