Estuarine Dynamics.
Summary of previous lessons.
Estuarine Dynamics
Equations format for Env. Modelling
Isolated System:
dck
 ( Sok  Sik )
dt
Material System Moving with the flow:
dck


dt x j
 c 

  ( Sok  Sik )
 x 
j 

Fixed region Space:
ck u j ck



t
x j
x j
 c 

  ( Sok  Sik )
 x 
j 

Conservation Principle
• Whatever is the form of the equation it always
states:
AccumulatioRate  inFlow outFlow Sources Sinks
•
That can be reworded as:
“The rate of accumulation is the symmetric of the divergence plus sources- sinks”
ck


t
x j

 u j ck  c

x j


  ( Sok  Sik )


Or,
• Using the Divergence Theorem:

  




dV    v .n  A   n dA  ( So  Si )

 t CV
surface
• All these forms of the equations are equivalent.
We knew it from maths and from physics.
Source and Sink terms. The Phyto Eq.
dP
  p  rp  e p  m p P  GZ 2 .Z1
dt
Lotka Volterra
http://home.comcast.net/~sharov/PopEcol/
http://home.comcast.net/~sharov/PopEcol/lec10/lotka.html
This model describes the dynamics, but it is quantitatively incorrect.
Results: no interannual variability
Why to study an estuary in the course?
• Estuaries are among the richest ecosystems,
• Estuarine ecosystems require knowledge of a
large number of disciplines,
• They are a good example to introduce a
general approach that can be simplified in
particular ecosystems.
Estuaries vs Coastal Lagoons
Fine (organic rich sediments settle in the upper estuary due to flocculation
induced by salinity
Estuary Definition
• http://en.wikipedia.org/wiki/Estuary
– An estuary is a partly enclosed coastal body of
water with one or more rivers or streams flowing
into it, and with a free connection to the open
sea.[1]
• In the Water Framework Directive:
– An estuary is a “Transition Water” ) from a fresh
water body into a coastal water body.
Estuarine Life
Estuaries are home to an astonishing variety of plants and
animals and important in the lifecycles of many more.
Salt Marshes importance
Salt marshes form in shallow, quiet water, where the water is salty and still enough
for the suspended particles to settle to the bottom. These marshes are some of the
most productive lands in the world and produce so many organic nutrients that
their influence can be seen far out into the coastal ocean waters. Marshes are
based on one plant, the Saltmarsh Cordgrass, which helps stabilize the
environment so that many other plants and animals to move in.
Why are Estuaries so much demanded
by people?
• Because they generate opportunities:
–
–
–
–
Goods,
Navigation,
Recreation,
……..
• The estuarine ecosystem is biologically rich
because estuaries are rich in nutrients/primary
producers. They provide food and protection to
many species of juveniles (they are nursery
zones).
• What about eutrophication?
Classification of Estuaries
• http://www.onr.navy.mil/focus/ocean/habitats/
estuaries1.htm
• Coastal Plain Estuaries or Drowned river valleys,
• Tectonic Estuaries,
• Bar-built Estuaries or Lagoon type,
• Fjords.
Coastal Plain Estuaries
1. Coastal Plain Estuaries are formed by the sea level rising
and filling an existing river valley. Examples of this are the
Chesapeake Bay in Maryland and the harbor in Charleston,
South Carolina
Tectonic Estuaries
2. Tectonic Estuaries are caused by the folding or faulting of
land surfaces. These estuaries are found along major fault
lines, like the San Francisco Bay area in California.
Bar-built Estuaries (Rias/Lagoas em
Português)
Bar-built Estuaries form when a shallow lagoon or bay is
protected from the ocean by a sand bar or barrier island.
Examples of these are found along the Eastern Seaboard
and the Gulf Coast of North America.
Fjords
Fjords are U-shaped valleys formed by glacial action. Fjords are
found in areas with long histories of glacier activity, like northern
Europe, Alaska and Canada.
Are this the only types of estuaries?
• Most of today's estuaries formed because the
sea level has slowly risen during the last
18,000 years, drowning river valleys and filling
in glacial troughs.
• This classification is relevant yes because it
helps us describing estuaries. It is not because
