ERDC/CHL CHETN-II-47
March 2004
A change in shoreline orientation was also identified as a hot spot cause, where there is a nodal point
with longshore sand transport away from the hot spot in one or both directions. Underlying geology,
inlet morphology, and/or nearshore shoals control local shoreline orientation changes in many cases.
CONCLUSIONS: Based on the case studies presented herein and discussions at the workshop the
following analyses are recommended as components of a feasibility or design phase detailed exami-
nation for the potential for hot spot development:
a. Examination of historic photographs, shoreline position, and rate change data.
b. Comparison of historic and existing shoreline orientation and morphology.
c. Comparison of line of upland development with existing and historic shoreline position (to
identify development which encroaches on the active beach).
d. Detailed nearshore wave transformation and an examination of breaking wave energy and
direction along the project shoreline (both for preproject conditions and also for postproject
conditions after dredging of nearshore borrow areas if applicable). Estimates of potential
longshore transport rates and gradients in rates can indicate potential locations of hot spots.
This may require detailed pre- and postproject hydrographic survey data.
e. Shoreline change modeling.
Further research is needed to develop, document, and provide field training on specific method-
ologies and procedures for assessing project vulnerability to flood and storm damages associated
with coastal storm impacts and nonuniform project performance due to hot spots. Based on this
review of recent and proposed beach nourishment project hot spots, the following paragraphs review
the frequently identified causes of erosion hot spots and some approaches to minimizing their
impact.
Nonuniform wave characteristics (height and direction) along the project shoreline was a common
factor on most of the projects, with the hot spot being located where wave focusing resulted in a
mechanism for higher erosion rates. Numerical simulation of nearshore wave transformation can
provide important information regarding the potential for hot spot development. Shoreline change
(one-line) modeling with nearshore wave information can be helpful in identifying longshore
transport gradients and net longshore transport reversals, which indicate the potential for hot spot
development. Shoreline change modeling is especially important in projects where the dry beach is
narrow or nonexistent, because in these cases, the highly eroded state of the beach may mask any
signal of hot spot erosion patterns in the historical shoreline position data set. Hot spots caused by
wave focusing have been addressed in a variety of ways including structural reduction in wave
energy, compartmentalization of the hot spot area shoreline with coastal structures, relocation of
project borrow areas, and placement of additional nourishment to "feed" the hot spot erosion while
maintaining the design shoreline width.
Underlying geology is often associated with wave focusing in that the underlying geology (be it
shoal features, reefs, or rock outcrops) produces bathymetric relief that results in wave focusing.
However, other geologic controls such as silt, clay or peat substrates may be more or less erodable
than the adjacent coastal sands. Other geologic controls, including inlet morphology and migration,
natural headlands and large-scale barrier island transgression, can be important factors associated
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