Hydraulic aspects of environmental flood management in boreal conditions

In environmental flood management, an essential task is to improve channel conveyance using environmentally preferable methods, which aim to preserve natural morphological and hydraulic characteristics of a river. This requires a reliable channel design method that accounts for complex hydraulics, i.e. two-stage channel or considerable bank vegetation. Hydraulic field measurements were carried out in two rivers to find out how different factors affected flow resistance. In one of the study reaches, the effects of bioengineering on channel hydraulics were investigated under boreal climatic conditions. The Darcy-Weisbach friction factor, the Manning coefficient and the roughness height were related to the characteristics of channel geometry and flow. Comparison between the field data and the investigated channel design methods gave accurate results only in reaches having simple hydraulic properties. In reaches with complex hydraulics the results were poor.