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Runoff and sediment yield on the US-Mexico border, Los Laureles Canyon
Citation:
Biggs, T., K. Taniguchi, N. Gudino-Elizondo, E. Langendoen, Y. Yuan, R. Bingner, AND D. Liden. Runoff and sediment yield on the US-Mexico border, Los Laureles Canyon. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-18/365, 2018.
Impact/Purpose:
Tijuana River Watershed (TRW) is about 4465 km2 (3,253 km2 in Mexico and 1,212 km2 in the U.S; or 73% and 27 %, respectively) and experienced heavy sediment loss from soil erosion (sheet and rill, gully erosion as well as channel). Excessive soil erosion, transport and deposition of sediment in the watershed have caused many detrimental effects to the people living in the watershed. Communities on both sides of the US-Mexico border are adversely affected by increased flooding from vegetation removal and paving, and communities in Mexico in particular experience disruption of services and transportation due to erosion of unpaved roads. Furthermore, Heavy sediment loss from the watershed also results in impaired conditions for aquatic life support in the Tijuana estuary. This project seeks to address Region 9 Science Council priorities associated with Sec. 303 [33 USC 1313] and Sec. 319 [33 USC 1329] of the Clean Water Act (CWA) and the National Environmental Policy Act (NEPA). The long-term research objective of this project is to gain better understanding on how urbanization affect both ecosystems and human populations. Detailed objectives to achieve the longer term protection of aquatic life in the Tijuana estuary and human population include field data collection and modeling and analysis of the critical factors impacting the watershed erosion and sediment processes (i.e. determine the dominant type of soil erosion: sheet and rill, gully, channel, etc.). The results of this effort will be used to determine an effective approach for sediment loading estimation as well as evaluating the reduction/prevention of sediment loads that could result from implementation of conservation easements, re-vegetation, sediment basins, paving, and other Best Management Practices (BMP).
Description:
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. Urbanization in Mexico differs from urbanization in the United States, with a longer duration of the phase of exposed soil, where vacant lots and unpaved roads may have high sediment production for decades. Over a decadal time-scale, urbanized watersheds gradually accumulate impervious surfaces and earthen channels are lined with concrete, resulting in decreased sediment production but increased runoff and perhaps increased channel erosion downstream of paved watersheds and channelized reaches. Communities on both sides of the US-Mexico border are adversely affected by human-induced watershed alteration, including increased flooding from vegetation removal and paving, and communities in Mexico in particular experience disruption of services and transportation due to erosion of unpaved roads. Despite the importance of erosion, sediment loads and runoff for the well-being of humans and ecosystems on the US-Mexico border, little data exists to successfully measure and model the impact of urbanization on watershed processes. This study is intended to fill this gap by presenting an integrated dataset necessary for supporting comprehensive study of runoff, soil erosion and sediment production in this region. Data were collected in a small watershed draining to the Tijuana estuary. The dataset includes rainfall, runoff, suspended sediment concentration, and sediment yield observed in sediment traps. In addition, the study describes the rainfall-runoff-sediment relationships in the watershed and how rainfall type and intensity affect those relationships. Furthermore, this study compares total sediment yield at the outlet with other natural and urbanized watersheds in southern California to better understand the impact of urbanization on sediment production.