MEMORANDUM - bendigo.vic.gov.au · 10385_M04_CoGB_OptionsCollationMemo.docx Page 1 MEMORANDUM To...

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10385_M04_CoGB_OptionsCollationMemo.docx

MEMORANDUM

To Maria McCrann, CoGB From Julian Skipworth

Copy Project Control Group Reference 10385-01

Date 7 October 2019 Pages 31

Subject Kangaroo Flat Golden Square Flood Mitigation Study – Mitigation Options Collation Memo

Dear Maria and the Project Control Group,

1.1 INTRODUCTION

The City of Greater Bendigo (CoGB) has engaged Water Modelling Solutions to undertake the Kangaroo Flat Golden Square

Flood Mitigation Study. CoGB is seeking to undertake a comprehensive flood mitigation study of the Kangaroo Flat and Golden

Square areas in the south of Bendigo. The study will focus on mitigating flood risk from Bendigo Creek which traverses the study

area from south to north. The key objectives of the study are to thoroughly consult with the community and key stakeholders in

order to seek mitigation ideas as well as feedback on the results of the investigation, and to identify and assess a large range of

potential mitigation options to improve flood risk across the study area.

This is the fourth memorandum for the study and collates the range of mitigation options put forward by the community and other

key stakeholders. Each option is described and a recommendation made as to if and how each option should be modelled in the

hydrological or hydraulic model.

1.2 SUMMARY OF FIRST ROUND OF COMMUNITY CONSULTATION

Effective community consultation is a critical part to the success of the Kangaroo Flat Golden Square Flood Mitigation Study. The

consultation to date has been aimed at gathering mitigation ideas, many of which will be tested in the modelling. The first round

of community consultation occurred over a 6-week period from the 29th July to 16th September 2019. It included the following:

• A survey in both hard-copy and online format (bit.ly/KFGS-Flood-Survey) which asked for historic observations of

flooding as well as mitigation ideas for testing. These have been collated in a spreadsheet which is included at the end

of this memorandum.

• An online mapping portal (bit.ly/KFGS-Flood-Maps) which presented the draft 1% AEP modelling results and allows

users to add comments and mitigation ideas. The mapping portal will be used further when it comes to presenting the

results of mitigation modelling.

• Three listening posts were hold in the week of 27th-31st August at the Kangaroo Flat IGA, Golden Square shopping strip

and Kangaroo Flat market. These allowed the community to discuss the project with the project team, ask questions

and submit surveys.

• The first round of community consultation culminated with a workshop held on the 5th of September at the Gateway

Function Centre in Kangaroo Flat. The was attended by more than 60 attendees. The workshop allowed the current

flood risk to be presented, questions to be asked and then feedback and mitigation ideas to be gathered. We consider

the workshop attendance and level of engagement to be highly successful and a reflection of the well-planned and

targeted consultation strategy developed by Make a Change Australia in partnership with WMS.

A number of photos from the workshop are shown in Figure 2-1.

mailto:[email protected]

http://www.watermodelling.com.au/

bit.ly/KFGS-Flood-Survey

bit.ly/KFGS-Flood-Maps


Figure 2-1 Photos from the first community workshop in Kangaroo Flat held on the 5th September 2019


2 COLLATION OF OPTIONS

A range of options have been suggested from the community and stakeholders. They are presented in the table below. The table

includes an Option ID number, description of the option, location and a recommendation regarding whether it should be included

in preliminary modelling and the reasons for this.

The following summaries the findings from the data collation:

• 42 options recommended to undergo preliminary modelling.

• Options that could be undertaken as part of a sensitivity assessment and variation to the project These include:

– Climate change scenarios;

– Scenarios which assume maximum development and maximum infill development with no flow attenuation from these

development areas; and

– Widespread catchment changes including vegetation changes.

• A number of general comments that can’t be modelled as they don’t relate to a specific option or location but will be noted by Council.

The options are presented in the table below.




Option ID

Location Option Details Source of the Idea

Recommendation Map

1 North bank of Bendigo Creek between High Street and Thistle Street, Golden Square

Levee along north bank of Bendigo Creek between High Street and Thistle Street, Golden Square.

