The section below provides an overview of flooding that occurred in various parts of the province in 2019.

As I was not able to visit or investigate the flooding that occurred in every part of the province, the information included below provides only a partial picture of the flooding that occurred and the associated impacts. While there may be some parallels between the areas discussed below and other parts of the province, it may also be more likely that the situation in other parts of the province are equally as unique.

4.1 Flooding along the Ottawa River

4.1.1 Ottawa River Basin and Ontario Power Generation facilities

The Ottawa River Basin is located on the border between eastern Ontario and southern Quebec, with 35% of the basin in Ontario and 65% in Quebec. The river has a length of more than 1,130 kilometres and a total basin area of 146,300 square kilometres. There are 13 principal reservoirs on the Ottawa River as defined by the Ottawa River Regulation Planning Board (i.e. > 200 million cubic metres of storage capacity). Ontario Power Generation operates three of the principal reservoirs, namely Bark Lake, Lady Evelyn Lake and Des Joachims Generating Station.

The vertical and horizontal profile of the Ottawa River varies considerably throughout the river, creating hydraulic constrictions throughout. Generally, the easiest place to create a dam and reservoir is at a natural restriction in the river or natural lake area. By selecting narrow river sections, the cost of building the dam is lower. There are also several natural shallow sections in the river. These create the rapids that many tourist companies rely on. Under high flow conditions, narrow or shallow sections of the river create natural restrictions that limit the amount of water that can pass through the section, in effect backing up the river. This is called a backwater effect. If the river flow is large enough, these natural restrictions may lead to flooding.

There is little significant storage available in the lower portion of the Ottawa River; in fact, over 60% of the basin is essentially uncontrolled due to lack of storage capability. Ontario Power Generation (OPG) operates four hydroelectric generation facilities on the lower portion of the Ottawa River, which consists of one or more dams and a powerhouse (Otto Holden, Des Joachims, Chenaux and Chats Falls). These stations operate under the authority of Water Power Leases with the Province of Ontario and with An Act Respecting the Water Powers of the River Ottawa (1943). During normal flow conditions, OPG has the legal ability to raise the water level to the limit prescribed in the license for the respective facility for the purposes of power generation. Under high flow conditions, OPG operates its dams and stations to minimize the impacts of flooding and to at least do no more harm than would occur under natural conditions.

Each station has known water level impacts related to flooding thresholds. For instance, the Des Joachims Generating Station has a known backwater affect on the Town of Mattawa when the combined Otto Holden Generating Station and Mattawa River flows are greater than 2,000 cubic metres per second. The operating strategy during the freshet is predicated on ensuring that Mattawa and Pembroke should not suffer unduly during high water periods, and that a balance must be sought between flows and levels at either site, despite the fact that balancing flooding at these sites reduces depth of water or flow at the generating station and thus energy production.

Reference is often made in this section to OPG’s facilities being operated as “run-of-river” facilities (i.e. facilities that have no storage capacity whatsoever and generate electricity by whatever flow is running in the river and through the generating station) during periods of flooding. Understanding what this term means conceptually is critical to understanding why water management approaches were used during periods of high flow and flood flow experienced in the spring of 2017 and 2019. OPG’s facilities are not normally operated as run-of-river, nor are they classified as run-of-river facilities. It must be highlighted that, outside of high flow or flood conditions, all of OPG generating stations operate on a daily peaking cycle as peaking or cycling facilities. Ontario’s Independent Electricity System Operator incentivizes power production to meet the needs of the Ontario energy market. Under normal operating conditions, outside of high flow or flooding events, OPG has significant control over the flows and levels to support power production, including daily ramping cycles that move water through the facilities in response to energy market demands, all within the licensed requirements approved for each facility. While some OPG generating stations on the Ottawa river have a minimum flow requirement, generating stations, including Otto Holden, completely shut flows off at night to store water for power production the next day. For transparency and full disclosure, the above facts must be emphasised as they can affect public perception of flow and level management regimes on the river and OPG’s ability to control flooding. OPG does have a heightened level of control and storage on flows and levels on the Ottawa River when flows are considered normal outside of freshet periods. However, OPG generating stations do not have the ability to store enormous amounts of water and manipulate levels that would prevent extreme high water and flooding in conditions experienced in spring 2017 and 2019.

4.1.2 Spring freshets – comparison of 2019 to 2017 and 2018 Weather and watershed conditions

During my tour along the Ottawa River and the sessions held with municipal and other representatives along the way, there were many questions posed regarding the differences in flooding between 2017 and 2019. Others asked why flooding didn’t occur in 2018, as many perceived that snow conditions were similar in 2018 to this past spring (2019) and to 2017.

Despite the occurrence of two large events in relatively close proximity to one another, the driving factors between the spring floods of 2017 and 2019 were different and impacted the basin in different ways. Watershed conditions in 2019

The snow on the ground as of April 1, 2019, was significantly higher than normal and higher than experienced in 2017 and 2018. Snow surveys showed the upper portion of the basin had 150 to 188% of the normal Snow Water Equivalent (SWE) for that time of year. Most of the watershed had an excess of 200 millimetres of SWE during the peak of the snowpack. The total precipitation throughout the watershed was also higher than normal, although not as high as in 2017. The accumulated April to May precipitation was approximately 125 to 175% of normal in 2019 for that time of year. While this precipitation was distributed more broadly over the basin than it was in 2017, major rainfall events coincided with the peak of the snowmelt period in 2019. Together, this led to historic flooding seen in much of the Ottawa River watershed in 2019.

The return period for the 2019 flood is estimated to be a 1:100-year to a 1:120 to 1:130-year flood depending on location and local factors affecting flows and levels. Watershed conditions in 2017

Leading up to the freshet of 2017, the snow conditions in the Ottawa River basin were considered to be average. A review of the 2017 winter and spring period showed a relatively average snow pack compared to 2016, in which there was not significant flooding. The major driver of this spring flood event was precipitation. In April and May of 2017, the precipitation over the entire basin totaled 257 millimetres, which is considerably higher than the 150-millimetre average (1981-2010) for those months. Local precipitation accumulation varied between 240 and 380 millimetres, with most precipitation falling in the central and southern portion of the basin. Much of this precipitation came during two events between April 30 and May 6, when 70 to 140 millimetres of rain fell on the lower unregulated portion of the basin. Receiving approximately two months of rainfall in a period of seven days in the uncontrolled portion of the basin was the major trigger for the flood that occurred in 2017. Watershed conditions in 2018

In contrast, in 2018, the snow survey campaigns indicated that SWE was above normal in the Quebec region of the basin upstream of Lac des Quinze and near normal for the rest of the watershed. The month of March was slightly warmer than normal, but the month of April was much colder than normal. The cold spell persisted until the third week of April, which resulted in very little snowmelt throughout the month. As a result, the Snow Water Equivalent (SWE) in mid-late April was considerably higher than normal for that time of year. From April 20 to 24, there was a strong warming event with temperatures reaching as high as 20 degrees Celsius. This resulted in a relatively sudden snowmelt in the basin. During the period of March to May, the accumulated amount of precipitation and its distribution was approximately normal. The peak flow on the Ottawa River in 2018 occurred relatively suddenly due to the quick snow melt, but the magnitude of the peak was mitigated with the storage in the principal reservoirs and flows were only slightly above a typical year.

