Natural flow scaling: a paradigm shift in environmental flow development for rivers subject to large inter-basin water transfers — ASN Events

Natural flow scaling: a paradigm shift in environmental flow development for rivers subject to large inter-basin water transfers (11640)

Ivars Reinfelds 1 , Simon Williams 1 , Matthew Russell 1 , Daniel Coleman 1 , Tim Haeusler 1 , Elizabeth Pope 2 , Andrew Nolan 2
  1. NSW Office of Water, Wollongong, NSW, Australia
  2. Snowy Hydro, Cooma, NSW, Australia
The ‘natural flow paradigm’ and reinstatement of aspects of natural flow regimes to within the bounds of natural variability, is one of the most commonly touted principles and approaches world-wide in the development of environmental flow regimes. Such an approach, however, is fundamentally not possible for many river systems subject to large inter-basin water transfers where water volumes allocated to environmental flows are multiples below the lowest naturally recorded annual flows. Simplistic application of the ‘natural flow paradigm’ under such situations can result in the development of environmental flow regimes that favour particular aspects of the natural (unregulated) flow regime to such an extent that the result is arguably, entirely un-natural. The concept of ‘natural flow scaling’ whereby environmental flow regimes are scaled proportionally to natural hydrographs on the basis of allocated flow volumes has been dismissed in ecological circles with simplistic arguments such as “…half of the peak discharge will not move half of the sediment, half of a migration motivational flow will not motivate half of the fish and half of an overbank flow will not inundate half of the floodplain (Poff et al., 1997 p. 781).” In this paper we outline ‘natural flow scaling’ at annual, daily and hourly time scales as an alternative approach to the development of environmental flow regimes for the Snowy River below Jindabyne Dam. We discuss the advantages that ‘natural flow scaling’ holds over more prescribed methods that until recently favoured the release of 50% of allocated annual environmental flow volumes as a single flood pulse in spring.
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