Development Application part 2 of 2 Report and Plans MCU13/0030

                                                                                                   ~
                                                                                               Callaghan & Toth


                     The Bioretention basin has been modelled to act as a detention basin. The basin size
                     and weir size is sufficient to reduce the increase in runoff from the additional roof area of
                     768m2 (3574-2806)and additional hard stand area of 957m2 for a Q10 storm and Q100
                     storm back to predevelopment levels as summarised in Table 6.1 and Appendix D.


                     TABLE 6.1:          DETENTION STORAGE


CATCHMENT                                PRE-           PRE-                  POST                     POST
                                DEVELOPMENT       DEVELOPMENT            DEVELOPMENT            DEVELOPMENT
                                         Q10            Q100                   Q10                     Q100
Old Roof + New Roof                 0.205 m;5/s      0.308 m;5/s            0.195 m;5/s             0.299 m;5/s
+   Grass/Carpark



          7          CONCLUSIONS & RECOMMENDATIONS

                     The proposed development area can be treated by a treatment train consisting of
                     rainwater reuse tanks, bio-retention swale and bio-retention basin, which are capable of
                     removing the nutrients and heavy metals.

                     The car parking and new building can be built to flood free levels in accordance with
                     Council’s requirements.


                     The rainwater tank and bioretention areas are able to attenuate the runoff
                     concentrations back to Pre Development levels and so the development will not have an
                     impact on the hydrology of the receiving waters.




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           1303, Kabara Hostel, Cooroy                IWMP.doc                               January 2013