Citation, Pravansal et al 2010, article sur les berges du Rhône

Notre article paru dans Geomorphology :

High-resolution evaluation of recent bank accretion rate of the managed Rhone: A case study by multi-proxy approach
Provansal, M., Villiet, J., Eyrolle, F., Raccasi, G., Gurriaran, R., Antonelli, C.
Geomorphology
volume 117, issue 3-4, year 2010, pp. 287 - 297

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Accelerated overbank accumulation after nineteenth century river regulation works: A case study on the Maros River, Hungary
Kiss, T., Oroszi, V.G., Sipos, G., Fiala, K., Benyhe, B.
Geomorphology
volume 135, issue 1-2, year 2011, pp. 191 - 202

Résumé :

Abstract

In the nineteenth century, the meandering rivers of the Carpathian Basin were extensively regulated, and their large (up to 100 km wide) floodplains were confined by artificial levees. On the narrow (0.5–4 km) artificial floodplains confined by these levees, overbank sedimentation has become the dominant geomorphological process, resulting in rising floodplain levels during the last century. The Maros River is an extreme example of this process, as it carries a significant amount of suspended sediment (4.6 × 10⁶ m³/y) and because its lowland reach was drastically shortened by cutoffs, resulting in bed scour and an increased sediment load. Simultaneously, a flood embankment system was constructed, reducing the floodplain width by 70–80%. The resulting accelerated overbank sediment accumulation increases the flood hazard along the river.The aim of this study is to determine the spatial and temporal pattern of overbank sediment accumulation on the artificial floodplain of the lower Maros River over the last 150 years and to identify its influencing factors. The lateral slope of the protected (natural) floodplain was projected towards the present-day channel, allowing the volume (m³) and rate (cm/y) of overbank sedimentation to be calculated using digital terrain modelling (DTM). Changes in the rate of sedimentation were determined by pollen analysis.
The studied reach was divided into five sections based on the rate of aggradation: (i) the distal surface of the alluvial fan, where no sedimentation was measured, only incision; (ii) the original front of the alluvial fan (1.0 ± 0.4 cm/y); (iii) the recently formed secondary alluvial fan (1.4 ± 0.3 cm/y); (iv) the low-lying floodplain (0.4 ± 0.2 cm/y); and (v) the outlet unit (2.0 ± 0.5 cm/y). The aggradation rate was slower on elevated forms, such as the pre-regulation natural levee (0.2 cm/y), and greater on the low-lying floodplain (0.6 cm/y). The greatest accumulation rate (1.3–2.4 cm/y) was measured in cutoffs. The sedimentation rate was high during the regulation period (1.9–2.4 cm/y) but later decreased to 0.5–0.9 cm/y. The rate of aggradation was determined by the width, height and slope conditions of the floodplain, the impoundment of the main river and the land use in the area.

Article Outline

• 1. Introduction
• 2. Study area
• 3. Methods
• • 3.1. Digital terrain modelling (DTM)
  • 3.2. Sedimentological and palynological analysis
• 4. Results
• • 4.1. Spatial pattern of aggradation based on DTM
  • 4.2. Temporal pattern of aggradation: analysis of sediment profiles
  • • 4.2.1. The sediment and pollen profile of a cutoff (Cs1) located on the fan-front unit
    • 4.2.2. The sediment profile of a natural levee (Cs2) on the fan-front unit
    • 4.2.3. The sediment profile of the floodplain bottom (Cs3) on the fan-front unit
    • 4.2.4. Sediment and pollen profile of the cutoff (Zu) located on the secondary fan unit
    • 4.2.5. Sediment and pollen profile of the cutoff (Ve) located on the floodplain unit
• 5. Discussion
• • 5.1. Spatial changes
  • • 5.1.1. Aggradation rate along the river
    • 5.1.2. Aggradation rate related to different floodplain forms
  • 5.2. Temporal changes
  • 5.3. Methodological results
• 6. Conclusions
• Acknowledgements
• References