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Lecture

EESB18H3 Lecture Notes - Surf Zone, Dune, Breaking Wave


Department
Environmental Science
Course Code
EESB18H3
Professor
Jovan Stefanovic

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Lecture Seven
x Waves
o Energy traveling along the interface between ocean and atmosphere
o Derive their energy and motion from wind
o Waves can travel great distance (> 10000 km)
o Circular orbital motion
o Parts
Crest
Trough
o Wave height, length and period depend on
Wind Speed
Length of time wind blows
Fetch distance wind travels
o As wave travels, water passes energy along by moving in a circle
Waveform moves forwad
At a depth of about one-half the wavelength, the movement of
water particles becomes negligible (wave base)
In very shallow water (depth < 0.05L where L = wavelength)
motion at bottom is nearly horizontal (rather than circular)
x Eg: 1 meter long wavelength would be 0.05(1M) = 5cm
o Swell Wave sets generated by storms far out at the sea
Any wave that has traveled out of its area of origination
o Rouge Waves When series of similar-size waves meet and coalesce
o Changes that occur when a wave moves onto shore
As wave touches bottom of shore the bottom of the wave
begins to slow down while the top of the wave rï
original speed.
The wave speed decreases, and the waves stack up against the
shore. Causing wavelength to decrease and height to increase.
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o Beaches and shoreline processes
Wave refraction
x Bending of a wave
x Wave arrives parallel to shore
x Results
o Wave energy is concentrated against the sides
and ends of headland
o Wave erosion straightens an irregular shoreline
Point furthest out on coast will be hit first resulting in most
wave energy being used to erode cliff.
The main reason behind wave refraction is the different
shoreline resulting in a different deceleration of the waves
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o Breaking Waves
With Wave Shoaling
x Length Decreases
x Height Increases
x Wave Steepness increases
Types of breaking waves
x Plunging Breakers Steep beaches, very erosive
x Spilling Breakers Wide, gently sloping, sandy beaches
Great energy dissipation
Shoreward mass transport of water
Turbulent water created by breaking waves is called surf
Swash (Up beach) Moves up slope of the beach
Backwash (Down beach) Flows back down the beach toward
the surf zone
o Beach Form
Composed of whatever material is available (bits of shell/coral,
fragments of basalt, rier sediments)
Gravel high energy, steep beaches
Sand gently sloping, lower energy beaches
Material does not stay in one place
x Wave energy moves large quantities of sand parallel
and perpendicular to the shoreline
o Role of beaches a buffer protected sea cliffs and coastal properties
from intense wave action & erosion
o Sand Transport
Movement perpendicular to the shoreline
x Relatively Light (Less energetic waves)
o During summer
o Swash dominates net movement of sand up the
beach face towards the berm (wide berm)
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