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Parasiewicz, P., J. Eberstaller, S. Weiss and S. Schmutz (1998). Conceptual guidelines for nature-like bypass channels. Pages 348-362 in M. Jungwirth, S. Schmutz and S. Weiss, eds. Fish Migration and Fish Bypasses, Fishing News Books, Vienna (Austria).

A wide range of technologies exist, and are being further developed, to pass fish both upstream and downstream around various obstacles primarily involving hydropower or irrigation projects. Most of these technologies are highly engineered and follow design criteria that have been developed with the aid of both hydraulic modelling and empirical data. Concurrent with these developments is an increasing interest in more nature-like bypass designs, especially at small-scale or low-head river barriers. This interest is not accompanied by specific or even general design criteria, and thus there may be some hesitance to apply such designs more broadly. This chapter presents conceptual guidelines for both defining and planning nature-like bypass channels, primarily based on experiences gained in Austria but also considering their potential application elsewhere. A basic planning strategy is presented based on river size and general channel morphology in consideration of the fish assemblage present, the goal being to mimic natural systems in which the species of interest are found, rather than engineering channels that accommodate set hydraulic criteria. Emphasis is placed on the site-specific nature of such constructions, their inherent heterogeneity, and necessity for post-construction monitoring and adaptation. The role that nature-like bypasses can play in providing critically needed flowing water habitat in heavily engineered rivers is also articulated.