Bruun and Gerritsen (1959) introduced a classification and empirical relation for inlet
bypassing and morphologic state of the channel based on a quantity:
P
r=
(3)
M tot
in which Mtot = volume of material carried to the inlet entrance by the longshore
transport in 1 year. Because the formula of Walton and Adams (1976) relates tidal
prism to ebb shoal volume, and Mtot is closely related to the gross longshore transport in
a year, the parameter r is directly connected with the characteristic time scale τ for inlet
morphology change, bypassing, and suitability of the channel for navigation.
Ebb shoals and, possibly flood shoals (Militello and Kraus 2001a) offer a source of
material for beach nourishment. Mining of the ebb shoal disrupts natural bypassing and
must be done with caution (Cialone and Stauble 1998). Ebb shoals can also be
reconfigured by storms (Mehta et al. 1996), which will also disrupt natural bypassing.
The Inlet Reservoir Model can be applied to estimate such processes. Dabees and Kraus
(2005) describe the general methodology of the Reservoir Model, embedded in regional
modeling of the tidal hydrodynamics and analysis of inlet morphology and shoreline
change, through several epochs with different forcing and engineering actions.
4. Inlet Stability
Stability can refer either to inlet plan-view location or to inlet channel cross-sectional
area. Jetties stabilize inlet location; however, the inlet navigation channel can migrate
in response to changes in the jetties (Cialone et al. 1999) or in the forcing conditions
(Militello and Kraus 2001a, 2001b). The desired cross-sectional area is determined by
tidal prism and other water discharges (such as by wind and rivers), distance between
jetties, length of jetties, longshore sediment transport rate, wave height (which figures
directly in sediment bypassing), and sediment type as the leading factors. O'Brien
(1931), Jarrett (1976), Hume and Hendendorf (1992) and others have found a simple
empirical relation between tidal prism and minimum channel cross-sectional area below
mean sea level of stable inlets AC as:
AC = CPn
(4)
in which C and n (~ 1) are empirical coefficients. Kraus (1998) derived a theoretical
form for the coefficient C to be:
0.3
⎛ απ3m2We4 / 3 ⎞
C =⎜
⎜ QgT 3 ⎟
(5)
⎟
⎝
⎠
in which α = empirical sediment transport coefficient of order unity, m2 = Mannings
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