Reference Documents - Stormwater Management Plan & Waste Management Plan - MCU26/0040, OPW26/0066 & RAL26/0013 (As Published)

Appendix 2 – Stormwater management
design objectives
Table A: Construction phase – stormwater management design objectives
Application:
•      Applies to all climatic regions.
Part 1 Construction phase – stormwater management design objectives12

     Issue                                           Desired outcomes
     Drainage control                                1. Manage stormwater flows around or through areas of exposed soil to avoid contamination.
                                                     2. Manage sheet flows in order to avoid or minimise the generation of rill or gully erosion.
                                                     3. Provide stable concentrated flow paths to achieve the construction phase stormwater
                                                        management design objectives for temporary drainage works (part 2).
                                                     4. Provide emergency spillways for sediment basins to achieve the construction phase
                                                        stormwater management design objectives for emergency spillways on temporary
                                                        sediment basins (part 3).

     Erosion control                                 1. Stage clearing and construction works to minimise the area of exposed soil at any
                                                        one time.
                                                     2. Effectively cover or stabilise exposed soils prior to predicted rainfall.
                                                     3. Prior to completion of works for the development, and prior to removal of sediment
                                                        controls, all site surfaces must be effectively stabilised13 using methods which will
                                                        achieve effective short-term stabilisation.

     Sediment control                                1. Direct runoff from exposed site soils to sediment controls that are appropriate to the
                                                        extent of disturbance and level of erosion risk.
                                                     2. All exposed areas greater than 2500 metres2 must be provided with sediment controls
                                                        which are designed, implemented and maintained to a standard which would achieve
                                                        at least 80% of the average annual runoff volume of the contributing catchment
                                                        treated (i.e. 80% hydrological effectiveness) to 50mg/L Total Suspended Solids (TSS)
                                                        or less, and pH in the range (6.5–8.5).

     Litter, hydrocarbons and other                  1. Remove gross pollutants and litter.
     contaminants                                    2. Avoid the release of oil or visible sheen to released waters.
                                                     3. Dispose of waste containing contaminants at authorised facilities.

     Waterway stability and flood                    1. Where measures are required to meet post-construction waterway stability objectives
     flow management                                    (specified in table B), these are either installed prior to land disturbance and are
                                                        integrated with erosion and sediment controls, or equivalent alternative measures
                                                        are implemented during construction.
                                                     2. Earthworks and the implementation of erosion and sediment controls are
                                                        undertaken in ways which ensure flooding characteristics (including stormwater
                                                        quantity characteristics) external to the development site are not worsened during
                                                        construction for all events up to and including the 1 in 100 year ARI (1% AEP).

12
   	Note: Drainage, erosion and sediment controls should be appropriate to the risk posed by the activity for the relevant climatic region e.g. considering the
     potential soil loss rate, monthly erosivity or average monthly rainfall.
13
   	Note: An effectively stabilised surface is defined as one that does not, or is not likely to result in visible evidence of soil loss caused by sheet, rill or gully erosion
     or lead to sedimentation water contamination.


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