1909-13367 SRA referral response approved docs

Table 1 – Existing catchment details (refer figure 2 and Appendix BA)

  Catchment        1.01      1.02       1.03            1.04            1.05            1.06


   Area (ha)      158.33     39.95      14.38           10.32           5.13            13.53


 % impervious
                   10%       10%        10%              5%              5%              5%



  Catchment
                   8.63      4.36       1.90            4.07            5.50            3.90
   Slope (%)


  Catchment        1.07      1.08       2.01            3.01            3.02            3.03


     Area          4.13     14.148      0.61            50.35           32.70           8.36


 % impervious
                   5%         5%         5%             10%             35%              5%



  Catchment
                   5.71      6.48       2.68            5.95            4.20            4.95
   Slope (%)


  Catchment        4.01      5.01       5.02


     Area         12.46      21.19      1.39


 % impervious
                   60%        5%         5%



  Catchment
                   3.64      3.29       8.06
   Slope (%)


3.1.2 Fr act ion i mp e rv iou s

The external catchments has been classified as rural residential. QUDM (2017) specifies in table 4.5.1
that rural residential developments shall range between 10 – 20% impervious. The lower bound of this
range has been adopted. Catchments 3.02 and 4.01 have been determined to be more developed than
other parts of the catchment from aerial imagery. Catchment 4.01 is considered to be urban residential
– low density (including roads). Table 4.5.1 gives a range from 45% - 85% for this landuse. Catchment
3.02 is also considered to be urban residential – with roads, however due to the large open space area
the overall fraction impervious has been reduced.


3.1.3 M anning’ s r ough ne s s

The external catchments are largely undeveloped and well grassed. In addition catchments 1.01
through 1.04 have sections of dense vegetation surrounding the banks of the existing creek. Therefore
within the runoff model for pervious areas a Mannings roughness of 0.045 has been adopted for all
catchments. These values have been adopted based on Appendix C of ‘Brisbane City Council’s’ (BCC)
Natural Channel Design Guidelines (2003).


                                             Flood Study                                            9
S19-007                               122 & 144 Myall St, Cooroy