Bed load transport in an Alpine river after a high magnitude flood: results from the 2008 field campaign

Landslide dams are common features in glacially sculpted valleys. The failure of these dams can be dramalic, producing high magnitude floods and mobilizing vast quantities or sediment. High magnitude floods are rare and ill-represented in the literature, despite the frequent occurrence of landslide dams in glacial valleys. In 2005 a landslide dam was breached during heavy rain. This event has substantially transformed the downstream channel reach of the Partnach River in the Bavarian Alps. In this study we present field data on discharge, unit bed load and grain size from the 2008 season. Compared with pre-dambreak data, preliminary results show increased bed load transport in the Partnach post dam-break, even at times of lower discharge. The critical discharge threshold for bed load entrainment has decreased from 1.9 m 3 /s pre-dambreak, to I m 3 /s post-dambreak. This is a case study from the Bavarian Alps which contributes to the general characterization of sediment fluxes in highly volatile systems, specifically after high magnitude floods.