in which all terms have been previously defined except for "*C*," which is termed the "potential shoaling

factor." As stated previously, the quantity of material entering and depositing in the channel increases with

the depth of the cut. However, until sufficient channel depth is attained to intercept all materials moving into

the inlet, some material continues to bypass the inlet via the sloping face of the ocean bar below the bottom

of the channel cut. Accordingly, *C *is defined as the portion of the total alongshore transport to the inlet

entering the domain of the channel. In order to determine *C*, a regression analysis was conducted to correlate

the inlet bar siltation with those factors judged to be most influential in the filling and flushing of such

channels.

(5) Phase III: Regression analysis. The following three factors were selected as dominant in influencing

the magnitude of shoaling at a particular inlet site having a dredge-maintained ocean bar channel. These

factors are described as follows:

(a) Ebb tide flow is the primary factor acting to flush intrusive littoral materials from the inlet

environment. Its influence in the analysis is represented by the symbol *E*∆T , which is the difference between

the mean ebb tide flow energy flux across the ocean bar at its natural elevation and the mean ebb tide flow

energy flux through the cross section of the excavated ocean bar navigation channel. It is assumed that the

tidal discharge is not significantly altered from one condition to the other. A basic concept in the tidal energy

flux difference is that the tidal flow velocities directed seaward over the ocean bar at its natural elevation, in

combination with wave agitation, are rapid enough to prevent accumulation of sediments above the natural

bar depth. If a section of the ocean bar is deepened by a navigation channel, the related average local flow

velocity is diminished and sediment deposition is initiated.

(b) Wave energy reaching the littoral zones adjacent to the inlet is the primary factor controlling the

quantity of littoral material moving toward the inlet and, as such, determines the shoaling characteristics of

an ocean bar navigation channel. In the analysis, the unrefracted wave energy flux per unit width of wave

crest offshore of the area of interest, designated *E*w , is the basic measure of sediment transport toward the

inlet.

(c) The depth of an ocean bar channel determines the degree to which a channel will trap the littoral

sediments entering the inlet environment. In the analysis, the amount of channel entrenchment, and hence

the measure of sediment entrapment potential, is taken as the ratio *D*R of the depth of the channel to the depth

at which the seaward slope of the ocean bar meets the sea bottom. Each of these depths is measured from the

natural elevation of the ocean bar; therefore, the ratio *D*R represents the extent to which the ocean bar's

seaward slope has been incised by the channel.

(6) Normalized, independent filling index. The channel sedimentation potential increases or decreases

as each of the three factors *E*∆T, Ew, and *D*R increases or decreases, respectively. The factors were combined

as follows to establish a normalized, independent variable FI (filling index) for the regression analysis.

(*E*∆*T *@ *E*W @ *D*R)

(II-6-37)

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The normalized, dependent variable selected for the analysis was the ratio of the volume of channel infill to

the computed volume of the total alongshore sediment influx to the inlet multiplied by 100. This percentage

value *V*R is referred to as the "volume ratio." The regression analysis was based on data from four dredged-

maintained inlets within the boundaries of the Wilmington District: Oregon, Beaufort, Masonboro, and

Lockwoods Folly Inlets. Information available consisted of: (a) measured tidal discharges or inlet throat

cross-sectional areas, which permitted tidal discharge computations by means of tidal prism-inlet area

relations, (b) site wave statistics representing one or more years of wave gauge records, (c) detailed

II-6-58

Hydrodynamics of Tidal Inlets

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