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<br />(c) The run-off coefficients shall be as follows: <br />Before development or redevelopment, <br />Flat slope, less than 2 percent 0.01 to 0.05 <br />Average slope, 2 to 7 percent 0.05 to 0.12 <br />Steep slope, greater than 7 percent 0.012 to 0.18 <br />After development or redevelopment, <br />Roof surface 0.85 to 0.95 <br />Asphalt surface 0.85 to 0.95 <br />Concrete surface 0.80 to 0.90 <br />Gravel roadway surface 0.65 to 0.75 <br />Grassed area 0.60 to 0.70 <br />Other surfaces As approved by City Engineer <br />Each type of area shall be calculated separately and the <br />individual run-off quantities added together to give the <br />total storm water run-off. <br />The run-off coefficient used for each site within each given <br />range shall be subject to the approval of the City Engineer. <br />(d) The time of concentration shall be determined as follows: <br />(1) Residential Areas: <br />The concentration times to the critical inlet varies <br />between 12 and 20 minutes with 15 minutes to be used as <br />the general case based upon full development of the land. <br />(2) Industrial/Commercial, Multi-Family and School Areas: <br />The concentration time to the critical inlet varies <br />between 10 and 15 minutes with 12.5 minutes to be used as <br />the general case based upon full development of the land. <br />(3) Major Urban Business Areas and Shopping Centers: <br />The concentration time to the critical inlet varies <br />between 5 and 12 minutes with 10 minutes used as the <br />general case based upon full development of the land. <br />Runoff characteristics which vary from the expected for either <br />residential, commercial, or industrial development will be <br />supported by data submitted for approval by the City Engineer. <br />(e) The rainfall intensity shall be based on Table 1 entitled <br />"Standard Rainfall Intensity Duration Table". <br />Page - 18 - <br />