B07056.W-01A Complete - Stormwater [As Published] · 132007.2398

Concept Stormwater Management Plan
RSL Care – Cooroy Retirement Village


3.4                Existing and Developed Catchment Results
Peak discharge rates for the existing and developed catchments from DRAINS modelling are shown in
Table 3.3.
                      Table 3.3: Existing and Developed DRAINS Modelling Peak Flow Rates
                                          Existing Peak Discharge Developed Peak Discharge
                            ARI                    (m3/s)                    (m3/s)
                                                          Sub Catchment: North
                          2 Year                    1.12                      1.81
                          5 Year                    1.56                      2.36
                         10 Year                    1.82                      2.73
                         20 Year                    2.16                      3.18
                         50 Year                    2.62                      3.62
                         100 Year                   2.91                      3.94
                           ARI                            Sub Catchment: South
                          2 Year                    0.95                      1.53
                          5 Year                    1.32                      2.02
                         10 Year                    1.54                      2.30
                         20 Year                    1.83                      2.69
                         50 Year                    2.22                      3.11
                         100 Year                   2.46                      3.46


Results show that both developed catchments require stormwater detention controls to mitigate the increase in
peak flows that result from the development. Stormwater detention measures are discussed in Section 5.0.

A check was made using the Queensland Rational Method as a comparison with the existing scenario peak
discharge results from DRAINS. Input data for the Rational Method calculation is presented in Table 3.4.

          Table 3.4: Rational Method Input Data for Existing Scenario North and South Sub-Catchments
                               Sub-Catchment                        North                 South
                            Sub-Catchment Area                      7.40 ha              6.26 ha
                             Fraction Impervious                     0.05                 0.05
                                     C10                             0.71                 0.71
                              Frequency Factor
                                                                      1.2                  1.2
                            (100 year ARI event)
                        *Time of Concentration Range           21 - 30 minutes       21 – 31 minutes
                                                                Interpolated           Interpolated
                               Rainfall Intensity
                                                              (See Appendix B)      (See Appendix B)
              * Time of Concentration Range determined from various calculation methods (See Appendix B).

The 100 year ARI event peak DRAINS discharges for each sub-catchment are compared with the Rational
Method peak discharges in Table 3.5.




B07056.W-01A.doc                                                                                            Page 6