1909-13367 SRA referral response approved docs

For impervious areas a Mannings roughness of 0.014 has been adopted for all catchments as these
areas are likely to be concrete, asphalt and roof areas.
The adopted Mannings coefficients used in the runoff layer have been summarised below.



                          Pervious Area n = 0.045

                          Impervious Area n = 0.014



The roughness in the 1D links (shown below) have been based on a meandering channel with an
irregular cross section (pg. 148, BCC, 2003). This value has been used for both the channel and the
overbank area. Manning’s roughness used for the 2D modelling will be detailed in table 2 below.



                          1D Links n = 0.045

2D Landuse Mannings Roughness

The external catchments consist of a combination of paved surfaces, pasture areas with short to
medium height grasses (including sports field areas) and areas with thick vegetation. To reflect this
various Mannings roughness values have been adopted. The adopted values for each landuse is
present in the below table.
Table 2 – 2D Landuses

      Landuse                                         Mannings (n) value


        Creek                                               0.045


        Grass                                               0.045


          Road                                               0.02


    Trees (Heavily
                                                             0.1
     Vegetated)




3.1.4 Init i al an d cont inu ing lo s se s

The values for initial and continuing losses for pervious areas as provided by ARRDatahub ((for
coordinates -26.445, 152.897) sourced on the 30 March, 2019) are shown below.



          Pervious Area

                                 Initial Loss 32mm
                                 Continuing Loss 2.6mm/hr




                                              Flood Study                                         10
S19-007                                122 & 144 Myall St, Cooroy