212 SEWER DESIGN 



particular uses of the various sections which have been used 

 or the needs of various conditions nor would it be desirable 

 to consider the hydraulic properties or the structural weak- 

 nesses of such sections without reference to their uses. It is 

 only possible, therefore, here, to point out that these various 

 sections are used and that for large outfalls where the flow of 

 sewage is reasonably uniform, the economy of construction of 

 other forms should be compared with the economy of material 

 which for the same capacity always remains as an advantage 

 to the circular form. 



PROBLEMS 



82. Compare the velocities and discharges of two conduits laid on 

 the same grade (s=. 0003), one being circular, 6 feet diameter, flowing full, 

 and the other of the same area but rectangular with width twice the depth. 



83. Using the diagram of Fig. 60, determine the velocities of flow in a 

 36-inch tile sewer, laid on a 0.2 per cent grade, with depths of flow varying 

 by 2-inch intervals from o depth to half-full. Plot a curve showing variation 

 of velocity with depth. 



84. A brick sewer is to be laid on a .0002 grade and is to carry 100 cubic 

 feet per second flowing half full. If the flow sometimes drops to 5 cubic 

 feet per second, how much gain in velocity would be had by using an old- 

 style egg-shaped sewer? 



85. Using Kutter's formula, find the value of V, for a conduit of wooden 

 plank nailed together edgewise to form a trough of triangular section. 

 Assume the depth at the centre to be 12 inches and the grade to be .05 

 per cent. 



86. An outfall sewer has a section formed by a semicircular invert, 

 surmounted by vertical side walls. If the radius of the invert is 3 feet 

 and the total depth of flow 6 feet, find the slope, by Kutter's formula, 

 necessary for a velocity of 2 feet per second. 



