DOES ALL FLOODING COME FROM A RIVER? - Flooding is a shared responsibility between di erent agencies and individuals.
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DOES ALL FLOODING COME FROM A RIVER? Flooding is a shared responsibility between different agencies and individuals. Riverine flooding occurs when rivers and streams overflow into surrounding areas. Conservation Authorities, like Toronto and Region Conservation Authority (TRCA), work to reduce riverine flood risks. Urban flooding is street and basement flooding and flooding of other low-lying areas due to the overflow of local drainage systems. These infrastructure systems are municipal assets. TRCA has mapped the area of risk for riverine flooding which is called the floodplain. Within the floodplain, there are some areas that were developed before land-use planning practices kept people away from the risks. These areas, where there are many buildings inside the floodplain, are called Flood Vulnerable Clusters, or FVCs. These FVCs include Special Policy Areas (SPAs), as well as historical flood damage centres.
FLOODING CAN HAPPEN AT ANY TIME OF YEAR
Summer
Thunderstorms – With a large amount of rain in a short period of time, intense,
localized downpours from thunderstorms can produce flash flooding.
Fall
Seasonal weather systems – Large wet weather systems, such as tropical
storms and hurricane remnants, can last several days. Prolonged and heavy
precipitation on top of already saturated soils can cause rivers to rise.
Winter
Ice jams – When temperatures and/or water levels rise, river ice breaks into large
chunks. These chunks can become jammed at bridges or other obstructions.
Rivers can become backed up and can overflow their banks.
Spring
Spring freshet – Accumulation of snow during the winter season can lead to
flooding during the early spring if conditions are right. When temperatures
rise, snow melts and turns to runoff.
UNDERSTANDING FLOOD RISK IN BOLTON
As a community that was historically developed around
river-based mill industries, well before the advent of
land use management practices to reduce flood risk, the
majority of downtown Bolton is within the floodplain
of the Humber River. The community is susceptible to
flooding during heavy rainfall events, the spring freshet,
and as most recently experienced, from ice jams.
TRCA identifies Flood Vulnerable Clusters as an area within the floodplain
that has a high concentration of buildings and roads that could be impacted
by riverine flooding. Bolton is ranked among the top 10 Flood Vulnerable
Clusters within TRCA’s jurisdiction. The cluster is in the village of Bolton in
the vicinity of Highway 50 and King Street, within the Town of Caledon. It
is a designated Special Policy Area.
While the Bolton berm and channel have served to provide functional flood
protection for most rainfall events, flooding occurred in 2019 due to an ice
jam in this area. Historical and recent ice jams have occurred in Bolton, in
the river reaches of Hickman Street (west of Queen Street), King Street and
Old King Road, and Sneath Road, downstream to Albion-Vaughan Road.
FLOOD PROTECTION IN DOWNTOWN BOLTON
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2009 Ortho-photography O D RD
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Bolton Berm: How
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Toronto and Region Conservation Authority Special Policy Area
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BOLTON - Existing Flood Mitigation Structures and TRCA Property
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flood infrastructure in
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the area works
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In the early 1980s, TRCA constructed a
network of berms and a flood control
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channel in downtown Bolton from Highway
DIVERSION CHANNEL
50 to King Road. Berms were built along the MI LL
south bank of the river to prevent floodwater ST
DROP STRUCTURE BERM
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from entering the Bolton core. A flood control WEIR
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channel was constructed downstream of REPLACEMENT BRIDGE
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Humber Lea Road to bypass the oxbow BERM
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section of river. A culvert was placed under
King Road, which releases a maximum flow
of 10m3/ second into the oxbow section
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LOW FLOW
CRIB WALL
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CULVERT
of the river. KING S T
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NEW BRIDGE
When high flows are present, most of the
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water runs through the flood control channel.
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This configuration maximizes the capacity
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of the river and reduces the risk of flooding Flood Control Structures
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for the homes around the oxbow. Berm Drop Structure Bridge TRCA Property
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Crib Wall Weir Low Flow Culvert
Diversion Channel
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BOLTON CORE
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FLOOD RISK MAP
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River flooding occurs when a body of water exceeds its KIN
capacity. A river can only carry so much water within its
banks and it will fill up until it overflows, typically due to
heavy rainfall. Flooding can cause property damage and pose
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a threat to safety, but the degree of risk varies depending on E A S
the location within the floodplain.
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• The greatest risk is to areas directly adjacent to the river. Q
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Because the watersheds are small, short, and full of hard O
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landscape, rainfall will make water levels rise very quickly. ET D
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Most watercourses in the GTA rise so quickly that sand- N
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bagging is typically not an effective protection measure.
