114 SMALL WATER SUPPLIES. 



In works of large magnitude, it is usual to deal 

 with the water during progress of the work by means 

 of a canal cut along the side of the valley above the 

 top level of the embankment and joining the stream 

 farther down. It is called the " bye-wash ". In 

 small works such an expense would not be warranted. 

 In such cases the best expedient is to divert the 

 stream, which will probably only be small, to one 

 side, and in its bed set a line of pipes on a very firm 

 foundation of concrete. When finished and complete 

 with a valve, the work on the bank may proceed on 

 each side and above it. The culvert should be large 



FIG. 82. 



enough to pass the greatest floods, and must be so 

 solidly constructed as to avoid any after settlement 

 due to the load of the bank. This method of pro- 

 cedure is not employed in large banks, but may be 

 safely used for banks sustaining less than 20 ft. of 

 water, which in small works will usually be the maxi- 

 mum. 



Another useful form of bank to impound moderate 

 depths of water is a clay bank lined with concrete 

 as shown in fig. 82, care being taken that the clay 

 rests on a firm, and is carried down to an impervious, 

 foundation. The concrete would be reinforced be- 



