6.13 Thomson basin The Thomson basin (Figure 6-23) is located in south-east . The Thomson and Macalister rivers join the before flowing into the Lakes.

Figure 6-23 Map of the Thomson basin

6.13.1 Management arrangements Management of water in the Thomson basin is undertaken by various parties as shown in Table 6-75.

Table 6-75 Responsibilities for water resources management in the Thomson basin Authority Management responsibilities  Operates Thomson Reservoir, which supplies water to the Greater Yarra system – Thomson River Pool entitlement holders (Melbourne surface water supply system) and irrigators in the Macalister Irrigation District  Releases water to the Thomson River for environmental flows and Southern Rural Water

Southern Rural Water  Provides irrigation supplies to the Macalister Irrigation District  Manages groundwater and surface water licensed diversions  Provides bulk water supply to Gippsland Water  Operates Lake Glenmaggie

Gippsland Water  Supplies towns including Sale, Maffra, Heyfield, Stratford and Boisdale

West Gippsland Catchment  Responsible for waterway and catchment management in the Thomson basin Management Authority

6.13.2 2018–19 Water resources overview In 2018–19, rainfall throughout the Thomson basin was mostly 60% to 80% of the long-term average. The north- western corners — above the Thomson Reservoir and south of Mount Buller — received between 80% to 100% of the long-term average. Catchment inflows were 48% of the long-term average of 936,400 ML, less than the inflows recorded in 2017–18, which were 58% of the long-term average. The long-term average presented has been revised from the previous accounts: see chapter 6.1.2 for details. Storages started the year at 52% of capacity and ended the year slightly lower, at 43% of capacity. Figure 6-24 Storage volumes and catchment inflows in the Thomson basin

1,400,000 2,000,000 1,800,000 1,200,000 1,600,000 1,000,000 1,400,000

800,000 1,200,000 1,000,000 600,000 800,000 Inflow (ML) Inflow 400,000 600,000

Storage Volume (ML) 400,000 200,000 200,000 0 0

Volume in storage at end of year Unfilled capacity Catchment Inflow Long-term average inflow

In 2018–19, the first seasonal allocation for the Macalister Irrigation District for high-reliability water shares was announced on 4 July 2018 at 40% and increased to 100% by the end of August 2018. A seasonal allocation for low- reliability water shares was announced at 35% in December 2018. Both sections of the Avon River had restrictions on licensed diversions from September to December 2018 and total bans from January to May 2019. Licensed diversions from Valencia Creek were restricted from August to December 2018, with total bans also implemented between January and May 2019. All streams reverted to a stage 1 roster in June 2019. There were no restrictions on urban water use in the Thomson basin in 2018–19, with all towns in the basin remaining on permanent water-saving rules throughout the year. In 2018–19, 418,827 ML of water was diverted for consumptive uses: town, domestic and stock, irrigation and commercial supply. This was more than the 377,070 ML diverted in the previous year. 6.13.2.1 Water for the environment The are important environmental assets partially dependent on water in the Thomson basin. The lakes are listed as internationally significant wetlands under the Ramsar Convention and rely on freshwater inputs from basins including the Thomson basin to function ecologically. Other important environmental assets include:  the upper Thomson River (a heritage river reach) and its Australian grayling populations  the , supporting seven migratory native fish species, platypus and the water rat. In 2018–19, water for the environment in the Thomson basin comprised:  the Bulk Entitlement (Thomson River – Environment) Order 2005 comprising 3.9% share of inflows (on average 8,000 ML a year) and 10,000 ML of high-reliability entitlement held by the VEWH and water set aside for the environment through the operation of passing flows  the Macalister River Environmental Entitlement 2010 comprising 12,461 ML of high-reliability and 6,230 ML of low-reliability entitlements held by the VEWH  water set aside for the environment through the operation of passing flows released as a condition of consumptive bulk entitlements held by Southern Rural Water  water set aside for the environment through the operation of passing flow conditions on licensed diversions  all other water in the basin not allocated under entitlements: this water also provides social, recreational and cultural benefits. In 2018–19, a total of 27,823 ML of environmental water was delivered in-stream in the Thomson basin. 6.13.3 Water balance The total volumes of water available and supplied from water resources in the Thomson basin in 2018–19 are shown in Table 6-76.

