ERDC/CHL CHETN-IV-12 (Revised)
December 2000
Where and Why Inlet Channels Shoal:
A Conceptual Geomorphic Framework
by Joan Pope
is to present a generalized conceptual framework of mechanisms which contribute to channel
shoaling in different areas of inlets. This information provides a common nomenclature and
classification scheme for grouping various types of channel shoaling. This framework serves as
a base for future modification and expansion as the Coastal Inlets Research Program (CIRP),
Diagnostic Modeling System (DMS) research work unit and other research experiences develop
methods for analyzing, predicting, and treating various types of channel shoaling problems.
BACKGROUND: In support of its navigation mission, the U.S. Army Corps of Engineers
removes in excess of 229,500,000 cu m (300 million cu yd) of material per year from 40,233 km
(25,000 miles) of Federally maintained navigation channels at an annual cost of more than 0
million. This mission includes the maintenance of more than 100 coastal inlets at a projected
25-year budget in excess of billion. Cost-effective sediment management associated with
maintaining navigation through coastal inlets requires an understanding of the various
hydrodynamic and geomorphic regimes that influence the entire inlet system.
Although each inlet will have its own distinguishing characteristics, similar hydrodynamic and
geomorphic processes control sediment transport and depositional patterns in all inlets.
Consequently, similar types of shoaling problems are repeatedly observed in most inlets. Sand
wave formation, channel migration, and sand shoaling across the ends of the entrance structures
are common inlet shoaling problems. The processes that generate channel shoaling are systemic
to all inlets, with only their relative strengths and variability and site-specific constraints such as
underlying geology and engineered elements differing.
To develop and apply predictive analytical procedures and sediment management strategies for
resolving specific channel shoaling situations, it is necessary to understand those mechanisms
that are responsible for the development of that particular shoal. This CHETN is presented in
three parts. First, the general mechanisms responsible for various characteristic shoaling patterns
will be discussed. Second, inlets and depositional zones are classified from a channel shoaling
perspective. Finally, the types of shoaling typically observed at navigation channels in each of
the defined inlet zones are summarized.
SHOALING MECHANISMS: The following lists some typical mechanisms which can cause
channel shoaling in inlet systems. This list is not all-inclusive, but it attempts to document the
dominant shoaling processes that cause shoaling in inlet system navigation channels. There are
other shoaling processes which may be unique to certain channel regions or sediment types, such
as debris or density flows that can sometimes cause dramatic, but localized, shoaling in estuarine
or riverine channels dominated by very fine sediments. The conceptual cross-sectional and
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