1070

S.A. Hughes / Coastal Engineering 51 (2004) 10671084

Fig. 1. Variation of (H/Lo)1/2 with h/gT2 for constant values of H/h.

limit as defined by Williams (1985) and expressed

surf zone processes due to plunging and spilling wave

by Sobey (1998) as a rational function. The

breaking.

horizontal chain-dashed lines represent the demarca-

tion (no=3.3) between surging/collapsing breakers

(above the line) and plunging/ spilling breakers

3. Criteria for a new wave parameter

(below the line) for different slopes. Similar trends

arise if H/Lo is replaced with local wave steepness

Partial motivation for developing a new wave

H/L.

parameter for nearshore coastal processes and coastal

structure design comes from the Hudson armor

same value of deepwater wave steepness. In partic-

stability equation and other stability equations based

on the armor stability parameter, H/DDn50. Examina-

ular, a wave in shallow water having the same height

and period as a wave in deeper water will have the

tion of Hudson's (1959) development of the stability

same deepwater wave steepness, but different wave

equation reveals that wave height enters the armor

kinematics. The wave in deeper water will behave

stability parameter as a near-breaking long-wave

more like a linear wave whereas the wave in shallow

approximation of horizontal water velociffitffiyffiffi in the

p ffiffi

water will exhibit more nonlinearity. Furthermore, a

vicinity of the still water level, i.e., Vw~ gH . From

change in wave height occurs as the deeper water

a physical perspective, this seems to be a gross

wave moves into shallow water, so it is possible that

simplification of wave effects on armor stability.

by the time the deeper water waves reaches the depth

However, because of other complexities related to

of the shallow water wave, the wave height will be

armor stability (randomness of armor matrix, armor

different. Thus, deepwater Iribarren number based on

support points, interlocking, etc.), the lack of a more

local wave height may not be the best parameter for

rigorous description for wave loading may not have

correlations involving waves prior to breaking, or for

been too detrimental. Most established stability

waves described as surging or collapsing breakers,

coefficients for use with the Hudson equation were

because the influence of water depth is not included.

based on the more conservative observations rather

However, ample evidence supports the use of deep-

than the mean of the data. Nevertheless, there remains

water wave steepness H/Lo (and no) for correlations to

the possibility that the observed scatter in armor

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