Reducing the perversion of diversion: Applying world‐standard fish screening practices to the Murray–Darling Basin

Abstract

Summary The impact of water diversion on fish populations is a global issue. Many countries have invested substantial funding into research and implementation strategies to ensure fish are protected at diversions that take water out of rivers for agriculture and other human uses. The most common management action is the installation of fish screens, and a wide range of designs are presently available that suit a large range of diversions. The Murray–Darling Basin is the largest catchment in Australia and has been substantially developed over the past 100 years to store and divert water for that protect fish from escaping into the irrigation systems. Recent studies have determined that water diversions have substantial impacts on native fish populations, but there are presently no coordinated efforts for mitigation strategies. The purpose of this review is to highlight aspects of successful screening programmes worldwide and identify those that could be directly applied to the Murray–Darling Basin. The development of similar programmes in the United States, New Zealand and the United Kingdom has identified that sufficient information and technology exists to inform the development of fish screening programmes. There is no need to commence implementation from first principles, and substantial progress can be achieved by applying successful aspects of other programmes. By identifying existing designs, defining ecological targets, developing generalised guidelines appropriate for local conditions and engaging the community, a co‐ordinated and successful fish screening programme could be directly applied to the Murray–Darling Basin. This would have substantial benefits for the long‐term sustainability of native fish without compromising water supply requirements.

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

“…Such an approach velocity is in line with the accepted standard for the protection of fish fry in other parts of the world (e.g. [13], [25]) and there are many screen designs already available which could meet these standards [12]. If approach velocity can be optimised, it would appear from this study that the aperture size of screen mesh may be a less important consideration for fish protection.…”

“…It may be that most benefit can be gained from using a screen design which optimises approach velocity whilst minimising debris accumulation and flow restriction. Identifying a solution which satisfies all three of these criteria will ensure solutions are fish-friendly, require little maintenance and satisfy irrigation delivery needs [12].…”

“…Although the impact will undoubtedly differ between locations based upon local fish populations, time of year and size of diversion [9], [11], given the sheer volume of water that is diverted across the Murray-Darling Basin and the fact that at times the volumes diverted can significantly exceed that flowing downstream, it is likely that the numbers of fish removed are significant and will need to be reduced if fish population declines are to be addressed [22]. Currently programs to rehabilitate fish populations in the Murray-Darling Basin do not incorporate fish screening activities [46] and the development of fish screen criteria to support the initiation of screening programs is urgently required [12].…”

“…In many countries, irrigators and environmental agencies utilise fish screens on diversion points to decrease the numbers of fish being entrained without compromising the delivery of water to where it is needed [11]. The success of screening programs has been based upon having well-developed guidelines on screen design, that provide guidance on maximum velocities in front of the screen and the types of material that screens are made from [12]. Irrigation screening legislation exists in North America [13], [14], New Zealand [15], United Kingdom, Ireland, Switzerland, Netherlands, Denmark [16] and France [17].…”

“…Most fish screen guidelines in these countries (except New Zealand) were developed to protect migratory salmonids during seaward migration phases [11], [18]. It is increasingly accepted that other species impacted by diversions have been poorly considered in screen guidelines [19] and it is important to consider larger components of the migratory fish assemblage when developing guidelines [12].…”