BMT WBM Pty LtdLevel 5, 99 King StreetMELBOURNE VIC 3000AustraliaPO Box 604Collins Street West VIC 8007

Tel: +61 3 8620 6100Fax: +61 3 8620 6105

ABN 54 010 830 421 007

www.wbmpl.com.au

Our Ref: MAT: document.docx

1 March 2012

Hydrox Nominees Pty LtdC/o Robert Luxmoore Project ManagementLevel 1, 11A Newton Street, Richmond VIC 3121

Attention: Emanuele Raffaele

Dear Emanuele

RE: MASTERS HOME IMPROVEMENT CENTRE AND 240 BACCHUS MARSH ROAD, CORIOFLOOD IMPACT ASSESSMENT

This letter report documents BMT WBM’s assessment of flooding and a potential mitigation scenario for the proposed Masters Home Improvement Centre and 240 Bacchus Marsh Road sites, Corio, as per our proposal dated 16th December 2011. This letter summarises the methodology and results of the analysis.

IntroductionThe objective of the assessment was to determine the flood impacts of the proposed developments under a specific flood mitigation scenario. The scenarios to be considered were:

1. Existing conditions (pre-development)

2. Development of the Masters site and 240 Bacchus Marsh Road with a defined floodway. The floodway extends from the existing culverts beneath the Geelong Bypass Bacchus Marsh Road overpass/on-ramp to Council's retarding basin at the corner of Plantation Road and Hendy Street (Plantation Road RB). An overview of the location of the proposed development sites and associated land-use is shown in Figure 1. The drainage concept is illustrated in Figure 2, while more detailed plans for each development are illustrated in Figures 3a, 3b and 4. This scenario is referred to as 'developed conditions' in this report.

The sites fall within the catchment investigated as part of the Kosciusko Avenue Main Drain Catchment Drainage / Flood Study (BMT WBM, 2011) undertaken for the City of Greater Geelong (CoGG). The primary objectives of the study were to characterise existing flooding and to develop an appropriate flood management strategy to mitigate stormwater flooding in the area. Runoff (flow) from the catchment was determined using a hydrological model called RORB. Flood levels and extents within the study area were determined using a hydraulic (flood) model called TUFLOW. CoGG provided permission for the RORB and TUFLOW models from the study to be used to undertake the current assessment.

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Figure 1 – Location of Proposed Development Sites and Associated Land-Use

Figure 2 – Drainage Concept Sketch (Overview)

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NOT TO SCALENOT TO SCALE

NOT TO SCALENOT TO SCALE

MethodologyFor planning and building approval purposes, the 100 year average recurrence interval (ARI) flood event, alternatively known as the 1% average exceedance probability (AEP) event, is commonly used. The 1% AEP event has a 1% chance, or 1 in 100 odds, of being exceeded in size in any given year. Smaller flood events that occur more frequently, are also used to determine whether the frequency of flooding of existing properties increases or decreases as a result of development. As such, it is common to analyse smaller flood events. For the current assessment, the same events analysed as part of the Kosciusko Main Drain study were analysed; namely the 100, 20 and 5 year ARI (1%, 5% and 20% AEP) flood events.

The existing RORB model was modified to reflect the land-use changes as part of the proposed developments (Figure 1). The RORB model was run for both pre-development and post development conditions. Fraction impervious values for developed conditions were in line with Council’s Standard Specification for Roadworks and Drainage, with adjustments to reflect the proposed development plans. The RORB model was then run for the 1%, 5% and 20% AEP events, for all storm durations. The critical storm durations, ie those causing the peak flows and volumes, were used to undertake the TUFLOW flood modelling.

