While it is convenient to consider the quantity of rainfall for which provision is to be made in terms of the rate of fall in inches per hour, it will be useful for the practical application of the figures to know the actual rate of flow of the storm water in the sewers at the point of concentration in cubic feet per minute per acre. This information is given in the following Table No. 8, which is prepared from the figures given in Table No. 7, and is applicable in the same manner. TABLE No. 8. MAXIMUM FLOWS OF STORM WATER. --------------------------+---------------------------------- | Maximum storm water flow in | cubic feet per min per acre | of impervious area. Time of Concentration. +------+------+------+------+------ | A | B | C | D | E --------------------------+------+------+------+------+------ 5 minutes | 106 | 121 | 181 | -- | -- 10 " | 75 | 91 | 121 | -- | -- 15 " | 64 | 75 | 91 | -- | -- 20 " | 57 | 64 | 79 | 73 | 181 25 " | 51 | 57 | 70 | -- | -- 30 " | 48 | 54 | 64 | 61 | 151 35 " | 45 | 51 | 57 | -- | -- 40 " | 42 | 48 | 54 | -- | -- 45 " | 39 | 45 | 51 | -- | -- 1 hour | 30 | 36 | 42 | 45 | 109 1-1/2 " | 24 | 30 | 36 | -- | 85 2 " | 18 | 24 | 30 | 30 | 67 --------------------------+------+------+------+------+------- l inch of rain = 3,630 cub. feet per acre.