The Minimum Flow Requirement node is used to ensure that there is a minimum flow rate at a point in a river system to meet various demands (stock, domestic or environmental needs). It is also used to generate transfers between an upstream and downstream storage. This node imposes a constraint which must be met at that point in the river model, even if additional water must be released from a storage. The requirement can be specified either using a time series, via an expression or as daily values in megalitres. You can also enter minimum daily flow requirements manually or load the data from a file. Table 5 shows the format of a comma-separated (.CSV) file for importing minimum flow requirement data.
You can also nominate the 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 such as tributary flows.
Minimum Flow Requirement node (Configuration)
In the ordering phase, when the amount of ordered water expected (ie. forecast) to flow down the river past a minimum flow requirement is less than the requirement, then an order is placed such that the forecasted flow meets the requirement. If orders are more than the value specified by the requirement, no adjustment is made. In the flow distribution phase, orders cannot be adjusted, so where the actual amount of water flowing down the river past a minimum flow requirement is more than forecast, there may be more water than is required to meet orders. Requirements in the order phase take into account travel time, which can be specified by Travel Time in the node’s feature editor. This is used when the Daily Minimum Requirement is specified for each month (in the Monthly Requirement table). If an Expression Editor is specified, the travel time is not used to calculate the requirement.
When ownership is enabled, you can define a sharing hierarchy to control how the constraint is apportioned between downstream owners (#anchor-24-anchor). See the chapter on Ownership Feature Editor 64). Refer to Minimum Flow Requirement for more information.
As you make changes to owners’ percentages, Source recalculates the column such that any water left over is allocated to "Owner 1". If you enter values that sum to more than 100%, "Owner 1" is set to zero and highlighted in red. Although you can click OK and close the feature editor in this situation, you should avoid doing this as the results may be undefined.
Checking constraints
When a Minimum Flow Requirement minimum flow requirement is enforced, there may be a difference between the amount of water ordered and water released. The differences are recorded by the Recording Manager. For more information, see Identifying Constraints.
Table 5. Minimum Flow Requirement node (data file format)
Row | Column (comma-separated) | |
|---|---|---|
1 | 2 | |
1 | Month | Daily Minimum Requirement (ML) |
2 | month | value |
Where: month is the first three characters of the month name with a leading capital letter (eg "Jan")
value is the minimum daily flow requirement in megalitres for the corresponding month.