BBNE00529_0002_0001-REP-001-1-73 Eumundi-Noosa Rd SMP

4.2        Townhouse Site
An assessment completed of the existing stormwater drainage network to determine if it can convey the additional flow from the Townhouse
site and achieve compliance with the QUDM drainage criteria. It was found that with the increase in flows that some of the minor storm
(10% AEP) drainage criteria became exceeded. As such, a detention tank is proposed to be installed within the townhouse site to ensure the
10% AEP peak flows are detained back to the development intensity that the drainage system was designed upon. The existing drainage
network assumed the contributing catchment of the original development had an imperviousness of 50%. With the Townhouse site
increasing the imperviousness of this catchment to 90%, the detention tank has therefore been sized to mitigate flows back to the original
design intent.


  4.2.1       Catchment
The catchment reporting into the existing drainage network is catchment 1/3, which is 0.687 ha, of which 0.506 ha is the townhouse site. An
excerpt of the catchment plan from the original design drawing is detailed in Figure 2.3.




Figure 2.3: Excerpt of the Catchment Plan from Design Drawing (catchment 1/3)

TABLE 4.8: WBNM SUB-CATCHMENT FRACTION IMPERVIOUS VALUES – DEVELOPED SCENARIO

 WBNM Sub-Catchment                Area (ha)                          Design Impervious (%)             Proposed Impervious (%)

 Townhouse                         0.506                              50                                90

 Balance                           0.181                              50                                50

 Total                             0.687                              -                                 -


  4.2.1       Results
The aim of this assessment is to size a detention tank within the townhouse site to ensure peak flows in the 10% AEP are reduced to be below
the existing 10% AEP, from which the drainage network was design (that is going from 50% to 90% impervious). The drainage design flows
reporting from Catchment 1/3 are 0.24m3/s in the 10% AEP, which align with estimates from the WBNM model (0.26m3/s).

A summary of the storage size and outlet configuration and key details provided below:




73 EUMUNDI - NOOSA ROAD, NOOSAVILLE I BBNE00529_0002_0001-REP-001-1                                                                      17