www.jacobs.com | worldwide

Melbourne Metro Rail ProjectSurface Water Impact Assessment

25 August 2016

Surface Water Impact Assessment

1. Assessment of surface water quantity-related impacts during construction and operation– Potential flooding of tunnels and stations– Impact on existing flow regimes – Compensatory storage requirements

2. Minimum level of flood protection provided for a 1%AEP event during construction (temporary) and operation (permanent) consistent with Melbourne Water guidelines.– 600mm freeboard for riverine flooding– 300mm freeboard for local flooding

3. Potential influence of climate change included in the assessment of permanent structures.

2 Melbourne Metro

Major waterways & drainage in the study area

3 Melbourne Metro

• Maribyrnong River • Yarra River

• Moonee Ponds Creek • Drainage systems

Methodology

4

1. Desktop assessment using available baseline and background data

2. Review of relevant legislation and guidelines3. Hydrologic and hydraulic modelling4. Site visits to each precinct5. Consultation with responsible authorities including

Melbourne Water and affected Councils6. Preparation of Surface Water impact Assessment report7. Independent peer review

Melbourne Metro

Environmental Performance Requirements (EPR)

1. Surface Water EPRs– SW1: Protect project infrastructure to appropriate level of immunity

informed by a flood immunity risk assessment and to satisfaction of responsible authority

– SW2: Undertake necessary work to confirm no adverse impacts upon existing flooding conditions, all works to be completed to satisfaction of responsible authority

2. Aquatic Ecology EPR’s relate to surface water discharge quality objectives during operation and construction

3. Other relevant EPRs include LV1 which requires compliance with the Urban Design Strategy

5 Melbourne Metro

Flood Defence Options

6

• EES identified a need for the provision of flood defence measures during construction and operation:1. Tunnel portals2. Station entrances3. Associated infrastructure4. Melbourne Underground Rail Link (MURL) tunnel

portals or cross connection

• A number of options are available for the provision of flood defence

• Actual measures implemented will depend on the location, risk and detailed design – to be informed by flood immunity risk assessment in accordance with EPR SW1

Melbourne Metro

Tunnel Portal Flood Defence Options

7 Melbourne Metro

Flood Door

Sluice Gate (80 ton) uplifted position in housing chamber above tunnel section(Airport Railway, Hong Kong)

Tunnel Portal Flood Defence Options

8 Melbourne Metro

Resilient Tunnel Plug

Demountable Flood Defence

MURL Cross Connection Flood Defence Options

9 Melbourne Metro

Automated flood door

Compensatory Storage

10 Melbourne Metro

• EES assessed the compensatory storage requirements for each precinct

• EPR SW2 relates to compensatory storage requirements

• Compensatory storage is required during construction and operational phases of the project at:1. Arden precinct 2. Western Portal

• Since preparation of the EES, indicative locations for the compensatory storage have been identified

Indicative Arden Precinct Compensatory Storage

• Compensatory storage requirements during operation is 1,600m3 (plus 200m3 for the preferred electrical substation)

• Melbourne Water has provided a letter confirming no-objection to the proposed activity on the Arden site

11 Melbourne Metro

Potential operational phase compensatory storage basin (solution contained on-site)

Indicative Western Portal Compensatory Storage

• Compensatory storage requirements during operation is 9,000m3

• Newell's Paddock provisionally identified

12 Melbourne Metro

Drainage Infrastructure

• EPR SW2 requires that permanent and temporary works do not adversely impact upon existing flooding conditions including existing drainage infrastructure

• Hydrologic and hydraulic modelling of catchments and drainage networks will be necessary to determine potential impacts and assess mitigation options to the satisfaction of responsible authorities.

• Mitigation of impacts is required to the satisfaction of responsible authorities including Melbourne Water and affected councils

• These impacts will be managed using a combination of diversion works, flow attenuation, Water Sensitive Urban Design, etc.

13 Melbourne Metro

Surface Water EPRsSW1 For all precincts (with the exception of the western turn back) design permanent

and temporary works and, if necessary, develop and implement emergency flood management measures for the tunnels, tunnel portals, access shafts, station entrances and Arden electrical substation to provide appropriate protection against floodwaters and overland stormwater flows. This would be informed by a flood immunity risk assessment that considers a range of events, and to the requirements and satisfaction of the responsible authority

SW2 For all precincts: • Maintain existing flood plain storage capacity potentially impacted by the

project, to the requirements and satisfaction of the responsible authority • Permanent and associated temporary construction works must not increase

flood levels that result in an additional flood risk to the requirements and satisfaction of the responsible authority

• Ensure permanent and associated temporary works do not increase flow velocities that would potentially affect the stability of property, structures or assets, and/or result in erosion during operation or construction, to the requirements and satisfaction of the responsible authority

• Undertake modelling of the design of permanent and temporary works to demonstrate the resultant flood levels and risk profile to the satisfaction of the responsible authority

14 Melbourne Metro

EPR AE7

Recommend AE7 be amended so it applies to all precincts: Fully integrate the stormwater treatment system into the design of the western portal and eastern portal all precincts to ensure that stormwater entering the receiving water body complies with SEPP (Waters of Victoria). The best practice performance objectives for achieving compliance with SEPP (Waters of Victoria) during operation phase…

15 Melbourne Metro

Summary

• Responsible authorities have been consulted throughout the EES process

• Nominated surface water EPRs acceptable

• Recommend EPR AE7 be modified to include all precincts

• Viable flood defence systems may be applied to tunnel portals and MURL cross connection subject to completion of a risk assessment and detailed design

• Compensatory storage can be provided as required. Subject to detailed design and approval by responsible authorities

16 Melbourne Metro