Macquarie Roscco

MACQUARIE ROSCCO

Update on Current Flows 21 January 2020

The recent rain in the catchment below Burrendong Dam has produced some inflows in the tributaries downstream. The flows are being managed under the tributary flow management plan.

The rainfall over three days since 16 January in Burrendong catchment has ranged between 10 and 26 mm. The rainfall in the tributary catchment below Burrendong Dam has ranged between 8 and 66 mm.

The rainfall has been patchy and the consequent catchment response to flows has been varying. Bell River at Neurea peaked at 3400 ML/d and then rapidly dropped. Little River @ Obley peaked at 6000 ML/d and rapidly dropped. Little River @ Arthurville estimated to have produced double the volume produced at Obley. Talbragar with nil flows.

The resultant flows in the Macquarie River at Dubbo has peaked at 4,500 ML/d on midnight 17 Jan and Baroona has peaked at 3,900 ML/d on 18 Jan and Gin Gin has peaked at midday today 20 Jan at 2500 ML/d.

It is estimated that the flows arriving Warren will peak at about 2000 ML/d on 21 Jan with a total volume from the event over 7 days is estimated at about 5000 ML at Warren.

Over the weekend WaterNSW have contacted several representatives of the regulated creeks and the Macquarie River below Warren from the Macquarie Cudgegong ROSCCo to ascertain the stock and domestic water requirements and also to understand the risks and benefits from diverting some of the flows.

WaterNSW have also met with the environmental agencies on the weekend to discuss the critical environmental needs in the regulated creeks and river where the flows are stopped in response to drought operation.

Following these consultations and discussions WaterNSW have resolved to deliver access to Basic Landholder Rights (BLR) and to meet the critical needs of the environment in the following sections,

• Duck Creek at the offtake 60 – 70 ML/d for 6 to 7 days • Gunningbar Ck below Gunningbar Weir at 60 – 70 ML/d for 6 to 7 days • Continue to deliver regulated demand via Albert Priest Channel at 65 ML/d • Remaining flows arriving Warren Weir delivered d/s of Warren Weir • When flows arrive Marebone Weir, about 100 -150 ML/d into Bulgeragar Ck and the rest down the river. • At the end of the event fill Marebone Weir pool for fish refugia • At the end of the event partially fill Warren Weir against the shutters

The landholders in these sections of the river and creeks are advised to take the necessary precautions to manage their stock operations and also by moving pumps to higher locations as appropriate.

Tributary Flow Management Plan is included under appendix 1 in the Annual Operations Plan Macquarie Valley 2019-20 and can be viewed at Annual Ops Plan.

Discussions with the environmental agencies considered the following critical needs of the environment

The current small fresh will assist with destratifying pools, replenish and reinstate refuge areas and provide connectivity along sections of the Gunningbar, Macquarie, Bulgeraga and Duck creek systems, giving some respite for resident freshwater fish, mussels and other biota that have not received baseflow for many weeks or months. It will assist with providing much needed watering for some areas of vegetation that provide essential food and resources to native fish and animals.

Currently, field data from refugia pools, in combination with maximum known cease-to-flow thresholds, indicate that the critical environmental water demands for tributary flows are located in the mid-Macquarie Regulated River, these being:

1. Burrendong to Bell River confluence: this section has not been affected by poor water quality over the weekend and under worst case scenarios, holds the in-situ insurance native fish population. Therefore, this is strongest priority for fish maintenance flows.

2. Bell River to Warren Weir, representing the reach sustained by regulated flows for the near future. Noting that this reach is currently subject to an extreme hypoxic/anoxic water quality event that commenced from 17th January 2020 rainfall event, which may continue downstream and is the location of a lot of fish relocation from below Warren.

Following those priorities, the next set are:

3. refugia pools between Warren Weir and Marebone Weir, including Marebone weir pool

4. Below Marebone, most pools are either dry or have been subject to fish relocation activities to deliver water to long-lived riparian and core wetland vegetation is the environmental priority. Watering the main stream channels and directing larger flows to the northern Macquarie Marshes reedbed, given it was burnt in late October 2019, would be a priority. This would require the closing of the North Marsh Bypass Channel.