long term cost benefit considerations (culvert economics) · long term cost benefit considerations...

Long term cost benefit considerations (culvert economics)

Jon Simonsen – DNR

April 2017

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?

Economic benefits of healthy waters

What is the challenge?

Stream impacts on the road (time & money):

• Structure durability

• Geomorphic factors

• Hydraulic factors

• Structure durability

• Geomorphic factors

• Hydraulic factors

Stream impacts on the road (time & money):

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.)

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.

Woody debris transported during floods is often < BFW in length

Gravel deposits downstream from frequent road failures

Hydraulic factors

Ability of the culvert to convey water during a wide range of flows (including floods)

Be careful with resurface/ overlay projects!

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.

Culvert life cycle cost

Culvert life cycle cost

Initial replacement & construction

+ _annual maintenance _

+ _lifespan ______ _

+ _added cost of emergency repairs

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

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.

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

• 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

• Avoid impacts to local business, tourism, industry, etc.

Cost-saving strategies

• “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???

Lifespan of culvert (to minimize long term costs) has a 53% - 63% chance of experiencing a 100 year storm event.

What are the chances???

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%

• 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?

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

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.

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/