Table 6-76 Water balance – Thomson basin Water account component Note 2018–19 (ML) 2017–18 (ML) Major on-stream storage Volume in storage at start of year 1 650,555 690,671 Volume in storage at end of year 1 534,357 650,555 Change in storage (116,198) (40,116) Inflows Catchment inflow 2 451,419 546,194 Rainfall on major storages 1 12,605 14,931 Return flow from irrigation 1,184 1,745 Treated wastewater discharged back to river 3 28 31 Total inflows 465,237 562,902 Outflows Diversions Urban diversions 1,614 1,490 Transfers to basin for urban use 198,850 133,540 Irrigation district diversions 191,057 211,347 Licensed diversions from regulated streams 29,954 26,155 Licensed diversions from unregulated streams 4 3,596 4,060 Small catchment dams 5 335 478 Total diversions 425,406 377,070 Losses Evaporation losses from major storages 5 16,543 18,756 Evaporation from small catchment dams 415 538 In-stream infiltration to groundwater, flows to floodplain and evaporation 10,695 12,761 Total losses 27,652 32,055 Water passed at outlet of basin River outflows to Latrobe River 106,794 164,487 River outflows to Lake Wellington 21,583 29,406 Total water passed at outlet of basin 128,377 193,893 Total outflows 581,435 603,018

6.13.3.1 Notes to the water balance 1. Storage Major on-stream storages in the Thomson basin are included in the water balance. Table 6-77 shows how storage volumes changed during the year.

Table 6-77 Storage volumes in the Thomson basin Catchment Total Start End volume Rainfall Evaporation inflows less Storage capacity volume in in store (ML) (ML) regulated (ML) store (ML) (ML) releases (ML) On-stream storages Lake Glenmaggie 177,640 42,936 364 1,261 316 42,355 Thomson Reservoir (1) 1,068,000 607,619 12,241 15,282 (112,576) 492,002 Total 2018–19 1,245,640 650,555 12,605 16,543 (112,261) 534,357 Total 2017–18 1,245,640 690,671 14,931 18,756 (36,291) 650,555 Note (1) Volumes in store in the Thomson Reservoir do not include 55,100 ML in dead storage.

2. Catchment inflow Catchment inflow is the balancing item in this water balance. It is the difference between the total outflows, the known inflows and the net change in storage volume. The 2017–18 catchment inflow volume has been corrected from the previous accounts. An error was made with the unregulated diversion, which in turn caused an error in the catchment inflow amount. 3. Recycled water Water recycled at wastewater treatment plants can be used to supplement water available in the basin. Table 6-78 lists the wastewater treatment plants in the Thomson basin. Water discharged to the environment from treatment plants is included as an inflow to the water balance. In addition to the recycled water reported below, 1 ML was returned from to Charity Creek and other waterways during the water year.

Table 6-78 Volume and use of recycled water in the Thomson basin t e e Type of end use (ML) e dis um um um um rec rec Vol Vol Vol Vol pro Per cen oce duc e of Wastewater treatment plant process industrial allocation allocation Beneficial Urban and Agriculture Within plant Within

Heyfield 32 32 100% 0 32 0 0 0 0 Maffra 279 279 100% 0 279 0 0 0 0 Rawson 27 0 0% 0 0 0 0 27 0 Sale 923 923 100% 0 923 0 0 0 0 Stratford 66 66 100% 0 66 0 0 0 0 Total 2018–19 1,327 1,300 98% 0 1,300 0 0 27 0 Total 2017–18 1,427 1,395 98% 0 1,395 0 0 31 0

4. Licensed diversions from unregulated streams The volume of diversions from unregulated streams reported for 2017–18 has been amended from the Victorian Water Accounts 2017–18, due to a change in the definition of unregulated licences, which chapter 6.1 explains. 5. Small catchment dams Water harvested and used by small catchment dams (farm dams) is included in the water balance. Table 6-79 provides information about small catchment dams in the basin.

