A New Approach to Determining Environmental Flow Requirements

MANAGEMENT doi: 10.1111/j.1442-8903.2011.00581.x REPORT A new approach to determining environmental flow requirements: Sustaining the natural values of floodplains of the southern Murray-Darling Basin By Paul Peake, James Fitzsimons, Doug Frood, Mel Mitchell, Naomi Withers, Matt White and Rick Webster Paul Peake is Remnant Vegetation Investigation Summary Large overbank flood events play an important role in maintaining large- Team Leader at the Victorian Environmental Assess- scale ecological processes and connectivity along and across the floodplains and between ment Council (VEAC) (8 Nicholson Street, East Mel- the rivers and their floodplains in the southern Murray-Darling Basin. However, the regulation bourne VIC 3002, Australia; Tel: +61 3-9637-9896; of rivers means that extensive overbank flooding can only occur in the rare circumstance of Email: paul.peake@dse.vic.gov.au). James Fitzsi- extreme flood events. Recent environmental water allocations have focussed on the largest mons was a Senior Project Officer at VEAC and is floodplain blocks (‘icon’ sites) and a small set of specific values (e.g. colonial nesting water- currently with The Nature Conservancy (Suite 3-04, birds), as well as on trialling fine-scale manipulation of infrastructure (e.g. pumping) to water 60 Leicester Street, Carlton VIC 3053, Australia) and relatively small areas. There has been no comprehensive systematic assessment of the entire the School of Life and Environmental Sciences, Dea- floodplain and its wider set of flood-dependent natural assets (such as ecosystems and spe- kin University (221 Burwood Highway, Burwood cies; herein referred to as ‘natural values’) to maximise the effectiveness of environmental VIC 3125, Australia; Email: james.fitzsimons@ water use and to catalogue values likely to be lost. This paper describes an assessment of deakin.edu.au). Doug Frood is a botanist with some 220 000 ha found to support flood-dependent natural values in Victoria. We mapped Pathways Bushland and Environment (PO Box 360, the geographic distribution and estimated components of the flooding requirements (natural Greensborough VIC 3088, Australia; Email: flooding frequency, and maximum period without flooding and minimum duration of each dfrood@bigpond.net.au). Mel Mitchell is a Senior flooding event before significant deterioration) for each natural value. Using an example of ProjectOfficeratVEAC(8NicholsonStreet,EastMel- one stretch of the River Murray, we show how the resultant spatial data can be used with bourne VIC 3002, Australia; Email: mel.mitchell@ floodplain inundation modelling to compare the outcomes of real or planned environmental dse.vic.gov.au). Naomi Withers was Senior GIS watering events; potentially providing tools for management agencies to conserve a wider Project Officer with VEAC and is now with the range of floodplain values than is currently the case. That is, water managers and the public Department of Sustainability and Environment (8 can see what ecosystems and threatened species are intended to be maintained by environ- Nicholson Street, East Melbourne VIC 3002, Australia; mental watering and what values are intended to be abandoned across the whole floodplain, Email: naomi.withers@dse.vic.gov.au). Matt White is rather than just seeing the small subset of values and ‘icon’ sites that are intended to be an ecologist with the Arthur Rylah Institute for Envi- maintained. Examples are provided to illustrate how information about the location, water ronmental Research, Department of Sustainability requirements and extent covered by potential floods for specific values can be used to build and Environment (123 Brown Street, Heidelberg VIC adaptive watering strategies for areas as large as the whole floodplain. 3084, Australia; Email: matt.white@dse.vic.gov.au). Rick Webster is a Director ⁄ Ecologist at Ecosurveys Key words: critical flood intervals, environmental flows, flood requirements, floodplains, threa- Pty Ltd (PO Box 13, Deniliquin NSW 2710, Australia; tened species. Email: ecosurveys@bigpond.com). This paper is a result of work commissioned by the Victorian Envi- ronmental Assessment Council to better identify the environmental watering needs of flood-dependent species and ecosystems in the southern Murray- Darling Basin. Wales (VEAC 2008a; NRC 2009) are recent These flood events also maintain ecological Introduction attempts to redress this deterioration. connectivity along the length of the flood- he deteriorating state of the Murray- Pulsed flooding is the major factor influ- plains, across the floodplains and between TDarling Basin has been a cause of con- encing biota in river-floodplain systems the major rivers and their floodplains, siderable concern amongst ecologists, land (Ballinger & Mac Nally 2006). The flood- thereby