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<br />. <br /> <br />. <br /> <br />. <br /> <br />HYDRAULIC ANALYSIS <br /> <br />Mapping <br /> <br />The U.S. Bureau of Reclamation contracted with Horizons, lnc, to take orthophotos of the <br />Los Pinos flood plain and to provide electronic format survey information, The elevation tagged data <br />collection included the Los Pinos River and its tributaries, the transportation infrastructure, fault lines, <br />spot elevations, and contours, <br /> <br />To get the most accurate cross sections possible, a digital terrain model (DTM) of the study <br />area from Vallecito Dam to Bayfield was developed by Resource Technology, lnc, using Softdesk@ <br />software, With the exception of the contours, all of the electronic surveyed information was utilized <br />to create the DTM, Contours were then created from this DTM and compared to the contour <br />information provided by the Bureau of Reclamation to insure accuracy, The comparison did not <br />show any significant differences, <br /> <br />A channel centerline alignment was determined and stationed for the Los Pinos River. In <br />locations where the river split, the predominant flow channel was selected The existence of several <br />historic channels along this reach indicates the channel alignment is continuously changing as a result <br />of erosion and sedimentation, <br /> <br />Cross Sections <br /> <br />Locations of cross sections were initially determined by visual inspection of the topographic <br />data and by selecting representative channel reaches of the river near transitions, bridges, and other <br />structures, Ninety-seven digital cross sections were selected along this reach of the Los Pinos River <br />at approximately 100- to 2000-foot distances, depending on the channel geometry, with closer <br />spacing at the bridges, The cross sections were digitally cut using the Boss' River Modeling System <br />(RMS) software which includes the HEC-RAS software, See Appendix B for plots of the cross <br />sections, and the flood plain maps for the location and orientation of the cross sections, <br /> <br />The information used to create the DTM indicated the top of the water surface at the time the <br />photographs were taken and not the channel invert, To accurately compute the water surface <br />elevations, a channel invert needed to be determined. Field inspections indicated normal channel flow <br />depths at approximately 1,5 to 2 feet. Utilizing a conservative depth of I-foot will force more of the <br />flow onto the overbanks, which will prevent the flood plain and water surface elevations from being <br />underestimated, The minimum channel elevations in each cross section were consequently lowered 1- <br />foot while maintaining a typical bank slope for the area, <br /> <br />12 <br />