The four reduction factors involved in calculating overtopping rate are

discussed further in the following subsections.

The presence of a berm in the nearshore profile can significantly reduce

runup and overtopping relative to a continuously sloped profile. The reduction

factor which accounts for the influence of a berm in the nearshore profile is

given by VJ as

γb = 1 - *r*B (1 - *r*dh )

(13)

where

The factor γb is confined to the range 1.0 ≥ γb ≥ 0.6.

The factor based on berm width is given by

tan αeq

(14)

tan α

where

tan αeq = equivalent slope gradient to represent berm width effects

tan α = representative slope gradient without consideration of berm

Equivalent slope gradient is determined as the slope of a straight line between

two points on the nearshore profile: one point is at elevation *H*s above the most

seaward point of the berm; the other point is at elevation *H*s below the most

seaward point of the berm (Figure 8). Equivalent slope gradient is independent

of water level.

Representative slope gradient is determined by extending an imaginary line

up from the most seaward point of the berm (Figure 9). Slope of the imaginary

line is equal to the slope of the nearshore profile shoreward of the berm. Effec-

tively, the berm is removed from the nearshore profile. Representative slope

gradient is defined as the slope of a straight line between two points: one point

is at elevation *H*s below the swl; the other point is at elevation *H*s above the swl.

If the upper elevation is higher than that of the most seaward point on the berm,

then the upper point is taken on the imaginary line. This approach is based on the

consideration that the slope most influencing wave runup is that within one

significant wave height above and below the swl.

22

Chapter 3

Modeling Approach

Integrated Publishing, Inc. |