MCU10/2083 Development Application part 2 - Attachment 7 - Stormwater Management Plan





3.0 WATERQUANTITY
3.1      INTRODUCTION

TheRationalMethodFormulawasusedtocalculatethestormwaterrunoffflowsthroughandoffthesiteforthe
Pre,PostandUltimateDevelopmentscenarios.TheRationalMethodformulaisasfollows.

Q=CIA/360Where, Q=PeakFlowRate(m3/s)
 C=RunoffCoefficient
                            A=AreaofCatchment(ha)
                           I=RainfallIntensity(mm/hr)

3.2      CATCHMENTS

Thepreandpostdevelopmentscenarioswereanalysedasasinglesiteduetothelargeimperviousareas(preand
post)andoutfalllocations.Detailsonthepreandpostdevelopmentcatchmentsaretabulatedbelow.

                                              Table1CatchmentDetails
                                PreDevelopmentArea       PreDevelopment       PostDevelopmentArea       PostDevelopment
               Catchment
                                         (ha)             FractionImpervious             (ha)              FractionImpervious

                    A                   0.386                    0.9                      0.386                        0.9

3.3      COEFFICIENTOFRUNOFF

ForthePreDevelopmentscenarioaC10valueof0.88(fractionimperviousof0.9)wasassumedfortheexisting
retailusefromTable4.05.3(a),QUDM,2ndEdition,2007.

ForthePostDevelopmentscenarioaC10valueof0.88(fractionimperviousof0.9)wasassumedforthedevelopment
fromTable4.05.3(a),QUDM,2ndEdition,2007.

3.4      TIMEOFCONCENTRATION

Fortheundevelopedcatchment,thetimeofconcentrationwasdeterminedfromstandardinlettimesandpipe
velocitiesfortheremaininglengthofflow(Table4.06.1,4.06.5&Section4.06.9,QUDM,2ndEdition,2007).

                                Table2TimeofConcentrationPreDevelopment
                            StandardInletTime
           Catchment                              PipeFlowLength(m)    PipeVelocity(m/s)    PipeTime(mins)         Totaltc(mins)
                                  (mins)

               A                   5                     40                     2.0                     0.33                 5.33
                                                           
For the developed catchment, the time of concentration was determined from standard inlet times and pipe
velocitiesfortheremaininglengthofflow(Table4.06.1,4.06.5&Section4.06.9,QUDM,2ndEdition,2007).

                                Table3TimeofConcentrationPostDevelopment
                            StandardInletTime
           Catchment                              PipeFlowLength(m)    PipeVelocity(m/s)    PipeTime(mins)         Totaltc(mins)
                                  (mins)

               A                   5                     50                     2.0                     0.42                 5.42



    SITEBASEDSTORMWATERMANAGEMENTPLAN–RevisionD            37GibsonRoad,Noosaville                                                     Page 6



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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=CIA/ 360 Q = Peak Flow Rate (m?/s)

C = Runoff Co-efficient

A = Area of Catchment (ha)

| = Rainfall Intensity (mm/hr)

Where,

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

 

 

 

 

 

 

ann , Pre Development Area Pre Development Post Development Area Post Development
‘atchmen
(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 Cio value of 0.88 (fraction impervious of 0.9) was assumed for the existing
retail use from Table 4.05.3 (a), QUDM, 2” Edition, 2007.

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

Table 2 - Time of Concentration - Pre Development

Standard Inlet Time
(mins)

 

Catchment Pipe Flow Length (m) Pipe Velocity (m/s) Pipe Time (mins) Total t. (mins)

 

A 5 40 2.0 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"! Edition, 2007).

Table 3 - Time of Concentration - Post Development
Standard Inlet Time
(mins)

A 5 50 2.0

 

Catchment Pipe Flow Length (m) Pipe Velocity (m/s) Pipe Time (mins) Total t, (mins)

 

0.42 5.42

 

 

 

 

 

 

 

 

 

SITE BASED STORMWATER MANAGEMENT PLAN — Revision D 37 Gibson Road, Noosaville 6