HomeMy WebLinkAboutApplication Files_85048_pg0183 HydroCAD data sheets. Table I compares the pre-development peak flows with the post-
development peak_flows at the design p nmen
oint. The resulting�nos -d�v� t fl peak ows
are less than the pre-development peak flows for both design points. In addition, upon
review of the data sheets, a minimum of 1-foot of freeboard is maintained in all of the
' basins during the 100-year design storm.
Table 1 —Summary of Pre-and Post Development Peak Flow Rates
at the Design Point(CFS)
DesignPoint#1 DesignPoint#2
Storm Pre Post Pre Post
2-year 15.15 15.11 1.14 0.95
10- ear 30.17 21.41 5.50 4.21
25- ear 39.21 22.60 8.81 6.63
100- ear 55.16 25.87 15.62 11.52
D. Wipe Sizing
Pipes not analyzed as part of the HydroCAD analysis were sized using a combination of
the Rational Method (to determine the peak flows) and the Culvert Calculator program
(to determine the headwater required to achieve the required flow rate in the pipes). The
calculated headwater was compared to the top of frame elevation at the upstream end of
the pipe to determine whether the pipe will have sufficient capacity. In accordance with
the Town requirements, the pipe sizing criteria for the storm drain collection system is to
maintain a minimum of one foot of freeboard in the upstream catch basin during the 10-
year design storm.
' The design roughness coefficient used for the pipe collection system is 0.012. A pipe
capacity analyses is provided in Appendix 7. As shown in the Table in Appendix 6, all
pipes have sufficient capacity for the 10-year design storm.
In addition, based on the tabulated calculations, the 10-year design storm peak flow rate
' at the proposed trench drain in the northern paved area is 7.5 cfs (same as for CBI). As
shown in the product literature for the trench drain provided in Appendix 7, each 120'
section of trench drain has a capacity of 3,000 gpm or 6.7 cfs. Thus, the two 120'
sections of trench drain combined have a capacity of 13.4 cfs which is sufficient to handle
the 10-year peak flow rate.
E. Stormwater Treatment
' As discussed above, Basins 1-5 will serve as forebays. In addition, two Stormceptor
Model 450 stormwater treatment units are proposed after catch basins 34 and 59 to
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