Weathering the Storm The City of Burlington learns from the August 4 - - PowerPoint PPT Presentation

Weathering the Storm

The City of Burlington learns from the August 4th, 2014 flood

September 13, 2016

Agenda

• 1. The Flood
• 2. Characterization of the Storm
• 3. The Response
• 4. The Study
• 5. Lessons Learned
• 6. Next Steps

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• 1. The Flood

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4

• 1. The Flood

Burlington Halifax

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• 1. The Flood

Halifax

Burlington

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• 1. The Flood

Weather Network chief meteorologist Chris Scott called this summer storm an “Epic flash flooding event”, caused by training storms, a series of thunderstorms that moved over the same area several times in a short period of time.

196 mm of rain in 8 hours

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Riverine Flooding - Tuck Creek at Driftwood Park

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• 1. The Flood

Riverine Flooding - Tuck Creek @ Elwood Drive

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• 1. The Flood

Riverine Flooding - Shoreacres Creek @ Mainway

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Creek

• vertopping

road

• 1. The Flood

Riverine Flooding - Shoreacres Creek south of New Street

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• 1. The Flood

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Overland Flooding - ETR-407 south of Dundas Street

• 1. The Flood

Overland Flooding - Tuck Creek @ Regal Road

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• 1. The Flood

Overland Flooding - Tuck Creek

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• 1. The Flood

Overland Flooding - Shoreacres Creek @ North Service Road

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• 1. The Flood

Overland Flooding - Appleby Creek @ Walkers Line – Lakeshore rail underpass

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• 1. The Flood

Local Flooding - Tuck Creek @ Notre Dame High School

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Heaving

• 1. The Flood

Local Flooding - Shoreacres Creek @ Commercial Building

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• 1. The Flood

Local Flooding - Underground Parking Garages

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• 1. The Flood

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Guelph Line north of Dundas Street

• 2. The Response

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After the Storm

• 2. Characterization of the

Storm

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What caused the storm?

► Meteorological condition referred to as “Training” – a series of storm

cells that pass over a single area

► Causes:

• Cold front meets hot humid air mass
• Thunderstorm sets up
• Strong winds created by leading thunderstorm create another storm

in its ‘wake’

• These repeat like a train on a

track

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• 2. Characterization of the Storm

Rainfall Measurement

► Rain is measured using two technologies: radar and local (point)

gauges

► Radar data for Burlington are available from the US National Weather

Service (Buffalo) and Environment Canada (King City & Exeter)

► Conservation Halton determined that Buffalo data were most accurate by

comparing it to 34 local gauges (this was independently confirmed by AFW)

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• 2. Characterization of the Storm

Rainfall Statistics – Comparing August 4, 2014 to design storms

► Rainfall period August 4, 2014 2:00 PM to 9:00 PM (Approximately 7 hours) ► Maximum rainfall depth = 196 mm (Roseland/Tuck Creek) ► Maximum rainfall intensity = 22.7 mm in 10 minutes (Shoreacres/Appleby Creek) ► Average rainfall depth by watershed

Design Standards

► Tuck Creek

150 mm

► Shoreacres Creek 140 mm ► Appleby Creek

130 mm

► Roseland Creek

120 mm

► Sheldon Creek

100 mm

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100 Year (6 hours) is 87.7 mm Hurricane Hazel (12 hours) is 212 mm

• 2. Characterization of the Storm

• 2. Characterization of the Storm

26 May 2000 5 Year Storm 100 Year Storm August 4, 2014 Regional Storm 50 100 150 200 250

Rainfall Amount (mm) Rainfall Events

RAIN EVENT COMPARISON

• 3. The Response

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• 3. The Response
• Field Surveys of Damage
• Debris Cleanup
• 311 Call Registry / Database Development
• The Study

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Field Surveys of Damage

► City Operations staff was working during storm ► The following morning City staff was deployed to inspect and record

damage at key infrastructure locations

► Conservation Halton staff deployed to inspect high water levels and

damage

► Halton Region staff surveyed sanitary sewer related flooding ► Coordination between City, Halton Region and Conservation Halton

was very important.

• 3. The Response

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Debris Cleanup

► Creek blockages from trees, shrubs, vegetation, sediment and rock ► Granular shoulders scoured away ► City tree crews, road crews and creek maintenance crews provided

cleanup services.

► Halton Region crews provided cleanup services ► Contractors hired to assist

• 3. The Response

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Creek Debris Clean-Up by City

► Over 120 creek clean-up locations

• 3. The Response

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Tuck Street south of New Street August 5, 2014 Trees, shrubs & vegetation

• 3. The Response

After clean up

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Tuck Creek at Fairview Street August 5, 2014 Debris at major culverts

• 3. The Response

After clean up

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Shoreacres Creek south of New Street August 5, 2014 Trees, shrubs & vegetation

• 3. The Response

After clean up

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Shoreacres Creek south of South Service Road August 5, 2014 Broken shale transported downstream

• 3. The Response

After clean up

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311 Call Registry / Database Development

► Over 3000 calls received regarding stormwater flooding and sanitary

sewer back-ups

► Coordinated effort between City of Burlington and Halton Region ► All 311 calls logged. Names, addresses and description of flooding

mechanisms recorded.