Table 6-79 Estimated small catchment dam information for the Thomson basin Evaporation loss Total water Type of small catchment dam Capacity (ML) Usage (ML) (ML) harvested (ML) Domestic and stock (not licensed) 5,396 250 378 628 Registered / licensed commercial and irrigation 3,175 85 37 121 Total 2018–19 8,572 335 415 749 Total 2017–18 8,572 478 538 1,016

6.13.4 Compliance against entitlements Compliance against water entitlements is reported for this basin in three areas:  entitlement issued: the volume of entitlements issued in a basin does not exceed formal caps or has not increased without appropriate approvals  water taken: the volume of water taken during the year does not exceed the volume considered to be available for consumptive and/or in-stream use during that year  bulk entitlement provisions: holders of entitlements do not breach any provisions that are documented in their bulk entitlement orders.

Thomson – Key compliance points  There was no net increase in the total entitlement volume from the previous year.  The total volume diverted (452,370 ML) was within the volume available for the year (469,720 ML.  No individual bulk entitlement holder took more than the annual volume made available to them.  Melbourne Water’s Thomson River bulk entitlement has an annual diversion volume of 171,800, and in 2018–19 Melbourne Water took 198,850 ML under this entitlement. Annual exceedance is acceptable as long as the cumulative credit/debit balance meets the requirement of the diversion limit compliance method.  Individual bulk entitlement holders complied with all provisions in their entitlements.

Entitlements in the Thomson basin provide the basis for how water is shared in the basin. Rights to water in the Thomson basin are outlined in Table 6-80. Melbourne Water holds a bulk entitlement to divert surface water from the Thomson River. This entitlement is one of four which contribute to the Greater Yarra system – Thomson River Pool which primarily supplies Melbourne and supports regional urban water corporations Barwon Water, Western Water, South Gippsland Water and Westernport Water (Table 6-104 and Table 6-105). Details of the entitlement arrangements are provided in the Yarra basin chapter. Surface water is also diverted by licensed diverters and is harvested in small catchment dams. The VEWH holds environmental entitlements for the Thomson River and the Macalister River. Water available under these entitlements is used to support streamflows and is not diverted out of waterways in the basin. Table 6-80 Entitlement volumes in the Thomson basin Annual Water entitlement entitlement volume (ML) Bulk Entitlement (Thomson Macalister – Southern Rural Water) Conversion Order 2001 (1) High-reliability water shares 155,819 Low-reliability water shares 74,605 Bulk Entitlement (Thomson Macalister Towns – Gippsland Water) Conversion Order 2005 2,335 Macalister River Environmental Entitlement 2010 (3) Macalister River Environmental Entitlement – high-reliability 12,461 Macalister River Environmental Entitlement – low-reliability 6,230 Subtotal: Macalister River Environmental Entitlement 2010 18,690 Subtotal: Bulk Entitlement (Thomson Macalister – Southern Rural Water) Conversion Order 2001 251,449 Bulk Entitlement (Thomson River – Melbourne Water) Order 2014 (2) 171,800 Bulk Entitlement (Thomson River – Environment) Conversion Order 2005 (3) Thomson River – high-reliability 10,000 Share of inflows (3) n/a Subtotal: Bulk Entitlement (Thomson River – Environment) Conversion Order 2005 10,000 Take and use licences – unregulated surface water 17,207 Licensed small catchment dams – on-waterway (4) 30 Licensed small catchment dams – off-waterway (4) 3,145 Total (30 June 2019) 453,632 Total (30 June 2018) (4) 453,632 Notes (1) Under this bulk entitlement, Southern Rural Water operates Lake Glenmaggie and Cowwarr Weir to supply water share holders in the Macalister Irrigation District and diverters on the Thomson and Macalister rivers and Rainbow Creek, and to supply water to Gippsland Water’s Thomson Macalister towns bulk entitlement. (2) Melbourne Water holds the source bulk entitlement on the Thomson River. The annual entitlement volume is the annual diversion limit for Melbourne Water’s Yarra River, Thomson River and Silver and Wallaby Creeks bulk entitlements. The limit is calculated using a method for showing compliance with diversion limits approved by the Minister for Water in February 2018. This water is used to supply primary entitlement holders — City West Water, South East Water, Yarra Valley Water, Barwon Water, Western Water, South Gippsland Water and Westernport Water — with entitlement to the Greater Yarra system – Thomson River Pool, which sources water from the Yarra River, Thomson River, , Silver Creek and Wallaby Creek. (3) The Bulk Entitlement (Thomson River – Environment) 2005 previously consisted of a 10,000 ML high-reliability entitlement only. On 1 June 2017, the bulk entitlement was amended to reflect the addition of a new component of the entitlement, consisting of a 3.9% share of inflows into storage, with the actual volume available in any year varying, depending on inflow conditions (8,000 ML a year on average). (4) Reporting for unregulated entitlement volume has changed in 2018–19. The definition of ‘take and use licences – unregulated surface water’ was amended and a separate category for small catchment dams included. The prior-year entitlement volume has been adjusted from the 2017–18 accounts to reflect this change, which chapter 6.1 explains.

