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Sand classifications along the Colorado River in Grand Canyon derived from 2002, 2009, and 2013 high-resolution multispectral airborne imagery

October 9, 2018

These data are remote sensing image-based classification maps of unvegetated river-derived sand along the Colorado River. One map is based on imagery acquired in May 2013 and is a classification of sand located above the wetted river channel in the imagery which was acquired at the approximate contemporary low-flow river discharge of 8,000 cubic feet per second (227 cubic meters per second) and extends from Glen Canyon Dam at Lake Powell to Separation Canyon at Lake Mead, a total distance of approximately 255 river miles (410 river kilometer). Three other maps are based on imagery acquired in May 2002, 2009, and 2013, respectively, and are classifications of sand located above the wetted river channel (at river discharge of approximately 8,000 cubic feet per second, or 227 cubic meters per second) and below the approximate maximum contemporary flood stage of the river at a discharge of 45,000 cubic feet per second (1,274 cubic meters per second). Those three maps extend from Lees Ferry (approximately 15 miles downstream of Glen Canyon Dam) to Diamond Creek, a total distance of approximately 226 river miles (364 river kilometers). These three maps only have sand classified within large sand deposition zones (SDZs) in the river corridor. Sand transported by the Colorado River through Grand Canyon is stored on the river bed and in recirculation zones, or eddies, that typically house separation or reattachment sandbars in the lee of debris fans (Schmidt, 1990; Hazel et al., 2006). Alternatively, sand can also be found lining pools and channel margins upstream of debris fans (Schmidt, 1990). The SDZs were identified by delineating individual large eddies and adjacent debris fans, pools and channel margins which contain a majority of the areas of exposed unvegetated river-derived sand that can be classified by multispectral image analysis. The more comprehensive 2013 sand map extends outside of the SDZs and encompasses all river-derived sand within the entire width and length of the river corridor above the low-flow river stage. Each classification map was derived from a combination of unsupervised and supervised image classification methods followed by exhaustive image interpretation and map editing to identify river-derived sand that was not vegetated and not obviously colonized by biologic soil crust. The sand classifications have the same 0.2-meter ground resolution as the imagery. No formal accuracy assessment has been completed at this time for these data.