NCCMA To be modelled. Will model by placing a levee along the entire section of breakout blocking out completely along the entire section of breakout which ensures it won't overtop in the 1% AEP Event.

2 Gurri Wanyrra Wellbeing Centre, 9 Browning St, Kangaroo Flat)

Cardno prepared a design of a bund around the centre as part of the development which Council would have record of.

NCCMA To be modelled. Will model using 2d_zsh to create a bund surrounding the facility with infinite height to block off flood water. This will allow afflux and bund height requirements to be determined (assuming 300mm freeboard)




Option ID


Recommendation Map

3 Clarcoll Crescent, Kangaroo Flat

Levee along Clarcoll Crescent to prevent breakout flows. This subdivision appears to only be constructed to the BUFS 1% AEP flood level. New mapping shows higher levels through here which causes breakout flows through the back other residential areas.

NCCMA To be modelled. Area has been remodelled with new survey however some breakouts still occurring onto properties and roadways. Trial levee to present breakout flows with levee at infinite height to ensure it won’t overtop. This will allow afflux and levee height requirements to be determined (assuming 300mm freeboard)

4 South end of Grantham Terrace

Low levee/bund to protect low-lying properties at the south end of Grantham Terrace.

NCCMA To be modelled. Will model by blocking out completely which ensures it won't overtop in the 1% AEP Event using infinite height levee near corner of Grantham Terrace and Sovereign Gardens. This will allow afflux and levee height requirements to be determined (assuming 300mm freeboard). Note: results have changed slightly in this area as a result of new survey.


Option ID


Recommendation Map

5 Breen Street adjacent to Camp St, Golden Square

Retarding basin upstream of Breen St and/or adjacent to Camp St.

NCCMA To be modelled. Will model by digging out a retarding basin using 2d_zsh, with the basin invert based on channel invert at downstream end of basin footprint. Basin embankment height will be based on natural surface at upstream end of footprint.

6 5693 Calder Highway, Kangaroo Flat

Retarding basin to reduce flows into Bendigo Creek. Previous BUFS showed flow reduction of approx. 30%.

NCCMA To be modelled. Will model by dig out a retarding basin using 2d_zsh in the open area, with the basin invert based on channel invert at downstream end of basin footprint. Basin embankment height will be based on natural surface at upstream end of footprint.


Option ID


Recommendation Map

7 Crusoe Reservoir

Improve retardation and/or flow attenuation of Crusoe Reservoir by installing low flow outlet, increasing capacity, changing operation protocol.

NCCMA To be modelled, will undertake sensitivity of using different initial water levels in the dam which would reflect a lower flow outlet level than current resulting in more effective storage in a flood event.

8 9-43 Chum St Golden Square and Thistle St

Retarding basin at 9-43 Chum St and upgraded drainage on Thistle St.

NCCMA Not for modelling, basin has been included as have current pipe layers provided by CoGB. A larger basin in this area could be trialled given the available space?


Option ID


Recommendation Map

9 Alder St, Rotary Park

Improve retardation of Rotatory Park to alleviate flooding on properties immediately upstream of Alder St.

NCCMA To be modelled, trial converting the Rotary Park Lake in a large retarding basin to understand impact on properties upstream of Alder Street

10 Dower Park Use Dower Park oval for flood storage.

NCCMA To be modelled. Direct flow to the oval by doubling the collecting pipes on Olympic Parade and connect the channel behind Christian's Bus Co to Downer Park. Also, look to lower oval surface level by 0.5 metres to create more storage.


Option ID


Recommendation Map

11 Tributary parallel to Lockwood Road

Move retarding basin further upstream from the tributary

NCCMA To be modelled. Will model by digging out a retarding basin southwest of the bushland reserve. with the basin invert based on channel invert at downstream end of basin footprint. Basin embankment height will be based on natural surface at upstream end of footprint.

12 Kangaroo Flat Public Park adjacent to eastern end of Camp St

Put retarding basin at Kangaroo Flat.

NCCMA To be modelled. Will model by dig out a retarding basin using 2d_zsh in the open area with the basin invert based on channel invert at downstream end of basin footprint. Basin embankment height will be based on natural surface at upstream end of footprint.


