Weir Nodes are different to Storage nodes in that it provides a method of modeling the upstream reach and storage relationship in the stretch of river that the weir inundates. You can define the weir in the same manner as a link, which may be important for constituent modelling. If you do not want to configure storage routing through a weir, you can define the upstream storage relationship as 0. Configuration of a weir is similar to that of a storage routing link. Refer to Configuring storage routing.
Conversion between a storage node and a weir node is available through Tools >> Convert Storages and Weirs. The retained settings during conversion are:
- All the weir setting (geometry, rainfall, etc) will be kept
- The downstream link and outlets will be retained
- Modelled variables will be retained
- Function and data sources will be retained
- Ownership and Constituent data will be retained
Note: Operations override data is lost
Two weir shapes can now be defined. By default the Weir Node will have a rectangular effective storage area, as in the original Source Weir Node. By selecting the Triangular check box the Effective Storage Area of the Weir Node will be calculated using a triangular method which represents the more correct geometry of normal river reaches. Refer to Weirs - SRG for further details.
The weir-related data entered for the storage node refers to the volume of the upstream reach that is inundated for a given operating level of the weir. The outlet relationships of the weir allow you to define a default outlet, which represents the main downstream flow path from the weir. For a re-regulating weir, this should be a Gated Spillway. Ensure that you incorporate the rating curve further downstream of the default outlet to constrain the maximum outlet capacity of the Gated Spillway.
gure 1. Weir, Upstream Reach
Specifying operating targets
Under Operating Targets, both Minimum operating level and Maximum operating level are only used when the storage is configured as a weir. The storage will not release water to satisfy downstream requirements if this results in the water level dropping below the minimum operating level. Likewise, water will be released to prevent the storage rising above the maximum operating level.
Gauged Level and Releases
As for storages, it is possible to overwrite modelled data with observed data in a weir using either Gauged Level and/or Gauged Releases. When you do so, the weir icon changes to indicate this (Figure 2). See Gauged Level and Gauged Releases for more information.
Figure 2. Weir, observed data replaces modelled data
Configuring ordering
When configuring ordering for a weir, refer to Ordering at storages.
Weirs and constituents
Weirs only currently work with marker constituent routing and does not yet work for Lump constituent routing.
Flow processing options in weirs
In the previous versions of Source, only 'Piecewise-linear Integral Method' was available as an option for flow processing and storage volume calculation in weirs . In the new version from 5.13 beta, 'Backwards Euler' Release Manager for Weir Node Models is also available from Edit > Scenario Options> Storages. As in Figure 3, the user can select either Backward Euler Method or Piecewise-linear Integral Method for weirs.
Figure 3. Scenario Options showing weir options
Selecting Backward Euler Method enables some functionality. You can configure storage operating constraints, and also configure outlet path priorities as in Storage nodes. When this method is selected:
- the use of operating constraints will become optional
- each outlet path will have an option to enable releases associated with operating constraints
- a safe release volume will be specifiable
In the previous versions, the option for operating constraints was forced on for weir node as it had only Piecewise-linear Integral Method. Similarly, safe release options were not visible in the previous versions.