CHAPTER XIV 

 USE OF DIAGRAMS 



IN order to understand better the use of Kuichling's 

 method for determining the amount of rain-water to be consid- 

 ered and the proportion of the fall reaching the sewers, the 

 following hypothetical example is given of its use in Ithaca, 

 N. Y., the plan of which city is given on Plate I. 



It is assumed that the surface-water above Eddy Street 

 will be taken care of by a drain discharging from the end of 

 that street into Six Mile Creek, and that all the storm-water 

 falling on the area between Eddy Street and Aurora Street 

 at the foot of the hill is to be taken care of by a drain run- 

 ning from State Street north to Cascadilla Creek. Evidently 

 three main laterals will lead into this drain one coming down 

 the hill on State Street, one on Seneca Street, and one on Buffalo 

 Street; while a fourth line, smaller than the others, will enter 

 from Mill Street. 



To determine the rate of rainfall the duration required 

 for a maximum flow at the outfall is necessary, that is, the 

 length of time for rain to get from the upper end to that point. 

 The point farthest from the outfall is at the corner of State 

 and Eddy streets, and, scaling from the map, it is 2375 feet 

 to the corner of Aurora and State streets and 1325 feet on 

 Aurora Street to the creek. Down the hill the average grade, 

 from the contours, is about 7 per cent, and if we assume a 1 2-inch 

 pipe, according to the diagram on Plate 3 the velocity will be 

 10 feet per second. That is, it will take water about 2375^10 

 = 237 seconds, or four minutes, to reach the bottom of the hill. 



On the flat there are 1720 feet, and the velocity will be 

 that due to a fall shown by the contours to be 10 feet in that 

 distance, a .58 per cent grade. 



190 



