P0198-25-001_12_Gympie_Street_Tewantin_SWMP

3.2        Time of Concentration Inputs into DRAINS
The time of concentration (Tc) for each catchment has been determined using a combination of:

    1.   Roof inlet time (time for runoff to travel from impervious surfaces to the drainage system)

    2.   Kerb travel time (time for runoff to reach the stormwater pipe network)

    3.   Pipe flow time (travel time through the underground drainage system)

Each component is broken down below for the catchment, as shown in the provided screenshot.



Catchment

    •    Total area: 5,897 m² (0.5897 ha)

    •    Tc components:

              1.   Roof inlet time Q 5 minutes

                            Assigned based on standard inlet times from QUDM Table 4.6.2 for urban residential
                             areas.

              2.   Kerb travel time Q 0.5 minutes

                            Assumed minor due to short travel distances along roads and paved areas.

              3.   Time in pipe flow → 1.5 minutes

                            Pipe length: 80m

                            Slope: 1.00%

                            Manning's n: 0.012

                            Using Manning’s equation, the travel time is calculated based on hydraulic parameters.

              4.   Total Time of Concentration (Tc): 7 minutes



Calculation Methodology

    •    Roof inlet and kerb travel times were estimated using QUDM guidelines and empirical flow path analysis.

    •    Pipe flow times were determined using Manning’s equation for open channel and pipe flow, referencing
         the chart provided in the screenshot for additional validation.

    •    Catchment delineation and flow paths were confirmed using the subdivision layout and area tool
         measurements.



Final Considerations

    •    A single catchment has been adopted for the entire development, as all overland flows will be fully
         intercepted within the site and conveyed to the proposed detention basin.

    •    These times of concentration will be used in hydrological modelling to determine peak flow rates and
         ensure adequate stormwater infrastructure design.




 12 GYMPIE STREET, TEWANTIN
 Stormwater Management Plan                                                                                     13
 Client Reference: P0198-25-001             4 November 2025
 Prepared for Novato Group