Changes in the water surface profile of the Colorado River in Grand Canyon, Arizona, between 1923 and 2000

In 1923, a U.S. Geological Survey expedition surveyed the water surface profile of the Colorado River through Grand Canyon with theodolite and stadia rod. In 2000, lidar overflights collected topographic data centered on the river corridor, allowing construction of a new water surface profile and detection of change in the profile since 1923. By registering the surveys with respect to each other on the basis of 11 locations that were independently determined to have been unchanged between 1923 and 2000, 80 rapids were directly compared for change between 1923 and 2000. The average change for all measured rapids was +0.26 m, indicating net aggradation of the coarse‐grained alluvium forming the rapids throughout Grand Canyon. In addition, comparison of the two water surface profiles showed enhanced pool‐and‐rapid morphology. While 50% of the total drop of the river occurred in just 9% of the river distance in 1923, that value increased to 66% by 2000.