A. Bayram et al. / Coastal Engineering 44 (2001) 7999
83
specific location in the surf zone during a certain
called VR formula). Bed load and suspended load are
time was collected using streamer traps oriented so
calculated separately, and the approach of Bagnold
that the traps opposed the direction of the longshore
(1966) is adopted for computing the bed load. Sus-
current. The traps, each consisting of a vertical
pended load is determined by integrating the product
array of polyester sieve cloth streamers suspended
of the vertical concentration and velocity profiles,
on a rack, were deployed across the surf zone. The
where the concentration profile is calculated in three
polyester cloth allowed water to pass through but
layers. Different exponential or power functions are
retained grains with diameter greater than the 0.105
employed in these layers with empirical expressions
mm mesh, which encompasses sand in the fine
that depend on the mixing characteristics in each
grain size region and greater. From knowledge of
layer.
the trap mouth area, the trap efficiency, and the
measurement duration, the local transport rate was
2.6. The Watanabe formula
derived. The trapping efficiency has been exten-
sively investigated through laboratory experiments
Watanabe (1992) proposed a formula for the total
(Rosati and Kraus, 1988) allowing for confident
load (bed load and suspended load) based on the
estimates of the local longshore sediment transport
power model concept. The volume of sediments set
rate.
in motion per unit area is proportional to the com-
Wave height and period were measured using the
bined shear stress of waves and currents, if the
photopole method described by Ebersole and Hughes
critical value for incipient motion is exceeded, and
(1987). This method involved filming the water
this volume is transported with the mean flow
surface elevation at the poles placed at approxi-
velocity. This formula has been widely used in Japan
mately 6-m intervals across the surf zone utilizing
for the prediction of, for example, beach evolution
as many as eight 16-mm synchronized cameras. The
around coastal structures and sand deposition in
bottom profile along the photopole line was surveyed
harbors and navigation channels. The Watanabe for-
each day. Fig. 1 shows surveyed bottom topography
mula (hereafter, called W formula) and its coefficient
along the measurement transect on September 6,
values have been calibrated and verified for a variety
1985. The root-mean-square (rms) wave height
of laboratory and field data sets during the last
(Hrms) at the most offshore pole was in the range
decade (e.g. Watanabe, 1987; Watanabe et al.,
1991). However, it has not yet been established
of 0.4 0.5 m, and the peak spectral period (Tp) was
whether the value of the non-dimensional coefficient
in the range of 9 12 s (see Table 2). Long-crested
in the formula (A) is a constant or it depends on the
waves of cnoidal form arriving from the southern
wave and sediment conditions. Different values are
quadrant prevailed during the experiment, producing
employed for laboratory and field conditions,
a longshore current moving to the north with a
whereas the same value is typically used for mono-
magnitude of 0.1 0.3 m/s.
chromatic and random waves.
3.2. SUPERDUCK surf zone sand transport experi-
ment
3. Longshore sediment transport data sets
Patterned after the DUCK85 experiment, the
3.1. DUCK85 surf zone sand transport experiment
SUPERDUCK surf zone sand transport experiment
was conducted during September and October 1986
The DUCK85 surf zone sand transport experi-
(Rosati et al., 1990). However, at SUPERDUCK a
ment was performed at the U.S. Army Corps of
temporal sampling method to determine transport
Engineers' Field Research Facility at Duck, NC in
rates was emphasized in which traps were inter-
September, 1985. Kraus et al. (1989) measured the
changed from 3 to 15 times at the same locations.
cross-shore distribution of the longshore sediment
Fewer runs are available where the cross-shore dis-
transport rate using streamer traps. Eight runs were
tribution was measured (two runs were employed
made where the amount of sediment transported at a
here; see Table 2).
Previous Page
