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Attachment I:Flood Study

Flood Study Final v6

Prepared for Johnstaff Projects, November, 2016161372 P

(Taylor Thomson Whitting (NSW) Pty Ltd. Consulting Engineers I ABN 81 113 578 377 48 Chandos Street. St Leonards NSW 2065 I +612 9439 7288 I ttw.com.au

)Consulting Engineers

Johnstaff ProjectsNovember 2016

The New Museum, Parramatta — Flood Study161372

Contents

1.0Executive Summary3

2.0Introduction4

2.1The Site4

2.2Proposed Development5

3.0Flood Study6

3.1Existing Flooding6

3.2Flood Risk Hazard8

3.3Planning Development Controls9

4.0Flood Modelling10

4.1Flood Model10

4.2Flood Model Results10

4.3Extended Basement Option14

5.0Future Work15

Appendix A

Appendix B

Appendix C

.Taylor Thomson Whitting (NSW) Pty Ltd2

© Taylor Thomson Whitting



1.0 Executive Summary

TTW has been appointed by Johnstaff Projects to provide flood risk advice for the proposed New Museum development, Parramatta. Two-dimensional flood modelling has been completed for the existing scenario and for the post-development scenario. The findings show that the proposed development has no impact on the flood level for the Parramatta River or neighbouring land.

The ground floor level of the new building is set at 7.50m AHD. This provides 500mm freeboard above the 100 year ARI overland flood level (7.00m), and around 1.5m above the 100 year ARI Parramatta River flood level (6.00m).

Current development proposals are to use the existing vehicle access from George Khattar Lane to a new staff parking and loading area within the basement level of the proposed building. This existing access and basement level is set at 3.5m AHD, below the 5 year ARI flood level, and can be expected to flood to a depth of 1.14m during this event. The expected flood depth increases to 2.5m for the 100 year ARI. If this low level access is maintained, suitable flood mitigation measures will be required. An option for this mitigation is tanking with automated flood gates located at all entrances to this level. This option is currently allowed for in the concept design and cost plan.

We recommend that access to the basement level is provided above the 100 year ARI flood level and an alternative development option considers an extended basement with additional car parking space. This option removes the existing low level access from George Khattar Lane, with a new access provided from Philip Street lane. The level of this access would be set above the 100 year ARI flood level with 500mm freeboard.

Overland flow caused by local urban flooding is affected by the development. Works will be required to divert an existing 600mm storm pipe and overland flow path to the west of the new building. A minimum 12m offset between the western boundary and building outline is required to provide sufficient space and easement for the stormwater pipe and overland flow path. Allowances have been made in the cost plan for the diversion of the stormwater pipe, however the current concept includes a smaller 9m setback from the boundary. The additional 3m setback required can be accommodated in future planning schemes and would have minimal impact to the current concept planning.

Further assessment and modelling will be required as the development options and design details progress. This modelling will need to assess the option of increasing the capacity of the storm diversion with the aim of reducing the overland flow through the site.

(3)Taylor Thomson Whitting (NSW) Pty Ltd© Taylor Thomson Whitting


The New Museum, Parramatta — Rood Study161372

2.0 Introduction

This Preliminary Flood Study report has been prepared by TTIN to address the potential flooding issues at the New Museum, Parramatta. This report provides preliminary information to inform flood planning levels for the development and identify suitable flood mitigation measures.

2.1 The Site

The development site is bounded by the Parramatta River to the north, Wilde Avenue to the east, Philip Street to the south, and residential apartments and a hotel to the west (refer to Figure 1). The site is currently occupied by a multi-storey car park with access to the lower ground level from George Khattar Lane via an underpass below the Wilde Avenue bridge, and access to ground level from the lane off Phillip Street. An existing heritage building occupies the centre of the site with existing commercial buildings fronting onto Philip Street.

The site entrance at Philip Street is approximately RL 7.0m (all levels stated are AHD). The site is generally flat up to the existing multi storey car park where there is a level drop from 7.0m to RL 3.5m and then a continuous fall towards the riverbank at RL 2.0m. A topographical survey and site images are included in Appendix A.

