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Overview

Description and rationale

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Structure & processes

Theory

Introduction

The Murray Darling Basin Agreementenables the operators in the River Murray to exchange the ownership of volumes of water between the states of New South Wales (NSW) and Victoria when the lending state has water surplus to its requirements. An example of this is when state owned tributary inflows are greater than expected. These excess tributary flows result in a state’s share of water in the river being surplus to that required to meet to meet its ordered requirements. Where possible, this excess water is utilised by the other state (owner) and the amount of water that needs to be released from storage is reduced. The water used by the other state (owner) is termed a borrow and is reconciled against the state’s water share. In the case of the River Murray, payback and account balances are reconciled at Lake Victoria.

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Anchor
Assumptions and constraints
Assumptions and constraints
Assumptions and constraints

Table 1. Assumptions and constraints
NoAssumption/constraint
1An ownership system must have a global borrow and payback system.
2An ownership system’s global borrow and payback distribution hierarchy applies in all storages where there is no local borrow and payback system.
3Borrow and payback systems only operate when ownership is enabled.
4A borrow can occur anywhere in an ownership system when one or more owners has insufficient water to meet requirements.
5When a global borrow and payback system is reconciled/paid back at a storage, the payback storage must maintain a local borrow and payback system. 
6For payback at a storage, owners are checked to see if they have to forfeit lending credit if they do not have enough airspace available. This is to ensure that the owner has enough capacity to be repaid.
7When a global borrow and payback system is reconciled/paid back at a storage, all owners in the system must payback water at the same storage.
8

Borrow and payback accounting will occur prior to resource assessment. Resource assessment and accounting must consider the total sum of all borrows in the model, and thus includes:

  • the global net borrow-payback matrix 
  • any local net borrow-payback balances held at user configured storages
9 The borrow network for the global borrow and payback system must be complete. That is, there must be a connection between each owner and every other owner (the connection can be made at any priority level).
10 The borrow network for sharing a system constraint must be complete. An operator is not going to refuse service to an owner if there is surplus capacity available to use to serve them. 

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