playing a crucial role in the land- managers, politicians and the communities plains of northern Victoria support a scape ecology of the region (Ballinger & living in and relying on the basin. The unique biota in an otherwise semi-arid Mac Nally 2006). The floodplain forests guide to the Murray-Darling Basin Plan environment because of overbank riverine and woodlands not only provide important (e.g. MDBA 2010) and two significant flood events resulting from large rain habitat for a range of forest- and woodland- investigations into future land and water events in the somewhat distant Great adapted plants and animals, but also act as management in Victoria and New South Dividing Range to the south and east. a pathway extending the geographic range ª 2011 Ecological Society of Australia ECOLOGICAL MANAGEMENT & RESTORATION VOL 12 NO 2 AUGUST 2011 1 MANAGEMENT REPORT of a number of species, particularly birds allocating scarce and expensive water and While vegetation types and threatened (e.g. Tzaros 2001). for determining priorities for infrastructure species are typically the foremost natural The rivers of northern Victoria, how- investment to natural assets. However, values targeted in analyses such as this, we ever, are now highly regulated, and much consideration of the water requirements of make a range of suggestions for future of their flows are diverted for irrigated agri- the full suite of floodplain ecosystems and work that would further improve the envi- culture. They are currently managed so taxa has been limited (Ballinger & Mac ronmental management of the floodplains, that extensive overbank flooding occurs Nally 2005). including the incorporation of additional only when water storages are full and spill- This situation is not unique to the Mur- natural values such as high species rich- ing at sufficient volumes for the rivers to ray-Darling Basin or Australia. Internation- ness, key non-threatened species and eco- break their banks (VEAC 2006). As a result ally, fish are typically used as an indicator logical connectivity. of this management regime, the frequency species for flood requirements (e.g. Richter of small and moderate floods has declined et al. 2006; Wang et al. 2009; Beilfuss & to around a third or less of the natural Brown 2010) as they can be relatively How the Analysis of Flooding frequency of flooding for most of the easily monitored. Indeed, Smakhtin (2008) Needs was Undertaken floodplain (e.g. DSE 2008a). Consequently, notes very few countries have set clear Assessment area there are now many indications of wide- procedures for environmental flow estima- spread substantial decline in the biodiver- tion and allocation. The assessment covered the Victorian sity of the floodplains including an In this paper, we interpret for managers floodplains of the Murray, Goulburn, increase in the number of dead and dying an approach to environmental watering Ovens and King Rivers downstream of River Red Gum (Eucalyptus camaldulen- that explicitly focuses on the flooding Lake Hume, Goulburn Weir, Porepunkah sis) and Black Box (E. largiflorens)trees requirements of species and ecosystems and Cheshunt respectively – an area of (MDBC 2003; Cunningham et al. 2007), across the landscape. This approach high- approximately 507 000 ha, collectively reduced River Red Gum growth rates lights, for the first time, those species and referred to here as the River Murray flood- (VEAC 2008a), and the development of ecosystems most in need of flooding and plain. The area is a subset of the Victorian acid sulfate soils (McCarthy et al. 2006). the locations where they occur. The Environmental Assessment Council’s River Despite a recent flood event, climate approach is management focused and can Red Gum Forests Investigation area (see change predictions translate to further easily incorporate new ecological and bio- Fitzsimons 2006; VEAC 2006) (Fig. 1). reductions in overbank flood frequency physical data. The process aims to move Determining the flooding (DSE 2008a) – and hence loss of biodiver- beyond the ‘icon sites’ approach to view requirements of natural sity into the future – if current river man- the River Murray floodplains as a dynamic values agement continues. Reduced precipitation interconnected system. This is based on an and increased evapo-transpiration resulting analysis undertaken as part of the Victorian Full details of how the flooding require- in reduced runoff are likely to greatly Environmental Assessment Council’s final ments for vegetation types and threatened reduce frequency and extent of floodplain recommendations for the floodplain forests flora and fauna were derived are provided inundation (e.g. DSE 2008a). and woodlands of northern Victoria (VEAC in Fitzsimons et al. (2011, contact the As a result, artificially generated and

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