Tides as a Major Influencing Factor to Shoreline Debris Deposition

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Tides as a Major Influencing Factor to Shoreline
Debris Deposition

• Scott Wilson
• Centre for Environmental Management

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Shorelines as sinks for marine debris

• Most commonly studied areas for marine debris
• Accessibility
• Visibility
• Directly effect most people
• Surveys and coastal cleanups target these areas
• Most however failed to understand the factor
  influencing the why and the how
• What causes debris to end up on our shorelines?

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Factors that influence coastal debris movement
and deposition

• Nearness to source
• Type of debris (eg. durability)
• Form of debris (eg. buoyancy, shape)
• Physico-chemical parameters
• Coastal geomorphology
• Wind
• Currents
• Rainfall and storm events
• TIDES

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Ocean Tides

• Rise and fall on a daily basis
• Moon and Suns gravitational forces along with
  the earth rotation influences tidal patterns
• Tides can be classed as diurnal, semi diurnal and
  mixed
• Shape of the coastline and bathymetry cause
  localised patterns

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Shoreline Morphology

• Wave dominated
• Low - Moderate energy
• Steep slope
• Intermediate
• High Energy
• Bars
• Tide-modified
• Low energy
• High tidal range
• Tide-dominated
• V. Low energy
• Gentle slope

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Tides and Debris

• Temporal debris collection shown to have a strong
  correlation with tidal height
• R2 0.69 0.62 (Plt0.05)

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Tides and Debris

• Not all beaches reflect this strong trend
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  R2 0.36 (pgt0.05)

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Tides and Debris

• Analysis of within beach zones draws further
  trends

R2 0.5
R2 0.4
R2 0.1
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Tides and Debris

• Debris type helps explain the differences

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Considerations for maximising outcomes

• Debris surveys and Clean-ups should consider site
  characteristics, weather and tidal patterns
• Potential to model and predict patterns of
  accumulation
• Maximum debris deposition after full and new
  moons
• Timing is everything!
• Other factors do play a part

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Tidal Clock