Leonard A' Nurse

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OCEANOGRAPHIC AND RELATED CONSIDERATIONS FOR
COASTAL ENGINEERING DESIGN IN THE SMALL ISLAND
STATES OF THE CARIBBEAN

• Leonard A. Nurse
• Coastal Zone Management Unit, Barbados
• lnurse_at_coastal.gov.bb

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OBJECTIVES OF PRESENTATION

• ?To highlight key oceanographic, ecological and
  related characteristics and processes which are
  critical to coastal engineering practice in the
  Caribbean and
• ?To identify ways in which IOCARIBE-GOOS can
  contribute to the improvement of coastal
  engineering design in the sub-region.

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SHALLOW WATER (NEARSHORE) WAVE CLIMATE

• Generally, deep water wave climate tends to be
  relatively constant, over large areas. However,
  close to shore wave climate exhibits marked
  spatial variation owing to changes in bathymetry,
  sheltering effects, presence of reefs, shoreline
  configuration, etc.
• ?Characterization of the nearshore wave regime is
  essential in coastal engineering design. For
  example
• ?Significant wave height, refraction and
  diffraction effects influence the crest
  elevation, length, width, armour size, slope and
  orientation of a structure.

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Nearshore Wave Climate (contd)

• For most of the insular Caribbean, relatively low
  energy is experienced most of the year, except
  during
• ?Winter Swells long-period high-energy waves,
  generated by extra-tropical (North Atlantic)
  synoptic scale weather systems. These events
  cause severe beach erosion and property damage.
  Typically, swell wave heights vary between
  1.5-3.0 m, period 8-12 s-1.

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Nearshore Wave Climate (contd)

• ?Passage of tropical storms and hurricanes Most
  countries in region fall within the Atlantic
  hurricane belt. Designing structures to withstand
  hurricanes presents a considerable challenge.
• ?Depending on the category of system, significant
  wave heights exceeding 10.0 m, with periods
  exceeding 14 s-1 can occur.
• ?Human and economic losses, and damage to
  infrastructure can be great.

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WATER LEVEL FLUCTUATIONS

• Storm Surge This is a major design consideration
  for both coastal and offshore structures in the
  Caribbean.
• ?Associated with an abrupt fall in atmospheric
  pressure, associated with passage of hurricanes.
• ?Triggers strong onshore winds and large surface
  waves, causing the piling up of water at the
  coast (a 1-inchdrop in barometric pressure
  produces approximately a 13-inch rise in water
  level). Flooding, erosion and infrastructure
  damage frequently result.

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WATER LEVEL FLUCTUATIONS (contd)

• Seiches These are standing waves of relatively
  long period, and often form at the cessation of
  winds which produce storm surge.
• ?Water mass sloshes back and forth, as disturbed
  sea surface attempts to regain equilibrium.
• ?Can pose serious problems in harbors and marinas
  - damage to boats and scour protection affects
  berthing, loading/offloading. Engineering design
  must take this phenomenon fully into
  consideration.

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WATER LEVEL FLUCTUATIONS (contd)

• Tides constitute a factor which coastal engineers
  cannot afford to ignore. In the insular
  Caribbean, astronomical tides are typically
  semi-diurnal, with a normal range of
  approximately 0.5 m, while extreme range is
  around 1.0 m.
• ?Although values may appear to be small,
  significant wave heights associated with
  high-energy events coinciding with high tide
  (especially high spring tide) can be so
  exaggerated, that allowances must be made to
  accommodate these in the design of coastal
  structures.

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WATER LEVEL FLUCTUATIONS (contd)

• Relative Sea-Level Rise For most of the
  sub-region available data is inadequate for
  discerning clear trends.
• ?However, where relative sea-level rise is real,
  it would be prudent for engineers to either (i)
  adopt such projections as part of the design
  criteria or (ii) design structures with
  flexibility for later adjustment, as far as is
  practicable.

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GEOMORPHOLOGICAL FACTORS

• Small Littoral Cells Shorelines of Caribbean
  islands are generally characterized by small
  beach cells. These cells communicate with each
  other via sediment exchange.
• Seasonal Changes in Beach Dynamics Beach
  planform, morphology and sand distribution change
  from winter to summer, in response to
  directional shifts in dominant waves.
• Limited Sand Typically, sediment supply is
  scarce, thus many beaches in precarious
  equilibrium. Where large sand reserves exist,
  they tend to be in deep water where the cost of
  extraction is prohibitive for these small states.

