THE ECONOMICS OF LOW IMPACT STORMWATER MANAGEMENT

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THE ECONOMICS OF LOW IMPACT STORMWATER MANAGEMENT

• GLENCOURT PLACE

Éva-Terézia Vesely Jan Heijs Chris Stumbles
David Kettle
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In this presentation

• Context Background information
• Methodology LCC
• Results
• Discussion

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Urban Stream Health

• Compromising factors
• Modified flow
• Poor water quality
• Lack of physical habitat
• Lack of riparian vegetation
• Barriers to migration of fish and other biota
• Exotic plants and animals
• Channelisation, erosion and sedimentation

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Framework for Stream Restoration
Christopher J. Walsh Cooperative Research
Centre for Freshwater Ecology, Monash University,
AU

• Low impact urban design approaches that reduce
  drainage connection are the most effective
  management solution to the protection of stream
  biota in urban catchments.

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Windows of Opportunity for Low Impact Design
Age Distribution
infrastructure inertia
STORMWATER INFRASTRUCTURE
REPLACEMENT
lock in effects / path dependency
Typical Lifetime
windows of opportunity to explore alternative
design
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Background information

• Location Windy Ridge, North Shore City
• Sub-catchment size 2.6 ha
• Historical disposal soakage (soakpits)
• The problem serious overland flow problems

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Two approaches

• 1. The conventional approach
• reticulating the area with stormwater pipes
  and/or flowpaths
• 2. The low impact approach
• using an engineered system of gravel trenches,
  contoured flowpaths and minimal piping backed up
  with raintanks retrofitted to existing properties

Photo by Nadine Wakim
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Methodology

• Compare the Life Cycle Costs of the two
  approaches
• Reveal aspects that impose higher costs on the
  low impact approach
• Highlight changes and potential for future cost
  savings

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Life Cycle Costing

• Australian and New Zealand Standard (AS/NZS
  45361999)
• Life cycle costing is the process of assessing
  the cost of a product over its life cycle or
  portion thereof.
• Life cycle cost is the sum of acquisition and
  ownership costs of an asset over its life cycle
  from design stage through manufacturing, use,
  maintenance and disposal.

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Life Cycle Costing
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Assumptions for the LCC

• Timeframe 50 to 100 years
• Type of cost real costs with 2005 as base year
• Discount rates 3.5 and 10 real discount rates
• Water savings 125/raintank/year

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Acquisition Costs

• Conventional
• - based on the pipe layout used for the initial
  engineering costing
• - new costing data from recent contracts
• Low Impact
• - cost data from the construction contracts
• - NSCC accounting data
• - costs occurred before 2005 ? 2 inflation
  factor

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Renewal Costs

• Pumps replaced every 10 years at NZ600
• Raintanks replaced every 25 years at NZ2350

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Operation and Maintenance Costs

• Conventional
• - maintenance pipe NZ 1/linear meter pipe
• Low Impact
• - maintenance pipe NZ 1/linear meter pipe
• - operation of one pump NZ 10/year
• - maintenance of one pump NZ 20/year
• - maintenance of one raintank NZ 80/year
• - raintank registry and inspection NZ
  10/raintank/year
• - maintenance gravel trench and channel -

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Not quantified

• Decomissioning costs
• Cost of land
• Risk costs

Photo by Nadine Wakim
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Results
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Results
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Results
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Lessons

• LCC a useful analytical tool for
• comparing different options
• potentially improve design
• highlight the importance of pre-acquisition
  costs
• budgeting
• cost sharing
• assess financial sustainability

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Looking behind the numbers

• In favour
• Staff interest / commitment
• Lack of conventional infrastructure in place
• Commitment to low impact at strategic level
  (NSCC Stormwater Strategy 2004)
• Funding opportunities (Infrastructure Auckland
  funding)

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Looking behind the numbers

• Disadvantages / Changes
• Expertise and experience with the conventional
  approach
• Lack of expertise and experience with the low
  impact approach
• Experience building up (pilot projects)
• Public perceptions
• ? Experience building up with the consultation
  process
• Technical uncertainties
• ? Technical flexibility exposed

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Looking behind the numbers

• Disadvantages / Changes
• Standard restrictions
• Restrictions removed
• Lack of legal arrangements
• Legal arrangements sorted
• High perceived risk associated with assuring
  continuous operation and maintenance
• ? Stormwater Policy Responsibilities for
  Stormwater Infrastructure

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Investment in eco-innovation

• The novelty of the project translated into higher
  costs for design, project management and
  consultation.
• These costs are expected to drop in the future.
• The externalities remained out of the scope of
  this analysis.
• Market distortions will impact such analysis.

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Dynamic framework

• Criteria
• Performance against these criteria

are changing.

• Increased data availability on cost elements
• Changing public attitudes
• Future water prices

Performance against the COST MINIMISATION
criterion
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Acknowledgements
The authors are grateful to Nadine Wakim, Barry
Carter, Frank Tian, Viv Eyberg and Ban Aldin for
insightful discussions.