17 Bottlebrush Avenue, · MCU26/0001

Key Observations

     1.   Increase in Flow Depths and Velocities

               •    The developed scenario shows higher water levels across all storm events, particularly at
                    constricted sections of the drainage network.

               •    Flow velocities have increased, indicating a higher runoff volume due to reduced permeability.

     2.   Peak Discharge Variations

               •    Peak discharge rates in the developed scenario have increased substantially, particularly for
                    higher return period storms (e.g., 1% AEP).

               •    The most significant changes occur at sections with concentrated overland flow paths,
                    suggesting increased runoff from new impervious surfaces.

     3.   Impact of Increased Impervious Area

               •    The development introduces more impervious surfaces (e.g., roads, driveways, rooftops),
                    reducing infiltration and increasing direct runoff.

               •    The loss of natural detention and permeability results in quicker times of concentration and higher
                    peak flows.



Table 3-1: Comparison of Pre-Development vs. Unmitigated Post-Development Peak Flows

 Storm Event (AEP)           Pre-Development Peak Flow                Post-Development Peak         Increase %
                                       (m³/s)                               Flow (m³/s)

          63.2%                            0.011                                  0.013                 8%

          50%                              0.013                                  0.015                 7%

          20%                             0.020                                  0.022                  5%

          10%                             0.024                                  0.027                  6%

           5%                             0.028                                   0.031                 5%

           2%                             0.034                                  0.037                  4%

           1%                             0.038                                  0.042                  5%




 17 BOTTLEBRUSH AVENUE, NOOSA HEADS
                                              7 January 2026                                           P a g e | 13
 Stormwater Management Plan
 Client Reference: P0433-25-001
 Prepared for Made Capital PTY LTD