CHANNEL INCISION AND LANDSLIDES IDENTIFED BY LIDAR IN THE LOWER REACHES OF SCHOHARIE CREEK, NEW YORK

The lower reach of the Schoharie Creek takes an unusual route through a glaciated bedrock high before its confluence with the Mohawk River. During the recent evolution, this section of the river has incised downward, likely to keep pace with downward incision of the Mohawk River. LIDAR and satellite imagery allow identification of subtle terrain features such as abandoned channels and landslides that reveal a complex history of incision, avulsion, and mass movement in the lower reaches of Schoharie Creek. The unique high-resolution topographic images that show bare-earth LIDAR-derived topography are made by subtracting the canopy and defining a "bare-earth" elevation model using only ground-points to identify evidence of recent and historical landslides, and the evolution of incision revealed by abandoned channels. Avulsion and subsequent abandonment of fluvial channels is analyzed by geomorphic mapping of these high-resolution topographic data. Our analysis suggests that locally, channels have been reactivated in a wake of landslide-induced sediment deposition. Statistical analysis of topographic profiles across abandoned channels show at least three times of significant channel deviation and incision, all currently undated. LiDAR data revealed significant historical landslides that affect channel development and presumably add large volumes of sediment to the system. The largest identified landslide is Burtonsville landslide, which has a minimum volume of more than 0.27 km². Movement of the Burtonsville landslide is undated, but is greater than 200 yr as it is populated by a mature climax forest. Failure of the Burtonsville landslide is inferred to have blocked the river channel and caused dramatic and profound revision of flow of the river.