Restoring the ecological integrity of a dryland river: Why low flows in the Barwon–Darling River must flow

Martin Mallen-Cooper, Brenton P. Zampatti

    Research output: Contribution to journalArticle

    Abstract

    For dryland rivers globally, understanding hydro-ecological function is fundamental to informing trade-offs between consumptive water use and aquatic ecosystem integrity. The Barwon–Darling is an Australian dryland river system recognised for its hydrological variability, which is considered a primary driver of the riverine ecosystem. Emphasis has been placed on extremes of zero flow and flood but examining low flow hydrology and hydraulics – through historical and modern droughts – demonstrates that under natural conditions, the river system also exhibits persistent and predictable flow characteristics. From 1885 to 1950, prior to flow regulation, the Barwon–Darling flowed 92% of the time, and throughout severe droughts (1895–1903 and 1939–1945) the river system was characterised by: near-perennial flows (85% of the time), with lotic (flowing water) habitats; and near-annual, in channel, flow pulses. Furthermore, evidence of lotic biota is found consistently in Aboriginal middens dating over the past 15,000 years, thus indicating the long-term persistence of lotic conditions. We propose these consistent hydrological and hydrodynamic features have shaped the ecology of aquatic biota in the Barwon–Darling River but are now experiencing unprecedented change. Flow storage and diversion have increased the frequency and duration of zero flows in some reaches, but arguably the most substantial impacts, along the entire river, are on: (i) low flows, which are now frequently below lotic thresholds, and (ii) the magnitude of near-annual flow pulses, which are reduced by over 90%. Consequently, in modern droughts, the river becomes predominantly lentic (still-water), an impact that is exacerbated by weirpools which create artificial lentic conditions for approximately 1000 km (40%) of river. The ecological impacts of these changes are increasingly apparent, with the loss of lotic biota and a reduction in biodiversity. An ecohydraulic perspective explains present impacts, provides new directions and some immediate solutions for river management, and clarifies choices for stakeholders.

    Original languageEnglish
    JournalEcological Management and Restoration
    DOIs
    Publication statusE-pub ahead of print - 16 Sep 2020

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