Environmental flows describe the quantity, timing, and quality of water flows required to sustain freshwater and estuarine ecosystems and the human livelihoods and well-being that depend on these ecosystems. For many Australian river systems, specific water dependent environmental assets have been identified. The decisions made by environmental water holders have a significant impact on the rest of the system and therefore need to be adequately represented in water planning models. For example, environmental requirements may affect water availability to other entitlement holders by competing for conveyance capacity, altering loss behaviour, imposing minimum targets for storages, and changing spill behaviour.

Most of the rivers in the southern Murray-Darling face intense competition between agriculture and the environmental water use (Chartres and Williams, 2006; Western et al. 2011). The water available for agriculture may be reduced in the future to preserve the relative balance between demands. In order to minimise the impacts on both agriculture and environment, innovative planning and management of water resources are essential. Integration of comprehensive environmental water management can help policymakers analyse the best way to use entitlements of environmental water holders across the system, and prioritise environmental flow events across the catchment.

Flow regimes are dynamic across multiple time scales and lead to a range of interconnected ecological responses which are often challenging to express. The desire to replicate historical watering of an asset or antecedent conditions can result in a need to create rules to replicate complicated patterns. The specification of the water requirements and the operating rules for delivering water to these assets can be complex.

Source functionality allows environmental flow rules to be implemented at individual points within the system and can be configured to reflect the interconnected, spatially and temporally diverse nature of ecological system requirements and the overall impact of environmental water holders on the rest of the system. This provides an explicitly defined, reliable environmental water management model in Source that can be easily related to the rest of the framework. The functionality can be used to fully realise a fit for purpose integrated modelling framework for water resources planning and management that enables the representation of planning, use and accounting of environmental water, and that can be used to carry out an analysis of alternative policy scenarios for water allocation and use. The implementation of tools to configure generalised rules is a better option than individual users configuring large numbers of custom functions (which is another option), for ease of use, management and transparency.

The majority of environmental flow sharing rules that currently exist in major jurisdictional basin plans can be represented with the core functionality. The remainder will be able to be configured using custom functions. The new functionality will address management of environmental entitlements across a range of sites and for different purposes using the proposed Environmental Flow Manager.

Table 1 shows the Commonwealth Environmental Water Holder Framework, which determines environmental watering actions whereby watering options for a specific asset are a function of water availability.

Table 1. Commonwealth Environmental Water Holder Framework for determining environmental watering actions 2009

	Extreme dry	Dry	Median	Wet
Ecological watering objectives	Avoid damage to key environmental assets	Ensure ecological capacity for recovery	Maintain ecological health and resilience	Improve and extend healthy and resilient aquatic ecosystems
Management objectives	Avoid critical loss of threatened species Maintain key refuges Avoid irretrievable damage or catastrophic events	Support the survival and growth of threatened species and communities including limited small-scale recruitment Maintain diverse habitats Maintain low flow river and floodplain functional processes in sites and reaches of priority assets	Enable growth, reproduction and small-scale recruitment for a diverse range of flora and fauna Promote low-lying floodplain-river connectivity Support medium flow river and floodplain functional processes	Enable growth, reproduction and large-scale recruitment for a diverse range of flora and fauna Promote higher floodplain-river connectivity Support high flow river and floodplain functional processes
Management actions	Water refugia and sites supporting threatened species and communities Undertake emergency watering at specific sites of priority assets Use carryover volumes to maintain critical needs	Water refugia and sites supporting threatened species and communities Provide low flow and freshes in sites and reaches of priority assets Use carryover volumes to maintain follow-up watering	Prolong flood/high-flow duration at key sites and reaches of priority assets Contribute to the full-range of in-channel flows Use carryover to provide optimal seasonal flow patterns in subsequent years	Increase flood/high-flow duration and extent across priority assets Contribute to the full range of flows including over-bank Use carryover to provide optimal seasonal flow patterns in subsequent years
Key goal	Damage avoidance	Capacity for recovery	Maintained health and resilience	Improved health and resilience

Environmental flows are represented and managed in Source using two main mechanisms, the Environmental Flow Node (EFN) and the Environmental Flow Manager (EFM).

The Environmental Flow Node is used to generate orders to meet in-stream environmental requirements at an individual asset. The desired flow patterns are defined by configuring one or more actions including start criteria, desired flow response and frequency, as well as criteria for success of the action and condition of the asset targeted by the action.

The Environmental Flow Manager will prioritise environmental flow actions defined at Environmental Flow Nodes throughout the system. The EFM will also handle management of accounts, and apportionment of water from the accounts to particular environmental events.

These two network elements interact with each other, and the rest of the network, including the Resource Assessment System, Ordering and Flow Phase to manage environmental water

The flowchart in Figure 1 depicts the overall process of eFlow management (Figure 2). The water available to the EFM (i.e. water available in account portfolios managed by the EFM) is calculated in the resource assessment and passed to the EFM. Water to be set aside in a reserve for later use or carryover (as specified by the user) is subtracted from the available water. The EFM manages all actions specified at EFNs that have been assigned to the manager. The EFM ranks the actions in priority order based on condition and an importance weighting specified for each action. The EFM then determines which actions are to be activated based on the cost (water requirement) of the action and the water available in accounts (see Figure 3, for more details). The Environmental Flow Nodes generate demands for actions activated by the EFM (see more detail in Figure 4). During the ordering phase, the EFN places orders for the eFlow demands, which are delivered during the flow phase. Subsequently, accounting for environmental flows is done through the EFM. The EFN assesses if actions have been successful and keep track of time since last success, and condition.

Figure 1. eFlow management process

Principal developer

Murray Darling Basin Authority and eWater, with assistance from

Office of Environment and Heritage, NSW,
Commonwealth Environmental Water Holder,
Department of Environment, Land, Water and Planning, Victoria,
Melbourne Water
Department of Primary Industry, NSW
Victorian Environmental Water Holder
Department of Environment, Water and Natural Resources, SA

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