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

    EP-SECP-01: Up:.slope stormwater flow diversion
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    1.0bjectiveslTargets                                                                                                               To reduce the transport capacity of stormwater crossing the building site

    2. Management Strategy                                                                                                             1)Divert up-slope stormwater around the building site;

                                                                                                                                       2) Divert stormwater around areas of soil disturbance; and
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                                                                                                          r....’..;,;                  3) Divert stormwater onto stable ground or areas where suspended
                                                                                                                                       sediment can settle.

    3. Tasks/Actions                                                                                                                   Building site
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                                                                                                                                       1) Construct a perimeter bank along the upslope (eastern)edge of the
                                                                                                          .                            development to divert flow around the building site, and onto grassed or
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                                                                                                                                       stabilised surfaces on the edge of the building site;
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                                                                                                                                       2) Stabilise the perimeter bank with erosion mats (e.g.jute mesh mat
                                                                                                             "          .~             anchored by cold anionic bitumen emulsion); and
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                                                                              ~                        \’,.1:"             1           Erosion prone hot-spots
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                                                                                                                                       3) Place geo-Iogs/straw wattles within the building site, upslope of areas of
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                                                                                                                                       high disturbance or high erosion hazard. Direct flow onto grassed or
                                                                                                                                       stabilised ground. Ensure secure pegging of geo-Iogs to prevent flow under
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                                                                                                                                       the log. The edge of the geo-Iog needs to overlap the stable or grassed
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                                                                                                                                       surface.
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    4. Periormance                                                                              r                ;
                                                                                                                                       1) Effective diversion of stormwater away from the building site, and in
    Indicators                                                                                                                         particular away from reas of high erosion hazard;
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                                                                                                                                       2) No evidrnce of soil’erosion on site, such as rills or sheet erosion.
    5. Monitoring                                                                                 ..                                   1) Inspect the structural integrity of the perimeter bank and geo-Iogs;

                                                                                                                                       2) Inspect the ground ~l:Jrface for erosion;
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                                                                                                                                       3) Inspect performance of the geo-Iog during a stormwater event (low
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                                        .                                                                                              turbidity of diverted water, no erosion under the geo-Iog;
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                                                                                                                                       4) Effective direction , diverted water onto grassed or stable ground).
    6. Frequency/Deadlines                                                                                                             1) Structural integrity’& evidence of erosion: daily
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                                                                                                                                       2) Performanc::e uring stormwater event: During significant stormwater
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                                                                                                                                       events.

    7. Responsibilities                                                                                                                Building contractor.
    8. Reporting and
    Review
                                                                                                                                       Exception reporting to the site manager and senior management.

    9. Contingency                                                                                                                     When loss of control of the upslope flow diversion occurs:
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                                                                                                                                       1) Inspect existing structure for points of failure;
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                                              ~                                r~                                                      2) Report situation to site manager immediately, and request support;
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                                                                                                                                       3) If feasible redirect flow away from the point of failure onto stable ground;
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                                                                                                                                       5) Bridge points of failure with stable material (e.g. sandbags);
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                                                                                                                                       6)Collect water quality samples at inflow and outflow points (section 11)
    10. Corrective actions                                                                                                             1) If necessary remove sediment mobilised on road surfaces with a spade
                                                                                                                                       and broom. Do not use water.
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           i~                                                                                                        :t                2) Repair perimeter bank: reinstall berm, secure the jute mat.
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                                                                                                                                       3) Repair or replace geo-Iogs if damaged. Securely peg to the ground to
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                                                                                                          ~                            4)Add a second geo-Iog 1 to 4m upslope if necessary;
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                                                                                                                                       5) Improve the stability of ground surface that receives diverted water.
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                                 :l’                                                                                                   Refer to EP-SECP-05.