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Topography and geomorphology of a catchment are major drivers of runoff generation. In an earlier publication by the authors, a novel approach of delineating Hydrologic Response Units (HRUs) was investigated with reference to high topographic relief catchments. In the present study, this approach is evaluated for low topographic relief catchment and found to be applicable. To verify the proposed HRUs delineation logic, the thresholds derived from the DEM analysis are evaluated here at catchment scale using high resolution aerial photograph analysis and associated site visits. The thresholds derived from the DEM analysis are found in the same range as obtained from the aerial photographs analysis. The adequacy of the HRUs delineation approach is further verified by soil moisture movement modelling across four cross-sections and sensitivity analysis test for one cross-section in the Little River catchment which further supports the application of HRUs delineation approach in low topographic relief catchment. [ABSTRACT FROM AUTHOR]

Abstract: We present here a basis for delineating Hydrologic Response Units (HRUs) to capture heterogeneity in the catchment's topography, landforms and geomorphologic attributes. To delineate topologically connected HRUs, the catchment is divided into four landforms and sub-basins. These four major landforms represent macroscopic changes in the catchment landscapes, using thresholds derived from a range of terrain analysis techniques – the Cumulative Area Distribution (CAD) curve, average local slope, curvature, Compound Topographic Index (CTI) and the MultiResolution Valley Bottom Flatness (MRVBF) index. The adequacy of the HRUs delineation approach is ascertained by soil moisture movement modelling in the unsaturated zone based on a two-dimensional solution of Richards' equation, across multiple cross-sections of the catchment. The modelling results of the four landform delineated cross-sections are compared with those from the simplest case of a single landform delineated cross-section and with the most complex case of cross-sections divided on a pixel basis. The modelling results indicate gain in accuracy when using the four landform formulation compared to the use of a single landform, and little loss of accuracy compared to simulations on a pixel basis. This study investigates the stability of this HRUs delineation methodology using the data for the Maclaughlin, Bombala and Delegate catchments of the Snowy River at Burnt Hut, New South Wales, Australia. [Copyright &y& Elsevier]

Abstract: This paper describes the development, testing and implementation of a generic pasture growth model (CLASS PGM) which can be used to simulate growth of composite pasture types of multiple species that may be summer or winter active, perennial or annual. The model includes carbon assimilation through photosynthesis and respiration followed by tissue growth, turnover and senescence. Environmental conditions as well as soil water, nutrient and salinity status influences pasture growth and tissue dynamics. The model allows the user to simulate a range of grazing management strategies. Concepts and theoretical basis of the pasture growth model is based upon the detailed technical report on pasture and crop growth modules (Johnson, 2003). For water balance computations, PGM is internally linked to the Richards’ equation - based hydrology tool, Unsaturated Moisture Movement Model U3M-1D (Vaze et al., 2004b) PGM is supported by a windows based user friendly graphical users interface (GUI). The model can be downloaded free from the Catchment Modelling Toolkit website supported by the eWater Cooperative Research Centre (http://www.toolkit.net.au/class). This paper gives an overview of the model structure, model inputs and outputs and the soils related inbuilt database. Results from model validation using long term observed data for soil moisture, pasture herbage mass and grazing for a grazing experiment at Wagga Wagga, New South Wales, Australia are discussed. When compared with herbage mass and soil moisture data from the experiment, PGM was found to adequately simulate the patterns and amplitudes of pasture growth and soil moisture recorded in the experiment. [Copyright &y& Elsevier]