A Geomorphological Map as a Tool for Assessing Sediment Transfer Processes in Small Catchments Prone to Debris-Flows Occurrence

Abstract. When connected to torrential channels, periglacial moving landforms (including rock glaciers, push moraines and high-altitude landsliding masses) may constitute important active sediment sources for gravitational and torrential transfer processes such as debris flows. However, still very little is known about the location and the number of such types of sedimentary connection in given regions, as well as about the typical sediment transfer rates that can be expected. Therefore, this contribution aims at (i) describing a new methodology developed to identify and characterize moving landforms connected to the torrential network system at a regional scale and (ii) presenting the results yielded from the application of this method in a 2000 km2 region in the southwestern Swiss Alps. The developed approach is based on the analysis of simple data such as a high-resolution digital elevation model (DEM), time series of aerial images and a slope movement inventory. The approach allowed both the fast identification of moving landforms connected to torrential channels and the estimation of annual sediment transfer rates for these inventoried landforms. In the study region, results showed that such types of sedimentary connection appeared to be rather rare. Results also showed that most connected moving landforms were characterized by relatively low sediment transfer rates (<500 m3 yr−1) but several sites were identified as transferring large amounts of sediment into the torrents (>1000 m3 yr−1). As sediment transfer rates depend on the kinematical behavior of the landforms, values calculated may change in regard to the evolution of the surface velocities, which are currently generally increasing in the European Alps. When connected to torrents, periglacial moving landforms may thus represent substantial active sources of sediments for the development of debris flows and should be considered in the management of torrential catchments.

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Headwater sediment dynamics in a debris flow catchment constrained by high-resolution topographic surveys

Earth Surface Dynamics ◽

10.5194/esurf-4-489-2016 ◽

2016 ◽

Vol 4 (2) ◽

pp. 489-513 ◽

Cited By ~ 10

Author(s):

Alexandre Loye ◽

Michel Jaboyedoff ◽

Joshua Isaac Theule ◽

Frédéric Liébault

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Laser Scanning ◽

Early Spring ◽

Sediment Dynamics ◽

Sediment Supply ◽

Power Law Distribution ◽

Sediment Reworking ◽

Sediment Budgets ◽

Sediment Transfer

Abstract. Debris flows have been recognized to be linked to the amounts of material temporarily stored in torrent channels. Hence, sediment supply and storage changes from low-order channels of the Manival catchment, a small tributary valley with an active torrent system located exclusively in sedimentary rocks of the Chartreuse Massif (French Alps), were surveyed periodically for 16 months using terrestrial laser scanning (TLS) to study the coupling between sediment dynamics and torrent responses in terms of debris flow events, which occurred twice during the monitoring period. Sediment transfer in the main torrent was monitored with cross-section surveys. Sediment budgets were generated seasonally using sequential TLS data differencing and morphological extrapolations. Debris production depends strongly on rockfall occurring during the winter–early spring season, following a power law distribution for volumes of rockfall events above 0.1 m3, while hillslope sediment reworking dominates debris recharge in spring and autumn, which shows effective hillslope–channel coupling. The occurrence of both debris flow events that occurred during the monitoring was linked to recharge from previous debris pulses coming from the hillside and from bedload transfer. Headwater debris sources display an ambiguous behaviour in sediment transfer: low geomorphic activity occurred in the production zone, despite rainstorms inducing debris flows in the torrent; still, a general reactivation of sediment transport in headwater channels was observed in autumn without new debris supply, suggesting that the stored debris was not exhausted. The seasonal cycle of sediment yield seems to depend not only on debris supply and runoff (flow capacity) but also on geomorphic conditions that destabilize remnant debris stocks. This study shows that monitoring the changes within a torrent's in-channel storage and its debris supply can improve knowledge on recharge thresholds leading to debris flow.

