General description

The energy balance equation for the physical process of a wave encounter­ing a structure can be stated as

(6.23)   

where K_t is the transmission coefficient, K_r is the reflection coefficient and K_l is the loss coefficient. The transmission coefficient, K_t, describes the intensity of a transmitted wave height relative to an incident wave height. The corre­sponding transmission of the wave energy for each individual spectral bin is taken as K_t². The reflection coefficient, K_r, describes the intensity of a reflected wave height relative to an incident wave height. The corresponding reflection of the wave energy for each individual spectral bin is taken as K_r².

Using Goda's formula the transmission coefficient is given by

(6.24)   

where a and b are two fitting coefficients and K_t,min and K_t,max are the mini­mum and maximum transmission coefficients. H_i is the incoming wave height and f is the freeboard which is determined as the crest level minus the sur­face elevation. The minimum and maximum relative freeboard is given by

(6.25)   

(6.26)   

Goda's formula can be used to estimate the transmission of waves over breakwaters, dams and caisons. Both submerged and emergent or subaerial structures can be taken into account. Using Goda's formula the transmission coefficient is calculated based on the freeboard and the incoming significant wave height and the transmission coefficient is independent of the wave direction. For a vertical wall breakwater a=2.2 and b in the range 0.1 to 0.8 with a mean value of 0.4. For more detail on the values of the two fitting coef­ficients see Goda et. al. (1967) and Goda (1969).