SCOURING AND SLUICING. 283 



of water to fly out, sufficient to sweep a large circular area, and 

 thus together clear the floor of the basin of sediment. 



This system has been in operation for some years without 

 the slightest mishap. Periodical examinations by divers have 

 proved the surface of the concrete to be perfectly clean, and its 

 face, as well as the lining of the pipes, in as good a condition as 

 when first put in. A special condition in connection with the 

 basin is that no anchors are to be let go within its area under a 

 heavy penalty. 



The intermediate fairway outside the basin, and within the 

 pier-heads, is also kept deep and clear of sediment by artificial 

 means. The timber jetties projecting into the river from the 

 north and south pier-heads serve as guides or fendei-s, against 

 which vessels entering or leaving the basin may bear; they 

 also serve to limit the area within which deep water has to 

 be maintained, whilst in their foundations a system of sluices 

 has been constructed by which the removal of deposit is effected 

 in the vicinity of the outlets. 



In the base of the north jetty, three pipes, each 8 feet in 

 diameter, are laid in connection with the main sluicing culvert 

 of 12 feet diameter in the west wall of the basin. A series of 

 sluicing outlets 4 feet in diameter, 24 feet apart, project 

 nearly horizontally from the 8-feet pipes. The discharge from 

 these outlets is regulated by clough-paddles in the basin 

 pier-head. A similar series of outlets is laid in the north-west 

 face of the south jetty, the supply of sluicing water being in this 

 case obtained from the Canada Dock. The combined action of 

 the discharge from these sluices and of the flow through the 

 Canada Basin, when its sluices are open, suffices to keep the fair- 

 way between the splayed piers at the required depth. 



Low-water Basin, Birkenhead. 1 In designing the scouring 

 arrangements at the Low-water Basin, at Birkenhead, the inten- 

 tion of the engineer (the late Mr. Renclel) was that the current, 

 when discharged from the sluices, should prevent an accumulation 

 of deposit in the basin, rather than remove it after it had been 

 allowed to form, and for that reason the water was to be run out 

 as often as the tides would permit, at a velocity of three or four 

 times greater than the flow of the tide into the basin, and there- 

 fore sufficiently powerful to remove any matter that might be 

 brought in. The velocity referred to was intended to produce 



1 M.P.LC.E., vol. xxviii. p. 520. 



