Experimental study of sediment traps permeable for frequent floods

Sediment traps created by partially open torrential barriers are crucial elements for flood protection in alpine regions. The trapping of sediment is necessary when intense sediment transport occurs during floods that may endanger urban areas at downstream river reaches. In turn, the unwanted permanent trapping of sediment during small, non-hazardous floods can result in the ecological and morphological depletion of downstream reaches. This study experimentally analyses a new concept for permeable sediment traps. For ensuring the sediment transfer up to small floods, a guiding channel implemented in the deposition area of the sediment trap was studied systematically. The bankfull discharge of the guiding channel corresponds to a dominant morphological discharge. At the downstream end of the guiding channel, a permeable barrier triggers sediment retention and deposition. The permeable barrier consists of a bar screen for mechanical deposition control, superposed to a flow constriction for the hydraulic control. The fail-safe clogging of the barrier and the sediment deposition upstream can be ensured for discharges that are higher than the bankfull discharge of the guiding channel.