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-----~- --"~,~~~~~......,- 3 compared backwater mapping results of aerial photography and airborne videography techniques on the Green River, including cost and turnaround times. METHODS 1986 Pilot Study Three study sites were selected by Reclamation and FWS that were considered important for backwater habitat: SDlit Mountain [rm 306-309.7J,~ur~ (!]I 254.8-257.8), and Willow Creek-(rm 237.8-251t. RM designations were taken from Evans and Belknap's Dinosaur River guide (rmO at Green River, Utah), Evans and Belknap's Desolation River Guide (rm 0 at Green River, Utah), and Belknap and Belknap's Canyonlands River Guide (rm 0 at the confluence of the Green and Colorado rivers). All rm designations were adjusted to 0 from the confluence of the Green and Colorado rivers. Study site locations for each year are illustrated in figure 1. Backwater numbers and area were examined at each site during three Green River f~: 1,889, 3,119. and 4,359 ft3/s. When flows relea~rom Flaming Gorge Dam were stabilized, CIR aerial photography was obtained for each site. Flows were measured at the Jensen Geological Survey (USGS) gauge. Two photographic scales were acquired, 1:4,000 and 1:2,000, to determine what scale would be adequate for backwater delineation. Field trips were taken to familiarize the photointerpreter with backwater delineation and to place panel markers at specified distances at each site to verify and correct photographic scale. Aerial photographs were fitted with mylar overlays upon which the river channel, backwaters, isolated pools, sandbars, vegetated sandbars, and vegetated Islands were delineated. The relatively large scale of the aerial photography would have made it difficult to transfer the interpreted classes to a standard 1:24,000 scale USGS quadrangle, as the integrity of the larger scale data base would have been lost. Therefore, to maintain interpretation accuracy, pseudomap bases of the same scale as the photography were created. Roads and other prominent features were delineated on photographs and compared to USGS maps to ensure photographic scale accuracy and provide a geographic reference. Following transfer of photointerpretated data to pseudomap overlays, the information was digitized into a GIS system utilizing Geographic Entry System software. Digitization was done in vector format using a Calcomp 9000 digitizing tablet linked to a Tektronix 4014 display screen. Software and peripherals were run by an HP 3000 Series III computer. Each study site was approximately 7.5 by 7.5 min making the internal resolution of the ~ computer 0.2 m. 1987 Study Five study sites were selected by the Reclamation and FWS in areas known to contain important backwater habitat for young-of-the-year Colorado squawfish (figure 1). The Island Park site, just above Split Mountain in Dinosaur