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.[123] 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 maximum 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 summer rain. But its behaviour is also influenced by the spring or autumn rains of the southern part of the Brazilian tableland. Its floods are sudden and violent. They reach a height of sixty or seventy feet in the region of the confluence of the Yguassu. They sweep rapidly down stream, and reach the lower Parana before the flood of the Paraguay, which they hold back. [123] 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 slowly 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 Parana is much heavier than that of the Uruguay, but far lower than that of the Mississippi. From Posadas the flood-waves reach Corrientes in five days (235 miles). From Corrientes they reach Parana in eight days (380 miles), travelling about two miles an hour. That is one-third the speed of the current, as the flood is retarded, and more or less absorbed, by the ramifications of the broader bed in which it moves. At Bajada Grande the lowest water is in September. The flood appears in December or January, though sometimes in October or November. The maximum is in March or April. The rise is rapid at first, but it gradually moderates, and the level of the water is raised about one metre per month during three months. It then sinks in corresponding order. The ebb is often interrupted in June, and sometimes as late as August, by a sudden leap upward of the curve, representing an ascensional movement of the water three times as rapid as that of the main flood (one metre in ten days). The level reached in this late flood is sometimes higher than that of the normal flood in April or May. The range of the ordinary flood-movements is from ten to sixteen feet. Exceptional floods rise to a height of twenty-three feet above the low-water mark.