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EXHIBIT A: CHAPTER 928 <br />Rainwater and Land Development or a hydrologic model <br />acceptable to the City Engineer. <br />To account for future post -construction improvements to the site, <br />calculations shall assume an impervious surface such as asphalt or <br />concrete for all parking areas and driveways, regardless of the surface <br />proposed in the site description except in instances of engineered <br />permeable pavement systems. From the volume determined in Section <br />928.09.13.3.a, determine the percent increase in volume of runoff due to <br />development. Using the percentage, select the 24-hour Critical Storm from <br />Table 3. <br />Table 3: 24 -Hour Critical Storm <br />If the Percentage of Increase in Volume of Runoff is: <br />The Critical Storm will be: <br />Equal to or Greater Than: <br />and Less Than: <br />---- <br />10 <br />1 year <br />10 <br />20 <br />2 year <br />20 <br />50 <br />5 year <br />50 <br />100 <br />10 year <br />100 <br />250 <br />25 year <br />250 <br />500 <br />50 year <br />500 <br />--- <br />100 year <br />For example, if the percent increase between the pre- and post -development runoff volume for a 1 -year <br />storm is 35%, the Critical Storm is a 5 -year storm. The peak discharge rate of runoff for all storms up to <br />this frequency shall be controlled so as not to exceed the peak discharge rate from the I -year frequency <br />storm under pre -development conditions in the development drainage area. The post -development <br />runoff from all less frequent storms need only be controlled to meet pre -development peak discharge <br />rates for each of those same storms. <br />The minimum storage volume for the stormwater retention system shall be <br />calculated following the requirements of subsections I through 3 above. <br />However, in no case shall the required storage volume be less than the total <br />proposed hardsurface area times two inches unless approved by the City Engineer. <br />Hard surface areas shall include roof areas, concrete areas, asphalt areas, brick <br />areas, stone paver areas, and other similar areas as determined by the City <br />Engineer. <br />E. Stormwater Management on Redevelopment Projects: <br />Comprehensive Stormwater Management Plans for redevelopment projects must <br />accomplish one of the following options: <br />a. Reduce existing site impervious areas by at least 25 percent, a one-for-one <br />credit towards the 25 percent net reduction of impervious area can be <br />obtained through the use green roofs. <br />