Final Engineering services report _62 Lake Macdonald Drive · OPW25/0057

Figure 6: Stormwater Drainage Catchments

3.9.3   Scenario Method

The proposed development was modelled using split catchment source nodes. Three (3) urban residential source
nodes were identified, comprising of road, ground cover and roof nodes. Sub-catchments were derived from the
proposed stormwater drainage plans.

Although the exact quantity of dwellings cannot be confirmed, it is expected that the average density of dwellings/ha
within Lots 1 and 2 will be approximately 65 dwellings/ha and should be roughly between the 40 dwellings/ha and 80
+ dwellings/ha impervious fraction recommendations in Table 3.5 of the MUSIC Modelling Guidelines – South East
Queensland Version 1.0 (WBD, 2010). The nominated fraction impervious for each source node modelled in MUSIC
was therefore:

•   Road source node:                          40% impervious
•   Ground cover source node:                  70% impervious
•   Roof source node:                          100% impervious

The roof area has conservatively been estimated to be approximately 90% of the lot area, with the remaining 10%
categorised as ground cover.

The ~20m wide access reserves that extend from Road 1 to the balance lot 100 have been included in the Road node.
40% fraction impervious has been adopted within the access reserves to allow for future driveway and path accesses.
This matches the impervious percentage within the Road 1 reserve.

Table 3: MUSIC Source Node Characteristic
           Source Node                               Road        Ground Cover       Roof                Total
    Catchment      Sub-Catchment                   Area (ha)       Area (ha)      Area (ha)           Area (ha)
        A               N/A                          0.73            0.09           0.85                1.67


62 Lake Macdonald Drive, Cooroy – Engineering Services Report                                                Page 9
233467 | M24-1037Rpt – Issue A – April 2025