The existing TUFLOW flood model was modified to include the proposed developed conditions as follows:

The proposed floodway was incorporated into the model based on a 3D design surface provided by Cardno Pty Ltd and Breese Pitt Dixon Pty Ltd. This included an 18m base width channel with approximately 1 in 3.8m side slopes within a 24m reserve adjacent to the Masters site. The floodway adjacent to 240 Bacchus Marsh Road varied to accommodate depths and services, etc within a 24m easement. The base width of the floodway varied but was generally 16m with side slopes varying between approximately 1 in 3 and 1 in 1.8m. The existing floodway running along the southern boundary of 240 Bacchus Marsh Road remained unchanged.

Road crossings of the floodway were incorporated into the model. Each crossing was approximate only (subject to detailed design), and consisted of rectangular concrete box culverts. The type of structure (e.g. arch, bridge or culverts) and associated dimensions would be optimised as part of the detailed design phase of the respective projects while ensuring specific conditions set by Council are met. The culverts modelled were:

o Crossing to the Master's site: Five 2.4m wide RCBC with soffit levels above flood level, i.e. not running under pressure. The designers indicated that the height of the access road across the floodway is such they believe the structure would not run under pressure, hence reducing hydraulic losses. The structure would either be either a number of RCBC or a concrete arch.

o Crossing to 240 Bacchus Marsh Road (De Havilland Way): Seven 2.4m wide x 0.9m high RCBC. The current height of Bacchus Marsh Road limits the height of the access road across the floodway and therefore the height of the culverts. The proposed culverts are the same size as those under the Bacchus Marsh Road overpass/on-ramp to the Geelong Bypass

The planned future widening of Bacchus Marsh Road by VicRoads was approximated by extending the existing road pavement to the edge of the proposed floodway.

To ensure that the floodway acts as the primary flowpath, the floodwaters that breakout of the drain adjacent to the abattoir under existing conditions are prevented from doing so by a proposed bund/levee. This ensures that all flows (and flood impacts) remain predominantly in the floodway.

For both developments, it was assumed that all runoff from the sites would be drained via the pipe and road networks to the proposed floodway.

TUFLOW was then run to determine flood levels and flood extents for each scenario for the different ARI events and storm durations. The model was run for the same events analysed as part of the Kosciusko Flood Study (BMT WBM, 2001). In all, 66 different combinations of storm, ARI and scenario were run. The results were then compiled in order to assess the current developments.

Results of Current AssessmentThe results of this analysis are presented in Figure 5 to Figure 10. Figure 5 and Figure 6 show the flood extents and depths for the 1% AEP event under pre-developed and developed conditions respectively.

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Figure 7 shows the 1% AEP flood depths and levels within the floodway under developed conditions. Figure 8 to Figure 10 illustrate the predicted changes in flood level (impacts) of the proposed development and floodway works. In these figures, yellow represents what are considered to be negligible impacts; green and pink areas represent decreases in flood level while orange and blue represent increases in flood level. The figures do not show the flood extent within the two development sites as the final levels are subject to internal drainage design and specific changes to the site topography required to ensure that the properties remain flood free with the specified freeboard during a 1% AEP flood. The modelling undertaken takes into account the increased runoff from these sites, and applies it to the proposed floodway in the hydraulic model. The specific results are discussed below.

Figure 5 illustrates the existing flood extents and depths during the 1% AEP event. The figure illustrates that there is a significant breakout flow immediately upstream of the existing culverts beneath the Bacchus Marsh Road overpass/on-ramp to the Geelong Bypass. This flow runs along the road reserve and fronts of private properties, and will need to be prevented to ensure the flows are fully contained in the proposed floodway. Also of note is the significant shallow flooding on the Masters and 240 Bacchus Marsh Road sites. Flooding is due to the lack of a clearly defined floodway with sufficient capacity to convey flood flows from the Kosciusko Main Drain catchment to the existing floodway into Council's Plantation Road Retarding Basin.

Figure 6 illustrates the flood extents and depths for the proposed developed conditions during the 1% AEP event. The modelling demonstrates that the proposed bund/levee and floodway are effective in channelling flood flows along Bacchus Marsh Road to the retarding basin and preventing flooding of adjacent properties. It is important to re-iterate that the two proposed crossings are indicative to demonstrate that the concept works. The type of structure (e.g. arch, bridge or culverts) and associated dimensions would be optimised as part of the detailed design phase of the respective projects while ensuring any specific conditions set by Council are met.