(Figure 1 Existing Site)Taylor Thomson Whitting (NSW) Pty Ltd© Taylor Thomson Whitting



2.2 Proposed Development

The proposed development includes demolition of the existing car park and commercial buildings fronting Phillip Street, with the construction of the new museum building. Several development options are currently being considered. Generally the proposals consist of a new six-level building with a continuous connection between the Civic Link, along Horwood Place, and riverbank adjacent to the Parramatta River (Refer to figure 2). Current development proposals are shown in Appendix B.

(Pnrr,i pedestrian JCCC SS to the site is achieved through the continuation of the proposed civic link (Horwood Place). along a north south vets connecting Parramatta with the RiverThe site can also be accessed from along the riverbank. with landscaped public space directing pedestnans into the buildingBus access is v.a Phillip Street. +with dedicated bus bay and access separate to the pedestrian accessGoods and delwenes access is also from Phillip Street.Basement level car parking for MAAS fleet vehicles is accessed through George Khattar Lane on the east of the site— # cmPk5.K &cuss* PEDESIRa:i ARRaral— ♦ 855 APR. nti.GOODSAhhiVAL4- io mpucrFcLiAro,)

Figure 2 Site Access Plan

Due to the existing level change across the site, the proposed building will have an at-grade basement level to the north area of the site (refer to figure 3). Access to the ground floor level from the south will be at-grade with Philip Street. A circulation spine provides access through to the north of the building, with steps down to the public space along the riverbank. Access to the basement level from the east will be at-grade with George Khattar Lane. Current proposals are for the basement to be non-habitable with circulation/processing, staff car parking and retail loading. The habitable floors above will consist of galleries, retail, offices, exhibition, and workshop spaces. The ground floor level to the north of the basement outline will be suspended, so that it does not interfere with flood flows up to the 100year ARI.

Figure 3 Proposed At-grade Ground Floor and Basement (basement on the right)

Taylor Thomson Whitting (NSW) Pty Ltd5




3.0 Flood Study

The purpose of this preliminary study is to identify flood risk, levels and hazards, and to provide recommendations relating to:

· Threshold and Floor levels

· Possible drainage solutions

· Possible flood mitigation measures

3.1 Existing Flooding

The development site is within the Upper Parramatta River Catchment and at this location, the river is not tidal. The Lower Parramatta River Catchment, and tidal influence, begins east of Charles Street Bridge and weir.

The City of Parramatta Council flood map (included in Appendix C) shows that the development site is affected by regional flooding from the Parramatta River. The site is located within the extents of the PMF and partially located within the extents of the 100 and 20 year ARI flood (refer to Figure 4).

(r .... li -.'''),Iet), _0

_"a .----____...J, .i' ST-r,,--0

) (....-:,. ,) (, 0,) (20 Year Flood (Lower Parramatta River) r.--7.] 100 Year Flood (Lower Parramatta River) PMF (Lower Parramatta River)Figure 4 Extract of CPC flood map) (r) (0)Taylor Thomson Whitting (NSW) Pty Ltd6 © Taylor Thomson Whitting



The regional flooding caused by the Parramatta River affects the development site and the associated flood levels for different ARI's are shown in Table 1.

CPC have confirmed that the Upper and Lower Parramatta River flood studies are currently being updated. At this time CPC have provided regional flood levels associated with the Parramatta River, they have not confirmed the local flood levels in Phillip Street, or the effects of climate change on flood levels. However flood studies have recently completed for nearby developments.

· Riverbank Precinct Master Plan Drainage and Flooding Study, Cardno, Mar 2016

· Flood and Storm water Management Report, 330 Church Street, Mott Macdonald, Dec 2011

Both reports include the UPRCT flood model levels (version d911c, June 2011) with the same allowance made for the impact of climate change. The climate change allowance includes an increase of 15% in design rainfall intensities, with no allowance made for sea level rise. Both reports confirm that this increase in rainfall raises the Parramatta River flood level at this location by 270mm, and this is included in Table 1.

River Flood Level (Metres AHD)

1:20 Year ARI

1:100 Year ARI

1:100 Year ARI + CC*

PMF

5.41

5.95

6.22

10.39

Table 1 Regional Parramatta River Flood Levels (CH 2537)

*CC - Allowance for climate change of 15% increase in rainfall, producing a 270mm rise in river flood level at this location.

Localised flooding, as a result of overland flows from the stormwater drainage network, affects Philip Street, the access road onto the site, and the central area of the development site. The local flood levels are not linked directly to the regional flood levels from the Parramatta River and are associated with ponding depths and existing topographical levels.

