Il6 SMALL WATER SUPPLIES. 



discharging the flood waters, and that water which is 

 not used for immediate consumption. Where the 

 dam is of masonry or concrete, it is a simple matter to 

 allow it to flow over the top in ways which will 

 be discussed. With earthen banks, however, the 

 provision of a waste weir is necessary to prevent the 

 water accumulating to a dangerous height. It is usu- 

 ally constructed of heavy masonry set in cement, and 

 the water being gradually let down to down-stream 

 level by a channel made of similar masonry in a series 

 of steps to break the fall, the rise of each step not being 

 greater than 2 ft. under ordinary circumstances. The 

 waste weir must not be formed in the bank itself but 

 at one side or the other, and should be of the most 

 solid construction. The method of drawing off the 

 supply from such reservoirs demands attention. In 

 masonry dams it is an easy matter to lead pipes 

 through the dam at any desired point. With large 

 reservoirs with clay banks the usual practice is to 

 build a tower of masonry or cast iron which contains 

 the valves and draw-off pipes, etc., which are then 

 led through the bank in a masonry culvert which it- 

 self is dry and easy of access for repair. This is 

 an expensive and elaborate construction which 

 is quite unnecessary for small works, and for which 

 purpose the one form of construction, which at the 

 same time cuts down expense and saves more pipes 

 than necessary running in the bank, is the syphon 

 outlet. The action of the syphon in connexion with 

 wells has already been fully discussed. The system 

 for use in the case of a reservoir is precisely the same, 

 the reservoir bank being the same as the side of the 

 well, that is, the obstacle over which the water has to 



