Screening water diversions to support freshwater fish conservation in the Murray–Darling Basin

Research output: ThesisDoctoral Thesis

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Abstract

Water abstraction from natural waterways for irrigated agriculture and potable water use is negatively impacting aquatic biodiversity. Every year, millions of native fish risk being entrained from Australian rivers into irrigation diversions and pumps. Characterised by low gradients and semi-arid rivers, the Murray–Darling Basin (MDB) is the most important agricultural region of Australia and irrigated agriculture is the primary user of water resources. Research suggests that irrigation diversions also impact both naturally recruited and stocked fish in the MDB, which may undermine native fish recovery and recreational fishing opportunities. Appropriately designed fish protection screens are recognised globally as an effective solution for protecting aquatic biota from becoming entrained, as well as excluding debris without affecting the water delivery and retaining the agricultural effectiveness. The overall efficacy of fish screening remains largely undocumented for many fish species and rivers globally. This is largely due to four key reasons. First, prior installations and research have primarily focused on salmonids or eels with relatively few studies on non-diadromous species or multi-species communities, or across different life stages. Second, where studies have been completed, they have been limited in scope (focused on power plant intakes) or were largely restricted to specific regions (mainly in North America or Europe). Third, they faced field-related challenges or provided inconclusive data. Fourth, where screening technologies have been developed to reduce fish losses (such as by Australian government agencies in the MDB), their performance remains largely untested. Improved understanding of the overall efficacy of fish screening in different contexts, and for multiple fish species across life stages is crucial to achieve the best possible outcomes.

Issues related to irrigation abstraction for multi-species assemblages have received scant attention. Research in Australia has established that significant numbers of fish are being extracted at water diversion points. There has also been a series of laboratory trials to understand the criteria needed to design effective fish screens for selected species in the MDB. Prototype screens have recently been installed, but a thorough evaluation is yet to take place to assess their functionality and efficiency under local conditions for multiple species and life stages (from eggs to adult).

This thesis seeks to fill these important knowledge gaps by conducting field surveys to examine a range of fish screening technology for implementation in Australian rivers. Research was conducted in a variety of riverine habitats in the Murray–Darling Basin and across a variety of diversions (gravity fed, different sized pumps), as well as under laboratory conditions. Main areas of enquiry include:
A)Fish losses at diversions are increasingly impacting fish species in Australia, as in other parts of the world. I review this in Chapter 1, discussing that fish losses at diversions are not only likely to contribute to population declines in Australia, but that up until recently the issue has been poorly recognised and is only now starting to be addressed. My review demonstrates, in the small number of studies published to date, fish entrainment rates are quite variable, making it difficult to prioritise where and what type of diversions should be screened.
B) I am addressing concerns that stocked fish may be entrained into irrigation systems thus offsetting the benefits of re-stocking programmes (Chapter 2). Using parental DNA analysis, I identified that recently stocked Murray cod were entrained at two pump diversions less than 24 hours after fish were released into the river. These results suggest unscreened intakes have the potential to reduce the effectiveness of re-stocking efforts. I discuss various options to mitigate this problem and identify fish screens as one of the most appropriate countermeasures.
C)I collected the first data in comparing entrainment rates into irrigation pump systems during screened and unscreened operations (Chapter 3). I found entrainment (up to 13 fish per extracted megalitre (ML; 1,000,000 litres)) occurred at irrigation pumps across a range of fish species and different life stages. Most species detected in the river were also found in the pumped water. When appropriately-designed screens were fitted to the pumps, entrainment was reduced by > 92% in all cases, benefiting a wide range of naturally recruited and stocked native species. The economic benefits extended to reduced debris loads in the diverted water reducing operating costs for irrigators in terms of time and maintenance.
D)Large gravity-fed diversion systems are expected to entrain high numbers of aquatic organisms and are also more complex to screen. In Chapter 4, I studied entrainment of aquatic organisms and debris into a gravity-fed irrigation diversion channel fitted with a conical screen. I conducted mark-release-recapture experiments with native species fingerlings and a fish community assessment approach. This allowed me to assess the effectiveness of the screen in reducing entrainment, given the considerable size of the irrigation channel, which diverts 600 ML of water per day (≈ 6.94 m³/s). Entrainment of debris, wild and released fish was significantly lower when the gravity-fed diversion was screened, while the screened fish community in the irrigation channel differed with fewer species dominating compared to the unscreened fish community.
E)Design specifications for fish protection-screens in Australia have been developed to guide screen construction, based on a small number of laboratory studies on juveniles of three species. To test whether these specifications are likely to protect the entire native fish community, the criteria need to be validated on a much larger number of species. Therefore, I determined in Chapter 5 whether the influence of approach velocity, a critical design parameter for effective fish protection screens, influenced the impingement rates in a multi-species trial. This assertion stemmed from the understanding that a screen's effectiveness is compromised if it merely shifts mortality from entrainment to being trapped, or impinged, upon the screen. Laboratory experiments using a flume were conducted with 17 Australian freshwater fishes and two crustaceans. The results indicate that approach velocities can be manipulated to reduce impingement rates. Besides indicating that the design specifications are appropriate for most tested species, the results provide important insights for the design of globally applicable fish protection screens, considering species-specific behaviour, to enhance aquatic biota conservation efforts.
F)Finally, I brought all this research together in Chapter 6 to show important outcomes and the implications of my results for screening water diversions to support freshwater fish conservation in the MDB. Additionally, I provide some considerations for managers to prioritise sites for screen implementations.
This thesis represents a comprehensive investigation into the impact of irrigation systems on fish entrainment, employing both field studies and laboratory experiments. The findings highlight significant concerns regarding the entrainment of naturally recruited and stocked native fish species, emphasising the potential detriment to re-stocking programmes and natural fish populations.

Through the analysis of various diversion types and the implementation of fish screens, effective mitigation strategies have been identified, highlighting the importance of screening technologies in reducing entrainment rates. Furthermore, this research identifies critical design parameters for fish screens, offering insights for the development of globally applicable solutions to enhance aquatic biota conservation efforts. By addressing these issues, this study contributes to the advancement of sustainable water management practices, ensuring the protection of aquatic ecosystems while supporting the needs of agricultural irrigation systems.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Charles Sturt University
Supervisors/Advisors
  • Baumgartner, Lee, Principal Supervisor
  • Boys, Craig, Co-Supervisor
  • Watts, Robyn, Co-Supervisor
  • Doyle, Katie, Co-Supervisor
Thesis sponsors
Award date04 Oct 2024
Place of PublicationAustralia
Publisher
Publication statusPublished - 08 Oct 2024

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