FIVE YEARS ON: Flood-proofing to start this year
River dredging, creating lakes, levee work and dams among myriad of options to protect Bundaberg in the future
Bundaberg
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DESPITE a $4 million 10-year plan to "flood proof Bundaberg” announced on the banks of the Burnett River in June 2016, no infrastructure has been started to protect Bundaberg five years on from the disaster.
The plan has construction starting this year.
At the time of the announcement State Government Local Government Minister Mark Furner, Assistant Infrastructure Minister Glenn Butcher, the former member for Bundaberg Leanne Donaldson said the $4m was to be used for technical investigations of four short listed flood mitigation options from the 11 mooted in the Bundaberg flood protection study.
At an estimated cost of $140m, the Bundaberg East levee, Bundaberg North evacuation route, upper floodplain evacuation improvements and a floodway house-purchase scheme were the four chosen.
"As of tomorrow there will be boots on the ground,” Mr Furner said at the time .
He said in the past three to four years there had been some "great consultancy with the community led by Leanne Donaldson” and the $4m was a step in the right direction to "flood proof Bundaberg”.
Mitigation options
The State Government's 10-year action plan is in its third year with government currently in the preliminary design and costing stage of the Bundaberg North evacuation route, the Bundaberg East Levee and the Upper floodplain evacuation improvements.
Work is scheduled to start on all three projects late this year.
The floodway house purchase scheme is not expected to be implemented until 2020 and beyond.
In the initial study 11 options were included. For history's sake they are all included below.
Option A: Burnett River conveyance improvement
This option involves river dredging along the town reach, removing Harriet Island, widening Millaquin Bend and regular maintenance dredging.
WHAT: This option would result in more flow in the river and less flow on the floodplain. This would reduce flood levels in some urban areas.
The increased flood flow in the river would result in some increased flood levels in Bundaberg North (up to 0.3m) for smaller, more frequent flood events.
Approximately 470 properties in the Bundaberg area would not be inundated in the 1 per cent AEP 1 flood event.
The option would require the treatment of dredged material and land-based disposal of dredge spoil due to the very low likelihood of at-sea disposal.
COST: $235 million, moderate to high cost option.
BENEFITS: The estimated reduction in flood damages would be in the order of $35 million.
ISSUES: It is expected that there would be difficulties in obtaining an environmental approval for such a large dredging program.
Option B: North floodway
This option involves construction of four lakes either side of Hinkler Avenue to improve conveyance through Bundaberg North and a channel from Queen St to Waterview Rd.
WHAT: This option would involve diverting floodwater through Hinkler and Federation Parks, reducing flood levels in the Burnett River and Bundaberg North.
Downstream of the lakes and floodway, some properties would experience increased flood levels.
COST: $124 million
BENEFITS: The estimated reduction in flood damages would be in the order of $7 million.
Benefits of this option are limited due to the ability to lower flood levels in this area. The flow rate through this area would not change and the flood levels in the urban area are not significantly lowered.
ISSUES: This option would have high costs due to the large volume of excavation and the need to treat and dispose of this material.
Option C: North levee and floodway
This option involves constructing a levee around most of Bundaberg North. Lakes and widening of the rail bridge at Hanbury St would also be required to improve conveyance through Bundaberg North.
WHAT: This option would direct floodwaters around Bundaberg North through the construction of a levee and floodway (lake) system.
This option would provide protection for about 450 properties up to the 1.5 per cent AEP 1 flood event.
For events rarer/larger than the 1.5 per cent AEP flood event, initial overtopping of the levee would occur along the northern (earth) sections, rather than a sudden overtopping, allowing safer evacuation.
COST: $100 million
BENEFITS: Estimated reduction in flood damages would be in the order of about $11 million.
ISSUES: There is a risk that people inside the levee may become complacent about flood risk.
The levee would have a major impact on the urban area, restricting access and creating a visual barrier.
Increased flood levels of up to 0.6m would be experienced by some properties outside of the levee.
Option D: Bundaberg East levee
This option includes construction of a levee along the south bank of the river to reduce flooding in Bundaberg East. It would require construction of two floodgates (with one large floodgate for Saltwater Creek).
WHAT: This option would prevent floodwaters from the Burnett River backing up into Bundaberg South for events up to the 1.5 per cent AEP1 flood event.
This option would provide protection for about 440 properties up to the 1.5 per cent AEP (70 year ARI) flood event.
It would reduce flooding for about 320 properties in the 1 per cent AEP 2 flood event.
A flood-gate structure would be required across Saltwater Creek to prevent Burnett River back-up flooding but allow local floods to pass.
COST: $38 million
BENEFITS: Estimated reduction in flood damages of this option is around $29 million.
ISSUES: Localised rainfall that causes flooding in Saltwater Creek may inundate properties to a greater amount if the event occurs concurrently with a Burnett River flood and the flood gate is shut.
Option E: Removal of Fairymead levee
This option involves removal of existing levees at Fairymead on the floodplain downstream of Bundaberg.
WHAT: The option increases flow over the floodplain to the north and west, increasing flood levels in this area.
Several buildings would experience an increase in flood level of 300 mm in a 1 per cent AEP 1 event.
Due to the distance between the Fairymead levee and the Bundaberg urban area, the removal of this levee would reduce flood levels by a very small amount in Bundaberg.
Reduced flood levels would be experienced upstream of the levees and on the eastern floodplain. In a 1 per cent AEP event the benefit is limited to a distance of about 3km upstream of the levee.
COST: $3.4 million
BENEFIT: The estimated reduction in flood damages would be in the order of $0.1 million.