Option ID


Recommendation Map

13 2 Alder Street, Kangaroo Flat

Put retarding basin upstream of said location.

NCCMA To be modelled. Will model by dig out a retarding basin using 2d_zsh in the open area with the basin invert based on channel invert at downstream end of basin footprint. Basin embankment height will be based on natural surface at upstream end of footprint.

14 Oak St bridge, Golden Aquare

Investigate and improve capacity of Oak St Bridge.

NCCMA To be modelled. Existing capacity will be approximately doubled by widening the channel through the bridge.


Option ID


Recommendation Map

15 Alder St Bridge, Kangaroo Flat

Increase capacity of Alder St Bridge.

NCCMA To be modelled. Existing capacity will be approximately doubled by widening the channel through the bridge.

16 Bendigo Creek between Oak St and Thistle St, Golden Square

Widening this section of the creek.

NCCMA To be modelled. Will widen the creek by 1m on each side to understand impact.


Option ID


Recommendation Map

17 Upstream of Bay St, Golden Square

Increase capacity of Bendigo Creek on vacant land upstream of Bay St.

NCCMA To be modelled by widening the north bank of the creek by 2m.

18 Mitchell Street, Kangaroo Flat

Lower level of Mitchell Street to convey floodwaters and reduce flooding on adjacent properties.

NCCMA To be modelled, Mitchell Street will be lowered by 500mm initially as a sensitivity test to see what impact it has.


Option ID


Recommendation Map

19 Symonds St, Golden Square

Improve drainage capacity along Symonds St.

NCCMA To be modelled. Will model by doubling the capacity of the drainage network along the south of Symonds Street. The trunk drainage along this reach varies from a 1.2-1.65m diameter pipe.

20 Rosedale Residential Village, Kangaroo Flat

Buy back vacated units to remove vulnerable members of community and create opportunity for future mitigation works, and achieve better waterway interface.

NCCMA Not for modelling, to be noted by Council

21 Hammil St and Aviva Communities Bendigo, Kangaroo Flat

Confirm RORB model included catch drain divert overflow from no.7 Reservoir.

NCCMA Not for modelling. Yes, can confirm catch drain diversion was included. Also, the area has now been modelled with the revised survey (results available soon).


Option ID


Recommendation Map

22 Aviva Communities Bendigo development, Kangaroo Flat

Divert overland flows from this area to adjacent waterway to the east.

NCCMA To be modelled, will include a catchment drain and waterway diversion into the waterway to the east. This may worsen impacts around the retirement village.

23 Barnet drive, Aviva Communities Bendigo, Clarcoll Crescent, Kangaroo Flat

Perform floor level survey of these areas

NCCMA Not for modelling, to be noted by Council. Note: this area has been remodelled with updates survey.

24 Overall study area

Consider climate change

NCCMA Could be modelled, to be discussed with CoGB. Not currently within scope, could be included as a variation to the project.

25 Overall study area

Remodel impacts of some of the Reimaging Bendigo Creek project which may impact on flooding such as removing concrete pilot

NCCMA Could be modelled depending on Council preference.


Option ID


Recommendation Map

channels and constructing pools and riffles from Oak through to Thistle St.

26 Gurri Wanyarra Wellbeing Centre, Karinya Gardens Residential Village, Kangaroo Flat

Floor level survey of Gurri Wanarra and Karinya Gardens Residential Village.

NCCMA Not for modelling. Comment to be noted by CoGB.

27 Subdivisions throughout study area

No infill subdivisions allow for onsite detention to determine the increased flood this may cause.

NCCMA Optional sensitivity analysis, can be modelled as a sensitivity run in RORB. Would require analysis to undertake and involve modifying Fraction Impervious map. It would be helpful if CoGB could provide locations where infill development is likely/possible.


Option ID


Recommendation Map

28 Surrounding forests within study area

Replace tall vegetation with shorter/denser vegetation

Community Optional sensitivity analysis. Would require changes to fraction impervious maps and losses and\re-running through RORB.

