Empirical Coefficient: The unknown coefficient in Eqn. 8 was empirically evaluated by
comparison to field measurements at two dual-jetty tidal inlets. Vertical profiles of horizontal
velocity were measured along transects at Shinnecock Inlet, New York, and at Ponce de Leon
width was estimated from the measurements by integrating the velocity profiles over the
depth. Profiling transects across the inlet throats occurred at or around the maximum ebb or
flood flow.
The results are shown on Figure 7 where calculated discharge per unit width is plotted
1/2 3/8 9/8
versus the term ( [g (Ss - 1)]
de h
) on the right-hand side of Eqn. 8. Grain-size for
the Shinnecock Inlet channel was taken as 0.6 mm, whereas a size of 0.21 mm was used for
Ponce de Leon Inlet. Both sands were assumed to have the same density as quartz.
Figure 7: Field Data From Two Dual-Jettied Inlets.
The data points on Figure 7 show a wide range of discharge per unit width measured at
the different depths. However, there is an upper limit to the data as indicated by the straight
dashed line. This dashed line represents the maximum discharge per unit width (qe) that can
3/8
1/2
de h9/8 ). The discharge
be sustained at a particular value of the parameter ( [g (Ss - 1)]
indicated by the dashed line is termed the equilibrium maximum discharge. Any increase
in discharge beyond the equilibrium value will result in an increase in water depth.
The scatter of measurements beneath the dashed line is pronounced, and this indicates
17
Hughes/Schwichtenberg
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