Reference Documents RAL21 0035

          3.2.3 Peak Flow Estimates – rational / Flood Data / TUFLOW
Analysis of the existing and proposed development area has been carried out using TUFLOW (a 2D flood modelling
engine) via the 12D interface. Rainfall from contributing catchments has been applied to the model as rain-on-grid
to simulate the behaviour of both 2D surface flows and 1D piped flows representing culvert crossings under the
peak 1%,10% and 50% AEP flood events.

ILSAX routing has been used for the run-off routing method as it allows non-linear run-off routing considering various
surface conditions for urban and semi-urban catchments as well as the interaction of surface flows entering into
piped drainage networks.


       3.3. Catchment Hydraulics

          3.3.1 Topography
The topography of the locality has been converted into a digital elevation model using LiDAR point cloud data
obtained from the Elvis system provided by the Intergovernmental Committee on Surveying and Mapping. The
data was captured as part of the Noosa-Gympie 2015 project with point information at 1m spacings and with a
vertical accuracy of +/- 150mm.

The terrain has been imported into 12D and converted into a TUFLOW grid comprised of 5m x 5m squares with a
sub-grid sampling rate of 5 intervals giving a high-resolution result of 1m grids. This resolution has been assessed
as adequate to capture the key drainage channels and ensure contributing surface flows are accurately
represented in the model.


          3.3.2 Inflows
The extent of the modelled catchment fully captures the upstream contributing areas that drain through the subject
site; therefore no additional inflows are incorporated into the model.


          3.3.3 Surface Characteristics
Catchment surface types were identified in the contributing areas based on an assessment of the typical land use
and surface characteristics within the catchment. The surface types are identified in Table 3.1 - Surface Material
Types. Infiltration rates for the surface types are based on the Australian Rainfall and Runoff (ARR) Datahub
parameters for the location.

Surface material adopted for each area is shown in Figure 3.1 – Adopted Surface Material .

Table 3.1 - Surface Material Types

  ID       Surface Type                         Description                 Manning’s ‘n’      Infiltration Characteristics
                                                                                                   (Initial, Continuing)
  1     Large rural lots or         Typically grassed and                   0.04             31, 3.4
        predominately               developed areas of large
        vegetated areas             allotments
        (default material
        not shown)

  2     Road Catchments             Predominately impervious                0.025            1,0
        (Blue)                      road surfaces and verges with
                                    minimal flow obstructions

  3     Heavily forested            Heavily vegetated areas                 0.07             31, 3.4
        areas (Green)               inside and outside of
                                    allotments


Project number 20220089                                                                                           Page 10 of 23
File 20220089 Jirrima Cr SWMP.docx, 2023-05-09 Revision 0


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