78 The Drainage of Fens and Low Lands. 



wheel In some wheels, both in Holland and England, the 

 divergence starts almost directly from the centre of the 

 wheel, while in most cases the divergence begins at the point 

 where the scoops are attached to the wheel The object of 

 this widening is to allow the water to get freely to the scoops 

 both at the end and sides. The outlet channel is provided 

 with either single or double self-acting doors, according to 

 the size of the channel These close automatically when 

 the wheel stops. In some cases these doors are placed 

 close to the wheel in a set-back in the masonry. A disturb- 

 ance is thus caused in the flow of the water by the alteration 

 in the size of the channel and by the water striking against 

 the framing of the doors and the angles of the masonry. 

 To ensure an even flow and prevent eddies, the outlet 

 channel should have the same width as the wheel, and 

 gradually widen outwards to the outfall drain ; the sides 

 should be smooth, and free from any projection or recesses ; 

 the door removed to some distance from the wheel ; and the 

 breast of the raised outlet sill rounded off. 



Where the wheel has to contend with a great depth of 

 water on the outside, the scoops as they come round, churn 

 up a large quantity without discharging it. The wheel thus 

 becomes choked, and does not part with its load as efficiently 

 as it otherwise would This churning up of the water causes 

 also a strong back undercurrent, which seriously impedes the 

 free discharge from the wheel. To show the effect of this, an 

 instance may be quoted of a case where, although at the time 

 a large body of water was being discharged by a wheel into 

 the outfall channel, the undercurrent near the raceway was so 

 strong that a small boat which had got loose near the wheel 

 was sucked down and got jammed in the scoops. The atten- 

 *^^ion of the superintendent being called to the circumstance, 

 winlNaused the self-acting door at the end of the raceway to be 



A' f isl 



aajust ^N^ horizontally, Avith the result that when the water 

 a certain er^^i ^^^ \{{^ owing to floods, the lower half of 



