Water Balance Dynamic Simulation Model-WBDSim for Water Policy options Analysis Case Study: Murray Darling Basin - Australia

Water is a key resource to sustain human life. Therefore, sustaining growth in the human population requires even more water to be available. Water sharing management is the major problem for water resources and irrigation management decision makers. The water Act 2007-Australia requires the newly formed Murray Darling Basin (MDB) Authority to develop an integrated plan which specifies amongst other things, long term sustainable diversion limits, water quality objectives, provision for critical human needs and environmental watering plans for all of the Basin’s rivers. A major challenge is to anticipate future water demands and supplies in a drying climate to accommodate the needs of Australia’s most rapidly growing area. The MDB system is very complex and interconnected, posing significant difficulties in managing irrigation economically and environmentally. In formulating the new basin plan the Murray Darling Basin Authority (MDBA) is required to ultilise the best available scientific and socio-economic knowledge. Given the relatively short time frames for plan development, there is therefore a requirement for rapid integration and synthesis of much of what is known about the basin, its environment, industries and communities. Therefore, it is imperative that innovative modelling approaches are employed to assist in better decision making by modelling the feedback loops inherent in the system and to analyse the impact of alternative land use and water policy scenarios (recommended by stakeholders) in order to better understand the trades off. These options include future land use changes, new water allocations, water buy back and carryover rules. Through the application of a system dynamics approach, a MDB-Water Balance Dynamic Simulation Model (WBDSim) was developed. The purpose of the WBDSim is to measure and identify the change in economic and environmental outputs of various allocations and demand scenarios. The WBDSim is forming the base to link irrigation economic impact, environmental response, and urban water economic impact of several water policy options. This paper details a systems approach to developing WBDSim to enable these complex land and water use options to be evaluated in economic, social and environmental dimensions. A total of 45 catchments are modelled. Each catchment is modelled by the main interconnected five modules (Rainfall-runoff module, River flow module, Irrigation demand module, Rainfed agricultural and vegetation module and simple economic module) that lead to the quantitative indicators (environment, economic and social) values. This model is designed to operate on a monthly basis and can assist managers in analysing the system’s behaviour under various management scenarios.The developed WBDSim model is being calibrated against recent CSIRO Sustainable Yields project climate scenarios carried out using a synthesis of the MDBC and State certified River operations Models for the MDB. Preliminary results from the WBDSim are presented with an emphasis on calibration and validation results against sustainable yield flows data of changing climatic conditions and landuse planning. The WBDSim model tool developed a dynamic system that can provide water balance and uses overview. It can also provide a basis for examining the impact of physical changes to the system and for interactions with agricultural productivity, economics and livelihoods. It is not a detailed catchment hydrology model but is a tool that has the potential to help stakeholders to simulate and optimize the system, by evaluating and analyzing the key decisions.