1909-13367 SRA referral response approved docs

              Figure 1 – Indicative Site location and property boundary (NearMap 2019)

3   HY DR O LO G Y


The hydrologic assessment of the existing site and external catchments has been conducted in
accordance with ARR2016 and QUDM 2017. The software packages that has been used to model the
external catchment are XPStorm version 2018.1 and CatchmentSim. This section of the report will detail
the methodology used to determine the critical storm or storms for the design events ranging from 50%
to 1% “Annual Exceedance Probability” (AEP).

The XPStorm 1D/2D modelling program, utilising the “Laurenson” runoff routing method, has been used
to model the catchment characteristics to determine the peak stormwater flow discharging from all
external catchments during each design storm event for durations ranging from 30 minutes up to 24
hours.

      3. 1   Cont ri but i ng c at chm ent pa r am et er s

3.1.1 Cat ch me nt a re a

The external catchments upstream of the development site have been determined using LIDAR (1m2
LIDAR dated 2015) sourced from the “Queensland government department of natural resources, mines
and energy” (QDNR). CatchmentSim has been used to determine external catchment areas. The
external catchments have been broken up based on areas of uniform slope. Figure 2 below (and
Appendix BA) depicts the catchments that were determined using this methodology.

The total area of the external catchments contributing to the downstream discharge point is
approximately 387 hectares. The external catchment has a low percentage impervious as the majority
is rural or undeveloped.




                                             Flood Study                                            7
S19-007                               122 & 144 Myall St, Cooroy