Abstract
The alluvial channel of the Langgriesgraben (Austria) is a highly active geomorphic riverine subcatchment of the Johnsbach River with intermittent discharge and braided river structures. The high sediment yield entails both issues and opportunities. For decades, the riverbed was exploited as a gravel pit. Today, as part of the Gesäuse National Park and after renaturation, the sediment yield endangers a locally important bridge located at the outlet of the subcatchment. High-resolution geospatial investigations are vital for the quantification of sediment redistribution, which is relevant in terms of river management. Based on unmanned aerial system (UAS) surveys in 2015 (July, September, and October) and 2019 (August and October), high-resolution digital elevation models (DEMs) were generated, which enable us to quantify intra- and multiannual sediment changes. As surface runoff at the subcatchment occurs on only a few days per year with flash floods and debris flows that are not predictable and thus hardly observable, the subsurface water conditions were assessed based on electrical resistivity tomography (ERT) measurements, which were conducted in 2019 (November) and 2020 (May, June). Results of the UAS-based surveys showed that, considering the data quality, intra-annual sediment changes affected only small subareas, whereas multiannual changes occurred in the entire study area and amount to net sediment deposition of ≈0.3–0.4 m3m−2, depending on the channel section. In addition, the elevation differences for both intra-annual surveys revealed linear patterns that can be interpreted as braided river channels. As in both survey periods the same areas were affected by changes, it can be concluded that the channel mainly affected by reshaping persisted within the 4-year observation period. The subsurface investigations showed that although both near-surface and groundwater conditions changed, near-surface sediments are mostly dry with a thickness of several meters during the observations.
Highlights
Fluvial landforms are of great importance from an ecological and economical perspective
With this section we aim to discuss the quality of the data and potential implications
The estimated achievable precisions of the five unmanned aerial system (UAS) surveys range from σx = ≈0.04 to ≈0.06 m and σz = ≈0.07 to ≈0.12 m
Summary
Fluvial landforms are of great importance from an ecological and economical perspective. Fluvial processes vary greatly in size, dimension, and intensity: floods regularly threaten engineered constructions and even human lives, while plenty of small-scale, short-term changes often go unrecognized. Riverine landforms form where water runs as overland flow and streamflow in river channels, which is based on runoff production as the difference between precipitation and evaporation rates [1] and relates to the removal and transfer of Earth surface materials [2]. Humans are considered geomorphological agents in riverine systems and channel reshaping could entail increased fluxes of water and sediments [3]. At the Langgriesgraben, the channel and downstream movement of sediments threaten a bridge and traffic pathway crossing the mountain torrent at the channel outlet [7]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