Figure 7 illustrates the flood depths and flood levels for the proposed developed conditions during the 1% AEP event. It is important to note the super-elevation of flood levels around the outside of the bend between the overpass and the Masters site. The bend re-directs flow from the existing culverts 90 degrees, and given the relatively high velocities, the super-elevation of flood levels is quite pronounced. The design should accommodate this phenomenon by ensuring sufficient scour protection and localised containment of quite turbulent flows. This could be achieved by ensuring the levels on the Masters site are sufficiently high to prevent the super-elevated turbulent flows from breaking out of the channel and/or through the use of a localised wall/levee incorporated into any safety fencing/landscaping.

Figure 8 to Figure 10 illustrate the flood level changes (impacts) with the developments and proposed floodway in place. For the critical 1% AEP event illustrated by Figure 8, reductions in flood level are shown immediately upstream of the existing culverts beneath the overpass. Reductions are in the order of 0.12 m. The construction of a bund/levee prevents breakout flows which in turn provide flood level reductions along Bacchus Marsh Road, the properties to the west of the road corridor as well as the Masters and 240 Bacchus Marsh Road sites. Increases in flood levels are shown within the floodway along the southern boundary of 240 Bacchus Marsh Road. These increases are up to approximately 0.17m and are contained within the floodway. There are also increases in flood levels along Kosciusko Avenue of up to approximately 0.07m. There is also an area of increased flood level around the railway culverts near the Shell Refinery and Refinery Road, not illustrated by the figure. Increases are in the order of 0.1 to 0.15m and are largely contained within undeveloped land. The impacts here are a result of the railway culverts being quite sensitive to changes in peak flows. For the 5% and 20% AEP flood events, flood level changes throughout the catchment are similar to those predicted for the 1% AEP event.

The duration of flooding within the area has not been significantly altered. In some instances it has been reduced as a result of the proposed floodway, while in others such as Kosciusko Avenue, is has marginally increased. The duration and frequency of inundation are not substantially different than under the existing conditions.

ConclusionThe analysis of the purposed developed conditions has been undertaken using comprehensive hydrological and hydraulic computer models. The results of the proposed developments and the associated floodway have been assessed with these models, and the changes in flood levels identified. The modelling results demonstrate that there are significant advantages in formalising a floodway along Bacchus Marsh Road to take the 1% AEP flood flows. Advantages include decreased areas of flooded

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private property to the east and west of Bacchus Marsh Road. With this also come areas of increased flood levels on residential properties, for example up to approximately 0.07m in areas along Kosciusko Avenue.

The analyses of the proposed developed conditions has been undertaken to demonstrate that there is a feasible solution. Further assessment would be undertaken as part of any subsequent detailed design, and to respond to any specific comments and conditions placed on the developments by Council.

If you have any questions regarding the analyses undertaken, or the results presented in the attached figures, please contact me on 8620 6100.

Yours FaithfullyBMT WBM Pty Ltd

Michael Turnley

Associate.

Manager, Flooding and Hydraulics (Victoria).

cc Rohan Jarvis (Breese Pitt Dixon)

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PDF Figures that could not be included in the Word document, but require adding to the PDF copy of the letter, are:

Figure 3a: Cardno SK02 Figure 3b: Cardno SK03 - Typical Cross-Section D Figure(s) 4a: BPD floodway layout and floodway typical cross-section(s)

BMT WBM MapInfo Figures:

Figure 5: 1% AEP Existing Figure 6: 1% AEP Developed Figure 7: 1% AEP Peak Flood Height Developed Figure 8: 20% AEP (5 yr ARI) Flood Impact Figure 9: 5% AEP (20 yr ARI) Flood Impact Figure 10: 1% AEP (100 yr ARI) Flood Impact

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