Evolution of an Alpine proglacial river during seven decades of deglaciation quantified from photogrammetric and LiDAR digital elevation models

Abstract

Abstract. Alpine rivers have experienced considerable changes in channel morphology over the last century. Natural factors and human disturbance are the main drivers of changes in channel morphology that modify natural sediment and flow regimes at local, catchment, and regional scales. In glaciated catchments, river sediment loads are likely to increase due to increasing snow and glacier melt runoff, facilitated by climate changes. Additionally, channel erosion and depositional dynamics and patterns are influenced by sediment delivery from hillslopes, and sediment in the forefields of retreating glaciers. In order to reliably assess the magnitudes of the channel-changing processes and their frequencies due to recent climate change, the investigation period needs to be extended to the last century, ideally back to the end of the Little Ice Age. Moreover, a high temporal resolution is required to account for the history of changes in channel morphology and for better detection and interpretation of related processes. The increasing availability of digitized historical aerial images and advancements in digital photogrammetry provides the basis for reconstructing and assessing the long-term evolution of the surface, both in terms of planimetric mapping and the generation of historical digital elevation models (DEMs). The main issue of current studies is the lack of information over a longer period. Therefore, this study makes a major contribution to research on fluvial sediment changes by estimating the sediment balance of a main Alpine river (Fagge River) in a glaciated catchment (Kaunertal, Austria) over nineteen survey periods from 1953 to 2019. Exploiting the potential of historical multi-temporal DEMs, combined with recent topographic data, we quantify 66 years of fluvial changes (i.e. the active floodplain) in terms of geomorphic changes, erosion, and deposition, and the amounts of mobilized sediment. We show that geomorphic changes and the cumulative sediment balance are mainly driven by glacier retreat as well as a short advance phase in the 1980s, sediment delivery from recently deglaciated steep lateral moraines, an increasing runoff trend and extreme runoff events (such as subglacial water pocket outburst, and heavy rainfall). Overall, this work has contributed to improving our understanding of the complexity of sediment dynamics and river changes across various spatial and temporal scales and their relationship to climate change factors.

Long-term monitoring (1953–2019) of geomorphologically active sections on LIA lateral moraines under changing meteorological conditions

“…3). The latest ALS datasets of each valley (2017 and 2019) were collected in own ALS flight campaigns of the Chair of Physical Geography at the Catholic University of Eichstätt-Ingolstadt (Table 3) (Stark et al, 2022).…”

“…In case of missing camera calibration certificate, an auto-calibration (no film camera) was performed. Both options were proposed by Stark et al (2022).…”

“…Furthermore, it should be noted that the accuracy and precision of the historical DEMs strongly depends on the respective generation, e.g. whether they were generated with or without a calibration certificate (as was the case, for example, with the 1959 aerial photo series in the Horlachtal/glacier forefield Hohenferner), which ultimately influences the SCA results and the calculated erosion rates (Stark et al, 2022).…”

“…The generation of multitemporal accurate and precise digital elevation models (DEMs) and the resulting DEM of Differences (DoDs) by different remote sensing methods and techniques, which have been established in geomorphological research in recent years, enabled the detection of changes in the Earth's surface in high spatial and temporal resolution (Pulighe and Fava, 2013;Nebiker et al, 2014;Tarolli, 2014;Smith et al, 2016;Eltner et al, 2016;Sevara et al, 2018;Okyay et al, 2019). By processing overlapping high-resolution digitised historical aerial images (HAI) of high alpine geosystems, using SfM-MVS (Structure-from Motion with Multi-View-Stereo) digital stereo-photogrammetry in combination with current airborne LiDAR (Light Detection And Ranging) data into DEMs and the corresponding DoDs, landscape changes in these areas can be reconstructed over several decades (Midgley and Tonkin, 2017;Mölg and Bolch, 2017;Lane et al, 2017;Betz et al, 2019;Altmann et al, 2020;Fleischer et al, 2021;Betz-Nutz, 2021;Stark et al, 2022;Piermattei et al, 2022). The spatial distribution of positive and negative DoD elevation changes enable various analyses, such as the reconstruction and interpretation of individual geomorphological processes (Dusik, 2019) or the calculation of morphological budgets (Altmann et al, 2020).…”

Quantitative long-term (1922 to 2021) monitoring of a large-scale landslide of a LIA lateral moraine due to glacial debuttressing

“…Fluvial and nival erosion processes, landslides and debris flows, are the predominant processes. Thus, some sections of the lateral moraine show strongly incised gullies, with high erosion rates during the last decades (Altmann et al 2020, Betz-Nutz et al 2022, Altmann et al 2023. However, several studies show a decrease in geomorphological activity of the lateral moraines, such as Altmann et al (2020), Betz-Nutz et al (2022, Stark et al (2022) and Altmann et al (2023) from the 1950s/1970s to 2019.…”