Attachment 6 - Stormwater Management Plan

R2015: NOOSA LANDFILL - STORMWATER MANAGEMENT PLAN



Due to the constraints around the flood levels and outlets, it is not recommended to augment the existing basin w hich
has a piped outlet and spillway below the Q2 flood level.

A concept of this approach is provided in Appendix A, Drawing Concept-06 for the ultimate catchment. The approach
would also require filling of the northern portion of the pad to grade back to the basin inflow.

       2.     Construct New HES Basin

Based on discussions with NSC, the preferred location for a new basin would be in the north-western corner of the pad,
being where the proposed filling is to occur. Two options for the direction of the basin are provided in Appendix A,
Drawing Concept-06 and Concept-07.

There are two main options in regards to levels for the HES basin:

       +      Design the piped outlet and spillway above nominated flood level (e.g. Q10)
       +      Design the spillway only above nominated flood level (e.g. Q10), with the piped outlet below flood levels and to
              include a frog flap to prevent backflows

Based on Figure 8, the ideal outlet location is along the northern boundary to prevent choked flows in the drainage
channel and existing high point to the west. An outlet along the northern boundary could be approximately RL 11.75.
The flood levels in this vicinity are approximately RL 12.50 (Q10).

Early discussions indicated the preference to locate the basin on the north-eastern corner of the pad. As the outlet
location here is approximately 2m higher than the proposed outlet, this location would require an additional 2m of fill
on the pad to achieve an outlet from the basin. As the pad level is governed by the outlet level and not the Minimum
Floor Levels, it is recommended that the lowest achievable outlet location be adopted to reduce fill requirements. Due
to the sensitivity of the outlet level, additional detailed survey is recommended along the northern boundary in the outlet
location.




Figure 8 – Northern Outflows (Proposed HES Basin)




Environment. Engineering. Education.                                                                                   PAGE 11