using gis to assess risk and prioritize storm sewer ...d96b0887-4d81-47d5-aa86-9d2fb8bc0… ·...
TRANSCRIPT
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Using GIS to Assess Risk and Prioritize Storm Sewer Maintenance,
Repair and Replacement
CEAM Conference January 27, 2016
Janna Kieffer, P.E. Barr Engineering Co.
Liz Stout, P.E. City of Minneapolis
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Agenda • History of storm sewer management • Objectives of the project • Project approach • Next steps
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History of storm sewer management
• Where we started – Mapping:
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History of storm sewer management
• Next step-Electronic mapping – Clearer and easier to read but not much more
helpful
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History of storm sewer management
• Mapping update into GIS - Goals
• Asset Management • MS4 requirements • Updated stormwater modeling
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History of storm sewer management
• Field Data Collection • Pipes:
• size, type, invert elevations, outlet and inlet type
• Structures: • Diameter, type, depth, condition
• We had a lot of data…
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History of storm sewer management
• Met the city’s primary goals: – Asset management
• Now using a software called CityWorks for work orders and maintenance records
– MS4 Requirements • System is mapped and spill vectors to receiving
waters are known – H&H modeling
• Flood areas have been mapped and pipe upgrades have been identified
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History of Storm Sewer Management
• Maintenance – Reactive: When there was a catastrophic pipe failure
creating a public nuisance, flooding or a sink-hole
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History of storm sewer management
We had a lot of data…BUT What we didn’t have: – Televising data for storm sewer – Field inspections and conditions of our pipes
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Objectives of this project
Use existing data to create a simple, cost effective analysis • Target areas for inspections • Target critical areas for replacement/lining • Create a logical CIP program • Minimize emergency maintenance
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Simplified approach to evaluating storm sewer fa ilure risk
Storm Sewer Failure Risk
Likelihood of Failure
Consequences of Failure
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Storm Sewer Failure Risk
Likelihood of Failure
Consequences of Failure
Simplified approach to evaluating storm sewer fa ilure risk
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Key factors affecting the likelihood of pipe fa ilure
– Pipe age – Pipe material – Susceptibility to corrosion – Susceptibility to abrasion – Joint separation
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Pipe age and material can affect fa ilure likelihood
– Pipe age- not historically tracked by City – Pipe material
• Vitrified Clay Pipe (VCP) • Metal (CMP, CIP, CSP, DIP) • Plastic • Reinforced Concrete
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Storm sewer materials in Minnetonka
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Soil properties affect failure likelihood
• Soil properties- from NRCS web soil survey – Corrosive soils- steel, concrete – Load supporting capacity
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Example: risk of steel corrosion (from NR C S web soil survey)
High Risk Moderate Risk
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Ground slope can also affect failure likelihood
-Add GIS graphic on ground slope
• Steep slopes identified – Somewhat steep (4:1 to
2:1 slopes) – Steep (2:1 to 1:1 slopes) – Very Steep (>1:1 slopes)
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Failure likelihood rating system
Factors used in Minnetonka rating system equation: • Pipe material • Corrosion risk • Soil structural support capacity • Ground slope
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Distribution of failure likelihood ratings
Top 10%
Top 2% -Most pipes in top 10% are metal or vitrified clay -Some RCP pipes w/steep slopes are in top 10% -All pipes in top 2% are metal or vitrified clay
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Top 10% Failure Likelihood - CMP - Soils w/high
corrosivity
Top 2% Failure Likelihood - CMP - Soils w/high
corrosivity - Steep Slope
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Storm Sewer Failure Risk
Likelihood of Failure
Consequences of Failure
Simplified approach to evaluating storm sewer fa ilure risk
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Potential consequences of pipe failure
www.dewattoport.com
• Four “consequence” scenarios considered: 1. Failure that results in significant
pooling/inundation 1. Failure at road crossing- potential road washout
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Potential consequences of pipe failure
• Four “consequence” scenarios considered:
3. Failures at steep slopes-
potential landslide/washout
3. Failures that impact
critical structures
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Failure causing significant pooling/inundation
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Example: Holiday-W ing-R ose C ha in of La kes
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Step 1- determine trunk storm sewer
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Step 1- determine trunk storm sewer
Wing Lake
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S tep 2- ma p potentia l inunda tion a rea s
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S tep 3- determine # of potentia lly impa cted structures
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Step 3- determine # of potentia lly impa cted structures
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Failure causing significant pooling/inundation
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Failure causing significant pooling/inundation
• Factors considered in scoring system – Trunk storm sewer identified – Inundation areas mapped – # of structures within inundation areas identified – Scoring based on number of potentially inundated
structures
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Failure at road crossing- potentia l roa d wa sh-out
• Step 1: Identify pipes that cross a roadway or railway (3500 of 11,000)
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Failure at road crossing- potentia l roa d wa sh-out
• Are these pipes part of the trunk storm sewer system?
• Are these pipes large (high flow capacity)?
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Failure at road crossing- potentia l roa d wa sh-out
• Crossings under “critical” roadways (major roads or evacuation routes)?
• Crossings under
railways?
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Failure at road crossing- potentia l roa d wa sh-out
• Does the
crossing have a high likelihood of overtopping based on flood elevations?
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Failure at road crossing- potentia l roa d wa sh-out
• Does the crossing embankment have steep
side slopes, increasing potential for wash-out?
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Failure at road crossing- potentia l roa d wa sh-out
Top 2% Failure Consequences - Road crossing - Trunk system - Critical roadway - Somewhat steep - Overtopping likely
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• Steep slopes identified – Somewhat steep (4:1 to
2:1 slopes) – Steep (2:1 to 1:1 slopes) – Very Steep (>1:1 slopes)
Consequences of pipe failure on steep slopes (increased slope failure risk)
• Scoring based on steepness and pipe size
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Consequences of pipe failure on steep slopes (increa sed slope fa ilure risk)
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Failure near critical infrastructure
Identified storm sewer located near: – critical roadways and emergency routes – critical structures
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What are the consequences of pipe fa ilure?
• Maximum rating of four primary “consequence” scenarios used as consequence rating – Failure at road crossing – Failure that results in significant pooling/inundation – Failure at steep slope – Failure that impacts critical structures
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Distribution of failure consequence ra tings
Top 10%
Top 2%
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Storm Sewer Failure Risk
Likelihood of Failure
Consequences of Failure
Combined storm sewer failure risk
• Rating scales normalized to compute combined risk
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GIS maps identify locations with highest fa ilure risk
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GIS data includes attributes used for fa ilure risk ra ting system
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Outcomes of storm sewer failure risk a na lysis
Pipes with highest combined risk rating have high failure likelihood AND high consequences
– these pipes should be prioritized for inspection and/or replacement
Some pipes with high failure consequences do not have high overall risk
– primarily concrete or plastic material (lower failure likelihood)
– City should consider inspecting these pipes periodically
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Project deliverables assist City with inspection progra m development
• Failure likelihood map with top 2% and top 10% flagged
• Failure consequence map with top 2% and top 10% flagged
• Combined failure risk map with top 2% and top 10% flagged
• Storm sewer database with scoring system
• GIS layers
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Next steps
1. Fill in details on unidentified pipe types 2. Pipes rated in top 2% - utilize existing staff to
evaluate actual pipe condition in the field. 3. Establish dedicated funding on an annual basis
to line or replace failing or deteriorating pipes. 4. Use data in conjunction with pavement
management data and water and sewer replacement schedule to coordinate replacements with road reconstructions.
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Questions?
Janna Kieffer, P.E. Barr Engineering Co. [email protected]
Liz Stout, P.E. City of Minneapolis [email protected]