MCU10/2083 Information Request Response 37 Gibson Rd Noosaville

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                                                                                                                         URBAN




3.1   INTRODUCTION

The Rational Method Formula was used to calculate the stormwater runoff flows through and off the site for the
Pre, Post and Ultimate Development scenarios. The Rational Method formula is as follows.

Q = C I A / 360         Where,         Q = Peak Flow Rate (m3/s)
                                       C = Runoff Co-efficient
                                       A = Area of Catchment (ha)
                                       I = Rainfall Intensity (mm/hr)


3.2   CATCHMENTS

The pre and post development scenarios were analysed as a single site due to the large impervious areas (pre and
post) and outfall locations. Details on the pre and post development catchments are tabulated below.


                                                   Table 1 - Catchment Details

                            Pre Development Area       Pre Development         Post Development Area           Post Development
            Catchment
                                       (ha)           Fraction Impervious                 (ha)                Fraction Impervious


                  A                  0.386                    0.9                       0.386                           0.9


3.3   CO-EFFICIENT OF RUNOFF

For the Pre Development scenario a C10 value of 0.88 (fraction impervious of 0.9) was assumed for the existing
retail use from Table 4.05.3 (a), QUDM, 2"d Edition, 2007.


For the Post Development scenario a C10 value of 0.88 (fraction impervious of 0.9) was assumed for the development
from Table 4.05.3 (a), QUDM, 2nd Edition, 2007.


3.4   TIME OF CONCENTRATION

For the undeveloped catchment, the time of concentration was determined from standard inlet times and pipe
velocities for the remaining length of flow (Table 4.06.1, 4.06.5 & Section 4.06.9, QUDM, 2nd Edition, 2007).

                                     Table 2 - Time of Concentration - Pre Development
                        Standard Inlet Time
        Catchment                              Pipe Flow length (m)      Pipe Velocity (m/s)         Pipe Time (mans)         Total t. (mans)
                              (minx)

            A                    5                     40                       2.0              I        0.33                     5.33

For the developed catchment, the time of concentration was determined from standard inlet times and pipe
velocities for the remaining length of flow (Table 4.06.1, 4.06.5 & Section 4.06.9, QUDM, 2"d Edition, 2007).

                                     Table 3 - Time of Concentration - Post Development
                        Standard Inlet Time
        Catchment                              Pipe Flow length (m)      Pipe Velocity (m/s)         Pipe Time (mine)         Total 4 ()


            A                    5                     50                       2.0                       0.42                     5.42




 SITE BASED STORMWATER MANAGEMENT PLAN - Revision E              "ibson Road, Noos                                                                6