Author(s): Fiona Maager, Benjamin Hohermuth, Volker Weitbrecht, Robert Boes

Linked Author(s): Benjamin Hohermuth, Volker Weitbrecht, Robert Boes

Keywords: Bed stabilization; Block arrangement; Design criteria;Man-made step-pool sequences; River engineering;

Abstract: In the past decades, mainly conventional bed stabilization measures, e.g. concrete check dams, were used to control bed erosion of steep mountain streams. We hypothesize that man-made step-pool systems, comprising boulder check-dams arranged to mimic a natural step-pool morphology, may be more advantageous than these concrete structures due to lower construction and maintenance costs and a more natural bed morphology. There are still no conclusive design criteria available regarding optimal block arrangement of man-made step-pool sequences. Stability and failure mechanisms of these step-pool structures during flood events were investigated in four experimental test series. The experiments were conducted in a 0.3 m wide laboratory flume with a slope of 8%. A sequence of step-pool units with a step spacing of 0.7 m was installed in the flume and the discharge was increased incrementally until the step-pool units failed. The results indicated that two rows of blocks stacked with an overlap of about half a block size were needed to create stable step-pool units. Scour depth and scour extent significantly decreased, when a middle sill consisting of three and an end sill consisting of two single blocks were placed in the section between two steps. The main failure mechanism of the investigated man-made step-pool units was related to scour development. The step-forming blocks slid into the downstream pool due to erosion of the fine material at the blocks’ foundations. Overall, these findings contribute to the development of design criteria regarding optimal block arrangement for man-made step-pool sequences.

DOI: https://doi.org/10.3850/38WC092019-0646

Year: 2019