Clustering of suspended sediment-discharge events and linking them to upstream geomorphic signals in a high-alpine catchment using DEMs of difference (2008–2025)

Sediment-discharge events recorded at the outlet of high-mountain catchments provide an integrated signal of upstream geomorphic activity. At the same time, a key limitation of DEMs of Difference (DoDs) is that sediment source areas and geomorphic responses cannot be directly linked to individual events, especially when DoDs span extended time periods. To address this, we apply the method proposed by Skålevåg et al. (2024) to detect, cluster and characterise sediment-discharge events, which can subsequently be related to observed sediment mobilization signals in the DoD.

15-min time series of water discharge and suspended sediment concentration from Gepatschalm, Kaunertal (Austria), covering the period 2008-2025, were used to detect the sediment-discharge events and derive 16 metrics, which were used to cluster the events with a Gaussian mixture model. Gridded meteorological data were used to characterise the clusters with respect to antecedent and intra-event forcing conditions. The resulting event catalogue was evaluated using DEMs of difference (DoDs) covering the entire catchment and investigation period.

Over the 16-year period we identified a total of 850 sediment-discharge events. Clustering results reveal three patterns: (i) melt-dominated events (average contribution ~30% to annual suspended sediment yield), (ii) early- and late-season freeze–thaw-modulated events (~15%), and (iii) compound rainfall–melt events (~33%). A marked increase in event frequency was observed in 2022, which also recorded the highest annual suspended sediment yield in the dataset. The majority of 2022 events were assigned to clusters 2 and 3. Combining multiple DoDs from summer 2022 with gridded precipitation data allowed the identification of a distinct sediment-discharge event on 28 June 2022, which triggered fluvial erosion in a specific sub-catchment of Kaunertal. For this event and other events, the main sediment source areas can clearly be delineated with the DoD analysis.

 

Skålevåg, A.; Korup, O.; Bronstert, A. (2024): Inferring sediment-discharge event types in an alpine catchment from sub-daily time series. In: Hydrology and Earth System Sciences Discussions.