ABSTRACT
To improve the flood protection at the Bregenzerach in Mellau/Austria the river bed was deepened by 2 m. The measure resulted in an increased bed slope in the upstream river reach which exceeds the equilibrium slope of the concerned river reach. Thus, a sustainable erosion process was to be expected. To counteract this erosion process and to stabilize the river bed two different measures were identified as possible solutions-a riprap and an artificially coarsened armor layer. Practical reference experiences exist for neither of the two measures as the bed slope is high. For these reasons the planned measures were tested for feasibility and optimized in a physical model experiment. While the artificially coarsened armor layer showed an insufficient stability already at discharges lower than HQ5 the riprap proved to be sufficiently stable over almost the whole bed cover up to a HQ300. The measure was successfully implemented in autumn 2012 .
