ERDC/CHL CHETN-IV-12 (Revised)
December 2000
Bay (lagoonal). Those inlets which are coastal-process dominated for the entire system tend to
have open-back bays or lagoons with only minor riverine contributions (Figure 2). These types
of inlets are more common along barrier island shores such as those of the mid-Atlantic.
Estuarine. These are usually wider entrance inlets that are equally influenced by coastal and
riverine-processes, although there may be seasonal periods where one process and sediment
source tends to dominate over the other (Figure 3).
Riverine. River discharge and sediment supply dominates the inlet shape and channel shoaling
characteristics (Figure 4). This type inlet is more common along tideless coasts (such as the
Great Lakes), geologically younger coasts where the river systems are steep (i.e., Pacific
Northwest), or where major rivers discharge into the sea.
WHERE CHANNELS SHOAL: Channel zones tend to experience shoaling mechanisms that
are characteristic of that area for most inlets. Sections of the inlet that are dominated by a
particular process tend to exhibit similar shoaling patterns. The most complex and dynamic
shoaling patterns are found in areas where the processes are mixed and where there are seasonal
or periodic fluctuations in the balance between these processes.
Geotechnical (slope failure) and regional sedimentation shoaling tends to occur in more
hydrodynamically stable portions of the channel (offshore or in the inland/interior channels).
Shoaling associated with a loss of hydraulic head tends to happen in areas of the channel where a
constricted flow discharges into a wider water body, for example at the transition between inlet
zones. Channel migration, morphodynamic pathways (migration shoal or sand bodies), and
channel abandonment are characteristic of areas that experience both a mix and changing balance
of the transport processes (the nearshore, inlet, and flood delta). Bed form evolution (i.e, sand
wave formation) tends to occur in confined portions of the channel where there are strong
unidirectional (upper river) or oscillatory (tidal flow through the inlet) currents.
Table 1 presents the various regions and zones for the three conceptual inlet models and
discusses those processes and shoaling mechanisms that tend to dominate each channel zone.
This table is based upon a generalized geomorphic framework for understanding the context in
which channels shoal. The last column of Table 1 is alphabetically coded to the channel
shoaling mechanisms presented in Figure 1 and discussed in the previous section titled "Shoaling
Mechanisms."
SUMMARY: The processes and locations of channel shoaling in inlet systems has been
examined and used to develop a classification scheme based on geomorphology. This
framework provides a basis for discussing and identifying the various mechanisms of channel
shoaling and where they may contribute to navigation system maintenance problems in inlets.
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