The response of source-bordering aeolian dunefields to sediment-supply changes 1: Effects of wind variability and river-valley morphodynamics

Source-bordering dunefields (SBDs), which are primarily built and maintained with river-derived sediment, are found in many large river valleys and are currently impacted by changes in sediment supply due to climate change, land use changes, and river regulation. Despite their importance, a physically based, applied approach for quantifying the response of SBDs to changes in sediment supply does not exist. To address this knowledge gap, here we develop an approach for quantifying the geomorphic responses to sediment-supply alteration based on the interpretation of dunefield morphodynamics from geomorphic change detection and wind characteristics. We use the approach to test hypotheses about the response of individual dunefields to variability in sediment supply at three SBDs along the Colorado River in Grand Canyon, Arizona, USA during the 11 years between 2002 and 2013 when several river floods rebuilt some river sandbars and channel margin deposits that serve as sediment source areas for the SBDs. We demonstrate that resupply of fluvially sourced aeolian sediment occurred at one of the SBDs, but not at the other two, and attribute this differential response to site-specific variability in geomorphology, wind, and sediment source areas. The approach we present is applied in a companion study to shorter time periods with high-resolution topographic data that bracket individual floods in order to infer the resupply of fluvially sourced aeolian sediment to SBDs by managed river flows. Such an applied methodology could also be useful for measuring sediment connectivity and anthropogenic alterations of connectivity in other coupled fluvial-aeolian environments.