5
Beach Morphology Control
Introduction
The goal of the experiments is to obtain an accurate rate of longshore
sediment transport and its cross-shore distribution with minimal longshore
variation and boundary influences. To achieve this goal, it is necessary to
maintain straight and parallel contours throughout the model. Beaches having
"three-dimensionality" affect incident waves and, subsequently, the longshore
currents and sediment transport associated with the waves are also affected.
Therefore, it was necessary to maintain straight and parallel contours throughout
the model to the greatest degree possible. This chapter describes the method used
to construct the beach morphology and maintain straight and parallel contours to
maximize the length of beach over which longshore uniformity of waves and
currents exist in the basin.
Maintaining Straight and Parallel Contours
Sand used in the initial experiments was fine quartz sand of uniform size,
D50 = 0.15 mm. A total of approximately 125 m3 of sand was transported into the
facility by means of a tractor (Figure 27) and placed on top of the fixed-bed
concrete beach. The tractor is equipped with a front-end loader and rear box-
blade, which are used to distribute sand along the beach (Figure 28).
Stainless steel rods mounted on the bridge at 1.0-m intervals in the cross-
shore direction are used as elevation indicators to help maintain straight and
parallel contours (Figure 29). The rods are lowered to the desired elevation at
each cross-shore location and fixed in place by an anchoring collar. Moving the
bridge along the facility leaves traces in the sand at the desired beach elevation,
and indicate locations that require cutting or filling. The tractor's boxblade and
front-end bucket are used in the longshore direction to scrape or fill sand to the
necessary elevation indicated by the rod traces (Figure 30). After a segment of
beach is cut or filled, it is necessary to check the elevations by again traversing
the rods over the beach. Several iterations of checking elevations with the rods
and grading the beach are required before the beach has acceptable uniformity.
To avoid possible breakage or bending of the rods, the depth of sand the rods are
dragged is limited to a few centimeters. Therefore, grading of the beach to an
approximate elevation may be required before the rods are used to indicate the
desired beach profile. Although most of the beach can be graded using the
tractor, it is necessary to manually cut and fill portions of the beach between rod
47
Chapter 5
Beach Morphology Control
Previous Page