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• Properties near the outskirts of the flood plain boundary
are less likely to see riverine flooding than the lower lying
ones close to the river.
• Many crossings and culverts don’t have the capacity to pass Flood Extents Flood Vulnerable Areas
flows from a flooded river – water can back-up and pool More likely 2-year storm - 50% Institutional
to occur in a
behind these structures. given year
5-year storm - 20% Residential
Commerical/industrial
• Engineers use statistical models of different rainfall amounts Q 10-year storm - 10% Flood cluster boundary
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25-year storm - 5% Flood-vulnerable roads
and durations, and simulate what flooding from those storms
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Non-real time stream gauge
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50-year storm - 2%
would look like through computer models. RE
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SO 100-year storm - 1%
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Very low
UT Precipitation gauges
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likelihood to
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given year Regional storm < 1% Watercourse
Flow direction
City of Brampton, City of Toronto, Region of Peel, York Region, Province of Ontario, Ontario MNR, Esri Canada, Esri, HERE, Garmin, INCREMENT P, Intermap, USGS, METI/NASA, EPA, USDA, AAFC, NRCa
WHO SHOULD I CONTACT DURING A FLOOD IN BOLTON?
• If you are in danger or there is a threat to life and safety, call 911 immediately.
• If you see any potential damage to your property, call your insurance
representative as soon as possible.
• For power outages or to report downed wires, call Hydro One at
1-800-434-1235.
• If water rises above your electrical outlets, baseboard heaters, or furnace, or
is near the electrical panel, call Hydro One to have your power disconnected.
• To report localized flooding on municipal roads, blocked catch basins, or
municipal infrastructure, contact the Town of Caledon: info@caledon.ca,
905-584-2272 Ext. 7750.
• For after-hours emergencies such as downed trees on roads or flooding,
call the Region of Peel at 1-800-563-7881.
• To report river flooding, leave a voicemail on the TRCA floodline at
416-661-6514. A flood duty officer will return your call.
BOLTON SPA - HISTORY OF FLOODING
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The Bolton SPA was established in the historic Toronto and Region Conservation Authority Special Policy Area
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downtown area of Bolton to permit a limited BOLTON - Regional Flood Lines (Various Modelling Years)
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scope of development and redevelopment,
BIRCHLAWN RD
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maintain the vibrancy of the community, and
address the significant social and economic
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hardships to the community, while recognizing
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and managing the potential additional flood
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risks, if no new development was permitted.
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In 2012, the Town of Caledon and TRCA
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initiated the Bolton Special Policy Area
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Update. New flood lines were created using HILLTOP CRT
modernized tools that included precision MI LL
mapping, new hydrologic data, and state-of-
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the-art hydraulic modeling software. STER NE S
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KING S T E
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This figure illustrates the historical delineation of the flood
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plain flood mapping (2013) and the existing SPA boundaries.
Generally, the extent of the flood line has not changed
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substantially but it has been refined based on the more Flood Line (1979) SPA Boundary (Existing)
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detailed topographical mapping and updated hydrologic
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Flood Line (2003/04)
CONNAUGHT CRES
and hydraulic modelling of open water conditions. LOUIS A S
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Flood Line (2013)
QUEEN ST S
Ice jamming is not the basis for floodline mapping, but ice
OLD KING RD
jams may contribute to the extent of flood inundated areas. AB E TH
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The updated floodlines and SPA area were communicated ELI Z
NE
to the public via a public open house on April 2, 2013, July 8, CHERRY LA VICTORIA ST
2013, and March 10, 2015.
Mar 2013
2009 Ortho-photography
WHAT IS AN ICE JAM? Long cold spells can cause the surface of rivers to freeze. When a rise in the water level or a thaw breaks the ice into large chunks, these chunks can become jammed at man-made and natural obstructions. With no way past the obstruction, the river will become backed up and can overflow its banks, causing flooding. Ice Jams: • Typically occur during spring thaw and rainfall • Result from broken ice cover when pieces flow downstream • Are very site-specific - accumulate at obstructions, bends, bridges, or sometimes just against other pieces of ice • Can develop rapidly • Multiple jams can form and release in the same place • Can cause problems downstream if suddenly realeased as ice can pile up farther downstream
CAUSES OF 2019 BOLTON ICE JAM FLOOD
TRCA/KGS Bolton Ice Jam Study Findings
• There were two different ice-jam events in the winter of 2019.
• The February 5 ice accumulation upstream of King Street subsequently
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cleared.
• A second period of ice formation in upstream reaches occurred from the
third week of February onwards.
• Rain and warm temperatures in March caused this ice sheet upstream of
Bolton to break up.
