Assessing Whitewater Difficulty Using Specific Stream Power Based on Site-Scale UAV Measurements on the Deschutes River

Boaters use class ratings to describe whitewater difficulty on a scale from I to VI, with ratings assigned and refined through the judgment of experienced boaters. These practices are effective, but the addition of physical measurements could improve their reliability and facilitate whitewater comparisons across different rivers and flows. This exploratory study considers specific stream power (SSP), a physics-based metric describing energy transfer in rivers, as an indicator of whitewater difficulty. Data were collected at eight study sites on the Upper Deschutes River in Oregon using a camera-mounted DJI Phantom 4 RTK quadcopter. Sites were assessed at one or two flows and whitewater difficulty ranged from Class I flatwater to Class V cascading rapids. Stream slope and width data were derived from a combination of unmanned aerial vehicle (UAV) photogrammetry and aerial light detection and ranging (LiDAR), and SSP was calculated for each site. Whitewater class ratings were strongly associated (df = 6, p < 0.05) with site average SSP, rs= 0.95, 95% CI [0.72, 1.00], site average slope, rs = 0.95, 95% CI [0.72, 1.00], and within-site maximum SSP, rs = 0.93, 95% CI [0.58, 1.00]. The within-site maximum slope, minimum width, and constriction ratio had significant but smaller relationships. Physical assessments of whitewater conditions may help support management decisions in dam removal, hydropower relicensing, or other instream flow negotiations.