ANALYTICAL MODEL OF INCIPIENT BREACHING OF COASTAL BARRIERS

Kraus2_CEJ_03
Page Navigation
1

3909 Halls Ferry Road, Vicksburg, MS 39180 USA

Nicholas.C.Kraus.@erdc.usace.army.mil

Received 21 September 2003

Revised 29 September 2003

A mathematical model is formulated to describe incipient breaching of coastal barrier

islands. The model is based on the assumptions of idealized breach morphology and is in-

tended to describe the growth of breaches prior to possible closure by longshore sediment

transport. The two coupled, non-linear equations governing breach width and depth are

solved analytically for special cases. The analytical solutions explicitly exhibit an expo-

nential behavior in breach dimensions and reveal that the macroscale process of breach

growth is controlled by seven variables: initial width and depth of the breach, equilibrium

width and depth of the breach, width of the barrier island, and maximum or initial net

sediment transport rates at the bottom and sides of the breach. The literature is reviewed

to compile general properties of coastal breaches, and sensitivity testing shows the model

to be compatible with those observations. The model is applied to simulate the 1980 breach

at Moriches Inlet, New York, and reasonable agreement is found.

Keywords : Breach; inlet; barrier island; mathematical model; Moriches Inlet; morphology

modeling.

1. Introduction

A coastal breach is a new opening in a narrow landmass such as a barrier island

or barrier spit that allows water to flow between the water bodies on each side.

Breaching is a common natural occurrence on barrier islands and spits, and at

ephemeral river mouths and coastal lagoons and ponds. Breaches are also induced

artificially for flood protection, to increase water quality, and as an environmental

enhancement. Natural breaching can be initiated in three ways: (1) inundation from

the sea combined with wave action, (2) elevated water level in the back bay or river,

511