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ECOLOGICAL FACTORS

• Coral Reefs These perform critical functions and
  provide various essential services along
  Caribbean coasts.
• ?It is vital to ensure that viability of benthic
  communities is not threatened by inappropriate
  engineering design and construction. In many
  cases the need for structures arises because
  these free functions are now lost.
• ?Reefs also add complexity to bathymetry, and
  thus influence patterns of wave energy
  distribution (refraction, diffraction, etc.)
  which impacts on the performance and stability of
  civil structures.

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ECOLOGICAL FACTORS (contd)

• Seagrasses Like coral reefs, seagrasses provide
  habitat, foraging and breeding areas for fish and
  other organisms. They also trap resuspended
  sediment in the water column, minimizing the
  smothering of communities such as corals.
• ?Seagrasses are highly susceptible to damage from
  activities such as piling, laying of armour and
  dredging operations, associated with marine and
  coastal construction.

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ADDITIONAL CONSIDERATIONS OF RELEVANCE TO
CARIBBEAN

• Based on empirical experience and engineering
  evaluation in selected countries in the region,
  the functionality and cost efficiency of coastal
  structures are enhanced where
• ?Indigenous materials are used to the maximum
  extent feasible, given the cost of imported fill
  and armor.
• ?structure configuration is such that routine
  maintenance is neither complex nor costly, and
  can be provided locally.

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ADDITIONAL CONSIDERATIONS OF RELEVANCE TO
CARIBBEAN (contd)

• ?Engineering design should seek to achieve
  multiple objectives or facilitate multiple uses,
  wherever feasible. For example
• ?Careful design can produce a breakwater which
  offers shoreline protection, habitat regeneration
  and organism recruitment (artificial reef)
• ?A revetment of appropriate crest elevation and
  slope can protect backshore property from wave
  atttack and also serve as the substructure for a
  coastal boardwalk.

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HOW CAN IOCARIBE-GOOS HELP?
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IOCARIBE ITS CURRICULUM VITAE AND QUALIFICATIONS

• IOCARIBE is respected in the region and beyond as
  a highly qualified, experienced institution in
  the fields of oceanographic, marine and coastal
  sciences.
• As a Sub-Commission of IOC, it automatically has
  well-established, functional linkages with key
  global, regional and national programs and
  scientific institutions.

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DATA ACQUISITION AND PRODUCT DEVELOPMENT

• An Inventory of Coastal Resources and Uses
  (CPACC, 2000), reveals that most Caribbean
  islands possess limited data sets for
• ?Wave climate (directional)
• ? Sea-level change
• ? Nearshore/oceanic currents (bottom/surface)
• ? Tides (measured as opposed to predicted)
• (Core inputs to coastal engineering design)
• ?IOCARIBE-GOOS envisages the coordination and
  assembly of these (and related) data sets.

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DATA ACQUISITION AND PRODUCT DEVELOPMENT (contd)

• IOCARIBE-GOOS can provide
• An evaluation of the existing network of marine
  and oceanographic stations in insular Caribbean,
  to facilitate improved coverage. The assessment
  should include recommendations for refurbishment,
  replacement, relocation and calibration of
  critical instrumentation.
• QA/QC and assistance with establishing a
  protocol for implementing standards for data
  collection, reduction and analysis. This will
  minimize the risk/uncertainty inherent in coastal
  engineering design.

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DATA ACQUISITION AND PRODUCT DEVELOPMENT (contd)

• Given its experience in coordinating
  oceanographic and marine science programs,
  IOCARIBE-GOOS can play a strategic and tactical
  role in ensuring that existing initiatives
• ?are better focused
• ?maximize efficiencies
• ?are configured to meet the specific user needs
  of the Caribbean.
• ?establish protocols and mechanisms for
  dissemination and sharing of data.

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SUMMARY

• IOCARIBE-GOOS can have a positive impact on the
  quality and effectiveness of coastal protection
  works in the insular Caribbean, in at least three
  (3) fundamental ways
• I. Data acquisition to facilitate improved
  coastal engineering practice.
• II. Capacity building and training.
• III. Facilitating the sharing and exchange of
  information and expertise among member
  countries and cooperating institutions.