allows treatment of the variability of waves with respect to period and direction of travel. The second

approach is to describe a wave record at a point as a sequence of individual waves with different heights and

periods and then to consider the variability of the wave field in terms of the probability of individual waves.

information for design. For example, information from the *Irregular Waves *section will be used to determine

the expected range of wave conditions and directional distributions of wave energy in order to select an

individual wave height and period for the problem under study. Then procedures from the *Regular Waves*

section will be used to characterize the kinematics and dynamics that might be expected. However, it should

be noted that the procedures for selecting and using irregular wave conditions remain an area of some

uncertainty.

amount of wave energy is dissipated in the nearshore region and on beaches. Wave energy forms beaches;

sorts bottom sediments on the shore face; transports bottom materials onshore, offshore, and alongshore; and

exerts forces upon coastal structures. A basic understanding of the fundamental physical processes in the

generation and propagation of surface waves must precede any attempt to understand complex water motion

in seas, lakes and waterways. The *Regular Waves *section of this chapter outlines the fundamental principles

governing the mechanics of wave motion essential in the planning and design of coastal works. The *Irregular*

(see for example, Kinsman 1965; Stoker 1957; Ippen 1966; Le Mhaut 1976; Phillips 1977; Crapper 1984;

Mei 1991; Dean and Dalrymple 1991). The Regular Waves section of this chapter provides only an

introduction to wave mechanics, and it focuses on simple water wave theories for coastal engineers. Methods

are discussed for estimating wave surface profiles, water particle motion, wave energy, and wave

transformations due to interaction with the bottom and with structures.

be called *linear theory*. Many engineering problems can be handled with ease and reasonable accuracy by

this theory. For convenience, prediction methods in coastal engineering generally have been based on simple

waves. For some situations, simple theories provide acceptable estimates of wave conditions.

often required to describe wave phenomena. These theories represent *nonlinear waves*. The linear theory

that is valid when waves are infinitesimally small and their motion is small also provides some insight for

finite-amplitude periodic waves (nonlinear). However, the linear theory cannot account for the fact that wave

crests are higher above the mean water line than the troughs are below the mean water line. Results obtained

from the various theories should be carefully interpreted for use in the design of coastal projects or for the

description of coastal environment.

beneath the surface. A wave that can be described in simple mathematical terms is called a *simple wave*.

Waves comprised of several components and difficult to describe in form or motion are termed *wave trains*

or *complex waves*. Sinusoidal or monochromatic waves are examples of simple waves, since their surface

profile can be described by a single sine or cosine function. A wave is *periodic *if its motion and surface

profile recur in equal intervals of time termed the *wave period*. A wave form that moves horizontally relative

to a fixed point is called a *progressive wave *and the direction in which it moves is termed the *direction of*

experiencing any change in shape.

II-1-2

Water Wave Mechanics

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