VOLUME OF WATER 241 



the Ministry of Public Works published a map, on 

 the scale i : 100,000, of the course of the river between 

 Posadas and San Pedro, at the beginning of the delta. 

 A precise survey was made, and twenty-six fluvio- 

 metrical scales were established, the zero of which 

 represents mean low- water. ^ Transverse soundings 

 were taken at equal distances of 670 and 1,000 feet, 

 the distance being reduced to 160 and even 80 feet 

 at critical points. Thanks to this work, the Parana 

 is now, no doubt, the best known of all rivers of that 

 size. 



Its output is estimated at 6,000 cubic metres a 

 second at mean low-water, in the latitude of Rosario, 

 and 25,000 to 30,000 cubic metres a second during 

 flood at a height of six metres above low- water. 2 Its 

 features bear the mark of its tropical origin. The 

 tropical character is typical on the Paraguay, which 

 is, by its situation in the central South-American 

 plain, the real continuation of the lower Parana. The 

 slightness of the fall of the Paraguay, however, and 

 the extent of the marshes over which it spreads in 

 Brazil and Paraguay, have the effect of regulating 

 and retarding the flood, which only attains its maxi- 

 mum at Asuncion in May. The flood of the Paraguay 

 extends the period of high water on the lower 

 Parana until the end of autumn. The upper 

 Parana has most of its basin in the tropical zone of 



' It is as well to notice that the profile determined by the altitude 

 of the zero of these different scales, or the low-water profile, is of a 

 purely theoretical character. The river is never at low-water over 

 its whole course. The real profile is always varied by slight move- 

 ments of flood and ebb. 



> Observations of the sediment held in the water have been made 

 at Campana, 32 miles from the estuary. At this point the Parana 

 only holds in suspension fine particles of clay, but sand travels slowlv 

 along its bed. The weight of the clay in suspension varies from 179 

 grammes per cubic metre in March during the flood, to 42 grammes 

 at low-water in July. The stuff mostly comes from the Bermejo, 

 which carries 5 kilogrammes of sediment per cubic metre. The load 

 of the Parang is much heavier than that of the Uruguay, but far 

 lower than that of the Mississippi. 



16 



