Further Advice Response letter SCG 31131(L4).pdf

Response:

  2.1    We have reviewed the guidelines on sediment basins by ICEA. We consider the proposed sediment basin
         for the subject site to be consistent with a Type D Basin. The reason behind this decision is that automatic
         chemical flocculation is not practical. The designs for IECA basin types A, B & D establish volumes for
         settling and storage of sediments. We agree with this principle and have revised our proposed basin to
         include these features, however we don’t believe this to be adequate enough to reduce sediment loads
         for this site and as such we have retained the proposed bidim and gravel filtration features in a forebay
         arrangement upstream from the basin. This decision is based upon the authors experience with projects
         over the last 20 years where similar filtration features have functioned well in reducing sediment loads
         during the construction phases.

  2.2    Noted.

  2.3    The sediment fence wrapped in builder’s plastic is proposed to divert runoff along the northern boundary
         towards the sediment basin and avoid runoff entering into the neighbouring Busy Bees Childcare Centre.
         An alternative solution such as a soil bund along the boundary will not work due to the proximity of the
         proposed building works that will occur along the boundary .

  2.4    The proposed overflow level of the weir wall in the basin will be RL 11.30m. We note Council’s concern
         and have shown an earth bund extending up from the corner of the sediment basin along the northern
         boundary to a point where the bund extends past the RL 11.5m contour.


Issue 3 & 4: Stormwater Drainage
There are a number of conditions of the higher-order approval and FIR which have not been addressed

Response:

         QUDM section 7.4 provides guidance on the roadway flow limits and capacities. It suggests flow width for
         major roads as not applicable.

         Site drainage entering the road will be from roof runoff only where gutter capacities are limited to Q20.
         Therefore, only Q20 flows require consideration of impact.

         Noosa Eumundi Road has a longitudinal grade of 1 in 30 where the site drainage will connect to the kerb.
         Q20 kerb flows without the site drainage would be approximately 90mm deep and 1.3m wide (kerb flow).
         When including the site drainage, the flow depth increases to 96mm and the flow width to 1.39m.

         We have included overland flow rates and driveway capacities at 4 critical points on the sites driveway.
         Year 2100 storm intensities have been used for these calculations and Mannings channel flow equations
         have been used for the driveway profile flow capacities. The results confirm the driveway has the capacity
         to convey the year 2100 flows.


Issue 5: Stormwater Quality
There are a number of conditions of the higher-order approval which have either not been addressed or for
which details require modification

Response:

  5.1    Noted and revised.

   5.2 Stone pitching has always been shown and SCG Consulting Engineers letter of response dated 19 May
       2022 (item 10) attempted to further clarify this. However, to satisfy Council we have reduced the height
       difference to 200mm and extended the stone pitching.

   5.3   Noted and revised.

   5.4   Noted and revised.



SCG Consulting Engineers                              Page 2 of 3                                  SCG Ref: 31131(L1)


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Response:

2.1

2.2

2.3

24

We have reviewed the guidelines on sediment basins by ICEA. We consider the proposed sediment basin
for the subject site to be consistent with a Type D Basin. The reason behind this decision is that automatic
chemical flocculation is not practical. The designs for IECA basin types A, B & D establish volumes for
settling and storage of sediments. We agree with this principle and have revised our proposed basin to
include these features, however we don’t believe this to be adequate enough to reduce sediment loads
for this site and as such we have retained the proposed bidim and gravel filtration features in a forebay
arrangement upstream from the basin. This decision is based upon the authors experience with projects
over the last 20 years where similar filtration features have functioned well in reducing sediment loads
during the construction phases.

Noted.

The sediment fence wrapped in builder’s plastic is proposed to divert runoff along the northern boundary
towards the sediment basin and avoid runoff entering into the neighbouring Busy Bees Childcare Centre.
An alternative solution such as a soil bund along the boundary will not work due to the proximity of the
proposed building works that will occur along the boundary .

The proposed overflow level of the weir wall in the basin will be RL 11.30m. We note Council’s concern
and have shown an earth bund extending up from the corner of the sediment basin along the northern
boundary to a point where the bund extends past the RL 11.5m contour.

Issue 3 & 4: Stormwater Drainage
There are a number of conditions of the higher-order approval and FIR which have not been addressed

Response:

QUDM section 7.4 provides guidance on the roadway flow limits and capacities. It suggests flow width for
major roads as not applicable.

Site drainage entering the road will be from roof runoff only where gutter capacities are limited to Qzo.
Therefore, only Q20 flows require consideration of impact.

Noosa Eumundi Road has a longitudinal grade of 1 in 30 where the site drainage will connect to the kerb.
Qzo kerb flows without the site drainage would be approximately 90mm deep and 1.3m wide (kerb flow).
When including the site drainage, the flow depth increases to 96mm and the flow width to 1.39m.

We have included overland flow rates and driveway capacities at 4 critical points on the sites driveway.
Year 2100 storm intensities have been used for these calculations and Mannings channel flow equations
have been used for the driveway profile flow capacities. The results confirm the driveway has the capacity
to convey the year 2100 flows.

Issue 5: Stormwater Quality

There are a number of conditions of the higher-order approval which have either not been addressed or for
which details require modification

Response:

5.1

Noted and revised.

5.2 Stone pitching has always been shown and SCG Consulting Engineers letter of response dated 19 May

2022 (item 10) attempted to further clarify this. However, to satisfy Council we have reduced the height
difference to 200mm and extended the stone pitching.

5.3 Noted and revised.

5.4 Noted and revised.

SCG Consulting Engineers Page 2 of 3 SCG Ref: 31131(L1)