6.8 MODIFIED FLOW From an environmental perspective, the full range of flows are necessary to maintain a healthy river system. These include flood flows to scour channels, rework sediments, and inundate floodplains; medium flows to oxygenate water and allow fish passage; and low flows to maintain connectivity and assist the survival of aquatic and riparian flora and fauna.43 Key stressors on flow rates in the Manning include extraction for potable water and irrigation, drought, climate change, sedimentation and infilling of deep pools, and increased peak run-off due to land-clearing and urban development. The total volume of surface water extracted via licenses in the Manning catchment is relatively low, authorised at 78,100 megalitres (ML) from an annual average flow of 2,530,000 ML.44 MidCoast Council’s Water Services team delivers potable water and sewerage services to over 40,000 homes across the LGA. The Manning Water Supply Scheme makes up 90% of water supply in the MidCoast LGA. An entitlement of 17,256 ML/ year is allocated to MidCoast Council for potable town water extracted at Barrington and Bootawa.
43, 44, 45, 47,48: Betterridge & Rabbidge, 2016 46: MidCoast Council, 2020 49: MidCoast Council, 2019
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The majority of extraction licenses in the catchment are used for irrigation for beef pasture and dairy farms.45 Other irrigators include citrus and vegetable growers, turf farms, equine industries and hobby farms.46 Irrigation in the Manning catchment is below the licensed capacity. Of the 180 irrigation licences only about 20% are active; the balance are ‘sleeper’ licenses.47
Manning River Estuary and Catchment Management Program (ECMP)
Basic landholder rights for stock and domestic use are also allowed. All properties with river/creek frontage are entitled to unregulated access for stock and domestic supplies and can store runoff in surface dams up to a volume of 10% of the rainfall falling on the property. Extraction from the tidal pool has the potential to impact on estuary values and requires further study to ensure adequate protection measures are put in place through the Water Sharing Plan.48 Groundwater extraction via bores can impact on both river base flows and Groundwater Dependent Ecosystems (GDEs). An increase in demand of water from aquifers is likely as a result of increasing insecurity in surface water supply.49 This could be a significant risk during drought when the base flow through much of the system is made up of groundwater. In addition to extraction, drought can be a significant stressor on flow, as was seen in 2017-19 when the Manning experienced the worst drought since instrumental records began in 1880. Manning River flow fell below 50 megalitres per day (ML/d) for 90 days, compared to the previous record of 26 consecutive days. Council received reports of illegal pumping when cease-to-pump rules were in place, which were investigated by the Natural Resources Access Regulator (NRAR).
