RELATION OF DENSITY TO PERCENTAGE 



75 



TABLE XI 



TABLE SHOWING PERCENTAGES OF DIFFERENT KINDS OF SUR- 

 FACES IN A TYPICAL DISTRICT OF ITHACA, N. Y. 



If this be reduced to the total amount of impervious surface, 

 by assuming that 80 per .cent of the rain was delivered from 

 the improved streets and 40 per cent from the hard-earth and 

 macadam roads, and nothing from the lawns and flower-beds, 

 the amount becomes 29.4, while the maximum percentage 



10 20 30 40 50 60 



Proportion of RainfallReacnmq sewers 

 FIG. 14 



found in the experimental work was 34.8, an earlier rain prob- 

 ably adding a small run-off from the grass. 



In another thesis by Mr. H. E. Green, '06, a portion of the 

 campus was studied and the run-off measured by a weir across 

 the small creek that furnished drainage for this particular district. 

 The percentages of relatively impervious areas were as follows: 



