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Off-allocation system components

As stated in Overview, an off-allocation flow sharing system is described by:

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• Using a matrix to solve the owner's share:
  
  

  
  

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Equalise shares of off-allocation water Equalise shares of off-allocation water

Equalise shares of off-allocation water

This is an optional process that is undertaken only if the modeller specifies that it should be done. The following steps are repeated until either there is no more off-allocation water to assign, or the lowest account usage to share ratios are equal (see step 3).

1. For a given priority level of accounts, the usage to shares ratio for every OAN account at the current priority level is calculated:
   
   

   
   

2. The two accounts at this priority level with the lowest ratios are found
   
   

   

   
   

3. Check to see whether the two lowest ratios are the same:
   1. If this is the case (MinRatio = NextRatio), the equalised allocation process is finished – exit this priority level and move on to the next one.
      
      
   2. Otherwise continue on.
      
      
4. For each account a at the current priority level, the following occurs:
   1. If Vol_OffAlloc = 0 then equalisation ends.
      
      
   2. If the account request/usage limit has been reached (LimitUsage(a) = 0), this account is skipped and processing of the next one starts.
      
      

   3. The volume required to bring the ratio of the current account up to the second lowest accounts ratio is calculated:
      
      
      
      
      
      
      
      

      
      

   4. Water is allocated to the account and limits are updated
      
      

      

      

      
      

   5. Reduce the volume of off-allocation water available to share
      
      

      
      

5. Return to step 1 to continue equalisation.

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Allocate off-allocation water to accounts based on shares Allocate off-allocation water to accounts based on shares

Allocate off-allocation water to accounts based on shares

Firstly, at the current priority level, p :

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1. Limit the share volume for an account (Note that if LimitUsage(a) is not specified by the modeller its value defaults to a very big number):
   
   
   
   

   
   

   
   

2. Reduce the volume of off-allocation water available to share
   
   
   
   
3. Calculate the volume that this represents at the source
   
   
   
   

4. Calculate allocations for the account for each user and adjust the usage limits if required.
   
   
   
   
   
   

   
   

5. If a system cap has been specified and would be exceeded by allocations in the current time step, then allocations are reduced to fit within cap (otherwise this step is skipped).

   1. Sum the allocations for each user in the current priority level
      
      

      
      

   2. Calculate the volume by which the system cap would be exceeded based on potential allocations
      
      

      
      

   3. Calculate the proportion that each allocation would have to be reduced by to meet the system cap restriction
      
      

      
      

   4. For each OAS node account at the current priority level allocations are adjusted so that they do not exceed the system cap, taking into account the efficiency factors, then the limits for the adjustment are updated:
      
      
      
      
      
      
      
      

      
      

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Re-distribute off-allocation excess Re-distribute off-allocation excess

Re-distribute off-allocation excess

When there are multiple owners, excess water may have been allocated as the water user's requested volume was duplicated for each owner. This method redistributes the excess, then determines the new excess volume for each owner once losses met by other owners at all water users are taken into account.

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Each OAN processes the orders for its direct users downstream (including the next downstream OAN) and passes the combined orders up to the next OAN (if there is one). This means that it is possible to share off allocation water between multiple downstream reaches.
In the example illustrated in Figure 6, below, OAN3 has a share component in OAN2 which also has a share component in OAN1. This means that the off-allocation requirements of water user 3 and 4 are accumulated up the system and are reported as the off-allocation requirement of OAN2. This means that the allocation of off-allocation water to reach 1 takes into consideration the downstream requirements. It is possible to give priority access to downstream requirements by assigning the highest priority to OAN2 in the OAN1 allocation table.
Note that while OAN1 assigns a volume of off-allocation water to OAN2, the processing of OAN2 may result in a change in the volume of off-allocation water available to that reach as the rules specific to OAN2 are used to calculate the available water.

Figure 6 — Example of multiple off allocation reaches

Off allocation and storages

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