6.8 Modified Flow

43, 44, 45, 47,48: Betterridge & Rabbidge, 2016 46: MidCoast Council, 2020 49: MidCoast Council, 2019

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.

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

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).

Potential impacts caused by reduced freshwater

inflows from water allocations and drought include upstream saline intrusion and hyper-salinity in upstream aquatic habitats, coastal wetlands, riparian zones and groundwater dependent ecosystems.50

Other potential impacts on the estuary include

reduced nutrient and organic inputs for primary production and alterations to the physical features of the estuary mouth.51

The drought of 2019 caused a range of impacts

across environmental, social and economic dimensions. Farming families experienced personal and financial stress, buying feed from as far afield as Victoria and struggling to de-stock as cattle prices plummeted. Much of the catchment ran dry. Platypus and turtles were exposed to predation by foxes. Large river oaks died. There were significant impacts to water quality such as increased salinity and algal outbreaks.

Water governance is complex, and MidCoast

Council has limited influence. In NSW the key legislation to manage flow and extraction is the NSW Water Management Act 2000 (WMA 2000). It is administered by WaterNSW (rural landholders, rural industries) and the Natural Resources Access Regulator (NRAR). Under the WMA 2000, Water Sharing Plans provide a legal basis for sharing water between the environment and consumptive water users. The sharing of water must protect the water source and its dependent ecosystems as well as basic landholder rights. The NSW Government’s Water Sharing Plan for the Lower North Coast Unregulated and Alluvial water sources (2009) regulates license allocations for town use, farms, irrigators and industry, and reserves environmental water for the overall health of the river and aquifer. DPIE is responsible for managing and allocating groundwater resources as set out in the Water Sharing Plan. To ensure local impacts are monitored and managed, all applications for new bores and trades are individually assessed. Bores for basic landholder rights (stock and domestic use) are exempt. DPI Water licences irrigators. Licences set out how much water can be taken; what size pumps and other equipment can be used; where pumps can be located and where water can be applied. During low flow periods, cease-to-pump (CTP) rules protect environmental flows, excluding licences held by local water utilities, licensed stock and domestic users, and licences used for food safety and essential dairy care (Betterridge & Rabbidge, 2016). Stakeholders include: NSW Department of Planning, Industry, and Environment DPIE – Water Planning Group; NSW DPIE – Water and Science Group; Natural Resources Access Regulator (NRAR); MidCoast Council (MCC); Department of Primary Industries DPI – Water; Manning Water Users Association; Barrington Irrigators Group; farmers and irrigators; large water users. Related issues: Biodiversity loss