Science Inventory

Stream channel erosion in a rapidly urbanizing region of the US–Mexico border: documenting the importance of channel hardpoints with Structure‐from‐Motion photogrammetry

Citation:

Taniguchi, K., T. Biggs, E. Langendoen, C. Castillo, N. Gudino-Elizondo, Y. Yuan, AND D. Liden. Stream channel erosion in a rapidly urbanizing region of the US–Mexico border: documenting the importance of channel hardpoints with Structure‐from‐Motion photogrammetry. Earth Surface Processes and Landforms. John Wiley & Sons Incorporated, New York, NY, 43(7):1465-1477, (2018). https://doi.org/10.1002/esp.4331

Impact/Purpose:

Excessive flooding and sedimentation threaten both ecosystems and human populations. On the US-Mexico border, urbanization has increased runoff and sedimentation loads. In the Tijuana-San Diego region, the Tijuana Estuary in the United States suffers from “excessive sedimentation”, and determining the source of the sediment and mitigating its production is a primary management goal of the US EPA and other cross-border agencies. This study is intended to fill the gap of quantifying sediment sources from rapidly urbanized trans-border watersheds (US-Mexico border). A combination of field surveys and Structure-from-Motion (SfM) photogrammetry 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 photogrammetry was used to map channel dimensions with 10 cm vertical accuracy in three four stream reaches (155100-300 m long) that were highly variable and difficult to survey with differential GPS. Regional channel geometry curves for LLCW had statistically larger slopes and intercepts compared to regional curves developed for comparable, 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 one third of all channel erosion. Channels downstream of hardpoints should be stabilized to prevent increased inputs of sediment to the Tijuana Estuary and local hazards near the structures, especially in areas with urban settlements near the stream channel.

Description:

Urbanization can lead to accelerated stream channel erosion, especially in areas experiencing rapid population growth, unregulated urban development on erodible soils, and variable enforcement of environmental regulations. A combination of field surveys and Structure‐from‐Motion (SfM) photogrammetry techniques was used to document spatial patterns in stream channel geometry in a rapidly urbanizing watershed, Los Laureles Canyon (LLCW), in Tijuana, Mexico. Ground‐based SfM photogrammetry was used to map channel dimensions with 1 to 2 cm vertical mean error for four stream reaches (100–300 m long) that were highly variable and difficult to survey with a differential GPS. Regional channel geometry curves for LLCW had statistically larger slopes and intercepts compared with regional curves developed for comparable, 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. Percentage 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 one‐third of all channel erosion. Channels downstream of hardpoints should be stabilized to prevent increased inputs of sediment to the Tijuana Estuary and local hazards near the structures, especially in areas with urban settlements near the stream channel.

URLs/Downloads:

https://doi.org/10.1002/esp.4331   Exit

https://doi.org/10.1002/esp.4331   Exit

Record Details:

Record Type: DOCUMENT (JOURNAL/PEER REVIEWED JOURNAL)
Product Published Date: 06/03/2018
Record Last Revised: 07/16/2018
OMB Category: Other
Record ID: 341666

Organization:

U.S. ENVIRONMENTAL PROTECTION AGENCY

OFFICE OF RESEARCH AND DEVELOPMENT

NATIONAL EXPOSURE RESEARCH LABORATORY

SYSTEMS EXPOSURE DIVISION