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. The model can 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 can be applied in both regulated and unregulated systems.
In Source, the environmental demand node is used to model environmental demand, which can be set up in two ways:
- As an in-stream requirement (In-stream requirement); or
- To act as a floodplain (Floodplain).
Further detail about the node's configuration is described in their respective links shown above.
Table 1 shows the different objectives that can be achieved using the EDM using a set of flow rules. These rules can be grouped and prioritised to ensure that the required environmental needs are met. The Commonwealth Environmental Water Holder Framework (shown in Table 1), 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 |
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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 |
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The following assumptions are made when 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 every individual , flow rule water requirement can requirements for more than one environmental asset can potentially use the same water in accounting for the success of a their flow rule 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 EDM determines the daily demand, however before passing the demand for this 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 a 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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These rules are configured in the environmental demand node's feature editor. For details on what to configure each of these rules in Source, refer to Environmental Demand node.
To combine the flow rules into a collective environmental flow requirement, rules can be grouped so that they are either always considered, or considered as a subset of the flow requirements. You can define the priority order of rules, and where there is a conflict in being able to meet the water demand, ( ie. insufficient availability of water) the additional water demands for the lowest priority rule is removed until the demand matches, or is less than the available waterThe EDM has four different types of flow rule, and for each, you can configure several flow characteristics that can be altered. A common feature across the flow rule types is the concept that they can be applied to a specific time of the year. This is termed the ‘season’ of the rule and is defined by a start and end day and month value.
Rule sets and priorities
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 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 functionality)[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 using Disable in in the rule's contextual menu.
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The basic approach to determining the water order 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 EDM allows you to define the ‘look ahead’ period, which is the period that can be accurately forecasted. You can use the Expression Editor to define the method of forecasting. The recommended methods for determining the forecast period are to refer to an upstream node with a known travel time.
In Source, the environmental demand node is used to model environmental demand, which can be set up in two ways:
- As an in-stream requirement (In-stream requirement); or
- To act as a floodplain (Floodplain).
Further detail about the node's configuration is described in their respective links shown above.