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Understanding Waves on Inner Shelf and their Impact on Beaches

This article explores the behavior of waves as they approach the shore, break, and contribute to mass transport and beach characterization. It also discusses factors that affect net transport and the power of oblique waves on sediment movement.

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Understanding Waves on Inner Shelf and their Impact on Beaches

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

  2. 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

  3. 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.

  4. Beach Characterization: • Dimensionless ratio • Iribarren Number • As a storm approaches, tend to go from reflective towards dissipative

  5. 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:

  6. 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.

  7. 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

  8. Convert power to: • per unit length of shoreline - cos  • in the longshore direction - sin  • Assumes: all longshore current due to obliqueness of waves • no wave-current interaction

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