4.1.3 Reservoir and station operations in spring 2019

At the beginning of the 2019 freshet season (the end of March), Ontario Power Generation’s strategy was to continue to pass the inflow coming to its facilities in order to maintain low reservoir levels, with the exception of Bark Lake, which is the most southern principal reservoir on the watershed. Early in the week of April 15, the weather forecast showed a large precipitation event of 40 to 70 millimetres approaching for the end of the week. At this time, outflow from Lake Timiskaming and other principal reservoirs in the upper Abitibi-Timiskaming area was being decreased, as was the outflow from Otto Holden and Des Joachims.

This strategy would place water in storage as the snowmelt and a heavy rain event could significantly increase flow on the lower Ottawa River. Bark Lake was filling and expected to rise as much as 50 centimetres per day. The discharge from Bark Lake was allowed to increase as the lake level rose in order to maintain some storage space for later events. By the middle to end of April there was flooding on the Madawaska River, particularly around Kamaniskeg Lake. This was due to very high unregulated flow to Kamaniskeg Lake from the York and other rivers, and increasingly limited storage at upstream Bark Lake. Also, on April 15, the high flows prompted a strategy change at Chats Falls to begin following the high flow curve. Under high flows, the restriction upstream of the station becomes an important hydraulic control and the guide curve provides information on the relationship between Chats Lake water levels and the Chats Falls Generating Station headwater elevation. By April 21, the weather forecast, now with a shorter lead time, had decreased (20 to 30 millimetres) and inflow being passed at Otto Holden and Des Joachims was continuing a slow build rate.

4.1.4 The May 6 flow increase from Otto Holden affecting Mattawa

At the end of April, another significant rainstorm was forecast to bring up to 60 millimetres of precipitation to the upper portion of the basin. The principal reservoirs in the upper basin at the end of April were continuing to fill, and more specifically Lake Timiskaming was filling rapidly. The strategy at the Des Joachims Generating Station switched to passing inflows so that the reservoir level would not continue to rise. By the beginning of May, the flow on the lower Ottawa was expected to slowly decline; however, inflows to the upper portions of the Ottawa River were continuing to increase. Model results and inflow forecasts for May 5 continued to project that inflows within Lake Timiskaming and Otto Holden would remain well below 3,000 cubic metres per second. It was not until the following day, May 6, that conditions changed significantly, and model results projected inflows to exceed the 3,000 cubic metres per second threshold. As Lake Timiskaming was continuing to rapidly approach its maximum operating level, with significant further increases in inflows now being forecast, a strategic decision to further increase discharge from Lake Timiskaming was made. Over the course of May 6, there were two significant flow increases from the Timiskaming reservoir, one having been completed in the morning and another performed in the afternoon. This was to account for projected increases to come. The travel time from Lake Timiskaming to Otto Holden is approximately three to four hours, therefore any flow changes from Lake Timiskaming arrives at Otto Holden within a very short timeframe.

In response to the increased discharge from the Timiskaming reservoir, Otto Holden staged flow increases accordingly throughout the day to ensure that all adjustments corresponded with the changes upstream. Otto Holden performed seven flow adjustments throughout the day as inflows climbed, with the subsequent releases upstream. This was intentionally completed during daylight hours. The flow increases from the Timiskaming reservoir and Otto Holden were significant enough to result in the Ottawa River elevation rising approximately 65 centimetres within the Town of Mattawa throughout the day. Over the following five days, flows and elevations continued to increase within the upper Ottawa River basins, as the inflows and discharges at Lake Timiskaming and Otto Holden rose accordingly until they finally peaked at 3,316 cubic metres per second on May 10 and 3,355 cubic metres per second on May 11. At all times throughout freshet, flow changes were performed strategically with regard for impacted areas and ultimately, with a mindset of providing as much flood mitigation as possible. As flows stabilized and declined towards the end of May, the strategy at all Ontario Power Generation reservoirs changed to begin increasing reservoir and forebay water levels. This allowed the flow of water on the Ottawa River to decrease more quickly than would have occurred under natural conditions. The reservoirs and forebays continued to rise to their normal operating levels, with the Des Joachims reservoir reaching its normal summer operating range in mid-June.

4.1.5 Explanation of conditions at Des Joachims and the dry section at Deux-Rivieres

When Des Joachims was originally constructed, in order to maximize the potential for electricity generation, the license granted in 1946 allowed for the elevation of the water upstream of Des Joachims to be artificially elevated to the natural high-water mark. This serves as the reservoir for the Des Joachims generating station and can be used to store water for power generation or other purposes, such as flood relief. This portion of the artificially elevated water levels can be seen from the Trans-Canada Highway (Highway 17) in the vicinity of Deux-Rivieres. A review of media articles has identified the observation of the de-watered section of the reservoir in other years (including 2017), which again was a significant topic of discussion during sessions with municipal representatives.

A complicating factor for providing flood relief at the Des Joachims Generating Station is the hydraulic conditions upstream of the generating station. The Ottawa River has several reaches that are naturally shallow, narrow or have changes in gradient, which leads to the development of the rapids for which the river is famous. There is a flat shallow region between the upstream Otto Holden Generating Station and Des Joachims Generating Station. This area, around the old village of Klock several kilometres upstream of Des Joachims, is known as the Rocky Farm Rapids. This section of the river becomes an important control point under high flow conditions. The two analogies below may be useful to help the reader understand the situation:

The rapids section at Klock has a similar impact on the Ottawa River. Where the analogies become imperfect is the fact that there is also a connection in the gradient or slope of the river. This is related to the elevation of the water downstream and the ability of the channel to pass water. During normal flow conditions, the Des Joachims reservoir can be maintained at a higher level for energy production, because the flow does not exceed the capacity of the channel and the rapids do not create an appreciable backwater effect. When the flow is high (and typically when the Des Joachims reservoir is low), the rapids become a hydraulic control and begin to cause a backwater effect creating a higher water elevation upstream at the Town of Mattawa. Even if the water level was raised at Des Joachims, it would have a muted influence at Mattawa and Otto Holden. As flow continues to increase, differences in water level between the two sites becomes larger, and the restriction at Klock becomes a more powerful control. High flow weakens but does not eliminate the influence of Des Joachims on the upstream water level.