► GIS Mapping created for records. ► Coordinated with Halton Region

• 3. The Response

Database Development – GIS Mapping

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• 3. The Response

Mapping Identifying Flood Locations & Mechanisms

► Engaged Consultant - Amec Foster Wheeler ► No initial Terms of Reference; Scope consultatively developed with

City

► Need for early actions

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• 3. The Response

The Study

• 4. The Study

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• 4. The Study
• Governance
• Purpose/Approach
• Flood Characterization
• Flood Vulnerable Areas
• Outcomes

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• 4. The Study

Region of Halton

• Basement flooding due to sanitary system back-up
• Basement flooding due to foundation drain (weeper) back-up

where connected to sanitary

City of Burlington

• Riverine (creeks overflowing their banks)
• Roads (overtopping culverts and bridges)
• Urban (overland/depressional)
• Lot Level / Grading (private)

Conservation Halton

• Riverine (creeks overflowing their banks

Governance

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Purpose/Approach

1.

Characterization of the August 4, 2014 flood response using hydrologic and hydraulic modelling

2.

Identification of prioritization of flood vulnerable areas, City wide

3.

Identification of mitigation opportunities

4.

A recommended list prioritized of capital flood mitigation projects

5.

Detailed site scale analysis and mitigation of flooding at sixteen (16) priority locations

• 4. The Study

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Flood Characterization

► Methodology

► Establishing a single rainfall event hyetograph for the August 4, 2014 event,

based on the maximum recorded radar cell

► Simulating the cell uniformly across an entire subwatershed (conservative)

using a hydrologic model

► Extracting resulting flows and comparing

• 4. The Study

Max Cell

Flood Characterization

► August 4, 2014 (max. cell) and Regional Storm typically govern in medium to

large watersheds (combination of volume and intensity)

► 100 Year event governs in smaller (governed by intensity)

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• 4. The Study

Governing Design Storm August 4th, 2014 (Max cell) Regional Storm 100 Year Storm Watersheds Most Impacted Aug 4, 2014

• 4. The Study

Flood Vulnerable Areas Desired outcome

► A list of the most flood vulnerable areas across the City ► A recommended list of prioritized flood mitigation projects

Approach 1. Identify Flood Vulnerable Areas (FVAs) 2. Characterize FVAs (quantitative) 3. Prioritize FVAs 4. Establish feasibility and cost of mitigation for priority FVAs 5. Prioritize mitigation projects (cost-benefit)

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Flood Vulnerable Areas (FVAs) Flood Mechanisms Riverine Urban (road conveyance)

► Distinct analytical methods ► To allow prioritization, ‘vulnerability’ must be characterized using

common and comparable measures

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Source: CTV News Source: CTV News

• 4. The Study

Identify Riverine FVAs

► Buildings within flood limits ► Primarily a mapping exercise

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• 4. The Study

Characterize Riverine Flood Vulnerability

► Hydrologic and hydraulic modelling used to determine the frequency

buildings are vulnerable

► 2 Year? ► 100 Year?

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Regional WSEL

• 4. The Study

City-Wide Riverine Flood Vulnerability

► 75 distinct Riverine FVAs identified ► 526 vulnerable buildings ► Residential land uses make up 90% of flood vulnerable buildings ► Southern part of the City is most vulnerable due to historic

development practices (pre-1970’s)

► 73% of vulnerable buildings are located within 3 subwatersheds – the

same 3 subwatersheds most affected August 4, 2014!

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• 4. The Study

Identify Urban FVAs

► Identify ‘depression’ areas – no major system outlet

► Primarily a GIS assessment

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• 4. The Study

Characterize Urban Flood Vulnerability

► Field reconnaissance and GIS analysis used to identify factors that

increased urban flood vulnerability:

► *Reverse driveways ► Potential depth of flooding ► Length of road impacted (related to emergency ingress/egress)

City-Wide Urban Flood Vulnerability

► 92 reverse driveways within depression areas identified ► 10 km of flood susceptible roadway identified

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• 4. The Study

Prioritizing Vulnerability (Riverine and Urban)

► A fulsome flood damage reduction study considers social,

environmental and economic factors when prioritizing FVAs

► Schedule necessitated a simpler approach ► A ‘flood score’ (measure of risk) was developed for each FVA based on:

► Number of buildings at risk ► Land use ► *Frequency of flood risk (significant weight assigned to more frequent

flooding)

► Provided consistency between two (2) fundamentally different flood

mechanisms – critical to prioritizing capital expenditure

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• 4. The Study

Flood Mitigation Opportunities Long List of Alternatives

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► Site Scale (Individual FVA)

► Conveyance Improvements ► Flood Proofing ► Property Acquisition

► Subwatershed Scale (Multiple

FVAs)

► Stormwater Management ► Diversions

• 4. The Study

Flood Mitigation Opportunities FVA Specific Assessment

► Feasible and effective mitigation options were modelled ► Mitigation reduces vulnerability by a measurable amount (reduced

flood score i.e. reduced risk)

