Coastal Structure Foundations

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Shore Protection for Alaska
Constructed Shore Protection
Steven A. Hughes, PhD, PE
Coastal and Hydraulics Laboratory
US Army Engineer Research and Development Center
Waterways Experiment Station 3909 Halls Ferry Roa
d Vicksburg, Mississippi 39180-6199
Email Steven.A.Hughes_at_erdc.usace.army.mil
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Constructed Shore Protection
Contents

• Shore Protection Alternatives
• Non-Structural Alternatives
• Armoring Alternatives
• Shore Stabilization Alternatives
• Shore Protection Project Planning

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Constructed Shore Protection
Key Points About Shore Protection

• Each project site is unique
• A variety of shore protection options are
  available
  
• One size does NOT fit all
• Project monitoring and maintenance are essential

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Shore Protection Alternatives
Major Reasons for Shore Protection

• Storm damage reduction
• Coastal flooding
• Wave damage
• Coastal erosion mitigation
• Ecosystem restoration

Oosterschelde storm surge barrier
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Shore Protection Alternatives
Categories of Engineering Response

• Armoring (draw the line)
• Moderation (slow the loss)
• Restoration (fill it up)
• Adaptation (live with it)
• Abstention (do nothing, abandon)

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Constructed Shore Protection
Contents

• Shore Protection Alternatives
• Non-Structural Alternatives
• Armoring Alternatives
• Shore Stabilization Alternatives
• Shore Protection Project Planning

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Structural Alternatives
Armoring Alternative

• Draw the line
• Use of hard structures
• Seawalls
• Bulkheads
• Revetments / Dikes
• Cost justified when substantial human investment
  is threatened

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Armoring Alternatives
Seawalls
Seawalls are vertical structures, constructed
parallel to the shoreline that separate land and
water areas, and are primarily designed to
prevent erosion and other damage due to wave
action.
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Armoring Alternatives
Bulkheads
Bulkheads are vertical structures that are
designed primarily to prevent sliding or
retention of the land. A secondary purpose is to
protect upland areas against damage from wave
action.
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Armoring Alternatives
Example Structures
Seawall
Bulkhead
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Armoring Alternatives
Seawalls and Bulkheads

• Materials
• Timber
• Sheetmetal
• Vinyl
• Concrete
• Design Considerations
• Functional Performance
• Low to high wave energy
• Wave reflection
• Wave overtopping
• Structural Stability
• Toe scour
• Drainage
• Tie-backs
• Impacts
• Fronting beach
• Adjacent shoreline

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Armoring Alternatives
Do Seawalls Cause Erosion?

• Concerns that are probably false
• Profile steepening
• Delayed beach recovery after storms
• Increased longshore transport
• Sand transport farther offshore
• Increase in average long-term erosion rate
• Concerns that are probably true
• Frontal effects (increase in toe scour, depth at
  wall)
  
• End-wall effects (flanking)
• Blockage of littoral drift when projecting into
  surf zone
  
• Decreased beach width fronting the seawall

Based on Dean 1987
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Armoring Alternatives
Revetments

• Materials
• Armor stone, riprap
• Geosynthetic fabric
• Gravel/filter stone
• Concrete
• Marine mattresses
• Design Considerations
• Functional Performance
• Moderate to high wave energy
• Wave reflection
• Wave runup and overtopping
• Structural Stability
• Armor stability
• Toe scour
• Drainage
• Foundation
• Impacts
• Nearshore habitat

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Armoring Alternatives
Revetments
Revetments are shoreline structures constructed
parallel to the shoreline and generally sloped in
such a way as to mimic the natural slope of the
shoreline profile and dissipate wave energy as
the wave is directed up the slope.
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Armoring Alternatives
Example Revetments
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Armoring Alternatives
Dikes and Levees
Dikes and levees are mounded structures, made of
natural or man-made materials, built around low l
ying areas to prevent flooding.
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Constructed Shore Protection
Contents

• Shore Protection Alternatives
• Non-Structural Alternatives
• Armoring Alternatives
• Shore Stabilization Alternatives
• Shore Protection Project Planning

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Structural Alternatives
Shore Stabilization

• Slow the loss
• Moderate local sediment transport processes
• High local erosion rate
• Diminished sediment supply causing chronic
  erosion
  
• Usually involves hard structures
• Groins, headlands, nearshore breakwaters, sills,
  and reefs
  
• Structures with beach nourishment reduce
  downdrift effects
  
• Purpose Slow the loss of shore material and/or
  beach fill without trapping too much littoral
  sediment

