Influence of Approach Velocity and Mesh Size on the Entrainment and Contact of a Lowland River Fish Assemblage at a Screened Irrigation Pump

Abstract

Fish screens can help prevent the entrainment or injury of fish at irrigation diversions, but only when designed appropriately. Design criteria cannot simply be transferred between sites or pump systems and need to be developed using an evidence-based approach with the needs of local species in mind. Laboratory testing is typically used to quantify fish responses at intake screens, but often limits the number of species that can studied and creates artificial conditions not directly applicable to screens in the wild. In this study a field-based approach was used to assess the appropriateness of different screen design attributes for the protection of a lowland river fish assemblage at an experimental irrigation pump. Direct netting of entrained fish was used along with sonar technology to quantify the probability of screen contact for a Murray-Darling Basin (Australia) fish species. Two approach velocities (0.1 and 0.5 m.sec−1) and different sizes of woven mesh (5, 10 and 20 mm) were evaluated. Smaller fish (<150 mm) in the assemblage were significantly more susceptible to entrainment and screen contact, especially at higher approach velocities. Mesh size appeared to have little impact on screen contact and entrainment, suggesting that approach velocity rather than mesh size is likely to be the primary consideration when developing screens. Until the effects of screen contacts on injury and survival of these species are better understood, it is recommended that approach velocities not exceed 0.1 m.sec−1 when the desire is to protect the largest range of species and size classes for lowland river fish assemblages in the Murray-Darling Basin. The field method tested proved to be a useful approach that could compliment laboratory studies to refine fish screen design and facilitate field validation.

Approach velocity and impingement duration influences the mortality of juvenile Golden Perch (Macquaria ambigua) at a fish exclusion screen

“…As fish screening becomes more widely considered as a means to preserve native fish populations, it is recognized that effective implementation requires biological evaluation of screening criteria (Boys et al 2013a,b). In the MDB, studies have focused on perforated plate (Boys et al 2013a) and woven mesh (Boys et al 2013b), but few have looked at wedge-wire screen which is a material widely used for fish exclusion screens throughout the world (Zeitoun et al 1981;Weisberg et al 1987). More detailed screen design guidelines are required for the MDB so that screening technologies suitable for local species and conditions and be produced.…”

“…Although this work has been limited to a small number of species, life stages and screen types, it has been preliminarily recommended, based upon field and laboratory experiments, that approach velocities should not exceed 0.1 m/s to protect native Australian juvenile fish ). Furthermore, criteria for exclusion screens have focused primarily on approach velocity (Peake 2004;Boys et al 2013b) or its interaction with sweeping velocity (Danley et al 2002;Swanson et al 2004Swanson et al , 2005White et al 2007;Young et al 2010); however, the role of pumping at different velocities and durations may play in influencing fish impingement and subsequent survival has not been investigated. Since there are a wide variety of species and life stages vulnerable to extraction at pump offtakes in the MDB (King & O'Connor 2007;Jones & Stuart 2008;Baumgartner et al 2009;Baumgartner & Boys 2012), guidelines will need to protect a diverse fish community.…”

Demonstration reaches: Looking back whilst moving forward with river rehabilitation under the Native Fish Strategy

“…Not all reaches, however, reported improvements following resnagging. In the Bourke to Brewarrina reach, no significant effect of resnagging was found on Golden Perch and Murray Cod abundance, or the 'nativeness' metric (Boys et al 2013b). Native fish did aggregate at reintroduced snags, but across a suite of replicated resnagging sites, there was no consistent measurable response relative to natural background or interannual variability evident at control and reference sites.…”

“…Smaller fish (<150 mm) were significantly more susceptible to entrainment and screen contact than larger fish, and whilst screen mesh size had little impact on fish entrainment, even modest reductions in the approach velocity in front of the screen (from 0.5 to 0.1 m/s) afforded significantly greater protection for fish (Boys et al . ). The pilot was a temporary trial, and other demonstration reaches could now test the preliminary screen design criteria outlined in Boys et al .…”

“…cantly increased at two sites relative to nearby untreated control and reference sites (Norris et al 2011(Norris et al , 2012a. At the other four reaches, overall change in reach condition was either not reported or was considered to have little association with the demonstration reach activities, For example, in the very large (200 km) Bourke to Brewarrina reach, 2 years of pre-intervention and 3 years of post-intervention monitoring failed to detect a response in key native fish indicators (such as species diversity, abundance and 'nativeness': i.e., proportion of native fish to alien fish) that could be attributed to rehabilitation interventions (Boys et al 2013b). The authors suspect that this result was not helped by the large amount of interannual variability in fish abundance associated with episodic floods in the Barwon-Darling River.…”