Because of the geography of the Ottawa River, there are two distinct strategies that can be employed at Des Joachims to alleviate flooding. If the flooding is occurring mainly downstream of the station (for example due to heavy rain) and storage capacity is available, water can be retained in the reservoir to decrease the amount of water in the lower reaches of the Ottawa River. However, if the combined flow out of the Otto Holden Generating Station and the Mattawa River is greater than 2,000 cubic metres per second, the rapids at Klock can begin to create backwater flooding. This is when there is a lot of water coming from the upper portion of the Ottawa River. In these circumstances, the water level in Mattawa can be influenced but not fully controlled by the elevation at Des Joachims Generating Station. As flow increases, the reservoir at Des Joachims is maintained at a lower elevation to avoid backwater flooding. This can be achieved either by not refilling the reservoir after the winter drawdown or by releasing more water from the reservoir. A draw down must be timed to avoid releasing an amount of water that would generate or worsen flooding downstream. Typically, the Des Joachims reservoir will be refilled in two stages. The water level will be built up to a level that is known to not increase flooding in Mattawa. Once this risk subsides, the second stage begins and the reservoir is built up to its summer operating level.

In most years, including 2019, the Ottawa River tends to experience two flow peaks. The first is generated by snowmelt and rain in the lower portion of the watershed. The second occurs if/when the primary reservoirs in the upper portion of the watershed have filled and are forced to pass inflowing water downstream. In 2019, there was substantial snowmelt in the upper reservoirs leading to the second peak being larger than the first. Leading up to the first spring peak, water was slowly stored at Des Joachims Generating Station bringing the reservoir up to the first refill stage. As the second peak approached, driven by the upper reservoirs becoming full and having to pass their inflow, the elevation at Des Joachims Generating Station was held low with the goal of not subjecting the Town of Mattawa and other upstream communities to worse flooding than would have occurred under natural conditions. As upstream flow decreased toward the end of the event, Des Joachims Generating Station was filled, reducing the flow downstream.

A criticism during the 2019 flood event was that the reservoir was empty and could have been used to alleviate flooding at Pembroke. This would have made the overall impact from the event worse, as the Des Joachims reservoir has a finite storage capacity. If the Des Joachims reservoir had been at the top of its operating range, the water level in Mattawa would have been approximately half a metre higher. If the Des Joachims reservoir had been filled, the only option would have been to pass the flow coming into it, having no downstream benefit during a prolonged event. At peak flow, the Des Joachims reservoir would have filled from an empty state in less than half a day. A refill rate that could have had a meaningful impact on flooding in Pembroke could not have been sustained for the multi-week duration of the 2019 event. Therefore, using the storage capacity at Des Joachims Generating Station to alleviate downstream flooding would have had a large impact on Mattawa and provided negligible to no benefits at Pembroke.

4.2 Flooding in the North Bay-Mattawa area

The North Bay-Mattawa area is one of the most densely populated districts in northern Ontario and is home to more than 83,000 people, with the major population centres of North Bay (51,553), Callander (3,900) and Mattawa (2,000). The region includes two distinct watersheds, the Sturgeon-Nipissing-French and the Upper Ottawa River.

4.2.1 Sturgeon-Nipissing-French watershed

Lake Nipissing is a Provincially Significant Inland Fishery, which receives water from Lake Temagami in the north through the Sturgeon River and flows west to the Great Lakes Basin (Georgian Bay of Lake Huron) through the French River. The Lake Nipissing and French River system is part of a 19,000 square kilometre watershed. Lake Nipissing is the fourth largest inland lake in Ontario, covering over 850 square kilometres. From it, the French River runs 105 kilometres to Georgian Bay. The headwaters of the Sturgeon River-Lake Nipissing-French River (SNF) watershed are the northern portions of the Sturgeon and Wanapitei Rivers, with the Sturgeon River watershed flowing directly into Lake Nipissing. The Wanapitei River joins the French River System in the last reach of the French River below Lake Nipissing. The SNF system is quite complicated, being comprised of several large lakes, numerous rivers and more than 40 control structures and power stations. Public Services and Procurement Canada (PSPC) operates four dams that effectively control the outflow from Lake Nipissing.

There is no Water Management Plan (WMP) in place for the SNF watershed; however, there is a WMP for the South River subwatershed, which flows into Lake Nipissing. PSPC operates the dams that effectively control the outflow from Lake Nipissing at the French River. PSPC operates the dams according to guidelines that were published in 1992. The Ministry of Natural Resources and Forestry (MNRF) supports integrated water management decisions on this watershed by holding daily or as needed calls during freshet with other dam operators, known as the “SNF Technical Committee.” The MNRF also coordinates daily or as needed calls with elected or emergency management representatives from local and Indigenous communities, known as the “SNF Stakeholder Committee,” to share information on water management decisions and foster a shared understanding of water-related impacts.

During freshet 2019, the Technical Committee, with consensus from the Stakeholder Committee, took the approach of incrementally increasing outflows from the French River dams in order to avoid exceeding the flood allowance on Lake Nipissing. Water was also stored in Lake Temagami’s flood allowance during a time when Lake Nipissing was vulnerable to exceeding its flood allowance. The whole watershed experienced significant flooding during freshet 2019.

4.2.2 Upper Ottawa River watershed

The Upper Ottawa River watershed’s primary reservoir is Lake Temiskaming in the north. It also receives water flowing east from North Bay through the Mattawa River at Mattawa, which means “meeting of the waters” in Algonquin. The Ottawa River flows southeast to the St. Lawrence River, with many other uncontrolled inflows from Quebec and Ontario on the way down. The Mattawa River watershed typically flows into the Ottawa River at the Town of Mattawa. The lower Mattawa River portion of the watershed (below the Hurdman Dam) is hydraulically dominated by backwater effects from the Ottawa River. The Ottawa River drainage basin is 146,300 square kilometres, including regions of Ontario and Quebec. It is twice the size of New Brunswick. More than 3,000 people live within the three municipalities and townships that border the lower Mattawa River, with 2,000 people living in the Town of Mattawa.

Water Management Plans are in place for many of the subwatersheds in the Upper Ottawa River, including Hurdman Dam, the Matabitchuan River and the Montreal River, with each flowing into the Upper Ottawa River. The Ottawa River Regulation Planning Board is responsible for water management on the Ottawa River (see more detail in Section 4.1).

