January 13, 2004
14:37
WSPC/101-CEJ
00097
512
N. C. Kraus
causing piping and liquifaction, and (3) narrowing of a barrier island or spit by
reduction of sediment supplied through longshore transport (Pierce, 1970; Kraus,
Militello, and Todoroff, 2002). Coastal barrier breaching is expected to become more
prevalent with rise in sea level, erosion of the coast, and continued length of service
of jetties.
Once breaching occurs, tidal exchange and river discharges will typically widen
the initial opening. A breach may close naturally, but, if the tidal exchange is strong
and longshore sediment transport weak, it can increase in size and become a new
inlet. An inlet created by breaching may compete for stability with existing inlets
in the same bay system, promoting their closure. A breach adjacent to a jetty has
potential for undermining and isolating the structure, and it will convey a portion
of the flow that would otherwise scour the navigation channel, promoting shoaling
of the channel. In addition, nearshore and beach sediment that had been protecting
the structure and the shore may move through the breach and into the navigation
channel, increasing dredging requirements and adding unanticipated cost to inlet
entrance maintenance. A trend toward closure of an existing inlet will make the
navigation channel unreliable, as well as alter the environment because of changes
in water level, circulation, and salinity.
Breaches can cause loss of human life, property, infrastructure, and transporta-
tion corridors; endanger navigation and stability of adjacent inlets; and harm the
environment by the exposure of bay perimeter to sea waves and by the change in
bay salinity. The cost of breach closure can be high, so unintended breaches that
will be a concern should be avoided by counter measures and breach contingency
planning. Most breaches open rapidly and then gradually evolve over a period of
weeks to months if they continue to remain open. Quantitative predictive tools are
necessary to assess vulnerability of coastal barriers, design breach-prevention mea-
sures, develop breach-closure plans, estimate the fate of a breach, and evaluate the
consequences of a breach to the neighboring inlets, beach, and estuarine system.
Measurements and reliable predictive models of coastal breaching are lacking.
This paper introduces a mathematical model of the breaching of alluvial coastal
barriers based on a macro-scale or morphologic approach. The model provides a
heuristic framework for understanding the breaching process and makes apparent
key dependencies that control the growth of a coastal breach.
2. Breaching Process
Review of the literature indicates that little quantitative information is available
on the process of coastal barrier breaching and that predictive capability is lacking
(Basco and Shin, 1999; Kraus, Militello, and Todoroff, 2002; Kraus and Wamsley,
2003). During hurricanes and storms, large numbers of ephemeral breaches can open
(e.g. Texas coast, USA -- Price, 1963; Hayes, 1967; and Pierce, 1970; Louisiana
coast, USA -- Wright, Swaye, and Coleman, 1970; and New Brunswick, Canada
Previous Page
