Dynamique saisonnière des mouvements de l'eau et des particules en suspension dans un fleuve

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Summary

The water movements (discharge, current velocity) in the Rhône River, upstreams of Lyons (France), strongly modulate the transport of fine suspended matter and coarse organic particles. Measurements were carried out at 3 m from the riverside and in the middle of the channel, near the bottom and under the water surface. Stream velocities at different depths show a distinct correlation with the discharge values. Hence, water discharge can be used to describe the movements of the water at different levels of a river section. Whatever the discharge is, the flow rate near the riverside remains half as low as that of the channel; the flow rate in the channel is always maximum at a depth of 1 m from the surface; near the river bank it is maximum at half-depth. Suspended matter, of which the density is correlated with fluctuations in discharge, remains inferior to 50 mg · l⁻¹, except at the time of the first rise of the water in autumn, after the low water period (more than 100 mg · l⁻¹). The same holds true for the suspended organic particles, with a density of about 0.1– 0.3mg · l⁻¹, P. O. M. which at that time may attain 4mg · 1⁻¹ of dry matter; this phenomenon is reinforced by the fall of the leaves. Then, the successive winter floods bring about the loading of the river, which decreases progressively with the wash of the river bed. This loading of the river continues for a much longer period during the winter following the emptying of the hydroelectric reservoir upstream of Génissiat. The average amount on non-living material carried yearly by the river is estimated at 400000 tons for the suspended matter and at 4000 tons for the P. O. M.