Page 34 - GENERACION Y TRANSPORTE DE SEDIMENTOS

34 PEA BERMEJO

de la Plata, made mainly on the basis of particle ment entering and leaving the area or section of
size characteristics, confirms that the sediments river. To perform this analysis, it is appropriate to
dumped by the Bermejo River system are largely discuss separately the mechanics of sands, on the
those that are deposited in the delta of the Parana one hand, and the silts and clays, on the other.
and the channels of the Río de la Plata. Mineral- The bed of the main channels is sandy, and
ogical analysis of sediments from the study of the transport of such material is performed at a rate
clay fraction of suspended sediments in a stream, corresponding to the saturation capacity, which
show results in the same direction. means that if a deficit in contribution of the upper
So far we have analyzed the behavior of the sys- system is produced, this will be always completed
tem to nearly the mouth of the Paraná River, delta by solid contributions taken from the riverbed.
area. As noted, the transport of sediments in the For the analysis of the deposition of silt and clay,
river Paraná generally consists of sand and silt, with it is convenient to characterize the behavior of the
a lower proportion of clay. system in low and high waters.
The silts and clays are transported by the Paraná In the case of low waters, the silts are transport-
River as wash load. There are no practical limits to ed as wash load along with the water current. In
the amount of sediment driven by the water cur- this condition, the water flow through the courses
rent in this mode of transport. It must be remem- as channeled system, with some loss of material
bered that in all tests performed during the study, from the wash load in transverse arms and lateral
the fine fraction (silts and clays) has been consid- water bodies such as lakes and port docks, where
ered as wash load of the suspension transport mea- the conditions of speed of the current allow its de-
sured in solid gauging stations used, although this is position. Consequently, it can be said that the silt is
not strictly true. driven with high efficiency to the mouth of the river
The Paraná River receives a contribution of channels in the Río de la Plata.
suspended solid material which can be considered In the case of high waters, there is an exchange
in the order of 100 million tons annually. Accord- between the water of rivers and water bodies
ing to what has already been said, it may be con- flooding plains and islands in the Delta. When a
sidered as a basis for analysis, that the total is the body of water with wash load enters flooded ar-
contribution of fine fraction (mainly silt) due to eas of a very low speed, deposition of such ma-
the Bermejo River. As regards the density of de- terials occurs, thus contributing to the growth of
posited silt, it can take a value variable between the Delta.
1,100 and 1,600kg/m , depending on the diame- As for the rate of advance of the front of the
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ter of the particles, the type of sediment and time Delta, it proper to mention, that in the current situ-
of consolidation / deposition. ation, such rate is about 100 meters/year. The last
In the Paraná Delta area, fluviomorphological link in this analysis is the Río de la Plata.
changes relate largely to mass imbalances of sedi- The Upper Río de la Plata is the most active flu-