Intro Estuaries

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					                 Estuaries:


   Definition
 Examples
 Types
 Tides
 Circulation and stratification
 Sediment transport
                  Estuaries
• Note
  Transition from freshwater management
    (manipulation of habitat, restoration, control,
    poisoning, enrichment, stocking) to marine
    environment (largely prediction)
“An estuary is a semi-enclosed
coastal body which as a free
connection with the open sea and
within which sea water is
measurably diluted with freshwater
derived from land drainage.”
(Pritchard 1967)



                          Grays Bay, Washington
Regions of an estuary:


1.Marine or lower estuary, with a free
  connection to the ocean
2.Middle estuary: strong salt-fresh
  water mixing
3.Fluvial or upper estuary: water
  fresh but subject to tidal changes in
  elevation
Coastal plain, drowned
     river valley          Fjord




       Bar-built         Tectonic
Chesapeake Bay
Coastal Plain Estuary

 • Formed when
 glaciers melted and
 rising sea level
 invaded river valley

 • Largest estuary
 in the United States
Salmon River Estuary, Oregon
 Bar-Built Bay

 • Formed
 when river
 water collects
 behind
 sandbar
              Puget Sound




Fjord carved by glaciers
San Francisco Bay
  Tectonic Estuary

  • Formed by
  subsidence of land
  from tectonic
  activity

  • Highly modified
  system with
  greatest number of
  exotic species of
  all estuaries
Kennedy Creek, Totten Inlet, Puget Sound
Kennedy Creek, Totten Inlet, Puget Sound
Coastal Oregon bar-built estuary
                        Coastal
                        Oregon



                      Jetties



Not all rivers have
estuaries of equal
or comparable size
Fresh water starts
higher in elevation
than the ocean, and
is much lighter.
(Salinity has a much
stronger influence
on density than
temperature). The
extent to which the
estuary remains
stratified varies
greatly, being
influenced by wind
and topography.
  Highly Stratified Salt-Wedge Estuary
    Lower density freshwater flows over higher density seawater

Freshwater



                                                Salt water
      Sea floor
 Vertically Homogenous Estuary
    Freshwater output is low vertical stratification does not occur

Freshwater                 Parts per thousand (ppt)             Saltwater
             0.1   0.9   1.5    3.0    7.5     9      11   19   25    31
  Fjord Circulation
    Freshwater lens forms near river mouths, but is disturbed by
    turbulence
Freshwater Lens

                  Mixed Layer
                                                      Saltwater
                                           Sill
                   Saltwater
             1              High tide 1                     1

Depth (m)
                                                High tide                High tide
            5                        5                      5

                 Low tide                                        Low tide
            10                       10   Low tide          10
                   10   20    30           10    20    30           10     20    30
                                          Salinity (ppt)




                                                                         1 km


                 Chehalis River, Grays Harbor estuary,
                             Washington
Unlike coastal plain estuaries, fjords can be very steep-
sided, like this site in Dean Channel, B.C..
                 Dean Channel, B.C.




      S         T        S       T            T         S


                             T




The sharpness of the halocline (and thermocline) decline
with distance from the river mouth in a fjord-type estuary
                  Tides
 The Seattle area has mixed, semi-diurnal tides,
meaning that there are two high tides and two low
      tides each day, of different heights
            Tides
Elevation is expressed relative to the
   mean lower low water (MLLW)
                     Tides




Note that the tidal cycle is not 24 hours, so the tides
          get later from one day to the next
               sun                                sun




 Earth


                             Neap tides, moon and sun in opposition
 Moon

Spring tides, moon and sun alligned
Elevation (ft)




                                             Time (hours)

                 Tidal elevations at Point Adams, Columbia River March – April 1978
             Columbia River Estuary
             Vertical distribution of velocity in feet per second,
                           at CRM 8.5, May 23, 1970.
Depth (ft)




                                          Time
             Columbia River Estuary
             Vertical distribution of salinity in parts per thousand
                            at CRM 8.5, May 23, 1970.
Depth (ft)




                                           Time
                 Columbia River Estuary
             Vertical distribution of suspended-sediment concentration in
                      milligrams per liter at CRM 8.5, May 23, 1970.
Depth (ft)




                                        Time
    Columbia River sediment
      transport estimates
    Million cubic yards per year
                  Sand        Total
Pre-Regulation     5.2        12.3

Post-Regulation   0.7           2.2




                         Grays Bay, Washington
  Annual volume of material dredged during the
development of and maintenance of the Columbia
 River navigation channel in the Columbia River
              estuary 1900 to 1996
Commencement Bay and
the estuary of the Puyallup
River, WA.
The development of coastal
cities as ports greatly
affected many estuaries.

				
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