Coastal Impacts: Beaches, Sand Spits, and Bluffs

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Coastal Impacts Beaches, Sand Spits, and Bluffs

• Amber Moore
• University of Washington School of Marine Affairs
• 12 February 2009

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Impacts on Beaches and Sand Spits

• Puget Sounds shoreline is estimated at 2411km
  (1477mi) in length
• SLR will cause the landward migration of the
  shoreline
• Coastal development could be threatened by
  increased vulnerability of coastal property

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Impacts on Beaches and Sand Spits

• Beaches protected by sea walls, riprap, or
  revetments are likely to be less stable than
  unprotected shores
• The beaches of Puget Sound act as critical habitat

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Bainbridge Island

• Contains 85.2km (53.3mi) of shoreline
• 82 currently in residential, recreational,
  commercial, or industrial use
• 48 is armored
• Uplifted beach terraces, bays, and coves are most
  susceptible to inundation

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Southwest Washington

• Ocean Shores has been actively eroding
• Shorelines are relatively well protected within
  the shallow bays
• Willapa Bay and Grays Harbor

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Bluff Erosion in Puget Sound

• Feeds sediment for beach formation but also
  threatens property and human lives
• The steepening of bluff slopes increases the
  probability of bluff failure
• Key factors are storms with large waves,
  especially when combined with high tides or
  elevated sea levels

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Western Whidbey Island

• Erosion rates have been measured from 1cm to more
  than 61cm (2ft) per year
• Whidbey Is. bluffs
• are frequently sites
• for residential development

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Western Whidbey Island

• Many homes built on Whidbey Island were placed on
  artificial fill at the base of landslide prone
  bluffs
• Along a 1 mile stretch of road, as much as 32
  million worth of property could be involved

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Bainbridge Island

• Bainbridge Island has 394km (246mi) of shoreline,
  20 of which is classified as unstable
• Bluff erosion rates average between 5.1cm (2in)
  and 15.2cm (6in) per year

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San Juan Islands

• Presently very little bluff erosion
• The islands are composed mainly of exposed
  bedrock coast
• Unlikely that an increase in SLR will affect the
  bluff erosion patterns

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Adaptation Options

• Accommodation
• Protection
• Sea walls, dikes, raising docks
• Retreat
• Moving or building on higher ground further
  from bluffs

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Research Gaps

• Incorporate additional sites into a future study
• Applied and basic research into movement of
  sediments and shifts in beach and bluff profiles
• How auxiliary structures will be and are being
  threatened by beach and bluff erosion
• Representation of more ports
• More research into the effects of increased SSTs
  and ocean acidification on shellfish

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Conclusion

• Global Climate Change is happening
• Will impact humans and coastal ecosystems
• Effective adaptive actions can enhance the
  resilience of vulnerable systems

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