The UPRCT flood model levels (version d911c, June 201) within the flood reports mentioned above, include local overland flood levels, and are shown in Table 2.

Local Overland Flood Level (Metres AHD)

1:20 Year ARI

1:100 Year ARI

1:100 Year ARI + CC*

PMF

Phillip St CH237

6.90

6.95

6.99

11.32

Access Road CH40

6.89

6.94

6.98

11.36

Table 2 Local Overland Flow Flood Levels

The overland flow path through the site, as shown on the CPC flood map, follows the existing ground contours, but does not seem to take into account the existing multistorey car park on site. The southern wall of the existing car park would in fact block this flow path (see site images in Appendix A). This is discussed in section 4.0.





3.2 Flood Risk Hazard

With regard to the flood risk to the site;

· High flood risk is land within the 100 year flood subject to high hydraulic hazard.

· Medium flood risk land within the 100 year flood subject to low hydraulic hazard.

· Low Flood risk is generally defined as land outside the 100 year flood but within the the PMF extent.

The CPC flood hydraulic hazard map shows that the development site is within the high and low hydraulic hazard. Within the site, the boundary between high and low hydraulic hazard correlates with the 5m ground contour (refer to Figure 5). Table 3 summarises the different flood risk precincts within the site and the associated ground level of the site.

AR.?PRA&1I

Figure 5 Extract of CPC hydraulic hazard map with ground contours labelled

Flood Risk Precinct

Ground Level (Metres AHD)

High Flood Risk

Less than 5.00

Medium Flood Risk

5.00 to 5.95

Low Flood Risk

Above 5.95

Table 3 Flood Risk Precincts within the site





3.3 Planning Development Controls

The current Parramatta Development Control Plan 2011 (DCP) sets development controls for different planning considerations. Table 4 below confirms the development controls for the medium risk flood precinct.

Planning consideration

Development Controls

Floor Levels

Habitable floor levels to be equal to or greater than the 100 year ARI flood level plus freeboard.

(Table 2.7, Note i states; Freeboard equals an additional height of 500mm)

A restriction is to be placed on the title of the land, pursuant to S.88B of the Conveyancing Act, where the lowest habitable floor area is elevated more than 1.5m above finished ground level, confirming that the subfloor space is not to be enclosed.

Buildingcomponents

All structures to have flood compatible building components below the 100 year ARI flood level plus freeboard.

Structural Soundness

An engineers report is required to certify that the structure can withstand the forces of floodwater, debris and buoyancy up to and including a 100 year ARI flood level plus freeboard.

Flood Affectation

An engineers report is required to certify that the development will not increase flood affectation elsewhere, having regard to: (i) loss of flood storage; (ii) changes in flood levels, flows and velocities caused by alterations to flood flows; and (iii) the cumulate impact of multiple potential developments in the vicinity.

Car Parking andDriveway Access

The minimum surface level of open spaces or carports shall be as high as practical, but no lower than 0.1m below the 100 year ARI flood level. In the case of garages, the minimum surface level shall be as high as practical, but no lower than the 100 year ARI flood level.

Garages capable of accommodating more than 3 motor vehicles on land zones for urban purposes, or enclosed car parking, must be protected from inundation by floods equal to or greater than the 100 year ARI flood. Ramp levels to be no lower than 0.5m above the 100 year ARI flood level.

The level of the driveway providing access between the road and parking spaces shall be no lower than 0.2m below the 100 year ARI flood level.

Enclosed car parking and car parking areas accommodating more than 3 vehicles, with a floor below the 100 year ARI flood level, shall have adequate warning systems, signage, exits and evacuation routes.

Restraints or vehicle barriers to be provided to prevent floating vehicles leaving a site during a 100 year ARI flood.

Evacuation

Reliable access for pedestrians and vehicles is required from the site to an area of refuge above the PMF level, either on site (e.g. second storey) or off site.

Applicant is to demonstrate the development is consistent with any relevant flood evacuation strategy or similar plan.

Adequate flood warning is available to allow safe and orderly evacuation without increased reliance upon SES or other authorised emergency services personnel.

Management and Design

Site Emergency Response Flood plan required where the site is affected by the 100 year ARI flood level, (except for single dwelling-houses).

Applicant is to demonstrate that area is available to store goods above the 100 year flood level plus freeboard.