• Higher flows, estimated around the 2-year event, facilitated the
movement of ice downstream.
• Ice jams began to form behind 181 King Street and downstream of the
King Road bridge due to the shallower channel slope in this area.
• Water began to back up the river toward the oxbow and overtopped in
several locations including the berm at 181 King Street East.
• The occurrence of ice jams is difficult to predict given the various factors
(weather, river morphology, flow conditions) that contribute to ice jam
formation. State-of-the-art river ice science does not provide means to
predict when or where an ice jam will form.
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2019 BOLTON ICE JAM MAP ¯
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Berms
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Ice Jam in Channel
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1. Image, Topographic Data, and High Water Marks provided by
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Toronto and Region Conservation Authority (TRCA)
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MI 21 2. All units are metric and in metres unless otherwise specified.
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ST 23 Transverse Mercator Projection, NAD 1983, Zone 17. Elevations are
R in metres above sea level (MSL).
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0BOLTON BERM AND CHANNEL REMEDIATION STUDY
AND SPECIAL POLICY AREA UPDATE
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In 2012 the Town of Caledon and 500-YR FLOOD DEPTH MAP (EXISTING CONDITION)
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TRCA initiated the Bolton Special UNSTEADY INFLOW HYDROGRAPH (USING 1981/1983 MMM LIT
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Policy Area Update to define the 500-YR FLOW = 155 CMS BASED ON FLOW N
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flood risk in the Bolton core and
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confirm that the berm and channel
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were performing as per the original SHE
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design. Several technical studies E NGLISH R
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were completed to investigate the CR
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hydraulic, geotechnical, structural, C7 G RD
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and fluvial conditions of the berm. TEN
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New flood lines were created using
modernized tools that include E
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precision mapping, new hydrologic
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data, and state-of-the-art hydraulic OC
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modeling software. DA
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The Bolton Berm and Channel SA
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Remediation Study and Special L OT
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Policy Area Update concluded
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that the berm and channel system
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does not provide the original level C2
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of service, which was the 500-year LT
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Bolton SPA Boundary
River Network
0.10 - 0.30
0.30 - 0.60
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flood (0.2% chance of occurring in PD NC S Existing Flood Berm 0.60 - 0.80
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a given year). The berm was never Buildings 1.20 - 1.50
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YV Flood Depth Mapping based on 2014 LiDAR DEM and 2015 Road Paved 1.50 - 1.80 D
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Orthophoto. This mapping is intended for the sole purpose of
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designed to protect against ice jams. CR IZA Culvert/Bridge C1..C9 1.80 - 2.60
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floodplain study. Any other use of this information by a third
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party requires verification and is at the sole risk of that party.
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DRBOLTON BERM AND CHANNEL - CURRENT CONDITIONS
During the Bolton Special Policy Area Update in 2012,
TRCA reviewed the technical investigations of the Bolton
Berm and Channel to determine their conditions. The
technical findings determined the following:
1. The berm and channel don’t provide protection up to
the 500-year flood. Current protection for the berm in
some sections only passes the 100-year flood.
2. There are some minor geotechnical issues, but the berm
meets factor of safety guidelines for most conditions. Bolton Channel - flap gate, south bank Bolton Berm
3. Flap gates and culverts require maintenance.
4. There are several areas of erosion that require repair, as
does the berm around the pumphouse.
In order to fully protect against the 500-year event,
additional berms upstream of Highway 50 and downstream
of King Road would be required. These structures require
a Class Environmental Assessment and are not part of
this project.
Bolton Channel - McFall damBOLTON BERM AND CHANNEL UPGRADES
TRCA has developed several options to upgrade the TRCA is proceeding with Option 3B because it restores the original level of flood protection
berm. These include: and meets current engineering standards for stability. Option 4, while providing a higher
level of flood protection, is not practical given the property constraints of the area. The
OPTION 1: Undertake general maintenance only and construction of the proposed option is to be completed in the following phases:
maintain the berm as is with 100-year flood protection.
