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Abstracts for Background papers

O'LOUGHLIN, E.M. (1986): Prediction of surface saturation zones in natural catchments by topographic analysis. Water Resour. Res., 22(5): 794-804.

The topography of hillslopes or whole catchments is analysed numerically to calculate local geometric and drainage attributes that can be combined to test for the expectation of soil waterlogging. At locations where accumulated drainage flux from upslope exceeds the product of soil transmissivity and the local slope, saturation to the soil surface occurs. Results of the analysis of specific landscapes are presented as a location dependent function. The function may be mapped as isolines to define successive boundaries of zones of soil saturation, depending on the wetness state of the landscape as a whole. The analysis is applied to two catchments, to predict the growth or contraction of zones of waterlogging for a range of drainage fluxes and to simulate the effects of transpiration changes in part or all of the catchment. In the second application, the predicted boundaries of saturated zones are used to calculate the minimum proportion of a catchments's area that produces rapid surface runoff. This proportion is shown to depend on the value of a normalized wetness parameter. Storm runoff data support the predicted form of the relationship.

VERTESSY, R., O'LOUGHLIN, E., BEVERLY, E. and BUTT, T. (1994): Australian experiences with the CSIRO Topog model in land and water resources management. In: Proceedings of UNESCO International Symposium on Water Resources Planning in a Changing World, Karlsruhe, Germany, June 28-30, 1994, pp. III-135-144.

This paper describes Australian experience with a distributed parameter hydrological modelling framework called TOPOG. TOPOG simulates the spatial and temporal dynamics of water movement in complex terrain characterised by heterogeneous soils and vegetation. The basis of TOPOG is an automated terrain analysis procedure which takes a contour map as input and generates an element network by calculating lines of minimum distance between adjacent contours. Flows are then routed downslope in one dimension. We describe various steady-state and transient water balance modelling routines embedded in TOPOG that can be used to predict soil saturation, erosion hazard, slope stability and water yield, as well as surface water and groundwater interactions. We demonstrate these capabilities by reference to a number of case studies that have been carried out in Australia over the last four years.

SHORT, D., DAWES, W.R. and WHITE, I. (1995):The practicability of using Richards' equation for general purpose soil-water dynamics models. Environment International, 21(5): 723-730.

Use of finite difference solutions of Richard's equation is generally considered to be impracticable for general purpose models of soil-water dynamics, because numerical performance is not predictable with unfamiliar parameter values, and because of excessive computer execution times. The Broadbridge-White model of soil hydraulic properties yields finite soil-water diffusivity, so that solutions of the finite difference equations always exist. Further, it permits the flow equation to be scaled to realistic soils in terms of three independent variables. Searching a practical three-dimensional parameter space yields criteria for numerical stability and for guaranteed convergence of the iterative procedure for obtaining the solution at each time step. An efficient numerical scheme yields soil-water models with practical execution times. Comparison shows higher computational speed and greater model simplicity, relative to an alternative, less rigorous, model based on generalising the sharp wetting front infiltration model of Green and Ampt.