EM 1110-2-1100 (Part II)
31 July 2003
Chapter II-4
Surf Zone Hydrodynamics
II-4-1. Introduction
a. Waves approaching the coast increase in steepness as water depth decreases. When the wave
steepness reaches a limiting value, the wave breaks, dissipating energy and inducing nearshore currents and
an increase in mean water level. Waves break in a water depth approximately equal to the wave height. The
surf zone is the region extending from the seaward boundary of wave breaking to the limit of wave uprush.
Within the surf zone, wave breaking is the dominant hydrodynamic process.
b. The purpose of this chapter is to describe shallow-water wave breaking and associated hydrodynamic
processes of wave setup and setdown, wave runup, and nearshore currents. The surf zone is the most dynamic
coastal region with sediment transport and bathymetry change driven by breaking waves and nearshore
currents. Surf zone wave transformation, water level, and nearshore currents must be calculated to estimate
potential storm damage (flooding and wave damage), calculate shoreline evolution and cross-shore beach
profile change, and design coastal structures (jetties, groins, seawalls) and beach fills.
II-4-2. Surf Zone Waves
The previous chapter described the transformation of waves from deep to shallow depths (including
refraction, shoaling, and diffraction), up to wave breaking. This section covers incipient wave breaking and
the transformation of wave height through the surf zone.
a. Incipient wave breaking. As a wave approaches a beach, its length L decreases and its height H may
increase, causing the wave steepness H/L to increase. Waves break as they reach a limiting steepness, which
is a function of the relative depth d/L and the beach slope tan β. Wave breaking parameters, both qualitative
and quantitative, are needed in a wide variety of coastal engineering applications.
(1) Breaker type.
(a) Breaker type refers to the form of the wave at breaking. Wave breaking may be classified in four
types (Galvin 1968): as spilling, plunging, collapsing, and surging (Figure II-4-1). In spilling breakers, the
wave crest becomes unstable and cascades down the shoreward face of the wave producing a foamy water
surface. In plunging breakers, the crest curls over the shoreward face of the wave and falls into the base of
the wave, resulting in a high splash. In collapsing breakers the crest remains unbroken while the lower part
of the shoreward face steepens and then falls, producing an irregular turbulent water surface. In surging
breakers, the crest remains unbroken and the front face of the wave advances up the beach with minor
breaking.
1
Ho
&
2
ξo ' tanβ
(II-4-1)
Lo
where the subscript o denotes the deepwater condition (Galvin 1968, Battjes 1974). On a uniformly sloping
beach, breaker type is estimated by
Surf Zone Hydrodynamics
II-4-1
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