The Coastal Ocean

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The Coastal Ocean
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Learning Objectives

• Students will be able to
• Describe various definitions for the coastal zone
• Differentiate between pelagic and neritic
  processes
• Classify estuaries in multiple ways and explain
  estuarine sedimentation processes
• Articulate and describe beach processes
• Describe the pros and cons to beach stabilization

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Outline

• Definitions
• 3-D Ekman spiral
• Estuaries
• Estuarine Measurements
• Habitat squeeze concept
• Beaches and Shoreline Processes
• Beach defense

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Coastal waters

• Relatively shallow areas that adjoin continents
• Heavily used for commerce, recreation, fisheries,
  and waste disposal
• Military purposes as well

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The Coast

• The land and waters extending inland for 1 km
  from high water mark on the foreshore and
  extending to the 30 m contour line including all
  beds, sediments, waters and land subject to the
  ebb and flow of the tide.

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Definitions

• A line extending 200 nm (370km) from the coast.
• The 500 m isobath
• A line a the foot of the continental slope
• Territorial water- water adjacent to a coastal
  nation. Majority favor 3 miles, US wants 200.

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EEZ

• The exclusive economic zone- 200 mile fishing and
  mineral rights.
• Legal-UN Convention on the Law of the Sea- the
  seabed and subsoil that extends to the edge of
  the continental margin or a distance of 200 nm.

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How does the Coastal Ocean Differ from the deep
ocean?

• Significant changes in Temperature, salinity and
  even pH. Very sensitive to environmental
  factors, like pollutants, contaminants, dissolved
  gases and nutrients.
• May or may not exhibit constant proportions.
• Bathymetry is a controlling factor in many
  physical processes.

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How does the Coastal Ocean Differ from the deep
ocean?

• The pycnocline tends to follow the ______,
• Instead of the ________. Why?
• Friction can not be ignored this leads to 3-D
  Ekman system near the coast rather than the
  familiar 2-D one you know. Important
  implications for management issues.
• The shoaling effect is prominent here.

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3-D Ekman

• We have all seen the 2-D Ekman spiral.
• But what happens when the depth of the sea floor
  is less than the theoretical Ekman depth? Where
  does this happen?

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Quasi geostrophic Flow
Pressure force
friction
coriolis
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Flow at interior?
Flow at bottom?
z
-x
Overlap of bottom and surface Ekman layers
Importance of shelf break depth
Problems with Ekman theory constant Az,
constant wind, linear flow, steady
state, infinite ocean, no pressure gradients
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Estuaries

• Estuaries are partially enclosed coastal bodies
  of water
• Examples of estuaries include
• River mouths
• Bays
• Inlets
• Gulfs
• Sounds
• Formed by a rise in sea level after the last Ice
  Age

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Classifying estuaries by origin

• Coastal plain
• Fjord
• Bar-built
• Tectonic

Figure 11-3
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Classifying estuaries by water mixing

• Vertically mixed
• Slightly stratified
• Highly stratified
• Salt wedge

Figure 11-5
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Classification by Tides
Amplitude
Current
Head
Mouth
Head
Mouth
Head
Mouth
Synchronous ConvergenceFriction
Hypersynchronous ConvergencegtFriction
Hyposynchronous ConvergenceltFriction
Friction is stronger and the tide diminishes
along the estuary
The tidal range currents increase towards the
head of the estuary until the convergence
diminishes friction reduces the tide
The friction and convergence have equal and
opposite effects on the tide
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AN interesting problem

• We all know that coastal lagoons tend to silt in.
  This seems to be a problem, because this occurs
  against the concentration gradient.
• The Dutch were the first to recognize this in the
  Wadden Zee.

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The silting in of harbors and lagoons

• So why does it happen?
• It turns out there are a number of dynamical
  processes all conspiring to create this effect.
• 1- general estuarine circulation (salt wedge)
• 2 - the time velocity asymmetry of the shallow
  tidal wave.
• 3 - the settling lag effect

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Beaches and Shoreline Processes
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Landforms and terminology in coastal regions
Figure 10-1
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Movement of sand on the beach

• Movement perpendicular (?) to shoreline
• Caused by breaking waves
• Light wave activity moves sand up the beach face
  toward the berm
• Heavy wave activity moves sand down the beach
  face to the longshore bars
• Produces seasonal changes in the beach

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Light versus heavy wave activity
Light wave activity Heavy wave activity
Berm/long-shore bar Berm grows and longshore bars shrink Longshore bars grow and berm shrinks
Wave energy Low High
Time span Long Short
Characteristics Summertime beach sandy, wide berm, steep beach face Wintertime beach rocky, thin berm, flattened beach face
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Summertime and wintertime beach conditions
Summertime beach
Wintertime beach
Figure 10-2
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Movement of sand on the beach

• Movement parallel (?) to shoreline
• Caused by wave refraction (bending)
• Each wave transports sand either upcoast or
  downcoast
• Huge volumes of sand are moved within the surf
  zone
• The beach resembles a river of sand

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Longshore current and longshore drift

• Longshore current zigzag movement of water in
  the surf zone
• Longshore drift movement of sediment caused by
  longshore current

Figure 10-3b
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Features of erosional shores

• Headland
• Wave-cut cliff
• Sea cave
• Sea arch
• Sea stack
• Marine terrace

Figure 10-4
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Sea stack and sea arch, Oregon
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Features of depositional shores

• Spit
• Bay barrier
• Tombolo
• Barrier island
• Delta

Figure 10-7
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Beach compartments in southern California

• Beach compartments include
• Rivers
• Beaches
• Submarine canyons

Figure 10-12
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Evidence of emerging and submerging shorelines

• Emergent features
• Marine terraces
• Stranded beach deposits
• Submergent features
• Drowned beaches
• Submerged dune topography
• Drowned river valleys

Figure 10-13
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Types of hard stabilization

• Hard stabilization perpendicular to the coast
  within the surf zone
• Jettiesprotect harbor entrances
• Groinsdesigned to trap sand
• Hard stabilization parallel to the coast
• Breakwatersbuilt beyond the surf zone
• Seawallsbuilt to armor the coast

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Jetties and Groins

• Jetties are always in pairs
• Groins can be singular or many (groin field)
• Both trap sand upstream and cause erosion
  downstream

Figure 10-21
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Breakwater at Santa Barbara Harbor, California

• Provides a boat anchorage
• Causes deposition in harbor and erosion
  downstream
• Sand must be dredged regularly

Figure 10-22
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Seawalls and beaches

• Seawalls are built to reduce erosion on beaches
• Seawalls can destroy recreational beaches
• Seawalls are costly and eventually fail

Figure 10-24
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Alternatives to hard stabilization

• Restrict the building of structures too close to
  the shore
• Eliminate programs that encourage construction in
  unsafe locations
• Relocate structures as erosion threatens them

Relocation of the Cape Hatteras lighthouse, North
Carolina
Figure 10C