3
Experiment Procedures
This chapter discusses the procedures performed and measurements obtained
in the inlet channel equilibrium area experiments.
Experiment Design
The purpose of this study was to examine tidal inlet equilibrium areas in a
laboratory (physical model) facility. Determining, or evolving, an equilibrium
area required a movable bed. The approach was to fill the inlet gorge area with
sand, cut a small pilot channel, and initiate the simulation of tides, permitting tidal
Once an equilibrium area was reached, waves with crests parallel to the shore
were run with the tide, and the test was continued until there was no significant
change in area. Periodic channel cross-section areas were measured to determine
channel area change through the inlet gorge. To study the effect of tide period T
(Equation 2), two tide periods were reproduced.
Description of Experiment Conditions and
Measurements
Two tidal periods were reproduced: 105.4 min (which is equivalent to a semi-
diurnal model tide period if a 1:50 scale is assumed) and a 26.35-min tide, or one
fourth the first period chosen. These tidal periods are greater than the minimum
period (25 min) that McDowell (1955) found was necessary to ensure well-
developed velocity gradients near the bottom for physical model studies. The tide
range for all tests was 30.5 mm (0.1 ft). Also, two sand sizes were used: median
diameter D50 of 0.13- and 0.26-mm quartz sand. Gradation curves for each sand
are shown in Figure 3. The finer sand was a packaged molding sand, and the lar-
ger sand was from a nearby natural sand source and was available from previous
movable-bed models at the U.S. Army Engineer Research and Development Cen-
ter. About 3,000 kg (7,000 lb) of each type of sand was spread in the model inlet
and adjacent regions. The following measurements were obtained: one velocity
station at the minimum cross-section area at the channel center line, measured
with the SonTek ADV at about 2 cm (0.8 in.) below the low-tide level (tide range
about 3 cm (1.18 in.)); tidal elevations for ocean and bay, measured well away
from the influence of high-velocity flow in the inlet; and cross-sectional area
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Chapter 3 Experiment Procedures