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

In settings where the transport of sand is partially or fully supply limited, changes in the upstream supply of sand are coupled to changes in the grain size of sand on the bed. In this manner, the transport of sand under the supplylimited case is ‘grain-size regulated’. Since the closure of Glen Canyon Dam in 1963, the downstream reach of the Colorado River in Marble and Grand Canyons has exhibited evidence of sand-supply limitation. Sand transport in the river is now approximately equally regulated by changes in the discharge of water and changes in the grain sizes of sand on the channel bed and eddy sandbars. Previous work has shown that changes in the grain size of sand on the bed of the channel (driven by changes in the upstream supply of sand owing to both tributary floods and high dam releases) are important in regulating sand transport over timescales of days to months. In this study, suspended-sand data are analysed in conjunction with bed grain-size data to determine whether changes in the grain size of sand on the bed of the channel or changes in the grain size of sand on the surface of eddy sandbars have been more important in regulating sand transport in the post-dam Colorado River over longer, multi-year timescales. The results of this study show that this combined theory- and field-based approach can be used to deduce which environments in a complicated setting are the most important environments for regulating sediment transport. In the case of the regulated Colorado River in Marble and Upper Grand Canyons, suspended-sand transport has been regulated mostly by changes in the surface grain size of eddy sandbars.

[1]  A. Howard,et al.  Geomorphology of the Colorado River in the Grand Canyon , 1981, The Journal of Geology.

[2]  R. Webb,et al.  Magnitude and frequency data for historic debris flows in Grand Canyon National Park and vicinity, Arizona , 1995 .

[3]  J. Smith,et al.  Sand Deposition in the Colorado River in the Grand Canyon from Flooding of the Little Colorado River , 1996 .

[4]  Robert H. Webb,et al.  The Controlled Flood in Grand Canyon , 1999 .

[5]  J. Schmidt,et al.  Computation and analysis of the instantaneous-discharge record for the Colorado River at Lees Ferry, Arizona : May 8, 1921, through September 30, 2000 , 2003 .

[6]  S. Mclean.  On the calculation of suspended load for noncohesive sediments , 1992 .

[7]  Aggradation and degradation of alluvial sand deposits, 1965 to 1986, Colorado River, Grand Canyon National Park, Arizona , 1990 .

[8]  Variations in sand storage measured at monumented cross sections in the Colorado River between Glen Canyon Dam and Lava Falls Rapid, northern Arizona, 1992-99 , 2003 .

[9]  M. Kaplinski,et al.  Recent sediment studies refute Glen Canyon Dam Hypothesis , 2002 .

[10]  L. B. Leopold.  The rapids and the pools - Grand Canyon: Chapter D in The Colorado River region and John Wesley Powell (Professional Paper 669) , 1969 .

[11]  E. Andrews.  Sediment Transport in the Colorado River Basin , 1991 .

[12]  Stephen T. Nelso.  Is there a hard money future after graduate school , 1994 .

[13]  D. Topping,et al.  Colorado River sediment transport: 1. Natural sediment supply limitation and the influence of Glen Canyon Dam , 2000 .

[14]  Robert H. Webb,et al.  Debris flows from tributaries of the Colorado River, Grand Canyon National Park, Arizona , 1987 .

[15]  J. Schmidt,et al.  Flume simulation of recirculating flow and sedimentation , 1993 .

[16]  E. Andrews,et al.  The effect of sand concentration on depositional rate, magnitude, and location in the Colorado River below the Little Colorado River , 2013 .

[17]  James P. Bennett,et al.  Flow and Sediment‐Transport Modeling , 2005 .

[18]  Susan P. Speece.  The Colorado River in the Grand Canyon. , 1991 .

[19]  Changes in the water surface profile of the Colorado River in Grand Canyon, Arizona, between 1923 and 2000 , 2005 .

[20]  M. Kaplinski,et al.  Influence of a dam on fine‐sediment storage in a canyon river , 2006 .

[21]  J. Schmidt,et al.  Origin, Structure, and Evolution of a Reattachment Bar, Colorado River, Grand Canyon, Arizona , 1990 .

[22]  D. Topping,et al.  Quantifying the relative importance of flow regulation and grain size regulation of suspended sediment transport α and tracking changes in grain size of bed sediment β , 2001 .

[23]  Comparison of sand distribution between April 1994 and June 1996 along six reaches of the Colorado River in Grand Canyon, Arizona , 1998 .

[24]  D. Topping,et al.  Colorado River sediment transport: 2. Systematic Bed‐elevation and grain‐size effects of sand supply limitation , 2000 .

[25]  D. Topping,et al.  Relation of inversely graded deposits to suspended-sediment grain-size evolution during the 1996 flood experiment in Grand Canyon , 1998 .

[26]  J. B. Graf,et al.  Streamflow and sediment-transport data, Colorado River and three tributaries in Grand Canyon, Arizona, 1983 and 1985-86 , 1993 .

[27]  M. E. Cooley,et al.  Effects of the catastrophic flood of December 1966, north rim area, eastern Grand Canyon, Arizona , 1977 .

[28]  J. Schmidt.  Recirculating Flow and Sedimentation in the Colorado River in Grand Canyon, Arizona , 1990, The Journal of Geology.