Sedimentological study of the fluvial environments from the Eastern Chaco

Abstract

Some sedimentological aspects of fluvial environments situated in the flood-plain of the Paraguay-Paraná river system (Northeastern of Argentina) were analized. The concentrations of suspended sediments, and the granulometric and textural characteristics of the bottom materials, were compared.

The suspended load had an inverse relation with the hydrometric levels with exception of the highly saline streams (conductivity values between 4300 and 11000 uS.cm^-1) showing the drastic succession of wet and dry seasons which periodically affected the region. The mean concentration of suspended sediments was 63,1 mg.l^-1 and 206,3 mg.l^-1 in flood and low water periods, respectively.

Bed sediments were relatively homogeneous along all the hidrological eyele. Silt-sandy bottoms were the predominant, followed then by sand-silty and silt-clayey bottom types.

Sediment transport was mainly carried out in acelerated flow suspensión, overcoming the erosion critical velocity. In flood period, some morphometric parameters overcome the 70% in relation with the values recorded in low water.

Besides, different elements of diagnostic value for the evaluation of natural or antropical erosión, are also discussed.