31 



Channel in a curved line Channel in a straight line 



Rock Iii.oeO M Rock SI. 51 M 



Sand and gravel. 256.000 „ Sand & gravel ... . L92.000 .. 



272.000 M 3 27:5.50o M 



From these figures results that the channel in a curved 

 line is the most convenient, as the difference in cube of 

 sand to be dredged is little, where as that for breaking up 

 and excavating sandstone is very visible. 



In orde'rto see the result which the opening of the chan- Local slopes. 

 nel might effect on the regime of the river in this part, 

 gauges have been placed which are based on a precise le- 

 velling which has been continued as far as the Estancia 

 Humaita ». 



With the observations which have been made simulta- 

 neously the mean slopes have been determined for different 

 sections and the heights of water resulting from their 

 examination that even if the formation of the uniform 

 slope over the whole extension of the bar were to take 

 place after the execution of the works of canalization, 

 this would not unfavorable modify the regimen of the 

 river in this zone, which, as has been seen, is navigable du- 

 ring a low river, not in consequence of the quantity of wa- 

 ter it brings down, but for the periodical high tides, which 

 maintain the water sufficiently high during three or 



four clays. 



On the contrary, it may be taken for sure, that by opening 

 the channel as projected, giving it a width of 80 meters by 

 levelling the shallow places of sandstone, this will help to 

 maintain the upper portion, in consequence of the increa- 

 sed slope which will be established. 



It is intended to mark this channel, in consequence of 

 its curved direction, with ten buoys, which position will 

 be referred to two fixed points placed with this object on 

 the island of « Chapicuy ». 



The last maned shallow place having been passed, the stretch of «Yem&> 

 river can be navigated with great facility, following the 



