Author(s): Clemens Hiller; Sebastian Leistner; Lukas Walter; Kay Helfricht; Klemens Weisleitner; Stefan Achleitner

Linked Author(s): Clemens Hiller, Stefan Achleitner

Keywords: Sediment; Glacier; Hydraulic Modelling; Parameterization; Outwash Plain

Abstract: The evident mass loss of glaciers over the past decades is coupled with shifting runoff dynamics and highly intensified geomorphic processes particularly in headwater catchments on the verge of deglaciation. The progressive down wasting of glaciers results in an increasing exposure of unconsolidated sediments impacting the catchment-scale sediment dynamics. The induced changes in sediment fluxes can have considerable implications for the operation and management of water resources, especially for hydro-electric power facilities in otherwise non-regulated glaciated catchments. Bedload-bearing outwash plains are a widespread feature in deglaciating catchments and often serve as an area of re-deposition under average runoff conditions. During high, respectively extreme runoff events, the proglacial areas connect with the downstream catchment, delivering subglacial sediments to lower stream sections. As such, they represent key elements in high-alpine river systems and are an important component in determining the upstream boundary conditions of a catchment. Yet quantifying bedload transport in the paraglacial transition zone is a challenging task. The typically remote location of outwash plains in the proximity of retreating glaciers usually complicate direct measurements, especially since the area under investigation is prone to frequent geomorphic processes and changes. However, quantitative data on sediment yields from glaciated catchments is needed in order to contribute to the sustained effort of the research community to understand global to local and inter- and intra-catchment controls (Carrivick and Tweed 2021) on sediment yields. In this work we present a feasible methodological approach to parameterise key characteristics of an exemplary proglacial outwash plain (Jamtal valley, Austria) in order to overcome data scarcity in the paraglacial process domain of mountain glaciers, enabling modelling of sediment fluxes on sub-catchment scale. The key parameters considered in this study include (i) high spatial and temporal resolution models of the frequently changing topography as well as (ii) discharge and (iii) sediment properties in the investigated proglacial outwash plain. Such data are crucial for model parameterisation and calibration in the context of hydro-morphological modelling. In this work, we employed UAV-based surveys using RGB imagery to reliably capture (i) topographic information together with surface roughness and (iii) grain size distribution in a combined approach. Discharge properties (ii) such as inundation areas and water level elevations are semi-automatically derived from stationary time-lapse images, supported by maximum water level gauges located in the outwash plain. This multi-method approach provides key input and calibration data for applied hydraulic modelling. In summary, we present how the different data sets are derived and combined to finally obtain a best estimate of the parameterisation of the hydraulic and morpho-dynamic model. Carrivick, J. L. & F. S. Tweed (2021) Deglaciation controls on sediment yield: Towards capturing spatio-temporal variability. Earth-Science Reviews, 221, 103809.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221484

Year: 2022