Comparison of gully erosion estimates using airborne and ground-based LiDAR on Santa Cruz Island, California

a r t i c l e i n f o Gully erosion removes comparatively large volumes of soil from small areas. It is often difficult to quantify the loss of soil because the footprint of individual gullies is too small to be captured by most generally available digital elevation models (DEMs), such as the USGS National Elevation Dataset. Airborne LiDAR (Light Detection and Ranging) has the potential to provide the required data density, but an even newer class of ground-based sensors may provide better local resolution at lower cost. In this study, we compared digital elevation models produced by airborne and ground-based LiDAR systems with ground-based geomorphic and geodetic survey data to determine their utility in quantifying volumetric soil loss due to gully erosion in a heavily degraded watershed (7.55 × 10 − 2 km 2), on southwestern Santa Cruz Island in southern California. Volumetric estimates of the eroded sediment were produced by comparing the LiDAR-derived DEMs of the gully system to a modeled pre-erosion surface. Average point densities were significantly higher for the ground-based LiDAR system and provided more detailed information; however, its limited scanning footprint and side-looking orientation presented serious challenges in collecting continuous data from deeply incised gullies, making the airborne system preferable for this type of investigation and likely for most applications where heavy topographic shadowing is prevalent. Gully erosion, the removal of soil from narrow channels via the accumulation of surface runoff, tends to produce more sediment loss than other forms of soil erosion such as overland flow or rilling (Wasson et al. Gullies are generally defined by their channel depth, which for permanent gullies can range from 0.5 to 30 m (Soil Science Society of America, 2001). They are also one of the most destructive forms of erosion, destroying soil, undermining infrastructure, damaging agricultural fields, altering transportation corridors, and lowering water tables (Valentin et al., 2005). Furthermore, their damage is difficult to reverse. Gully erosion dramatically affects sediment budgets and flux rates, and influences stream dynamics as evidenced from data on hydrographs Quantifying gully erosion will assist in understanding gully formation and spatiotemporal evolution. Although gullies are visually striking, their small spatial extent generally renders them undetectable in most generally available topographic datasets. The goal of this work was to test the viability of applying airborne and ground-based LiDAR technology to quantify gully erosion on southwestern Santa Cruz Island in southern California. Limited …