242 THE RIVER-ROUTES 



summer rain. But its behaviour is also influenced 

 by the spring or autumn rains of the southern part 

 of the Brazihan tableland. Its floods are sudden and 

 violent. They reach a height of sixty or seventy leet 

 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. 



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. Excep- 

 tional floods rise to a height of twenty-three feet above 

 the low-water mark. 



The curves established for the years 1908 to 19 10 

 by the Argentine hydrographical service enable us to 

 analyse the mechanism of the flood with a good deal 

 of confidence. The beginning of the flood at Bajada 

 Grande in October corresponds to the first flood of 

 the upper Parana. During this first phase the curve 



