Potential benefits and impacts of the proposed Chowilla Regulator

The Environment Institute Water Research Centre Water Wednesday Managing the Murray Icon Sites: can engineering save the environment

Environment Institute Water Research Centre Potential benefits and impacts of the proposed Chowilla Regulator Assoc. Prof. Justin Brookes

Chowilla

The current situation

The consequences

Droughts should be perturbations in otherwise sustainable systems They should not be catastrophic

What is the objective Provide water to the floodplain in a way that creates a mosaic of quality habitats, returns resources to the river, waters vegetation and ensures resilience during periods of low flow Pump Environmental Water Allocation Regulator construction

Environmental Watering Sites 2004 – 2009 Also many km of creek fringes during Sept 2005 (15,000Ml/day flow increase and 15cm weir pool raising)

CHOWILLA FLOODPLAIN Propping up ecosystems Chowilla Horseshoe pre- and post-watering.

What are the options for Chowilla • Brookes et al 2006 the construction and operation of an environmental regulator on Chowilla Creek to artificially inundate a large portion of the Chowilla floodplain was the only option considered that came close to halting the decline of Chowilla floodplain ecosystem But urged caution and rigorous risk assessments

A regulator

Natural inundation at 10,000 ML/day

Area inundated with regulator at 10,000 ML/day 9559 ha

Regulator 120000 Recorded Flow to SA 100000 Simulated Inundation Extent w ith Regulator 80000 Flow 60000 40000 20000 0 3/1/77 3/1/78 3/1/79 3/1/80 3/1/81 3/1/82 3/1/83 3/1/84 3/1/85 3/1/86 3/1/87 3/1/88 3/1/89 3/1/90 3/1/91 3/1/92 3/1/93 3/1/94 3/1/95 3/1/96 3/1/97 3/1/98 3/1/99 3/1/00 3/1/01 3/1/02 3/1/03 3/1/04 3/1/05 Year The regulator would be operated for 3 months every 3 years Otherwise totally transparent

Risk Assessments • Consideration of events & regime • Floodplain salinisation • Vegetation condition • Weeds • Algae • Water Quality • Geomorphology • Frogs • Fish • Birds

Vegetation – modelling results Area Dead Dead Poor Poor Good Good Vegetation (ha) (ha) (%) (ha) (%) (ha) (%) 2007 Red Gum 3,530 653 19% 1,019 29% 1,858 52% Black Box 4,689 1,106 24% 2,821 60% 762 16% Understorey 9,452 9,452 100% 0 0% 2037 Red Gum 3,530 892 25% 957 27% 1,681 48% Do-nothing Black Box 4,689 1,551 33% 2,503 53% 635 14% Understorey 9,452 9,452 100% 0 0% 2037 Red Gum 3,476 302 9% 537 15% 2,637 76% Regulator Black Box 4,589 1,100 24% 2,104 46% 1,385 30% Understorey 9,452 6,388 68% 3,064 32% 17,517

River Red Gum response to environmental watering • While the majority of trees respond to watering they do not fully recover until a second or third watering •River Red Gums have exhibited a significant increase in canopy cover following a second watering •A significant fraction of trees that respond to the initial watering, but do not receive a second watering can be expected to die

Painted Frog Peron’s Tree Frog Southern Bell Frog – EPBC Spotted Marsh Frog Act listed 20

Summary • Regulator will benefit frog species • Improve connectivity between wetlands • Improved habitat conditions (increased habitat diversity) • Increased breeding opportunities • Risk of increase in Common Carp • No major or significant impacts due to the regulator Long-thumbed Frog Eastern Banjo Frog

Fish in Chowilla system Key features • small-bodied species abundant • callop and cod population – associated with fast-flowing habitats Threatened species • healthy Murray cod population - high abundance - a range of length (age) classes (not in the main stem) • silver perch present • catfish present • Murray hardyhead recorded Non-native species • carp abundant

Summary • Using the Chowilla Regulator to simulate floods on the Chowilla Floodplain with low inflows (e.g 10,000 ML/d)  directly benefits some small-bodied native fish species and bony herring  would not benefit Murray cod, silver perch, callop or freshwater catfish • periodic reduction in fast flowing habitat  benefits non-native species (carp) with high inflows (e.g 30,000 ML/d)  would minimise all risks  benefits small-bodied fish and possibly callop but Murray cod passage remains an issue  benefits non-native species (carp)

Summary • Using the Chowilla Regulator to simulate floods on the Chowilla Floodplain with low inflows (e.g 10,000 ML/d) and low regulator height  directly benefits some small-bodied native fish species and bony herring  would not benefit Murray cod, silver perch, callop or freshwater catfish • with frequent use of the regulator these species are very likely to decline to some extent  benefits non-native species (carp)  potentially maintains fast-flowing habitats • less adult Murray cod would leave the system • Murray cod may continue to spawn at similar to present levels • Larval mortality and recruitment could be less  Murray cod passage remains an issue

Birds In general birds will benefit Ground-foragers – determined by abundance of terrestrial arthropods + suitable microhabitats Terrestrial birds – Greater tree health and canopy support higher diversity of herbivores – support a broader range of bird species Need to replace large trees that have breeding hollows

Cyanobacterial Risk • The major risk from cyanobacteria in the River is taste and odours entering the potable supply • Cyanobacteria restricted to the wetlands are of little consequence – Short-lived and little impact • The major risk is from cyanobacteria is return flows to river

Flow • Flow > 10000ML/day in river channel maintains mixed conditions and cyanobacteria are selected against

Summary Assessment • Do nothing is unacceptable • Significant benefit can be achieved • Most objectives & targets can be achieved • Risks need to be managed by maintaining flows • Further assessment of fish (large bodied) in progress – uncertainty remains • Detailed planning, extensive monitoring and caution essential

Should we proceed to construction? • On balance weighing up risks and benefits – YES • To not act and maintain this unique region would be irresponsible • Do we want more regulators in the river? – NO but we need to be pragmatic – Water is limited and we need to maximise ecological benefits

Adaptive management This proposal has no precedent in Australia, and the outcomes cannot be predicted with certainty. It is necessary to ‘learn by doing’ Imperative that a comprehensive, scientifically rigorous monitoring program is maintained, and that the data and conclusions are subject to critical review.

River operation • The regulator facilitates floodplain inundation but the ecological benefits comes with prudent operation – Define objectives of each regulator use – Monitor responses closely – Manage risks – Winter inundation to avoid carp spawning, cyanobacteria, blackwater problems • River planning also needs to determine a volume of water to maintain ecological assets

Potential benefits and impacts of the proposed Chowilla Regulator

by University of Adelaide on Oct 22, 2009

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