29 Bendigo Creek near Browning St, Station St, Windsor Gardens, Kangaroo Flat

Clear large trees limbs inside the Creek

Community To be modelled, will model by reducing roughness of creek channel by 20% along 400 metres of Bendigo Creek reach been Station St and Browning St.


Option ID


Recommendation Map

30 Windsor Gardens, Kangaroo Flat

Excavate under the bridge to reduce constriction

Community To be modelled. Will model by lowering the invert of the bridge opening by 500mm.

31 Clarcoll Crescent, Kangaroo Flat

Clear large trees limbs inside the creek near Clarcoll Crescent

Community To be modelled, will model by reducing roughness of creek channel by 20% along 250 metres of reach downstream from High Street.


Option ID


Recommendation Map

32 Calder Highway between Big Hill and Furness St, Kangaroo Flat

Increase culvert size

Community To be modelled. Will model by doubling the number of 1d culverts from the existing 1 x 1050 mm culvert and connect from the eastern side of the Calder Highway near Phillis St into the waterway downstream of Harvey Norman

33 Rosedale Village, Kangaroo Flat

Install drain next to Rosedale Village

Community Not for modelling. There's already a drain along the northern boundary of the Village. Additional drains may assist local runoff but not riverine inundation.

34 General Install storm gauging

Community Not for modelling, to be noted by Council.

35 Emmett St, Golden Square

Increase stormwater drainage pipe

Community Not for modelling, not within hydraulic model extent. To be noted by Council.


Option ID


Recommendation Map

36 Crusoe Rd, Kangaroo Flat

Clear large trees limbs inside the Creek

Community To be modelled. Will model by reducing roughness of creek bed by 20% along 400 metres of reach downstream of Crusoe Road.

37 Elliot St, Golden Square

Clean the Creek Community To be modelled. Will model by reducing roughness of creek bed by 20% along 400 metres of reach upstream of Oak Street.


Option ID


Recommendation Map

38 Hasker Dr, Kangaroo Flat

Clean the Creek Community To be modelled. Will model by reducing roughness of creek bed by 20% along 200 metres of reach in that area.

39 Booth St, Golden Square

Increase culvert size

Community To be modelled. Will model by tripling the number of 1d pipes. Existing capacity is 1 x 600mm pipe.


Option ID


Recommendation Map

40 Queen St, Kangaroo Flat

Increase drain capacity

Community To be modelled. Will model by doubling the number of 1d pipes initially. Existing capacity is 1 x 525mm, 1x 900mm, 1 x 750mm pipe (highlighted in yellow)

41 Hammill St, Big Hill

Increase drain capacity

Community Being examined in other options e.g. waterway diversion (Option 22)


Option ID


Recommendation Map

42 Bachhaus Oval Allow water to discharge into Bachhaus Oval to allow retention.

Community To be modelled. Lower Backhaus oval by 1-1.5 metres to create flood storage, include connection into Bendigo Creek channel.

43 General Speeding or slowing water flow through creeks. Limit development. Make VCAT accountable for overriding council

Community Not for modelling. General comments, no specific options or locations. To be noted by Council.

44 General Do not clear creek excessively.

Community No modelling required, to be noted by Council.


Option ID


Recommendation Map

45 Crusoe Road, Kangaroo Flat

Clean debris inside creek

Community To be modelled. Will model by reducing roughness of creek bed by 20% along 400 metres of reach in that area from near Symes St to level with Irene Court.

46 General Construct lakes and wetlands along creek floodplain.

Manage total catchment farm and forest to build soil ability to take in rain and hold in. Thins the forest for more grass to grow to improve infiltration.

Community Not for modelling. general comment, basins are being tested in other options.

47 General Create pervious footpaths and roads to allow water to infiltrate soil.

Community No modelling required, comment to be noted by Council.


Option ID


Recommendation Map

48 General Include existing and future development capacity of existing drains and future requirement.

Community Optional Sensitivity Analysis – similar to Option 27. Can be modelled as a sensitivity run in RORB. Would require some analysis to undertake and modify fraction Impervious map. Would helpful if CoGB could provide locations where infill development is likely/possible.


Put levee on the creek

Community To be modelled. Will model using 2d_zsh to create a levee along the east bank of the Creek at infinite height to ensure they won’t overtop. This will allow afflux and levee height requirements to be determined (assuming 300mm freeboard).

