Monitoring fine-sediment volume in the Colorado River ecosystem, Arizona: Bathymetric survey techniques

In 2002, a fine-grained sediment (sand, silt, and clay) monitoring effort was initiated in the Colorado River ecosystem, the river corridor downstream from Glen Canyon Dam, to directly survey channel topography at scales previously unobtainable in this canyon setting. This report presents an overview of the equipment and the methods used to collect and process the high-resolution bathymetric data required for this monitoring effort. The survey methods were employed in up to 11 discrete reaches during various time intervals. The reaches varied in length from 1.3 to 6.4 km. An assessment of depth-measurement uncertainty is presented that shows the surveys meet or exceed the requirement needed to detect changes at the 0.25-m level with 95 percent confidence. These data, in the form of high-resolution digital elevation models, will be integrated in a geographic information system and used to compare maps of topography, grain size, and other information to study the spatial distribution of fine sediment in this system.