5.2.-5.4. PCSR 09-13-2011 - Laserfiche WebLink

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storm events and the likelihood that infiltration of the dead storage has not fully taken place between storm events. Peak Peak Peak Top Permanent Peak Storage Pond Inflow Outflow Elevation Elevation Dead Storage From Storm cfs cfs ft) (ft ac-ft (ac-ft P-1 82.4 10.2 995.6 1000 3.1 2.4 P-2 58.3 3.9 1022.9 1028 2.7 2.1 The calculations above demonstrate that the sedimentation basins in the most conservative look manage the runoff from a 25 year 24 hour event with over 4-feet of freeboard in P-1 and P-2 therefore; the design of the sedimentation basins is acceptable. Routing the 100 yr-24 hr storm event through the storm water system results in the following assuming a dry pond at the start of the storm and that the dead storage has infiltrated.: Peak -Peak Peak Top Permanent Peak Storage Pond Inflow Outflow Elevation Elevation Dead Storage From Storm (ac- cfs) (cfs) (ft ft ac-ft ft P-1 115.7 5.8 994.4 1000 3.1 0.9 P-2 82.1 2.3 1021.8 1028 2.7 0.8 The table below takes a more conservative look at the sedimentation basin designs for the 100- year storm event by running the HydroCad model with the assumption that the pond dead storage is full. Peak Peak Peak Top Permanent Peak Storage Pond Inflow Outflow Elevation Elevation Dead Storage From Storm (ac- cfs) cfs (ft) ft ac-ft ft P-1 115.7 12.7 996.6 1000 3.1 2.7 P-2 82.1 4.9 1023.6 1028 2.7 3.1 Discharge from P-1 to the wetland west of the site has been designed to minimize the potential for significant adverse impacts to the wetland by limiting bounce, restricting flow rates, and treating stormwater prior to discharge in accordance with Section D of Appendix A of the General Permit for Construction Activity. T:\0742V406Vune1lCityApp\Comment response\Response_081811\Attachmem 1\Stuface Water Management Memo 081011.~c 5