long term cost benefit considerations (culvert economics) · long term cost benefit considerations...
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Long term cost benefit considerations (culvert economics)
Jon Simonsen – DNR
April 2017
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Overview
• Economic benefits of healthy waterways
• The challenge
• Stream impacts on roads
– Causing problems that take time and money to fix
• Cost savings lessons learned
• Long term cost saving strategies
• Mission impossible?
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Economic benefits of healthy waters
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What is the challenge?
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Stream impacts on the road (time & money):
• Structure durability
• Geomorphic factors
• Hydraulic factors
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• Structure durability
• Geomorphic factors
• Hydraulic factors
Stream impacts on the road (time & money):
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Structure durability
• Ability of the culvert to safely carry loads
• Structure material based on site water chemistry
• Avoid stream constriction to lower velocity and abrasive energy of water & sediment
• Avoid flood prone sites to preserve the integrity of the road core (by reducing erosion, overtopping, piping, etc.)
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Geomorphic factors
• Streams are always conveying sediment and wood.
• Often an overlooked but a very important design factor!
• Culverts that don’t constrict the stream are more likely to pass sediment and woody debris in a wide range of flows.
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Woody debris transported during floods is often < BFW in length
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Gravel deposits downstream from frequent road failures
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Hydraulic factors
Ability of the culvert to convey water during a wide range of flows (including floods)
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Be careful with resurface/ overlay projects!
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Hydraulic factors
• Culverts that don’t constrict the stream generally pass 100 year storm events without overtopping & road damage.
• Culverts 50% the width of the stream often don’t pass the 50 or 100 year storm event. The result is often overtopping and/or road damage.
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Culvert life cycle cost
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Culvert life cycle cost
Initial replacement & construction
+ _annual maintenance _
+ _lifespan ______ _
+ _added cost of emergency repairs
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Cost-savings lessons learned
• New York and Vermont- Tropical Storm Irene – Link between flood resiliency & ecological connectivity
– In many cases, municipality spends LESS $ and LESS TIME over the long term (50 to 75 years)
• Massachusetts – Culvert upgrades studies at 3 problem sites
– The upgrades were ~38% less expensive than in kind replacement and maintenance over 30 years
• Maine culvert cost study – Annual cost at 4 culvert replacements over a 50 year
timespan.
– 2 sites with cost savings, 2 sites with cost increase
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Cost-savings lessons learned
• Wisconsin- Green Bay (2016)
– Studied 461 culverts that were about ½ of the bankfull stream width.
– The total culvert lifetime savings of stream spanning culverts as ~ $13,000 at each crossing.
– This savings offset the initial improvement cost at 49% of sites.
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Cost-saving strategies
• Avoid durability, geomorphic, & hydraulic problems!
• Maximize the culvert service life to avoid cost of multiple replacements
• Long term thinking
Undersized culvert lifespan ~ 35 years
Stream spanning culvert lifespan ~ 75 years
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• Reduce maintenance costs
• Avoid added costs of flood failure – Project costs during a major flood are generally higher
than planned replacement costs.
– Added costs to repair streams, property, and delayed travel
– Public safety
Cost-saving strategies
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• Avoid impacts to local business, tourism, industry, etc.
Cost-saving strategies
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• “100 year flood”: Terminology itself can be unintentionally misleading.
• Encourage thinking in terms of the annual exceedance probability or percent chance of occurrence.
What are the chances???
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Lifespan of culvert (to minimize long term costs) has a 53% - 63% chance of experiencing a 100 year storm event.
What are the chances???
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0 0.01 - 5 5 – 10 10 – 15 15 – 20 20 – 25 25 – 30 30 – 35 35 – 40
100-Yr, 24-Hr Precipitation Depths
Percent Change From TP40 to NOAA Atlas 14 (Representative Location)
Shawano County: TP40: 5.40”
Atlas 14 (Rep. Loc. = Mean): 5.40” No Change
Ashland County: TP40: 5.40”
Atlas 14 (Rep. Loc. = Mean): 7.37” Increase 36.5%
Change in Precipitation Depth From TP40 to NOAA Atlas 14 (Rep. Loc.)
100-Year, 24-hour (Percent)
Grant County: TP40: 6.20”
NOAA Atlas 14: 7.69” Increase 24.0%
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• Culvert inventories to plan and prioritize
– Not all sites are problems
– Find and address flood prone and ecologically important crossings
– Find and address sites that will minimize disruption of emergency services
Mission Impossible?
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Local Example
• Town of Ackley: stream culverts = 24
~12 are fine (~50%)
8-9 minor problems easily fixed (~35%)
3-4 are bigger streams and bigger issues (~15%)
• For the bigger problems, evaluate resources, estimate costs, work with DNR and others to look for alternative funding sources
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Working with DNR
Department of No Reason?
Department of No Results?
Damn Near Russian?
Department of Norwegian Regulators?
Design of No-problem Roadways
The goal of each project: make reasonable decisions to best serve the public from a very broad range of perspectives and a long term view.
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References
Flood Effects on Road-Stream Crossing Infrastructure: Economic and Ecological Benefits of Stream Simulation Designs. (Gillespie et. al. 2014)
• http://fisheries.org/docs/wp/AFS-Fisheries-Magazine-February-2014.pdf
An Economic Analysis of Improved Road-Stream Crossings. (Levine 2013)
• http://www.nature.org/ourinitiatives/regions/northamerica/road-stream-crossing-economic-analysis.pdf
Cost-Benefit Analysis of Stream-Simulation Culverts. (Christiansen, et.al. 2015)
• https://www.lafollette.wisc.edu/images/publications/cba/2014-culvert.pdf
Conservation Leverage: Ecological-Design Culverts also Return Fiscal Benefits (O’Shaughnessy, et. al. 2016)
• https://fisheries.org/2016/12/conservation-leverage-ecological-design-culverts-also-return-fiscal-benefits/