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Shore Stabilization Alternatives
Groins
Groins are manmade structures constructed
perpendicular to the shoreline and help to create
or widen beaches by capturing sand moving
along the shoreline (littoral drift).
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Shore Stabilization Alternatives
Example Groins
Adjustable Groins
Terminal Groin
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Shore Stabilization Alternatives
Groin Fields
Westhampton Beach, New York
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Shore Stabilization Alternatives
Groins

• Materials
• Stone
• Concrete
• Timber
• Steel sheetpile
• Geotextile tubes
• Design Considerations
• Functional Performance
• Moderate to high wave energy
• Crest elevation, groin length, groin spacing,
  orientation
  
• Wave diffraction,overtopping, and transmission
• Structural Stability
• Armor stability
• Toe scour
• Flanking
• Foundation
• Impacts
• Nearshore habitat

T-Head Groin
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Shore Stabilization Alternatives
Breakwaters
Breakwaters are large scale structures
constructed seaward of, and usually parallel to,
the shoreline. They attempt to break incoming
waves before they reach the shoreline.
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Shore Stabilization Alternatives
Example Breakwaters
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Shore Stabilization Alternatives
Detached Breakwaters
Presque Isle, PA
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Shore Stabilization Alternatives
Breakwaters

• Materials
• Stone
• Concrete
• Geotextile tubes
• Design Considerations
• Functional Performance
• Moderate to high wave energy
• Crest elevation, gap width, distance offshore,
  orientation
  
• Wave diffraction,overtopping, and transmission
• Structural Stability
• Armor stability
• Toe scour
• Foundation
• Impacts
• Nearshore habitat
• Adjacent shoreline

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Shore Stabilization Alternatives
Reef Breakwaters
Reef breakwaters are smaller, submerged rubble
structures constructed seaward of, and usually
parallel to, the shoreline. They provide less
protection than emergent structures, but they do
not obstruct the view.
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Shore Stabilization Alternatives
Sills and Perched Beaches
A form of a "stepped" beach, where a beach sill,
constructed parallel to the shoreline, traps sand
brought in by wave action, or brought in by man
(beach nourishment or filling).
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Constructed Shore Protection
Contents

• Shore Protection Alternatives
• Non-Structural Alternatives
• Armoring Alternatives
• Shore Stabilization Alternatives
• Shore Protection Project Planning

Geotextile Tube Repair, Bolivar, TX
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Project Planning
Planning Process
1. Specify problems and opportunities
2. Inventory and forecast conditions if no
action taken 3. Formulate alternative plans 4.
Evaluate effects of each alternative plan
5. Compare alternative plans 6. Select alternat
ive(s) to carry on to design phase
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Project Planning
See What Others Have Done
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Project Planning
Lessons Learned from Other Projects
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Project Planning
Design Constraints

• Scientific and engineering understanding of
  nature
  
• Economics
• Environmental
• Institutional, Political, Social, Legal
• Aesthetics

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Shore Protection
Shore Protection Factoids

• No solution...
• No solution is permanent
• No solution will work everywhere
• No solution will work under all conditions
• No solution is low cost
• Most solutions
• Most solutions can have an effective economic
  life
  
• Most solutions have a predictable effect
• Most solutions can be applied properly

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Project Maintenance
Key Point
Ongoing maintenance at some level
is necessary for most existing coastal projects
to assure continued acceptable project
performance.
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Project Maintenance
Coastal Project Damage
Over the projected life of a coastal project the
structural components are susceptible to damage
and deterioration.
Damage is usually thought of as structure
degradation that occurs over a relatively short
period of time such as a single storm event, a
unique occurrence, or perhaps a winter storm
season.
Damage can be caused by
Waves exceeding design levels
Vessel impacts Wave and current combinations
Seismic events
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Project Maintenance
Deterioration of Project Elements
Deterioration is a gradual aging of the structure
and/or its components over time.
Deterioration...

• Can progress slowly
• Often goes undetected
• Weakened structure may continue to function
• Can lead to partial or complete failure of the
  project

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Project Maintenance
Failure Definition

• In general usage

The term "failure" implies total or partial
collapse of a structure

• In the context of design reliability

"Failure" is damage that results in structure
performance and functionality below the minimum
anticipated by design.
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Project Maintenance
Reasons for Project Failure

• Design Failure occurs when
• (1) Whole structure or some components cannot
  withstand loads beneath the design loads, or
  
  
• (2) Structure does not perform as intended.
• Load Exceedance Failure occurs because design
  loads are exceeded.
  
• Construction Failure arises due to incorrect or
  faulty construction practices or materials.
  
• Deterioration Failure is caused by structure
  deterioration and lack of proper maintenance.

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Constructed Shore Protection
Conclusions

• Shore protection is justified at some locations
• Options span hard structures to soft structures
  to no action
  
• Each project is unique
• Many solutions are temporary
• Projects should be monitored
• Maintenance is essential