Comparative Stormwater Storage Index for Various Sizing Criteria
38 acre Residential Development, 36% I
* Basic = 1/2 inch runoff control * I
2 yr peak discharge control
Notes:
The chart in this slide was developed to provide a general sense of how much storage the proposed unified sizing criteria approach requires in comparison to typical (referred to as �basic�) criteria frequently found in parts of the country. The �Basic� criteria assumes a water quality volume based on 0.5 inches of runoff per impervious area and 2 year peak discharge control. The �CWP� criteria assumes a water quality volume based on 1 inch of runoff times the runoff coefficient for the site and 1 year 24 hour extended detention channel protection control.
As the chart indicates, the relative volume requirements are higher under the proposed unified sizing criteria presented in this slide show. However, the additional storage requirements are not that substantial given the anticipated added benefits of pollutant load reduction and channel protection.