Background
The Los Angeles Department of Power and Water
started diverting Owens river water from Inyo county to Los
Angeles County with the completion of the Los Angeles aqueduct
in 1913. The primary source of water for Owens Lake was
thus diminished if not completely halted. Geologically, Owens
Lake had slowly (thousands of years) been drying up naturally
due to climatic conditions and desertification of the area;
however, this slow process allows stability to be reached.
After the Owens river diversion, it was only a matter of years
until the the lake was completely dried up leaving unstable
alkali soils which are susceptable to becoming airborne during
wind storms. The desert climate as well as the rain shadow
effect of the Sierra Nevadas allowed evaporation of the
remaining water. In addition, due to the meteorology of
the area, intense storm events occur due to lee cyclogenisis and
intense winds blow either northerly or southerly through the
Owens valley over the lake playa. These storms cause
intense dust storms which transport high concentrations of PM10
(particulate matter of 10 mm or smaller aerodynamic diameter)
into the atmosphere with estimated amounts to be 100,000-400,000
tons of particulate matter per year. These airborne
particles are small enough to travel great distances and can be
inhaled deeply into the human respiratory tract creating a
health hazard. The EPA uses PM10 levels as an indicator of
air quality and classified the Owens Lake area as a
"serious" non-attainment area. Research has
shown that the Owens Valley region PM10 concentrations are as
much as ten times the standard on a nearly daily basis during
active storm periods. The 1990 Clean Air Act Amendment
mandates that all areas must attain the PM10 standard and, thus,
California was required to file a State Implementation Plan
(SIP) which describes the process of attainment. Due to
the need for mitigation of the dust storms, the University of
California at Davis became active in many of the research
projects aimed at evaluating the problem of dust mitigation.
This specfic project is funded by the California Air Resources
Board and is one of many projects aimed at producing a
resolution.
Aerial View of the Owens Lake Region
Research Overview
An
important component of understanding the Owens dry lake bed
dust storms is determining the actual emission rates occurring
during severe storm conditions--these conditions are variable
and not easily characterized by a set of unique meteorological
conditions. Even less clearly understood is the composition
of natural surface soil when severe dust storms are initiated. It
is known that there are a range of of surface conditions that
can lead to the rapid emission of large amounts of PM10. The
lack of understanding of the complete emission process of
Owens dry lake bed is due to the size and complexity of the
lake bed. The lake bed is 110 square miles with approximately
35 square miles of the area subject to wind erosion. A more
comprehensive understanding is a must if a viable mitigation
plan is to occur.
Owens Dry Lakebed on a calm day, looking west
Goals
The goals of this research project are
-
to rank the emissivity of
different Owens dry lake surface bed types and identify
those which are most susceptible to wind erosion
-
determine the effects of
enhanced soil erosion due to surface scouring by saltating
particles
-
test the effects of wind
turbulence and wind gusts on erosion
-
test the effect of unstable
atmospheric conditions on the erosion process
Owens Lake with an oncoming dust storm, looking
east
Experimental Setup
Measurements will be made with the Saltation
Wind Tunnel at the University of California at Davis. This
open circuit wind tunnel was specially designed to simulate
particle flows or saltation movement, thus, it is ideal for
simulating the dust movements on Owens dry lake. The
Owens Lake soil of interest is placed in the test bed section
of the tunnel and tested at various conditions. The instrumentation
consists of twin traversing DustTraks, one measuring
PM10 levels and the other PM2.5 levels, a traversing pressure
transducer to measure the velocity field, and a pitot static
tube to measure the mean velocity. All of this information
is then collected in real time with a LabView data acquisition
program. From this information, the PM10 and PM2.5 flux
from the soil surface is calculated and the contribution to
total Owens Lake dust emissions estimated. For more specific
conditions, a heated bed is added to vary the stability. Likewise,
saltating sand particles can be introduced upstream of the
test bed to observe the effect of saltation on emissions. In
addition, the turbulent intensities that the bed is subjected
to can be varied by roughness elements or grids placed in
the tunnel.
Wooden pipes severely eroded by sand abrasion
Future
Work
In establishing a wind tunnel testing procedure
for estimating PM10 flux levels, the hope is that this research
can be extended beyond Owens Lake, and can ultimately aid
in producing emissions inventories to address and identify
sources of PM10 emissions in other non-attainment areas. One
obvious application of this technique is to the San Joaquin
Valley where agricultural practices as well as meteorological
conditions create another PM10 problem and ultimately a serious
health hazard.
