|
 racking pollutants in urban environments presents
a challenge for researchers, but predicting pollution levels
is necessary to ensure sustainability of urban areas. University
of Arkansas researcher Steven Burian has developed a linked air-water
modeling system that can predict concentrations of nitrogen compounds
from a Los Angeles watershed. Pollutants such as ammonia-nitrogen,
nitrite-nitrogen and nitrate-nitrogen degrade water quality and
promote the growth of algae and other undesirable elements.
 "The
different elements of a city are coupled, interacting and feeding
back with each other in nonlinear, sometimes counterintuitive
ways," explained Burian. "We are developing a system
of linked models to look at sustainability and vulnerability
issues for cities."
Burian, assistant
professor of civil engineering, is working with Timothy McPherson,
Michael Brown, Jerry Streit and H.J. Turin of Los Alamos National
Laboratory on a project funded through the Urban Security Initiative.
This multidisciplinary effort examines the relationship between
urban infrastructures - such as power, transportation, water
and wastewater systems and the natural environment.
Developed
for the Ballona Creek watershed in urban Los Angeles, Burian's
air-water modeling framework links the CIT airshed model and
the US EPA Storm Water Management Model (SWMM). The input and
output datasets are managed in a Geographical Information System
(GIS) environment. The modeling framework can be operated in
a high-fidelity mode to look at processes in detail and a low-fidelity
mode for planning-level assessments.
Ballona Creek
is located in an extremely urbanized catchment that drains a
substantial part of Los Angeles. It has been shown to be the
greatest source of non-point source pollution for Santa Monica
Bay. Running approximately 12 kilometers (7.5 miles) from downtown
Los Angeles to Santa Monica Bay, about half of Ballona Creek
is a concrete-lined trapezoidal channel, but the section from
Centinela Avenue to Santa Monica Bay has a dirt/sand bottom and
rock-lined sides. All of the tributaries to Ballona Creek are
man-made, primarily concrete channels or pipes.
During wet
weather, the flow rates in Ballona Creek can increase by a factor
of at least 100. Modeling of these events is complicated by the
effects of the high tide in Santa Monica Bay, which can hold
up the discharge despite high flow rates and substantial water
volume.
Burian's model
incorporates land use data from the Southern California Association
of Governments, elevations from the US Geological Survey and
road data from the US Census. In addition, the team collected
data on the location, size, slope and length of storm drains
by physically verifying data from the Los Angeles Department
of Public Works. Nearly 3,000 storm drains, with a length of
more than 587 miles, were characterized to develop the model.
Parameters for the water quality portion of the model were developed
with historical water quality provided by researchers at the
University of California-Los Angeles and the Los Angeles County
Department of Public Works.
Although his
model accurately predicted the nitrogen levels in a storm event
on Dec. 4, 1999, Burian and his team are seeking to further validate
and extend the model. Additional data are being collected to
calibrate the model and replace preliminary estimates with more
site-specific data.
Burian presented
his results at the Restoring Urban Wetlands Conference in Los
Angeles in May. The conference was sponsored by the Ballona Wetlands
Foundation, the Los Angeles and San Gabriel Rivers Watershed
Council, Santa Monica Bay Restoration Project, the UCLA Institute
of the Environment and the Trust for Public Land. 
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engr.uark.edu. Carolyne Garcia, science and research communication officer, 501-575-5555, cgarcia