Attachment F - Addendum to Engineering Report (00016989)

Unit Development 30-32
Doonella Street, Tewantin

T




     SUPPLEMENTARY INFORMATION TO ENGINEERING REPORT


        1. INTRODUCTION

      This report shall be read in conjunction with the Tod Consulting report dated 9 June
     2015 and has been prepared in response to item 5 of Noosa Council’s Request for
     Information dated 2 July 2015.


        2. PRELIMINARY STORMWATER DRAINAGE DESIGN

     A preliminary stormwater drainage plan has been prepared (marked up on
     architectural site plan) and is attached to this report. The plan shows proposed
     stormwater pipe levels within the site for various areas and demonstrates that a vast
     majority of the site can be conveyed to the proposed bio retention basin in the south
     east corner of the site. The exception is the ramp area to the basement car park.
     This area has been allowed for in the water quality modelling prepared by our sub
     consultant Aqua Intel. Roof water re-use has also been included in the modelling. It
     is proposed to locate the rainwater tank in the north east corner of the basement for
     irrigation purposes. The overflow pipe from the rainwater tank has been set 1.6m
     above the basement floor height at RL 6.2 to ensure there is sufficient fall to convey
     the overflow to the bio retention basin.

     The inlet to the bio retention basin from site drainage pipes has been set at RL 4.8
     which is approximately 200mm below the existing ground level at this location. Minor
     earthworks will be required to form the bio retention basin. The bio basin overflow pit
     is set at RL 5.1 to provide the 300mm extended detention depth required by the
     water quality modelling. Outflows from the bio basin flow to a 20m3 detention tank.
     The outlet pipe level from the basin of RL 4.0 allows for the depth of filter media
     specified in the water quality modelling report. A 300mm diameter outlet from the
     detention tank at RL 3.9 connects to the existing drainage pit in Doonella St at this
     location that has an invert level of RL 3.0. A 2m wide grass lined weir will also be
     provided from the bio basin to provide overflow capacity from the basin for the Q100
     event.




                                                                                       Rev B
     J/N 13672                                                                   August 2015
                                                                                  Page 1 of 2