1082
S.A. Hughes / Coastal Engineering 51 (2004) 10671084
Fig. 10. Ship-generated wave sea surface (upper) and MF (lower) time series.
to nearshore coastal processes on beaches and at
An alternative estimate of maximum depth-inte-
coastal structures. The wave momentum flux param-
grated wave momentum flux for the individual wave
eter has units of force per unit crest width, and it better
defined by zero-upcrossings in Fig. 10 was calculated
characterizes the flow kinematics at a given depth
using Eqs. (20), (21), and (22) which are intended for
than other wave parameters that do not distinguish
regular steady waves. The wave parameters were
increased wave nonlinearity. The wave momentum
originally given in English units as H=0.78 ft, T=1.38
flux parameter can be defined for regular, irregular,
s, and h=9 ft. A somewhat favorable comparison to
and nonperiodic (transient) waves such as ship-
the local Fourier approximation was found. . .
generated wakes and solitary waves. Thus, if a
&
55:1 lb=f t
local approx:
nearshore process can be successfully related to the
MFmax
wave momentum flux parameter, it may be possible to
Eq: 20
48:7 lb=f t
describe the same process being forced by different
or
wave types with a similar formulation. This hypoth-
&
0:0106 local approx:
MF
esis is presently unproven.
qgh2
0:0094 Eq: 20
31
The wave momentum flux parameter was derived
max
for linear and extended linear wave theory; however,
the results do not accurately estimate the maximum
Although this is only one comparison, it may
wave momentum flux in steep, nonsinusoidal waves
indicate that treating transient wave trains as a
which are likely to be more influential for coastal
succession of uniform waves might be reasonable
process response. Fourier approximation wave theory
for those processes thought to be related to wave
for regular steady waves over a horizontal bottom was
momentum flux.
used to develop an easily applied empirical expression
giving nondimensional maximum depth-integrated
wave momentum flux as a function of relative wave
6. Summary and conclusions
height and relative water depth. For irregular wave
trains, it is recommended that H and T in the empirical
A new parameter representing the maximum depth-
formation be replaced with frequencydomain irreg-
integrated wave momentum flux occurring in a wave
ular wave parameters H mo and T p. The wave
is proposed for characterizing the wave contribution
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