17.7 Entitled diversion of non–allocated surface water to users
The volume presented in the water accounting statements (17,571 ML) represents the volume of water diverted in the Melbourne region under take and use licences issued for irrigation, stock and domestic, commercial and industrial and other purposes . Take and use licences specify a maximum entitlement volume, but this does not represent a surface water liability.
Take and use licences exist for unregulated sections of the Bunyip, Maribyrnong, Werribee and Yarra rivers, as well as regulated sections of the Maribyrnong and Werribee rivers.
The following table presents the volume of surface water diverted under take and use licences in the Melbourne region during the 2011–12 year. The licenced entitlement volume is also shown.
|Diversion volume (ML) – metered and unmetered||Irrigation1||2,323||3,136||325||247||6,031|
|Stock and domestic||645||12||305||24||986|
|Commercial and Industrial||468||1,241||17||251||1,977|
|Total diversion volume (ML)||3,982||12,420||647||522||17,571|
1 The volume presented for irrigation does not include:
- water diverted to Melbourne retail authorities for the urban water supply system (17.12 Entitled diversion of allocated surface water to urban water system)
- water diverted under high and low reliability water shares (17.11 Entitled diversion of allocated surface water to users).
The volume presented for this item is a combination of metered diversion data and estimates of non-metered diversions. Southern Rural Water meter surface water diversions for take and use licences in the Maribyrnong, Werribee and Bunyip catchments. Melbourne water meter surface water diversions for take and use licences in the Maribyrnong and Yarra catchments. Diversion data is submitted to the Victorian Water Register.
Metered diversion volumes were obtained from the Victorian Water Register for all catchments for the 2011–12 year.
Where metered data were not available, the diversion was estimated using the following assumptions:
- Diversion volume was assumed to be equal to zero for licences in the Yarra catchment (as per Melbourne water assumptions)
- Diversion volume was assumed to be equal to the licensed entitlement volume for licences in the Bunyip, Maribyrnong and Werribee catchments (as per Southern Rural Water assumptions).
Assumptions, limitations, caveats and approximations
Broad assumptions have been made to estimate unmetered diversions:
- The assumption that the volume diverted under take and use licences in the Bunyip, Maribyrnong and Werribee catchments is equal to the entitlement volume is likely to overestimate the actual diversion.
- The assumption that the volume diverted under take and use licences in the Yarra catchment is equal to zero is likely to underestimate the actual diversion.
The uncertainty estimate for unmetered estimates of diversion were not quantified.