Attachment D amended SWMP

 5.3      Rational Method Peak Flow Comparison
A summary of the existing and developed peak flow rates calculated using the Rational Method is provided in
Table 3 below.
Table 3 - Comparison of Pre- and Post-Development Peak Flow Rates

                     Design Discharge (m3/s)
                         Q1           Q2          Q5          Q10         Q20          Q50          Q100
                      (63% AEP) (50% AEP)      (20% AEP)   (10% AEP)    (5% AEP)     (2% AEP)     (1% AEP)
Development Area

       Existing           0.059     0.079        0.110        0.128       0.153        0.193        0.222

     Developed            0.106     0.143        0.196        0.229       0.272        0.336        0.370

                          0.048     0.064        0.087        0.101       0.120        0.143        0.147
       Increase
                          55%        55%         56%          56%          56%         58%          60%


 5.4      Pre- and Post-Development Design Flow Rates (unmitigated)
The table below, provides a summary of the pre-development design flow rates off the Development Area only
calculated using DRAINS:

Table 4 - Comparison of Pre- and Post-Development Design Flow Rates

                     Design Discharge (m3/s)
                         Q1           Q2          Q5          Q10         Q20          Q50          Q100
                      (63% AEP) (50% AEP)      (20% AEP)   (10% AEP)    (5% AEP)     (2% AEP)     (1% AEP)
External Catchment Only

External Catchment        0.168     0.227        0.313        0.365       0.434        0.531        0.585

Development Area Only

       Existing           0.059     0.086        0.112        0.140       0.167        0.198        0.220

     Developed            0.124     0.161        0.207        0.242       0.279        0.327        0.363

                          0.065     0.075        0.095        0.102       0.112        0.129        0.143
       Increase
                          48%        53%         54%          58%          60%         61%          61%
Results show that, compared to pre-development design flow rates, without mitigation, there is an increase in
post-development flow rates off the Development Area.




 BR210522_SBSMP_Rev5.docx                                                                                 Page 9 of 25