Amphibious surveys in La Spezia, Italy
(photo: Daniel Conley, SACLANT Undersea Research Center)
Earth's surface and the processes that sculpt it form my primary research and teaching interests. Problems that connect disparate fields -- traffic and granular flow, for example -- are particularly fascinating to me. Problems that span a significant range of scales in both time and space hold considerable appeal as well: beach processes can be studied using grain-by-grain, second-by-second computer simulations at one end of the time-length spectrum, and by subsurface geophysical studies of ancient continental margin sediments on the other. Group members make a conscious effort to evaluate problems from a variety of perspectives; to that end we employ any combination of field, laboratory, computational and theoretical approaches in our work.
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Amphibious surveys in La Spezia, Italy (photo: Daniel Conley, SACLANT Undersea Research Center) |
Workshop Report Authors: Ed Thornton, Tony Dalrymple, Tom Drake, Edie Gallagher, Bob Guza, Alex Hay, Rob Holman, Jim Kaihatu, Tom Lippmann, Tuba Ozkan-Haller
A group of 68 scientists and engineers specializing in nearshore
process met from 14-16 September 1998 in St. Petersburg, Florida,
with the objective of assessing the current state of nearshore
science, and identifying the important scientific questions, research
strategies and the infrastructure needed to address the questions.
The workshop report synthesizes the progress of the last decade
and suggests where research effort should be focused to make the
continued progress.
A five-year, NSF- and ONR-sponsored collaborative effort starting August 1999 to develop and test a model for waves, currents and sediment transport in the nearshore ocean, between the shoreline and about 10 m water depth. Lead PIs Jim Kirby and Ib Svendsen at University of Delaware's Center for Applied Coastal Research head a group of researchers from across the country. Our group here at NC State will work on incorporating new and improved sediment transport models into the comprehensive model, in particular, we will focus on near-bed transport processes, including ripples, dunes and grain-size segregation by size and density. Here is a summary of the proposed work:
The partnership will develop and test a comprehensive community model that predicts waves, currents, sediment transport and bathymetric change in the nearshore ocean, between the shoreline and about 10 m water depth. The model will consist of a "backbone", handling data input and output as well as internal storage, together with a suite of "modules", each of which handles a focused subset of the physical processes being studied. A wave module will model wave transformation over arbitrary coastal bathymetry and predict radiation stresses and wave induced mass fluxes. A circulation module will model the slowly varying current field driven by waves, wind and buoyancy forcing, and will provide information about the bottom boundary layer structure. A seabed module will model sediment transport, determine the bedform geometry, parameterize the bedform effect on bottom friction, and compute morphological evolution resulting from spatial variations in local sediment transport rates. The project will support extensions to the science base associated with each module, and will support the use of existing field and laboratory data sets to define significant tests of the modules. Data assimilation techniques will be developed and employed to address the problems of insufficient boundary data information in model applications to field experiments as well as parameter determination.
Graduate student Dave Pierson is initiating work on acoustic time-reversal mirrors under ONR sponsorship. Dave has finished extensive analysis of sidescan sonar images obtained in the surf zone during the SandyDuck97 Coastal Field experiment. The images can be correlated with sonic altimeter data collected by Naval Postgraduate School collaborators Edie Gallagher, Ed Thornton and Tim Stanton to produce roughness maps for much of the surf zone on a daily basis.
Dr. Jesse McNinch and Chris Freeman led a mapping effort to delineate the bathymetry around the Queen Anne's Revenge after Hurricanes Dennis and Floyd exposed the wreck and artifacts during fall 1999. Smithsonian Magazine has a timely article on Blackbeard, who may not have been the "evil cutthroat of popular imagination." See the reference McNinch, Wells and Drake (2001) below as well.
Field and Modeling Studies of Nearshore Morphology
ARO-sponsored collaborative work with FRF-based NRC postdoctoral
fellow Dr. Jesse McNinch has developed an amphibious bathymetry
mapping system using the FRF's LARC. We've mapped
SandyDuck '97 Coastal Field Experiment
Graduate student Peter Dickson gathered side-scan sonar images
of the sea floor in the surf zone during the SandyDuck experiment
using the FRF's three-legged CRAB. The acoustic picture of the
bed provided by the side-scan complements bathymetric measurements
made by Edie Gallagher, Ed Thornton and Tim Stanton of the Naval
Postgraduate School using acoustic altimeters attached to the
CRAB. This work is supported by the Coastal
Dynamics Program, Office of Naval Research.
Surf Zone Sedimentary Structures in the Duck94 Field Experiment
During the Duck94 nearshore field experiment, my students and
I collected sediment cores from the surf zone in conjunction with
Scripps Institution of Oceanography investigators to study the
nearshore sedimentary structures
generated by migrating bedforms, and their relation to waves and
currents. Our long-term goal is to develop models of the several
sedimentological processes that govern barrier island migration.
Along the way we often manage to make direct
observations of natural phenomena. This work was supported
by the U.S. Army Waterways Experiment Station.
