UFC 4-150-06
12 December 2001
soil type. Properties and composition of coastal sediments are discussed in Section III-
1 of the CEM. Additional information can be found in Technical Notes, Technical Area
2: Material Properties Related to Navigation Dredging, published by the USACE
Waterways Experiment Station (WES) for the Dredging Research Program (DRP). The
Dredging Research Program Bibliography can be found on the web at
3-9
OPEN WATER DISPOSAL. Disposal of project-removed sediment in
open water can be an appropriate alternative where transportation costs for land
disposal become prohibitive. In some cases, it is also useful for replenishment of
shoreline where erosion is a problem. However, when foreign sediment is introduced
into the marine environment, associated environmental issues arise. Whether from
dredging operations or any other construction activity that affects the natural sediment
environment, the coastal engineer needs to evaluate the impact on bottom dwelling and
water column organisms due to such factors as blockage of light or toxicity of the
sediment. Additional information is contained in Technical Notes published by the U.S.
Army Engineer Waterways Experiment Station (WES) for the Dredging Research
Program (DRP).
3-9.1
Contaminated Sediment Risk Assessment. The sediment property of
most environmental consequence is grain size. Turbidity in the water column depends
on the fall velocity of the sediment particles, which is largely a function of the grain size.
Turbid waters can be carried away by currents from the immediate project site, blocking
the light to organisms over a wide area. As the sediments settle out, they blanket the
bottom at a rate faster than the organisms can accommodate. Fine sediments (silts
and clays) get greater scrutiny under environmental regulation because they produce
greater and longer-lasting turbidity, which will impact larger areas of the seafloor than
will coarser, sand-sized material. The dredging of sand usually encounters less severe
environmental objection, provided that there are few fine sediments mixed with it and
that the site has no prior toxic chemical history. Environmental regulation is changing,
and many regulatory questions are outside the usual experience of coastal engineers.
However, a basic coastal engineering contribution to facilitating the progress of a
project through regulatory review is the early collection of relevant sediment samples
from the site and obtaining accurate data on their size, composition, and toxicity. These
issues are discussed in Sections III-1-1-b(2) and V-6-1-d of the CEM. Environmental
requirements are discussed further in paragraph 5.3, "Regulatory Requirements," of this
handbook.
3-10
GEOLOGICAL INVESTIGATIONS. Effective coastal engineering studies
require appropriate understanding of the geology of the project area and its impact on
design parameters. A presentation of the considerations and procedures for coastal
geological investigations is contained in Section IV of the CEM.
3-11
SOURCES OF SEDIMENT PROCESS INFORMATION. A summary of
sources of available coastal information and data can be found in Section IV of the
CEM.
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