Effects of river regulation on aeolian landscapes, Colorado River, southwestern USA

Abstract

[1] Connectivity between fluvial and aeolian sedimentary systems plays an important role in the physical and biological environment of dryland regions. This study examines the coupling between fluvial sand deposits and aeolian dune fields in bedrock canyons of the arid to semiarid Colorado River corridor, southwestern USA. By quantifying significant differences between aeolian landscapes with and without modern fluvial sediment sources, this work demonstrates for the first time that the flow-and sediment-limiting effects of dam operations affect sedimentary processes and ecosystems in aeolian landscapes above the fluvial high water line. Dune fields decoupled from fluvial sand supply have more ground cover (biologic crust and vegetation) and less aeolian sand transport than do dune fields that remain coupled to modern fluvial sand supply. The proportion of active aeolian sand area also is substantially lower in a heavily regulated river reach (Marble-Grand Canyon, Arizona) than in a much less regulated reach with otherwise similar environmental conditions (Cataract Canyon, Utah). The interconnections shown here among river flow and sediment, aeolian sand transport, and biologic communities in aeolian dunes demonstrate a newly recognized means by which anthropogenic influence alters dryland environments. Because fluvial-aeolian coupling is common globally, it is likely that similar sediment-transport connectivity and interaction with upland ecosystems are important in other dryland regions to a greater degree than has been recognized previously.Citation: Draut, A. E. (2012), Effects of river regulation on aeolian landscapes, Colorado River, southwestern USA,

Gully monitoring at two locations in the Grand Canyon National Park, Arizona, 1996-2010, with emphasis on documenting effects of the March 2008 high-flow experiment

“…The 2008 weather station data showed that although the flood-formed sandbar riverward (southwest) of the study sites was enlarged substantially during the 2008 HFE, the dominant wind direction did not move sand from the sandbar into the dune field (Draut and others, 2009b). The dominant wind direction in 2008 was similar to conditions measured in previous years (Draut and Rubin, 2008;Draut andothers, 2009a, 2009b).…”

“…Although gully erosion is not a recent phenomenon in the Grand Canyon, gully erosion in the pre-dam era was partially offset by fine-sediment redistribution into gullies during annual spring runoff floods and migration of aeolian dunes into gully areas (McKee, 1938;Hereford and others, 1993;Sankey and Draut, 2014). In the post-dam era, the sediment load and magnitude of floods have been greatly reduced (Topping and others, 2003), along with the redistribution of flood sands by wind (Draut and Rubin, 2008;Draut, 2012); the degree to which these changes affect the preservation of irreplaceable archaeological resources in the Grand Canyon is a subject of on-going investigations (for example, others, 2009, 2012;Fairley and others, 2012;Sankey and Draut, 2014).…”

High-resolution topography and geomorphology of select archeological sites in Glen Canyon National Recreation Area, Arizona

“…This hypothesis posits that the reduction in the number and areal extent of high-elevation sand bars (Schmidt and others, 2004;Hazel and others, 2010;Schmidt and Grams, 2011a) has resulted in a reduction in the amount of sand available to be transported inland towards archeological sites by wind; this, in turn, has changed the depth and surface characteristics of aeolian sand cover at many archeological sites (Lucchitta, 1991;Thompson and Potochnik, 2000;Draut and Rubin, 2008;Draut, 2012). The post-dam decrease in large, unvegetated sandbars is therefore hypothesized to have resulted in a consequent increase in the amount and intensity of surface erosion at archeological sites due to a decrease in sand transport to the sites.…”

“…In 1963, with completion of Glen Canyon Dam 25 km upstream of the Grand Canyon, the Colorado River's natural hydrology was radically altered (Topping and others, 2003), with concomitant landscape effects and ecological consequences (U.S. Department of the Interior, 1995). These consequences include a reduction in the size and volume of sand bars (Schmidt and others, 2004;Hazel and others, 2010), an increase in riparian vegetation at low elevations and senescence of the riparian vegetation at higher elevations (Turner and Karpiscak, 1980;Waring, 1996), reduction in the amount of active aeolian sand dune areas (Draut, 2012), and lack of new sediment deposition by floods above the 1,274 m 3 /s (45,000 cubic feet per second, ft 3 /s) stage within the river corridor (Melis, 2011). In combination, these changes appear to have resulted in an increase in gully erosion and gradual exposure of buried archeological sites situated in and on the pre-dam alluvial terraces above the level of the active river channel (Fairley, 2005;Fairley and Sondossi, 2010).…”

“…Aeolian sand transport is able to counteract surface erosion to some degree by (1) creating expanses of surficial sand with high infiltration capacity that can absorb rainfall and (2) filling in small gullies that form during rainfall-induced overland flow events. Draut (2012) posits that today's aeolian processes are only effective at controlling gully erosion where there are large sand bars with surficial sediments available to be entrained by wind, and where the bars are appropriately positioned relative to the prevailing winds so that the sediment is transported toward downwind terraces and archaeological sites. However, in the pre-dam era, expanses of unvegetated sand were more common due to the frequency of high-magnitude sediment-enriched spring floods (Topping and others, 2003), and the effects of aeolian sand redistribution on slowing erosion might have been more widespread.…”