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ItemTwo-dimensional simulation model for overland flow in contour basin irrigation layouts in Southeast Australia( 2001)Contour basin irrigation layouts are used in Southeast Australia to irrigate rice, winter cereals and pasture. These layouts are developed predominantly on heavy cracking soils with low infiltration rates. Contour basins are made by constructing banks across the slope, which are built by borrowing soil from the adjacent area inside the basin and leaving a toe-furrow along the side banks. Irrigation in these layouts is carried out by sequentially watering a set of basins. This involves filling one basin to the desired depth and retaining the water until it infiltrates into the soil while at the same time allowing the excess water to drain into the next downstream basin as well as back into the supply channel. In this work a physically based two-dimensional simulation model that incorporates all the features of contour basin irrigation systems as used in Southeast Australia was developed. The model's governing equations are based on a zero-inertia approximation to the two-dimensional long wave equations of motion. The equations of motion are transformed into a single non-linear advection-diffusion equation in which the friction force is described by Manning's formula. The empirical Kostiakov equation and the quasi-analytical Parlange equation are used to model the infiltration process. The governing equations are solved numerically by using a split-operator approach. For a regular grid discretization, the method of characteristics coupled with bicubic spline interpolations is used. A two-dimensional Taylor series expansion, in conjunction with the method of characteristics, was used for irregular grid discretization. Field studies were conducted during the 1998-99 and 1999-2000 irrigation seasons on commercial lasered layouts to evaluate their irrigation performance. The trials were conducted in the vicinity of Deniliquin, N.S.W. Two irrigation events in each irrigation season were monitored. The first trial was conducted during the first irrigation of the season on a dry heavily cracked soil while the second event was carried out 10-20 days after the first irrigation. This latter irrigation represented a typical within-season irrigation. The studies involved the collection of all the soil and hydraulic parameters and followed typical water management practices used by a farmer. The trials yielded a full set of field data including surface elevations, inflow and outflow, waterfront advance, overland flow depth and pre- and post-irrigation soil moisture status. A full water balance was carried out to assess irrigation performance. The water balance of the experimental bay indicated that the deep percolation loss ranged from 22% to 37% of the total water applied. The main reason for high percolation loss is ascribed to poor drainage from the bay. This is attributed to several factors including local microtopography, poorly maintained toe-furrows and excess water application. The developed model was validated using the experimental data collected during the field studies and infiltration parameters collected from the literature. Different contour basin layouts are used for the model validation to demonstrate the model's capability for incorporating all the key layout features. The applicability of the model was demonstrated with line and point inflow, toe-furrows within the basin, drainage outflow into the supply channel and into a downstream basin. These characteristics are included in models of regular and irregular basins. Overall, the model performs well against the field data and in defining all the characteristic features of contour layouts. The model was also used to study the effect of key design and management parameters on irrigation performance. This was conducted simulating hypothetical cases of contour basins to study the effect of (i) aspect ratio (ii) longitudinal slope (iii) inflow rates (iv) local microtopography, in single basins and the effect of (i) contour interval and (ii) number of outlets in multiple basins. Finally, general design and management guidelines for contour basin layouts are suggested. In this regard it must be noted that these guidelines are only intended to assist irrigation designers and practitioners in conceptualising the effect of the main design factors on layout performance. It is implied that the model will be used to analyse alternative design options in each individual case.