Environmental demand model

The functionality provided by the Environmental Demand Model in Source is essential for Source to be able to fulfil a core role, which is to model existing and proposed water sharing arrangements that include environmental flow rules.

Source models the use of water by a combination of supply point and water user nodes. The water user node provides a range of demand models that include the Environmental Demand Model (EDM). The EDM operates on a daily basis generating demands for the environment at a water user node and extracting water to meet these demands via the water user and supply nodes. The model can be applied in both regulated and unregulated systems.

The EDM provides an interface for defining environmental water requirements at the project set up phase and then applies a series of heuristic routines in order to define the water required to achieve the specified environmental water requirements.

The EDM contains four types of environmental demand rules and allows modellers to construct a collective environmental water requirement by using combinations of these. The environmental demand rules reflect commonly observed descriptions of environmental water requirements. The four rule types are:

• Baseflow: specify a minimum flow; usually applied to maintain minimum habitat requirements;
• High Flow: specify a flood fresh; usually associated with a recruitment event such as to trigger fish movement, water floodplain vegetation;
• Translucency: specify the flow requirements in terms of some other time series; usually specify the release from a dam based on the inflow to the dam; and
• Pattern: specify the pattern of flow; used to define multi-peak events.

Common elements of each of the four rule types are:

• Season: the period of the year over which the rule should be considered (eg is this a winter flooding rule only);
• Reporting interval: What is the acceptable number of years between applying the flow rule (eg High flows are only required once in 5 years);
• Augmentation Options: The preference for achieving the watering requirement. There are three augmentation options;
• Match a reference time series (usually use a modelled natural scenario, and water demand for each rule will match the successful meeting of the rule that would occur under the reference flow);
• Extend: if a flow rule has started to be met, then water is ordered in order to extend the watering (eg tributary inflows have commenced a flood, and releases from the main channel dam may be used to extend the duration of the event); and
• Force: if by the end of the reporting interval, the flow rule has not been met then order a release. This is akin to waiting until the last possible time to meet the water requirements in the anticipation that the water requirements will be met by tributary flows or spills.
• When to use: each flow rule can have a ‘trigger’ specified, whereby for each day of the record, the trigger is checked against some relevant time series such as storage volume in order to set the flow rule to be on. This allows switching between rules at runtime to reflect watering options during dry vs wet periods.

In order to combine the flow rules into a collective environmental flow requirement, rules can be grouped if required.

The Environmental Demand Module is applied at a point scale and operates on a daily time-step.

Yorb Pty Ltd with funding support from eWater CRC.

The Environmental Demand Model is based substantially on the eFlow Predictor software tool developed by eWater CRC in 2010. The underlying computational code for the eFlow Predictor had to be rewritten in order to work within the Source environment, but the functionality remains substantially the same between the two products.

Source V 2.14.0

The Environmental Demand Module is applied through a water user node, which must be connected to at least one supply point node to provide water to satisfy the environmental demand.

Refer to the Source User Guide for detailed data requirements and formats.