Two of the cases, Case 1 with three groins of equal length and Case 3 with three
detached breakwaters located at the same distance offshore as the tips of the three
groins, were reported in the previous study of Hanson and Kraus (1991). Good
agreement was found between physical and numerical model results.
To illustrate the new capability with the improved representation of T-head
groins, Case 4 with three T-head groins was studied here. This case is a
superposition of Cases 1 and 3. Of particular value for evaluating models was
that the beach was aligned at a 14-deg angle to the wave generator, producing
obliquely incident waves and a predominant direction of longshore transport.
The design initial shoreline (y = 0) was located 4 m from the end of the basin,
and the entire beach from - 4 m to + 10 m was built of sand (median grain size,
0.27 mm). The bottom profile configuration replicated the field site, with the
foreshore going from the still-water shoreline to a depth of 10 cm on a 1/10 slope;
then tapering to a gently sloping beach to a depth of 20 cm located 8 m from the
shoreline. For two more meters the slope tapered to the bottom (-40 cm) on a
1/10 slope.
Offshore wave height was measured at hourly intervals at two locations and
found to deviate from the design height in time and across the basin. Shoreline
position was measured at 2-hr intervals at 0.25-m spacing alongshore. Shoreline
positions at 4 and 18 hr were used to calibrate and verify the numerical model and
provide a base model arrangement with which different input conditions could be
examined. Breaking wave height was measured at the beginning and end of each
case at 0.5-m intervals alongshore.
The groins were made of small cement blocks and were high and impermeable
to the waves. The groins were located 6 m apart, centered at x = 2, 8, and 14 m.
These locations are named A, B, and C, respectively. The groins extended 1.8 m
seaward of the average initial shoreline and extended landward to meet the basin
wall, so no bypassing could occur landward when the shoreline eroded. The
seaward ends of the groins were at a depth of 10 cm. At the seaward end of the
groins, the breakwaters rested on a foundation of gravel to prevent subsidence and
were made of three layers of tetrapods that were assumed here to allow wave
transmission in the numerical simulation presented here. The breakwaters were
1.6 m long and centered on the same lines as the groins, x = 2, 8, and 14 m. There
was 1.2 m between the far ends of the two outer breakwaters and the basin walls.
The design wave height was Ho = 5.8 cm in the horizontal section (depth h =
40 cm), and period T = 1.2 sec, giving Ho/Lo = 0.027, where Lo = deep-water
Because the waves, sand, and beach in the physical model tests were almost
identical for the three cases, it was appropriate to specify the same values for the
calibration parameters found in the previous study (Hanson and Kraus 1991).
In accordance with previous experience, modeling results for the groin
configuration were sensitive to changes in the K1-value, but insensitive to changes
in the K2-value. This result implies that obliquely incident breaking waves
account for most of the alongshore sand transport. In contrast, the DBW
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