EM 1110-2-1100 (Part V)
31 Jul 2003
with reliable data on sediment properties, and to show significant boundaries that may not have been
recorded by the seismic systems.
(e) Volume available. Most beach-fill projects require thousands or millions of cubic meters of suitable
fill material. The volume in each potential source must be calculated to determine if a sufficient amount is
available to construct and maintain the project for its entire economic life (including initial construction, all
subsequent renourishment, and emergency maintenance). In order to do this, it is necessary to delineate the
lateral extent and thickness of the deposit. Boundaries may be defined by physical criteria or, in large
deposits, arbitrarily set to encompass ample material for the projected fill operation. The thickness of the
usable material can be determined from an analysis of site stratigraphy.
If deposits have a uniform thickness throughout, the available volume can be calculated by multiply-
ing their areas by their thicknesses. Many deposits such as shoals and filled stream channels have
more complex shapes, including sloping boundaries and variable thickness. To determine the volume
of these deposits, an isopach map of the deposit must be created. An isopach map is a contour map
showing the thickness of a deposit between two physical or arbitrary boundaries. Figure V-4-7
shows an isopach map of a borrow area used at Ocean City, Maryland. In this case, the upper
boundary of the deposit is defined by the surface of the shoal and can be delineated by bathymetric
data. The lower boundary was fixed at a level seismic reflection horizon passing beneath the shoal.
Contours, at 1.52-m (5-ft) intervals, were drawn for all the shoal area above the base reflector.
Measurements from this type of map can be used to calculate the volume. Commercially available
Geographical Information System (GIS) software with Digital Terrain Modeling (DTM) capabilities
is now routinely used to generate isopach maps and calculate available sediment volumes.
Computation of the source's available volume must account for practical limitations of excavation.
Particularly for hydraulic dredging (excepting small suction dredge systems), sediment deposits less
than about 1-m (3-ft) thickness are impractical to specify. Buffers must be delineated between
suitable and nonsuitable sediments, which cannot be included in the source's available volume.
These buffers vary with the site and the nature of the sediment strata, but they typically have a
minimum thickness of 0.3 m (1 ft) to 0.6 m (2 ft) in subaqueous sources. Buffer areas around
sensitive environmental or cultural resources, or around known obstructions, must also be excluded.
The size of these radial buffers depends upon the resource or obstruction to be avoided, but a typical
radius is 45 to 90 m (150 to 300 ft). Computation of the source's volume must also be limited to
those areas or strata in which the sediment is known to be beach-compatible.
(f) Sediment composition. The physical properties of a sediment sample that are most important for
determination of suitability for fill on a project beach are composition and grain size distribution. The
desirable physical properties of beach-fill material are mechanical strength, resistance to abrasion, and
In most places, sand-sized sediment is predominantly composed of quartz particles with lesser
amounts of other minerals such as feldspar. Quartz has good mechanical strength, resistance to
abrasion, and chemical stability. In some deposits, particularly those of marine origin, there is a large
and sometimes dominant amount of calcium carbonate that is in most cases of organic origin
(biogenic). Calcium carbonate is more susceptible than quartz to breakage, abrasion, and chemical
dissolution; but, if it is not highly porous or hollow, it will make serviceable beach fill.
Beach Fill Design