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Modelling Macropores. Philipp Kraft. Schwingbach. ICON Project. Approach I. Use a 5-10x higher conductivity Examples : Everywhere , cmf applications until today. Approach II. Van Genuchten retention curve model is based on pore size distribution , assuming a normal distribution

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modelling macropores

ModellingMacropores

Philipp Kraft

approach i
Approach I
  • Use a 5-10x higherconductivity
  • Examples: Everywhere, cmfapplicationsuntiltoday
approach ii
Approach II
  • Van Genuchtenretentioncurvemodelisbased on poresizedistribution, assuming a normal distribution
  • Byoverlayoftwo normal distributionswithdifferingmeanandstdev a closed form retentioncurvefor a bimodaldistributionispossible
  • Example: Durner 1994, implemented in HYDRUS
approach i ii
Approach I+II
  • Onlyonestorage per numericallayer
  • Water in a numericallayerdoes mix perfectly
  • Macroporeandmicroporewaterhasthe same waterquality
  • Relation ofmacropores do not changewithwatercontent (noswellingeffects)
approach iii
Approach III
  • Waterinfiltratesthroughmacroporesintodeeperlayers
  • No additional waterstorage, infiltrationhas a by pass aroundthe top soil
  • Example: BROOK 90, cmf.LayerByPass
approach iii1
Approach III

Surface water

  • l=cell.surfacewater
  • r=cell.layers[0 ..1]
  • cmf.LayerByPass(l,r,Kmax,w0,beta)

Soillayer 1

Soillayer 2

Soillayer 3

approach iv
Approach IV
  • Distinctmodelsofmacroporespaceandmicroporespace.
  • Resultsgetaveraged
  • Example: someHydrus 1D/2D applications
approach v
Approach V
  • Twodistinctwaterstorages per layer
  • transportequationsformacropores (nocapillaryeffects)
  • transportequationsformicropores (Richards equation)
  • masstransferequationbetweenmacro- andmicropores
  • Example: MACRO
b a real macropore storage
b) A real Macroporestorage

Surface water

Richards eq.

Macrotransporteq.

Macropore 1

Soillayer 1

Macrotransporteq.

Richards eq.

Macropore 2

Soillayer 2

Richards eq.

Macrotransporteq.

Macropore 3

Soillayer 3

Masstransferequations

macro pore transport
Macroporetransport
  • Withoutcapillaryrise, kinematicwaveisusable
  • cmf:
  • V – actualstored Volume
  • C – Capacityoflayer
mass transfer
Masstransfer
  • saturationbased
  • headbased
saturation based mass transfer
Saturation basedmasstransfer
  • Philip 1968
  • Jarvis 1994
head based mass transfer
Head basedmasstransfer
  • Gerke & Van Genuchten
cmf gradientmacromicroexchange for macro micropore exchange
cmf.GradientMacroMicroExchangeforMacro/Microporeexchange

Δx

Ψ(Macro)

Aggregate

Macropore

z

Ψ(Micro)

examplary model setup
Examplarymodelsetup
  • 10 daysruntime
  • 1 daywith 50mm precipitation
  • 1 m soilcolumn, nogroundwaterpercolation
  • At thebeginning: hydrostaticequilibrium, 1m groundwaterlevel
  • siltysandsoil, 5% macropores, meanmacroporedistance 5cm
  • Non swellingsoil
why not use always dual porosity
Why not usealways dual porosity
  • Big jobforthesolver (anothertimescale, twicethestate variables)
  • Additional parameters (Conductivityofmacropores, macroporefraction, macroporedensity)
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