Connectivity of Sand Resources Along the Colorado River in Grand Canyon

Science Center Objects

We study the links among different geomorphic processes that affect river valley landscapes in the Colorado River downstream from Glen Canyon Dam, Arizona. Dam-released flows affect the deposition and retention of sandbars that serve as sources for other sand resources, such as windblown sand dunes, throughout the Colorado River ecosystem. The degree to which the landscapes are differentially affected by river, wind, rainfall, or gravity-driven redistribution of river-derived sand is called sediment “connectivity”. Connectivity is affected by several factors including the amount of sand supplied as well as physical and vegetative barriers to sand transport. Connectivity affects the condition of natural and cultural resources – such as archaeological sites – in the ecosystem. In particular, we assess the potential for Colorado River sand to enhance the preservation of river-corridor archeological resources through burial by wind deposition and/or mitigation of gully erosion.

A photograph/illustration depicting a stretch of river, sand deposition, and canyon walls that illustrate sediment movement

Figure 1: Overview of geomorphic processes and landforms that are important for sediment connectivity along the Colorado River in Grand Canyon. CLICK ON IMAGE TO ENLARGE IT. (Credit: Alan Kasprak, USGS. Public domain.)

Background & Importance

Dam-released flows affect the deposition and retention of sand bars that serve as sources for other sand resources throughout the Colorado River ecosystem. Wind transport of sand from sandbars located near the active river channel to higher elevation valley margins can, in turn, affect the geomorphic condition of archaeological sites and the characteristics of other cultural and natural resources in the ecosystem. The degree to which valley margins are affected by upslope wind redistribution of river-derived sand is called sediment “connectivity” (Figure 1). Connectivity is affected by several factors including the amount of sand supplied as well as physical and vegetative barriers to sand transport. Connectivity affects the condition of natural and cultural resources – such as archaeological sites – in the ecosystem. One primary hypothesis of this project is that high degrees of connectivity lead to greater archaeological site stability and increase the potential for preservation in place of buried archaeological features via windblown sand deposition and/or mitigation of gully erosion.

General Methods

We use geomorphic change detection to monitor topographic changes due to the erosion and deposition of sediment with a wide variety of digital topographic data sources that include photogrammetry, lidar, and total station surveys from ground, airplane, and UAS platforms. We also use geomorphic, ecological, geoarchaeological, and sedimentological assessments from detailed site investigations.

Windblown (aeolian) sand dune along the Colorado River in Grand Canyon.

Windblown (aeolian) sand dune along the Colorado River in Grand Canyon that formed from sand deposited in a river sandbar by a controlled flood in 2008. (Credit: Amy East, USGS. Public domain.)

Colorado River at Basalt Rapids. Foreground shows eddy sandbar and sand dune sediment deposits.

Colorado River at Basalt Rapids. Foreground shows eddy sandbar and sand dune sediment deposits (spring 2014). (Credit: Joel Sankey, USGS. Public domain.)