SCOURING AND SLUICING. 281 



through the sluice direct into the entrance channel in forty -five 

 minutes, attaining a velocity of 26 feet per second. 



Canada Basin, Liverpool. The following particulars of the 

 sluicing arrangements made for maintaining the depth in 

 the Canada Basin are abridged from Mr. G. F. Lyster's paper on 

 " Dock Extensions at Liverpool." l 



In designing the New North Docks, it was decided that the 

 sills should be placed on the same level as those at Birkenhead, 

 viz. 12 feet below datum, or 2 feet below low water of equinoctial 

 spring tides. 



This decision involved special arrangements to provide for 

 the maintenance of the required depths at all times without 

 dredging or such-like expedients. 



The area of the basin is about 9J acres, and the fairway 

 within the splayed piers about 3 acres. 



Mr. Lyster concluded that the only certain method of 

 BROCKLEBANK ^^^gj^oj^f^fe^ 



CANADA o o c 



SCALE SOUTH JET 



NORTH JETTY 100 9 100 590 300 400 FEET 



FIG. 283. 



effecting the object in view was by the flow of water through 

 culverts of such form, and placed in such positions, as would 

 command the areas in question. 



This has been attained by the construction of a system of 

 large culverts (Fig. 283), connected with the Langton Dock, 

 having short branches fitted with sluices, and carried into the 

 basin through the wing walls, similar culverts and sluices being 

 constructed through the masonry of the walls surrounding the 

 island between the entrances. The culverts are for the most 

 part of iron, with a special form of joint, and all are lined with a 

 |-inch coating of Portland cement, kept in place by dovetail ribs 

 cast on at near intervals. 



1 M.P.I.C.E., vol. c. p. 2. 