No storage of materials below the 100 year ARI flood level.

Table 4 Development Controls





4.0 Flood Modelling4.1 Flood Model

To support the New Museum development, TTW undertook a preliminary two dimensional flood modelling exercise for the site using TUFLOW. The pre-development 100 year ARl flood model uses Lidar data for existing ground levels with existing buildings, bridges and surfaces modelled using GIS software. Flood flows were routed across the model and adjusted for calibration with the Council's flood map to confirm expected flood extents. Post-development 100 year ARI flood models were also created that included the different options for the proposed museum building. The calibrated flows were then used to determine the flood extents following the development.

4.2 Flood Model Results

The flood modelling results show that there is a negligible effect on the 100 year ARI river flood extents with pre and post development flood levels adjacent to the river around 6.00m.

The existing (pre-development) flood model shows that the that lowest level of the existing multi storey car park will flood up to around 2.5m deep in the 100 year ARI (refer Figure 6). Flows into and out of the car park at this level are possible as the vehicle access from George Khatar lane is around 3.20m AHD and the car park walls are constructed of open panels. Refer to site images in Appendix A.

(100 year ARI Flood Depth (m)) (0.0000 to 0.20000.2000 to 0.4000) (him0.4000 to 0.6000) (in0.6000 to 0.80000.8000 to 1.0000) (MI>1.0000)Figure 6 Pre Development 100 year ARI flood results without existing car park

The existing overland flood route, as shown on the CPC flood maps, flows through the site and does not take into account the existing multi storey car park. Two existing flood models were created, one without the car park, and another including the car park wall with a crest level of 7.0m, above which flood water can enter through the vehicle access. The model without the car park correlates very closely with the CPC flood map (refer Figure 6).




The New Museum. Parramatta — Flood Study161372

However with the existing car park included, the overland flow route passes to the west with a greater ponding depth to the south of the car park (refer Figure 7).

(MI100 year ARI Flood Depth (m)0.0000 to 0.2000 ) (0.2000 to 0.4000 0.4000 to 0.6000 0.6000 to 0.8000 0.8000 to 1.0000 ) (>1.0000) (•)Figure 7 Pre Development '100 year ARI flood results with existing car park

The current development options show the new building offset 9m from the existing site boundary. However to provide a sufficient overland flow route, without flood affectation to the adjacent site to the west, a 12m offset is required between the building outline and the site boundary. The 12m offset can be implemented in future revisions of the development proposals and would have minimal impact to the current concept planning. This 12m offset could be reduced by increasing the size of the diverted pipe, subject to further investigation and modelling.

The proposed site external levels have not been designed at this stage and the flood model will need to be updated to include the design levels. The model will also need to analyse the proposed drainage diversion of the existing 600mm diameter stormwater pipe, to the west of the new building. The model will also need to verify if increasing the capacity of this diversion will alleviate the overland flooding.

The flood model results for the current development options, with allowance for a 12m offset between the new building and the western boundary are shown in Figure 8. These results show that maximum flood level of the overland flow is just less than 7.00m. The proposed ground floor level will be set with a minimum 500mm freeboard above the flood level at 7.50m in accordance with the DCP.

Taylor Thomson Whitting (NSW) Pty Ltd11 © Taylor Thomson Whiffing



(100 year ARI Flood Depth (m) ) (0.0000 to 0.2000 0.2000 to 0.4000 0.4000 to 0.6000) (gal0.6000 to 0.8000 0.8000 to 1.0000) (in>1.0000)

Figure 8 Post Development 100 year ARI flood results

The current options allow for a small staff car parking area within the basement level, with at-grade access from the existing George Khattar Lane. The proposed basement level is set at 3.5m AHD. This is below the 5 year ARI flood level and can be expected to flood to a depth of 1.14m during this event. The expected flood depth increases to 2.5m for the 100 year ARI. To remove this flood risk, the access level would need to be above the 100 year ARI flood level and this is considered in section 4.3. However if the vehicle access at the lower level is unavoidable, then this space will need to be designed in accordance with the DCP:

"enclosed car parking, must be protected from inundation by floods equal to or greater than the 100 year ARI flow"

"enclosed parking areas with a floor level below the 100 year ARI flood level, shall have adequate warning systems, signage, exits and evacuation routes."

