2.2.1. Imagery Acquisition
We acquired basemap imagery for the digitization of the valley plug in 2021 with an unmanned aerial vehicle (UAV; DJI Mavic 2 Pro) outfitted with a Hasselblad L1D-20c camera (20MP 1” sensor), or from available high resolution aerial photos. For 2021 imagery collected by UAV, we collected imagery at flight heights ranging from 300 to 350 m at 20 mph. We post-processed imagery in DroneDeploy (dronedeloy.com) to produce 2 cm resolution orthomosaic images (e.g., Carbonneau et al. 2020; Oakland 2020). We also used historic imagery from Google Earth (June 6, 2009, and April 2, 2015; Maxar Technologies, State of Utah, USDA/FPAC/GEO; ~0.15m resolution) to capture conditions prior to 2021 and for our reference reaches: Moonshine Wash and Spring Canyon.
We collected UAV imagery on September 23, 2021. Flows for the UAV imagery were a maximum of 0.40 and a minimum of 0.30 cms. Historic imagery flows were a maximum of 8.10 and a minimum of 7.14 cms for 2009, and a maximum of 0.26 and a minimum of 0.12 cms for 2015. Flows were measured at US Geologic Survey (USGS) gauge #09328500 San Rafael River near Green River, Utah.