2015-04-28 Planning and Organisation Committee Agenda

PLANNING & ORGANISATION COMMITTEE MEETING AGENDA                                        28 APRIL 2015


Constituent                   Reasons for management
Total Nitrogen                Nitrogen is a natural element in the atmosphere. Over vegetated
                              areas the nitrogen settles onto the ground and the plants are able to
                              absorb the nitrogen and release it to the atmosphere again as a gas.
                              When vegetated areas are replaced with non-vegetated areas, the
                              nitrogen settles on grounds and roofs and then in rainfall events
                              washes direct to the waterways. Once in the waterways the nitrogen
                              is like a fertiliser and is able to encourage algal growth within the
                              water and increased environmental weed growth along riparian areas.
                              This is called eutrophication. Eutrophication affects oxygen balance
                              in the water and also changes the natural habitat for water and
                              riparian dwelling fauna.

Total Phosphorous             Phosphorous is delivered via atmospheric deposition, as well as
                              cycling of animal and plant wastes through the soil to be taken up by
                              plants again. In urban areas, additional inputs of phosphorous enter
                              the system via external sources through general garden fertilisers and
                              detergents etc. As with nitrogen, when the ground surfaces become
                              impervious through urban development, the atmospheric
                              phosphorous, along with the additional imported phosphorous is able
                              to wash direct into the waterways to act as a fertiliser with similar
                              consequences as nitrogen increases.

Gross Pollutants              Gross pollutants can clog natural and man-made drainage lines then
                              affect local flooding. Non-degradable gross pollutants are harmful to
                              wildlife if ingested. It is also visual pollution.


4.    Computer Modelling and Stormwater Quality Treatment

The computer model used to determine whether the pollutant removal targets can be
achieved is called MUSIC (this is the acronym for its function which is “Model for Urban
Stormwater Improvement Conceptualisation”). MUSIC modellers are able to input site
specific rainfall data, the development footprint (i.e. roads, roofs, grassed areas etc) then the
MUSIC model is able to compare the estimated annual loads of Nitrogen, Phosphorous,
Suspended Solids and Gross Pollutants (i.e. litter) likely to be released from the proposed
development with the loads of these pollutants able to be reduced via the site specific
WSUD treatment strategies.

The most common WSUD treatment strategy that has been used in the MUSIC modelling is
called ‘bioretention basins’. Bioretention basins are basically a sandpit which contains
specially engineered sand, plants that are very effective at removing the nutrients and
underdrainage pipes to convey the treated water back to the conventional stormwater
system or discharge direct to the receiving watercourses. Typical cross sections of
bioretention basins showing the functions of each element of them are shown following.




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