To comply with the DCP, suitable mitigation measures will be required based on a risk/merit approach, and acceptable to both the client and CPC. A suitable mitigation measure may be tanking combined with automated flood gates at entrances to the car park, with internal emergency access provided to a floor within the building above the PMF level.

The NSW Floodplain Development Manual defines the PMF as 'The largest flood that could possibly occur at the location of interest'. It also states that 'The PMF is an extremely rare event and....is given an Annual Exceedance Probability of between 10,000 and 100,000 years'. The PMF is generally used for emergency and disaster planning. The PMF level is approximately 3.4m above existing ground levels, and affects a large proportion of Parramatta CBD. Setting the ground floor level above the PMF for this site this is not feasible.

Taylor Thomson Whitting (NSW) Pty Ltd12 © Taylor Thomson Whitting


The New Museum; Parramatta — Flood Study161372

Safe access and refuge will be provided within the building, on or above the first floor level (RL 14.50m), which will be above the PMF level (RL 10.39m). Development proposals will need to consider an internal emergency evacuation route up to level 1 from the ground floor, basement, and the public space adjacent to the river. Evacuation routes will need to allow for these areas to be cleared quickly and effectively, with particular attention to accessible needs.

All core museum spaces; commercial, collection, offices, and essential plant equipment, will be located on the ground floor or above, and above the 100 year ARI flood level. Flooding up to this event will not affect core functionality or visitation to the New Museum. The staff parking area at basement level will be affected if the existing low level access from George Khattar Lane is maintained. The ground floor level will not be protected against the PMF flood.

All building components within the lower ground level will need to be flood compatible.

A site specific Flood Emergency Response Flood Plan will be required for the development.





4.3 Extended Basement Option

One option currently being considered is an extended basement with around 6,000 sqm of additional space for around 224 cars (refer Figure 9). This option does not use the existing at-grade, low level access from George Khattar Lane. Instead a new access is provided near the Philip Street lane. This access would be set above the 100 year ARI flood level with 500mm freeboard.

The current DCP states that basement parking within the floodplain needs to be protected from all flooding up to and including the PMF event. At the development location, the PMF level is 10.39m. which is over 3m above the existing ground level. Raising the basement access above the PMF is therefore not suitable for this development.

Council have conceded this clause of the DCP for adjacent developments, that include multistorey basement car parks, and further discussions with Council are required. If Council do not concede this clause, then the only option for protecting the basement up to the PMF level is the use of a flood gates at the basement entrance.

LANDSCAPED OUTDOORPUBUC SPACE

(PUbidiSMICO 4.949 M2) (A) (Circulation + Processing 2.112 rn2) (#.4) (izkkrsa.,-utrar&c.);,..2-nw) (/4(

) (4;`,.) (7,0) (PEDESTRIAN CIRCULATION) (PEDESTRIAN --CIRCULATION)Figure 9 Extended Basement option




The New Museum. Parramatta — Flood Study161372

5.0 Future Work

As the design of the proposed development progresses, the following items will need to be modelled, reviewed, or designed.

1. The proposed 600mm stormwater diversion will require modelling with overland flows generated included in the flood model.

2. An assessment is required to confirm if increasing the pipe diameter of the proposed diversion will have a significant reduction in overland flow through the site.

3. Proposed external levels and stormwater drainage will need to be included in the post development flood model to accurately determine overland flow paths.

4. The building form, structure and site levels will need to be accurately modelled in the post development flood model.

5. Flood models for the detailed development proposals should include a sensitivity analysis with the inclusion of climate change allowance of up to 30% increase in design rainfall.

6. Stormwater drainage modelling will be required for the diversion works to the 900mm pipe to the west of the site.

7. An assessment of the PMF flood for the pre and post development scenarios.

8. Discussion with Council to confirm requirements for the basement parking options.

9. Engineered flood mitigation measures will need to be confirmed based on a risk/merit based approached and acceptable to both the developer and CPC. Such solutions may include the incorporation of flood gates into the development scheme.

Prepared byAuthorised By

TAYLOR THOMSON WHITTINGTAYLOR THOMSON WHITTING

(NSW) PTY LTD(NSW)LTD

EIRIAN CRABBESTEPHEN BRAIN

Senior Civil EngineerTechnical Director / Director

P:\2016\1613\161372\Reports\TTW\Flood Study\161118 New Museum flood study_v6.docx



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