224 Removal of Accumulations vjhich impede Navigation. [Sept. 



Article X. 



Observations on the Means of removing Accumulations lohich 

 impede Navigation.* By Joseph M'Sweeny, M.D. 



The utility of clearing the beds of rivers from accumulations 

 of sand or gravel needs no comment : any thing which shall 

 tend to diminish labour and expense' in the removal of them will 

 I hope be deemed worthy of consideration. The expense of 

 clearing rivers by dredging machines impelled by steam engines 

 must be very great, while the employment of men is objection- 

 able on account of the work being both expensive and laborious. 

 Here in -Cork, below St. Patrick's bridge, men have been recently 

 eno'ao"edin throwing gravel with shovels into a large boat resting 

 on the accumulation when the tide was out. The labour of 

 throwino- any thing from the bed of the river over the elevated 

 sides of a large boat may be easily conceived. The trouble of 

 clearing the boat afterwards of the stuff raised must also be taken 

 into account. I apprehend that the following expedient will 

 save a great deal of labour : A large receiver open at one end is 

 to be laid on the bed of the river, exactly similar to the contri- 

 vance used in salt works for weighing salt, and for pouring it off 

 when weighed. It should, in like manner, be provided with 

 chains uniting at a ring that it might be evenly suspended from 

 any fixed point. 



When the tide is out, this receiver can be easily filled with 

 gravel, and when the tide returns sufficient to allow a broad flat- 

 bottomed boat provided with a hook in the centre of the bottom 

 to float over it, the ring of the receiver is to be put on the hook. 

 The person who does this is now to get into the boat, and wait 

 tlie further rise of the tide. As the tide rises, the buoyancy of 

 the boat will raise a weight of gravel that would in ordmary cir- 

 cumstances sink it, provided what contains the weight be evenly 

 suspended from the hook. 



Ihe boat is now to be propelled out of the channel of the 

 river to any place most convenient for depositing the gravel here 

 by pulling a rope attached to the closed end of the receiver so 

 as to raise it, the persons in the boat can cause the gravel to 

 slide down and escape at the open end.f 



In this manner the surface of ground subject to be overflown 

 by the tide may be raised, and stone and other materials for 

 embankments can be deposited in places where it is intended to 

 erect them to keep off" the water. In the formation of a break- 

 water great trouble is experienced in raising out of the hold of a 



* Read at llie Cork Philosophical and Literary Society, on May 3» 1820. 



+ When fine sand, or any thing liable to be washed off, is to be conveyed, the 

 receiver at this end may be closed up with a board moving on hinges and united 

 by lynch pins. These pins should move so freely that they could easily be pulled 

 UL) '■>•■ ro;)(?s '.1 aHow the !)oarrl to fall down th;it thi sand might- escape. 