OPTION 2: Upgrade the berm to provide 350-year Phase 1: Phase 2: Phase 3:
protection and perform general repairs. Repair/replace flap Restore/raise the Restore/raise the
OPTION 3A: Upgrade the berm to provide 500-year gates, repair culvert flood berm west flood berm and
protection and maintain the current factor of safety end treatments of Humber Lea Rd. raise the crib wall
conditions including general repairs. and clean culverts and east of Queen east of Humber Lea
OPTION 3B: Upgrade the berm to provide 500-year (2019/2020) St. and repair the Rd. (2021/2022)
protection and to meet the current factor of safety diversion channel
guidelines. (2020/2021)
OPTION 4: Upgrade the berm to meet Regional storm
flood protection. TRCA has retained a consultant to complete final design drawings for Option 3B. TRCA is
also investigating the feasibility of raising the berm to protect against ice jams similar to
the event in March 2019. Property constraints may preclude raising the dyke to meet this
level. Additionally, there isn’t enough historical data on ice jams in this area to design for
ice jam protection.MITIGATING ICE JAMS
Options for mitigating ice jams are limited in this area
INFEASIBLE FEASIBLE
Pre-emptively breaking ice cover Ice jam removal
This option includes blasting and cutting ice before break up. This option involves using heavy equipment to mechanically
Due to the length of the Humber River and the unpredictable remove ice from the river, as was done in March 2019. This is
risks in blasting, this is not considered feasible. Blasting ice the most feasible option for ice jam mitigation in this area.
does not prevent re-formation of a jam elsewhere. Furthermore, Careful consideration is required to ensure that the movement
there are risks to property and nearby persons, as well as of jammed ice does not create or exacerbate flooding
potential damage to infrastructure including sewers and berms. conditions elsewhere. Staff should be available 24/7 to
respond when ice jams begin to form. Emergency support
Construction of ice control structures contracts should continue to be maintained with heavy
equipment contractors. An equipment access route to the
Ice control structures are similar to dams. The structures jam location can be identified and formalized.
capture and store ice upstream of areas at risk of ice jam
floods. This option is not feasible in Bolton because there Flood forecasting and warning upgrades
isn’t a suitable location upstream for this type of structure.
This is not a mitigation technique but instead provides early
River modifications warning when ice jams could be forming. Enhanced flood
warning components could include drone surveys, remote
This option includes modifications to the river to facilitate ice cameras, and additional gauges.
passage: deepening or widening the river to reduce the
possibility of ice jams. This option is also considered infeasible
in Bolton. The river is a natural watercourse and it is unlikely that
approval would be granted given the environmental impacts.TRCA FLOOD RISK MANAGEMENT
A principal mandate of TRCA is to reduce the risk to life and damage to
property caused by flooding. We do this by providing local agencies and PREVENTION & MITIGATION PREPAREDNESS
the public with notice, information and advice so that they can respond
Limiting exposure to risk: • TRCA’s flood contingency plan
during severe rainfall events that have the potential for flooding, and
• Implementing TRCA’s regulations and policies • Emergency plans
during flood related emergencies. • Emergency operations centre
Reducing risk:
• Training
• Operating a flood forecasting and warning program
• Public education
• Maintaining flood control infrastructure
• Creating a flood protection strategy for vulnerable areas
• Implementing remedial works projects Site-Specific Flood Response Plan
A Site Specific Flood Response Plan
Understanding the risks:
(SSFRP) is a tool to assist municipalities
• Climate, geology, watershed response, and potential for in responding to a flood emergency in a
climate change given flood-vulnerable neighbourhood.
It is meant to complement existing
Documenting the risks: emergency plans, such as a municipal
emergency plan or a risk-specific plan
• Floodplain mapping, identification of flood vulerable areas
for flooding.
RESPONSE RECOVERY
• Provide flood forecasting and warning • Flood event documentation and
(issuing flood messages) lessons learned
• Operate flood control infrastructure • Storm analysis
• Communicate information and advise
• Data managementREAL-TIME FLOOD MONITORING IN YOUR NEIGHBOURHOOD TRCA has a network of real-time river and rain gauges across the GTA to: • Monitor the water levels in specific streams and behind dams • Measure how much precipitation has fallen The measurements are displayed on TRCA’s Real-time Gauge flood monitoring website. While the website is primarily a tool for Flood Duty Officers to evaluate watershed conditions and assess the risk of flooding, the website is available to our municipal partners and the public: trca.ca/floodmonitoring The Station Map uses shapes, colours, and symbols to allow for a quick assessment of the conditions in the watersheds. TRCA Real-time Gauging Station Map Real-time Gauge
TRCA’S FLOOD MESSAGES
To support our municipal partners during storm events, Toronto and Region
Conservation Authority (TRCA) runs a Flood Forecasting and Warning
Program with staff on-call, 24/7. If flooding is possible or about to occur,
TRCA issues flood messages to designated individuals within municipalities,
local agencies, school boards, the media, and members of the public who
self-subscribe.
Sign Up for Flood Messages
To receive flood messages, you can either:
• Subscribe to email notices at trca.ca/floodmessages
• Follow us on Twitter at @TRCA_Flood
Flood messages are also posted on TRCA’s website at trca.ca/floodforecastingYou can also read