Graduate student Joe
Calantoni, Jr. is using a discrete-particle model to simulate
and visualize sheet flow transport. Large waves often generate
sheet flow sediment transport, in which a thin, planar carpet
of highly concentrated sand moves essentially horizontally over
the seafloor. Occasionally, and quite importantly, an instability
arises that disrupts the planar nature of the sheet, and the small
perturbation in bed elevation is not smoothed by the intense sediment
transport, but instead develops into a dune-like feature with
a slipface. Development of dunes significantly modifies the bed
roughness, in turn altering the gross flow field and thus sediment
transport. Similar processes occur in rivers and in slurries.
This work is supported by the Coastal Dynamics Program of the
Office of Naval Research.
High-resolution GPS and laser-rangefinder studies conducted at the Willo site in the Cretaceous Hell Creek formation reveal the spatial arrangement of concretions and other environmental indicators.
Sedimentation in NC Piedmont Lakes
Graduate student Walter Haven and I have surveyed sediments accumulated
in Lake Wheeler and other lakes and ponds in the Swift Creek watershed.
Lake Wheeler is immediately upstream of Lake Benson, which was
a water supply for the City of Raleigh in the past, and is expected
to again supply drinking water within a decade or so. We are using
a number of geophysical techniques, including ground-penetrating
radar, side-scan sonar and coring, to determine the thickness
of accumulated sediments. We have also initiated a study of sedimentation
in Lake Raleigh, a small lake on NCSU's Centennial Campus. Rainfall
during Hurricane Fran broke the dam creating Lake Raleigh, and
the newly-exposed sediments there are accessible without boats,
though boots are pretty handy. Walt's diligent shovel work put
us on the front page of the News
and Observer. This work is supported by an NCSU Faculty Development
Grant and the North Carolina Chapter of the Soil and Water Conservation
Society.
Eolian Dune Migration at Jockey's Ridge State Park, NC
The dunes at Jockey's Ridge (just south of Kitty Hawk, where Orville
and Wilbur Wright did their thing) won't stay within the park
boundaries. The North Carolina Department of Parks and Recreation,
together with the Friends of Jockeys Ridge, is sponsoring several
investigations into the geologic history and likely future of
Jockeys Ridge. We are developing a simulation model for dune migration
and evolution under a variety of scenarios, and will incorporate
variations in sand supply, vegetation, wind regime as well as
visitor impact on the dunes.
Here are some other topics I've worked on, and would like think about more:
Initiation and evolution of the braided channel pattern in rivers: The multi-channel braided pattern has been ascribed to a variety of factors: increased flow or sediment load or channel gradient, among others. Such transitions often occur seasonally on some glacial outwash plains due to variations in meltwater. Multiple pattern transitions can also occur spatially along the river profile, and these transitions appear to migrate both up and downstream. My own time-lapse photographic studies of braided outwash channels in the Canadian Rockies provide a detailed picture of the individual parts of the complex braided channel system; the problem has been to link the interacting elements. Cellular models using simple rules for interactions between individual channels in the network, derived from experimental and field observations, ought to allow exploration of the several existing hypotheses for the braiding instability.
High-speed and time-lapse photographic techniques: At UCLA I used high-speed photographic techniques to study granular flows in a narrow glass-walled chute. Since then, Ron Shreve (UCLA), Jon Nelson (U.S. Geological Survey) and I have employed similar techniques to study bedload transport in Duck Creek, Wyoming, and laboratory flumes. While purists prefer film, at NC State we have also actively used a number of videographic techniques including DPIV (Digital Particle Image Velocimetry) for studies of sediment transport.
Schooling Fish: High-speed techniques developed for sediment-transport studies also have the potential to be quite useful in studies of biological phenomena; and my hobby is studying animal aggregations as exemplars of complex, "many-particle" systems. In my spare time I've been slowly working on a vision-based model of synchronous fish-schooling behavior. That work was the subject of an invited presentation entitled Computer Simulation of Schooling Fish at the NSF Animal Aggregations Workshop, held at the Monterey Bay Aquarium, Monterey, California, in October 1991.
The surface processes group consists of five PhD students (three from the Department of Physics) and five MS students. Several students from other departments and colleges at NC State have worked in our group, including electrical engineers, computer scientists and physicists, in addition to earth scientists. We work closely with colleagues from Duke University, the UNC Institute for Marine Sciences at Morehead City, the Center for Marine Science and Research at UNC Wilmington. Prospective graduate students should expect to participate in team-oriented research and to use more than one approach -- field, lab, computational, theoretical -- during the course of their work. Computers are an essential element of all of our investigations and much of our work requires a strong quantitative background. Research-grant funding for first-year students not having an M.S. is uncommon; however, the department usually offers teaching assistantships to incoming M.S. and Ph.D. students. Research assistantships are subject to availability of funding and continued progress towards the degree.
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© Copyright 2001 Tom Drake
