MCU14/0056 Stormwater Quantity Management Plan Att D Information response

4.0     URBS MODELLING
      A hydrologic model was created using the URBS software to determine the peak flow at
      Point 1 (see Figure 1, Appendix A). The model represents the sub-areas that contribute to
      flows through the subject site. The sub-areas and layout for the existing URBS model are
      illustrated in Figure 2, Appendix A. The subject site contains a significant amount of storage
      which contains flows which back up from the downstream culverts (under Myall St). This
      storage has been included in the URBS model. The URBS model files are presented in
      Appendix C.

      4.1    Existing Model
      An URBS model of the existing site and catchment conditions was created. The URBS
      model parameters and results are presented in Tables 4.1 & 4.2 below.

      Table 4.1 – Existing URBS Model Parameters
                            Storage           Non-Linearity    Initial Rainfall     Continuing
            ARI
                           Coefficient           Index               Loss          Rainfall Loss
            years
                               α                   m                 mm              mm/hr
             1                 1.20               0.80                15                2.50
             2                 1.20               0.80                20                2.50
             5                 1.20               0.80                25                2.50
             10                1.20               0.80                30                2.50
             20                1.20               0.80                32                2.50
             50                1.20               0.80                15                2.50
            100                1.20               0.80                 0                2.50

      Table 4.2 – Existing Site URBS Model Results
              ARI               Existing URBS
              years                  m3/s
                  1                   8.55
                  2                   11.92
                  5                   17.08
                 10                   19.78
                 20                   24.75
                 50                   35.12
              100                     44.04


      The URBS model results show that a peak discharge of 44 m3/s flows through the waterway
      at the site during a Q100 event.

                                      J4279 Report 1.0.doc
                                        14 January 2015                                        Page 8