elevation of the most seaward berm point. As the swl deviates from this eleva-

tion, *r*dh soon reaches a value of one and the berm has no further impact on runup

and overtopping. When swl is near the elevation of the seaward berm point, then

berm width has an additional effect in reducing runup and overtopping. As berm

width increases, the value of *r*B approaches one, and the overall reduction factor

γb becomes smaller.

When water depth immediately seaward of the nearshore profile for runup

and overtopping calculations is relatively shallow, high waves in the train of

irregular incident waves will break. Thus, waves attacking the nearshore profile

will be somewhat diminished due to the presence of a shallow foreshore. VJ

suggest the following approximation for the reduction factor:

2

γh = 1 - 0.03 4 - s

(16)

where

If *d*s/Hss ≥ 4, then γh = 1.0.

Runup and overtopping on a rough slope is reduced relative to a comparable

smooth slope. This effect has traditionally been represented by a factor repre-

senting the ratio of rough slope runup to smooth slope runup. A table of

reduction factors, γf , is given by VJ for various types of slope. This factor is

comparable to reduction factors given in the *Shore Protection Manual *(1984) in

Table 7-2, Chapter 7, Volume II. VJ recommend that this factor be set to one for

cases in which the breaker parameter is relatively large, that is, γf = 1 when

ξop ≥ 4.

Waves approaching perpendicular to a nearshore profile can be expected to

cause higher runup and overtopping than waves approaching from an oblique

angle. For the case of long-crested waves approaching within 30 deg of normal

to shore, VJ suggest that obliquity has no impact and these cases can be treated

as directly approaching. For short-crested waves, even small oblique angles of

24

Chapter 3

Modeling Approach

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