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Title: Stream channel erosion in a rapidly urbanizing region of the US-Mexico border: the documenting importance of channel hardpoints with structure-from-motion photogrammetry

Author
item TANIGUCHI, KRISTINE - San Diego State University
item BIGGS, TRENT - San Diego State University
item Langendoen, Eddy
item CASTILLO, CARLOS - Universidad De Cordoba
item GUDINO-ELIZONDO, NAPOLEON - Centro De Investigacion Cientifica Y De Educacion Superior De Ensenada
item YUAN, YONGPING - Environmental Protection Agency (EPA)
item LIDEN, DOUGLAS - Environmental Protection Agency (EPA)

Submitted to: Earth Surface Processes and Landforms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2017
Publication Date: 6/3/2018
Citation: Taniguchi, K.T., Biggs, T.W., Langendoen, E.J., Castillo, C., Gudino-Elizondo, N., Yuan, Y., Liden, D. 2018. Stream channel erosion in a rapidly urbanizing region of the US-Mexico border: the documenting importance of channel hardpoints with structure-from-motion photogrammetry. Earth Surface Processes and Landforms. 43(7): 1465-1477. DOI: 10.1002/esp.4331.
DOI: https://doi.org/10.1002/esp.4331

Interpretive Summary: Many studies have documented the impact of urbanization on stream channel erosion and its relationship to watershed characteristics and proximity to hardpoints like road crossings or bridges. However, very few studies have been conducted in semi-arid climates in developing countries experiencing rapid population growth, unregulated urban development on erodible soils, and variable enforcement of environmental regulations. Scientists at the USDA, ARS, National Sedimentation Laboratory in collaboration with researchers at San Diego State University, the USEPA, the Ensenada Center for Scientific Research and Higher Education, Mexico, and the University of Cordoba, Spain, investigated urbanization and stream channel erosion in Tijuana, Mexico, through a mix of field topographic survey methods, and a comparison of channel geometry to undeveloped and urbanized watersheds in southern California. Proximity to upstream hardpoint, and lack of riparian and bank vegetation paired with highly erodible bed and bank materials were found to be the main cause of channel instabilities. Channel erosion due to urbanization accounts for approximately 25-40% of the total sediment budget for the watershed, and channel erosion downstream of hardpoints accounts for approximately 1/3rd of all channel erosion. Management needs to focus on stabilizing the stream channel downstream of hardpoints, especially in areas with urban development adjacent to the stream channel.

Technical Abstract: A combination of field surveys and Structure-from-Motion (SfM) techniques were used to document spatial patterns in stream channel geometry in a rapidly urbanizing watershed, Los Laureles Canyon (LLCW), in Tijuana, Mexico. Ground-based SfM was used to map channel dimensions with 10 cm vertical accuracy in three stream reaches (155-300 m long) that were highly variable and difficult to survey with differential GPS. Regional hydraulic geometry curves for LLCW had statistically larger slopes and intercepts compared to undisturbed reference channels. Cross sectional areas of channels downstream of hardpoints, such as concrete reaches or culverts, were up to 64 times greater than reference channels, with enlargement persisting, in some cases, up to 230 m downstream. Percent impervious cover was not a good predictor of channel enlargement. Proximity to upstream hardpoint, and lack of riparian and bank vegetation paired with highly erodible bed and bank materials may account for the instability of the highly enlarged and unstable cross sections. Channel erosion due to urbanization accounts for approximately 25-40% of the total sediment budget for the watershed, and channel erosion downstream of hardpoints accounts for ~1/3 of all channel erosion. Management needs to focus on stabilizing the stream channel downstream of hardpoints, especially in areas with urban development adjacent to the stream channel.