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DISTRIBUTION OF AQUATIC OFF-CHANNEL HABITATS AND ASSOCIATED RIPARIAN VEGETATION, WILLAMETTE RIVER, OREGON, USA
Cline, S P., W. W. Carson, AND P. K. Haggerty. DISTRIBUTION OF AQUATIC OFF-CHANNEL HABITATS AND ASSOCIATED RIPARIAN VEGETATION, WILLAMETTE RIVER, OREGON, USA. Presented at American Society for Photogrammetry and Remote Sensing Annual Meeting, Washington, DC, May 22-26, 2000.
The extent of aquatic off-channel habitats such as secondary and side channels, sloughs, and alcoves, have been reduced more than 50% since the 1850s along the upper main stem of the Willamette River, Oregon, USA. Concurrently, the hydrogeomorphic potential, and associated flood disturbance, has been reduced from historical levels by dam and revetment construction. We hypothesize that the resulting stability shifts the frequency and extent of off-channel habitats to predominantly older age classes. A contemporary map of riparian vegetation was needed to evaluate this hypothesis and establish if distinct vegetation types were associated with off-channel habitats and fluvial land forms with different flood frequencies and intensities. Digital maps of aquatic habitat, vegetation, and terrain were developed from aerial photos using standard photogrammetric techniques. Digital maps derived from aerial photographs, however, have variable accuracies depending upon the photo scale (1:24000 and 1:6000), the quality of ground control (orthophoto, map, GPS, and DTM), the mapping instrument quality, and the skill of the operator. This paper investigates the potential accuracy of absolute point measurements--as needed for riparian zone feature mapping--and relative measurements, as needed to measure vegetation heights, terrain elevations, log lengths, and vegetation polygons. The accuracy assessments were related to the traditional photogrammetric parameters--orientation residuals--and the feature measurements were repeated independently by two instrument operators with different skill levels on a second-order stereoscopic photogrammetric plotter. Implications of results are discussed with respect to effects on testing our research hypothesis and on end users involved with river restoration projects.