Inferring sediment-discharge event types in an alpine catchment from sub-daily time series
Abstract. Fluvial sediment dynamics in mountain rivers are changing rapidly in a degrading cryosphere, raising the potential for erosive rainfall and runoff, and detrimental effects on downstream areas. Hence, we need to understand better what characterises and drives episodic pulses of water and suspended solids in rivers. Here, we infer different types of such sediment-discharge events from 959 automatically detected events based on 16 metrics derived from 15-min time series of streamflow and suspended sediment concentrations from the Vent-Rofental in the High Ötztal Alps, Austria. We use principal component analysis to extract uncorrelated event characteristics and cluster event types with a Gaussian mixture model. We interpret thus inferred event types with catchment metrics describing antecedent conditions, hydrometeorological forcing, and catchment freezethaw state and snowcover. We find event magnitude, hysteresis, and event shape complexity to be the main factors characterising the overall event regime. The most important characteristics distinguishing the event types are suspended sediment and streamflow magnitude, and event shape complexity. Sediment-discharge hysteresis is less relevant for discerning event types. We derive four event types that we attribute to (1) compound rainfall-melt extremes, (2) glacier and seasonal snow melt, (3) freezethaw-modulated snow-melt and precipitation events, and (4) late season glacier melt. Higher magnitude glacier and snow melt events were the most frequent and contributed some 40 % to annual suspended sediment yield on average; compound rainfall-melt extremes were rarest, but contributed the second highest proportion (26 %). Our approach represents a reproducible method for objectively estimating the variety of event-scale suspended sediment dynamics in mountain rivers, which can provide insights into the contribution of different drivers to annual sediment yields in current and future regimes. Our findings highlight the importance of both meltwater and rainfall-runoff as drivers of high magnitude suspended sediment fluxes in mountain rivers.
Status: open (until 19 Mar 2024)
Sediment-discharge event types in Vent-Rofental, Austria https://doi.org/10.23728/b2share.4806f852f25541b4a3206b0d8110907c
Model code and software
Inferring sediment-discharge event types with clustering https://github.com/skalevag/hysevt/releases/tag/v0.1
Viewed (geographical distribution)