4.2.3 Spring 2019 flooding

An above average winter snowpack and slow start to the melt, with cool temperatures in the first three weeks of April, combined with substantial precipitation over the Easter weekend, resulted in substantial flooding throughout both watersheds. The April 15 snow pack readings within the region averaged 517% of the long-term average for that time of year, and water equivalence averaged 425% of the long-term average. April’s precipitation was 215% of normal and May was 150.8% of normal, according to the North Bay-Mattawa Conservation Authority (NBMCA). Northern watersheds outside of NBMCA’s jurisdiction, which flow into Lake Nipissing and the Ottawa River basin above Mattawa River, also experienced above average snow packs and high amounts of precipitation. Adding to the problem, the Sturgeon-Nipissing-French (SNF) watershed received between 50 to 75 millimetres more precipitation than normal in May 2019, with several large rain events causing spikes in inflows throughout the month.

On April 17, the NBMCA and MNRF North Bay District office each issued the first Flood Watch of the freshet event. The last bulletin issued by the MNRF North Bay District was issued on June 17 and expired June 21. The flood message status for all watersheds within NBMCA’s jurisdiction did not return to normal until on July 2.

The Municipality of Mattawa declared a State of Emergency on May 6, 2019. The Ottawa River rose 4.25 metres between April 17 and May 11, a significant portion of which occurred within 48 hours of the Emergency Declaration due to incoming runoff water from upstream reservoirs on the Ottawa River (see explanation in Section 4.1.4). Transport Canada issued a navigational warning for the Ottawa River near Mattawa that prohibited boat travel.

On May 9, the City of North Bay undertook precautions to protect the wastewater treatment plant by installing pumping equipment and temporary piping as part of a contingency plan. In addition, a lift station bypass plan was established to provide system relief where possible in order to limit flow to the wastewater treatment plant. While it was a worst case scenario, a failure at the wastewater treatment plant could have resulted in large volumes of untreated wastewater being released onto the shores of Lake Nipissing, damage to plant operations that would have likely led to weeks if not months of reduced wastewater treatment capabilities, sewer backups in low-lying areas of the City of North Bay, and the possible evacuation of city residents.

Nipissing First Nation experienced very high water levels and was preparing to evacuate residents if the lake level exceeded 196.59 metres. In the Jocko Point and Beaucage areas, high water levels and high winds damaged many properties. Approximately 60,000 sandbags were deployed in this area.

The Municipality of Callander and Nipissing Township all experienced very high water levels in low-lying areas along the Lake Nipissing lakeshore, impacting local businesses, roads and infrastructure.

The Municipality of West Nipissing declared a State of Emergency on May 9 due to damaging winds and damage to municipal infrastructure. All boat launches were closed until June.

Residents along the Upper French River began to see an increase in water levels, as local inflows peaked and increased discharges were made from the Chaudière Dam (together with Portage, Little Chaudière and Okikendawt Dams) to mitigate lake level rise on Lake Nipissing. On May 26, a State of Emergency was declared in the Municipality of French River, which remained in effect past June 17.

4.3 Flooding in the Muskoka River watershed

4.3.1 Physical characteristics and municipal governance

The Muskoka River watershed is located in south-central Ontario’s lake and cottage country, within the southern Boreal Ecozone of the Precambrian Shield. The main population centres include Huntsville, Bracebridge and Gravenhurst. The drainage basin encompasses an area of approximately 5,100 square kilometres and extends in a southwesterly orientation for a distance of approximately 210 kilometres, descending 345 metres in elevation from the western slopes of Algonquin Provincial Park, to its mouth at Georgian Bay of Lake Huron. The watershed originates along the height of land known as the Algonquin Dome and is comprised of three drainage systems, including the North and South Branches of the Muskoka River and the Lower Muskoka subwatershed, and includes 200 lakes covering an area of approximately 78,000 hectares. The Muskoka River is comprised of 19 quaternary basins that form its subwatersheds. The three largest lakes in the watershed include Lake Rosseau, Lake Muskoka and Lake Joseph.

The Muskoka River watershed is a complex, cascading system. There are a series of notable constrictions or pinch points that impede the flow of water and cause water to back up, creating what is referred to as a backwater effect, as affected by the hydraulic conditions. (As described in an analogy in Section 4.1.5, think of it like a funnel, where discharging a large volume of water is limited by the narrowest and/or shallowest point in the river. Putting water into the funnel at a larger volume than can pass through the tip of the funnel causes it to rise up the funnel and overflow.) Lake Muskoka is the last major lake in the system before water enters the Moon and Musquash rivers that flow into Georgian Bay, which represents the outlet of the funnel. All water from both branches of the Muskoka River and Lakes Rosseau and Joseph flow into Lake Muskoka, and the only outflow for Lake Muskoka is through the two dams at Bala. The MNRF Bala dams control the water levels on Lake Muskoka; however, during periods of high flows and levels, a difference in water levels develops between Lake Muskoka and what is known locally as Bala Bay. This is caused by three constrictions at Bala Park Island and Wanilah Island that restrict flow into Bala Bay, affecting how much water can be discharged from the Bala dams. During periods of flooding, a significant difference in water surface elevation (≥1 metre) is observed between Bala Bay and Lake Muskoka, which further exacerbates efforts to move water through the dams at Bala.

Muskoka is governed by a two-tier municipal system with the District Municipality of Muskoka as the regional municipality forming the upper-tier, working with the six area municipalities including the Towns of Bracebridge, Huntsville and Gravenhurst, and the Townships of Lake of Bays, Georgian Bay and Muskoka Lakes making up the lower tier. The drainage basin also includes components of other municipalities including the Township of Algonquin Highlands and Haliburton County, among slivers of others. Of the approximate 150,000 people populating the watershed, approximately 58% are seasonal residents according to the 2011 Canadian census. The majority of the big three lakes—Muskoka, Joseph and Rosseau—are located within the Township of Muskoka Lakes. The Wahta Mohawk and Moose Deer Point First Nations are also located within Muskoka’s boundaries.

There is extensive development with high value infrastructure within the main Muskoka Lakes (Lake Muskoka, Lake Rosseau, Lake Joseph, etc.) spread over approximately 14,000 lake lots, including 5,300-5,500 boathouses, greater than 6,500 docks, and approximately 41 marinas and 131 resorts.

4.3.2 Water management structures and operations

There are 42 water management structures within the Muskoka River drainage basin, including dams and/or dam-powerhouse combinations in addition to three navigation locks. The MNRF operates 29 of these structures, all of which are manually operated using stop logs or valves. Most MNRF dams were originally constructed to facilitate the transport of logs to sawmills, divert water to power the mills, and aid in commercial navigation. Over the intervening years, the operations emphasis of the dams has transitioned from commerce and transportation to the provision of a balance of social/recreational, environmental and economic interests.

