Regional water availability report Weekly edition 16 November 2020 1 Contents 1. Overview ................................................................................................................................................. 3 2. System risks ............................................................................................................................................. 3 3. Climatic Conditions ............................................................................................................................... 4 4. Southern valley based operational activities ..................................................................................... 7 4.1 Murray valley ............................................................................................................................................... 7 4.2 Lower Darling valley ................................................................................................................................... 9 4.3 Murrumbidgee valley ............................................................................................................................... 10 5. Central valley based operational activities ..................................................................................... 12 5.1 Lachlan valley ........................................................................................................................................... 13 5.2 Macquarie valley ..................................................................................................................................... 14 6. Northern valley based operational activities ................................................................................... 16 6.1 Namoi valley ............................................................................................................................................. 17 6.2 Gwydir valley ............................................................................................................................................ 19 6.3 Border rivers ............................................................................................................................................... 19 6.4 Barwon-Darling River system ................................................................................................................... 20 7. Coastal valley based operational activities ..................................................................................... 23 7.1 Bega river22 7.2 Hunter valley ............................................................................................................................................. 24 7.3 Toonumbar Dam ...................................................................................................................................... 26 8. Rural Dam Levels .................................................................................................................................. 27 9. More Information…………………………………………………………………………………………… ... 27 Water availability weekly report 2 1. Overview WaterNSW manages and operates 42 dams and storages to deliver water for environmental, domestic, town water, stock, industrial and irrigation purposes across the state. WaterNSW storages provide supplies to all the major river systems in Western NSW, Greater Sydney, the Southern Highlands, Shoalhaven Bay as well as the Hunter, Bega, and Iron Pot valleys in coastal NSW. The total active storage percentage of rural water supplies on 16 November 2020 was 55.1 percent of the total active storage capacity. This was a decrease of 0.4 percent since last week. The total storage level of urban water supplies on 16 November 2020 was 94.9 percent of the total storage capacity. This was a decrease of 0.6 percent since last week. 2. System risks WaterNSW is working with BOM in assessing the likelihood of filling storages, with the positive seasonal rainfall forecasts, particularly for Burrinjuck Dam, and preparing for pre-releases and flood operations. All floodplain landholders are recommended to review their flood operations plans and be aware of any notifications from BoM and SES. Any floods and floodplain flows that occur in the coming months may also trigger poor water quality, particularly low dissolved oxygen for fish, as floodwaters may pick up significant amounts of accumulated leaf litter. Cease to flow in parts of the Border, Gwydir and Namoi systems as well as the Barwon-Darling system from Mungindi to Menindee, except small flows from the Macquarie River near Brewarrina. Rainfall along the southern and central west slopes and ranges over recent months continues to maintain stream flows and inflows to the dams in the Murray, Murrumbidgee, Lachlan, Macquarie and Peel valleys. Operational plans are being reviewed as these inflows accumulate. Water availability weekly report 3 3. Climatic Conditions Figure 1 - Weekly rainfall totals A high-pressure system east of Tasmania is extending a ridge north along the New South Wales coast, promoting generally benign weather across the state. This system will slowly drift east across the Tasman Sea, to be located near New Zealand by Friday. A broad and slow-moving trough of low pressure will enter the far southwest on Wednesday and track across the interior of the state on Thursday and the east on Friday, bringing a period of unsettled weather. For the first part of the week, the majority of NSW is predicted to remain dry, with the state’s east predicted to receive negligible rainfall. As the week progresses, most of the state is forecast to receive negligible rainfall, with 5 -15 mm forecast to fall along the coastal and southern regions. Figure 2a – First 4-day forecast (17 - 20 November 2020) Figure 2b – Following 4-day forecast (21 - 24 November 2020) Water availability weekly report 4 Climate outlook overview Issued 12 November 2020 Wetter December to February for much of NSW • The fortnight of 16 – 29 November 2020 is likely to be wetter than average for much of NSW. • The outlook for December 2020 to February 2021 indicates a wetter than average three-month period for most of NSW (a greater than 75 percent chance). Figure 3 – 3-month rainfall outlook The ENSO Outlook remains at LA NIÑA. Central tropical Pacific Ocean sea surface temperatures (SSTs) have continued to cool over the past fortnight. The latest NINO3.4 and NINO3 values for the week ending 25 October are −1.0 °C and −0.8 °C. The latest 30-day and 90-day values for the SOI ending 25 October are +5.4 and +7.4. These SOI values have dropped over the last fortnight, most likely largely due to the Madden-Julian Oscillation (MJO) moving over the Maritime Continent region during this period; this influence has now passed. All climate models surveyed by the Bureau anticipate further cooling of the central equatorial Pacific Ocean, and for La Niña thresholds to be met at least until February 2021. The cooling forecast by the models suggest this La Niña event will be of a moderate to strong nature, though conditions are currently weaker than those observed in the 2010 event. Bureau climatologists will continue to closely monitor model outlooks and conditions in the tropical Pacific for further developments to this La Niña event Water availability weekly report 5 Water availability weekly report 6 4. 4Southern valley based operational activities 4.1 Murray Valley Storage and release status • Hume Dam is currently at 79 percent of active capacity and releasing about 14,700 ML/d. The release will vary in line with downstream tributary flows and regulated and environmental demands. • Release downstream of Yarrawonga Weir is at approximately 14,100 ML/d and is likely to remain steady as part of an order for environmental flows. • The Edward River offtake flow (1,550 ML/d) will remain within channel capacity of 1,600 ML/d. • The Gulpa Creek offtake flow (700 ML/d) will remain steady until first week of December 2020 to deliver environmental flow to Gulpa Creek wetlands. • Stevens Weir level is at approximately 4.68 m and will vary marginally to supply environmental water to Wakool-Yallakool system. Currently, the water level upstream of Wakool District Main Canal Regulator is approximately 1.81 m. • Flow downstream of Stevens Weir is approximately 2,700 ML/d and will remain steady. • Flows into Colligen Creek (350 ML/d) environmental water is continuing, the flow will decrease to 325 ML/d this week. • Flows into the Wakool River of (100 ML/d) will reduce to 50 ML/d this week meeting environmental demand. • Flows into the Yallakool Creek of (500 ML/d) will reduce to 480 ML/d this week meeting environmental demand. • Flow in the Niemur River at Mallan School is currently at approximately 300 ML/d and will remain relatively steady over the week. • Merran Creek flow upstream of its confluence with Wakool is approximately 200 ML/d with the flow remaining relatively steady over the week. • Flow in Wakool River at Stoney Crossing is currently at approximately 1,040 ML/d and will remain steady. • Flow at Balranald is approximately 3,300 ML/d. Held eWater volume of about 30,000 ML under The Living Murray (TLM) is being delivered at Balranald Weir to enable fish connectivity with Murray River. The boards that were removed from weir under the drown out conditions will be reinstated during the week as the water levels fall, to meet the November end of system target of 568 ML/day. • Lake Victoria is currently holding approximately 660 GL or 97 percent of active capacity.