Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : A geophysical and hydrological investigation of palaeochannels in northern New South Wales

Auteur : Vanags, Christopher P

Université de soutenance : University of Sydney

Grade : Doctor of Philosophy (PhD) 2007

Résumé
Palreochannels are common features in much of the irrigated landscape of the Murray Darling Basin. Exensive research has been carried out on palreochannels in the Namoi and Murrumbidgee River Basins and has indicated that these features are associated with irrigation water loss due to their sandier textures. While these features have been identified as potential sources of deep drainage, little is known about the pathways and movement of water after infiltration and how changes in soil properties and sedimentary layering govern this movement. This is particularly the case in the Gwydir River Basin, where palreochannels are less understood due to the expensive and invasive nature of direct physical measurement and the extreme variability of hydraulic properties in these structues. Previous research in this region has been aimed at identifying the characteristics of these structures through ancillary data, such as electromagnetic induction, but has generally been limited to one or two dimensions.
This study uses traditional measurements to identify the geomorphological and hydrological characteristics of a palreochannel in the Gwydir River Basin, where palreochannels are thought to affect water-use efficiency on farms relying on surface irrigation techniques. To improve on the information gained from a limited number of direct observations, the conceptual model is further refined through the use of geophysical information. Depth information was derived from the electromagnetic induction data by inverting bulk electrical conductivity readings from various combinations of electromagnetic measurements and using a regularisation process to stabilise the solution of the inverse problem. Four different inversion algorithms and three conceptually-different scaling relationships are subsequently used to derive saturated conductivity fields based on data from pedotransfer functions. To test the utilitity of the geophyhsical data, two interpolation procedures are used to distribute this information in three dimensions. Three-dimensional ordinary kriging was used to interpolate the limited soil measurements, and the scaling factorderived saturated conductivity predictions. A more sophisticated method, regression kriging, incorporates the electrical conductivity data into the interpolation of the direct observations, providing the maximum amount of information.

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