Tides

1
Tides Beaches
2
OUTLINE

• BEACHES
• Nearshore Sediment Transport
• Tides
• What are Tides?
• Tides in the Coastal Ocean
• What Causes Tides

3

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

4

• 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

5

• 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. . . .

Run UP
Backwash
CROSS SHORT TRANSPORT
6
Fig. 10.22
7

• BEACHES
• If Wave E High ? sediments carried offshore
• Stored as Sandbar
• If Wave E Low ? sediments carried onshore
• From Sandbar ? buildup of sand
• Storms etc. periodically
• disrupt the equilibrium profile

8

• 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 _at_ Manressa Beach, North of
  Lifegaurd tower. . .
• End up in Moss Landing. . .? Howd I get here?

?
?
9
Challenge Q What direction is the Long shore
current coming from?

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

S
N
10

• 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

11
Fig. 10.29
12
Fig. 10.29.a
13
Fig. 10.29.b
14
OUTLINE

• BEACHES
• Nearshore Sediment Transport
• Tides
• What are Tides?
• Tides in the Coastal Ocean
• What Causes Tides

15
(No Transcript)
16

• What are Tides?

17

• 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)

18
What is the Tidal Period?
Time b/w successive High and Low Tides (12 hrs)
What is the Tidal Day?
One complete revolution of Earth beneath Tidal
Bulges
What is the Tidal Range?
high tide mark (2.0 m) - low tide mark (0.5 m)
1.5 m Tidal Range
19

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

M2
S2
20
For H-work 3 will use F 2 x G x M1 x M2x a
R3 a radius of Earth R distance
b/w Earth and object in meters
21
So What is a diurnal tide anyway? Well . . .
22

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

23

• Challenge Question
• What are the definitions of the following and
  give examples of where they may occur
• Diurnal
• only one high and one low tide/day
• (e.g. Gulf of Mexico)
• Semi-diurnal tidal forces ? bulges both sides
  of earth
• Earths rotation causes
• 2 equivalent High Tides, 2 low tides/ day
• (e.g. N. Atlantic Coast)
• Mixed Semi-diurnal
• Unequal pattern of 2 high and low tides/
• (West. Coast N. America)

24

• Graphical Representation Three Types of Tides
• Diurnal
• Semi-diurnal
• Mixed Semi-diurnal

25

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

26

• Locations of the Occurring 3 Tide Types Worldwide

27

• 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 youd think
• heres a simplified explanation. . .

28

• Equilibrium Model

NOTE Moons Tidal Force Assists with bulging of
Tides
NOTE Moon also Orbits around Earth
29
(No Transcript)
30
(No Transcript)
31

• So Heres what you can get. . .

32
(No Transcript)
33

• Confirming your knowledge
• 3 different Types of Tides observed Around the
  Globe
• Diurnal (_at_ 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

34

• 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

Its Beach, Santa Cruz, CA
35
Fig. 11.7
Confirming Your Knowledge
Identify the date(s) of the following Figures
that Represent Spring or Neap Tidal Events.
36
Fig. 11.7.a
Identify the date(s) of the following Figure that
Represent a Spring or Neap Tidal Events.
37
Fig. 11.7.b
Identify the date(s) of the following Figure that
Represent a Spring or Neap Tidal Events.
38
Fig. 11.7.c
Identify the date(s) of the following Figure that
Represent a Spring or Neap Tidal Events.
39
Fig. 11.7.d
Identify the date(s) of the following Figure that
Represent a Spring or Neap Tidal Events.
40

• Challenge Questions
• What actually Influences a Spring or Neap Tidal
  event?
• Locations of the Sun and Moon

41

• Influences of a Spring or Neap Tidal event
  (celestial)
• Spring Tide
• Moon
• Sun
• Earth
• (in strait Line)
• Neap Tide
• Moon _at_ 90angle
• vs Earth/Sun Line

illuminated
dark
Half illuminated etc. Quarter (Crescent)
42
ANOTHER PERSPECTIVE
43

• END / Break
• Midterm
• Green Scantron Please
• Write your name on TEST and Scanton

44

• Lots to do with the moon and Sun

45
Fig. 11.6