31B-192 91 King Street-Peak flow Summary revision
St. Elizabeth Seton Parish, Northampton, MA April 13, 2011 Stormwater Drainage Report Supplemental Summary Page 1/1 Project Description: This supplemental summary is a revision to the
Table 1 from the drainage report for the St. Elizabeth Seton Parish Stormwater Permit dated 3/18/11. The table below and attached HydroCAD calculations shall supersede the 3/18/11 table
and calculations. The revision occurred based on a corrected impervious area calculation within sub-*catchment E-2. Table 1b. Peak Flow and Volume Summary Table Condition & Point of
Analysis 2-Year Storm 3.00” 10-Year Storm 4.50” 100-Year Storm 6.50” Peak Flow Rate(cfs) Volume (acre-ft) Peak Flow Rate(cfs) Volume (acreft) Peak Flow Rate(cfs) Volume (acre-ft) Existing
(E-CP1)* 2.23 0.179 4.51 0.353 7.72 0.607 Proposed (P-CP1)* 0.08 0.010 0.35 0.029 1.93 0.075 Existing (E-CP2)* 0.79 0.082 1.95 0.184 3.72 0.344 Proposed (P-CP2)* 0.76 0.236 1.94 0.458
3.69 0.781 Summary: The revised calculations illustrate the proposed site will maintain or reduce the peak flow rates in proposed conditions for the 2-, 10-, and 100-year storm frequencies.