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~; ClipGEtBPe <br />~°trf~'E'EF~°5&'EC1' <br />.'' t3&E?TE:B~~ZS <br />~ ,.;. <br />May 2016 <br />Table 3: 24-flour Critical Storm <br />If the Percentage of Increase in Volume of <br />Runoff is: <br />The Critical Storm will be: <br />Equal to or Greater Than: and Less Than: <br />---- 10 1 year <br />10 20 2 year <br />20 50 5 year <br />50 100 10 year <br />100 250 25 year <br />250 500 50 year <br />500 --- 100 year <br />For example, if the percent increase between the pre- and post-development runoff volume fora 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 1-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 />E. Stormwater Management on Redevelopment Projects <br />1. Comprehensive Stormwater Management Plans for redevelopment projects shall reduce <br />existing site impervious areas by at least 20 percent. Aone-for-one credit towards the 20 <br />percent net reduction of impervious area can be obtained through the use of green roofs. <br />Where site conditions prevent the reduction of impervious area, SCMs shall be implemented <br />to treat at least 20 percent of the WQv. <br />2. When a combination of impervious area reduction and stormwater quality control facilities <br />are used, ensure a 20 percent net reduction of the site impervious area, provide for treatment <br />of at least 20 percent of the WQv, or a combination of the two. <br />Where projects are a combination of new development and redevelopment, the total water <br />quality volume required to be treated shall be calculated by a weighted average based on <br />acreage, with the new development at 100 percent water quality volume and redevelopment <br />at 20 percent. <br />4. Where conditions prevent impervious area reduction or on-site stormwater management for <br />redevelopment projects, practical alternatives as detailed in Section 1128.10 may be approved <br />by the Village Engineer. <br />26 <br />