228 



SEWER DESIGN 



to carry away the obstruction, or until the discharge of the flush- 

 tank (and here is seen its true function) takes up the obstruction 

 and carries it to a point where the depth and velocity of the 

 sewage will hold it in suspension. Table XXVI and the dia- 



FIG. 67 



gram (Fig. 67) are given to show the requirements in grade to 

 maintain a velocity of 2\ feet per second in a 6-inch lateral, 

 assuming a constant contributing population of 76 persons 

 per 100 feet of sewer, with a daily flow of 60 gallons per capita, 

 and with the assumption of one-half flowing off in 6 hours. 



TABLE XXVI 



The diagram (Fig. 67) shows that, taking n equal to 0.013, 

 aixi computing velocities by Kutter's formula, a grade of i per 



