Innovative Approaches to Macropore and Micropore Modeling in Soil Hydrology
This document outlines five distinct approaches to modeling macropores and micropores in soil hydrology, emphasizing their implications for water movement and retention. Approach I uses enhanced conductivity, while Approach II utilizes the Van Genuchten retention curve for bimodal distributions. Approach III highlights infiltration through macropores without additional storage, and Approach IV averages results from distinct pore models. Finally, Approach V introduces dual water storages with separate transport equations for macropores and micropores, addressing intricate interactions and mass transfer dynamics.
Innovative Approaches to Macropore and Micropore Modeling in Soil Hydrology
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ModellingMacropores Philipp Kraft
Approach I • Use a 5-10x higherconductivity • Examples: Everywhere, cmfapplicationsuntiltoday
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 • Onlyonestorage per numericallayer • Water in a numericallayerdoes mix perfectly • Macroporeandmicroporewaterhasthe same waterquality • Relation ofmacropores do not changewithwatercontent (noswellingeffects)
Approach III • Waterinfiltratesthroughmacroporesintodeeperlayers • No additional waterstorage, infiltrationhas a by pass aroundthe top soil • Example: BROOK 90, cmf.LayerByPass
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 • Distinctmodelsofmacroporespaceandmicroporespace. • Resultsgetaveraged • Example: someHydrus 1D/2D applications
Approach V • Twodistinctwaterstorages per layer • transportequationsformacropores (nocapillaryeffects) • transportequationsformicropores (Richards equation) • masstransferequationbetweenmacro- andmicropores • Example: MACRO
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
Macroporetransport • Withoutcapillaryrise, kinematicwaveisusable • cmf: • V – actualstored Volume • C – Capacityoflayer
Masstransfer • saturationbased • headbased
Saturation basedmasstransfer • Philip 1968 • Jarvis 1994
Head basedmasstransfer • Gerke & Van Genuchten
cmf.GradientMacroMicroExchangeforMacro/Microporeexchange Δx Ψ(Macro) Aggregate Macropore z Ψ(Micro)
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 usealways dual porosity • Big jobforthesolver (anothertimescale, twicethestate variables) • Additional parameters (Conductivityofmacropores, macroporefraction, macroporedensity)
