Appendix D - Flood Assessment

R1593: FLOOD ASSESSMENT – 9A JIRRIMA CRESCENT, COOROIBAH



4                OVERLAND FLOW ASSESSMENT                                                          4.2.      CATCHMENT DELINEATION

4.1.             HYDROLOGY                                                                         The study area has been divided into 21 sub-catchments as part of this assessment.
                                                                                                   The fraction impervious was calculated using aerial photography. A summary of the
An integrated hydrologic and hydraulic model was constructed for the catchment                     catchment parameters applied to this assessment is included as Table 2, while the
and site using the XP-STORM 1D/2D software. The model represents the sub-                          catchment plan is included as Figure 5.
catchments as a network of 1D elements and nodes linked to the 2D geometric base.
Each node is defined by its pervious (undeveloped) and impervious (developed)                      Table 2 – Catchment Details Applied to Hydrologic Assessment
areas, fraction impervious and average catchment slope. The net rainfall is routed
through the network after appropriate losses (initial and continuing) and roughness                       CATCH ID         AREA (HA)        FRACTION IMPERVIOUS       SLOPE (M/M)
factors are applied, resulting in a surface runoff hydrograph for each sub-catchment.
                                                                                                             1                3.36                   9.9                   6.7
4.1.1.           RAINFALL DATA                                                                               2                3.78                   6.4                  4.4
Intensity Frequency Duration (IFD) data for the site has been derived using the Bureau                       3                1.72                    3.1                  6.7
of Meteorology (BOM) 2016 Rainfall IFD Data System. Modelling was undertaken for
                                                                                                             4                1.48                   10.6                  4.1
63 % to 1 % Annual Exceedance Probability (AEP) storm events using the IFD data
summarised in Table 1.                                                                                       5                 1.14                   1.7                  2.6

                                                                                                             6                0.63                   13.8                  2.9
Table 1 - Intensity Frequency Duration Data Applied to Hydrologic Assessment
                                                                                                             7                1.62                   0.0                   1.6
                                                    RAINFALL DEPTH (MM)
   DURATION                                                                                                  8a               0.59                    1.5                  2.6
                         63% AEP       0.5 EY      0.2 EY   10% AEP   5% AEP     2% AEP   1% AEP             8b               0.49                   0.0                   1.6

         15                 84.2        106         131       150         170     195      213               8c               0.10                   18.1                  4.8

         20                 73.5       92.2         114       131         149     171      187               8d               0.12                   21.8                  3.8

         25                 65.5       82.3         102       117         133     154      169               8e               0.67                   16.8                  3.2

         30                 59.4       74.5         92.7      106         121     140      155               8f               0.23                   6.0                   3.2

         45                   47        59.1         74      85.4         97.8    114      126               8g               0.50                   15.1                  4.1

         60                 39.4       49.7         62.6     72.6         83.5    97.9     109               8h               0.28                   13.9                  3.5

         90                 30.6        38.7        49.3     57.6         66.6    78.8     88.1              8i               0.23                   17.1                 4.4

         120                25.6       32.4         41.6     48.8         56.7    67.4     75.7              9                1.56                   0.0                   1.8

         180                 12.9       16.6         22      26.2         30.9    37.3     42.3              10               3.43                   4.6                   3.2

         270                 122        153         191       220         252     293      323               11               1.86                   2.9                   2.4

         360                99.3        125         154       177         201     231      253               12               1.69                   9.8                   5.1

                                                                                                             13               0.76                   0.0                   1.3

                                                                                                           TOTAL              26.21                   -                     -


Environment. Engineering. Education.                                                                                                                                             PAGE 3