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Quantification of sediment transfer in an exceptionally active Alpine catchment

English title Quantification of sediment transfer in an exceptionally active Alpine catchment
Applicant McArdell Brian
Number 119912
Funding scheme Project funding (Div. I-III)
Research institution Swiss Federal Research Inst. WSL Direktion
Institution of higher education Swiss Federal Institute for Forest, Snow and Landscape Research - WSL
Main discipline Geomorphology
Start/End 01.04.2008 - 31.03.2010
Approved amount 42'632.00
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Keywords (9)

Sediment budget; sediment sources; debris flow entrainment; aerial photogrammetry; Debris flows; aerial photography; sediment transport; sediment transfer; erosion

Lay Summary (English)

Lay summary
Debris flows, fast landslides of muddy soil debris, typically during intense rain storms. Debris flows are common, with an annual overage of nearly 20 damage-causing events per year in Switzerland. As a debris flow travels down a channel, it will typically pick-up (entrain) sediment lying on the channel bed, thereby increasing the total volume of the debris flow. This entrainment process often transforms a relatively small landslide into a large and rapid debris flow which may travel long distances and endanger communities or infrastructure. Unfortunately this process is poorly understood. In this proposal we will study the debris flow entrainment problem at the Illgraben catchment (Canton VS) where several large debris flows occur every year. The main method employed in this project is aerial photogrammetry. A series of flights is planned where closely-spaced high-resolution aerial photographs will be taken. This will allow us to construction digital elevation models what can be used to estimate sediment volumes by comparing images taken several times over a period of two years (existing aerial photos are insufficient for this work because the resolution is too small and the images are spaced too widely, resulting in many “shadows” where data are unavailable). The resulting geo-referenced photographs (orthophotographs) can also be used to identify changes in landforms such as the formation of new debris flow deposits which can be used to increase our understanding of debris flow initiation.

In the existing CCES Project TRAMM (a project funded by the ETH Competence Center Environment and Sustainability: “Transition to Rapid Mass Movement”) we are directly measuring debris flow entrainment at a place where it is safe to perform measurements, near the catchment outlet at the Rhone River. In the TRAMM project we are directly measuring debris flow entrainment using an array of special sensors buried in the bed of the Illgraben channel, along one short length of the channel. The project described here will provide data on the spatial distribution of sediment erosion within the entire catchment, thereby allowing us to increase our understanding of debris flow entrainment in general, from the initiation zone to the area inhabited by humans.

This project has broad practical significance in that it will increase our understanding of the formation of hazardous debris flows, a question that is of importance to the design of hazard scenarios used for land use planning and risk mitigation.
Direct link to Lay Summary Last update: 21.02.2013

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