Table 6-81 shows the amount available to be taken by entitlement holders and the amount they have taken during the water year.

Table 6-81 Available water and take for the Thomson basin Available water Total Water Water entitlement Opening Allocation Net trade available taken carryover issued in / (out) water Thomson Macalister – Southern Rural Water Water shares (1) - 184,034 () 184,034 176,872 Thomson Macalister Towns – Gippsland Water - 2,335 0 2,335 1,614 Macalister River Environmental Entitlement 2010 (2) (3) 7,773 14,641 0 22,414 15,124 Operating provisions (4) - 42,955 - 42,955 42,955 Diversion: Thomson Macalister – Southern Rural Water (5) 251,738 236,565 Thomson River – Melbourne Water (6) - 171,800 0 171,800 198,850 Thomson River – Environment (2) (7) 8,564 17,165 0 25,729 12,699 Take and use licences – unregulated surface water - 17,278 0 17,278 4,171 Licensed small catchment dams (8) - 3,175 0 3,175 85 Total 2018–19 16,337 453,383 0 469,720 452,370 Total 2017–18 (8) 17,388 453,659 0 471,047 409,676 Notes (1) Allocation issued includes 55,495 ML of spill allocation made available to water shares holders in 2017–18. This was available between 2 December and 15 December 2018, following a spill declaration for Lake Glenmaggie. (2) Water use reported reflects environmental in-stream use. This amount is not reflected in the water balance in Table 6-76 as it does not represent an actual diversion from the waterway. Unused water is available to be carried over under this entitlement (Table 4-4). (3) The environmental diversion reported here is not included in the total diversion for the Thomson Macalister – Southern Rural Water bulk entitlement as the water was not diverted out of the waterway. (4) This reflects use of water to manage the system. It includes any loss incurred in supplying the primary entitlements. There is no specified volume for operating provisions under this source bulk entitlement. (5) The water use reported in this line item represents the net diversion to supply primary entitlements and fulfil other operating requirements under the Thomson Macalister source bulk entitlement (net of return flow from irrigation). It includes in-stream environmental diversions of 15,884. (6) This is the volume diverted in 2018–19. Annual exceedance is acceptable as long as the cumulative credit/debit balance meets the requirements of the diversion limit compliance method. As noted in the 2017–18 accounts, the 2017–18 annual diversion (133,540 ML) was recalculated as part of a diversion limit compliance assessment undertaken by Melbourne Water using the method approved by the Minister for Water in February 2018 for showing compliance with diversion limits for the Yarra River, Thomson River and Silver and Wallaby Creeks bulk entitlements, and it was confirmed to be compliant with the Thomson basin diversion limit. (7) Allocation and use under the Thomson River – Environment entitlement included 2,500 ML allocated and used under the passing flows component of the entitlement. (8) Water taken from licensed small catchment dams has been reported in this table for the first time in 2018–19. The prior-year totals have been adjusted from the 2017–18 accounts to reflect this change, which chapter 6.1 explains.