This LWMS aims to demonstrate that there is sufficient open space area provided within the SP to incorporate drainage requirements from each catchment. Concept drainage design has been
completed by the project team engineers (KCTT) to understand the requirements across the site. The location and configuration of some WSUD measures (tree pits, bio-pockets and swales) require a level of detail that is beyond that required for SP support, therefore these elements have not been included in the drainage calculations presented in Appendix K.
A more detailed analysis of the design of the living stream (i.e. Saint Leonards Creek foreshore area) and surrounding POS areas has been completed by RPS to determine an appropriate foreshore area and demonstrate the design is capable of meeting pre-development peak flow rates discharging from the eastern boundary of the site. This analysis is provided as part of the foreshore area report in Appendix I).
Detailed civil and landscape designs will be completed as part of subdivision which will incorporate WSUD capacities and presented in the future UWMP for the site.
6.4.1 Drainage calculations
The drainage designs across the site have been carried out by KCTT and are presented in Appendix K, summarised in Table 6 and shown in Figure 9. These calculations have utilised the most current Bureau of Meteorology Inundation Frequency Depth data (C. Kleyweg [KCTT] 2018, pers. comm., 27 September).
Table 6: Drainage design details
Catchment area number
Catchment area (ha)
Relevant POS areas (as show on LSP)
Stormwater drainage detention top water level area (m2) Small rainfall
event
Minor rainfall (20% AEP) event
Major rainfall (1%
AEP) event
1 10.53 1 736.8 1,465.8 4,633.0
2 2.62 2 210.0 522.2 1,422.0
3 16.96 3 1,488.2 3,125.6 7,886.0
4 16.86 Part 4 1,424.6 2,471.0 6,577.0
5 36.78 6 3,092.1 7,378.8 19,308.0
6 26.38 10 2,380.0 4,414.1 11,211.0
7 18.58 Part 4 and 7 2,499.6 4,551.0 11,323.0
8 16.69 5 1,392.8 2,811.4 7,508.0
9 42.20 8 3,503.8 7,956.4 14,712.0
10 17.22 9 1,465.9 3,064.8 5,793.0
11 30.91 11, 12 and 13 2,336.0 4,656.2 9,096.0
**Portions of Catchment 7 (i.e. Catchment 7B), 9 and 10 have been modelled in more detail as part of the foreshore area report summarised in Section 6.4.1.1 below and provided in Appendix I, and therefore, the results in Table 6 are superseded.
The drainage areas shown in Table 6 and illustrated in Figure 9 are based on the following key assumptions:
• It is assumed that 27.5% of the total lot area within each catchment will be composed of lots
< 300 m2 in size. These lots will be provided with lot connection pits for roof runoff (as required by the CoS). Therefore, roof runoff from these lots is required to be treated within development drainage structures.
• Bottomless pits are assumed to service 10% of the total road reserve area within each catchment with one pit located every 60 m of road reserve.
• All BRAs and FSAs are located in POS areas (as shown in drawing KC00334.000 C371-P in Appendix K).
• BRAs and FSAs are collocated (treatment and detention) up to the 100 year ARI event, with the exception of Catchment 11 where 100 year ARI event runoff is provided, in part, separately from the small and minor events (shown in drawing KC00334.000 C371-P in Appendix K).
• The BRAs and FSAs have varying side slopes. The small rainfall event has a maximum flooded depth of 300 mm and 1:3 side slopes. The minor rainfall event has a maximum flooded depth of 600 mm (from the invert) and 1:6 side slopes. The FSA then flattens out into an area with 1:10 side slopes up to the 1% AEP top water level (see runoff calculation sheets provided in Appendix K).
• As noted in the runoff calculations sheets (in Appendix K), varying infiltration rates have been utilised to determine treatment and detention volumes within basins.
• The inundation area in each rainfall event is illustrated in Figure 10 through Figure 12.
Additional assumptions are noted in Appendix K.
6.4.1.1 Saint Leonards Creek foreshore area
As discussed previously, a more detailed analysis of the design of the living stream (i.e. Saint Leonards Creek foreshore area) and surrounding POS areas was completed by RPS. Specifically, dynamic post-development surface runoff modelling was undertaken utilising XPSWMM software consistent with Australian Rainfall and Runoff (Ball J et al. 2019). This modelling is presented in Appendix I and results are summarised in Table 7. Figure 9 and Appendix J illustrate how these drainage requirements can be integrated across the living stream and surrounding POS areas.
