A rapid method for settling velocity and flocculation measurement within high suspended sediment concentration rivers.
Résumé
In headwater catchments, fine sediment transport is a main issue with regard to monitoring erosion, pollutant fluxes, and reservoir siltation. In these environments, suspended sediment concentrations exhibit high temporal variations during runoff events and commonly exceed 10 g/l. The settling velocity of suspended sediment is a key variable to understand and model sediment transport. For such concentrated events, hindered settling and flocculation processes increase the difficulty to model sediment transport. Currently, no automated method for the measurement of settling velocity and propensity to flocculate within high concentration sediment environments exists. Methods used to measure individual particle settling velocity (e.g., LISST, video) are limited to low concentrations (<1g.l). They can be adapted to higher concentration after dilution in particle-free water, however, measured settling velocities may not be representative of the initial sample as hindered and flocculation effects are eliminated or reduced. In order to measure quasi in situ sediments settling velocity spectrum and propensity to flocculate in high concentrated environment, we assessed a processing method based on light transmission measurement within a quiescent settling column condition.
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