RFI (rec. 5.06.26) 2567 - Appendix B - Site-Based Stormwater Management Plan (SBSMP) (Ver. 2)

The overall site discharge for the unmitigated scenario shows a net increase for all storm
events, due to the increase in imperviousness across the site. The increase in peak site
discharge ranges from 70% to 160%, with a greater increase in more frequent events. Note
that LPODs are hydrologically disconnected and overall values are only provided for gross
assessment. These increased flows will be mitigated through stormwater management
measures to ensure discharge rates do not exceed pre-development conditions.

4.6    WBNM Analysis Post-Development, Mitigated Scenario

To mitigate the effect of the increase in runoff volume from the developed site, a detention
basin has been proposed to attenuate flows such that post-development peak discharge rates
do not exceed pre-development rates for all design storms. The WBNM results confirm this
objective is met, with a reduction in flows from the pre-development peak discharge across all
events.


                                           MITIGATED CASE - LPOD1
                                                 Peak Flow Rates - Q (m3/s)
                          AEP            EXISTING       MITIGATED        Difference
                         63.2%             0.197           0.187            -5.1%
                          50%              0.242           0.228            -5.8%
                          20%              0.457           0.365           -20.1%
                          10%              0.485           0.437            -9.9%
                          5%               0.578           0.525            -9.2%
                          2%               0.725           0.608           -16.1%
                          1%               0.801           0.662           -17.4%
               Table 4-8 WBNM discharge flow rates at LPOD1 for the mitigated post-development scenario


                                           MITIGATED CASE - LPOD2
                                                 Peak Flow Rates - Q (m3/s)
                          AEP            EXISTING       MITIGATED        Difference
                         63.2%             0.000           0.012          #DIV/0!
                          50%              0.000           0.013          #DIV/0!
                          20%              0.000           0.018          #DIV/0!
                          10%              0.000           0.024          #DIV/0!
                          5%               0.000           0.025          #DIV/0!
                          2%               0.000           0.026          #DIV/0!
                          1%               0.000           0.029          #DIV/0!
               Table 4-9 WBNM discharge flow rates at LPOD2 for the mitigated post-development scenario




2576-SBSMP-01_Version 2.0 (April 2026)                                                                    Page 19 of 23
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