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• The start of the off allocation water year,
• Whether the sharing arrangement is on the basis of trying to equalise access opportunity to account holders, however, the Equalise Shares function is no longer accessed by the user since version V4.10.2 of Source.
• Optional annual system cap on the amount of off allocation water that can be allocated in a water year,
• Optional rules for resetting account balances when specified storages spill,
• Configurable list of storages that are considered for off allocation access, and
• Off allocation accounts.
  
  

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During the flow phase, when an OAN is reached the off allocation sharing process is undertaken.  The process is illustrated in Figure 4.  The first step in the process is to check if accounts need to be reset and the second step is to determine the off allocation volume to share. Finally if there is off allocation volume to share this volume is shared to users according to shares and account type sharing rules. Initially the volume is constrained to the system and account type cap. If volume still remains the appropriate sharing threshold and associated priorities are determined. Noting that if the first threshold is not reached then no sharing occurs. Users’ shares are then constrained to their remaining cap. Starting at the highest priority users first, signified by the lowest priority number, group these users together for sharing. If equalise access opportunity has been specified then users with less access share are brought up to the next highest access share. This is repeated until all access shares are equalised or no more off allocation volume remains. Any remain volume is then shared to water users according to their shares. If there is any remaining off allocation and there are more priority levels then the process moves to the next priority level and repeats the process until there is no more off allocation volume of all the users in all priority levels have been satisfied.

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1. Save each owner's request for off-allocation water (the volume at the OAN; i.e. adjusted for losses).
   
   
   

2. If ownership is enabled and there is more than one owner, the owner loss contribution, Loss(wu, owner), in meeting the request for each water user at the OAN, are determined. Determine the loss contribution of each owner describes how this is done.
   
   
3. The volume of off-allocation water that is available, Vol_OffAlloc , is calculated. See Determine the off-allocation volume below for details.
   
   
4. The off-allocation water is allocated. If ownership is not enabled or there is only one owner, the steps below are only performed once. When there are multiple owners, they are repeated until either there is no off-allocation water to share, or all requests are met, or the system's usage limit has been reached (if there is such a limit).
   
   

   1. A check is made to see whether there is any off-allocation water to allocate, or not. If there is no off-allocation water (remaining) to share (ie. if Vol_OffAlloc = 0  or Vol_OffAlloc < lowest volume allocation level ), the allocation procedure stops here.

   2. How much of the total requested volume at the OAN can be met/supplied is determined.

      

      
      

      If met ≤ 0 , the allocation procedure stops here.

      
      

   3. If there is a usage cap defined for the off-allocation system, a check is made to see if there is remaining usage capacity. This is calculated based on the current usages of all accounts a at every OAN in the off-allocation system:

      

      
      

      If LimitUsage(system) = 0 , there is no remaining system cap to share, so the allocation procedure stops here.

   4. The off-allocation delivery efficiency is determined for each account using the following equation:
      
      

      
      where a is the account for a downstream water user. (Recall that each water user which requires off-allocation flow to be allocated to them from a particular OAN in the river system holds one off-allocation account at that node.)
      
      

   5. Determine the maximum volume of a request remaining to be fulfilled for each off-allocation account a at downstream water users:

      1. If there is a usage cap configured, it is the smaller of the request and the remaining usage cap
         
         

      2. Otherwise, it is the requested volume
         
         
         
         
      3. If no account has LimitUsage(a) > 0 , the allocation procedure stops here.
         
         
   6. Off-allocation water is allocated to accounts at the OAN. At every priority level, in order from highest to lowest, the following occurs:If the equalise shares option has been selected, account allocations/usages at a given priority level are equalised based on their usage to shares ratio. Equalise shares of off-allocation water describes how this is done.
      

Remaining off-allocation water is allocated to accounts at the given priority level according to account shares. Allocate off-allocation water to accounts based on shares describes how this is done.

1. 1. At this stage the OAN may have met each of the water user's owner requests and thus supplied more water than the water user requires – as the total request was placed for every owner. The steps that follow check for this and re-distribute any excess allocation – firstly to other water users of the same ownership, then to other water users. The process depends on how many owners there are:
      
      If ownership is disabled or there is only one owner, usage is simply updated:
      
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      Otherwise (i.e. there is more than one owner):

      1. Any excess is redistributed according to the method described in Re-distribute off-allocation excess.
         
         
      2. The usage for this round of allocation is updated
         
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      3. Return to step 3. The next round will redistribute any losses met by other owners to water user accounts with insufficient water to meet requests.
         
         

2. Account balances for every account at the OAN are updated
   
   

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1. The excess off-allocation volume available for re-distribution is initialised:
   
   

2. For each water user, excess off-allocation water is redistributed:

   1. The access ratio for each off-allocation account and the total of these account ratios for each water user are determined, 
      where a is the account for water user and owner owner.
      
      

   2. The access ratio is checked to determine whether water in excess of the total request has been allocated:

      1. If AccessRatio ≤ 1 , there is no excess to redistribute. The remaining request to be met is calculated as:
         
         

         
         Skip to the next water user.
         
         

      2. Otherwise processing continues in order to redistribute excess between owner accounts.
         
         
      Distribution of a water user's excess off-allocation water
      Assuming that a water user will try and maximise its access to off allocation water, Source uses each owner's off-allocation water on the basis of its allocation (an indication of licence priority), or its remaining capacity to receive water if accounts are capped. The account with the largest allocation has this adjusted first until it is the same as the next largest, and so on. This cycle is repeated until all the excess off allocation water is allocated or accounts have no remaining capacity to receive water.
      
      
   3. The new allocation for each water user's off-allocation account is initialised:
      
      

      1. If accounts are capped:
         
         

         

      2. Otherwise
         
         

         
         where a is the account for water user and owner owner.

         

   4. The owner accounts for each water user are ranked in order of allocation, newAlloc(owner), from highest to lowest.
      
      

   5. Excess is allocated to owners in the ranked order until the total remaining request volume is met, but the allocation is equalised so that lower priority owners also get some water – the result is a new 'equalised' allocation, newAlloc(owner).

Note that this process is no longer activated since Source V4.10.2.

remvol= Requestwu
do i= 2, nowner
	sum= 0
	do j= 1, i-1
		sum= sum +rembal(ptr(j))
	end do
	vol= min(remvol,sum-rembal(ptr(j)*(i-1))
	do j= 1, i-1
		rembal(ptr(j))= rembal(ptr(j))-vol/(i-1)
	end do
	remvol= remvol - vol
	If( remvol <= 0 ) exit
end do
if( remvol > 0 ) then
	sum = 0
	do j= 1, nowner
		sum= sum + rembal(ptr(j))
	end do
	vol= min(remvol,sum)
	do j= 1, nowner
		rembal(ptr(j))=rembal(ptr(j))-vol/nowner
	end do
	remvol= remvol- vol
end if

1. The allocation for this time step is updated for the re-distribution: 

   Image Modified

2. The remaining volume of off-allocation water not required by this water user is added to the total to be reallocated to other water users:

   Image Modified

3. The off-allocation volumes are adjusted for losses met by other owners:

   Every owner's ratio of the total off-allocation volume is calculated:
   Image Modified

   The loss met by every other owner is their loss volume (calculated in Step 2 under Flow Phase (Resource Assessment and Allocation)) multiplied by their share of the off-allocation volume. This means that for a given owner, the off-allocation volume adjusted for other owner losses is:
   
   Image Modified

1. Indicate that the water user's request has been met: 
   
   

   Request(a,owner) = 0

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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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