ERDC/CHL CHETN-III-64
June 2002 (revised)
A similar equation relating mean damage to spectral wave characteristics was given by Melby
and Kobayashi as
( Nmo )5
(t 0.25 - tn.25 ) for tn ≤ t ≤ tn+1
0
n
S (t ) = S (tn ) + 0.022
(3)
(Tp )0.25
n
where Nmo = Hmo / (∆Dn50), Hmo = 4(mo)1/2, mo is the zero moment of the incident wave spectrum,
and Tp is the spectral peak period. The empirical coefficients in Equations 2 and 3 will be
primarily a function of structure slope, wave period, beach slope, and structure permeability.
These equations have been verified for the following range of laboratory conditions:
Structure slope, tan α: 1V:2H
Significant wave height, Hs: 5.05 cm 15.80 cm
Toe depth, h: 11.9 15.8 cm
Mean wave period, Tm: 1.23 s 1.80 s
Iribarren parameter: tan α/(Hs/Lom)0.5: 2.08 4.17
Beach slope: 1V:20H
Structure crest height, hc: 30.5 cm
Stone density, ρa: 2.66 g/cm3
D85/D15 = 1.53
Filter layer: (M50)armor/(M50)filter = 25, (Dn50)armor/(Dn50)filter = 2.9
acceleration of gravity.
Equations 2 and 3 are plotted in Figure 3, where S (t) is plotted as a function of number of waves,
Nw. Here Nw = t/Tm. In Figure 3, the measured mean eroded area plus and minus one standard
deviation are plotted. These data are from one very long series of six different storms with two
water levels. Equations 2 and 3 should be conservative for most applications because they are
based on severely breaking waves, a relatively steep beach slope, and a relatively impermeable
core. Deviations from the range of tested conditions are likely to produce different empirical
coefficients in Equations 2 and 3. Caution should be exercised in applications of these equations
outside of the range of conditions tested.
The mean parameters S , E , C, and L and the standard deviations σS, σE, σC, σL were used to
describe the tendencies, variabilities, and ranges of damage and the damaged profile. All
measured values from all measured series were in the following ranges
Damage: -2.7<(S -S)/σS <3
(4)
Eroded depth: -2.7<(E - E)/σE <2.7
(5)
Cover depth: -2.7<(C-C)/σC <2.8
(6)
4
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