Exploring the utility of small unmanned aerial system products in remote visual stream ecological assessment

Many restoration projects' success is not evaluated, despite available conventional ecological assessment methods. There is a need for more flexible, affordable, and efficient methods for evaluation, particularly those that take advantage of new remote sensing and geospatial technologies. This study explores the use of illustrative small unmanned aerial system (sUAS) products, made using a simple structure-from-motion photogrammetry workflow, coupled with a visual assessment protocol as a remote evaluation and ecological condition archive approach. Three streams were assessed in the field (“surface assessments”) using the Stream Visual Assessment Protocol Version 2 (SVAP2) and later illustrated in sUAS products. A survey of 10 stream experts was conducted to (1) assess the general utility of the sUAS products (high-resolution video, orthomosaics, and 3D models), and (2) test whether the experts could interpret the products and apply the 16 SVAP2 elements remotely. The channel condition, bank condition, riparian area quantity, and canopy cover elements were deemed appropriate for remote assessment, while the riparian area quality, water appearance, fish habitat complexity, and aquatic invertebrate complexity elements were deemed appropriate for remote assessment but with some potential limitations due to the quality of the products and varying site conditions. In general, the survey participants agreed that the illustrative products would be useful in stream ecological assessment and restoration evaluation. Although not a replacement for more quantitative surface assessments when required, this remote visual approach is suitable when more general monitoring is satisfactory.