Grain size effects on energy delivery to the streambed and links to bedrock erosion

Turowski, Jens M.; Wyss, Carlos R.; Beer, Alexander R.

doi:10.1002/2015gl063159

Cited by 40 publications

(53 citation statements)

References 33 publications

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“…However, the primary seismic source is associated with the debris-flow front (Burtin et al, 2014), where large boulders are mobilized . This is in agreement with independent studies of bedload transport, suggesting that such large grain sizes dominate the energy transmission to the ground even though their contribution to the overall mobilized volume is small (Turowski et al, 2015). The seismic signal strength can thus be used to trace the debris-flow propagation through the seismometer network.…”

Section: Seismic Datasupporting

confidence: 90%

“…Ground motion sensing is almost exclusively confined to sediment moving directly across the steel plate. This has become an attractive method to monitor bedload transport (e.g., Turowski et al, 2015;Wyss et al, 2016) and can increase the detection and location accuracy of the debrisflow front . However, such in situ installations are technically more challenging and sediment accumulation above the steel plate often compromises detection.…”

Section: Introductionmentioning

confidence: 99%

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Testing seismic amplitude source location for fast debris-flow detection at Illgraben, Switzerland

Walter

Burtin

McArdell

et al. 2017

Nat. Hazards Earth Syst. Sci.

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Abstract. Heavy precipitation can mobilize tens to hundreds of thousands of cubic meters of sediment in steep Alpine torrents in a short time. The resulting debris flows (mixtures of water, sediment and boulders) move downstream with velocities of several meters per second and have a high destruction potential. Warning protocols for affected communities rely on raising awareness about the debris-flow threat, precipitation monitoring and rapid detection methods. The latter, in particular, is a challenge because debris-flow-prone torrents have their catchments in steep and inaccessible terrain, where instrumentation is difficult to install and maintain. Here we test amplitude source location (ASL) as a processing scheme for seismic network data for early warning purposes. We use debris-flow and noise seismograms from the Illgraben catchment, Switzerland, a torrent system which produces several debris-flow events per year. Automatic in situ detection is currently based on geophones mounted on concrete check dams and radar stage sensors suspended above the channel. The ASL approach has the advantage that it uses seismometers, which can be installed at more accessible locations where a stable connection to mobile phone networks is available for data communication. Our ASL processing uses time-averaged ground vibration amplitudes to estimate the location of the debris-flow front. Applied to continuous data streams, inversion of the seismic amplitude decay throughout the network is robust and efficient, requires no manual identification of seismic phase arrivals and eliminates the need for a local seismic velocity model. We apply the ASL technique to a small debris-flow event on 19 July 2011, which was captured with a temporary seismic monitoring network.The processing rapidly detects the debris-flow event half an hour before arrival at the outlet of the torrent and several minutes before detection by the in situ alarm system. An analysis of continuous seismic records furthermore indicates that detectability of Illgraben debris flows of this size is unaffected by changing environmental and anthropogenic seismic noise and that false detections can be greatly reduced with simple processing steps.

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Section: Seismic Datasupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Testing seismic amplitude source location for fast debris-flow detection at Illgraben, Switzerland

Walter

Burtin

McArdell

et al. 2017

Nat. Hazards Earth Syst. Sci.

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“…These effects include, for example, cratering and compaction of the sediment bed, which are discussed below. In addition, new field data from the Erlenbach, a catchment instrumented for bedload transport and erosion observations, indicate that the largest transported particles are responsible for the bulk of the energy transfer to the bed (Turowski, Wyss, & Beer, 2015). Thus, it seems that a large particle impacting a bed composed of small particles is the relevant situation to consider for the transfer of the results to the field.…”

Section: Discussionmentioning

confidence: 99%

The influence of sediment thickness on energy delivery to the bed by bedload impacts

Turowski

Bloem

2015

Geodinamica Acta

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Fluvial bedrock erosion rates due to impacting sediment particles are thought to be proportional to the energy delivered to the bedrock. When sediment particles cover the bed, they reduce the energy transmitted to the bed by an impacting particle. We measured the decline of energy transferred through sediment cover of increasing thickness in laboratory experiments. The energy arriving at the bed is a function both of the cover thickness and the grain size of the covering sediment. Using a simple stochastic model of cover distribution, the experimental results were upscaled to the reach scale. Although cover thickness influences energy delivery heavily at a given point, when averaging over the whole bed, cover-free areas dominate total energy delivery, making partial energy transfer through the cover negligible when a small or intermediate fraction of the bed is covered by sediment. Partial energy delivery through the bed cover is not negligible when a large fraction or the complete bed is already covered, but in this situation, an erosion threshold may become important. On grounds of the presented data, we expect that the areal distribution of sediment in a bedrock channel dominates total energy delivery and that partial energy delivery to the bed through a sediment layer can be neglected for most modelling purposes.

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“…Future developments of such models will need to explore more realistic sediment transport characteristics, for example by including all modes of transport, including saltation, rolling and sliding on the river bed (cf. Turowski et al, 2015). In addition, field and laboratory tests of the model on high-quality independent data are necessary.…”

Section: Discussionmentioning

confidence: 99%

“…However, large sediment particles usually concentrate in the snout of a debris flow (Iverson et al, 1997), and they can be assumed to produce larger seismic sources than the tail end of the flow (cf. Turowski et al, 2015). Thus, the method of velocity estimation described above should at least give results that are correct to first order.…”

Section: Linear Geometrymentioning

confidence: 99%

Seismic monitoring of torrential and fluvial processes

2016

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Abstract. In seismology, the signal is usually analysed for earthquake data, but earthquakes represent less than 1 % of continuous recording. The remaining data are considered as seismic noise and were for a long time ignored. Over the past decades, the analysis of seismic noise has constantly increased in popularity, and this has led to the development of new approaches and applications in geophysics. The study of continuous seismic records is now open to other disciplines, like geomorphology. The motion of mass at the Earth's surface generates seismic waves that are recorded by nearby seismometers and can be used to monitor mass transfer throughout the landscape. Surface processes vary in nature, mechanism, magnitude, space and time, and this variability can be observed in the seismic signals. This contribution gives an overview of the development and current opportunities for the seismic monitoring of geomorphic processes. We first describe the common principles of seismic signal monitoring and introduce time-frequency analysis for the purpose of identification and differentiation of surface processes. Second, we present techniques to detect, locate and quantify geomorphic events. Third, we review the diverse layout of seismic arrays and highlight their advantages and limitations for specific processes, like slope or channel activity. Finally, we illustrate all these characteristics with the analysis of seismic data acquired in a small debris-flow catchment where geomorphic events show interactions and feedbacks. Further developments must aim to fully understand the richness of the continuous seismic signals, to better quantify the geomorphic activity and to improve the performance of warning systems. Seismic monitoring may ultimately allow the continuous survey of erosion and transfer of sediments in the landscape on the scales of external forcing.

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Grain size effects on energy delivery to the streambed and links to bedrock erosion

Cited by 40 publications

References 33 publications

Testing seismic amplitude source location for fast debris-flow detection at Illgraben, Switzerland

Testing seismic amplitude source location for fast debris-flow detection at Illgraben, Switzerland

The influence of sediment thickness on energy delivery to the bed by bedload impacts

Seismic monitoring of torrential and fluvial processes

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