RFI - Kauri St Civil RFI response · MCU22/0144

                    13. Provide updated OPW plans which:
                       • fully contain the bioretention device within communal open space; and
                       • provide details of the proposed high-flow outlet from the basin and
                       downstream scour protection and flow dissipation in order to demonstrate
                       how flows will be discharged to downstream land without causing
                       concentration of flow or scour; and
                       • Revise and confirm the in-situ infiltration rate and whether this is suitable for
                       a ‘pipeless’ bioretention basin; and
                       • If a pipeless bioretention basin is suitable, revies the basin section to
                       encourage infiltration by having a flatter basin surface and provide some
                       extended detention depth.

            The updated plans provide additional information to detail the bioretention area.

            Details of the weir outlet have been provided which rely on a 1.4m wide rock spillway
            to discharge run-off at the south eastern corner of the site. Based on the survey,
            natural surface grades are typically around 5% at this location, therefore downstream
            scour is considered unlikely, and the rock outlet will assist by dissipating energy from
            the overflow and dispersing run-off from the outlet.

            Based on the previous geotechnical analysis, the soils at the location have a saturated
            hydraulic permeability of 0.0998cm/min, equivalent to 59.88mm/hour of infiltration
            capacity. The MUSIC modelling has been updated to reflect this, and in turn a smaller
            bioretention garden will achieve the required pollutant reduction targets. To
            encourage infiltration, a typical 1% surface grade to the garden has been applied, and
            200mm of extended detention depth is available below the weir spillway level.

            For further details on the other items of the information request, please refer to the town
            planning response.

            We believe that the above satisfactorily addresses the engineering matters raised in the
            information request however, should additional information be required, please contact
            our office directly.

            Yours faithfully,
            RECOR Pty Ltd

            Prepared by



            Ben Parry
            Civil Engineer
            BEng (Hons), MIEAust CPEng NER
            RPEQ: 28084




P +61 7 5211 1003           A 75 Noosa Dr, Noosa Heads Qld 4567   E [email protected]    recorconsulting.com