Measuring ephemeral gully erosion rates and topographical thresholds in an urban watershed using unmanned aerial systems and structure from motion photogrammetric techniques

Authors: GUDINO-ELIZONDO, NAPOLEON - Centro De Investigacion Cientifica Y De Educacion Superior De Ensenada; BIGGS, TRENT - San Diego State University; CASTILLO, CARLOS - Universidad De Cordoba; Bingner, Ronald - Ron; Langendoen, Eddy; TANIGUCHI, KRISTINE - San Diego State University; KRETZSCHMAR, THOMAS - Centro De Investigacion Cientifica Y De Educacion Superior De Ensenada; YUAN, YONGPING - Us Environmental Protection Agency (EPA); LIDEN, DOUGLAS - Us Environmental Protection Agency (EPA)

Submitted to: Land Degradation and Development
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2018
Publication Date: 6/15/2018
Publication URL: http://handle.nal.usda.gov/10113/5982557
Citation: Gudino-Elizondo, N., Biggs, T., Castillo, C., Bingner, R.L., Langendoen, E.J., Taniguchi, K., Kretzschmar, T., Yuan, Y., Liden, D. 2018. Measuring ephemeral gully erosion rates and topographical thresholds in an urban watershed using unmanned aerial systems and structure from motion photogrammetric techniques. Land Degradation and Development. 29:1896-1905. https://doi.org/10.1002/ldr.2976.
DOI: https://doi.org/10.1002/ldr.2976

Interpretive Summary: Rural and urban development can accelerate gully erosion by removing surface cover and disturbing the soil through the construction of unpaved roads on highly erodible sediments. Quantification of erosion from gullies is challenging in environments where gullies are rapidly repaired, and in urban areas where small changes in topography can complicate determining where the contributing drainage areas are. This study used unmanned aerial vehicles (UAVs) and Structure-from-Motion (SfM) photogrammetric techniques to quantify gully erosion in the Los Laureles Canyon watershed, which is a rapidly urbanizing watershed in Tijuana, Mexico. The gully network extent was mapped following a storm event, along with the local slope and watershed area contributing to each gully using detailed photogrammetric and topographic maps. Sediment production from gully erosion in this area was 2-5 times higher, while values of slope and drainage area that contribute to gully incision were lower, compared with ephemeral gully values reported in the literature for agricultural settings. These values indicate this area is highly vulnerable to gully erosion, which is consistent with the high soil erodibility and low critical shear stress values measured with these soils in a laboratory setting. Future studies evaluating the effect of different soil types on gully erosion rates on unpaved roads, as well as modelling the effects of management practices such as road paving and their impact on runoff, soil erosion, and sediment loads are crucial for proper sediment management in urbanizing watersheds.

Technical Abstract: Rural and urban development can accelerate gully erosion, including on unpaved roads. Quantification of erosion from gullies is challenging in environments where gullies are rapidly repaired, and in urban areas where microtopographic complexity complicates delineation of contributing areas. This study used unmanned aerial vehicles (UAVs) and Structure-from-Motion (SfM) photogrammetric techniques to quantify gully erosion in the Los Laureles Canyon watershed, which is a rapidly urbanizing watershed in Tijuana, Mexico. The gully network extent was mapped following a storm event (~50 mm precipitation total and 15-minute maximum intensity of 4.8 mm with a 1 year recurrence interval) using an orthomosaic (0.038 m pixel size), and the local slope and watershed area contributing to each gully were mapped using a DEM (0.3 m pixel size). Sediment production from gully erosion was higher and threshold values of slope and drainage area for gully incision were lower compared with ephemeral gullies reported in literature for agricultural settings, indicating high vulnerability to gully erosion, which is consistent with the high soil erodibility and low critical shear stress measured in the laboratory with a mini-jet erosion test device. Gullies formed after removal of vegetation and the construction of unpaved roads on highly erodible sediments. Future studies evaluating the effect of different soil types on gully erosion rates on unpaved roads, as well as modelling the effects of management practices such as road paving and their impact on runoff, soil erosion, and sediment loads are crucial for proper sediment management in urbanizing watersheds.