31B-192 91 King Street-Peak flow Summary revisionSt. 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
(acre-
ft)
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.