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Starting a programme for research and monitoring of sediment transfer processes in the periglacial zone of Bulgaria (Bulgarian Periglacial Programme)

Norsk Geografisk Tidsskrift - Norwegian Journal of Geography ◽

10.1080/00291950802095152 ◽

2008 ◽

Vol 62 (2) ◽

pp. 132-134

Author(s):

Emil M. Gachev

Keyword(s):

Transfer Processes ◽

Periglacial Zone ◽

Sediment Transfer

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Erosion and sediment transfer processes at the front of rapidly moving rock glaciers: Systematic observations with automatic cameras in the western Swiss Alps

Permafrost and Periglacial Processes ◽

10.1002/ppp.1960 ◽

2017 ◽

Vol 29 (1) ◽

pp. 21-33 ◽

Cited By ~ 12

Author(s):

Mario Kummert ◽

Reynald Delaloye ◽

Luc Braillard

Keyword(s):

Swiss Alps ◽

Transfer Processes ◽

Rock Glaciers ◽

Sediment Transfer ◽

Western Swiss Alps

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Sediment-water flows in mountain catchments: Variability in response to high-magnitude hydrological events

10.5194/egusphere-egu21-4605 ◽

2021 ◽

Author(s):

Andrea Brenna ◽

Marco Borga ◽

Massimiliano Ghinassi ◽

Lorenzo Marchi ◽

Mattia Zaramella ◽

...

Keyword(s):

Debris Flow ◽

Water Flow ◽

Debris Flows ◽

Transport Mechanisms ◽

Stream Network ◽

Water Flows ◽

High Magnitude ◽

Sediment Transfer ◽

Flood Deposits ◽

Debris Floods

Sediment transfer in mountain streams occurs by processes classified as debris flows, hyperconcentrated flows, debris floods, and water flows. One of the most important tasks in investigating floods in mountain catchments is to identify the transport mechanisms since different sediment-water flows induce peculiar geomorphological dynamics and hazards. This study aims at testing how the energy of water and the amount of sediment involved during a high-magnitude hydrological event can modify the mechanisms of sediment transfer with respect to those occurring during ordinary floods.The selected case study is the Tegnas catchment (Dolomites, Italy), which, in October 2018, was affected by a severe hydrological event (Vaia Storm) with a recurrence interval of about 200 years. The studied catchment drains an area of 51 km2, with a range in elevation between 2872 and 620 m a.s.l.. The classification of flows that occurred during the Vaia storm was addressed at the sub-reach scale applying a field survey protocol developed to classify the flood deposits based on their sedimentological and morphological features. Following the same approach, we also determined the flow types typifying the stream network during ordinary floods. Additionally, we considered flows predicted by three morphometric approaches for high-magnitude events, and took into account the geomorphological dynamics (e.g., channel changes) and the hydraulic constraints (i.e., unit stream power) that occurred during the Vaia storm.Water flow was the dominant process during Vaia storm in the Tegnas main steam (12 sub-reaches), although debris flow and debris flood deposits were documented at 3 and 7 sub-reaches, respectively. Water flow was observed in response to ordinary events along the entire Tegnas Torrent. Most of the steep tributaries were affected by debris flows (6 tributaries), but also debris floods were recognized at 3 steep channels. The morphometric approaches had a satisfactory performance in predicting the two end-member flows, but often failed in recognizing sub-reaches affected by debris floods.The comparison between the occurred high-magnitude flows, and the ordinary flows allowed us to infer the existence of relationships between the transport mechanisms, the hydraulic forcing, and channel dynamics. The upheaval of the ordinary flow types did not occur along the entire stream network. The transition from water flows to debris floods occurred for unit stream powers exceeding the threshold of 5000-6000 Wm-2 or downstream of a channel delivering a large amount of sediment mobilized by debris flow to the receiving stream. The occurrence of debris floods, causing higher channel widening than water flows, appears to be facilitated by the injection of fine material into the flow, which can occur as consequence of channel-bank erosion and overbank floodwater re-entering the channel. Finally, morphometric approaches turned out to be adequate to provide a first-order discrimination of expectable high-magnitude flow types. However, the complex relationships found between flow types and a range of hydraulic, morphological, and geological controlling factors, reveal that a more detailed characterization is necessary for understanding the transport mechanisms and predicting geomorphic hazard that can affect specific channel sites during high-magnitude to extreme hydrological events.

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Multi-temporal geomorphological maps based on historical aerial images for the investigation of geomorphic changes in an Alpine catchment

10.5194/egusphere-egu2020-22605 ◽

2020 ◽

Author(s):

Tobias Heckmann ◽

Livia Piermattei ◽

Jakob Rom ◽

Moritz Altmann ◽

Fabian Fleischer ◽

...

