In: Proceedings Coastal Sediments '03. 2003. CD-ROM Published by World Scientific Publishing
Corp. and East Meets West Productions, Corpus Christi, Texas, USA. ISBN 981-238-422-7.
lead one to anticipate this would be the optimal cross-section area according to Skou. It is interesting
to note that the response ability of the Escoffier analysis equilibrium cross-section area is about half
that of the area with maximum response ability.
For the Barnegat Inlet case we have seen that anthropogenic changes between 1968 and 1998
contributed to opening the cross-section area of the inlet from about 900 m2 to 2000 m2. The inlet is
still a low K inlet with a long friction dominated channel system. According to the location for
equilibrium on the Escoffier analysis, the channel has a potential to reach 15,000 m2. Using the
Mota Oliviera idea that some inlets stabilize with a Keulegan K value in the 0.6 to 0.8 range, an
expected area of 4,300 m2 would be reached (K = 0.8). A value of the best channel response is
achieved for an area of 10,000 m2.
OTHER FACTORS
This relatively simple analysis indicates that it may be difficult to determine "the ultimate
equilibrium area" value for an inlet. If the opportunity occurred for shortening the inlet, e.g., say an
alternative shorter channel was to be dredged, or barrier beach breached, the potential for an
equilibrium channel could occur. An inlet with a low Keulegan K value is typically a high friction
loss system, so it may maintain this state for some time and may be in a "temporary equilibrium,"
until natural or human forces intervene. It has to be recognized that there is potential for
enlargement of the channel. Nature may intervene and create a new connection to the bay due the
breaching of a new inlet, creating a shorter channel from ocean to bay. With a shorter channel,
friction may be less and the new cut may supplant the older inefficient channel. A larger cross-
section may develop and soon a larger tidal prism could fill the bay with its attendant greater tide
range, flooding areas that were dry when the old friction dominated channel-controlled flow. A
storm surge could cause scour and increase channel efficiency. In a similar manner, dredged cuts to
shorten navigation routes may likewise develop into more efficient channels and perhaps contribute
to scour in the entrance channel as the response ability increases rapidly.
The above has discussed the negative responses of a rapid change of an inlet moving along the
closure curve toward stable equilibrium. As an inlet reaches its equilibrium area, there most likely
will be very positive responses occurring. Channel location stability and thus its reliability for
navigation safety will be improved. The stable inlet will enhance water circulation and water quality
due to a larger tidal prism relative to the low Keulegan K inlet.
CONCLUSIONS
The Escoffier analysis of tidal inlet channel cross-section area equilibrium for cases of inlets with
existing low Keulegan K values typically indicates that the equilibrium area will be much larger than
the existing area. A low Keulegan K inlet has a bay that only fills to a fraction of its potential tidal
prism. The equilibrium channel area determined by the Escoffier analysis has a bay that fills
completely. The high friction channel of a low Keulegan K inlet appears to be difficult to move
toward the Escoffier equilibrium area unless society or nature improves the efficiency of the channel.
Other approaches to an equilibrium area seem to indicate that smaller values of equilibrium other
than that of Escoffier analysis may be the limiting maximum area that could exist for a given low
Keulegan K inlet system.
Seabergh
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