Debris Fans and Cobble Bars found along the Colorado River between Lees Ferry, Arizona and Lake Mead.

Features classified as debris fans and cobble bars were delineated using a combination of automated and manual techniques. These classes are composite features because they encompass rough, smooth and vegetated areas within their boundaries. Previous and current research on debris flows in Grand Canyon were used as a basis for delineating areas along the river characterized by debris fans (Melis, 1994; Webb, 2000). These studies produced a coarse GIS polygon coverage of tributary drainages associated with debris fans along the Colorado River in Grand Canyon that we utilized to identify debris fans at the river’s edge. Because debris fans and cobble bars do not change appreciably over short periods of time, the initial shoreline developed in a previous mapping project for GCMRC (Mietz, 2003) was also used in our preliminary analysis for these two classes to limit the amount of on-screen digitizing required to achieve a final product.