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Changes in sediment connectivity due to a heavy precipitation event in lower Grastal, Tyrol


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Himmelstoss, Toni ; Betz-Nutz, Sarah ; Rom, Jakob ; Altmann, Moritz ; Fleischer, Fabian ; Haas, Florian ; Becht, Michael ; Heckmann, Tobias:
Changes in sediment connectivity due to a heavy precipitation event in lower Grastal, Tyrol.
Veranstaltung: Mid-European Geomorphology Meeting 2022, 24.-27.11.2022, Kaprun, Österreich.
(Veranstaltungsbeitrag: Kongress/Konferenz/Symposium/Tagung, Poster)


Sediment connectivity is an important factor regulating the propagation of change in alpine geomorphic systems. Such changes include altered discharge rates and the exposing of unconsolidated material due to glacier melt. Whether increasing sediment supply and transport capacity lead to an increase in sediment yield at the catchment outlet depends, among others, on the coupling of sediment sources to the channel network. Connectivity is not a static property – but is subject to continuous and sometimes rapid change, especially in catchments with high process dynamics. Major hydrogeomorphic events affect functional connectivity and have the capacity to change structural connectivity.
In this study we investigate the changes in functional and structural sediment connectivity due to a major precipitation event in Grastal (Austria) in July 2022. With regard to sediment transfer, the investigated lower Grastalbach is longitudinally decoupled from the glacier forefield by a lake. Due to a high debris flow activity in the catchment, a lateral coupling to adjacent talus slopes exists at some points. During the event, several debris flows delivered sediment into or deposited it nearby the channel. While this represents a temporary change of functional connectivity, a major relocation of the main channel took place and the fluvial corridor was restructured in some parts.
To assess these changes, two surveys were conducted in the weeks after the event: One UAV survey covering the fluvial corridor and one helicopter-based ALS survey with additional image capturing, covering the whole catchment. Those data have been used to generate post-event orthomosaics and digital elevation models. Similar surveys have been carried out in the years before, hence pre-2022 DEMs and orthomosaics already exist. On this basis, two geomorphological maps are created, one reflecting the pre-event and one the post-event system structure. These maps are used to derive toposequences and sediment cascades. In addition, a DEM of difference was calculated, which is used to detect sediment fluxes and hence to validate the coupling between landforms. Our research also highlights the merits of rapid post-event surveys to document and quantify changes (attributable to a single event), and to understand their implications for system structure.

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Publikationsform:Veranstaltungsbeitrag (unveröffentlicht): Kongress/Konferenz/Symposium/Tagung, Poster
Schlagwörter:sediment connectivity, sediment budget, geomorphological mapping
Sprache des Eintrags:Englisch
Institutionen der Universität:Mathematisch-Geographische Fakultät > Geographie > Lehrstuhl für Physische Geographie
Titel an der KU entstanden:Ja
Eingestellt am: 20. Mär 2023 08:12
Letzte Änderung: 20. Mär 2023 08:12
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