An integrated modeling framework to evaluate water allocation strategies in the Broken catchment, Victoria

Abstract

River basins in Australia face increasing competition between economic and environmental water use. The competition for water for agricultural, urban, industrial and ecological uses is exacerbating due to increasing climate variability, urbanization, economic activity and population. This paper presents an integrated modelling framework for water resources planning and management that can be used to carry out an analysis of alternative policy scenarios for water allocation and use. The integrated modelling framework consisted of farm economics, hydrology, ecology and water allocation. The framework was implemented in the Broken catchment, Victoria where there is significant competition between agriculture and the environment. The first step towards developing a water allocation model is to take account of the current resource situation, its spatial and temporal distribution and any recent trends. The hydrologic model AWBM, a lumped model running on a daily time step, was calibrated and validated using data from two gauges in the catchment, using the GLUE framework to evaluate the model performance and estimate upper and lower bounds to the predicted flows. Parameter sets obtained from the calibration were used to estimate the ungauged inflows in the catchment. The catchment was split into 17 sub catchments and 5 reaches. Two water availability scenarios were simulated-water availability based on the historical climate, and under a projected drier and hotter climate representative of 2030, similar to the 2030 dry climate scenario used in the CSIRO Murray Darling Basin Sustainable Yields (MDBSY) study. Irrigation water is used the Broken catchment for improved pastures in the dairy industry, perennial horticulture (orchards and vineyards) and irrigated cropping. The irrigation demands were quantified through representative farm models solving for profit maximising water use, and scaled up to the catchment level according to the land-use areas. Changes in water quantity and quality can have significant effects on the natural ecosystem of rivers. To estimate environmental flow requirements of the Broken system an expert panel developed a set of 17 environmental objectives and associated flow rules. These flow rules were modelled in eFlow predictor toestimate the augmented flow to meet the rules. In this research, allocation of water to meet environmental and irrigation demands is based on the integration of water supply and demand through a network allocation model Source Rivers, developed by the eWater CRC. Source Rivers model uses a node-link network to represent the river basin and it works on a daily time step and has the capability to route the flows in the system. The framework was implemented in the Broken catchment, Victoria and was used for modelling different water allocation scenarios to analyse the tradeoffs between agricultural and environmental outcomes.