A Reproducible Methodology for High-Resolution 3D and Orthomosaic Mapping in Forested Streams

1 - Frequent, fine-scale assessments of forested stream morphology are essential for understanding habitat conditions and guiding management, yet dense canopy and budget constraints often limit airborne LiDAR and conventional surveys. 2 - We present a reproducible, ground-based photogrammetry workflow using a chest-mounted action camera (GoPro) and the Agisoft Metashape software to generate scaled, georeferenced 3D models and orthomosaics of stream reaches. The workflow details image acquisition under variable lighting and flow conditions, image alignment, dense cloud/mesh generation, and export of GIS-ready products. 3 - Applied in Mont-Tremblant National Park and Kenauk Nature (Quebec, Canada) across 56 forest-stream reaches in a single summer field season, the workflow produced scaled, GIS-ready orthomosaics with nominal pixel sizes as low as [~]1.36 mm/pixel. These products captured fine-scale channel morphology, enabling consistent reach-scale habitat mapping and temporal comparisons for restoration monitoring. 4 - By reducing equipment costs and simplifying logistics relative to airborne or terrestrial LiDAR, this practical tool enables frequent, high-resolution surveys in dense-canopy streams. Future extensions (e.g., automated substrate classification via machine learning) can further standardize habitat assessment and support long-term ecological monitoring.