200 



SEWER DESIGN 



(D) Fan system. In this the mains radiate from the out- 

 fall to serve different parts of the city, each main having its 

 own branches and laterals (Fig. 51). Whether this or the 

 perpendicular system is used will evidently depend on the topog- 

 raphy and on the requirements of the outfall. 



(E) Radial system. In this system, of which Berlin is the 



FIG. 52. 



only city offering a good example, the sewage is cared for at a 

 number of points in the circuit of the outskirts, and the sewage 

 is brought to these points by different mains. The drainage 

 is thus from the centre outward in several directions, and the 

 sewage is cared for on filtration areas in these several localities 

 (Fig. 52). Baumeister notes the great advantage of this method 

 in that the sewers in the centre of the city are laid after that 



