TRANSACTIONS OF THE SECTIONS. 



205 



wide and 2 feet high. After the mattresses were sunk, the piles were pulled up to 

 give a passage-way to vessels. 



The soft nature of the bottom is shown by the fact that in places where the water 

 was 30 feet deep, it was necessary to use piles 70 feet long, to make them stand. 



The idea is that this sill will prevent scour in these channels. When I visited 

 the works last spring this apron had stood the test of one flood, and no movement 

 of the mattresses had occurred. 



A similar apron is in course of being laid across the head of the Pass a Loutre. 



The results of the whole works so far are, that a deep-Avater contour-line, of from 

 about 22 feet to 23 feet, has been earned through the shoal at the head of the 

 Pass ; at the lower end on the outer bar the depth, which in June 1875 was 9 feet 

 2 inches, had increased in March of this year to 20 feet 10 inches. 



The general result of the works to the last date at which I have obtained reports 

 is shown in the following table, which gives the depth of water that could be carried 

 through each 2000 feet below East-Point station at different dates : — 



Distances in feet. 



The principal effect takes place when the river is in flood. These periods of flood 

 occur about three times a year. 



It will be seen that the principle upon which the works are designed is to allow 

 nature gradually to excavate the channel in the line laid out for it. 



The work of excavation carried on by the river has been irregular, in consequence 

 of the varying conditions of the river and of the amount of sediment which is 

 carried in suspension ; it has been, moreover, affected by the difference in the material 

 composing the bar at various places, the state of the tides, the direction and force 

 of the winds, the storms and resulting seas that rolled in against the current, as 

 veil as by the conditions of the works at Grand Bay on and the head of the pass 

 and the varying conditions of the jetties. 



But the general advance of the channel in width and depth has been constant 

 aud steady ; and the effect of the jetty construction has shown that the volume of 

 water issuing from the pass will eventually obtain the section which it has normally 

 above. 



A very important question, and one that cannot be definitely determined by facts 

 until the completion of the jetties, is that of an accelerated bar-advance due to the 

 construction of the jetties. All that can be now stated, bearing on this question, is, 

 that there has been pushing outward of the upper part of the outer slope of the bar, 

 due to three or more temporary causes— -Jirst, the impossibility of constructing the 

 whole line of jetties instantaneously ; second, the large amount of material excavated 

 and carried out to sea ; third, the closing of Grand Bayon and a new load of sediment 

 given the water in addition to its already heavy burden ; and fourth) the non-com- 

 pletion of the sea-ends of the jetties. 



But yet careful surveys and calculations show a deepening instead of a shoaling 

 immediately in front of the sea-ends of the jetties. 



The volume of the bar removed during the first year of the work, without 

 reference to amount moved in the channel as required by law, or, in other words, 

 the total excavation, exceeds 3,000,000 cubic yards. 



The following table shows the volume of the bar moved in reference to a channel 

 20 feet deep and 200 feet wide at that depth. 



