EM 1110-2-1100 (Part II)
30 Apr 02
advanced models could be set up and run in an exploratory mode to help the engineer understand possible
problems.
d. Selection of input data site. Based on project formulation and site analysis, offshore/nearby sites are
evaluated in terms of any feature that would preclude their use (see Part II-3-1d). In particular, the use of
nearby sites in similar depths of water must be evaluated in terms of whether waves reaching the site have
broken. As an example, if waves at a nearshore site have propagated over a shoal where breaking can occur,
there is no way to "unbreak" the waves. So they cannot be used to eliminate offshore wave conditions. In
general the offshore data site will need as a minimum information on wave height, period, and direction.
If adequate data are not available, methods for hindcasting, as described in Part II-2, may be used to simulate
the information required. The methods of Parts II-2 and 3 should be used to develop the wave information
to be transformed.
e. Selection of wave transformation method. Table II-3-2 provides guidance on the applicability of the
various methods described in this chapter. It does not provide guidelines for all cases. With some skill, the
models described can be pushed somewhat beyond their inherent limitations (but such results must be
carefully scrutinized and used conservatively). In very complicated cases or in cases in which a time-
dependent model is required, use of an expert consultant to provide assistance is recommended. In some
complicated cases, a physical model may be required.
Table II-3-2
Guidance for Selection of Wave Transformation Methods
Case
Fig.II-3-6 or ACES
NMLONG
RCPWAVE
REFDIF1
STWAVE
Planar topography (no shoals, etc)
yes
yes
yes
yes
yes
Highly Irregular Bathymetry
Swell, no structures
no
no
yes
yes
yes
Swell, structures
no
no
no
yes
yes
Complicated directional
no
no
no
yes
yes
Spectra, but narrow
frequency spectra
High winds or broad band
no
no
no
no
yes
frequency spectra
Irregular Bathymetry, High resolution Computations Near Structure
Swell
no
no
no
yes
no
f. Calibration/verification. After the method is set up, it is important to check the calculations with
observations if at all possible. If measured wave data are not available, then aerial photographs can be helpful
in deciding if the model reproduces observed wave patterns. If no wave data or photographs are available,
the method should be applied to a range of heights, periods, and directions and the results should be carefully
scrutinized for odd or unstable results. If the calculations are overly sensitive to small variations in input data,
a careful decision should be made as to whether the technique should be applied. A physical model may be
appropriate in situations with very irregular bathymetry, complicated or multiple structures, reefs, and where
currents are important.
Estimation of Nearshore Waves
II-3-33
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