Investigating environmental watering options using Source IMS: a case study – the River Murray, Australia

The integrated modelling tool Source IMS developed by eWater and its partner organisations provides a common modelling platform to investigate the increasingly complex nature of water resources management in Australia. This paper describes how a recently built model of the River Murray using Source IMS has incorporated the management, delivery and accounting of water recovered for the environment to achieve required hydrological behavior. The River Murray model in Source IMS is fundamentally different from previous models of the River Murray in that it is run completely on a daily timestep, and has the capacity to run both as a planning model for policy development, and also as a daily operational tool used by River Operators to manage the competing demands for water in this complex system. In the last few decades, there has been significant reform of water resources management in the MDB to address declining environmental condition within the Basin, including an increased focus on delivering water to environmental sites along the river system to achieve specific environmental outcomes. This paper shows how the Source model has been developed to investigate various environmental watering options in river systems planning. One of the major projects to recover water for the environment is The Living Murray (TLM), a joint partnership between the States of the River Murray to recover an average annual volume of 500 GL, to be used to deliver environmental outcomes at nominated icon sites along the river (MDBA, 2011). Icon sites were chosen for the high environmental and ecological values. Specified ecological objectives at each site dictate water requirements: the timing, frequency and magnitude of environmental diversions to the site. Two of the TLM icon sites the Koondrook-Perricoota forest and Hattah Lakes have been presented in this paper. The ordering of water to the icon sites is accomplished through a Source Plugin; a dynamic-link library exposing purpose-built functionality to the Source River Murray project. This plugin triggers environmental watering events at the icon sites based on need and the volume of water available to the TLM. The Resources Assessment functionality in Source undertakes allocation of water to TLM held entitlements over the simulation period. Due to the entitlements being held in a number of different allocation systems, triggers have been developed in Source IMS that transfer the TLM’s available water from the State allocation systems to a TLM system to determine the total available water to the TLM. Individual use at each icon site is tracked across the model simulation, and the total use of TLM water is then accounted for in the State allocation systems based on an assumed priority of use. During a simulation, the model records watering events at each icon site, either by overbank flow or TLM intervention. Once the elapsed time since the last flood exceeds the optimal inter-flood period, the model identifies a watering need at the icon site. During subsequent months, the model attempts to operate the works opportunistically, without placing an order but using flow that is not necessary to meet downstream demands. If the site was able to operate opportunistically for the first month, then it places a demand for subsequent months to complete the intervention. This type of intervention is termed an opportunistic watering. If a site’s dry spell passes the resilience inter-flood period without starting opportunistically, then it registers a demand and initiates a forced watering. When watering needs exist at multiple sites, they are ranked according to need by a rostering algorithm. The paper demonstrates how Source IMS has been able to model the complexity surrounding environmental watering in the River Murray. Further confirmation of the model’s ability to represent the hydrological states of the TLM sites should make the model a useful tool when undertaking future work in environmental water planning and delivery on the River Murray