ISSUES: The assessment of Option E found that this option is likely to have significant impacts on areas outside of the benefited area.
Option F: Millaquin bend
This option involves deepening, widening and regular maintenance dredging of a section of the left bank of the Burnett River by excavation and dredging to improve flood conveyance through a constricted part of the river.
WHAT: This option reduces flood levels within Bundaberg through increased conveyance in the Burnett River.
Approximately 440 properties would not be inundated in the 1 per cent AEP1 flood event.
Much of the benefit from this option occurs within Bundaberg East, meaning that the majority of benefits of this option would be lost if it was built in conjunction with another option that reduces damages in East Bundaberg (e.g. a levee).
COST: $95 million
BENEFIT: The preliminary flood damages assessment for this option suggests that the estimated reduction in flood damages would be in the order of $30 million.
ISSUES: Dredging and mangrove removal works may negatively impact the local environment, and there is no opportunity for staging.
Option G: Diverting flood to Elliott River
This option involves construction of a diversion channel from the Burnett River into the Elliott River.
WHAT: This option would reduce flow in the Burnett River and increase flow in the Elliott River. This would reduce flood levels in Bundaberg.
This option would reduce flooding for about 3000 properties in the 1 per cent AEP 1 flood event and prevent over-floor flooding in 1450 properties in the 1 per cent AEP flood event.
COST: $9000 million
BENEFIT: The estimated reduction in flood damages for this option is around $90 million.
ISSUES: This option would have significant costs. These costs would be approximately 100 times the benefits realised through reduced damages.
Increased flood flow in the Elliott River would result in increased flood levels (up to 8m higher) and very high velocities for properties along this river. This would impact about 60 houses along the Elliott River.
Environmental issues would arise from diverting very large flows into the Elliott River, which has a small catchment and small flows compared to the Burnett River (100 times smaller).
Option H: Improving access to Tallon Bridge
This option involves improving emergency access to Tallon Bridge by creating an extension to the bridge from Gavin St through to the roundabout near Bundaberg North State School.
WHAT: This option would enable 1400 properties in Bundaberg North to have emergency access to Bundaberg South during a 1 per cent AEP flood event.
It would assist in reducing impacts on people as isolation is reduced and access to emergency services is increased.
It would also decrease stress due to reduced isolation and improved access to emergency services during flood events.
COST: $42 million.
BENEFIT: Although there is no reduction in flood damages, approximately 1400 properties would no longer be isolated in a 1 per cent AEP 1 flood event. In addition, the available evacuation times for Bundaberg North would increase by about four hours.
ISSUES: This option has limited benefits in very large events (e.g. larger than 2013).
This option would have limited benefit for those properties to the east of Hinkler Drive or south of Hinkler Park.
Afflux from the viaduct has not been assessed and would need to be considered in future design development.
Option I: Dams in upper catchment
This option involves construction of dam(s) in the upper Burnett River catchment to temporarily store floodwaters. No specific sites have been chosen.
WHAT: This option would temporarily detain floodwater from the Burnett River and could reduce flood levels from the 1 per cent AEP 1 flood event to the 5 per cent AEP flood event level. This would reduce flooding for about 3000 properties in the 1 per cent AEP flood event and prevent over-floor flooding in 1450 properties in the 1 per cent AEP flood event.
COST: $1300 million
BENEFIT: The estimated reduction in flood damages for this option is about $90 million.
ISSUES: Environmental approval of this option would be unlikely due to the environmental impacts in the impounded area.
The temporary impounding of floodwaters would require the acquisition of large areas of agricultural and forested land.
The costs would be very high ($1300 million) and more than 14 times the benefits realised through reduced damages.
Option J: Scheme to buy houses over North
This option would involve either purchase or relocation (via land-swap) of select residential blocks in Bundaberg North that are deemed to be in a floodway with high depths and velocities.
WHAT: This option would remove 130 properties from the floodplain. The purchase of houses would result in social impacts in this area.
In rare floods (i.e. larger than 2013 flood), the flooding conditions in this area become extremely hazardous and would likely result in destruction of many houses.
The costs of the option are more than eight times the benefits to be realised through reduced flood damages. However, there are other non-tangible benefits associated with reducing the risk to life during floods, especially rare floods.
COST: $39 million
BENEFIT: The preliminary flood damages assessment for this option suggests that the estimated reduction in flood damages would be in the order of $5 million.
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Option K: Upper floodplain evacuation improvements
This option involves provision of better evacuation routes and access during floods to the communities of Goodnight, Morganville, Pine Creek, Givelda and Electra through raising of the Perry River Bridge and construction and upgrading of 4WD tracks.
WHAT: This option would reduce isolation time for communities in the Goodnight Scrub, Givelda, Pine Creek localities during large flood events. Approximately 400 to 600 properties would have improved access during flood periods requiring less reliance upon emergency supplies.
Construction of this option would be in the order of $16 million for the Perry River Bridge and $1 million for construction of the 4WD evacuation routes.
This option has minimal impacts on others and would have a high likelihood of obtaining environmental approval.
COST: Perry River bridge: about $15 to $17 million
Pine Creek evacuation route: about $0.5 to $1 million
BENEFIT: This option would not reduce flood inundation of any houses. However, it would significantly reduce the duration of isolation.
Based on the history of flood levels in the Burnett River, it is estimated that the Perry River bridge is cut for approximately 14 days per decade. The proposed bridge upgrade would reduce the time that the bridge is cut to one day per decade.
Based on the loss of income, this reduction in isolation would result in an estimated benefit of $0.7 million. However, the intangible benefits of reduced isolation and the decreased costs of emergency management during flood events would result in greater economic benefits for this option.
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