The Search for Offshore Sand Resources in Areas with No Pre-Existing Data
Abstract
The normal plan for an offshore sand search would have been to start with a grid of geophysical survey
lines to map sand shoals or other sand bodies where previous research had indicated potential sand
resources were available. These sites would then have been sampled in detail with the Vibracore to
determine grain size distribution within the block. However, in areas such as the central and southern
Texas coastline, where there is no pre-existing survey data adequate to form a basis for such work, this
method of survey design is not likely to work.
Alpine contracted with Shiner-Mosley to identify a sand borrow site to be used in the renourishment of
South Padre Island, Texas beaches. Costs were based around a budget adequate to mobilize the R/V
Atlantic Twin and personnel to the site and conduct 250 line miles of geophysical survey plus 50
Vibracores. The initial plan proposed to the town and Texas General Land Office (GLO) by Shiner-Mosley
included a box of 200 line miles of seismic survey tracklines offshore of the town. With no sediment
data available on this area, Alpine proposed, in an initial meeting at the site with the client and
representatives of the town and GLO, to conduct a few cores across the site prior to using up the budget
on an unknown area. These initial cores were conducted the next day and they were found to contain
only silt, clay and a limited amount of very fine sand. The results were reported back to the town the
following day, at which time a new strategy for the survey was put into place.
This paper will present the methods used by Alpine to find a suitable offshore borrow site for use in the
renourishment of South Padre Island, Texas beaches. The key part of the procedure was to have both
geophysical equipment and a Vibracore onboard, so that each area could be surveyed quickly with
several miles of geophysical survey line followed by a few Vibracores to determine if the sand quality
warranted additional work in the area. Frequent meetings were held with the client to review data and
update them on findings. This method of doing all the work in real time saved the client significant time
and money, and, in the end, resulted in identification of two million cubic yards of sand suitable for use
in renourishment of project beaches.
Chuck Dill
Senior Geologist
Alpine Ocean Seismic Survey, Inc.
155 Hudson Avenue
Norwood, New Jersey 07648
201-768-8000
e-mail: chuck@alpineocean.com
Brief Biography for Chuck Dill:
As a geologist for Alpine Ocean Seismic Survey, Mr. Dill has been conducting offshore research since
1971, utilizing geophysical profilers and Vibracore samplers to delineate offshore borrow sites. Work
areas extend from Portland Maine and South Padre Island, Texas plus southern California. Beach
projects reconstructed with data collected by Mr. Dill include the major metropolitan areas of Long
Island, NY, New Jersey, Delaware, Maryland, Virginia, North Carolina, South Carolina, Georgia, Florida,
Louisiana and Texas, plus southern California. Clients on these projects include numerous Districts of
the US Army Corps of Engineers plus several engineering companies working for government agencies in
these states.