It must be emphasised that dams in central Ontario, including those in the Muskoka River watershed, are not flood control structures. Flood control structures require a large lake or reservoir and associated drawdown capacity to store or hold back flood waters. Analyses have confirmed that lakes in the Muskoka River watershed that are regulated by dams have a limited capacity to drawdown water to affect flooding, and during periods of large volume rapid runoff, the available drawdown capacity is insufficient to reduce peak flood water levels. In this sense, the greater the magnitude of the flood event, the less ability the MNRF has on affecting or mitigating flooding through operation of its dams. Once the dams are fully open, the MNRF does not have the ability to increase the rate of flow, as it is then based on the amount of water in the system and the natural rate of flow and elevation as it moves through the wide-open dam sluice ways.

To the extent possible, the MNRF operates dams to maintain water levels within the ranges identified in the established dam operating plan. For the Muskoka River, these ranges were formalized in the Muskoka River Water Management Plan in 2006. The range of operations is based on a range of factors, including recreational and environmental considerations. The plan applies to normal water conditions, while there is recognition that unusually high rainfall or snowmelt can result in high water and flooding. Water Management Plans can help regulate flows to ensure that one activity does not take primacy over another (e.g. waterpower generation over recreational use); however, they do not and cannot prevent flooding. The goal of water management planning, in the context of Section 23 of the Lakes and Rivers Improvement Act, is to contribute to the environmental, social and economic well being of the people of Ontario through the sustainable development of waterpower resources, and to manage these resources in an ecologically sustainable way for the benefit of present and future generations. The management of floods and flooding is not explicitly a goal of water management planning, and Water Management Plans are not designed to manage floods.

4.3.3 Land use planning and flood-prone development in the Muskoka River watershed

Floodplain mapping for most of the area was originally completed in the late 1980s and early 1990s under the Canada-Ontario Flood Damage Reduction Program (FDRP). Areas mapped include the Big East River in Huntsville and the Muskoka River, including the major lakes in the Muskoka River Watershed. This exercise identified that a considerable number of cottages and associated docks and boathouses were located within the floodplain of rivers and lakes. In the intervening time since these studies were undertaken, development in the area, particularly related to recreational properties, has increased dramatically.

Recommendations included in FDRP mapping reports from the late 1980s and early 1990s include vertical water levels and horizontal setback criteria to give potential developers a choice in floodproofing criteria: either 1) build dwellings above a minimum vertical water level described in a table; or 2) build dwellings beyond a horizontal setback, also described in a table within the report. Further, this included recommendations that no encroachment be allowed where the depth of flooding during the regulatory event would exceed 1.0 metres, and no encroachment be allowed within 20 metres of either riverbank. More explicitly, the FDRP program, which focused on the identification of high flood risk designated areas in the province, included strong policies to encourage the authority, where the zoning authority is neither provincial or federal, to impose land use restrictions that will prohibit all further projects in a designated area that are vulnerable to flood damage. Furthermore, assistance under any federal or provincial disaster assistance program shall not extend to costs or losses incurred as a result of a flood with respect to any project commenced or any moveable property placed within an area after its designation or interim designation as a flood risk area.

The District Municipality of Muskoka is in the process of updating its floodplain mapping using matched funding from the Federal National Disaster Mitigation Program. It must be emphasised that such mapping only adds value when used to inform development, with the intention of keeping people and property out of the floodplain. The available information suggests that land use planning and development approvals have not been proceeding in this fashion, particularly within the Township of Muskoka Lakes, which has seen significant numbers of boathouses constructed every year. For instance, between 2013 and 2016, the Township of Muskoka Lakes issued building permits for 267 new boathouses with a total value of construction of $46,263,584. As boathouses are situated atop the water, at or near the high-water mark, boathouses are always within the floodplain (or floodway) and add to the impacts during a high-water event.

There is significant concern that the construction of new boathouses within Muskoka Lakes are being approved without regard for the potential damage from flood and ice heaving. Designs presented to Council include first floor plans with utility rooms, games rooms, elevators and washrooms, which are much more than a basic boathouse, and there appears to be no direction or regard for incorporating floodproofing measures into the construction plans. As these structures continue to be built in harm’s way, flooding and ice damage will only increase as will costs associated with the inevitable damage from these natural phenomena. It is unreasonable to expect that water levels can be controlled within a finite range and be kept below the damage level of docks and boathouses, or other structures, when dealing with a large river system with limited means to mitigate the magnitude and extent of flooding. With a changing climate, damages to these boathouses and other infrastructure in the floodplain as a result of flooding and ice movement will continue to occur, and most likely at increased frequency. It is not a question of if these lakes and river systems will flood again, it is only a question of when.

4.3.4 Spring 2019 watershed conditions, flood mechanisms and water management activities

The Muskoka River Watershed has experienced flooding on numerous occasions in the past, including in 1976, 1980, 1985, 1998, 2008, 2013 and most recently, in 2019. Throughout the winter, MNRF staff monitor snowpack across the Muskoka River watershed to determine snow depths and snow water equivalents at which time they also evaluate soil conditions. During winter/spring 2018/2019, as in other years, the MNRF monitored the snowpack beginning in December and over the winter. In anticipation of the snowmelt and spring rainfall, the MNRF commenced the drawdown of lakes within the watershed in late fall 2018 and continued through the winter to help mitigate runoff. At this time, the MNRF took an aggressive approach, targeting the lower limit of the operating zone for the lakes.

Over the winter, the MNRF continued to monitor weather conditions. To help mitigate the anticipated spring runoff, the MNRF continued to draw down water levels at the dams. There were several rain events that caused water levels to rise over the winter period and the MNRF took measures to continue the drawdown. Lake Muskoka was drawn down to one of its lowest levels in preparation for the rain, snowmelt and warmer weather expected through April. Complaints from the public about low water levels were received in late March 2019.

By mid-March, the amount of water contained within a snowpack in the Muskoka River watershed was on average 171 millimetres, which is above average for this time of year but not as high as in some prior years. It is important to highlight that above average snow water equivalent does not mean flooding will occur and is one of many factors that water managers must consider when making decisions related to water management. By the beginning of April, the snow water equivalent in the snowpack had increased to 192 millimetres, representing 208% of average, with an average snowpack depth of 66 centimetres and depths exceeding 80 centimetres in the upper headwaters of the watershed within Algonquin Provincial Park. The snow survey conducted on April 15 showed that the snowpack depth had been reduced by approximately one-third (to 43 centimetres) with an average snow water equivalent of 134 millimetres, representing 148.5% of the historic average.

