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Volume 22, issue 7 | Copyright
Hydrol. Earth Syst. Sci., 22, 3903-3921, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 19 Jul 2018

Research article | 19 Jul 2018

Contributions of catchment and in-stream processes to suspended sediment transport in a dominantly groundwater-fed catchment

Yan Liu1, Christiane Zarfl1, Nandita B. Basu2, Marc Schwientek1, and Olaf A. Cirpka1 Yan Liu et al.
  • 1Center for Applied Geoscience, University of Tübingen, 72074 Tübingen, Germany
  • 2Department of Civil and Environmental Engineering, University of Waterloo, Waterloo, ON N2L 3G1, Canada

Abstract. Suspended sediments impact stream water quality by increasing the turbidity and acting as a vector for strongly sorbing pollutants. Understanding their sources is of great importance to developing appropriate river management strategies. In this study, we present an integrated sediment transport model composed of a catchment-scale hydrological model to predict river discharge, a river-hydraulics model to obtain shear stresses in the channel, a sediment-generating model, and a river sediment-transport model. We use this framework to investigate the sediment contributions from catchment and in-stream processes in the Ammer catchment close to Tübingen in southwestern Germany. The model is calibrated to stream flow and suspended-sediment concentrations. We use the monthly mean suspended-sediment load to analyze seasonal variations of different processes. The contributions of catchment and in-stream processes to the total loads are demonstrated by model simulations under different flow conditions. The evaluation of shear stresses by the river-hydraulics model allows the identification of hotspots and hot moments of bed erosion for the main stem of the Ammer River. The results suggest that the contributions of suspended-sediment loads from urban areas and in-stream processes are higher in the summer months, while deposition has small variations with a slight increase in summer months. The sediment input from agricultural land and urban areas as well as bed and bank erosion increase with an increase in flow rates. Bed and bank erosion are negligible when flow is smaller than the corresponding thresholds of 1.5 and 2.5 times the mean discharge, respectively. The bed-erosion rate is higher during the summer months and varies along the main stem. Over the simulated time period, net sediment trapping is observed in the Ammer River. The present work is the basis to study particle-facilitated transport of pollutants in the system, helping to understand the fate and transport of sediments and sediment-bound pollutants.

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Short summary
We present a model for water and sediment transport in a small catchment. For the water balance, we use a simple hydrological model that can explain the observed sudden increase in river flow between storm events. This model drives a hydraulic model of the river, which is needed to determine erosion and sedimentation in the river. Sediments are mainly generated in urban areas as the topography of the catchment is smooth. During storm events, erosion and deposition in the river becomes relevant
We present a model for water and sediment transport in a small catchment. For the water balance,...