Keyword(s):

Climate Change ◽

Spatial Configuration ◽

Aerial Images ◽

Ice Age ◽

Anthropogenic Factors ◽

Channel Network ◽

Multi Temporal ◽

Geomorphological Map ◽

Sediment Transfer ◽

Geomorphic Processes

Since the end of the Little Ice Age, alpine geosystems have been subject to changes due to the effects of ongoing climate change, affecting e.g. the cryosphere, topography, surface materials and morphodynamics, landcover, landuse, and other anthropogenic factors. Our work forms part of the SEHAG project that investigates the sensitivity of alpine geosystems to climate change during that period.In order to identify and assess such changes, we aim at generating multi-temporal geomorphological maps of three alpine catchments (Upper Kaunertal, Horlachtal, Austria; Val Martello, Italy). In contrast to &#8220;traditional&#8221; geomorphological maps, we do not use areal, linear and point symbols to represent landforms, their properties, and geomorphic processes. Our approach is entirely based on non-overlapping polygon features that represent a landform- and process-centered subdivision of the catchment. This enables the analysis of the resulting map in a GIS framework with respect to the type, size and other properties of landforms. Most importantly, it allows for the assessment of their spatial configuration (adjacency, topology) within the catchment in terms of toposequences and sediment cascades.Mapping is based on photogrammetric products of aerial photos, that are orthophotos, digital elevation models (DEMs) and derivatives of the latter. Furthermore, DEMs can be used for the orientation of historical terrestrial photographs, making them an additional mapping basis through monoplotting. Depending on the availability of imagery (area-wide aerial images dating back to the mid of the 20th century; local terrestrial photos starting from the second half of the 19th century), an area-wide geomorphological map representing the present state of the system forms the basis of our investigations. Historical images are then used to &#8220;update&#8221; the map back into the past wherever differences to the temporally subsequent situation are conspicuous. This especially regards the massive decline of glaciers, but also the build-up and depletion of storage landforms, the development of lakes, and changes in the channel network.At a later stage, the maps will be used for a network-based, multitemporal assessment of sediment connectivity. Nodes represent landforms contained in the geomorphological map(s), and all kinds of evidence (visible features indicating sediment transfer between adjacent landforms, measurements based on DEMs of difference, connectivity indices) will be used to establish edges that represent (potential) sediment transfer by geomorphic processes. As the configuration of system components and/or the activity of processes changes between maps of subsequent epochs, these changes will affect connectivity measures of the corresponding network model.

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Headwater sediment dynamics in debris flow catchment: implication of debris supply using high resolution topographic surveys

10.5194/esurf-2015-48 ◽

2016 ◽

Author(s):

A. Loye ◽

M. Jaboyedoff ◽

J. I. Theule ◽

F. Liébault

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Laser Scanning ◽

Early Spring ◽

Bedload Transport ◽

Sediment Dynamics ◽

Power Law Distribution ◽

Sediment Reworking ◽

Sediment Budgets ◽

Sediment Transfer

Abstract. Debris flows have been recognized to be linked to amounts of material temporary stored in torrent channels. Consequently, sediment production, debris supply and storage changes from low-order channels of the Manival catchment (French Alps) were surveyed periodically during 16 months using terrestrial laser scanning (TLS) to study the coupling between sediment dynamics and torrent responses in terms of debris flow events, which happened twice during the monitoring period. Sediment transfer in the main torrent was monitored with cross-section surveys. Sediment budgets were generated seasonally using sequential TLS data differencing and morphological extrapolations. Debris production depends strongly on rockfall occurring during winter–early spring season, following power law distribution for volumes of rockfall events above 0.1 m3, while hillslope sediment reworking dominates debris recharge from spring to autumn. Both debris flows originate in channels exclusively, but their occurrence is linked to recharge from previous debris pulses coming from the hillside and from bedload transport. Headwater debris sources display an equivocal behaviour in sediment transfer: despite of rainstorms inducing debris flows in torrent, low geomorphic activity occurred in production zone. Still, a general reactivation of sediment transport in headwater channels was observed in autumn without new debris supply, suggesting no exhaustion of debris storages. The seasonal cycle of sediment yield seems therefore to depend not only on debris supply and runoff (flow capacity), but also on geomorphic conditions that destabilize remnant debris stocks. This study shows that a monitoring of torrent in-channel storage changes coupled to debris supply can readily improve knowledge on recharge threshold leading to debris flow, so their prediction.

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