Appendix E v 2 - Revised Integrated Water Mangement Plan

1.0     INTRODUCTION AND SUMMARY

This report has been prepared by Brisbane Stormwater Management P/L at the request of Noosa Care
Inc’s civil consultant Callaghan & Toth P/L. The report describes the definition of a stormwater
detention volume for the management of peak rates of stormwater runoff from the proposed extension
of Cartwright Village at Carramar, at 186 Cooroy – Noosa Road, Tewantin. A plan of the overall site,
including the existing facilities and the proposed extension, is shown in Figure 1 below below.

The eastern boundary of the 4 hectare site borders a tributary of Wooroi Creek, and stormwater runoff
from the entire site discharges to that tributary. The 0.82 hectare stormwater catchment area for the
proposed extension is outlined in red on Figure 1.

                                                          SITE BDY

                                                                                                  VILLA 5


                                                                                                                  VILLA 6




                                                                                                        VILLA 4



                                                                                                                            WATER
                       EXISTING FACILITIES                                                                                  HOLE


                                                                                            VILLA 3     PROPOSED




                                                                                                                                   EK
                                                                                                        EXTENSION




                                                                                                                                CRE
                                                                 ENTRY
                                                                           LANDSCAPED
                                                                            PODIUM




                                                                 VILLA 1                VILLA 2
                                   SITE BD                                                                                  NORTH
                                             Y

                 STORMWATER CATCHMENT BOUNDARY
                 FOR POPOSED EXTENSION             COOROY - NOOSA ROAD
Figure 1:     Overall Site Plan

The design catchment is mostly open space at present, with a car-park and some pathways constituting
an impervious fraction of 22 percent. The proposed extension will consist of an entry facility and seven
villas, with associated pathways and podium areas and an extension of the existing carpark under two of
the proposed villas, which will increase the catchment’s impervious fraction to 65 percent.

Urbs modelling of the pre-development and post-development scenarios has indicated that the proposed
extension will increase the peak runoff rates from the site by about 35 percent. The modelling has
further indicated that complete mitigation of this increase will require a detention volume of 118 cubic
metres if the difference in critical storm durations between the pre- and post-development scenarios is
ignored; or as much as 140 cubic metres for complete mitigation at like-for-like durations.

An arrangement of underground detention cells, based on the ecoAid system, and providing a total
detention volume of 131 cubic metres, is shown in Figure 4 on page 12 of this report. A description of
the ecoAID system is shown in Appendix A hereto.

It is expected that the required detention volume will be slightly reduced at the detailed design phase.


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      Brisbane Stormwater Management Pty Ltd Document File: Carramar.Doc