Table 7: Drainage design details for living stream and adjacent POS
Catchment area number
Relevant POS areas (as show on LSP)
Stormwater storage requirements (m3)
Small rainfall event Major rainfall (1%
AEP) event Total
7B, 9 and 10 Part 7, 8 and 9 1,897 8,303 10,200
The drainage requirements summarised in Table 7 are based on the following key assumptions:
• The model uses the Laurenson runoff-routing method. The areas of lot, POS and road reserve within each sub-catchment along with the assumed impervious fraction, initial loss (mm) and continuing loss (mm/hr) are provided in Appendix I.
• All BRAs, the FSA in Catchment 10, and the living stream are located in POS areas (as shown in Appendix I).
• BRAs will be located beyond and off-line from the living stream and are sized to retain the small rainfall event. BRAs have varying configurations, though the majority are assumed to be 300 mm deep and have an infiltration rate of 2 m/day. Runoff beyond the small event will overtop BRAs into the living stream or an FSA (in Catchment 7B only).
• The FSA in Catchment 7B (referred to as Sub-catchment 10c in Appendix I) is also located beyond the living stream and will detain runoff up to the major rainfall event and discharge runoff into the living stream via a controlled outlet.
• The living stream will generally be 900 mm deep, has a 1 m base and 1:4 side slopes and is consistent with the existing Creek. The living stream will contain the minor rainfall event. The major rainfall event will also be contained within the living stream with the exception of overtopping into detention areas located adjacent to the living stream or on-line, which have been designed through the use of pedestrian crossings.
• The inundation area in each rainfall event is illustrated in Figure 10 through Figure 12.
• A future roadside drain along Henley Brook Avenue will convey flows from the living stream to the south in order to meet pre-development peak flow rates at both eastern discharge locations shown in Figure 7.
Additional assumptions made within the dynamic surface runoff model are provided in Appendix I.
6.4.2 Treatment areas
As discussed in Section 6.2, there are a number of treatment options, all of which will utilise nutrient retentive vegetation and high PRI soils to enable removal of nutrients and treatment of surface runoff.
The areas illustrated as inundated in the small event in Figure 10 represent BRAs that will be vegetated to ensure the small rainfall event runoff will be treated. The specific layout of POS incorporating drainage will be progressed at detailed design however concept landscape plans are provided in Appendix J. No BRAs are proposed to be located within the foreshore area (i.e. living stream).
The final configuration of treatment areas will be reviewed at subdivision in the context of any higher in catchment capacity provided with more detailed landscape and drainage plans presented in future UWMPs.
6.4.3 Detention areas and the living stream
The minor and major event detention areas and minor and major event runoff within the living stream are show in Figure 9 and detailed in drawing KC00334.000 C371-P in Appendix K and Figure I in Appendix I. Landscape concept plans in Appendix J illustrate how these will be integrated with the treatment provisions and usability of the wider POS areas.
All detention areas and the living stream will be constructed with top water levels providing a minimum of 300 mm clearance to finished floor levels of adjacent lots. All detention areas will be designed with appropriate clearance from MGL or CGL where groundwater control is proposed, consistent with IPWEA guidelines (2016).
The living stream is assumed to grade evenly towards the existing culverts beneath Brooklands Drive.
This is generally consistent with inverts of the existing Creek and results in a minor lowering of up to 300 mm, in some sections of the living stream.
6.4.4 Drainage locations
As shown in Figure 9, drainage is spatially located across the site within open space areas at existing low points, and in order to tie in with existing levels at site boundaries.
The gas pipeline corridor that runs through the site (discussed in Section 5.3.2.1) is situated within POS however all BRAs are positioned outside of the easements associated with these pipelines.
Indicative landscape plans illustrating how drainage will be integrated into the POS incorporating the easement is provided in Appendix J.
Saint Leonards Creek foreshore (i.e. the living stream) is also located in the central eastern portion of the site, as discussed in Section 6.2.9. Indicative concept plans for how adjacent POS will be
integrated with the living stream and required drainage are provided in Appendix J.
As discussed in Section 3.4.1 and shown in Figure 5 there are a number of WHPZs that sit across the site associated with existing abstraction bores in the area. There are a number of drainage areas located in POS that are located within WHPZs (POS 1, 2, 5 and 10). These drainage locations have been driven by existing low points and the need to tie in to existing levels at site boundaries, therefore it is considered appropriate to locate drainage in these areas.
The specific use and function of each POS in relation to other constraints (e.g. easements, WHPZs etc.) along with drainage requirements will be detailed in future UWMPs on completion of detailed civil designs and landscape plans.