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Constructing and optimising a parsimonious groundwater recharge model using neutron probe data

Lookup NU author(s): Joseph Pollacco, Dr Paul Quinn

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Abstract

Simulating the actual groundwater recharge rate of groundwater models is often a difficult procedure and is usually determined from an inverse method based on observations of water table depth alone. However, when studying land use change, it is necessary to understand how the local unsaturated zone controls recharge rates. The complicating factors of soil heterogeneity and macroporosity effects are difficult to represent in a physical-based model of the unsaturated zone. However, it is possible to observe soil moisture patterns across the unsaturated zone across space and time using Neutron Probe (NP) data. This can be done in-situ and under a range of land uses. Whilst it is appreciated that NP data can have its own errors and does not actually depict the recharge rate itself, it does give valuable information of unsaturated zone soil moisture activity. Equally, the physical processes of unsaturated zone activity, although well established, in the Mualem-van Genuchten (MVG) equations, are themselves quite complex with parameters that are difficult to determine a priori. Here, this paper shows two techniques for addressing these problems. The first analysis will clearly show that a number of the MVG parameters can be fixed without affecting the recharge rate of the model, this gives rise to a simplified model called the Simplified MVG (SMVG). Secondly, an inverse optimisation technique is proposed that capitalises on the observed NP soil moisture profile data which minimises soil heterogeneity and NP errors effects by 'smoothing' moisture fluxes across multiple soil layers. The technique gives a physical-based origin to the SMVG model parameters even though the soil output hydraulic conductivity profile model uses 'effective', optimised parameters. The method proposed can capitalise on field observation and may allude to even better hydro-geophysical data measurements that can be used to establish a simple, field characterisation technique to understand the groundwater recharge term across space.


Publication metadata

Author(s): Pollacco J, Quinn PF

Publication type: Conference Proceedings (inc. Abstract)

Publication status: Published

Conference Name: International Congress on Modelling and Simulation

Year of Conference: 2003

Pages: 195-200

Publisher: University of Western Australia

Library holdings: Search Newcastle University Library for this item

ISBN: 174052098X


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