Impact of the initial condition on the simulation of water movement in variably saturated zone of so

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Impact of the initial condition on the simulation
of water movement in variably saturated zone of
soil(Is it necessary to take the temporal
variability of hydro-physical properties, which
describe the water flow in variably saturated
soil, during modeled period into account?)
The Institute of Hydrology of the Slovak Academy
of Sciences, Department of Soil Hydrology

• May 1, 2007 Vladimir Mikulec

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Solution of Richards equation using method of
finite elements in model GLOBAL
Upper boundary condition (the climate and
phenological parameters)
Initial condition (the moisture profile at the
beginning and the hydro-physical parameters (C,
WRC)) - Parameters of porous medium
Output (calculated moisture profiles)
Bottom boundary condition (the pressure head at
the bottom of the soil profile or the depth of
ground water level under the soil surface)
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Examined locality
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Initial and boundary conditions of simulation

• The upper boundary condition was constituted by
  the phenological parameters of corn and by the
  climatic characteristics measured at the
  meteorological gauge station Bratislava-airport
• The bottom boundary condition was defined by the
  time series of the pressure head measured at the
  examined locality in the depth of 115 cm
• The initial condition is represented by the
  moisture profile at the beginning of the
  simulation and also by the definition of modeled
  environment variably saturated zone of soil.
• The modeled environment is defined by
  measurement of main hydrophysical properties of
  soil saturated hydraulic conductivity (C) and
  water retention curve (WRC). The measurements
  conducted in soil layer 0 115 cm at the
  examined locality have shown that the soil
  profile consists of the set of roughly
  homogeneous soil layers. From the point of view
  of simulation, was therefore possible to define
  the simulated soil profile as homogeneous
• This study is focused on the impact of the
  temporal variability of values of C on the
  results of simulation of water movement in the
  variably saturated zone of soil.

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Variants of simulation according to application
of measured hydro-physical parameters

• In the first variant was the value of C applied
  as a constant counted from the measurements
  realized in the first day of simulation
• In the second variant was the value of C applied
  as a mean counted from the measurements realized
  in the whole modeling period
• And finally in the third variant, the values of C
  changed in time as they were counted for all days
  of sampling during whole modeling period

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The time change in modeled moisture profiles (?
cm3cm-3) during the time period 17.3.
20.10.2003 (day 76 293) in the first variant of
simulation (C17.3.)
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The time change in modeled moisture profiles (?
cm3cm-3) during the time period 17.3.
20.10.2003 (day 76 293) in the second variant
of simulation (Cmean)
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The time change in modeled moisture profiles (?
cm3cm-3) during the time period 17.3.
20.10.2003 (day 76 293) in the third variant of
simulation (C f(t))
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The time change in measured moisture profile (?
cm3cm-3) during the time period 17.3.
20.10.2003 (day 76 293)
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Conclusion Modeled and measured moisture profiles
at the examined locality in the time period 17.3.
20.10.2003 were compared using method of
correlation.

• The correlation coefficients (r) between all
  variants of simulation were higher than 0.99. At
  the examined locality it is therefore fully
  sufficient to simulate the water movement with
  constant C counted from measurements performed at
  the beginning of simulation as it is shown in
  variant with Cconst..
• Compared to the measurements, the best
  information about volumetric water content in
  studied soil profile gave the third variant of
  simulation (r 0.55) followed by the second (r
  0.54) and first (r 0.51). But the differences
  between outputs from all modeled variants are
  marginal in comparison with amount of effort
  invested into laboratory measurements of
  saturated hydraulic conductivity

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Thank you for your attention