Response to Information Request - Received on 19/04/2012 · OPW11/0335

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6.1        Management of Stormwater

          This sub-section describes the treatment train                                 (Drawings 02 & 06) used to manage
          stormwater flowing through the Essence of Peregian development. The treatment train
          is designed to keep stormwater within the landscape of the proposed development site.
          There are three treatment units in the design treatment train:


           6.1.1         Roof Water capture


          Guttering provides capture of the rainwater incident upon the roofs of the buildings
          within the development. 100% of the roof guttering is connected to rainwater tanks,
          which provide both rainwater storage for re-use within the development, and attenuation
          of stormwater flows.


          These tanks have been sized in line with MP-4.3 of the Queensland Building Code to
           meet water savings targets, and sized are as follows
                .     Beach Shacks: 3 kL
                .     Building A: 100 kL
                .
                      Building B: 100 kL
                .     Hotel/Commercial Area: 100k L


           These tanks are to be provided with appropriate inlet arrangements, including first-flush
          diverters. Overflow of the tanks are to be ~connectecl to the Bioretention trenches for
          treatment before release to the r~ceivi(lg environment.
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           6.1.2         Vegetated Buffers                      "



                                                                       ’f>.

          Vegetated buffers provide stable grounocover,
                                                  "
                                                        thereby minimising the erosion potential
          of the landscape surface. Vegetation includes grassed surfaces and deep rooted
          vegetation. Energy from rainfall is di’S.sipated over a broad, stable surface, and shallow
          sheet-flow of accumulated
                                      stormwate~ is slowed by the rough surface provided by the
          vegetation. The  soil binding capacity of the plant roots, and the capacity of the plants to
          assimilate nutrients from infiltration....water, provides the first step of the treatment train.
          Stormwater flows from the vegetated buffers into Bio-retention devices.


           6.1.3         Bio-retention Trenches


          The Bio-retention Trenches are generally dry, but during a stormwater flow the trenches
          may contain accumulated water to a depth of 200 mm, and 150 mm shortly thereafter
          when the trench is dewatering.


          Flow out of the Bio-retention Trenches is underground, with filtered water percolating
          through the base of the retention trench, through a gravel layer to the surrounding soil.
          Flow out of the Bio-retention Trenches during high flow will be via rock weirs. Maximum
          flow depths over the weir crests in the 100 year local runoff event are estimated to be
          less than 25 mm. Outflow is towards the existing Heath Wetland.


           Overland sheet-flow for the majority of the development is to be piped from stormwater
          collection pits to the bio-retention trench. For the periphery, where it is not possible to
          use stormwater collection pits, an interceptor drain, essentially a grassed swale, will be

           used     to    capture and divert incident stormwater to the bio-retention trenches for
          treatment.


          Pipe and swale entrances to the bio-retention trenches are to use rock basins and
          energy diffuser arrays to protect against scouring (drawing 04 & 05).




@2012 Simmonds & Bristow Pty LId                                Contrast Constructions                                J-1 005-31 0   -
                                                                                                                                         22 March 2012
I :\CLlENTFILES\Contrast Constructions\11 08-155c   -
                                                        Essence of Peregian SCEP Stage 1 Update\09   _
                                                                                                         Output Documents\11 08-155C SWMP
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SCEMP_Scanlon Properly Group_V4 O_ta_120321.doc                                                                                            Page 9 of 24