Development Application part 7 of 10 Stormwater Management Report - MCU13/0092

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4.2 Operational Phase


During the operational stage of the development, the following impacts have been identified in relation to stormwater
runoff and water quality of the receiving waterways:


    Potential exists for gross pollutants which include human derived litter, course sediment and vegetation affecting
    the drainage capacity of stormwater systems. Gross pollutants are also typically unsightly reducing the visual
     amenity of the site. Gross pollutants can also physically affect the downstream waterway habitats and
     organisms such as entangling birds and marine animals in plastic;

    Sediment and Suspended Solids can become mobilised by stormwater as suspended solids from the erosion of
    exposed soil areas, un-mulched garden beds and sediment deposited on car park and hardstand areas by
    vehicles and by atmospheric deposition of sediment. Sediment can affect receiving waterways physically
    through smothering aquatic flora and fauna. Sediments can also block stormwater systems leading to local
    flooding. Suspended solids may also be used as a transport medium for nutrients and heavy metals making
    their way into waterways; and


    Nutrients can enter the waterways from stormwater runoff through many sources including, detergents used in
    car washing, fertilizers from landscaping and lawn areas, nitrous oxide deposition from vehicle exhausts, and

    organic waste. Large nutrient levels can lead to eutrophication of the receiving waterways resulting in algal
    blooms and excessive macrophyte growth.


Implementation of the appropriate SQID’s would ensure that stormwater leaving the developed site shall be
acceptable to Healthy Waterways, Water Sensitive Urban Design Guidelines for South East Queensland’s
requirements.


4.3 Selection of Storm water Management Options


The Performance Criteria required to be met for discharges from development sites during the ’operational’ (post-
construction) phase of the development is detailed in Table 2.2 of the Urban Stormwater Quality Planning Guidelines
2010.


The load-reduction targets that must be achieved when assessing the post-developed sites treatment train,
(comparison of unmitigated developed case versus developed mitigated case) are listed in Table 2.

                   Table 2: Storm water Quality Objectives for the Site. (Operational Stage)


                        Pollutant Issues                Load Reduction Objectives (%)
                     Total Suspended Solids                             80
                       Total Phosphorus                                 60
                         Total Nitrogen                                 45
                     Total Gross Pollutants                             90




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