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.
Scale
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.
Principal developer
eWater CRC
Scientific provenance
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.
Version
Source v2.10
Dependencies
The Minimum Flow Requirements node needs to have at least one Storage node upstream of it.
Availability/conditions
Automatically included with Source.
Theory
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 a specified Storage from which water should be released to satisfy minimum flow requirements if they are not met by water ordered by users or other water entering the system.
When the amount of water expected to flow down the river downstream of a storage 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.
Order phase
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 storage to make up the shortfall, what happens? What other constraints apply to minimum flow requirement nodes due to restricted water availability, such as low allocations?
Flow phase
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.
Input data
Minimum daily flow requirements for each month are entered as values in megalitres.
Minimum flow requirement can also be specified using the expression editor. The storage to meet the requirement must also be specified. If ownership is enabled, then the owners of the minimum flow can be specified as a fixed value (%) or by using the expression editor.
Parameters or settings
Model parameters are summarised in Table 1.
Table 1. Model parameters
Parameter | Description | Units | Default | Range |
|---|---|---|---|---|
Storage | Identifies the storage from which the order will be supplied flow | |||
Daily Minimum Requirement | Minimum volume of flows required on a daily basis | ML/d | 0 | Positive number |
Output data
Output data comprises:
- Constituent Output (time series)
- Downtream flow (time series)
- Downstream flow volume (time series)
- Order time
- Orders
- Required Water
- Storage volume (time series)
- Upstream flow (time series)
- Upstream flow volume (time series)
 Orders can also be increased or generated. |