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<br />..~ <br /> <br />1998 Duffy Tunnel and Sevens Surveys <br /> <br />During July and August of 1998, we used the Pentax PTSrn total station to obtain <br /> <br />n <br />)<:-J <br />iJ <br /> <br />XYZcoordinates for two reaches on the Yampa River (Figure 1). The first reach was located <br /> <br />approximately 15 miles upstream of Juniper Hotsprings near the Duffy Tunnel diversion. <br /> <br />This site is approximately 1.3 km long and 3777 data points were collected. The second site. <br /> <br />was located adjacent to Cross Mountain Ranch approximately five miles upstream of Cross <br /> <br />~O.. <br />i; <br /> <br />Mountain Canyon. This site was approximately 1.2 km long and was represented by 1900 <br /> <br />data points. <br /> <br />[....,.:,1...:., <br />,1 <br />:.iJ <br /> <br />To make sure that the data collected at each of the sites could be used in future <br /> <br />research, a conscious effort was made to tie the surveys into permanent benchmarks. Due to <br /> <br />",:. <br /> <br />the remote nature of the Y amp a study sites, it was determined that the use of existing <br /> <br />benchmarks would impractical. In order to place the surveys into a real world reference <br /> <br />l.......jl <br />" <br />L <br /> <br />system, a Trimble GeoExplorer IT was used to GPS in at least two benchmarks for each site. <br /> <br />f;iJl <br />I <br /> <br />The BLM in Craig maintains a base station that was used to differentially correct the GPS <br /> <br />data though post-processing. By letting the GPS average the position for each point for <br /> <br />10minutes and post-processing, it was possible to determine the positions with a horizontal <br /> <br />~ <br /> <br />accuracy of approximately 10cm. These positions were then converted into the State Plane <br /> <br />1983 coordinate system with a NAD83 datum using the Colorado North zone. The State <br /> <br />f1 <br />tJ <br /> <br />Plane coordinate system was chosen because it was the coordinate system of choice for the <br /> <br />r ~ <br /> <br />CDOW and is based on the English unit system, which the PTSIII allows. At each site, one <br /> <br />, <br />, \ <br />L_cl <br /> <br />ground control point was selected to be the reference position and other GCP's were used for <br /> <br />E;l <br />U <br /> <br />determining azimuth and as a rough check on total station coordinates. <br /> <br />1:1 <br />{ ., <br />t",'j <br />f _ .:_~ <br />f-'-:! <br />L..,;-J <br /> <br />17 <br />