Transcript Waves on the Inner Shelf into Beaches: As offshore waves approach the shore, they shoal, refract, and then break.

Waves on the Inner Shelf into Beaches:
As offshore waves approach the shore, they shoal, refract,
and then break.
As waves feel the seabed, Stokes Drift occurs:
(function of the non-linearity of waves in shallow water)
Orbit at wave crest
slightly larger than
orbit at wave trough
Results in Mass Transport
Wave breaking
Type of breaking is a function of:
wave steepness
beach slope
As the waves break
they lose energy
and diminish in
wave height.
Beach Characterization:
Dimensionless ratio
H b 2

2 gS 2
Iribarren Number
b 
S
H b / Lo  2
1
As a storm approaches,
tend to go from
reflective towards
dissipative
Bedload transport on beaches (under waves)
Models are largely inherited from uni-directional
models.
Two Examples: Madsen (1971) and wave power due to
oblique waves
Madsen reaffirmed the Meyer-Peter Muller model
under time-dependent oscillating velocity:
8( (t )   cr )
Qs (t ) 
(s   )g
1
 f wu~b (t ) 2
 (t )  2
(  s   ) gD
3
2
Factors that produce a net transport:
1. Bottom slope
2. Non-linear waves
3. Superimposed currents
*Net transport arises from a small difference between
two large quantities.
Wave power due to oblique waves
For larger grain sizes (sediment that isn’t going into
suspension), can use the “power expended on the seabed”
concept of Bagnold’s.
Instead of looking at the energy flux through the boundary
layer -
wave energy flux = power/unit length of wave crest
= (E·Cg)b
where: E = 1/8  gH2
All of this power must be expended within the surf zone
Convert power to:
per unit length of shoreline
- cos 
in the longshore direction
- sin 
Qlongshore  ( s   ) gjl  K ( ECg )b sin  cos
Assumes: all longshore current due to
obliqueness of waves
no wave-current interaction