Wave momentum flux parameter: a descriptor for nearshore waves

Hughes-MomFlux-CEv51
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Vicksburg, MS 39180-6199, USA

Received 23 April 2003; received in revised form 29 June 2004; accepted 16 July 2004

Available online 7 October 2004

Abstract

A new parameter representing the maximum depth-integrated wave momentum flux occurring over a wave length is

proposed for characterizing the wave contribution to nearshore coastal processes on beaches and at coastal structures. This

parameter has units of force per unit crest width, and it characterizes flow kinematics in nonbreaking waves at a given depth

better than other wave parameters that do not distinguish increased wave nonlinearity. The wave momentum flux parameter can

be defined and estimated for periodic and nonperiodic (transient) waves. Thus, it has potential application for correlating to

processes responding to different types of waves. This paper derives the wave momentum flux parameter for linear, extended

linear, and solitary waves; and it presents an empirical formula estimating the parameter for nonlinear steady waves of

permanent form. Guidance is suggested for application to irregular waves. It is anticipated that the wave momentum flux

parameter may prove useful for developing improved semiempirical formulas to describe nearshore processes and wave/

structure interactions such as wave runup, overtopping, reflection, transmission, and armor stability. Surf zone processes where

waves break as plunging or spilling breakers may not benefit from use of the wave momentum flux parameter because the

breaking processes effectively negates the advantage of characterizing the wave nonlinearity.

Keywords: Coastal structures; Iribarren number; Nonlinear waves; Solitary waves; Wave forces; Wave momentum flux; Wave parameters

criteria associated with the specified design wave.

1. Introduction

For example, a rubble-mound breakwater design

Coastal shore protection and navigation struc-

must assure armor stability; and there may be

tures are designed to withstand waves up to an

specified values for maximum wave runup, allow-

expected level (sometimes referred to as the bdesign

able average rate of wave overtopping, and max-

waveQ), and there are often multiple structure design

imum height of transmitted waves. These design

criteria are dependent on project functional require-

ments, so specified criteria may vary between

* Tel.: +1 601 634 2026; fax: +1 601 634 3433.

projects.

E-mail address: steven.a.hughes@erdc.usace.army.mil.

doi:10.1016/j.coastaleng.2004.07.025