Managing vegetation to protect small towns from floods

Managing vegetation for flooding in smalltownsIan Rutherfurd, John Riddiford and Paul Bennett(Department of Sustainability and Environment)Avoca River at Charlton – September 2010

• 82 towns affected in January 2011 flood• About 10 have stream capacity concerns

Community concerns aboutvegetation in the channelGaribaldi Ck, Beaufort“After the township flooding of the 14th January 2011 where 35 houses wereflood affected a public meeting demanded that the creeks be better maintained” 4

Evidence to the ENRC Inquiry“During the past 20 years, the Avoca Rivernear Natte Yallock has become a disgracewith fallen trees and uncleared debris thathave been left to lie and subsequentlyblocking the river flow. This has impactedon the river to overflow and spread…..3kmwide and 1.3 metres depth in the January2011 flood”

Creswick , 3000 people (trib of Loddon River) 2011flooded 4 times

The Courier (Ballarat)Creswick floods: Residents question creek tree plantingBY BENJAMIN PREISS07 Sep, 2010 12:26 AMAS THE clean-up effort gathered pace in Creswick, residents began asking whetherman-made conditions could have exacerbated the floods. Some residents believetree planting in the Creswick Creek may have impeded the water's flow andintensified the flood on the weekend.The council will begin to investigate whether tree planting in the waterways isworsening the flood."It's a reasonably general consensus with a lot of people that I've spoken to," hesaid.

Effect on flooding in towns of:1. Instream vegetation2. Vegetation upstream of the town3. Fallen wood in the channel.

Flooding in Beaufort“We raised this issue initially two yearsago with the modelling and we asked, ‘Ifthe vegetation was removed what effect wouldthat have on flood levels?’. The answer thatcame back from the consultants at that stagewas, ‘Very little’. It is more the physicalinfrastructure in the railway line culverts whichis causing the flooding” (ENRC p.117).Councillor O’Connor stated that although it would have littleeffect on flood levels, work was undertaken to removevegetation in Beaufort after the floods to alleviate communityconcerns (p.118)10

CRESWICK CHANNEL CLEARING•Channel carries

BENALLA (Broken creek) Effect of veg removal –1993 flood1100 properties flooded27/10/2012 12

27/10/2012 13

Benalla 100 year flood – impact of veg removal• $1m• 50 – 100 mm drop in level• 100 less floors go under

What about revegetation upstream ofthe towns?Genoa River, EastGippsland, Vic.1985 flood (80,000 ML/day)$3m damage.2011 flood (83,000 ML/day)$40,000 damage.20091989

Riparian reveg and town flooding• Richard Sharpe (BWT WBM Brisbane, 2012)• 100 year flood in Caboolture, SE Qld• Modelled 120 km of channel, 20m wide,• n = 0.15

Change in flood peak: Caboolture

Debris blocking bridges andculvertsPhoto Pip Wilson

Sailors Creek, Daylesford, Central Vic

What should we do?• Don’t expect veg management to protectrural towns from floods• Do manage veg through towns• Don’t let town arguments justify clearingveg from rural streams• Do encourage revegetation upstream oftowns for flood benefits in towns• Do encourage large wood in the bedupstream of towns to reduce floodblockages

Vegetation will now be includedin the new Victorian floodstrategy!