Etude des débits de charriage sur le Cady en utilisant les traceurs radioactifs

摘要

Summary. The river Cady, a tributary of the Tet, rises on the north face of the Canigou and flows through the basin of Vernet-les-Bains. Spring and autumn rainfall are both intense and abundant in the region, and maximum floodwater appears at that time. The transportation of sediment has benn studied in the middle part of the Cody, using mostly radioactive tracers. The river bed is not very twisty and well- graded (average width 10 metres), but slopes fairly steeply (43 %c), and is littered with rocks and boulders. The critical phase of déplacement of sediment starts at about 6 m ? per sec. The alluvium moves over the entire width of the bed and is deposited either in the axis of flow or on a convex bank. Transport for q floods (maxima 10.5 and 36.5 ma per sec.) is respectively 7 and 34.6 tons per metre of width. A q flood of max. 10 m3 per sec. can carry away blocks of 20 cm. in diameter, and a q flood of max. 36.5 m3 per sec. larger blocks of 30-40 cm. diam. These values for the beginning of the critical phase provoking transport are in agreement with others calculated by the means of formulae. Values for the transport itself, however, are lower than those calculated by the Meyer-Peters formula (qs = k (t-t0)3/2 where k = 1,29). These results may explain renewed erosion in the bed of the Cady, amongst the chaos of pebbles, rocks and boulders, and may be used to interpret forms of accumulation of the larger material, also the evolution of these forms in intermontane basins and in piemont an foothill.