SCOURING AND SLUICING. 273 



the water is discharged through several openings in the length 

 of the recess 4 feet 9 inches long by 9 inches high. The bed of 

 the recess, which is paved, is thus flushed out, and any deposit 

 of mud or other matter washed away. 



Calais Entrance Channel. 1 A discharge from the old sluicing- 

 basins of 450 cubic yards per second, lasting with efficiency 

 from one-half to three-quarters of an hour, produced first, in the 

 channel between the jetties, a depth of 5 feet 9 inches to 8 feet 

 2 inches below the zero of the charts, or the level of the lowest 

 tides known; and secondly, outside the jetties for a width of 

 130 feet a minimum depth, varying according to the frequency 

 of storms from 10 inches to 4 feet below the lowest tide level. 



Dunkirk Entrance Channel 2 With an average discharge of 

 510 cubic yards per second, and an efficient duration of about 

 three-quarters of an hour; the effect of the scour on the sand 

 in the inner channel was to maintain a depth of from 5 feet 9 

 inches to 8 feet 2 inches, and, outside, from zero to 2 feet 6 

 inches below zero, or the lowest tide level. 



St. George's Stage, Liverpool. 3 For the removal of a part of 

 the Pluckington sand-bank, which by its extension northward 

 projected under, and endangered the stage, Mr. G. F. Lyster 

 adopted a method of sluicing along the foreshore in front of the 

 river wall and at the rear of the landing-stage. The sluicing 

 takes place at low water, when the working of the docks 

 permits, when a vast quantity of water is ejected, which 

 effectually keeps the sand clear. 



The system as carried out consists of a series of twenty-two 

 cast-iron pipes, spaced 20 feet apart ; they are nearly semicircular 

 in section, having a diameter of 4 feet and a sectional area of 

 12 feet 5 inches. The outfalls are 10 feet below the old dock 

 sill, and 47 feet from the east side of the landing-stage (Figs. 

 274, 275, 276). 



These pipes are connected to a main culvert of somewhat 

 similar section, 8 feet in diameter, which is laid along the foot 

 of the river wall, and is in direct communication with the south- 

 end docks, from which the water for sluicing is obtained. 



By the time the sluices were ready for use, the sand-bank 

 had increased to such an extent that from 5 to 7 feet needed 

 removal before the pontoons of the landing-stage could be water- 

 borne at low water of spring tides. 



1 M.TJ.C.K, Isx. 75. * Ittd. * Ibid., vol. G. p. 78. 



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