RFI - Attachment 3 - Stormwater Management Plan

      3.1. Flood modelling parameters
Analysis of the existing and proposed development area has been carried out using TUFLOW (a 2D flood modelling
engine) via the 12D interface.

LiDAR survey data (0.25m interval obtained from the Noosa-Gympie 2015 project for Queensland LiDAR Data) and
design data has been used to create a digital terrain model of the site and its upstream catchments under existing
and proposed conditions. 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% and 10% 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.

The TUFLOW model was set up in 12D, using a grid size of 5m and sub-grid sampling of 3 intervals to model the
largescale terrain accurately ensure the drainage channel and contributing surface flows were accurately
represented in the model. Catchment surface types were identified in the contributing areas based on an assessment
of the typical land use and surface characteristics. Types 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 3.2 – Adopted Surface Material . Boundary conditions
were generated for outflow channels having a depth greater than 0.3m along the downstream boundary, with the
boundary energy slope at the outlet channel set at 1.3% as measured from the lidar data for the downstream
drainage feature channel. A cut-off depth of 1cm was used for the modelling results to minimise superfluous output.

Table 3.1 - Surface Material Types

 ID        Surface Type                        Description                 Manning’s ‘n’      Infiltration Characteristics
                                                                                                  (Initial, Continuing)
 1      Road Catchments            Predominately impervious                0.025            1,0
        (default material)         road surfaces and verges with
                                   minimal flow obstructions

 2      Large rural lots or        Heavily vegetated areas                 0.07             28, 2.6
        predominately              without significant levels of
        vegetated areas            development
        (Magenta)

 3      Urban or                   Urban residential style                 0.04             28, 2.6
        developed                  development and/or
        Allotments (Red)           industrial areas




Project number 21020                                                                                             Page 12 of 36
File RECOR Concept Stormwater Management Report - 21020.docx, 2022-09-05
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