Towards building an integrated urban water system model to inform the identification of optimal water source mixes for Adelaide

Abstract

The South Australian Water for Good Strategy outlines the actions that are required to ensure South Australia's water supplies are secure, safe, reliable and able to sustain continued growth. It supports diversification of supplies to reduce the reliance on rain-dependant sources. A study has been initiated by the Goyder Institute for Water Research in this regard, in particular to inform the identification of optimal mixes of water sources for metropolitan Adelaide. As part of this study an integrated system simulation model of metropolitan Adelaide's water system is being developed. This is to quantify supply implications and stormwater and wastewater discharges at defined points in the urban water system, when utilising different mixes of water sources, under both historical and future climatic conditions. This information is used to evaluate an objective function that aims at minimising life cycle cost of infrastructure, energy consumption and the potential impact on Adelaide's coastal waters, and maximising supply security, as part of a multi-objective optimisation based decision-support framework. The aim of the decision-support framework is to generate knowledge that can support the identification of the most cost-effective mix of fit-for-purpose water sources available to meet the needs of the community in metropolitan Adelaide, in an environmentally and financially sustainable manner. The sources to be considered are River Murray, surface water from Mount Lofty Ranges catchments, desalinated sea water, recycled wastewater, stormwater including roof water, ground water and the potable water savings through various demand management options. The objective of this paper is to describe the process followed to develop the simulation component of the combined simulation-optimisation approach. The modelling platform used to develop the simulation model is Source Integrated Modelling System (IMS), which is emerging as Australia's national hydrologic modelling platform for river basins. Hence it has not been applied widely yet, particularly for urban water systems. The study reported in this paper one of the first application of eWater Source to urban water systems. The application process has been an exploratory process where modelling methods have to be developed for the each water source considered in this study using the available functionalities. Also, there are modelling methods currently in place in most cities to inform planning and operation of each city's water supply system. In general, when a new modelling method is introduced, quantitative evidence is required to demonstrate the performance of the new methodology is comparable to that of the existing methodology. Thus the process to develop the simulation component of the simulation-optimisation approach was staged and comprised the development of firstly a Test Case, secondly a Base Case before developing the Scenario Cases. In this paper, we describe the Test Case and the Base Case. Development of Scenario Cases is in progress. The purpose of the Test Case is to examine the ability of the eWater Source to represent key features of metro Adelaide's water supply system, to an adequate level. The 'adequacy' was defined as the ability of eWater Source to generate outputs (e.g. pumping volumes and storage volumes) of a similar order of magnitude from an existing water supply planning and operation model that is currently used by the South Australian Water Corporation. The Base Case model represents the 'business as usual' scenario for supplying water from the three main drinking water supply sources for Adelaide, i.e. River Murray, Mount Lofty Ranges catchments and Adelaide Desalination Plant. The simulation is performed over 50 years, on a monthly basis. The optimisation time horizon is 25 years, from 2013. The simulation model is provided with functionalities using the Expression Editor capability in the eWater Source to evaluate the objective function, consisting of net present value of life cycle cost of infrastructure, energy consumption and the volumetric reliability of supply. Development of Scenario Cases is in progress, which will include adding the other sources mentioned above. The Scenario Cases will also provide information to minimise potential impact of wastewater and stormwater discharges to Adelaide's coastal waters. The results of the Test Case showed that eWater Source can adequately represent the existing water sources in Adelaide's water supply. The results of the Base Case showed that eWater Source can produce the expected behaviour of the supply system. The project is in progress.