50 General Clean out creek.

Install rocks to slow flow.

Community No modelling required, general comment, no specific locations.


Option ID


Recommendation Map

51 Alder St, Golden Square

Levee along Bendigo Creek behind the properties on Beverley St.

WMS To be modelled. Will model using 2d_zsh to create levee at infinite height to ensure they won’t overtop. This will allow afflux and levee height requirements to be determined (assuming 300mm freeboard).

52 Tomkinson Dr, Golden Square

Construct table drain adjacent to Symonds St and divert overland flow to the channel.

Community To be modelled. Will model with a 2m bottom width and 3m top width table drain from Asphall St, along Symonds St to Bay St.


Option ID


Recommendation Map

53 Oak St, Golden Square

Raise Oak Street to prevent overtopping

WMS To be modelled. Will model using 2d_zsh to create a road crest with infinite heights to ensure it won’t overtop. This will allow afflux and road crest height requirements to be determined.

54 Adjacent upstream of Breen St, Golden Square

Retarding basin upstream of Breen St.

NCCMA To be modelled. Will model by digging out a retarding basin using 2d_zsh, with the basin invert based on channel invert at downstream end of basin footprint. Basin embankment height will be based on natural surface at upstream end of footprint.


Option ID


Recommendation Map

55 Crusoe Road, Bridge, Kangaroo Flat

Trial levee upstream side of bridge to prevent significant breakout towards High St

WMS To be modelled. Trial levee to present breakout flows with levee at infinite height to ensure it won’t overtop. This will allow afflux and levee height requirements to be determined (assuming 300mm freeboard).

56 Crusoe Reservoir, Kangaroo Flat

Install pumps system to store water in Crusoe Reservoir.

Community To be modelled, however unlikely to be effective as pump flow rate will be insignificant compared to peak flow during flood events. The largest pumping rates achievable are in the region of 0.3 m/s which is around 1% of the 1% AEP peak flow rate at Furness Street. Model by pumping water from near Furness St, back into Crusoe using a flow rate of 0.3 m3/s.


Option ID


Recommendation Map

57 91 – 105 Crusoe Road, Kangaroo Flat

Trial earth levee on the bank along the creek.

Community To be modelled. Trial levee to present breakout flows with levee at infinite height to ensure it won’t overtop. This will allow afflux and levee height requirements to be determined (assuming 300mm freeboard).

See Option 49

59 Rotary Gateway Park Lake

Control flow in the creek using flume gates to discharge water out of lake in Rotary Gateway Park prior to heavy rain

Community To be modelled. Trial with deepened Rotary Gateway Park lake which is set up in the model to be empty at the start of the flood event.

60 Burn St, Golden Square

No flooding at Burn St

Community Not for modelling. Unsure if a comment or a mitigation suggestion. Burn St is not within the hydraulic model extent. To be noted by Council.


Option ID


Recommendation Map

61 Hope Street and Jamison Park Drive, Kangaroo Flat

Trial levee to protect properties on Hope Street and Jamison Park Drive


62 Hope Street and Jamison Park Drive, Kangaroo Flat

Trial levee between Bank St and Lockwood Road to protect numerous properties in central Kangaroo Float



Option ID


Recommendation Map


Put levee on the creek

Community To be modelled. Will model using 2d_zsh to create a levee along the east bank of the creek (downstream of Crusoe Rd to Wesley St) of the Creek at infinite height to ensure they won’t overtop. This will allow afflux and levee height requirements to be determined (assuming 300mm freeboard).




3 SUMMARY

This is the fourth memorandum for the study and collates the range of mitigation options put forward by the community and other

key stakeholders. Each option is described and a recommendation made as to if and how each option should be modelled in the

hydrological or hydraulic model. We recommend that this memo be reviewed and feedback provided as to the options to undergo

preliminary modelling. Should Council feel it beneficial we can arrange a PCG meeting to discuss this memo and which options

should undergo preliminary modelling.

Yours sincerely,

Julian Skipworth

Principal Engineer / Regional Manager - Victoria

Water Modelling Solutions



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