Cardno Amended flood report July 2018

Table 3-2 compares the peak flow values from RORB to the results of the Rational Method. The
values indicate that the hydrologic model is generating consistent peak flows compared to the
Rational Method. Kc values were selected for all events that gave the best match to the Rational
Method discharges without underestimating flow at the outlet
Table 3-2 Hydrology Cross check
           AEP                                Peak Flow
                                                                             Kc
           (%)                                  (m3/s)
                                                                           Inputs
                            Rational Method               RORB
            39                    41.3                    41.3              1.61
            18                    58.3                    58.2              1.44
            10                    68.8                    68.8              1.77
            5                     82.9                    82.9              1.97
            2                    106.2                    106.1             2.00
            1                    122.9                    122.6             1.84



4 Hydraulic Model
The hydraulic model built for the previous flood study was adapted for the additional analysis. The
model was altered to integrate the additional storms and new development layout of the buildings.
Plate 4-1 depicts the lot layout of the development.




                          Plate 4-1 Development Lot Layout

4.1     Model Setup
4.1.1    Grid Cell Size
A grid cell size of 4 m was adopted for the model area as per the original study. This size was
considered a fine enough resolution to appropriately define topographical features such as roads
and open drains whilst remaining computationally efficient.