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Low-dimensional modeling of hillslope sub-surface flow processes : developing and testing the hillslope-storage Boussinesq model

Authors
  • Hilberts, A.G.J.
Publication Date
Jan 01, 2006
Source
Wageningen University and Researchcenter Publications
Keywords
Language
English
License
Unknown
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Abstract

Key words: hillslope hydrology, low-dimensional modeling, Boussinesq equation, Richards equation, water table dynamics.In this thesis the focus is on investigating the hillslope hydrological behavior, as a crucial part in understanding the catchment hydrological response. To overcome difficulties associated with most of the existing models, i.e., high computational costs and difficulties in model parameterization and calibration, the focus is on low-dimensional physically based models. The central question is whether it is possible to formulate low-dimensional physically based models such that the essential physical behavior of the natural system is preserved.Several models are compared to each other and to measurements from a laboratory and from a field site. The comparisons are carried out for a diversity of bedrock slopes, hillslope shapes, and profile curvatures. The low-dimensional models that are formulated are essentially based on the hillslope-storage Boussinesq (HSB) model. Several modifications to the model are conducted in order to investigate the model response under different conditions: a) a generalized HSB formulation is derived that allows model evaluation on curved bedrock profiles, b) a new HSB model is derived in which the effects of capillarity are partly accounted for based on the assumption of hydraulic equilibrium in the unsaturated zone, and c) a coupled saturated-unsaturated HSB model is derived in which the unsaturated zone dynamics are described with a one-dimensional Richards model. Evaluation of the developed low-dimensional models generally shows that: a) the HSB model saturated zone dynamics alone can describe the outflow rates and water table dynamics accurately when the influence of capillarity is small; b) for very shallow soils or water tables in the proximity of the soil surface, the effects of capillarity are more clearly noticeable and it is possible to improve the simulated water table dynamics during drainage experiments significantly by regarding the parameter drainable porosity as a state-dependent parameter of which the value depends on the unsaturated depth; c) for drainage and recharge scenario's, a low-dimensional coupled saturated-unsaturated model that is developed to dynamically account for the unsaturated zone processes is very well capable of describing outflow rates and water table dynamics; d) the comparison of the results of the coupled model run in an uncalibrated mode to field data yields a reasonable match in terms of hydrographs and water table dynamics. However, the water table response is highly sensitive due to limited free pore space caused by capillarity effects.

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