Reference Documents - MCU23 0070

3.4      PRE-DEVELOPMENT SITE XP-STORM
A peak flow analysis has been undertaken using the XP-STORM version 2021.3 for sizing the detention
tank. The pre-development site was modelled using a single node and peak flows verified against the
Rational Method Calculation.

3.4.1    CATCHMENT DATA

Table 3 presents the catchment modelled in XP-STORM. Refer to Drawings No. M3024E_DA1_SK01 in
Appendix D for the catchment plan.

                                   Table 3 – Pre-Development Catchment Data
                                                                     Fraction              Vectored Slope
                  Catchment                Area (ha)
                                                                    Impervious                  (%)
                     E1                     0.0486                     57%                      10%

3.4.2    RAINFALL DATA

The site specific 2016 rainfall intensities obtained from BOM coupled Australian Rainfall & Runoff (AR&R)
1987 temporal patterns for zone 3 have been used to generate peak flow hydrographs in XP-STORM.

3.4.3    HYDROLOGICAL LOSSES

The following initial loss, continuous loss and Manning’s n values have been adopted for the
hydrological modelling. They are within the ranges recommended in the AR&R (1987) for Southeast
Queensland.
                                            Table 4 – Hydrological Losses
                                                                              Continuing Loss
         AEP                   Area Type         Initial Loss (mm)                                    Manning’s n
                                                                                 (mm/hr)
                          Impervious Area                    0                      0                       0.014
      63% to 1%
                           Pervious Area                   15                       2                       0.07

3.4.4    BX FACTOR

A Bx factor of 1.8 has been used across all AEPs modelled.

3.4.5    EXISTING PEAK DISCHARGE

The XP-STORM hydrology was run for the standard AEPs from a 63% AEP to a 1% AEP and 15 to 180-
minute standard durations. Table 5 presents pre-development site peak flows.

                                      Table 5 – Pre-Development Peak Flows
                                                 Pre-Development Peak Flows (m³/s)
                     63% AEP       39% AEP        20% AEP           10% AEP       5% AEP        2% AEP         1% AEP
  Rational Calc        0.010         0.013           0.018           0.022         0.026         0.033         0.037
    XP-STORM           0.012         0.017           0.021           0.027         0.032         0.034         0.038
      Variance        +0.002        +0.004           +0.003         +0.005        +0.006        +0.001         +0.001

The XP-STORM peak flows are generally similar to the Rational Method Calculation, particularly for the
larger 1% and 2% AEP storms. On that basis, the XP-STORM peak flow rates have been used for the
peak flow and detention tank analysis for this site.

SITE BASED STORMWATER MANAGEMENT PLAN – Revision B                                   36 & 38 DUKE STREET, SUNSHINE BEACH
                                                       P a g e |7