FOR GREAT BRITAIN AND IRELAND. 109 



quantity of water will never effect if liberated more 

 slowly. 



The first example of artificial scouring in this country 

 seems to be due to Smeaton, who used it effectively at 

 Ramsgate in 1779. At Bute Docks, Cardiff, designed by 

 the late Sir W. Cubitt, the access to the outer basin is kept 

 open most successfully by means of artificial scouring on a 

 gigantic scale. The entrance was cut through mud banks 

 for a distance of about three-fourths of a mile seaward of 

 high-water mark. The initial discharge when the reservoir is 

 full is stated to be 2500 tons per minute. I have known 

 even so limited a discharge as one ton per second, produce 

 very useful effects in keeping a small tidal harbour clear 

 of sand." 



DURATION OF SCOURING. 



"Minard remarks that when a channel has to be 

 maintained by regular and habitual scouring, the whole 

 effect is generally produced in the course of the first quarter 

 of an hour. This was made the subject of particular 

 investigation at Dunkirk, where sections of the channel 

 were made before and during the scour ; and it was found 

 that there was no alteration of the sectional area after the 

 first quarter of an hour. 



"He also points out, as the best form of scouring 

 reservoirs, that which will admit of the largest discharge 

 in a given time, or, in other words, where the mean distance 

 from the orifice is a minimum. Such a form is obviously 

 the semicircle having the point of discharge in the centre." 



EFFECTIVE VELOCITIES OF CURRENTS. 

 The following are results of experiments, made by 



