6. Wave Run-up and Overtopping
195
single — impact events (i.e. every wave crest) with a frequency equal to
the wave period. It should also be realized that overtopping calculation
methods hâve limitations to their accuracy and the physical model data
from which the methods are derived generally exhibit considérable scatter.
It is generally accepted that even the most reliable methods cannot provide
absolute discharges, and they can only be assumed to produce overtopping
rates that are accurate to within one order of magnitude. Likewise, the
tolerable discharges defined in various publications should not be taken as
absolute values. They represent an order of magnitude for which damage
or unsafe conditions may exist.
6.3.2
Calculation of overtopping rates
Some of the initial data on calculating the overtopping rates was undertaken
in the 1950s, the results of which are presented in the Shore Protection
Manual [SPM, 1984]. Later this information was outmoded by the work
carried out by a number of researchers, most remarkably Owen [1980] who
established the formulation outline that continues to be used today. The
most recent definitive and comprehensive work, which reports overtopping
for various forms of structures, and has been taken over and published by
Besley [1999].
The mean discharge due to overtopping over a plain rough-armoured
slope may be calculated from the following équation
where, Rc is the freeboard from the still water level to the top of the crest
élévation and Eq. (6.22) is valid only between the limits of 0.05 < R* < 0.30.
The second parameter is shown as,
<5* = Aexp ---- j
(6.23)
whereas, B is the empirical coefficient which dépends on the slope of the
structure slope (see Table 6.3) and r is the roughness coefficient as given in
Table 6.1. This équation is valid in the range 0.05 < R* < 0.30. The average
overtopping discharge rate per meter length of the structure in m3/s/m is
Qm = Q.TmgH,
(6-24)
195
single — impact events (i.e. every wave crest) with a frequency equal to
the wave period. It should also be realized that overtopping calculation
methods hâve limitations to their accuracy and the physical model data
from which the methods are derived generally exhibit considérable scatter.
It is generally accepted that even the most reliable methods cannot provide
absolute discharges, and they can only be assumed to produce overtopping
rates that are accurate to within one order of magnitude. Likewise, the
tolerable discharges defined in various publications should not be taken as
absolute values. They represent an order of magnitude for which damage
or unsafe conditions may exist.
6.3.2
Calculation of overtopping rates
Some of the initial data on calculating the overtopping rates was undertaken
in the 1950s, the results of which are presented in the Shore Protection
Manual [SPM, 1984]. Later this information was outmoded by the work
carried out by a number of researchers, most remarkably Owen [1980] who
established the formulation outline that continues to be used today. The
most recent definitive and comprehensive work, which reports overtopping
for various forms of structures, and has been taken over and published by
Besley [1999].
The mean discharge due to overtopping over a plain rough-armoured
slope may be calculated from the following équation
where, Rc is the freeboard from the still water level to the top of the crest
élévation and Eq. (6.22) is valid only between the limits of 0.05 < R* < 0.30.
The second parameter is shown as,
<5* = Aexp ---- j
(6.23)
whereas, B is the empirical coefficient which dépends on the slope of the
structure slope (see Table 6.3) and r is the roughness coefficient as given in
Table 6.1. This équation is valid in the range 0.05 < R* < 0.30. The average
overtopping discharge rate per meter length of the structure in m3/s/m is
Qm = Q.TmgH,
(6-24)