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Wageningen University (2012)

Coupled heat and water transport in bare soils in semi-arid and arid regions

Berends, T.

Titre : Coupled heat and water transport in bare soils in semi-arid and arid regions

Auteur : Berends, T.

Université de soutenance : Wageningen University

Grade : Master of Science (MS) 2012

For more than 50 years coupled heat and water transport is an interesting topic in the field of vadose zone hydrology. One basis is the theory by Philip & de Vries (1957) which couples the mass balance for water, the Richards equation, with a heat conservation equation based on Fickian diffusion process. In this thesis the contribution of water vapour flow to the total water movement on a daily time scale is analysed. At first the literature is reviewed, starting from the theory of Philip and de Vries and the many papers which have continued on this theory. Next to the theory also the literature on experiments associated to coupled transport is reviewed, distinguishing field and laboratory experiments. Data were collected during field work in Trabadillo, Spain under semi-arid weather conditions. Soil water pressure, soil water content and soil temperature were measured for 149 days on an hourly interval during the dry period. The soil hydraulic and soil thermal parameters are calibrated on this data in Hydrus-1D by using an inverse parameter estimated method. In the calibrated Hydrus model Monte Carlo simulations are performed to include the uncertainty in the parameters. Instantaneous fluxes of liquid water, isothermal water vapour and thermal water vapour flow are examined at multiple moments in time. Selecting fluxes for inclusion on an daily time basis in the SWAP model, the Hydrus 1-D isothermal water vapour flow is zero during night and day and is therefore not included in the SWAP model. A significant daily pattern is identified for the thermal water vapour flux and this flux is implemented in SWAP in addition to the standard isothermal liquid water flux. The cumulative net flux is computed for four different models, a Hydrus and SWAP model with only liquid water transport and a Hydrus and SWAP model with both coupled heat and water transport. Intercomparison between the four model versions showed that the contribution of water vapour flow is insignificant compared to the total transport of water. As a sensitivity analysis in addition to the soil hydraulic parameters from the field situation, simulations are also performed for a European set of soils from the HYPRESS project Wosten et al. (1999). The Hydrus model did not converge to a satisfactory numerical solution with a maximum spatial discretisation of 1 cm, which is advised by Simunek et al. (2008). In SWAP the contribution of water vapour movement to the total water transport is insignificant on a daily time scale for all the soil types. Finally a laboratory experiment design is proposed with the focus on coupled heat and water transport. The plan for the laboratory experiment will be based on the experience from the fieldwork and the literature study. Important components for this plan are the type of measurement devices, the spatial set-up of those devices and the boundary conditions. A model study is executed to look for the optimal measurement set-up for a laboratory experiment to liquid water and water vapour transport. Inverse modelling is used to determine the soil hydraulic and soil heat parameters from a selection of data and direct modeling is performed with the determined parameters to compare the accuracy of these parameters and so the data selection. The optimal laboratory design according to the model study includes measurements of soil temperature, soil water content and soil water pressure at depths of 5, 25 and 50 cm beneath the soil surface.

Mots clés : soil water movement / heat transfer / hydraulics / water vapour movement / geohydrology / arid zones / semiarid zones / soil water


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