A new approach to determining environmental flow requirements: Sustaining the natural values of floodplains of the southern Murray-Darling Basin

Authors

  • Paul Peake,

  • James Fitzsimons,

  • Doug Frood,

  • Mel Mitchell,

  • Naomi Withers,

  • Matt White,

  • Rick Webster


Paul Peake is Remnant Vegetation Investigation Team Leader at the Victorian Environmental Assessment Council (VEAC) (8 Nicholson Street, East Melbourne VIC 3002, Australia; Tel: +61 3-9637-9896; Email: paul.peake@dse.vic.gov.au). James Fitzsimons was a Senior Project Officer at VEAC and is currently with The Nature Conservancy (Suite 3-04, 60 Leicester Street, Carlton VIC 3053, Australia) and the School of Life and Environmental Sciences, Deakin University (221 Burwood Highway, Burwood VIC 3125, Australia; Email: james.fitzsimons@deakin.edu.au). Doug Frood is a botanist with Pathways Bushland and Environment (PO Box 360, Greensborough VIC 3088, Australia; Email: dfrood@bigpond.net.au). Mel Mitchell is a Senior Project Officer at VEAC (8 Nicholson Street, East Melbourne VIC 3002, Australia; Email: mel.mitchell@dse.vic.gov.au). Naomi Withers was Senior GIS Project Officer with VEAC and is now with the Department of Sustainability and Environment (8 Nicholson Street, East Melbourne VIC 3002, Australia; Email: naomi.withers@dse.vic.gov.au). Matt White is an ecologist with the Arthur Rylah Institute for Environmental Research, Department of Sustainability and Environment (123 Brown Street, Heidelberg VIC 3084, Australia; Email: matt.white@dse.vic.gov.au). Rick Webster is a Director/Ecologist at Ecosurveys Pty Ltd (PO Box 13, Deniliquin NSW 2710, Australia; Email: ecosurveys@bigpond.com). This paper is a result of work commissioned by the Victorian Environmental Assessment Council to better identify the environmental watering needs of flood-dependent species and ecosystems in the southern Murray-Darling Basin.

Abstract

Summary  Large overbank flood events play an important role in maintaining large-scale ecological processes and connectivity along and across the floodplains and between the rivers and their floodplains in the southern Murray-Darling Basin. However, the regulation of rivers means that extensive overbank flooding can only occur in the rare circumstance of extreme flood events. Recent environmental water allocations have focussed on the largest floodplain blocks (‘icon’ sites) and a small set of specific values (e.g. colonial nesting waterbirds), as well as on trialling fine-scale manipulation of infrastructure (e.g. pumping) to water relatively small areas. There has been no comprehensive systematic assessment of the entire floodplain and its wider set of flood-dependent natural assets (such as ecosystems and species; herein referred to as ‘natural values’) to maximise the effectiveness of environmental water use and to catalogue values likely to be lost. This paper describes an assessment of some 220 000 ha found to support flood-dependent natural values in Victoria. We mapped the geographic distribution and estimated components of the flooding requirements (natural flooding frequency, and maximum period without flooding and minimum duration of each flooding event before significant deterioration) for each natural value. Using an example of one stretch of the River Murray, we show how the resultant spatial data can be used with floodplain inundation modelling to compare the outcomes of real or planned environmental watering events; potentially providing tools for management agencies to conserve a wider range of floodplain values than is currently the case. That is, water managers and the public can see what ecosystems and threatened species are intended to be maintained by environmental watering and what values are intended to be abandoned across the whole floodplain, rather than just seeing the small subset of values and ‘icon’ sites that are intended to be maintained. Examples are provided to illustrate how information about the location, water requirements and extent covered by potential floods for specific values can be used to build adaptive watering strategies for areas as large as the whole floodplain.

Ancillary