The Muskoka Airport weather station received 129.5 millimetres of precipitation in the month of April, exceeding the monthly average by 164%. Temperatures in April were lower than the long-term average for the month, affected by values considerably lower than average for a little over the first half of the month. Notable increases in maximum temperature on April 7 (12.2 degrees Celsius) and April 12 (14.5 degrees Celsius) accompanied by overnight temperatures above 0 degrees Celsius were important in increasing runoff and sustaining snowmelt and runoff generation. Water levels on Lake Muskoka began to rise on April 7 with the warmer weather and melting snow, as runoff entered the river system. (Once inflows to the lakes are more than the maximum capacity of the dams, with all logs out, water levels will rise.)

From April 10 through April 23, daily average temperatures exceeding 5 degrees Celsius and maximum temperatures ranging from 8.3 to 17.2 degrees Celsius, combined with overnight temperatures above 0 degrees Celsius, were important in sustaining runoff increases, particularly when combined with the 114 millimetres of rainfall that was recorded in the latter half of the month. The existing snowpack and associated snow water equivalents present at the middle of the month, combined with the significant rain on snow, moved considerable water volumes to rivers and lakes draining these areas. On April 17, Parry Sound District MNRF issued a Flood Watch that was upgraded to a Flood Warning on April 19, given the significant rainfall (60 to 70 millimetres), temperature increases and snowmelt that had occurred in the intervening period. Between April 7 and April 28, water levels on Lake Muskoka rose by 1.59 metres, eventually peaking on May 3. Flows in the north and south branches of the Muskoka River peaked on April 26 and April 29, experiencing the highest flows on record.

Actions taken to operate the dams in spring 2019 were consistent with the Muskoka River Water Management Plan, including specific triggers to further draw down water levels when snow water content is high. Specifically, March 15 and April 1 are the key dates identified in the plan.

4.4 Flooding in the Magnetawan River watershed

The Magnetawan River watershed is situated immediately north of the Muskoka River watershed and also experienced significant flooding in spring 2019. While measured snowpack and snow water equivalent values in the Magnetawan basin were lower than in the Muskoka watershed, they remained considerably higher than average at 260% of normal (for snow water equivalent) in the upper portion of the watershed at the beginning of April. While the Magnetawan River is less developed than the Muskoka River watershed, defined areas of the Township of Armour, the Township of Ryerson, and the Village of Burks Falls were significantly affected by flooding in the spring of 2019. The small village of Katrine, one of the areas hardest hit in the Township of Armour, is built on a floodplain at the mouth of Doe Lake, where approximately 50 homes were flooded.

4.5 Flooding in the County of Haliburton

The County of Haliburton includes the headwaters of the Trent Severn Waterway (TSW) system, which controls water flows and levels for more than 18,000 square kilometres of the Trent Severn Watersheds. The Trent River basin encompasses 218 lakes in the Haliburton Highlands region, 37 of which are directly controlled by TSW dams. There are some 600 named lakes in Haliburton County with significant waterfront property ownership, including a notable number of water-access only properties.

Watersheds represented in Haliburton County include—the Black River watershed that flows south and west to the Muskokas; the Burnt River watershed; the Gull River watershed (which encompasses the Burnt River system); and the Nogies Creek, Eels and Jack Lake watershed.

As experienced in other regions of Ontario, Haliburton County has been experiencing significant flooding, most notably in 2013, 2016, 2017 and 2019. Declarations of Emergency were declared in 2013, 2017 and 2019, with near misses in 2016 and 2018.

4.6 Flooding along Lake Ontario and the St. Lawrence River

4.6.1 Flooding conditions in 2019

Following an extended period of below average water levels from 1999 to about 2013, all Great Lake water levels were well above their average in 2019. Lake Superior, Lake St. Clair, Lake Erie and Lake Ontario all exceeded record highs in May, while Lake Huron rose to within one centimetre of the previous record in July.

Significant precipitation and snowmelt around the Lake Ontario basin, combined with record inflows from Lake Erie, set a new record for total water inflows, or supply, to Lake Ontario for the month of May, exceeding the previous record set in 2017. Total inflows in May 2019 were the second highest inflows of any month of the year dating back to 1900. Total inflows to Lake Ontario in June were the second highest on record. From January to June 2019, the six-month combined total inflows were the wettest January to June period on record due to a combination of record inflows from Lake Erie and wet conditions on and around Lake Ontario itself. Downstream of the lake, flows from the Ottawa River emptying into the lower St. Lawrence River also set a new record high during the spring freshet 2019. The flows in May 2019 exceeded the previous monthly record in 1974 by more than 1,000 cubic metres per second.

As described by the International Joint Commission’s (IJC) International Lake Ontario-St. Lawrence Board, Lake Ontario was caught between a flooding Lake Erie upstream and a flooded lower St. Lawrence River downstream. Upstream, Lake Erie water levels were exceeding historic record highs by the beginning of May. Downstream, several months of wet weather followed by heavy rains and snowmelt over late April and early May caused record Ottawa River flows, resulting in severe flooding along the Ottawa and lower St. Lawrence River. This combination of record high inflows from Lake Erie and above average precipitation across the Lake Ontario and Ottawa River basins was the main driver of Lake Ontario-St. Lawrence record high water levels in 2019. Lake Ontario water levels ultimately reached 75.92 metres in early June, exceeding the record daily peak of 75.88 metres reached previously in late May 2017.

Water levels of Lake Ontario change in response to the difference between the supply (total inflow) it receives and its outflow. While outflows are controlled by the Moses-Saunders Dam, inflows are uncontrolled. While the IJC’s Plan 2014, brought into effect in 2017, regulates flows through the Moses-Saunders Dam (outflows), inflows are uncontrolled. While increasing outflows through the Moses-Saunders dam can help reduce water levels in Lake Ontario, the amount of control this structure has over water levels in Lake Ontario is very limited, as there are physical limits to the amount of water that can be released. Larger releases, while they may reduce flooding in Lake Ontario, can have drastic impacts downstream. Increasing outflows enough to reduce flood levels in Lake Ontario by one centimetre in a week will result in increasing flood levels below the dam in Montreal by 10 centimetres.

