Site Based Stormwater Management Plan

4.4                 Post-Development Hydrology

Table 4.3 presents the comparison between the post-developed flow rates estimated using
the Rational Method and XPSTORM modelling software.


                                                 Peak Discharge Comparison (m3/sec)
    Design Storm                           Existing            Post-Developed             Difference         % Change
                    (AEP)

                    63%                    0.125                    0.186                  0.061              49%
                    39%                    0.160                    0.234                  0.074              46%
                    18%                    0.223                    0.292                  0.069              31%
                    10%                    0.279                    0.304                  0.025               9%
                     5%                    0.333                    0.346                  0.013               4%
                     2%                    0.413                    0.369                  -0.044             -11%
                     1%                    0.456                    0.408                  -0.048             -11%
                                          Table 4.3 Post-Developed Stormwater Flow Validation



From Table 4.3 the results compare well between the Rational Method and XPSTORM
model for estimates of the post-developed peak stormwater discharge from the site. The
results generally differ by less than ±20% for storm events ranging between 10% AEP and
1% AEP. The estimates for stormwater discharge from the XPSTORM model are
conservative for minor storm events (63% AEP to 18% AEP). The results from Table 4.3
are presented in Figure 4.1 below, and shows the XPSTORM results for the minor storms
are conservative, and comparative for the major storms. The XPSTORM results will be used
to represent the post-developed case and will ensure a robust stormwater detention design.


                    0.500
                    0.450
                    0.400
                    0.350
   Flow Rate (m3)




                    0.300
                    0.250
                    0.200
                    0.150
                    0.100
                    0.050
                    0.000
                                63%          39%         18%           10%           5%          2%            1%
                                                                 Design Storms

                                                           RM DEV         XP DEV


                            Figure 4.1 Post-Developed Stormwater Flow Comparison Rational Method v XPSTORM

Site Based Stormwater Management Plan                                                                        Page 6 of 19
2123-SBSMP-01_Version 1.0 (October 2021)