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Transport des matières en suspension et du carbone organique à l'échelle d'un bassin versant agricole : analyse de la dynamique et modélisation agro-hydrologique (SWAT)

Abstract : The study of the fluvial suspended sediment and organic carbon transport through the world's streams and rivers provides information on the erosion rate of continents, the cycling of carbon on earth, and the contribution of terrestrial carbon to the oceans. The objectives of the research are, on the one hand, to describe and analyse the transport dynamics of suspended sediment (SS), and dissolved and particulate organic carbon (DOC and POC) during flood events with assessment of flood load contribution and, on the other hand, to quantify the long term fluxes by agro-hydrological modelling approach. The experimental study is based on the field experiment for extensive data collection at the catchment outlet from both manual and automatic sampling within the Save agricultural catchment, 1110 km2, a tributary of the Garonne River in Southwest France from January 2007 through June 2009. For modelling approach, the SWAT model (Soil and Water Assessment Tool) was applied to study long term trend of sediment transport processes, sediment and particulate organic carbon yield taking into account hydrolo-climaitic data (1999-2008), landuse, and agricultural management practices within the catchment. Our results revealed high temporal variability in transport dynamics during different seasonal flood events. SS, DOC and POC load were strongly transported during spring resulting from frequent flood events of high magnitude and timing of flood. The quantification of flood loads of SS, DOC and POC contributing to annual load was estimated. Annual sediment transport in 2007 yielded 16 614 tonnes, representing 15 t km-2 (85% of annual load transport during floods for 16% of annual duration), while the 2008 sediment yield was 77 960 tonnes, representing 70 t km-2 (95% of annual load transport during floods for 20% of annual duration). The transport of POC and DOC during flood events exhibited 76% and 62% of their total loads within 22% of the whole duration (January 2008 to June 2009). POC and DOC export from the Save catchment amounted to 3091 t and 1238 t, representing 1.8 t km-2 y-1 and 0.7 t km-2 y-1, respectively. The hydro-climatic factors conditioning the transport dynamics using statistical analyses revealed strong correlations between total precipitation, flood discharge, total water yield with SS, POC, DOC load transport. Moreover, SS, POC and DOC dynamics using concentration-discharge relationship (hysteresis patterns) at different flood events during rising and falling flow were also examined. SWAT agro-hydrological model results show strong temporal variability of annual sediment and POC yield from the Save catchment (1999-2008). Annual sediment yield ranged from 4766 t to 123000 t, representing a mean specific sediment yield of 48 t km-2 y-1 and annual POC yield ranged from 120 t to 3100 t, representing a mean specific POC yield of 1.2 t km-2 y-1. A regression between annual water yield and simulated annual sediment yield was established and potential source areas of erosion were also identified by modelling for the Save agricultural catchment.
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Submitted on : Monday, October 15, 2012 - 3:01:19 PM
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  • HAL Id : tel-00741915, version 1

Citation

Chantha Oeurng. Transport des matières en suspension et du carbone organique à l'échelle d'un bassin versant agricole : analyse de la dynamique et modélisation agro-hydrologique (SWAT). Hydrologie. Université Paul Sabatier - Toulouse III, 2010. Français. ⟨tel-00741915⟩

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