|
The Tijuana River Watershed is a bi-national basin
spanning 4,483 km2 on the United States (U.S.)-Mexico border.
One-third of the watershed is in the U.S. with two-thirds in Mexico.
The highest point of the watershed is Mt. Laguna, California (elevation 1,900 m), and the lowest
point at sea level at the Tijuana River Estuary on the border near
Imperial Beach, California. The main stem of the Tijuana
River flows through highly developed regions characterized by extensive
agriculture, industrialization, and dense urbanization, before entering southern
San Diego County and discharging into the Pacific Ocean. Transborder flows of
the Tijuana River are contaminated with sewage, sediment, trash, nutrients,
pesticides and heavy metals due to rapid regional land use change since the late
1970s. Impaired waters impact human and environmental health on both sides of
the border and historically have been the focus of local, State, and Federal
remediation.
In
southern San Diego County in the U.S.,
elevated pathogen concentrations have historically led to extensive
beach advisories and closures each year. This problem is
particularly pervasive under stormwater conditions when pathogens are
transported through the watershed. The pathogens have
wide-reaching economic implications that range from suppressed tourism
to devalued property and widespread ecological damage. In Mexico,
thousands of residents in Tijuana’s periphery inhabit unsewered areas
where vegetation has been removed to allow for dense development on
unstable slopes. Extensive pathogen and sediment loading is occurring in these unplanned border developments. California State
and U.S. Federal funding has been allocated to focus on source
identification and remediation in U.S. territory, while few if any
quantitative studies have worked to identify areas of concern and the
transport mechanisms regarding constituents of concern to the border in
Mexican territory.
This Bren
Master's Thesis Group Project addresses this problem by focusing on
one representative sub-basin of the larger watershed: Los Laureles
Canyon, on the outskirts of Tijuana, Mexico. This canyon is
one of 28 similar canyons in the Tijuana River Watershed, and as
such is the focus of our research for controlling and mitigating impaired stormwater in the larger watershed.
The canyon is 9.6 km in length, and contains a main channel which
transports stormwaters and runoff from higher parts of the canyon through
community settlements to the coastal zone and estuary on the U.S.
side of the border. However, during heavy storms the channel
is insufficient to control most of the runoff, and consequently
three constituents of concern (pathogens, sediment and
refuse/debris) are transported through the canyon and crossing
the U.S. border to contaminant the Tijiuana River Estuary.
Using Los Laureles Canyon as a case study, we identified pathogen
loading in and transport through the canyon by employing the WARMF
(Watershed Analysis Risk Management Framework) model. We also identified the most feasible
and viable Best Management Practice (BMP) options
to control and mitigate sediment and refuse/debris in the catchment,
and make recommendations for implementing stormwater control
technologies and community actions to tackle this significant
pollution problem.
Our final
Project Report will be delivered stakeholders and our client, California's
State Water Resources Control Board (SWRCB) to contribute to stormwater control and mitigation in Los Laureles Canyon and the
greater watershed.
For information on the
approaches, methods and findings of this research project, we welcome
you to view our final thesis Project Report under 'Project Documents'.
|
