DEVELOPING SUAS METHODS FOR MEASURING CHANGES IN RIVER TOPOGRAPHY FOLLOWING DAM REMOVAL

Dam removal is an increasingly popular management solution to address ecological impacts of aging dam infrastructure. However, the river ecosystem responses from dam removal are poorly understood due to minimal pre-/post-removal studies (Foley et al. 2017; Hart et al. 2002; Poff & Hart, 2002). In addition, administrative, technical, and financial barriers often prevent sufficient collection of data for restoration project evaluation (Roni & Beechie, 2012; Bernhardt et al. 2005; NRC 1992). This work seeks to develop photogrammetric techniques using small unmanned aerial systems (sUAS, a.k.a. “drones”), to assess geomorphic changes in riverine systems and validate them against conventional techniques. A DJI Phantom 3 Professional sUAS collected imagery downstream of a small dam removal in Dover, NH pre- and post-removal. Topographic changes to the reach were evaluated using digital surface models and orthomosaics created using commercially available structure-from-motion photogrammetry software (Agisoft PhotoScan Professional). For conventional approaches, monumented cross sections and multiple checkpoints throughout the landscape were surveyed with a total station. The results from the conventional measurement approaches were compared to the measurements made from the sUAS products to help determine the efficacy of the aerial approach for measuring changes in topography. In addition, ways to potentially correct inaccuracies in the sUAS-derived topography are discussed. The sUAS methods are a promising, low-cost approach to evaluating ecological impacts from dam removal and other river management.