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The figure also demonstrates that the critical values of stored water volume for changing Restriction Levels are allowed to change on a monthly basis. For example, a water storage might be expected to have lower levels at the end of a dry season because of water use through this season – and lower levels can be tolerated when an upcoming wet season is expected to provide inflows to the water storage and reduction in water demand. An example consistent with the restrictions above is provided in the figure below. This figure shows that the change in Restriction Level (shown on the y axis on the right) from Level 1 to Level 2 occurs at 45% storage as storage volumes are getting lower and then returns from Level 2 to Level 1 at 55% storage.
The Restriction Curves approach provides a look-up table for Restriction Level that is dependent on the antecedent stored water volume conditions. When applying the Restriction Curves in a Source model the Restriction Level is used to adjust the time series demand for water supply.
The approach is particularly relevant to urban water supply but can also be used to trigger events such as releases from a certain storage, desalination plant supply rates or environmental flows based on salinity levels. The aim of the trigger/restriction curves is to provide a time series that tracks what level of restriction the system is in. This time series can then be used to modify some other variable such as demand or inflow (desalination) as well as being a measure of the standard of service delivered.
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