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Title: Soil water flow processes : a critical evaluation using numerical simulations and lysimeter data
Author: Goldenfum, Joel Avruch
ISNI:       0000 0001 3501 9690
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 1996
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Physically-based soil water flow models generally use approaches based on Darcy's law and Richards' equation, and, although Darcy's law is itself an empirical approximation, such models have been well proven for ideal soils. Failures of Richards' equation to describe unsaturated water movement, however, are also reported. Anomalies have been attributed to the presence of a system of large, continuous, surface-connected pores in the soil, here referred to as macropores. Also, other phenomena, such as hysteresis of the soil hydraulic properties, can cause difficulties to adequately represent water flow. A detailed data set for water movement in the unsaturated zone is available from Imperial College's experimental station at Silwood Park, where field lysimeters containing a sandy loam soil are being used to monitor the processes affecting radionuclide transport from a contaminated water table through the unsaturated zone and into a wheat crop. The main goal of this thesis is to study the data from this experimental facility, selecting relevant events and trying to understand and explain the physical phenomena involved, mainly those related to the problems of preferential pathways in soils. Mathematical modelling is applied to test the hypotheses proposed and to examine the weaknesses related to the use of Richards' equation, in order to identify its limitations and to develop ways to overcome them. Results from a dual porosity model are compared with the traditional single porosity approach and also with a model incorporating hysteresis in the relationship between moisture content and matric potential. The data from the experimental station and the results of the simulations provided evidence of rapid, or preferential, flow mechanisms occurring in the lysimeters. The single porosity model showed weaknesses when trying to reproduce observed rapid flow events. This representation was improved by hysteretic simulations, but it was not possible to determine a unique set of parameters for all selected events. The results obtained by the application of a dual porosity model strongly suggest that tensiometer data can be represented by a combination of macro- and micropore effects. A physical interpretation of these results provides a theoretical basis for the future development of a model combining inputs from both macro- and micropores, which can allow a better understanding of soil water potential measurements.
Supervisor: Wheater, Howard S. Sponsor: Conselho Nacional de Desenvolvimento Científico e Tecnológico, Brazil ; Instituto de Pesquisas Hidráulicas, Universidade Federal do Rio Grande do Sul
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Hydrology & limnology