The Minimum Flow Requirement node represents the minimum flow required for particular activities, such as irrigation, dilution of waste waters, water for environmental flows and urban water supply. The Minimum Flow Requirement node works by imposing a minimum flow which must be met at that point in the stream network, even if additional water must be released from a Storage, but subject to sufficient water being available to supply it.
This node, in common with all others, represents a location and can therefore be considered to be site scale. It is used at every model time-step.
The Minimum Flow Requirements model is based on conceptual representations of rules used for regulating rivers to meet demands. The origin of this model is empirical, arising from practical experience and testing that the model adequately represents actual practice.
The Minimum Flow Requirements node needs to have at least one Storage node upstream of it.
Automatically included with Source.
Minimum Flow Requirement nodes are used only when a storage is included in the model. This node is used to specify a minimum flow requirement that is to be met at that point in the river model, even if additional water must be released from a Storage, provided sufficient water is available. The requirement is applied to the ordering system.
When the amount of water expected to flow down the river downstream is less than the minimum flow requirement, then the specified orders are increased or an order is created if there are no downstream orders. Any additional orders needed to meet the minimum flow requirement are "piggybacked" onto the existing orders and adopt their travel times.
If orders are more than the value specified by the requirement, no adjustment is made to the releases from a storage. Subsequent to a storage releasing water to satisfy orders, there is no adjustment to the flow at a minimum flow node.
During the order phase, orders to meet demands from downstream are increased if they are less than the minimum flow requirement, or an order is created if there are no other downstream orders. Release requirements are subsequently calculated based on the orders, adjusted as appropriate, and forecast unregulated tributary inflows (see Chapter 2 for more information on the need for forecasting of unregulated tributary inflows).
If forecast unregulated tributary inflows are less than the minimum flow requirement and insufficient water is available in storages to make up the shortfall, the minimum flow will not be met.
During the flow phase there is no adjustment to the flow at a minimum flow requirements node, such as further adjustment to releases to compensate for any discrepancy between forecast and "actual" unregulated tributary inflows.
Key assumptions and constraints
Key assumptions and constraints are:
- The constraint applies only to regulated flows.
- Minimum daily flow requirements for each month are input as values in megalitres per day.
The Minimum Flow Requirement can be specified as a value, Data Source, a Funciton, Monthly Pattern, or using Rule Curves.
Minimum flow requirement can also be specified using the function editor. If ownership is enabled, then the owners of the minimum flow can be specified as a fixed value (%) or by using the function editor.
Rule Curves are used to manage storage release for each month based on a trigger. A trigger normally refers to water level or volume of an upstream storage. For more details about rule curves, please see Source User Guide.
Parameters or settings
Model parameters are summarised in
Table 1. Model parameters
|123 Value||A constant flow requirement||ML/d||0||Positive number|
|Data Source||A pre-defined time series represents a series flow requirement||ML/d||Positive number|
|Function Editor||A function to determine flow requirement||ML/d||0||Positive number|
|Monthly Pattern||A value for each month of what the flow requirement will be||ML/d||0||Positive number|
|Rule Curves||A trigger defined using a function||0|
|There is a boolean to enable Interpolate or not||Boolean||False||True/False|
- Constituent Output (time series)
- Downtream flow (time series)
- Downstream flow volume (time series)
- Order time
- Required Water
- Storage volume (time series)
- Upstream flow (time series)
- Upstream flow volume (time series)
Orders can also be increased or generated.