EGU2020-7671
https://doi.org/10.5194/egusphere-egu2020-7671
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Diffused and localized sediment production processes in a distributed transport model

Giulia Battista1, Peter Molnar1, Fritz Schlunegger2, and Paolo Burlando1
Giulia Battista et al.
  • 1Institute of Environmental Engineering, Department of Civil, Environmental and Geomatic Engineering, ETH Zurich, Zurich, Switzerland (battista@ifu.baug.ethz.ch)
  • 2Institute of Geological Sciences, University of Bern, Baltzerstrasse 1, 3012 Bern, Switzerland

The identification of preferential sediment production areas within a river basin is essential to improve predictions of sediment load and its sources, and to identify sources of potential water pollution. The role of these localized sediment sources is especially relevant in the sediment budget of alpine basins, where erosion in highly non-uniform and mass movements play a major role in the mobilization of sediments. While sediment tracers are useful to assess the origin of river-borne sediments, currently very few spatially distributed sediment transport models include the sediment production from a variety of sources and track sediment from source to outlet.

In this work, we present a new approach to include the production of sediment from localized sources, in addition to diffusive overland flow erosion, in a spatially distributed sediment production and transport model. This extension of the hydrological model Topkapi-ETH simulates the mobilization of sediments by (i) overland flow erosion, (ii) sediment pickup from landsliding areas by overland flow and (iii) river discharge, and (iv) sediment pickup from deeply incised valleys by channel flow. Landslides and incised valleys were identified from geological/geomorphological maps and a high resolution DEM of the study basin. To model the contribution of landslides, we introduce a parameter λ for gully competence, which describes the effectiveness of overland flow in mobilizing the sediments. Overall, λ affects the contributions of the different sediment production processes to the modelled sediment load at the basin outlet. To estimate a value of λ for the case study, we propose the local surface roughness to quantify the gully development onto the landslide surfaces. Additionally, we use available 10Be measurements across the basin to assign a concentration to each sediment production process and select the end member value of λ that best reproduces the observed 10Be concentrations at the outlet.

Our simulations indicate that including the production of sediments from localized sources with processes (ii) to (iv) is essential to capture the highest observed concentrations with the model. Moreover, the same observed suspended sediment concentrations at the outlet may be obtained with different combinations of sediment production processes in function of the gully competence. Finally, the local surface roughness analysis and the use of 10Be concentration as a sediment tracer suggest that channel processes are dominant over hillslope sediment production in the study basin.

In conclusion, our work shows that combinations of physically-based sediment transport modelling with geomorphological mapping of localized sediment sources, high-resolution topographic information and point measurements of cosmogenic radionuclide concentrations allow to infer the dominant sediment production processes in river basins.

How to cite: Battista, G., Molnar, P., Schlunegger, F., and Burlando, P.: Diffused and localized sediment production processes in a distributed transport model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7671, https://doi.org/10.5194/egusphere-egu2020-7671, 2020