EM 1110-2-1100 (Part V)
31 Jul 2003
Sediment core sites are usually selected after the seismic reflection survey, to allow time for
preliminary analysis of the records to determine the most prudent and informative core locations.
Cores should be examined as they are taken. Inspection of cores is often hampered by the presence
of silt and by scratching of the acrylic core liners. However, the top and bottom sediments can be
directly viewed before the core is capped. As work progresses, changes can be made in core
locations.
(c) Detailed site survey. The third phase of borrow site exploration and investigation consists of a
detailed investigation of potential sites, which are selected on the basis of data collected during the general
exploration survey. If sufficient seismic reflection data were collected at potential sites during the general
exploration phase, the detailed site study may only require the collection of additional, more densely-spaced,
cores. Since few large sand bodies have uniform size characteristics, it is important to obtain a sufficient
number of cores and borings to accurately reflect the variations in size characteristics throughout the deposit.
The number of cores and spacing between cores should be determined based on a review of survey and
seismic data as well as other geological studies of the area. These values will vary throughout a borrow site,
and from one borrow site to another. But in most cases, collection of cores at less than 300-m (1000-ft)
nominal spacing is recommended for purposes of ultimately defining the borrow site(s) to be used in
construction. It is important to have adequate data for reliably defining the borrow site. Additional seismic
reflection data, if needed, should be collected at this time.
Sometimes the general and detailed field surveys are made in succeeding years so that ample time
is available to study results of the seismic reflection survey before coring is undertaken. However,
it is possible to complete the operation entirely in one season. This can be done by mobilizing both
geophysical and coring equipment early in the most favorable season, and allowing sufficient lag
time between the seismic work and the bulk of the coring work for thorough data analyses and
selection of core sites.
Additional data collection is typically required to fully examine the selected borrow area or areas.
These additional data include: magnetometer survey to detect cultural resources of historical
significance (shipwrecks, etc.) and obstructions to dredging; archaeological-diver survey to
investigate magnetic anomalies; sidescan sonar survey to detect obstructions, hard-bottom, or other
environmental resources; detailed bathymetric survey suitable for preparation of construction
drawings; and benthic or other biologic surveys, if required, to assess the existing biotic resource.
(3) Borrow site characterization. Any beach erosion or shore protection study in which beach fill is
considered should include examination of all potential borrow sources and a comparative evaluation of their
suitability. The characteristics of potential borrow sources that are most important in evaluating suitability
are: location, accessibility, site morphology, stratigraphy, volume of material available, sediment
characteristics, geological history, environmental factors, and economic factors.
(a) Location. The distance that the material must be transported and the feasible means of transport have
a large influence on project costs and may be decisive in selecting the most suitable source. Location is also
important in terms of the surroundings. Use of terrestrial sources located in developed areas may have a
direct impact on the population by creating undesirable noise, traffic congestion, and spillage. Offshore
sources may involve questions of jurisdiction and be situated in areas where the dredging and transport
activities impede or endanger navigation.
Beach Fill Design
V-4-19
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