Fluvial erosion in the Bermejito river basin (Chaco Province, Argentina) | Erosión fluvial en la cuenca del río Bermejito (Prov. del Chaco, Argentina)

English. Size, distribution and longitudinal changes of suspended load was analized in Bermejito River, located in the Chaco subtropical plain. Temporal variability was compared with hydrometric levels and rainfalls in selectionated areas of the drainage basin. Field activities were carried out in three sections with free runoff and one section with reduced velocity for natural causes. Sampies were taken with an instantaneous point-sampler placed at 20X, 60X and 80X of depth, through equally spaced verticals across the sections. Laboratory procedures ineludes filtering through 62 a open sieve and subsequently through filters with 4 a and 0,45a por es, for retention sand, sllt and clay fractions, respectively. Mean textural composition in the free-runoff sections comprised silts (95X) and clays (5X). Concentration had an homogeneous distribuíiuon in the flow, owing to the turbulence effect. Longitudinal changes were related with the transport capacity of the water course. Rainfall determined a quick increment of the suspended sediment concentration by wash-load incorporationowing to the scarce vegetal protection. The restrict runoff section had fewer suspended sediment concentration and a greater clay fraction proportion. Sediment yield was estimated in 12.4 tn/km'/yr and the present erosión rate was calculated in about 5 mm for each 1000 years.

Spanish; Castilian. Size, distribution and longitudinal changes of suspended load was analized in Bermejito River, located in the Chaco subtropical plain. Temporal variability was compared with hydrometric levels and rainfalls in selectionated areas of the drainage basin. Field activities were carried out in three sections with free runoff and one section with reduced velocity for natural causes. Sampies were taken with an instantaneous point-sampler placed at 20X, 60X and 80X of depth, through equally spaced verticals across the sections. Laboratory procedures ineludes filtering through 62 a open sieve and subsequently through filters with 4 a and 0,45a por es, for retention sand, sllt and clay fractions, respectively. Mean textural composition in the free-runoff sections comprised silts (95X) and clays (5X). Concentration had an homogeneous distribuíiuon in the flow, owing to the turbulence effect. Longitudinal changes were related with the transport capacity of the water course. Rainfall determined a quick increment of the suspended sediment concentration by wash-load incorporationowing to the scarce vegetal protection. The restrict runoff section had fewer suspended sediment concentration and a greater clay fraction proportion. Sediment yield was estimated in 12.4 tn/km'/yr and the present erosión rate was calculated in about 5 mm for each 1000 years.