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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union

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https://doi.org/10.5194/esurf-2017-52
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
05 Sep 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Earth Surface Dynamics (ESurf).
Topographical changes caused by moderate and small floods in a gravelly ephemeral river – 2D morphodynamic simulation approach
Eliisa Lotsari1,5, Mikel Calle2, Gerardo Benito2, Antero Kukko3,4, Harri Kaartinen3, Juha Hyyppä3, Hannu Hyyppä4, and Petteri Alho3,4,5 1Department of Geographical and Historical Studies, University of Eastern Finland, Joensuu, Yliopistokatu 2, P.O. Box 111, 80101 Joensuu, Finland
2National Museum of Natural Sciences, Spanish Research Council (CSIC), Madrid, Calle de Serrano 117, 28006 Madrid, Spain
3Department of Remote Sensing and Photogrammetry, Finnish Geospatial Research Institute, National Land Survey of Finland, Kirkkonummi, Geodeetinrinne 2, 02430 Masala, Finland
4Department of Built Environment, Aalto University, Espoo, Vaisalantie 8, P.O.Box 15800, 00076 Aalto, Finland
5Department of Geography and Geology, University of Turku, Turku, 20014 Turun yliopisto, Finland
Abstract. In ephemeral rivers, channel morphology represents a snapshot at the end of a succession of geomorphic changes performed by a flood. In most cases, the channel shape and bedform evolution during different phases of a flood hydrograph are not recognized from field evidence. This paper analyzes the capabilities of morphodynamic modelling (Delft 2D) for resolving the evolution of a gravelly ephemeral river channel during consecutive, moderate- and low-magnitude discharge events. We pursue for schematic concepts for simulations in ephemeral gravely rivers that provide an outcome with the closest similarity to the post-flood reality. Based on the simulations, we analyze the morphodynamic evolution of Rambla de la Viuda (Spain) to find out when and to what extent the channel changes occur during the phases of moderate- (March 2013) and low-magnitude (May 2013) discharge events, and what influence the discharge has on the rate of morphological changes. The model performance is examined with different parameterizations.

The spatially varying grain size data and transport equations were the most important factors, in addition to the quality of recorded discharge, for the simulation results of the channel evolution. The total load equation worked better, compared to the deterministic equation. The erosion and deposition can be in total greater during the longlasting receding phase than during the rising phase. The deposition and erosion peaks are predicted to occur at the beginning of the moderate-magnitude discharge event, whereas deposition dominates throughout the event. On the contrary, the low-magnitude discharge event only experiences the peak of channel changes after the discharge peak. These different predicted erosion/deposition patterns suggest a hysteresis effect on the morphodynamic changes, and stress the importance of previous flood history (timing, succession and magnitude) in understanding the geomorphic response of gravelly ephemeral rivers.


Citation: Lotsari, E., Calle, M., Benito, G., Kukko, A., Kaartinen, H., Hyyppä, J., Hyyppä, H., and Alho, P.: Topographical changes caused by moderate and small floods in a gravelly ephemeral river – 2D morphodynamic simulation approach, Earth Surf. Dynam. Discuss., https://doi.org/10.5194/esurf-2017-52, in review, 2017.
Eliisa Lotsari et al.
Eliisa Lotsari et al.
Eliisa Lotsari et al.

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This paper analyzes the capabilities of morphodynamic modelling for resolving the evolution of a gravelly ephemeral river channel during moderate- and low-magnitude discharge events. We also analyze when and to what extent the channel changes occur during these events. The spatially varying grain size data and transport equations were the most important factors for the simulations. The channel changes can be in total greater during the long-lasting receding phase than during the rising phase.
This paper analyzes the capabilities of morphodynamic modelling for resolving the evolution of a...
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