The Environmental Flow Node (EFN) is designed to simulate environmental flow requirements according to a set of actions. Environmental flow requirements may generally be classified as either in-stream or floodplain requirements , 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.
Actions
The EFN provides a means of capturing prescriptive descriptions of water patterns that the environment requires. These definitions of watering patterns are captured as ‘actions’ within the EFN and many combinations of actions can be prescribed. The two types of actions presented in the EFN have been designed to capture the most commonly defined environmental flow requirements specified in environmental flow studies and water regulations. These actions allow you to construct a collective environmental water requirement by using combinations of environmental demand rules. These are:
- Spell based - A spell can be defined as a period of time that the flow has a set of desired characteristics. The environmental flow node can only currently create high flow events i.e. flows over a specified threshold. This type of action can by used to specify a flood fresh, usually associated with a recruitment event such as to trigger fish movement, water floodplain vegetation;, a flow pattern or a minimum flow, usually applied to maintain minimum habitat requirements; and
- Translucency - specifies the flow requirements in terms of some other time series, usually the release from a dam based on the inflow of the dam.
A combination of these actions can be used to meet specific environmental outcomes. They are configured in the environmental flow node's feature editor..
For each action in the EFN, you can configure several characteristics that can be altered. A common feature across action 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.
Using the node in Source
Double-click the node to open its feature editor, shown in Figure 1.
The Specify maximum account deduction parameter allows you to specify maximum account deduction which will limit water debited to an accounting system; if this deduction cap is more than total order water, the total order water is debited. This parameter can be specified as a value or a function.By default the volume a node orders (on top of the downstream order), i.e. the residual requirement, is accounted for. Here, the user can specify a function to limit that volume to a maximum, for example: Min(0, Residual Requirement – Minimum Constraint), so that water already in transit is not included in the account deduction. This could also allow for re-crediting of return flows, if the maximum volume would be allowed to go negative.
Right clicking on the top Action menu item allows you to add either a Spell Based or Translucency Action. Multiple actions and action types can be added to a single node. The actions will work together to determine a total requirement per timestep.
Right clicking on the action title allows you to rename, delete or enable/disable the action.
Figure 1. Environmental Flow Node
Spell Based
Flow rules can be made active or inactive dynamically during a modelling run. In order to control rules throughout the model run, each rule can have a defined condition threshold. This condition threshold is compared to the ‘condition’ time series for each time-step and the flow rule is 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.
Figure 2. Spell Based Action menu
| Season:
[IT1] : [IT2] : | Period in which action is required (this is to specify a season within a year, the year specified has no relevance). |
| Number of spells in season: | Action could include a number of independent spells. |
| Minimum interval between planned spells: | only relevant in case the action consists of more than 1 spell. This is to specify the required period between spells to consider them independent spells. |
| Desired frequency: | Determines the desired return (or recurrence) interval. |
| Initial condition: | This is to determine the initial condition when the flow node is operating independently from an Environmental Flow Manager. The initial condition is based on how Desired Frequency has been defined. The user specifies the number of successful spells in the period (as used for the Desired Frequency) before the start of the run. |
| Allow orders: | If this box is not ticked, the flow node will only record (natural/unregulated) success of the actions. It will not place any orders. |
| Allow forcing of spells: | Turn this on if the flow node should try to force an action without the flow trigger being met. |
| Number of season failures before forcing | When the tick box above has been turned on, the user needs to specify after how many unsuccessful seasons the EFN should start forcing the action. This would usually be a longer period than the return period (e.g. if an event is desired 1 in 3 years, you may want to force after 5 unsuccessful years). |
| Time since last successful spell | : This is to initialise ‘Time since last successful season’ (so that initial Antecedent Condition can be determined). |
| Time since last successful spell in a successful season | This is to initialise ‘Time since last successful spell’ (so that initial Antecedent Condition can be determined. |
Spell Definition
Figure 3. Spell Definition menu
Figure 2. Spell Based Action menu
Success Criteria
Figure 4. Spell Based Action Success Criteria Menu
Rise and Fall
Figure 5. Spell Based Action Rise and Fall Menu
Translucency Action
This action allows you to define conditions (in the Condition item) where flow would be allowed to pass through a storage or restrictions be placed on extraction in an unregulated system. It does not require an augmentation method as orders will be determined based on the inflows to the storage for the current time-step.
Figure 6. Translucency Action Menu
