COASTAL INLET FUNCTIONAL DESIGN: ANTICIPATING MORPHOLOGIC RESPONSE

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Laboratory, 3909 Halls Ferry Road, Vicksburg, MS 39180-6199 USA.

Abstract: Inlets are part of the coastal sediment-sharing system, and the

presence of a new inlet will greatly modify the nearshore and bay

morphology, as well as the up-drift and down-drift shorelines. Morphologic

response to an inlet varies over several time and spatial scales. This paper

analyzes general morphologic responses to the presence of a new coastal

inlet in the context of functional design considerations that typically must

balance navigation and shore-protection requirements.

INTRODUCTION

Construction of new coastal inlets with jetties is rare. As coastlines have become more

developed, however, environmental and engineering consequences for new or modified

inlets have never been greater. For example, the jetties at many of the larger stabilized

coastal inlets in the Unites States were constructed around the turn of the 20th Century,

with federal jetties in the Great Lakes being the oldest in dating to the 1840s. When

these early jetties were constructed, knowledge of coastal processes was limited. Main

concerns were to furnish a reliable navigation channel and the feasibility of construction

in the marine environment (The Engineer School 1932). Many of the earlier inlet

stabilization projects were built on the shifting sediments of tidal flats and estuaries, far

from infrastructure and development. The coast of the United States was relatively

unpopulated, so consideration of the beaches adjacent to the inlets was minimal. This

paper attempts to be an introductory resource of information about inlet engineering and

morphologic responses, with focus on navigable inlets. Small breaches in barrier

islands and in river mouths are made for environmental enhancements (Wamsley and

Kraus 2005) and as a means of providing sand to the beach through relocation typically

by closing and reopening the inlet up drift of the original location (e.g., Kana and