202 



SEWER DESIGN 



intermediate pumping-plants are required to avoid excessive 

 depths at the outfalls. 



When possible, the laterals should be laid to reach the mains 



FIG. 53. 



in the shortest path, though topographical conditions do not 

 always admit of this. In Fig. 53 it is more expedient to build 

 two sewers from c to the water at a and b than to take the 



V 



FIG. 54. 



sewage from the whole area from d, both because the grades 

 would be greater from the centre both ways than from water 

 to water, and because the longer sewer would require greater 

 size and greater depth of cutting. Where there are a number 



