A new option called 'Use Airspace' has been added to 'Ownership' in storage and weir nodes as of Source 5.16. In this release further changes have been made to the ownership in storages calculations to better support this functionality.
Description and rationale
In some circumstances certain storage owners may be able to exceed their share of storage temporarily. These owners should only spill when external spill occurs, and they should be the first to spill in that case. The owner who can exceed their share using the available airspace is called an airspace owner. There are certain conditions of ownership while enabling this functionality.
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Modelling of ownership at nodes is an essential component of modelling water ownership in Source, as it enables ownership to be tracked at nodes in Source models. The rationale for modelling water ownership, and the overall principles, are discussed in Ownership - SRG. This SRG entry deals with those aspects of ownership that apply to water entering, leaving and residing in a reservoir (storage nodes). Rules-Based Ordering - SRG describes how owner orders are created, adjusted and released at storage nodes. More information on the storage node is available in Piecewise Linear approach to Reservoir Routing - SRG.
The ownership in storages is guided by certain calculations such as borrow and payback, spill calculations, suspension of ownership and outlet path ownership. The spill calculations are based on two types of proportional losses sharing method and hence there are two methods of ownership in storage calculations.
The two methods are:
- Owner Capacity Share Proportion - This is the original calculation method (default) and the calculations are based on the storage capacity share of owners.
- Owner Working Volume Proportion - the new calculation method
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- and is based on the requirement of an owner to exceed its share of storage capacity temporarily. This method uses additions/modifications to the original method.
The required method can be selected from Scenario Options as in Figure 1 below.
Figure 1. Two methods of ownership calculations in storages
The method 'Owner Working Volume Proportion' will be used when a new option called 'Use Airspace' is enabled in the Ownership tab of the Storage node editor. This option has been added to 'Ownership in nodes and links' as of Source 5.16.