► Example:

► Short-List Alternatives

1. Upgrade selected culverts 2. Upgrade culverts and improve channel 3. Acquire property to facilitate larger culvert upgrades and wider channel

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• 4. The Study

Flood Mitigation Opportunities Cost Benefit & Prioritization

► A relative “cost-benefit” can be calculated and used to prioritize the

most “effective” solutions

► Cost - Capital $ ► Benefit – Reduction in flood vulnerability

► Example:

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Option ΔFlood Score Capital Cost Relative Cost-Benefit

Upgrade culverts

• nly
• 3.9

$2.4M 1.6

Upgrade culverts + channel

• 17.0

$7.3M 2.5

Acquire property + upgrade channel + upgrade culverts

• 19.4

$14.8M 1.3

• 4. The Study

City-Wide Recommended Flood Mitigation

► Eleven (11) capital projects were advanced

► Eight (8) culvert upgrades ► 800 m of channel conveyance improvements ► Two (2) major flood control facilities

► > 300 homes – reduced or eliminated flood risk

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• 4. The Study

• 5. Lessons Learned

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Creek Maintenance – Additional funds for improved level of service

► Recognition of watercourses as ‘natural infrastructure’ – need to

maintain conveyance capacity

► $100,000 additional base budget funding ► Enhanced level of service ► Bi-annual creek debris inspection program ► New equipment to assist debris cleanup in areas with access

challenges

► Rural ditch maintenance program

• 5. Lessons Learned

Data Collection / Management / Forms

• Quality of data crucial to post-storm analyses
• Need for pre-established data collection procedures
• Assigned/trained supervisory and field staff
• Recording templates and forms
• Data collection needs to be coordinated across agencies to ensure

efficient use of resources and prevent duplication of effort

• Joint committee may be warranted (City/Conservation

Authority/Region)

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• 5. Lessons Learned

Lack of Contemporary Analytical Tools

• City of Burlington watersheds modelled over multiple time periods (1980’s to

present) in multiple platforms

• Hydrology
• HYMO-based, SWMM-based,

GAWSER, HSP-F

• Hydraulics
• HEC-2 to HEC-RAS
• Numerous changes/updates not included in most current models
• Hydrology
• land use changes
• stormwater management
• design storm
• Hydraulics
• culvert/bridge upgrades
• channelization
• design features
• Municipalities need to keep models current as these are the fundamental

assessment and planning tools; considerations include:

• Updating frequency
• Process
• Cost
• Staffing

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• 5. Lessons Learned

• 5. Lessons Learned

► Design Standards

i.

Short duration thunderstorms can produce peak flows comparable to longer duration post-tropical events (Regional Storm)

ii.

Regional Storm remains an appropriate basis for flood hazard planning in the City of Burlington

iii.

Functioning major overland flow route is critical to conveying flows from extreme storm water runoff events - this was not a design standard prior to 1977, upgrading older areas of the city to this standard is a challenge – the piped system (storm sewers ) cannot be relied on to provide flood protection

iv.

Lot grading and drainage around the building foundation is critical: largely on private property and easily compromised over time by homeowners if not aware of the importance.

v.

Owners of older homes are best advised to understand the limits and flooding risk associated with their basements – many steps can be take to mitigate the losses in the event of flooding

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• 6. Next Steps

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• i. City-wide Assessment
• Preparation of riverine and urban (all-pipes) modelling, City-wide, in a

common hydrologic/hydraulic platform

• Refine existing prioritized list of FVAs, if justified
• Identify additional FVAs (likely primarily urban)
• New models could be utilized in other studies (erosion, infrastructure

upgrades, floodplain mapping, post-storm analysis, etc)

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• 6. Next Steps

• 6. Next Steps

City of Burlington Study Recommendations

► Include $20.04M in storm water infrastructure improvements for

consideration in the 2016 Capital Budget and 2017-2025 Capital Forecast.

► Majority of the Capital Improvements relate to Improvements to Riverine

Flood Hazard through either Channel Upgrades, Bridge Upgrades or Flood Storage.

► Need to increase funding to maintenance activities and pond renewal

has been identified.

► Review viability of a Storm Water User Fee as a long term sustainable

funding mechanism

► Increased Public Education & Outreach on Flood Risk and Mitigation

Opportunities.

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6 Home Adaptation Assessment Program

(HAAP)

• Limits the potential for basement

flooding

• Limits potential damage if flood occurs
• Based on best practices from flood risk

mitigation programs across the globe Educating Homeowners

• Integrates additional key messages from

municipalities and insurance companies

Intact Centre on Climate Adaptation (ICCA)

7Shared Funding Model

• $275 per home shared by homeowner,

government and insurance companies

• Average $125 cost to home owner

Technical Aspects of Assessment

• Pre-screening survey
• Certified HAAP Assessor with home owner
• 1-1.5 hours inside and outside home
• Review 50 points of potential water entry
• Report
• Prioritized action list
• Web Resources
• Customer helpline
• Follow-up surveys and on-site visits at 6

and 12 months

Home Adaptation Assessment Program

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