The physical habitat that controls ecosystem functioning is determined by local hydraulics and channel morphology. Hydraulic field studies were conducted in a boreal stream (1) to test the hypothesis that the local hydraulic conditions are determined by cross-sectional geometry and flow resistance in boreal conditions by analysing the relationship between flow velocities, cross-sectional geometry and flow resistance, and (2) to suggest success criteria for the restoration of local hydraulic conditions. Results suggest that, in the case of small channels, cross-sectional geometry and flow resistance are weakly interconnected and influenced by factors such as local roughness elements and channel forms. The study showed that both flow resistance and cross-sectional geometry are vital factors in determining local hydraulics. In stream restoration, a design based on consideration of only one of these two factors is inadequate and may result in a failure to replicate natural hydraulic conditions. Simple success criteria for the restoration of local hydraulics are developed.

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