EM 1110-2-1100 (Part III)
30 Apr 02
detached breakwaters, beach fills, and seawalls, with a primary limitation in this regard being the size and
speed of the computer and the maximum number of grid cells that can be accommodated by the program.
Compound structures (such as T-shaped, Y-shaped, and spur groins) may be simulated with varying degrees
of realism. At least five grid cells are required to reasonably model the shoreline behind and between
structures. Sand bypassing around and transmission through groins and jetties may be simulated, as well as
diffraction at detached breakwaters, jetties, and groins. Transmission through detached breakwaters may be
simulated. GENESIS allows multiple wave trains to be input (such as from independent wave sources), and
the wave information may include arbitrary values of wave height, period, and direction. As presented in
Equation 2-42, sand transport is calculated due to oblique wave incidence and a longshore gradient in wave
height.
(c) GENESIS is not applicable to simulating a randomly fluctuating beach system in which no trend
in evolution of the shoreline is evident. In particular, GENESIS is not applicable to calculating shoreline
change in the following situations which involve beach change that is not related to coastal structures,
boundary conditions, or spatial differences in wave-induced longshore sand transport: beach change inside
inlets or in areas dominated by tidal flow; beach change produced by wind-generated currents; storm-induced
beach erosion in which cross-shore sediment transport processes are dominant; and scour at structures.
GENESIS also does not include wave reflection from structures; cannot reliably simulate tombolo or salient
development at a detached breakwater; and there is no direct provision for changing tide level. In addition,
the basic assumptions in the development of shoreline change modeling theory apply.
(4) Example application - Bolsa Chica, California.
(a) As discussed by Hanson and Kraus (1989) and Gravens (1990b), GENESIS (either its predecessor,
Version 1, or the current Version 2) has been applied at numerous project sites, including locations in Alaska
(Chu et al. 1987); California (Gravens 1990a); Louisiana (Hanson, Kraus, and Nakashima 1989; Gravens
1994); New Jersey (Gravens, Scheffner, and Hubertz 1989); New York (Cialone et al. 1994); Florida (by the
U.S. Army Engineers District, Jacksonville); and outside the United States (Hanson and Kraus 1986;
Kraus 1988). Application of the model to assess a proposed structured inlet system at Bolsa Chica,
California, is summarized below (Gravens 1990a) to illustrate model use in coastal project evaluation and
refinement.
(b) GENESIS was applied to an approximately 10-mile-long shoreline reach from Anaheim Bay to the
Santa Ana River, California (Figure III-2-47) as part of a comprehensive multi-tasked engineering
investigation for the California State Lands Commission (SLC). The shoreline change modeling effort was
directed towards quantifying the potential long-term impacts of the proposed entrance on adjacent shorelines,
and to investigate mitigation of any adverse impacts induced by the entrance. Three major components were
involved in the shoreline modeling effort: (1) a preliminary shoreline response study, in which available
wave and shoreline data were used to provide preliminary estimates of the introduction of a littoral barrier
in the local littoral cell; (2) a comprehensive wave hindcast of locally generated wind sea and North Pacific
swell conditions from 1956 to 1975 at 3-hr intervals, and an 18-month hindcast of South Pacific swell; and
(3) comprehensive shoreline response modeling using the hindcast wave data to predict response of the
project area to various design alternatives. Discussion herein is focussed on this third component, including
preparation of input data sets and analysis of model output, as they pertain to application of GENESIS. For
a more complete description of the project, the reader is directed to Gravens (1990a).
III-2-82
Longshore Sediment Transport
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