The mapping of surface microtopography (meter to centimeter scales) is important in studies of large-scale fluvial geomorphology. In dam-influenced environments, accurate evaluation of sand resources is a necessary component in monitoring changes through time to the entire riparian ecosystem. Traditional methods of ground surveying and mapping geomorphic features associated with fluvial systems is an often time-consuming and costly process. The use of aerial photography for mapping these same features has been shown to provide data consistent with labor-intensive field surveys for above-surface geomorphic features along reaches of the Colorado River within the Grand Canyon; however the laboratory interpretation and development of the GIS database is still a lengthy process. Present day needs for large-scale mapping at reduced times and cost is increasingly being met through the use of digital photogrammetry. Digital photogrammetry can provide excellent resolution in the X, Y, and Z directions - up to 10 cm spatial resolution for a 1:4000-scale photo. If a template for a fluvial geomorphic surface map can be created from digital aerial photography, then subsequent updates of the data would be relatively time and cost effective. We are testing the use of digital photogrammetric techniques for mapping fluvial geomorphic features at two sites for two dates - pre- and post-flood, Spring, 1996. Previously created maps, as well as topographic surveys will be used to gauge how well the digital photogrammetric methods worked for mapping fluvial geomorphic features and for evaluating sandbar evolution.

Keyword: remote sensing, geomorphology-fluvial, Grand Canyon