Pre-Request Response Application 132001.210310.1

Flood Investigation & Storm water Quantity Management Plan                                                     BROWN
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Proposed Residential Development at Doonella Stage C
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                                Table 3.5: Adopted WBNM Loss Values & Lag Parameter

                            Initial Loss (mm)             Continuing Loss            Lag Parameter (C)
                                                              (mm/hr)
                                   25                            2.5                          1.8
                                                 ..   .



                                         Note: Inlllallmpervlous loss of 1mm also adopted.


3.2.4     WBNM Calibration

In order to calibrate the WBNM Queensland Rational Method calculations were undertaken to determine peak flows at

the downstream site boundary.        For the calibration the catchment has been assumed to be in an undeveloped

condition, therefore the calculations and WBNM have been configured with an impervious fraction of zero. The
Rational Method calculations have been estimated for a range of design storm events including the 2, 10, 20, 50 and
100 year ARI in accordance with Council’s DDPSP as well as QUDM (2007).

Time of Concentration

The time of concentration (tc) is an input parameter to derive relevant rainfall intensity to adopt in the Rational Method

calculation. Given the size of the site catchment and condition of the main flow path the tc has been determined

following a methodology consistent with the procedure for ’(c) Bush/and catchments to small to allow the formation of a
creek with defined bed and banks.’ as per Section 4.06.3 of QUDM (2007).The following travel time components were

calculated to derive the tc:

      .   Friend’s Equation (Section 4.06 of QUDM). This is the preferred QUDM method to derive overland sheet

          flow time, based on existing site slopes, surface roughness and length of flow path; and

      .   Concentrated overland flow time based             on   assumed channel flow        velocity of 1 m/s within   the

          environmental corridor

Rainfall Data

Intensity Frequency Duration (IFD)data for the Rational Method calculations were sourced from Noosa Shire Council’s
Rainfall/ntensity Chart as per Council’s DDPSP.
Runoff Coefficients

As sated in Section 3.2.4 the fraction impervious for the calibration of the WBNM has been set to zero. The C10 value
for the site catchment has therefore been set to 0.7 in accordance with Table 4.05.3(b) of QUDM (2007). Frequency

Factors (Fy)from Table 4.05.2 of QUDM (2007) were then applied to determine the coefficients for the remaining

design storms.
Peak F/ows

Peak flows from the WBNM model configured for the calibration (zero percentage impervious for each sub-catchment)

and the Queensland Rational Method calculations are presented in Table 3.6. Detailed Rational Method calculations

are   presented in Appendix A.

                                     Table 3.6: Peak Flows for Calibration of WBNM

                                                                        Peak Flow (m3/s)
                    ARI
                                                                 QRM                          WBNM
                    2                                            0.98                          0.84

                    5                                            1.36                          1.33

                      10                                         1.61                          1.64
                    20                                           1.92                          2.08
                    50                                           2.53                          2.48
                      100                                        2.85                          2.93




B09182.W-02A                                                                                                                  Page 5