Comparison of sand distribution between April 1994 and June 1996 along six reaches of the Colorado River in Grand Canyon, Arizona

Abstract

Two geophysical surveys in April, 1994 and June, 1996 collected data along 15 reaches of the Colorado River in Grand Canyon. This report discusses six of those reaches between the Little Colorado River and Tanner Rapid. The surveys imaged the distribution of sand and mixtures of sand with pebbles, cobbles and boulders stored within the reaches. The surveys established a baseline of sand distribution before an experimental flood in March, 1996 and mapped changes in the areal distribution of sand within each reach after the 1996 flood. This study does not attempt to estimate the volume change in sediment stored within the reaches. Survey control relied on a network of monuments established by the Glen Canyon Environmental Study (GCES) and the United States Geological Survey Water Resources Division (WRD). The 1994 survey utilized a high-resolution seismic-reflection profiler, a side-scan sonar system, a bathymetric profiler, and underwater video system. The 1996 survey did not use the high-resolution seismic profiler because the system was generally unsuccessful in detecting subsurface structure due to multiples created in shallow water. Both surveys used underwater video to collect images of the river bed to validate our interpretations of the side-scan record. This report describes data collection, interpretation, and discusses trends found along the reaches studied in detail.

Influence of a dam on fine‐sediment storage in a canyon river

“…Thus, as in the case of the predam observations of scour and fill in the pools at the Lees Ferry and Grand Canyon gauges, the magnitudes of scour and fill measured in pools probably overestimates the average magnitude of scour and fill elsewhere in the main channel. Also, as observed at the Grand Canyon gauge [ Topping et al , 2000b] and elsewhere in selected reaches during the 1996 Controlled Flood [ Anima et al , 1998], scour of sediment from main‐channel pools during high flows is partially balanced by deposition of sediment outside of the deeper pools. Another and perhaps more likely possibility is that the overestimation is a result of coarser material mobilized in areas of high sheer stress produced by the high flows [ Wiele et al , 1999].…”

“…The bed of the postdam river is primarily composed of gravel, boulders, and bedrock. Overlying this coarse material are discontinuous patches of sand [ Wilson , 1986; Anima et al , 1998]. Many of these sand patches are thin in Marble Canyon, because gravel can be observed protruding through the troughs of dunes [ Rubin et al , 2001].…”

Regulation of sand transport in the Colorado River by changes in the surface grain size of eddy sandbars over multi‐year timescales

“…Analysis of aerial photographs (Schmidt et al. , 2004) and side‐scan‐sonar data (Anima et al. , 1998; Wong et al.…”

“…, 2004; Hazel et al , in press). Side‐scan‐sonar data collected in the study area between 1994 and 2000 suggest that, on average, the channel bed is composed of by area 40% finer gravel (pebbles and cobbles of probable fluvial origin), 20–30% sand, 20–30% bedrock, and 10–20% large, immobile boulders that are either derived from tributaries or the hillslopes and cliffs adjacent to the river (Anima et al. , 1998; Wong et al.…”

Self‐Limitation of Sand Storage in a Bedrock‐Canyon River Arising From the Interaction of Flow and Grain Size

“…Large increases in sand-patch thickness will therefore cause an increase in the spatially averaged τ b over a patch, thus leading to an increase in the reach-averaged τ b . Bed-sand area is generally 10%-70% over the reach scale (Anima et al, 1998;Grams et al, 2019Grams et al, , 2013Schmidt et al, 2007;Topping et al, 2007) and substantial changes in sand-patch thickness are localized. For example, between 2009 and 2012, 70% of the total change in sand volume in a 50-km river segment occurred over only 12% of the length of this segment (Grams et al, 2019).…”