210 



SEWEJl DESIGN 



cent for both sections, and by repeated trials the depths in the 

 egg shape necessary to give the same discharges as the circular 

 were found. The benefit then is seen in the increased value of 

 v in the former case. 



According to the table, a gain of about 30 per cent in the 

 velocity is obtained by using the egg-shaped sewer. 



Since egg-shaped sewers are less stable and substantial 

 than circular sewers, since for the same area of cross-section they 

 require more masonry, and since they are more difficult of 

 construction, it is of value to note the alleged advantage in 

 velocity of this form and compare it with the increased cost of 

 construction. 



Fig. 60 shows a diagram by which the discharge and the 

 velocity of flow in the circular pipe can be read directly in 

 terms of the discharge and velocity when the pipe is flowing 

 full. The ordinates give the proportionate depths of flow and 

 the horizontal line through any given or desired proportionate 

 depth extended to meet the two curves given show by the 

 abscissae the proportions of the discharging velocity when the 

 pipe is flowing full. Similar curves may easily be made for the 

 two forms of egg-shaped sewer referred to above or for any 

 other section which is being used. 



Interesting curves of this sort applied to the sections sug- 

 gested for the main intercepting sewers at Boston and called 

 respectively, the basket-handle section, the gothic section, and 

 the catenary section, will be found in the report on the Boston 



