498 



Transactions. 



Art. XLV. — An Arrangement for quieting the Flow of a Stream oj 



Disturbed Water. 



By Professor R. J. Scott, M.Inst.C.E., M.I.Mech.E., F.A.I.E.E. 



[Read before the Philosophical Institute of Canterbury, 6th September, 1916 ; received by 

 Editors, 30th December, 1916; issued separately, 10th December, 1917.] 



In order to measure with reasonable accuracy the discharge of water over 

 a notch or weir it is necessary to first destroy the waves and eddies present 

 in the stream — in fact, to approximate as closely as possible the conditions 

 of stream-line flow. In practice the following methods have been adopted : — 



(1.) The use of a pond above the notch. 



(2.) The use of deflector plates. 



(3.) The use of perforated plates. 



(4.) The use of wire-gauze screens. 



The use of a pond above the notch is an efficient and simple method of 

 dealing with the discharge of small streams. The pond is easily constructed ; 

 the water is brought nearly to rest and eddies are damped out. It is, how- 

 ever, ineffective in windy weather, and evidently cannot be adopted for 

 flows of any magnitude, nor in the laboratory. 



Deflector plates reduce surface-disturbances, but the presence of the 

 plates gives rise to a new series of eddies (fig. 1). For this reason deflector 

 plates are often combined with the perforated plates or wire-gauze screens. 



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Fig. 1. — Action of deflectors. 



With perforated plates the dead-water behind the unperforated portion of 

 the plate gives rise to eddies ; surface-disturbance also occurs owing to the 

 drop of a number of small streams (fig. 2). 



These disturbances are smaller in the case of wire-gauze screens, which, 

 however, are difficult to keep in a sufficiently clean condition to permit of 

 the necessary freedom of flow. 



None of these methods being sufficiently effective to quiet the flow to the 

 degree required for some experiments on surface friction, the author devised 

 the following arrangement :— 



