Stormwater Mgmt Plan

SC-8407 – 45 Maple Street, Cooroy                                                              8




4.3.2    Catchment Areas
The subject site has been modelled in its existing pre-development and proposed post-development states
with the catchment areas illustrated in Tables 4.1 & 4.2. In its pre-development state the subject
catchments were each modelled as one hydrologic node to replicate the existing drainage situation for the
lot. XP-STORM model layouts and outputs are included in Appendix B of this report.


                 Catchment                  Description          % Impervious        Area (Ha)

                                                Roof                  100              0.068
                      ‘A’
                                             Landscape                  0              0.244

                            Table 4.1 - Pre Development Node Sub-Catchment Areas


                 Catchment                  Description          % Impervious        Area (Ha)

                                                Roof                  100              0.106

                      ‘B’              Carpark/hardstand areas        100              0.180

                                             Landscape                  0              0.045

                                                Roof                  100              0.016
                      ‘C’
                                             Landscape                  0              0.034

                                                Roof                  100              0.022
                      ‘D’
                                             Landscape                  0              0.077

                             Table 4.2 - Post Development Sub–Catchment Areas

4.3.3    Roughness Coefficients
The conduits and links used within the model are based on the ultimate design scenario for the internal
roadways and overland flow paths. Mannings “n” roughness coefficient values are specified as 0.014 for
RCP pipes and 0.011 for uPVC pipes.


For overland flow within the sub-catchment areas a Mannings “n” value of 0.014 for concrete areas and
0.025 for vegetated areas was adopted.


4.3.4    Storm Events
Storm patterns were setup using Australian Rainfall and Runoff (ARR 2016) storm patterns with intensity
frequency duration data taken for the local area. Storm durations of 10, 15, 20, 25, 30, 45, 60, 90, 120 and
180 minutes were investigated for the pre and post developed scenarios.