Streamflow in a river can be used to calculate loads of constituents of concern in rivers but obtaining streamflow data using traditional streamgaging techniques in ephemeral channels can be cost prohibitive. Because of the remote location and infrequent flow occurrences, collecting paired stage-streamflow measurements for sufficient flow events during a 2-year study to develop a rating curve for estimating loads led to a novel approach. By combining uncrewed aerial system (UAS)-based imagery, digital surface models (DSM) derived from structure-from-motion (SfM) photogrammetry, and continuous pressure transducer data during flow events, streamflow can be modelled using a safe and cost-effective way to rapidly estimate streamflow in ephemeral streams. UAS photographs were collected for 22 tributaries upstream of their confluence with the San Juan River. Additionally, airborne lidar data were collected in four of the tributaries because SfM is unable to penetrate heavy vegetation cover in those channels. These data were used to construct DSMs and orthomosaics for all 22 streams.
