Engineering report 1 George St rev C · REC15/0011

Page 2

Proposed Subdivision
1 George Tewantin




    thus the long term maintenance requirements for Council would effectively be
    greater not less.

    Our concept design therefore proposes bio retention basins to treat the stormwater
    run-off from the site, however instead of one larger basin, two smaller basins have
    been proposed to minimise impacts on existing trees and to make use of the natural
    lay of the land. Following discussions with Council at the prelodgement meeting,
    water from the lots is conveyed to the bio retention basins via a conventional piped
    interlot drainage system. A gravel access originally proposed down the eastern
    and western side of the site to provide access for maintenance of the bio retention
    basins has now been deleted as per Councils information request dated 4 August
    2015.

    In regard to run off from the existing road and footpath area of George Street,
    Council has now indicated a desire replace the existing flush kerb with a
    conventional kerb and channel, however the footpath levels shall generally remain
    as they are. There is a large gum and a strand of melaleuca trees immediately
    adjacent to the existing road pavement that will need to be removed to allow the
    installation of the new kerb and channel, but following further discussions with
    Council staff it is understood that this is desirable due to the potential for long term
    damage to the road pavement. Water collected in the new kerb and channel will be
    collected in new gully pits at each end for the development site and conveyed by a
    conventional pipe system to the proposed outlets.

    The gully pit at the eastern end will drain to the proposed bio retention basin behind
    lot 2 within the drainage/environmental reserve, however the outlet for the western
    end will be directed into the Council reserve and ultimately to Wooroi Creek to
    minimise impacts on exiting trees in the environmental/drainage reserve caused by
    further pipe drainage installation. It should be noted that this pit is only collecting
    water from the existing George Street road pavement area that already flows into
    Wooroi Creek without any quality treatment. This has been depicted on the revised
    concept plans.


        4. CONCEPT DESIGN FOR WATER AND SEWER

    In regard to the sewer service we are able to command all of the new lots using a
    gravity sewer system connecting to an existing sewer manhole in George St. To
    avoid trenching adjacent significant trees along the frontage on George St we have
    elected to take the sewer down the side boundary of lot 1 (in the balance lot) on an
    alignment that avoids any existing significant trees. The manhole at the north east



    J/N 15513                                                                  October 2015
     Rev C                                                                       Page 2 of 3

Page 3

Proposed Subdivision
1 George Tewantin




    corner of the site is 3.65m deep but has now been located more than 15m from the
    large tree in front of lot 1 and as such is not anticipated to impact on this tree. The
    sewer main then traverses the rear of lots 1, 4, 5, 7, 10 and 11 to service these lots
    and two manholes connect to sewer pipes along the side boundary of lots 2 and 8
    to provide a connection to the rear of lots 2, 3, 6, 8 & 9. The proposed sewer system
    has been forwarded to Unitywater for initial comment and they have no objection in
    principle to the proposed alignment.

    The sewer connects to the existing network on the north side of George St. It is
    proposed to tunnel bore under the existing George St pavement and new footpath
    at this location. This will also assist in minimising damage to two existing trees on
    the south side of the road. The alignment of the sewer on the south side of George
    St in front of number 35 is 1.75m off the property boundary. There are a few
    significant trees within number 35 but these are set back between 3 and 5 metres
    from the boundary and are unlikely to be impacted upon by the installation of the
    new sewer. If necessary arborist services will be engaged to undertake minor root
    pruning during excavation for this section of the sewer and to provide advice on
    protection of any other trees potentially impacted on by the sewer construction.

    In order to avoid disturbance of significant trees at the George Street frontage the
    development site the water service to each block has been positioned accordingly.
    Two road crossings (tunnel bores) are proposed to avoid trenching in front of a large
    tree in the front of proposed lot 1 and lot 10. Note a similar approach is proposed
    for the underground electrical service.

    The above information is provided in support of the response to Council’s
    information request dated 9 July 2015.




    Prepared by
    Doug Reynolds
    RPEQ 9072
    Tod Consulting Pty Ltd
    8 October 2015




    J/N 15513                                                                 October 2015
     Rev C                                                                      Page 3 of 3