Throughout April and May 2019, the IJC’s International Lake Ontario-St. Lawrence Board continued to regulate Lake Ontario outflows by the maximum flow limits prescribed by Plan 2014. In June, as Ottawa River flows began to moderate below their record highs, the Board rapidly increased outflows from the Moses-Saunders Dam to provide relief from shoreline flooding on Lake Ontario. Outflows were ultimately increased to the maximum sustained flow on record, as the Board was now undertaking major deviations from the plan to provide relief from shoreline flooding on Lake Ontario. These outflows reached 10,400 cubic metres per second, equivalent to the record high outflows released for several weeks in the summer of 2017. These major deviations of flow are significant departures from the outflows prescribed in Plan 2014; however, the IJC was doing so in response to extremely high Lake Ontario levels and in accordance with IJC policies. In Ontario, flooding occurred around Lake Erie, Lake Ontario and the upper St. Lawrence River, especially during periods of active weather.

From media reports, Prince Edward County, the Bay of Quinte, Toronto Island, Municipality of Clarington, Brighton, and the Thousand Islands shoreline area in the upper river, among other areas, experienced flooding.

4.6.2 Comparison to flooding conditions in 2017

The causes of record high Lake Ontario water levels in 2017 and regulation of outflows under Plan 2014 were studied and reported on by the Board (see the IJC report titled: “Observed Conditions and Regulated Outflows in 2017,” May 25, 2018, PDF). The Board attributed the extreme high levels mainly to record precipitation received across the Lake Ontario-St. Lawrence River basin, noting that wet weather was also experienced upstream in the Lake Erie watershed. Lake Ontario water levels rose rapidly, setting record highs by the end of May. In response, in all but three weeks of the year, outflows from the lake were determined by either the maximum flow limits set by Plan 2014 or by deviations from Plan 2014. The Board concluded that Plan 2014 did not cause the high levels in 2017 or contribute to them in any significant way.

Flooding in 2017, among other impacts, were reported on by the IJC’s Great Lakes-St. Lawrence River Adaptive Management Committee as part of their ongoing evaluation of the IJC’s regulation of lake outflows in the Great Lakes (see the IJC report titled: “Summary of 2017 Great Lakes Basin Conditions and Water Level Impacts to Support Ongoing Regulation Plan Evaluation,” November 13, 2018, PDF). The Committee evaluated the impacts on multiple interests, including flooding, from a variety of sources. They noted, however, that much of the quantitative economic and environmental data was not available at the time of reporting.

Impacts to coastal properties in 2017 were reported as widespread, with reports of flooded homes, roads, driveways, trails, lawns, emergency response, and extensive sandbagging efforts to protect houses and properties. In Ontario, flooding of residential property and buildings along the Lake Ontario shoreline was observed with particularly hard-hit areas including portions of Toronto Island, Clarington, Brighton, and Prince Edward County. On the upper St. Lawrence River, shoreline flooding was observed particularly in the Thousand Islands area. From the IJC’s report, Figure 5-25 highlights the percent of shoreline survey respondents that indicated flooding impacts. In Ontario, along the lake shoreline, a local State of Emergency was declared for a portion of the Municipality of Clarington shoreline as well as all of Prince Edward County. The Mohawks of the Bay of Quinte also declared an emergency for their territory in response to high water levels.

4.7 Flooding along Lake Erie and Lake St. Clair shorelines

Since March 2019, water levels in Lake Erie and Lake St. Clair have remained above locally determined Flood Watch thresholds, with monthly mean lake levels in Lake Erie and Lake St. Clair reaching all time highs in July 2019. Lake Erie is approximately 84 centimetres above long-term monthly average lake levels (or 13 centimetres above previous highs in 1986 and 35 centimetres higher than July 2018). Lake St. Clair is approximately 86 centimetres above long-term monthly average lake levels. This is 10 centimetres above previous 1986 highs and 35 centimetres higher than July 2018.

These record levels have resulted in the Windsor Essex region being under an Extended Flood Watch for more than six months. Similarly, the Lower Thames Valley Conservation Authority has issued 50 flood bulletins (Watershed Conditions Statements/Flood Watches/Flood Warnings) warning shoreline residents of potential flood events so far this year (2019).

Portions of Essex Region, in the Southeast Leamington area between Hillman Marsh and Point Pelee, lie behind earthen dikes built in the late 1800s that have been “spot-repaired” sporadically over time as emergencies required. Approximately 400 homes and 2,100 hectares of farmland are, in some instances, 3 to 3.35 metres below Lake Erie water levels.

While lake levels are currently undergoing seasonal decline, they remain above previous 1986 record levels, meaning these declines have not resulted in any reduction in the level of flood/erosion risk in the region. Making matters worse, fall rain events, wind and winter ice is expected to result in further flooding and erosion.

4.7.1 2019 flooding

Flooding and erosion along the Lake Erie shoreline resulting from high water levels has had, and in most cases continues to have, significant impacts on residents, businesses and infrastructure.

Three sections of roads have been closed along Lake Erie in Chatham-Kent (total length of road closed is 9.6 kilometres). Similarly, LaSalle and Kingsville have closed sections of road due to high water levels.

High water levels have closed marinas in Windsor and Lakeshore, closed waterfront trails in Windsor, and closed sections of the Holiday Beach Conservation Area and Tremblay Beach Conservation Area.

Residents along the Lake Erie Shoreline between Point Pelee National Park and the Town of Wheatley experienced 10 flood events between March 2019 and August 2019.

This area was developed on a naturally eroding clay shoreline. Therefore, even without the existing development, they would continue to erode. Under the current condition (high lake level), wave action is causing erosion at the shore. Under low lake levels, the erosion is happening on the clay bottom as the waves attack the surf zone.

Shoreline protection structures (sheet pile walls and armour stone breakwalls/revetments) have been used in some areas to try and slow down erosion rates in front of the shoreline protection. However, these structures do not stop erosion of the lake bottom in front of the structures, which results in a deeper and deeper nearshore lake bottom slope. This has allowed larger waves and waves with greater energy to impact the shoreline. In the end, the shoreline protection constructed to reduce the hazard is progressively making it worse. As a result, the flood hazards are getting worse with each passing storm.

Numerous homes and properties have suffered and continue to suffer from flooding with limited access into and out of the community. Some of these areas are not municipally serviced and are sitting in water, which results in failing septic systems, mould and related health and safety and structural concerns, in addition to the physical and mental health effects associated with these conditions.

Current high water conditions have caused significant damage across the shoreline. High waters have also prevented many repairs leaving existing development exposed to both erosion and flood hazards.

With high water levels, lake waves have created a 100+ metre breach in Hillman Marsh Barrier Beach, posing significant risk to inland dikes, which are now exposed to direct wave attack. The inland dikes are now holding back high water levels and over an extended period of time, which they were not constructed to withstand. Inland communities protected by the flood protection dike are also at risk of flooding under this condition.

The Marentette breakwater breached and exposed the interior dikes to open lake wave conditions, which this system was not designed to withstand. Some nominal repairs have proceeded through the provisions of the Drainage Act, but these repairs are essentially a temporary fix.

