Hydraulic Structures: Fourth Edition

in which Hsis offshore significant wave height, Tis the mean wave period,


is the approach angle, dis the depth at the toe of the wall, Ris freeboard

of the wall from SWL and sis the beach slope.

Overtopping of non-porous vertical walls due to regular waves may

be determined from the model tests reported in Shore Protection Manual,

(US Army, 1984) (see also Thomas and Hall, 1992).

For simple slopes, the test results of Owen (1980) with random waves

are applied for the prediction of discharge due to overtopping. The results

are expressed in terms of a relationship between two non-dimensional

quantitiesQ* and R*.

QAexp (^)  (15.31)
in which Q and R*. Q is the mean discharge in
m^3 s^1 per m run of the wall overtopping the crest of the sea wall, Tis the
mean wave period, Ris the freeboard of the wall from the still water level
to the crest and ris the roughness factor as given in Table 15.1. The results
are valid for the range of slopes from 1:1 to 1:4 and wave steepness from
0.035 to 0.055.
Typical values of AandBare given in Table 15.2
For values of the coefficients AandBof equation (15.31) to estimate
the mean overtopping discharge to include bermed sea wall and the effects
of angle of wave attack, refer to Owen (1980).
Tolerable overtopping discharges
For vehicles Besley et al.(1998) suggest mean values of overtopping dis-
charge0.001 l/s/m as safe at all speeds, between 0.001 and 0.02 l/s/m as
unsafe at high speed and 0.021 l/s/m as unsafe at any speed. For pedestri-

R



T g H (^) s

Q



TgHs

BR*



r

Table 15.2 Values of coefficients AandBfor simple sea walls

Seawall slope A B

1:1 7.9 103 20.12

1:1.5 1.02 102 20.12

1:2 1.25 102 22.06

1:2.5 1.45 102 26.1

1:3 1.63 102 31.9

1:3.5 1.78 102 38.9

1:4 1.92 102 46.96

1:4.5 2.15 102 55.7

1:5 2.50 102 65.2

646 COASTAL ENGINEERING