Comparing LiDAR-Generated to ground- surveyed channel cross-sectional profiles in a forested mountain stream

Airborne Light Detection and Ranging (LiDAR) holds promise to provide an alternative to traditional ground-based survey methods for stream channel characterization and some change detection purposes, even under challenging landscape conditions. This study compared channel characteristics measured at 53 ground-surveyed and LiDAR-derived crosssectional profiles located in six study reaches of Little Creek, a forested headwater stream on Cal Poly’s Swanton Pacific Ranch, near Santa Cruz, CA. Three LiDAR datasets were compared in this study, with flights in 2002, 2008, and 2010, a period of rapid improvement in LiDAR technology. Visual and statistical agreement between field-surveyed and LiDARderived channel characteristics (bankfull depth, bankfull width, bankfull area, and thalweg elevation) show improvement as LiDAR technology has matured. Improvements are explained, in part, by the decrease in point spacing along the cross-sectional profiles (averaging 3.0 m in 2002, 1.0 m in 2008, and 0.49 m in 2010). Bankfull width was more accurately measured than bankfull depth or cross-sectional area. In 2010, two thirds of the LiDAR-derived cross-sections provided bankfull width within 10 percent (0.46 m) of the field-surveyed width. These initial findings show the improvements in LiDAR capabilities over time, though also point to difficulties that remain for remotely measuring channel geometry on small, headwater mountain streams.

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