along the crest of a wave moving at an angle to underwater contours because
that part of the wave in deeper water is moving faster than the part in
shallower water. This variation causes the wave crest to bend toward alignment with the contours. (See Figure 2-17.) This bending effect, called
refraction, dépends on the relation of water depth to wavelength. It is
analogous to refraction for other types of waves such as, light and Sound.
In practice, refraction is important for several reasons such as:
(1) Refraction, coupled with shoaling, détermines the wave height
in any particular water depth for a given set of incident deepwater wave
conditions, that is wave height, period, and direction of propagation in
deep water. Refraction therefore has significant influence on the wave
height and distribution of wave energy along a coast.
(2) The change of wave direction of different parts of the wave
results in convergence or divergence of wave energy, and materially affects
the forces exerted by waves on structures.
(3) Refraction contributes to the alteration of bottom topography
by its effects on the érosion and déposition of beach sédiments. Munk and
Traylor (1947) confirmed earlier work by many indicating the possible interrelationships between refraction, wave energy distribution along a shore,
and the érosion and déposition of beach materials.
(4) A general description of the nearshore bathymetry of an area
can sometimes be obtained by analyzing aerial photography of wave refraction
patterns. While the techniques for performing such analyses are not well
developed, an experienced observer can obtain a general picture of simple
bottom topography.
In addition to refraction caused by variations in bathymetry, waves
may be refracted by currents, or any other phenomenon which causes one part
of a wave to travel slower or faster than another part. At a Coastal inlet,
refraction may be caused by a gradient in the current. Refraction by a
current occurs when waves intersect the current at an angle. The extent
to which the current will refract incident waves dépends on the initial
angle between the wave crests and the direction of current flow, the
characteristics of the incident waves, and the strength of the current.
In at least two situations, wave refraction by currents may be of practical
importance. At tidal entrances, ebb currents run counter to incident waves
and conséquently increase wave height and steepness. Also, major océan
currents such as the Gulf Stream may hâve some effect on the height, length
and direction of approach of waves reaching the coasts. Quantitative
évaluation of the effects of refraction by currents is difficult. Additional research is needed in this area. No detailed discussion of this
problem will be presented here, but an introduction is presented by
Johnson (1947).
The decrease in wave celerity with decreasing water depth can be considered an analog to the decrease in the speed of light with an increase in
2-63
that part of the wave in deeper water is moving faster than the part in
shallower water. This variation causes the wave crest to bend toward alignment with the contours. (See Figure 2-17.) This bending effect, called
refraction, dépends on the relation of water depth to wavelength. It is
analogous to refraction for other types of waves such as, light and Sound.
In practice, refraction is important for several reasons such as:
(1) Refraction, coupled with shoaling, détermines the wave height
in any particular water depth for a given set of incident deepwater wave
conditions, that is wave height, period, and direction of propagation in
deep water. Refraction therefore has significant influence on the wave
height and distribution of wave energy along a coast.
(2) The change of wave direction of different parts of the wave
results in convergence or divergence of wave energy, and materially affects
the forces exerted by waves on structures.
(3) Refraction contributes to the alteration of bottom topography
by its effects on the érosion and déposition of beach sédiments. Munk and
Traylor (1947) confirmed earlier work by many indicating the possible interrelationships between refraction, wave energy distribution along a shore,
and the érosion and déposition of beach materials.
(4) A general description of the nearshore bathymetry of an area
can sometimes be obtained by analyzing aerial photography of wave refraction
patterns. While the techniques for performing such analyses are not well
developed, an experienced observer can obtain a general picture of simple
bottom topography.
In addition to refraction caused by variations in bathymetry, waves
may be refracted by currents, or any other phenomenon which causes one part
of a wave to travel slower or faster than another part. At a Coastal inlet,
refraction may be caused by a gradient in the current. Refraction by a
current occurs when waves intersect the current at an angle. The extent
to which the current will refract incident waves dépends on the initial
angle between the wave crests and the direction of current flow, the
characteristics of the incident waves, and the strength of the current.
In at least two situations, wave refraction by currents may be of practical
importance. At tidal entrances, ebb currents run counter to incident waves
and conséquently increase wave height and steepness. Also, major océan
currents such as the Gulf Stream may hâve some effect on the height, length
and direction of approach of waves reaching the coasts. Quantitative
évaluation of the effects of refraction by currents is difficult. Additional research is needed in this area. No detailed discussion of this
problem will be presented here, but an introduction is presented by
Johnson (1947).
The decrease in wave celerity with decreasing water depth can be considered an analog to the decrease in the speed of light with an increase in
2-63