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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union
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Volume 6, issue 1
Earth Surf. Dynam., 6, 163-185, 2018
https://doi.org/10.5194/esurf-6-163-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Earth Surf. Dynam., 6, 163-185, 2018
https://doi.org/10.5194/esurf-6-163-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 05 Mar 2018

Research article | 05 Mar 2018

Topographical change caused by moderate and small floods in a gravel bed ephemeral river – a depth-averaged morphodynamic simulation approach

Eliisa S. Lotsari1,5, Mikel Calle2, Gerardo Benito2, Antero Kukko3,4, Harri Kaartinen3,5, Juha Hyyppä3, Hannu Hyyppä4, and Petteri Alho3,5 Eliisa S. Lotsari et al.
  • 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, 20014 Turku, Finland

Abstract. In ephemeral rivers, channel morphology represents a snapshot at the end of a succession of geomorphic changes caused by floods. In most cases, the channel shape and bedform migration during different phases of a flood hydrograph cannot be identified from field evidence. This paper analyses the timing of riverbed erosion and deposition of a gravel bed ephemeral river channel (Rambla de la Viuda, Spain) during consecutive and moderate- (March 2013) and low-magnitude (May 2013) discharge events, by applying a morphodynamic model (Delft3D) calibrated with pre- and post-event surveys by RTK-GPS points and mobile laser scanning. The study reach is mainly depositional and all bedload sediment supplied from adjacent upstream areas is trapped in the study segment forming gravel lobes. Therefore, estimates of total bedload sediment mass balance can be obtained from pre- and post-field survey for each flood event. The spatially varying grain size data and transport equations were the most important factors for model calibration, in addition to flow discharge. The channel acted as a braided channel during the lower flows of the two discharge events, but when bars were submerged in the high discharges of May 2013, the high fluid forces followed a meandering river planform. The model results showed that erosion and deposition were in total greater during the long-lasting receding phase than during the rising phase of the flood hydrographs. In the case of the moderate-magnitude discharge event, deposition and erosion peaks were predicted to occur at the beginning of the hydrograph, whereas deposition dominated throughout the event. Conversely, the low-magnitude discharge event only experienced the peak of channel changes after the discharge peak. Thus, both type of discharge events highlight the importance of receding phase for this type of gravel bed ephemeral river channel.

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This paper analyses the timing of topographical changes of a gravel bed ephemeral river channel during consecutive and moderate- and low-magnitude floods by applying a morphodynamic model calibrated with pre- and post-event surveys using RTK-GPS and mobile laser scanning. The channel acted as a braided river during lower flows but as a meandering river during higher flows. The channel changes can be greater during the long-lasting receding phase than during the rising phase of the floods.
This paper analyses the timing of topographical changes of a gravel bed ephemeral river channel...
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