UTILIZATION OF LIDAR–DERIVED TOPOGRAPHIC DATA FOR LANDFORM MAPPING AND SLOPE STABILITY ANALYSIS

The Trask River basin (Oregon) is one of several research watersheds in the Pacific Northwest where the effects of forest practices on aquatic resources are being examined. An understanding of geomorphic processes and landform characteristics that potentially exert first-order control on channel morphology, hydrology, and aquatic habitat characteristics is necessary in order to interpret the potential influence of management actions. As a tool to aid these interpretations, a geomorphic terrain map was developed from geomorphic and geologic derivatives calculated in GIS from models of slope gradient, shaded relief, landform characteristics, lithology, and mapped landslide features. Airborne LiDAR was used to create a DEM that provided high-resolution topographic data. Visualization technology (2–D and 3–D) in combination with the topographic data allowed us to interpret and map landforms with greater accuracy and resolution at less cost than traditional aerial photo and photogrammetric-based mapping methods, particularly given the rugged terrain and dense vegetative cover. Older, dormant slides with subtle geomorphic expression, reforested shallow slides, colluvial inner gorge landforms with active stream erosion, and stream valleys with forced alluviation upstream of landslide dams, are examples of geomorphic features that were readily detected. We are also comparing field-surveyed topographic sections of slides with those derived from the DEM to investigate the potential use of these remotely–sensed data for mechanistic slope stability analyses and landslide hazard assessments.