Report relating to: Stormwater Management for …

1 9 June 2017 Our Reference: 1784 Report relating to: Stormwater Management for Schofields Aerodrome Development Stage 1 Revision A For Defence Housing Australia Prepared by: Craig & Rhodes Pty Ltd Suite 400, Level 4 16-18 Cambridge Street Epping NSW 2121 P: 02 9869 1855 F: 02 9869 2341 E: W: _____ Stormwater Management Report Schofields Aerodrome Development Stage 1 Page ii INDEX 1 1 Site Description .. 1 Proposed Works .. 1 2 Reference Policies and guidelines .. 2 3 Stormwater Quantity Management .. 3 Objective .. 3 Methodology .. 3 Pre-Development Conditions .. 4 Post-Development Conditions .. 4 4 Stormwater Quality Management .. 6 Objectives .. 6 Methodology .. 6 Data Inputs .. 6 Overall Treatment Effectiveness .. 8 Stream Erosion Index.

2 8 5 Flood Assessment .. 9 Hydrology .. 9 Hydraulics .. 10 Culvert Blockages .. 10 Results .. 10 Discussion .. 11 6 Conclusions .. 12 Appendix A MUSICLink Report .. 13 Appendix B Blockage Assessment Form .. 14 Appendix C HEC-RAS Model Results .. 15 DOCUMENT CONTROL Revision Date Details Author Reviewed A Issued for DA Submission _____ Stormwater Management Report Schofields Aerodrome Development Stage 1 Page 1 1 Background Craig & Rhodes has been engaged by Defence Housing Australia (DHA) to prepare the Development Application (DA) documentation for the civil works as well as the Stormwater drainage, Stormwater detention and water sensitive urban design treatment train for Stage 1 of the proposed development within the old Schofields Aerodrome.

3 The full set of engineering drawings to accompany the DA is referred to as Drawings 1784C-DA-S1-0001 0902 Revision B. The proposed development is located within the North West Priority Growth Area on the northern portion of the old Schofields Aerodrome. This site is located within the Blacktown Local Government Area. Site Description The site is relatively flat with some existing airport runway infrastructure. The Richmond railway line is immediately to the east of the site. The extension of Burdekin Road will be to the north of the site, and Eastern Creek to the west of the site. The Nirimba Education Precinct is to the south of the site. Proposed Works The total site area for Stage 1 of the development on the Schofields Aerodrome is approximately hectares.

4 Stage 1 also consists of the construction of Mustang Drive to the north of the development area to link with Schofields Road to the north. It is proposed to provide 112 residential lots, 6 residue lots with associated roads, Stormwater drainage and utility infrastructure. It is also proposed to provide temporary Stormwater detention and water quality treatment for the development. It is proposed to partially construct Basin of the Section 94 Contributions Plan No. 24 Schofields Precinct (refer to Basin 5 and 5A on drawings 1784C-DA-S1-0751 0754) and utilise this in providing temporary Stormwater detention and water quality treatment for the proposed development. Under the bulk earthworks development application (Ref: DA15-0999), drainage channel 3 (refer drawing 1784C-DA-S1-0755) was approved as a trapezoidal channel as part of the Stage 1 development.

5 It is proposed to construct a turf lined urban channel adjacent to the proposed Burdekin Road to convey Stormwater generated from the external catchments to the east of the Richmond railway line through the development area to Eastern Creek to the west of the development (refer to the BG&E Flood Assessment previously approved under DA15-0999). This channel is referred to as channel within the Section 94 Contributions Plan No. 24 Schofields Precinct. _____ Stormwater Management Report Schofields Aerodrome Development Stage 1 Page 2 2 Reference Policies and guidelines The following documents have been referenced in developing the Stormwater drainage and water sensitive urban design strategy for the proposed development: 1. Blacktown City Council, 2005, Engineering Guide for Development 2.

6 Blacktown City Council, 2015, Delivery of S94 Stormwater Infrastructure by Developers in the North West Growth Centre 3. Blacktown City Council, 2013, Developer Handbook for Water Sensitive Urban Design 4. Blacktown City Council, 2015, Blacktown Development Control Plan Part J Water Sensitive Urban Design and Integrated Water Cycle Management 5. Engineers Australia, 1987, Australian Rainfall & Runoff: A Guide to Flood Estimation 6. Geosciences Australia, 2016, Australian Rainfall & Runoff: A Guide to Flood Estimation 7. NSW Government, 2010, Draft NSW music Modelling guidelines _____ Stormwater Management Report Schofields Aerodrome Development Stage 1 Page 3 3 Stormwater Quantity Management Objective The Stormwater Management objective for the proposed development is driven by the Growth Centre Precinct Development Control Plan (DCP) and the Blacktown City Council Engineering guidelines .

7 As the site is part of the North West Priority Growth Area, regional detention basins are proposed to be provided on a regional basis with Section 94 contributions collected from the developments as they are released. However as the timing of these regional basins has not been confirmed, Council has requested that developments provide temporary Stormwater detention systems that will be decommissioned when the regional basins have been constructed and become operational. Blacktown Council s temporary Stormwater quantity Management requirements request that the post-development flows generated by the development be limited to the pre-development levels for all storm events up to and including the 100 year ARI event. Methodology A RAFTS based model was prepared to assist with the sizing of the temporary Stormwater detention basins to the west of the proposed development.

8 The following table is a summary of the inputs used within the model: Parameter Catchment Condition Value PERN All LOSSES Initial Loss Pervious Catchment 15 mm Continuing Loss Pervious Catchment mm Initial Loss Impervious Catchment mm Continuing Loss Impervious Catchment 0 mm Bx Table 1 - RAFTS Model Parameters This RAFTS model was used to size the temporary basins to accommodate the future stages of the development that will drain to the basins, while ensuring that the temporary basin will operate to Council requirements as each stage is constructed. Rainfall intensities were adopted from Table of Blacktown City Council s Engineering Guide for Development (2005). _____ Stormwater Management Report Schofields Aerodrome Development Stage 1 Page 4 Pre-Development Conditions The existing site consists of both pervious and impervious areas.

9 The site survey was used to determine the approximate fraction imperviousness of the catchment for using as part of the pre-development hydrological model. The approximate fraction imperviousness for the catchment is 17%. This has been adopted for all catchments within the proposed development extents. The peak pre-development peak flows have been summarised in Table 2 & Table 3. Post-Development Conditions A second drains model was prepared to assess the extent of temporary Stormwater detention which is required to achieve Blacktown Council s Stormwater quantity objectives of post-development flows not exceeding pre-development flows. In accordance with the Blacktown Council s Engineering guidelines for Development (2005), new residential areas have a fraction imperviousness of 85%.

10 This has been adopted for all catchments covering residential areas upstream of the proposed temporary Stormwater basins. To cater of the increased peak flows under the developed site conditions, it is proposed to provide a temporary basin to detain Stormwater runoff temporarily and release it at a flow that does not exceed the existing site flows from the catchment. The basin levels and flows shown in this Report have been calculated based on only Stage 1 being fully developed, however an allowance has been considered for the basins to allow for the development of the future stages. The following tables summarise the performance of the temporary detention basins for a range of ARI events up to and including the 100 year event. It is noted that the basins have been designed to operate under both free draining and drowned conditions based on the BG&E flood Report levels.