2021-093 Ordinance - Laserfiche WebLink

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Section 928.09(D)(3)(a), determine the percent increase in volume of runoff due to development. Using the percentage, select the 24-hour Critical Storm from Table 3. Table 3: 24 -Hour Critical Storm If the Percentage of Increase in Volume of Runoff is: The Critical Storm will be: Equal to or Greater Than: and Less Than: ---- 10 1 year 10 20 2 year 20 50 5 year 50 100 10 year 100 250 25 year 250 500 50 year 500 --- 100 year For example, if the percent increase between the pre- and post -development runoff volume for a 1 -year storm is 35%, the Critical Storm is a 5 -year storm. The peak discharge rate of runoff for all storms up to this frequency shall be controlled so as not to exceed the peak discharge rate from the 1 -year frequency storm under pre -development conditions in the development drainage area. The post -development runoff from all less frequent storms need only be controlled to meet pre -development peak discharge rates for each of those same storms. 4. The minimum storage volume for the stormwater quantity control system shall be calculated following the requirements of Subsections 1 through 3 above. However, in no case shall the required storage volume be less than the total proposed hard surface area times two inches unless approved by the City Engineer. Hard surface areas shall include roof areas, concrete areas, asphalt areas, brick areas, stone pavers, and other similar areas as determined by the City Engineer. An access manhole or inspection port as approved by the City Engineer shall be provided at each end of an underground storage facility for sufficient inspection, maintenance and discovery of the system from the surface. E. Stormwater Management for Previously Developed Areas SCMs on previously developed sites must meet the criteria in the Construction General Permit.