Attachment 6 - Stormwater Management Plan

R2015: NOOSA LANDFILL - STORMWATER MANAGEMENT PLAN



1.5.                PRINCIPLES OF SURFACE WATER MANAGEMENT FOR THE SITE

Ongoing soil and water management will be required through the life of the project. The three cornerstones of the
erosion and sediment control industry are drainage control, erosion control, and sediment control. The primary function
of each of these principles is summarised below:

       +      Drainage control measures aim to prevent or reduce soil erosion caused by concentrated flow-including the
              management of rill and gully erosion and to appropriately manage the movement of "clean" and "dirty" water
              through the site.
       +      Erosion control measures aim to prevent or reduce soil erosion caused by raindrop impact and sheet flow (i.e.
              the control of splash and sheet erosion)
       +      Sediment control measures aim to trap and retain sediment either moving along the land surface (bed load) or
              contained within flowing water (suspended sediment) (IECA, 2008).

The proper management of stormwater is critical to the implementation of effective erosion and sediment control. The
effective management of stormwater lies in the appropriate control of runoff velocities and volume.

1.6.                DRAINAGE CONTROL

The primary function drainage controls are to:

       +      minimise the risk of rill and gully erosion;
       +      minimise the risk of hydraulic damage to the adopted erosion and sediment control measures;
       +      control the velocity, volume and location of water flow through the site; and
       +      appropriately manage the movement of "clean" and "dirty" water through the site (IECA, 2008).

The Guideline - Stormwater and environmentally relevant activities (DES, 2021) requires that high erosion hazard sites
implement the following design and management measures:

       +      Erosion protection and sediment control measures should be installed and maintained for all stages of the
              activity to minimise erosion and the release of sediments.
       +      All areas of soil disturbed and exposed should be managed to minimise the loss of sediment through
              revegetation and/or use of other stabilisation techniques.
       +      All concentrated stormwater flows (including ‘clean’ stormwater and ‘dirty’ stormwater) should have
              concentrated flow paths, such as drainage lines, diversion drains, channels and batter chutes (where applicable)
              which have been designed, constructed, effectively armoured and maintained to convey the runoff from events
              up to and including the average recurrence interval (ARI) of:
                   o 1 in 10 year critical duration ARI storm event without causing water contamination, sheet, rill or gully
                        erosion, sedimentation, or damage to structures or property.
       +      Stormwater runoff from external or undisturbed catchments should be diverted around or away from disturbed
              areas as much as possible.
       +      Sediment basin(s) should be installed and maintained to collect and treat stormwater runoff from all disturbed
              areas of the site(s) approved as part of the ERA application, and areas in which any earthen material is stored.
       +      For events up to and including a 24 hour storm event with an ARI of 1 in 10 years, the following must be achieved
                   o a sediment basin must be designed, constructed and operated to retain the runoff at the site(s)
                        approved as part of the ERA application;
                   o the release stormwater from these sediment basins must achieve a total suspended solids (TSS)
                        concentration of no more than 50mg/L for events up to and including those mentioned above.

              For events larger than those stated above, all reasonable and practical measures must be taken to minimise the
              release of prescribed contaminants.

              An alternative basin design (such as a high efficiency basin) can be used provided it has been demonstrated
              that the contaminant load to be released to the receiving environment for the life of the project will be equal to
              or less than the standard design.

              The department supports high efficiency basin technology especially as it may lead to both flexibility
              for the site operator and if appropriately designed and managed, sound environmental outcomes.

       +      All sediment basins should have a spillway, designed, constructed and effectively armoured to convey
              anticipated flows. Design for a 50 year ARI critical event is considered a minimum.
       +      Any sediment basin designed in accordance with this list must be operated in such a manner that within 120
              hours of the most recent rainfall event, the required design capacity of the upper settling volume is available for
              capture and storage of stormwater runoff from the next rainfall event.

Environment. Engineering. Education.                                                                                      PAGE 4