Attachment 6 - Stormwater Management Plan

R2015: NOOSA LANDFILL - STORMWATER MANAGEMENT PLAN




Figure 9 – Proposed HES Basin Outlet and Flood Levels

With a Q10 flood level of RL 12.50, the emergency spillway would be required to be as a minimum RL 12.50. To achieve
fall in the outlet channel to the low levels on the northern boundary, the piped outlet would be required to be above
approximately RL 12.1. The outlet pipe could be set at a minimum of RL 12.1 to minimise fill required on the pad. A frog
flap would be required to be installed on the outlet to limit backflows during flood events, however, the basin would still
be operational during these events with outflows able to occur over the spillway (above the flood event) with settling
occurring in the basin. If this does not occur another 0.5m of fill will be required across the entire pad.

Based on a basin settling depth of 1.2m and piped outflow of RL 12.1, the emergency spillway would be approximately
13.3, with an inflow at approximately RL 13.9 to allow for fall through the basin and inlet channel. Pad levels would be
required to be above RL 14.0 to ensure fall to the basin. Where drains are used instead of bunds to direct flow to the
basin (recommended to avoid ponding on pads), additional fill would be required to achieve fall and freeboard within
drainage channels.

Details on the SW2 HES basin sizing are provided in Appendix D.

4.2.1.           MANAGEMENT OF NUTRIENTS FROM GREEN WASTE AREA
The current arrangement on site is to utilise a bio-retention basin to treat runoff from the Green Waste Area. To avoid
construction of a bio-retention basin and a HES basin, the use of a floating wetland could be trialled in the end of the
HES basin. Sunshine Coast Council are currently trialling this at their facilities and should be contacted prior to proceeding
to design.




Figure 10 – Floating Wetland installed at SCC landfill

4.2.2.           DETAILED DESIGN
Detailed design of the proposed HES basin and drainage will be required in consultation with NSC once pad layout and
levels have been determined. This options provided for the SW2 augmentation in this report are concept only to provide
guidance around potential options.

Environment. Engineering. Education.                                                                                  PAGE 12