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� <br /> t � <br /> � <br /> � � <br /> � �ITYi OF ZEPHYRHILLS <br /> i <br /> � The Clity requires that the greater of the first half inch volume of rainfall or the difference <br /> between the site's pre- and post-development runoff volume for a 25 year storm event <br /> , with an intensity of 3.6 inches of rainfall in one hour be retained on-site. <br /> � <br /> i <br /> I <br /> � PRE-DEVELOPMENT <br /> The fillowing data was used to determine the pre-development runoff coefficient: <br /> � i oof - 18,000 sf <br /> � asphalt - 36,148 sf <br /> ' concrete - 5,358 sf <br /> � pervious - 81,486 sf <br /> i <br /> � Total: 140,992 sf <br />' C ure = 18,000 (0.95) x 36,148 (0.951 x 5,358 f 1.0) x 81,486 (0.2) = 0.52 <br /> ' � 140,992 <br /> The offsite drainage area's runoff will be conveyed via swales and/or on-site <br /> conveyance pipes to the existing FDOT basin/ outfall (see Figure 3, Pre- <br /> , ' Development Plan). <br /> � POST-DEVELOPMENT <br /> The fillowing data was used to determine the post-development runoff coefficient: <br /> � � i oof - 15,563 sf <br /> f sphalt - 61,833 sf <br /> � � i oncrete - 9,476 sf <br /> ; i tormwater facility— 13,833 sf <br /> ' pervious - 40,287 sf <br /> I <br /> Total: 140,992 sf _ <br /> � � <br /> C post = _i_5,563(0.95) x 61,833 (0.95) x 9,476(1.0) x 13,833(0.98) x 40 287(0.2) = 0.74 <br /> , 140,992 <br /> � <br /> I , <br /> CadM/data/99/6001-99/6001-99drainage <br /> � <br />� � � <br />