EM 1110-2-1100 (Part V)
31 Jul 2003
(b) Accessibility. In order to be usable, a borrow source must be accessible or made accessible for the
equipment needed to excavate and transport the material. Access to terrestrial deposits may involve road
construction or improvement of existing routes. Onsite reconnaissance is the best method of determining the
adequacy of access and any necessary improvements. A cost estimate of work needed to create accessibility
should be prepared and included in the economic analysis.
In evaluating subaqueous deposits, one of the principal factors is water depth. To be accessible, the
deposit must lie in the depth range between the maximum depth to which the dredge can excavate
material, and the minimum depth to keep the dredge afloat when laden with fuel and/or sediment.
Subaqueous borrow sites should be located sufficiently far offshore and in deeper water so that
excavation does not induce adverse shoreline impacts by altering to the incident wave climate.
Another aspect of accessibility is the presence of incompatible overburden above the usable
sediments. The composition, areal extent, and thickness of any overburden should be determined and
considered in the economic analysis (i.e., the cost to remove and dispose of it).
(c) Site morphology. Information on borrow site morphology is valuable in defining and evaluating site
characteristics. In many cases, the source deposit has surface morphological features that can be used to
delineate boundaries and to assist in interpolating between seismic and coring data points. In addition, site
morphology may provide indications of the origin and history of the deposit. Subsurface deposits such as
filled stream channels are more difficult to delineate because the only sources of data are seismic reflection
records, cores, and borings.
Description of borrow site morphology should contain information on dimensions, relief,
configuration, and boundaries, and be illustrated by large-scale maps or charts. Information for
compiling the reports can usually be found in hydrographic survey data available from the National
Ocean Survey (NOS), National Oceanic and Atmospheric Administration (NOAA), for submerged
deposits, and in published U.S. Geological Survey (USGS) topographic maps for terrestrial sources.
Fathometer records, which should be made concurrently with the seismic reflection profiles, are
valuable for supplementing and updating other sources.
In cases where the existing information is inadequate, a special detailed bathymetric survey of the
site should be made before the main field collection effort is undertaken.
(d) Site stratigraphy. The stratigraphic relationships within and peripheral to the site deposits should be
developed from the existing sources and the seismic and coring records to define: limits of the deposit;
thickness of usable material; thickness of any overburden; sedimentary structures, and sediment
characteristics of each definable bed. The detail and reliability of the stratigraphic analysis depends on the
complexity of the deposit, the number of outcrops, number of cores or borings available, and the degree to
which stratigraphic features are revealed by seismic reflection profiles.
In terrestrial areas, outcrops of potentially useful materials may or may not be present. In many
cases, such deposits have no topographic expression and must be defined solely on the basis of
borings. Seismic refraction surveys in such situations are valuable in defining the areas between data
points. Seismic refraction techniques for subsurface exploration are covered in detail in Engineer
Manual 1110-1-1802, "Geophysical Exploration for Engineering and Environmental Investigations."
In submerged areas, site characteristics must be determined by a combination of bathymetric survey,
seismic reflection profiling, and sediment coring. It is important, in both seismic reflection and
refraction surveys, to collect enough cores or boring samples to identify and correlate the reflectors
V-4-20
Beach Fill Design
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