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[1] Flow regulation between irrigation storages and demand offtakes often results in prolonged elevated flows in the river channel during a period that would otherwise typically experience lower flows. This is a growing concern worldwide with negative implications for aquatic flora and fauna susceptible to changes in the hydraulic environment. Slackwaters, a hydraulic patch characterized by low velocities and shallow depths, are important habitat for zooplankton and have been associated with an order of magnitude more fish and shrimp than midchannel patches. Slackwaters are vulnerable to flow regulation and reductions in slackwater area have been shown to reduce abundances of juvenile and larval fish with poor swimming abilities; invertebrates dependent on slackwater refugia; and organic matter retention. It is therefore surprising that the relationship between flow regulation and slackwaters has not been explicitly quantified. In this study, we quantify changes to slackwaters (by surface area relative to inundated area) under the influence of flow regulation, specifically total area, patch area, and number of patches. Using twodimensional hydraulic modeling for sites on the Broken River, southeastern Australia, we demonstrate that the area of slackwaters decreases with increasing discharge until inundation of higher-elevation bars and benches. We assess changes in slackwaters against three levels of increasing flow regulation intensity and find that increasing levels of regulation reduce slackwater area: With a heavily regulated scenario resulting in half the slackwater area and patch sizes 5 times smaller, compared with natural conditions. These findings provide the conceptual model and quantifiable relationships for testing population dynamics, identifying key hydrologic drivers of ecological decline and assisting river storage operators to manage flows during critical periods for biota.

Expanding cities worldwide are gradually absorbing peripheral greenfield streams that often require some level of improvement to fulfil their role as central public spaces in the urban landscape. Restoration is often impossible due to physical constraints imposed by urban development coupled with fundamental biophysical modification from previous land use. However, it is possible to provide social amenity and improve stream ecosystem condition through the process of naturalisation -an implicitly social undertaking reliant on the well-informed participation of stakeholders. Urbanising greenfield sites present a special case of naturalisation that does not include a local community as it is absent in advance of development. The authors present a case study where they were involved as advising scientists in a stream naturalisation project in Melbourne, Australia. In the case study, the lack of this founder community in the consultation process coupled with limited integration between other stakeholders resulted in naturalisation goals unlikely to result in improved in-stream ecosystem condition. The final design adopted some features that extended beyond baseline regulatory standards for drainage schemes in new developments, but with insufficient provision for catchment-scale treatment of stormwater runoff, which has been recognised as a primary source of urban stream degradation. This study expands the concept of naturalisation -originally developed in the context of rural stream management -to include urbanising greenfield catchments where advocacy groups and urban planning officials from local government hold chief responsibility to represent the values and attitudes of the founder community in the consultation process.

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