1909-13367 SRA referral response approved docs

Table 5 – Blockage factor risk assessment

                                                Category (High, Medium, Low)


                       1         2             3               4                 5                   6
   Risk Factor
                                           2 x (1800
                    Proposed    Rail                      Miva St Road    2 x (2.4 x 3.0        450 diameter
                                           diameter
                     Bridge    Bridge                      Crossing            RCBC)               RCP
                                             RCP)


     Debris
                      High     Medium       Medium            High              High                Low
   Availability


 Debris Mobility      High     Medium       Medium          Medium              High                Low


     Debris
                      Low      Medium         High            High              Low                 Low
 Transportability


 Debris Potential   Medium     Medium       Medium            High             Medium               Low


   Inlet Clear       W>3x      W>3x       W ≥ L10 ≤ 3 x
                                                            W ≤ L10        W > 3 x L10      W ≥ L10 ≤ 3 x L10
    Width (W)         L10        L10           L10


Table 6 details the percentage blockage to be applied to the model for each design event.

Table 6 – Blockage percentage (design AEP) for existing and proposed 1D elements

   Risk Factor                                  Category (High, Medium, Low)


  Item Number          1          2            3               4                       5                  6


                                           2 x (1800                                                     450
                    Proposed     Rail                     Miva St Road
  Description                              diameter                      2 x (2.4 x 3.0 RCBC)       diameter
                     Bridge    Bridge                      Crossing
                                             RCP)                                                        RCP


   ≥ 5% AEP            0%        0%           0%              50%                    0%                  0%


      > 1.0% <
                       0%        0%           0%              50%                    0%                  0%
       5% AEP


   ≤ 1.0% AEP         10%        10%         10%             100%                    10%                 10%


The blockage factors have been applied by reducing the area of each link by the desired blockage factor
using the XP function for the number of barrels in each link.

As a sensitivity the 1% AEP event has been run with the blockage of items 3, 4 and 5 at 100%. This will
show the worst case scenario for the maximum design event (the 1 in 500 year, 1 in 2000 year and
PMP are not considered to be design events).
1D/2D Interface

1D/2D interfaces were modelled using interface lines which were connected to 1D elements which in
the case of this project were either pipes/culverts or bridge structures. The interface lines were created



                                               Flood Study                                                      19
S19-007                                 122 & 144 Myall St, Cooroy