Aeolian response to sediment supply changes during large-scale drying events: a fluvial-aeolian experiment in the Colorado River in Grand Canyon
Abstract
Throughout the geologic history of Earth and other planetary bodies, transgression and regression of water levels in river channels, lakes, and oceans have influenced sediment transport in adjacent aeolian landforms. We empirically studied this phenomenon by leveraging an experimental five-day drop in river flow within the Colorado River in Grand Canyon during April 2021. Discharge from the upstream Glen Canyon Dam dropped to 142 m3/s, approximately 85 m3/s lower than the regularly occurring contemporary base-flow discharge of the river and exposed an estimated 26,154 m2 of sand per kilometer of the river. This represented a >100% increase in the source area of sediment supply for at least 57 aeolian dunefields and 60 additional areas of unvegetated sand located adjacent to the active river channel along the >400 km segment of the Colorado River within Grand Canyon National Park, AZ. We measured the threshold friction velocities for sand saltation and PM10 dust emissions on a 18,000 m2 sandbar at Lees Ferry on the Colorado River in Grand Canyon using the portable in-situ wind erosion lab (PI-SWERL) during each day of the low river flow experiment. We measured particle size distribution, gravimetric and volumetric water content at the threshold friction velocity sample locations. We also surveyed the elevation, topography, and surface roughness of the sample locations using ground-based lidar remote sensing. These measurements allowed us to quantify the variability in threshold friction velocity as a function of time since inundation by the river, sediment water content, grain size, topographic position, and surface roughness. Results show that threshold friction velocity decreased as time since inundation increased. However, relationships at individual locations were complex, owing to the other measured hydrologic and physical factors. For example, sediment moisture content decreased non-linearly as time since inundation increased, and threshold friction velocity was negatively related to height above the river water surface elevation. The work provides practical insight into how river flows might be managed to promote desirable aeolian landscape habitat in Grand Canyon and other dam-regulated rivers by optimizing the timing and duration of periods of low flows that might become increasingly necessary in light of drought-mitigation needs. The work provides theoretical insight into the response of aeolian landforms to sediment supply changes driven by periods of drought and climate change throughout the geologic history of Earth and potentially other planets.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFMEP11A..06S