Estuary Classification

8/6/2019 Estuary Classification

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Estuaries Basic Info

Estuary: a body of water partially enclosed byEstuary: a body of water partially enclosed by

land that has a connection to the ocean as wellland that has a connection to the ocean as well

as to a river or it is an area where saltwater andas to a river or it is an area where saltwater and

freshwater mixfreshwater mix

The mouth is where the freshwater emptiesThe mouth is where the freshwater empties

into the ocean and the head is at the oppositeinto the ocean and the head is at the opposite

end where it receives the freshwater from a riverend where it receives the freshwater from a river

or streamor stream


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Heuningnes Estuary

Heuningnes Estuary - the Southernmost in Africa


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General Information

Its water has very large changes in temperatureIts water has very large changes in temperature

and salinityand salinity

Two way movement of waterTwo way movement of water

Fresh water from the river flows seaward along theFresh water from the river flows seaward along thesurfacesurface

Saltwater (denser) from the ocean flows landwardSaltwater (denser) from the ocean flows landward

along the bottomalong the bottom


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General Information

(contd)

Mixing between two different types of water isMixing between two different types of water is

determined by factors such as wind, tidal range,determined by factors such as wind, tidal range,

shape of estuary, relative inflow of river andshape of estuary, relative inflow of river and

ocean waterocean water


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Geomorphology

Classification1. Drowned River Valleys: a rise in sea level flooded river1. Drowned River Valleys: a rise in sea level flooded rivervalleys creating estuarine systemsvalleys creating estuarine systems egeg. Chesapeake Bay. Chesapeake Bay

2. Bar Built: semi isolated from ocean waters by barrier2. Bar Built: semi isolated from ocean waters by barrierbeaches and contains narrow inlets allowing contact frombeaches and contains narrow inlets allowing contact fromocean watersocean waters

3. Fjord Type: formed in deeply eroded valleys formed by3. Fjord Type: formed in deeply eroded valleys formed byglaciers, U shaped and shallower at mouthglaciers, U shaped and shallower at mouth

4. Tectonically Produced: formed by subsidence or land4. Tectonically Produced: formed by subsidence or landcutoff, associated with faulting, volcanoes and land slides.cutoff, associated with faulting, volcanoes and land slides.There is a very small number of them producedThere is a very small number of them produced


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San Francisco Bay

The San Francisco Bay

originated from faulting in the

earths crusts. This is an

example of a tectonically

produced estuary. This area was

completely covered by iceduring the last ice age and then

over 4000 years, the ice melted

and the sea level rose 91

meters.


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Water Circulation

Classification

1. SaltWedge: fresh water floats on top of the1. SaltWedge: fresh water floats on top of the

seawater in a layer that gradually thins as itseawater in a layer that gradually thins as it

moves seawardmoves seaward

2. Partially Mixed: current induced turbulence2. Partially Mixed: current induced turbulence

causes mixing of the whole new water column;causes mixing of the whole new water column;

moderately stratified conditionmoderately stratified condition

3. Well Mixed: water column with uniform salinity3. Well Mixed: water column with uniform salinity


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Water Circulation

Classification (contd)

4. Inverse: evaporation greatly exceeds river4. Inverse: evaporation greatly exceeds river

flow, seawater and freshwater both flow close toflow, seawater and freshwater both flow close to

surface & this water is then pushed downwardsurface & this water is then pushed downward

5. Intermittent: estuary type varies depending on5. Intermittent: estuary type varies depending on

freshwater input and can change to any anotherfreshwater input and can change to any another

estuary typeestuary type


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Fun Facts

Because of the access to salt and fresh water, estuaries are aBecause of the access to salt and fresh water, estuaries are apopular place for humans to populate. This in turn, makespopular place for humans to populate. This in turn, makesestuaries one of the most polluted kinds of water sourcesestuaries one of the most polluted kinds of water sources

The pollution that is dumped in estuaries are a concernThe pollution that is dumped in estuaries are a concernbecause the original algae and plankton that is supportedbecause the original algae and plankton that is supportednaturally may be killed off and replaced with othernaturally may be killed off and replaced with other

microorganismsmicroorganisms

Many ocean creatures are dependent on estuaries forMany ocean creatures are dependent on estuaries forbreeding or feeding during part of their livesbreeding or feeding during part of their lives egeg. cod spawn. cod spawnin freshwater and after hatching/developing, make their wayin freshwater and after hatching/developing, make their wayto the seato the sea


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Fun Facts (contd)

A shallow estuary that is fairly isolated from the circulationA shallow estuary that is fairly isolated from the circulationwith the open ocean is sometimes called a lagoonwith the open ocean is sometimes called a lagoon

An estuary that is so shallow that large portions of itsAn estuary that is so shallow that large portions of itsbottom appear at low tide is commonly called a sloughbottom appear at low tide is commonly called a slough

The excess of evaporation over precipitation causes veryThe excess of evaporation over precipitation causes veryhigh salinities resulting in large fish kills during summerhigh salinities resulting in large fish kills during summermonths when the salinity and temperature rises too highmonths when the salinity and temperature rises too highfor some species to toleratefor some species to tolerate


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References

Stowe, K. (1979).Stowe, K. (1979). Ocean ScienceOcean Science. John Wiley &. John Wiley &

Sons, United States.Sons, United States.

Ross, D. (1988).Ross, D. (1988). Introduction to OceanographyIntroduction to Oceanography

Fourth EditionFourth Edition. Prentice. Prentice--Hall Canada Inc.,Hall Canada Inc.,

Toronto.Toronto.

Estuary Classification

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