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- --..._--. . ----~.- --..:_-.:..,;.:..;,.:~~~~~~~&~-,--: 6 was considered suitable for comparison with the 1987 1:4,000 photography. Two gaps occurred in the aerial photographic coverage because of omission by the pilot. These occurred from approximately rm 48 to rm 51 (see below for rm mile calculations for 1988) just south of Rock Creek in Desolation Canyon, and from about rm 12 to rm 13 above the confluence of the Green and Colorado Rivers. Avera e dail flow at tes was 1 188, 1 270 234 f s, respectively. Average daily flow at the reen River gau~e for these dates was 1.989, 1,764. and 1,918 ft3/s, A':)2.~Z7/ 2...:;' respectively. Backwater area and numbers as well isolated pools were recorded on photo mylar overlays. Backwaters were digitized with the same equipment as above. Photographic overlays were placed directly on a multi-point lat-long computer generated grid mounted on the digitizing board as a reference for area calculations. Grids were generated at the same scale as the photography. Backwaters which were too small to digitize were recorded as points or lines. The area of lines was estimated by assuming a width of 3 m (approximate pencil width at 1:6,000) and multiplying times the length of the line. Point backwaters were assumed to be 9 m2 or 3 by 3 m2. Backwaters and isolated pools were recorded by rm. RM were calculated from the estimated centerline of the river on USGS quadrangles. Mile segments were measured with an electronic planimeter. The river was arbitrarily divided into 20-mile segments for comparison purposes. Backwater characteristics were also compiled for the sampling strata reported in Tyus et al. (1987). In addition, data were recorded by specific segments of the river corresponding to the 1987 study sites to compare backwater area and numbers between years. 1988 Videography methods On August 23, 1988, aerial photography and videography were acquired concurrently for the Island Park and Jensen sites from a fixed- wing aircraft flying at 3,000 feet above mean terrain (AMT). The aerial photography was acquired at an approximate scale of 1:6,000. Riverflow for August 23 was 1,180 ft3/S at the Jensen USGS gauge. Panel markers were placed at specified distances at each site to verify photographic and videography scale. Aerial photography was interpreted as described above for the 1988 photography. A standard Panasonic Video camera, model WV 3260\8AF was mounted on the same aircraft flight used for aerial photography on August 23, 1988. The video camera zoom lens was adjusted to a 55 degree field of view. In contrast, the 9- x 9-in camera gathers imagery at a 90 degree field of view covering more of the river and its banks. At 3,000 ft AMT, the Panasonic video camera produced imagery with a pixel size of 1.4 m. On September 7, 1988, an Ikigami video camera was attached to a helicopter with a Tylor mount and connected to a monitor viewed by the flight scientist. The monitor allowed altitude adjustments to be made until the field of view exceeded the maximum width of the river. The riverflow on September 7 was recorded as 912 ft3/s at the USGS Jensen gauge. At