Transcript Artificial Reef Design for Surfing

Artificial Reef Design for
Surfing
By: Spicer Bak, M.S.
Stevens Institute of Technology
This material is based upon work supported by the National
Science Foundation under Grant No.. NSF DGE-0742462
Why do this?
• Rising Sea Levels/Wave heights
• Growing Conflict with Surfer
Groups and local
Government
Long Branch, NJ - October 2006
ASBPA National Conference
Beach Protection
• Waves are a type of
energy
– Waves = energy
– Energy moves sand
– Beach gets narrower
• 2 basic causes of erosion
– Longshore Sediment transport
– Cross-shore erosion
• Current popular protection
– Groynes - Long-shore
– Breakwaters/seawalls
• Cross-shore
Groynes - Long-shore sediment
transport protection
• Advantage:
– Keeps sand
– Encourages sea life
• Disadvantage
– Eyesore - not pretty
– Need a field to
adequately protect
http://changingcoastline.com/dunes-edge/beach-restoration/hard-engineered-solutions/
Break waters & sea walls
• Seawall
– Wall at edge of water
– Stops wave energy
• Breakwater
– Parallel to shore
– Dissipates waves
Galveston, Texas
Science Of Surfing
• Peel Angle
• Velocity
• Wave
Classification
– Vortex Ratio
– Surf Similarity
Parameter
Peel Angle
• Used to classify the wave
• Surfer Velocity
VS 
VW
sin 
VW  ghb
Peel Angle
Classification of Waves
BEGINNER
INTERMEDIATE
ADVANCED/EXPERT
Hutt, Black and Mead (2001)
Vortex Ratio
Vortex ratio (Y) = Vortex length to width
ratio
Y  0.065 X '0.821
X '  X cos 
Wave parameters used for curve fitting; vortex length (l), vortex width
(w), angle (θ), and wave height (H), orthogonal seabed gradient (X’)
Mead and Black (2001)
Surf Similarity Parameter
b tan 
Hb
Lo
Surf
Similarity
Parameter
ξb > 2.0
0.4 < ξb < 2.0
ξb < 0.4
Breaker Type
Surging or collapsing
Plunging
Spilling
Surfing
Terminology
‘Unsurfable’ wave
‘Tubing’ or ‘hollow’
wave
‘Full’, ‘fat’, or ‘mushy’
wave
Surging/Collapsing
Plunging
Spilling
Example Classifications
Mead and Black (2001)
Reefs
• Advantages
– Out of sight
– Design to protect against
long- shore/cross-shore
– Provides:
• Capability for design for
•
•
•
surf
Adds marine life habitat
Sheltered swimming
Diving
– Comparable Cost
• Disadvantages
– Construction difficult
– Time consuming
– Still an emerging
technology
– Mostly proprietary (as
of right now)
Refraction - Energy
• Wave straightens out
• Snell’s Law
sin  sin o

C
Co
( – measured w.r.t. shore
normal)
• E=1/8  * g * H
2
Unprotected
Coastal protection
Design
• Giant Sand bags
– Placed then filled
• V - Shaped
pattern
Narrow Neck - Aus
• Both Right and left
– Beginners wave on
inside
ASR
• design overview
• india goes off