Investigating the sensitivity of river wetted habitat to changes in flow: a literature review

Water flow is fundamental to the existence of river ecosystems, shaping the habitats and interactions that support ecological communities. Because flow is more readily measured than other physical variables, e.g. through automated gauging stations, it is used as a variable to support the determination of ecological status of rivers or, in the case of heavily modified water bodies, ecological potential. Flow has a direct effect in terms of water chemistry and habitat volume, but species cannot detect flow per se. Species detect secondary variables such as the hydraulic habitat, e.g. water velocity, that is determined by the interaction of flow and channel form. Natural rivers have a defined relationship between flow and channel form (mediated by other factors such as downstream slope), allowing predictions to be made about ecological condition. However, a key issue is that UK rivers are highly modified so the relationship between flow and physical habitat is broken. In order to ensure that using flow as an explanatory variable provides robust evidence to support river management, it is necessary to improve our understanding of the relationship between flow and the hydraulic habitat to which the ecology responds. This project will review the current literature on the use of hydraulic habitat in environmental flow setting.