Introduction
The Environmental Demand Model (EDM) in Source operates on a daily basis generating demands and extracting water to meet these demands using the environmental demand and supply point node. This model is used to define 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. It can be applied in both regulated and unregulated systems. The EDM is designed by default to represent an environmental flow requirement at a specific location within a river system. is designed to simulate environmental flow requirements according to a set of rules. Environmental flow requirements may generally be classified as either in-stream (refer to In-stream requirement) or floodplain requirements (refer to Floodplain), where the former creates flow conditions that remain within the river channel, and the latter creates flow conditions that spill over bank. How these situations are configured in Source is largely dependent on the conceptualisation used to model the interaction between the channel and the floodplain.
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| In Source, the EDM environmental demand is modelled using the environmental demand node. Refer to Environmental Demand node for details on configuring the node. |
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| 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 |
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| Management actions |
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| Key goal | Damage avoidance | Capacity for recovery | Maintained health and resilience | Improved health and resilience |
One example where you would use environmental demand is say, for example, Consider a river with a historic flow regime that used to be dominated by dominated by high flows in late winter and early spring. Due to irrigation demands,the flow is now high regime has changed to having high flows in late spring – to summer. For There is also a large reduction in flow during the rest of the year there has been a large reduction in flow as the city water supply is extracted at the reservoir and flows via pipe to the cityas a result of urban water requirements. In this case, environmental flow rules need to be incorporated, so that the environmental demands can be met, even in periods where flows are lowincorporated to meet environmental demands.
Assumptions
The following assumptions are made when an EDM is configured in Source:
- Water requirements are not additive - A basic assumption used in the EDM is that environmental water is not consumed and, as such, flow rule water requirements for more than one environmental asset can potentially use the same water in accounting for the success of their flow rules being met. For example the minimum flow requirement for fish passage is not necessarily a separate parcel of water from the minimum flow required to prevent an algal bloom;
- Flow rules can be co-dependent: A flow rule can be conditionally contingent on another flow rule also being met;
- Flow rules should only be attempted if their requirements are likely to be met: The the EDM determines the daily demand, however before passing the demand for this a day, the EDM checks to see if the total water required to complete the rule is available; and
- The highest priority environmental water demand is for environmental flow rules which have commenced but not yet completed. If an environmental flow rule has started to be met, then the continuation of meeting this flow rule requirement has precedence over commencing water ordering to meet a new flow rule.
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The EDM provides a means of capturing prescriptive descriptions of water patterns that the environment requires. These definitions of watering patterns are captured as ‘flow rules’ within the EDM and many combinations of flow rules can be prescribed for a single supply point. The four types of flow rules presented in the EDM have been designed to capture the most commonly defined environmental flow requirements specified in environmental flow studies and water regulations. These environmental demand rules allow you to construct a collective environmental water requirement by using combinations of environmental demand rules. These are:
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Flow rules can be grouped and prioritised. The first (default) group allows consideration of every rule in the default group for every day of the simulation. For all other groups of rules, only one rule from the group is considered at any time-step. For any group of rules, the rules are prioritised by according to the order in which they appear in Source.
Rules can be made active or inactive during a modelling run. In order to control rules throughout a model run, each rule can have a defined condition threshold. This condition threshold is compared to a ‘condition’ time series (which is entered using the Expression Editor functionalityFunction Editor)[for each time step and the flow rule turned on or off for that time step as required. This functionality is specifically designed to allow the construction of asset based rule sets that vary according to water availability. A good example is Table 1 whereby watering options for a specific asset are a function of water availability (Table 2). In this case, a group of four flow rules can be created as a flow rule group and the decision as to which rule is considered for each time-step can be based on the flow rule based ‘condition threshold’. Hence rules are turned on and off dynamically throughout the modelling run based on water availability.
Rules can be made active or inactive during a modelling run using Disable in the rule's contextual menu.
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The basic approach to determining the water order ordered for environmental demand is to consider the collection of flow rules and determine how much water is required for a given day to meet these rules. As water is not consumed by the EDM, the water order is simply the difference between the calculated water required and the forecast flow at the extraction point on the future delivery day.The EDM allows two forecasting periods, a short term and a medium term. This approach is to reflect real world water management decision making, whereby, depending on the size of the catchment, river operators can generally make a very accurate prediction of the likely flow for the next few days to weeks. After that time the prediction is less accurate. The In this way, the EDM allows you to define the ‘look ahead’ period, which is the period that can be accurately forecasted.