Mapping the Riverscape of the Middle Fork John Day River with Structure-from-Motion

Abstract:

Aerial photography has proven an efficient method to collect a wide range of continuous variables for large sections of rivers. These data include variables such as the planimetric shape, low-flow and bank-full widths, bathymetry, and sediment sizes. Mapping these variables in a continuous manner allows us to explore the heterogeneity of the river and build a more complete picture of the holistic riverscape. To explore a low-cost option for aerial photography and riverscape mapping, I used the combination of a piloted helicopter and an off-the-shelf digital SLR camera to collect aerial imagery for a 32 km segment of the Middle Fork John Day River in eastern Oregon. This imagery was processed with Structure-from-Motion (SfM) photogrammetry to produce high-resolution 10 cm orthophotos and digital surface models that were used to extract riverscape variables. The Middle Fork John Day River is an important spawning river for anadromous Chinnook and Steelhead and has been the focus of widespread restoration and conservation activities in response to the legacies of extensive grazing and mining activity. By mapping the riverscape of the Middle Fork John Day, I explored downstream relationships between several geomorphic variables with hyperscale analysis. These riverscape data also provided an opportunity to make a continuous map of habitat suitability for migrating adult Chinook. Both the geomorphic and habitat suitability analysis provide an important assessment of the natural variation in the river and the impact of human modification, both positive and negative.