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 4 th , 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 2

1. The Flood 3

1. The Flood Halifax Burlington 4

1. The Flood Halifax Burlington 5

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 6

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1. The Flood Riverine Flooding - Tuck Creek at Driftwood Park 8

1. The Flood Riverine Flooding - Tuck Creek @ Elwood Drive 9

1. The Flood Riverine Flooding - Shoreacres Creek @ Mainway Creek overtopping road 10

1. The Flood Riverine Flooding - Shoreacres Creek south of New Street 11

1. The Flood Overland Flooding - ETR-407 south of Dundas Street 12

1. The Flood Overland Flooding - Tuck Creek @ Regal Road 13

1. The Flood Overland Flooding - Tuck Creek 14

1. The Flood Overland Flooding - Shoreacres Creek @ North Service Road 15

1. The Flood Overland Flooding - Appleby Creek @ Walkers Line – Lakeshore rail underpass 16

1. The Flood Local Flooding - Tuck Creek @ Notre Dame High School Heaving 17

1. The Flood Local Flooding - Shoreacres Creek @ Commercial Building 18

1. The Flood Local Flooding - Underground Parking Garages 19

2. The Response Guelph Line north of Dundas Street 20

After the Storm 21

2. Characterization of the Storm 22

2. Characterization of the Storm 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 23

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) 24

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 100 Year (6 hours) is 87.7 mm ► Appleby Creek 130 mm Hurricane Hazel (12 hours) is 212 mm ► Roseland Creek 120 mm ► Sheldon Creek 100 mm 25

2. Characterization of the Storm Regional Storm RAIN EVENT COMPARISON 250 August 4, 2014 200 100 Year Storm Rainfall Amount (mm) 150 May 2000 5 Year Storm 100 50 0 Rainfall Events 26

3. The Response 27

3. The Response • Field Surveys of Damage • Debris Cleanup • 311 Call Registry / Database Development • The Study 28

3. The Response 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. 29

3. The Response 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 30

3. The Response Creek Debris Clean-Up by City ► Over 120 creek clean-up locations 31

3. The Response Tuck Street south of New Street Trees, shrubs & vegetation August 5, 2014 After clean up 32

3. The Response Tuck Creek at Fairview Street Debris at major culverts After clean up August 5, 2014 33

3. The Response Shoreacres Creek south of New Street Trees, shrubs & vegetation After clean up August 5, 2014 34

3. The Response Shoreacres Creek south of South Service Road Broken shale transported downstream After clean up August 5, 2014 35

3. The Response 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 36

3. The Response Database Development – GIS Mapping Mapping Identifying Flood Locations & Mechanisms 37

3. The Response The Study ► Engaged Consultant - Amec Foster Wheeler ► No initial Terms of Reference; Scope consultatively developed with City ► Need for early actions 38

4. The Study 39

4. The Study • Governance • Purpose/Approach • Flood Characterization • Flood Vulnerable Areas • Outcomes 40

4. The Study Governance • Basement flooding due to sanitary system back-up • Basement flooding due to foundation drain (weeper) back-up Region of where connected to sanitary Halton • Riverine (creeks overflowing their banks) • Roads (overtopping culverts and bridges) • Urban (overland/depressional) City of Burlington • Lot Level / Grading (private) • Riverine (creeks overflowing their banks Conservation Halton 41

4. The Study Purpose/Approach Characterization of the August 4, 2014 flood response using 1. hydrologic and hydraulic modelling Identification of prioritization of flood vulnerable areas , City wide 2. Identification of mitigation opportunities 3. A recommended list prioritized of capital flood mitigation projects 4. Detailed site scale analysis and mitigation of flooding at sixteen 5. (16) priority locations 42

4. The Study 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 Max Cell 43

4. The Study Flood Characterization Governing Design Storm August 4 th , 2014 (Max cell) Regional Storm 100 Year Storm Watersheds Most Impacted Aug 4, 2014 ► 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) 44

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) 45

4. The Study Flood Vulnerable Areas (FVAs) Flood Mechanisms Riverine Urban (road conveyance) Source: CTV News Source: CTV News ► Distinct analytical methods ► To allow prioritization, ‘vulnerability’ must be characterized using common and comparable measures 46

4. The Study Identify Riverine FVAs ► Buildings within flood limits ► Primarily a mapping exercise 47

4. The Study Characterize Riverine Flood Vulnerability ► Hydrologic and hydraulic modelling used to determine the frequency buildings are vulnerable ► 2 Year? ► 100 Year? Regional WSEL 48

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! 49

4. The Study Identify Urban FVAs ► Identify ‘depression’ areas – no major system outlet ► Primarily a GIS assessment 50

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 51