88
R.H. Charlier and Chr. P. De Mercer
In this section the attention is focused on the wave-related sediment
concentrations and transport processes, presenting the following subjects :
analysis of measured concentrations and transport processes,
* computation of time-averaged concentration profiles,
. computation of transport rates.
2 Analysis of Measured Concentration
Profiles and Transport Rates
2.1
Instantaneous concentrations
In section 1 it has been shown that instantaneous concentrations are especially
important with respect to the wave-related transport processes
2.1.1
Ripple regime
Fig. 13 shows ensemble mean concentrations within a wave period in a wave
tunnel measured by Bosman (1982). A sinusoidal oscillatory motion with a
period of T = 1 sec and a velocity amplitude of U3 = 0.3 m/s (0.96 ft./s) was
generated over a sand bed (d.~o = 200 ~tm, d9o = 240 ~tm). The bed was covered
with almost perfectly two-dimensional ripples (length = 0.055 m or 0.176 ft.,
height = 0.01 m or 0.032 ft.). An optical instrument was used to measure the
concentration values above the ripple crest and trough. The exact measuring
locations are shown in Fig. 13. The ripple crest measurements show ensemble
mean concentrations and standard deviations based on 100 periods. About 70%
of all measurements fall within the standard deviation lines. As regards the
trough measurements, only ensemble mean values are shown. The following
phenomena can be observed above the crest :
* the (random) scatter is quite large (roughly + 50%),
. two large concentration peaks just after flow reversal and probably generated
by leeside eddy-velocities,
* two smaller concentration peaks at the moment of maximum flow, probably
generated by stoss-side velocities,
. asymmetrical-concentration distribution (water motion being symmetrical).
R.H. Charlier and Chr. P. De Mercer
In this section the attention is focused on the wave-related sediment
concentrations and transport processes, presenting the following subjects :
analysis of measured concentrations and transport processes,
* computation of time-averaged concentration profiles,
. computation of transport rates.
2 Analysis of Measured Concentration
Profiles and Transport Rates
2.1
Instantaneous concentrations
In section 1 it has been shown that instantaneous concentrations are especially
important with respect to the wave-related transport processes
2.1.1
Ripple regime
Fig. 13 shows ensemble mean concentrations within a wave period in a wave
tunnel measured by Bosman (1982). A sinusoidal oscillatory motion with a
period of T = 1 sec and a velocity amplitude of U3 = 0.3 m/s (0.96 ft./s) was
generated over a sand bed (d.~o = 200 ~tm, d9o = 240 ~tm). The bed was covered
with almost perfectly two-dimensional ripples (length = 0.055 m or 0.176 ft.,
height = 0.01 m or 0.032 ft.). An optical instrument was used to measure the
concentration values above the ripple crest and trough. The exact measuring
locations are shown in Fig. 13. The ripple crest measurements show ensemble
mean concentrations and standard deviations based on 100 periods. About 70%
of all measurements fall within the standard deviation lines. As regards the
trough measurements, only ensemble mean values are shown. The following
phenomena can be observed above the crest :
* the (random) scatter is quite large (roughly + 50%),
. two large concentration peaks just after flow reversal and probably generated
by leeside eddy-velocities,
* two smaller concentration peaks at the moment of maximum flow, probably
generated by stoss-side velocities,
. asymmetrical-concentration distribution (water motion being symmetrical).