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The 15-Mile reach of the Colorado River runs through Grand Junction, CO, so it was possible to tie the river survey into the Mesa County Survey System. The Mesa County Dept. of Public Works Engineering Division/Survey Section maintains a web page where it is f-l possible to lookup survey information. The latitude and longitude of the brass marker at the intersection of31 and C Road was determined through the use of this web site. Using the rUl brass marker reference point, it was possible to use the Javad RTK GPS to pinpoint the location of a rebar pin on the "Government Property" near the river. This point was (j subsequently used as the reference point for the entire IS-Mile reach survey. n The bathymetric survey data was collected using the Javad RTK GPS and ODOM m f.....i t ;j Hydrographic 3000HZ narrow beam sonar. 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 [ "j these instruments was sent to a laptop and recorded using the COMLOG ~oftware 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 , , : j f i U the computer's clock. [.:l_...... W On October 22nd, additional topographic points were collected at the waterline with the GPS, Psion data collector, and Field Face software. These additional points were used for calibrating the Manning roughness. values. (.........1..:.: U 1999 Duffy Tunnel and Sevens Surveys f- ~ 1.J , , (J Over a three-day period beginning July 9th and ending July 12th 1999, bathymetric data ( j was collected along a 2.25 km section of the Yampa River near Duffy Tunnel and a1.3km f- :} ~.>~ tJ section near Sevens. In order to compare the 1998 and 1999 data sets, the 1999 survey used the coordinates for the primary base pins of the 1998 surveys. Bathymetric data was collected Fi Ii r.-',:1 19