many estuaries do not fit in any of these
types….
Continuação da Aula Anterior
Estuarine Hydrodynamics: Tides
• http://www.onr.navy.mil/focus/ocean/motion
/tides1.htm
• Tides are the periodic rise and fall of the
ocean waters. They are caused by the
gravitational pulls of the Moon and (to a lesser
extent) Sun, as well as the rotation of the
Earth.
Classification based on water circulation
http://en.wikipedia.org/wiki/Estuary
Salt wedge
In this type of estuary, river output greatly exceeds marine input and tidal effects
have a minor importance. Fresh water floats on top of the seawater in a layer that
gradually thins as it moves seaward. The denser seawater moves landward along
the bottom of the estuary, forming a wedge-shaped layer that is thinner as it
approaches land. As a velocity difference develops between the two layers, shear
forces generate internal waves at the interface, mixing the seawater upward with
the freshwater. An example of a salt wedge estuary is the Mississippi River.[5]
Partially mixed estuary
As tidal forcing increases, river output becomes less than the marine input. Here,
current induced turbulence causes mixing of the whole water column such that
salinity varies more longitudinally rather than vertically, leading to a moderately
stratified condition. Examples include the Chesapeake Bay and Narragansett Bay.[5]
Vertically homogenous
Tidal mixing forces exceed river output, resulting in a well mixed water column and
the disappearance of the vertical salinity gradient. The freshwater-seawater
boundary is eliminated due to the intense turbulent mixing and eddy effects. The
lower reaches of the Delaware Bay and the Raritan River in New Jersey are examples
of vertically homogenous estuaries.[5]
Fjord
Inverse estuary
Inverse estuaries occur in dry climates where evaporation greatly exceeds the inflow
of fresh water. A salinity maximum zone is formed, and both riverine and oceanic
water flow close to the surface towards this zone.[6] This water is pushed downward
and spreads along the bottom in both the seaward and landward direction.[3] An
example of an inverse estuary is Spencer Gulf, South Australia
Intermittent Estuary
Estuary type varies dramatically depending on freshwater input, and is capable of
changing from a wholly marine embayment to any of the other estuary types.[7][8]
(See also Estuarine water circulation)
Estuarine hydrodynamics
• Shallow water equations:
• Hydrostatic pressure,
• Vertical velocity is much smaller than
horizontal velocity (coriolis),
• Boussinesq approximation (density)
Shallow Water Equations
Pressure forces
Free surface elevation
Hydrostatic pressure:
Pressure force
MOHID Bathymetry Module
• Bathymetry
– Defines the horizontal grid
– The grid can be uniform or variable
– The number of grid points is typically 200x200
Vertical grid
• Sigma coordinate
• Cartesian coordinate
MOHID main Modules
• Hydrodynamic
– Propriedades de escoamento (niveís, velocidades, fluxos)
• Waterproperties (Eulerian, )
– Propriedades de águas (temperaturua, salinidade, phytoplankton, etc)
– Abordagem euleriana
• Lagrangian
– Propriedades de águas (temperaturua, salinidade, phytoplankton, etc)
– Abordagem lagrangiana
• WaterQuality (Sources – Sinks)
– Processos de qualidade de água (fontes e poços)
– Funciona como um modelo 0D
Mohid – Input Data File
• Ficheiros ASCII
• Palavras Chaves
• Organização por
blocos
Mohid – Results (Time Series)
• Séries temporais
– Escrevem resultados
pontuais com
intervalos de tempos
pequenos
– São analisados no
Excel
• Para escrever
–
–
–
–
–
–
–
<BeginTimeSerie>
LOCALIZATION_I
: 44
LOCALIZATION_J
: 27
LOCALIZATION_K
:1
<EndTimeSerie>
DT_OUTPUT_TIME
: 3600.
TIME_SERIE
:1
Mohid – Results (HDF)
• HDF
– Escrevem resultados
de todo o dominio
com intervalos de
tempos maiores
– São analisados com a
interface Gráfica
• Para escrever
–
OUTPUT_TIME : 0. 3600.
Mixed coordinate system
Boundary Conditions
• Open boundary
• Closed boundary
• Moving boundary
The 2D model
• Is equivalent to a 3D model using just one
layer and sigma coordinate!