080624 2383-01 FINAL Engineering Report for DA.pdf [As Published] · 132008.1128

BLUE CARE SUNRISE BEACH
ENGINEERING REPORT FOR DEVELOPMENT APPLICATION



2.6 STORMWATER QUANTITY

    2.6.1          Site Hydrology

    The drainage system within the development will consist of underground pipe systems
    and surface overland flow. With the completed development, the locations of the
    discharges to the national park will be maintained across the western and northern
    boundaries of Lots 1 and 6, respectively.

    The development will result in a significant increase in the site impervious area. The
    undeveloped site has been assumed to have no impervious area, while the developed
    site has been assumed to have a fraction impervious of 0.9.

    Catchments within the developed site will consist of paved areas, roads, carparks and
    roof areas.

    The site, prior to development, had an estimated time of concentration of 18 minutes for
    Lot 6 and 22 minutes for Lot 1. The estimated times of concentration for the developed
    site are 8 minutes, for both catchments.

    The reshaping of the site for the development will also result in runoff from an additional
    catchment area of 0.626ha at the north-eastern corner of Lot 1 being redirected to the
    west through Lot 1. Currently, runoff from this area discharges to the east, to Ben
    Lexcen Drive.

    Attenuation of peak discharges from the developed site is necessary to comply with
    Council’s non-worsening requirements.

    For the site in its undeveloped condition, peak discharges have been calculated, using
    the Rational Method, for rainfall events with average recurrence intervals of 2, 10, and
    100 years. These calculations are summarised in the Tables 2.7 and 2.8.

    The catchment areas for Lots 1 and 6, used in the calculations below, represent the
    areas of the lots excluding the dedicated buffer strips and fire breaks. No development
    works which will affect site runoff characteristics are proposed within these areas and,
    therefore, they have not been included in the catchment areas used for the calculation
    of the pre-development peak discharges to be used for comparison with those from the
    developed site.

    Table 2.7, Lot 6 Undeveloped Site – Peak Discharges
                ARI                             C             I                     A       Q
               years                                       mm/h                    ha     m3/s
                 2                             0.15          99                  0.7774   0.033
                 10                            0.18         134                  0.7774   0.052
                100                            0.22         194                  0.7774   0.090

    Table 2.8, Lot 1and Road Undeveloped Site – Peak Discharges
                ARI                             C            I                     A        Q
               years                                       mm/h                    ha     m3/s
                 2                             0.15         90                    3.65    0.140
                10                             0.18         122                   3.65    0.223
                100                            0.22         176                   3.65    0.385




Blue Care Property Development Unit                        Version 1.1                            24 June 2008
2008 06 24 2383-01 Engineering Report for DA          Commercial in Confidence                         Page 10