Estimating Ephemeral Gully Erosion Rates in a Norwegian Agricultural Catchment Using Low-Altitude Uav Imagery
34 Pages Posted: 16 Apr 2022
Ephemeral gully erosion occurs regularly on Norwegian agricultural soils. Few observation based estimates are available for the assessment of its relative contribution to soil loss at the catchment scale. Measurement of ephemeral gully erosion dimensions is traditionally done by determining profile cross sections or manual depth and width evaluations with certain intervals along the gully's length. More recently, methods to obtain three-dimensional data have become available to researchers that allow for the constructions of high-resolution Digital Elevation Models (DEM). The availability of Unmanned Aerial Vehicles (UAV), equipped with digital cameras, has significantly improved the potential of stereophotography for mapping at the field and hillslope scales. Processing high-resolution DEMs for the estimation of gully volumes by means of monotemporal imagery consists of two phases: delineation and the construction of a, pre-event, reference surface. Several methods exist for the delineation of gullies, and methods for reference surface construction are limited to spline-based approaches. This study presents a delineation and a soil surface reconstruction algorithm that are almost parameter free. Its robustness for parameterisation and for the spatial resolution of the input DEM is assessed. The tests show little sensitivity to both these factors. The method is then applied to measured ephemeral gullies for an agricultural catchment in southeastern Norway. The contribution of ephemeral gully erosion as a fraction of the total seasonal soil loss varies between 7\% (2019) and 30\% (2021).
Keywords: ephemeral gully erosion, unmanned aerial vehicle, microtopography, catchment sediment balance
Suggested Citation: Suggested Citation