Sammendrag
In the last decade, anthropogenically impacted (partially destroyed) spawning habitats of Atlantic salmon and anadromous brown trout have been restored in Western Norway. Mitigation measures have consisted of artificial gravel dumping and the restoration of fluvial processes induced by the removal of weirs. Reproduction enhancement has been documented in most cases, but the durability of restoration actions varied due to the flush out of spawning gravel in some cases. The aim of the present study was to evaluate the application of step-backwater modelling for a bimodal analysis of spawning suitability during low-flow conditions and bed stability during high-flow conditions. A successful model would provide a management tool to reach a longer durability of spawning restoration measures. Five different study sites were selected: three were classified as ´lake outlet´ and two as ´river´ sites. We performed a detailed analysis of the Froude number (-), cross sectional flow velocity (ms-1), and bottom shear stress (Nm-2). This allowed site specific power functions to be established in relation to discharge variations from 10 m3s-1 to 250 m3s-1. Friction slope Sf was determined as the trigger factor for both habitat suitability (Sf
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