SDAG Monthly Meeting
Wednesday, March 18, 2015
Emiliano's Mexican Restaurant
6690 Mission Gorge Road,San Diego, CA 92120
On Mission Gorge Road overlooking Admiral Baker golf course.
You will probably have to drive about 1/2 mile past the restaurant and make a U-turn to get into the parking lot.
Menu: Mexicano Fantastico, Cash Bar
Cost: $30.00 for non-members, $25.00 for members, $15.00 for students
if pre-registered by the deadline, $5 extra if you did not make a reservation.
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no later than NOON, Monday, March 16th.
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Speaker 1: Tyler Barnes - Undergraduate Environmental Studies, University of San Diego
SDAG 2014 Scholarship Recipient
"MONITORING TURBIDITY IN BAYS WITH CORAL REEFS: ST. JOHN, US VIRGIN ISLANDS"
Land-based sedimentation and turbidity contributes to declining coral reef conditions in the US Virgin Islands.
Not only does turbidity smother corals, but also blocks light, which interferes with the ability of zooxanthellae
to photosynthesize. Unpaved roads and other watershed development activities increase runoff volumes to
near-shore marine systems, often resulting in increased turbidity. Residents of Coral Bay, St. John, USVI are
concerned with the impact of local development on turbidity, but are unsure how to monitor turbidity
effectively. The objectives of this study were: 1) to determine the appropriate frequency of sampling to
capture turbidity variation, and 2) to describe what factors influence nearshore and offshore turbidity in Coral
Bay, St. John, USVI. At a nearshore and an offshore site within Coral Bay, St. John, USVI, turbidity was
monitored at a monthly frequency by measuring water sample total suspended solids (mg/L) and at a ten-
minute frequency by measuring the backscatter of light using nephelometers (NTU). A simulated storm
experiment was conducted to produce a calibration between the two measurement techniques and test the
duration of turbidity plumes. Turbidity was found to be highly variable and turbidity plumes relatively short-
lived (minutes- hours). However, the monthly sampling did not capture the natural variation. Therefore, high
frequency sampling (minutes) is necessary to properly monitor turbidity variation in Coral Bay. Regional wave
height, used as a proxy for hydraulic energy in the bay, and rainfall data were collected to investigate factors
that influence turbidity. Regression analysis showed a correlation between regional wave height and turbidity,
suggesting that energy influences turbidity variation. Though particularly high rainfall events may result in high
turbidity at the nearshore location, there was no correlation between rainfall and turbidity. However, the
terrigenous composition of both nearshore and offshore suspended solids suggests that rainfall introduces
land-derived sediment into the system but that waves re-suspend sediment from the seafloor and produce
turbidity plumes. Thus, proper land-use planning, aimed at reducing runoff volumes, may decrease turbidity.
As a San Diego native, Tyler grew up fascinated by the workings of the natural world, particularly coastal
environments where he spent most of his summers. Tyler enjoyed an interdisciplinary education in
environmental studies at the University of San Diego, where he soon met Dr. Sarah Gray and became involved
in her US Virgin Islands sedimentology research. While working in Dr. Gray's lab, Tyler has enjoyed not only
the fieldwork that included scuba diving in the Caribbean, but also the satisfaction of communicating findings
with peers. He looks forward to continuing his education and research in marine geology, hopefully beginning
his graduate studies this fall.
Speaker 2: Dr. David Cruden - Emeritus Professor, Civil & Environmental Engineering and Earth and Atmospheric Sciences
University of Alberta, Canada
"USING THE WORKING CLASSIFICATION OF LANDSLIDES TO ASSESS THE DANGER FROM A NATURAL SLOPE"
An essential input to any calculation of the stability of a natural slope is a hypothesis about how the slope may
move. No formal method for estimating likely kinematic modes of slopes exists unless the slope is currently
moving or has moved in the past. A working hypothesis is that similar slopes in similar materials move in
similar modes in response to similar causes.
During the IDNDR (1990-2000), the IAEG Commission on Landslides contributed to the Working Classification
which records an international consensus on types of landslides. A landslide can be typed by a term describing
the natural materials before they were displaced and a second term describing the movement. Materials are
rock, debris or earth; earth may be sand, silt or clay. Movements may be falls, flows, slides, spreads or topples.
Water conditions in the displaced material may range from dry thru' moist and wet to very wet. In permafrost
terrain, frozen and thawed displaced material may occur. Water conditions, material and mode of movement
may govern the rate of movement of the displacing mass. It can range from extremely slow to the extremely
rapid movements which may have catastrophic impacts.
Activity, its distribution and style may affect anticipated modes of movement in assessed slopes. Slopes may
be active suspended, reactivated, dormant, abandoned, stabilized, repaired, or relict. Styles of movement may
be complex, composite, successive and multiple. Compilations of the historic activity of similar slopes as
landslide inventories suggest hazard scenarios which can form plausible initial hypotheses for risk
Dr. David Cruden, Emeritus Professor of Civil & Environmental Engineering and of Earth and Atmospheric
Sciences at the University of Alberta, Canada, is a recent Varnes medalist of the International Consortium on
Landslides, a Legget medalist of the Canadian Geotechnical Society and a Julian Smith medalist of the
Engineering Institute of Canada for his contributions to landslide studies. During the International Decade for
Natural Disaster Reduction (1990-2000), he led the collaboration of the International Geotechnical Societies
that produced the Working Classification of Landslides for the International Union of Geological Sciences. He
chaired IAEG's Commission on Landslides from 1988 to 1995. He has published textbooks on engineering
geology and terrain analysis along with three hundred technical papers. He was an Associate Editor of the
Canadian Geotechnical Journal for 20 years & is presently an Advisor to the Editorial Board of "Landslides". He
continues to suggest extensions to the Working Classification of Landslides.
Upcoming SDAG meetings - 2015
March 18: Student Presentations
April 15: Student Presentations - part 2
TUESDAY May 12: Monte Marshall - Geology of the Polynesian Islands
MONDAY June 1: Eric Drummond - Ice Cold Gold - Joint SDAG/SCGS Meeting
Meetings are usually scheduled for the 3rd Wednesday evening of the month. Meeting information on this website is normally updated the second week of the month.
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