Hydraulic Assessment 29 August 2024

3.2         Hydraulic Model
Hydraulic modelling of the local catchment has been carried out using TUFLOW software developed by BMT WBM. TUFLOW is a
computational engine that provides one-dimensional (1D) and two-dimensional (2D) solutions for the free surface flow equations to simulate
flood and tidal wave propagation. The Heavily Parallelised Compute (HPC) computational method has been applied using 2023-10-AE version
of TUFLOW. Modelling assumptions and outcomes are described below.


  3.2.1       Model Setup
The assessment has considered a range of storm durations (15 min to 720 min) and temporal patterns, and the identified critical event was
the 120-minute duration, temporal pattern 4. The critical duration was identified as the storm duration producing the peak water level, based
on the temporal patterns producing peak levels just above the median. A summary of the model setup is detailed below with TUFLOW model
setup presented below in Figure 3.2.

3.2.1.1 Topography
The model topography has been based upon 2015 Light Detection and Ranging (LiDAR) along with the detailed site survey.

The catchment has been modelled using a 1m hydraulic model grid size.

3.2.1.2 Boundaries
The inflow boundaries for the catchment have been read into the model using inflow polygons (2d_sa) to represent inflow from the WBNM
hydrology model.

The outflow boundaries for the model have been applied 300m downstream of the existing dam, and 11m below the dam spillway elevation.
Normal depth rating curves have been adopted for the downstream of the site with a water surface slope of 0.01 m/m, and the downstream
of the adjacent road with a water surface slope of 0.02m/m.

3.2.1.3 Roughness
The model roughness is represented by the Manning’s roughness coefficient, n, in the TUFLOW materials file. Manning’s coefficients have
been applied to reflect the land use within the catchment, based on aerial imagery and conditions noted during a site visit. Roughness
coefficients are outlined in Table 3.4, while the spatial distribution of material types in the TUFLOW model extent is included in Figure 3.2.

TABLE 3.4: ADOPTED MANNING’S ‘N’ ROUGHNESS

 Land Use                                                               Manning’s ‘n’

 Road                                                                   0.025

 Water                                                                  0.025

 Low Density Vegetation                                                 0.035

 High Density Vegetation                                                0.090




38 BARINA COURT, POMONA I BBNE00000_0020-REP-001-0                                                                                          8