Beaches nearshore Sediment Transport Tides

• BEACHES

• Nearshore Sediment Transport

• Tides

• What are Tides?
• Tides in the Coastal Ocean
• What Causes Tides

• Nearshore Sediment Transport –

• What influences the loss of sediment on Beaches?
• Waves
• Winds
• Tidal Currents
• River discharge
• Runoff

• Beaches divided into Segments

• Nearshore/Offshore
• Submerged portions
• backshore\foreshore
• Exposed portions
• Low-tide terrace
• Aka swash zone
• Alt. periods
• Of run up
• Waves/
• backwash

• BEACHES

• Waves supply E  affect Beach Profile
• Back/fourth movement of sediments is called?
• Cross-shore transport
• What does this result it?
• Change in the beach slope as sand is piled up or removed from beach
• b/c E of Wave run up ~ exceeds E or Backwash
• Sediments typically pile up on beaches. . . .

• BEACHES

• What is Longshore transport?
• Sediments moved parallel to beach face
• What type of current influences this?
• Longshore currents – strikes beach at angle
• e.g. gone out @ Manressa Beach, North of Lifegaurd tower. . .
• End up in Moss Landing. . . How’d I get here?

• Beaches

• Preventing beach erosion
• Groins, Jetties, etc.
• Mitigates Longshore
• Currents sediment removal
• e.g. Marin Co.
• Bolinas Bay

• Erosion Control

• Artificial Importation or beach nourishment
• Sediment budgets embody concept of a Littoral cell
• Littoral Cell
• Self contained section of coast whose beach sediments
• Controlled by identifiable local mechanisms of Supply/ loss
• E.g. So. Cal Beaches (N. Pacific) or N. Atlantic Outer Banks

• BEACHES

• Nearshore Sediment Transport

• Tides

• What are Tides?
• Tides in the Coastal Ocean
• What Causes Tides

• What Causes Tides?

• They are just Big Waves

• Most basic understanding

• Originally proposed by Newton
• Incorporates Equilibrium Model
• As earth rotates, locations on surface
• Pass b/w beneath
• Tidal bulges
• Directly beneath
• = High Tide
• Other locations
• = lower Tide(s)

• Tides

• Variations in Height/ Time ~ involve MOON and Sun
• Both create Tidal Bulge via Tidal Forces
• Moon = M2 tide
• Sun = S2 tide

• Challenge Questions

• How many different types of tides actually exist/ day &
• What are they?
• Diurnal
• Semi-diurnal
• Mixed Semi-diurnal

• A typical Mixed – semi Diurnal Tide (Santa Cruz, Ca)

• Locations of the Occurring 3 Tide Types Worldwide

• Rough Explanation as to why SUCH Tidal differences exist

• Depends on MANY Factors (very COMPLEX)
• Geometry of Coastline
• Where Sun/ Moon located
• Oceans have vibratory modes (like a drum) aka Harmonic Modes, 300+ exist
• Get stimulated in changing ways from minute to minute
• Storms move large quantities of water
• e.g. Variations Tidal Sea Ports:
• Velocity of water – depends on Salinity & depth in area it passes
• Bathymetry
• Overall Harmonics play major role
• NOT as Simple as you’d think
• – here’s a simplified explanation. . .

• Equilibrium Model

• So Here’s what you can get. . .

• Confirming your knowledge

• 3 different Types of Tides observed Around the Globe
• Diurnal (@ High Latitudes & Equator)
• Semi-diurnal (Mid Latitudes)
• Mixed semi-diurnal (Mid Latitudes)
• Some known factors that influence which type of Tide is present/where are:
• Storms
• Geometry of Coastline
• Bathymetry
• Velocity of water – depends on Salinity & depth of area
• Overall Harmonics (vibrations)
• esp. declination of the Moon

• Further Insights - Challenge Questions

• What are Spring & Neap Tide?
• Spring Tide
• – when the tidal Range reaches a Maximum
• Neap Tide
• – when the Tidal Range reaches a Minimum

• Influences of a Spring or Neap Tidal event (celestial)

• Spring Tide
• Moon
• Sun
• Earth
• (in strait Line)
• Neap Tide
• Moon @ 90˚angle
• vs Earth/Sun Line

ANOTHER PERSPECTIVE

• END / Break

• Midterm

• Green Scantron Please
• Write your name on TEST and Scanton

• Lots to do with the moon and Sun