Inlet Geomorph Bibliography

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A literature review of several topic papers on inlet geomorphic parameterization and classification are given in the below annotated bibliography. The Papers are categorized by subject matter: 1) Classification, 2) Processes, 3) Relationships, and 4) Structural Response.

Inlet geomorph fig3 Hayes.png

1) Classification

  • Shoreline classification based upon tide range
    • Microtidal coasts (T.R. 0-2 meters) (wave dominated coasts)
    • Mesotidal coasts (T.R. 2-4 meters)
    • Macrotidal coasts (T.R. > 4 meters) (tide dominated coasts)
  • Variation in inlet planform morphology can be caused by
    • time variation of wave energy
    • time variation of tidal energy (prism),
    • space variation of tidal energy (prism), and
    • evolution of ebb-tidal deltas and adjacent shorelines.

2) Processes

  • Equilibrium properties of coastal structures exist over all time scales and can be used to simplify models and relationships.
  • North Carolina and northern South Carolina are classified as microtidal wave dominated, southern South Carolina and Georgia as mesotidal tide-dominated, and the northeast coast of Florida as microtidal wave dominated.
  • Physical and geological parameters impact tidal inlet variability.
  • The tide dominated inlets are characterized by large ebb-tidal deltas extending far out from shore, well-defined deep main channels and inlet throats, and an absence of inner shoals, except where fresh water inflow induces stratification and landward bottom sediment transport.
  • Sediment is bypassed at inlets through:
    • Stable inlet processes
    • Ebb-tidal delta breaching Inlet migration and spit breaching
    • Outer channel shifting
    • Spit platform breaching
    • Bypassing at wave dominated inlets
    • Jetty-weir bypassing
    • Jettied inlet bypassing
    • Outer channel shifting at jettied inlets
  • Degree of sheltering at an inlet and the back bay environment can effect flood or ebb dominance and create a tidal velocity asymmetry at the inlet. This can, in turn, effect the morphology of the inlet.
  • The direction of tidal forcing was the main parameter governing orientation of the main inlet channel and ebb delta.

3) Relationships

  • The two main principles in bypassing of sand by natural action; bypassing on an offshore bar and bypassing by tidal flow action or a combination of these two methods.
  • The ratio of Mmean/Qmax=r (magnitude of littoral drift) and quantity of flow through the inlet can assist in the identification of these mechanisms. If the ratio is high r>200-300, bar bypassing is predominant. A lower ratio, r<10-20 indicates tidal flow bypassing.
  • A relationship between inlet area and tidal prism of the form A=CPn exists
  • Symmetry is a product of (1) meandering of the channel thalweg, (2) inlet shoreline configuration, and (3) dominant longshore transport direction.
  • A method called the “no-inlet contour method” has been introduced to calculate ebb shoal volumes
  • A relationship is introduced between ebb shoal volume and tidal prism of the form V=aPb
  • The ebb shoal volume appear to be a function of spring tidal prism, inlet area, tidal amplitude and the ratio of inlet width to depth (which arises as a result of the effect of wave induced sediment transport at varying depths over the ebb shoal).
  • Delta growth is explained based upon an analysis of bottom shear stress from current and wave influence (Tb) and the critical stress for scour (Tcr) where, when Tb<< Tcr deposition occurs until they are approximately equal. At this point there is no further deposition and there is an equilibrium water depth above the delta and the delta reaches an equilibrium volume. The influence of wave energy would increase the delta volume (increased wave energy) or decrease the delta volume (decreased wave energy) and the shoal would move away from this equilibrium volume.
  • A linear relationship between the average shoal bypassing event interval (I) and the tidal prism (Tp) was found of the form I=0.046Tp+4.56. It was found that larger inlets undergo shoal bypassing events less frequently than smaller inlets and that the variable I is related to the longshore sediment transport rate.
  • A relationship of the form S=6.42Tp+113.4 has been used to describe the relationship between the average bypassing shoal volume (S) and the tidal prism (P).
  • Four types of inlet instability have been identified: geographic, rotational, meandering and channel stretching.
  • Inlet stability may be thought about in terms of (1) hydraulic parameters (width and length) and (2) positional parameters (migration).
  • Relationships between tidal prism and the planview shape of the ebb shoal have been developed.

4) Structural Responses

  • The introduction of jetties have caused ebb shoals to extend further offshore than previously with a more symmetrical shape.
  • A methodology for determining a net drift direction at a project site was introduced that includes:
    • Office examination of data
    • Field visit with aerial over flight
    • Discussions with specialists
    • Review of wave records
    • Collection of supplemental field data
  • The Inlet reservoir Model (IRM), calculates sediment transport rates and volume change of identified morphologic features and bypassing rates for an inlet.
  • The IRM can be used as an inlet management tool with a general methodology for simulating the evolution of different features and assessing consequences of interruption in sediment transport across inlets.
  • When the combined shear stress (τb) is smaller than the critical shear stress (τcr) deposition will occur until the shear stresses are balanced τb=τcr , when equilibrium is reached.


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