Large blocks of peat continue to be eroded out of the marsh areas in Leamington and Rondeau Bay, with the most recent evidence of this occurring in late summer 2019.

Due to sediment balance issues—a result of shoreline hardening—the barrier beach that forms the southwestern barrier within Rondeau Bay has now been removed for approximately 100 metres. This allows Lake Erie waves to enter Rondeau Bay, putting the low-lying community of Shrewsbury and 470 homes at risk. Continuing and long-term future flooding is anticipated based on present conditions and climate change forecasts.

A State of Emergency was declared along Erie Shore Drive on August 27, 2019, due to significant flooding caused by high winds (peaked at 35 kilometres per hour) and rain. There are 123 homes at risk along Erie Shore Drive, with 35% being permanent residents. The event resulted in significant damage to 12 homes, the roadway, supporting slope, drain and three breakwalls.

A voluntary evacuation took place in a localized area of Erie Shore Drive, comprising 50 homes. Electricity and natural gas services were shut off where there was a safety risk. The water pressure in the water main (under Erie Shore Drive) that provides drinking water to the community of Erieau was reduced due to fears of failure. In the short time period during and around the event, the municipality shored up the roadway and drainage works.

4.7.2 Erosion

While the flood issues are significant, they cannot be isolated from erosion on the Great Lakes. Many of the areas with the highest flood risks also feature a significant long-term erosion rate. This includes Marentette to Wheatley and Erie Shore Drive and many high bluff areas. In keeping with the 1990s Technical Guide, new development has been allowed to be located as close as possible to shoreline hazards, once the landward limit of the erosion hazard is applied. However, due to climate change, the risk profile is changing. Reductions in lake ice have already and will continue to expose the shorelines to higher amounts of wave energy/erosion. Landowners who thought they were 100 years away from erosion hazards might now only be 50 years away, and significant lengths of municipal infrastructure (roads and utilities) are at risk of failure.

Shoreline erosion on Pelee Island is particularly concerning because it has washed out sections of roadway that provide ingress/egress for residents. Bluff failures have occurred in 2019 related to the erosive effects of the high waters. These failures have impacted existing development with at least one home within 1.5 metres from the precipice. These types of failures are expected soon even as water recedes in the region, as the erosive effects have already occurred at the toe of these bluffs.

The Municipality of Chatham-Kent has closed a significant portion of Talbot Trail (West) (length of road closed is 3.8 kilometres). The road was closed due to erosion on the south side of the road (rotational failure). The solution will require a high level of investment estimated at $640 million up front and $12 million per year in maintenance costs.

4.7.3 Recent severe rain events

Risks of flooding in southwestern Ontario are not only a result of high lake levels.

In September 2016, Windsor, Tecumseh and Lakeshore were impacted by a severe and isolated rain event that tracked from the northwest, dumping over 200 millimetres of rainfall in six hours, causing flooding in thousands of urban area basements.

In August 2017, a similar system tracked out of the southwest that formed two distinct storms dumped 146 millimetres of rainfall in less than three hours, which followed a 100-millimetre rainfall earlier. The storm total of 246 millimetres in less than six hours surpasses all accepted design standards. This event exceeded $300 million in insurable losses.

Because both Essex Region and Lower Thames Valley are low lying, high lake/river levels mean that water from stormwater and drainage systems has no place to go.

For example, 30,000 residents living in parts of the Town of Lakeshore, the Town of Tecumseh and the City of Windsor are fully urbanised centres that exist within Lake St. Clair’s historic flood extent. Pumping systems that provide for drainage are now regularly overcome by rainfalls that exceed acceptable design standards. These areas have protection systems to prevent lake flooding (either berms or pumping schemes); however, record lake level elevations are challenging the existing protection systems. Any measurable rainfall, such as those events that happened in 2016 and 2017, will cause significant flooding, especially in the urban centres.

4.8 Other notable recent flooding events

While flooding in spring 2019 resulted in significant damages to many parts of Ontario, several other recent flood events were also brought to my attention during the review. I’ve noted some of these other recent flood events in this section for the purpose of demonstrating that the flooding that occurred in 2019 does not appear to be an isolated event. Again, this section is not meant to provide an exhaustive account of notable flooding events in Ontario’s recent history— an account of that nature was outside the scope of my assignment. However, I felt it important to include some of these events to help demonstrate that flooding is a common occurrence in Ontario and something that can occur at any time of the year.

4.8.1 Recent flood events in the City of Toronto

Over 2.7 million people live in the City of Toronto with nearly six million people living in the Greater Toronto Area (GTA). While 2019 was not a significant year for flooding in Toronto when compared to other areas, significant events and associated impacts have occurred there in the past and are worth noting as part of this report.

With drainage areas ranging from 38 square kilometres for the Carruthers Creek to 900 square kilometres for the Humber River, watersheds within the City of Toronto tend to be relatively small. These small drainage areas, with short stream lengths and highly urbanized (impervious) surfaces, leave little lead time between rainfall and flood impacts. Year-round flood threats include ice jams in the winter, snowmelt in spring, unpredictable thunderstorms in the summer, and hurricane remnants in the fall.

While land use planning has effectively reduced risk in greenfield areas, many neighbourhoods were historically settled near rivers prior to floodplain management. Examples include old downtowns in Brampton, Bolton, Unionville and Stouffville. There are 41 Flood Vulnerable Clusters (areas where there is a high concentration of buildings in the floodplain) within the jurisdictional area managed by the Toronto and Region Conservation Authority (TRCA) alone.

The most severe flooding on record in Ontario occurred in October 1954, when Hurricane Hazel passed over the Toronto area. Eighty-one lives were lost and damages were estimated at $25 million (in 1954 dollars). TRCA’s recent Flood Risk Assessment study estimates that if Hurricane Hazel were to occur today, it could result in almost $3 billion in property damages, business disruption and population displacement. While Hurricane Hazel-type storms remain a possibility that must be prepared for, recent events have shown that significant damages and disruption can also occur from significantly smaller events.

On July 8, 2013, a severe thunderstorm dropped more than 120 millimetres of rain over parts of the GTA during the afternoon rush hour, causing roughly $1 billion in insurable losses and stranding thousands of commuters, including over 1,400 passengers who needed to be rescued from a GO train marooned in floodwaters from the nearby Don River.

In the spring of 2017, water levels in Lake Ontario reached levels higher than ever recorded. The impact was significant on Toronto Islands, home to over 800 residents, almost 30 businesses and two schools. The islands’ parks experienced significant shoreline erosion, damage and debris accumulation. Direct and indirect damages to the City of Toronto due to the closing of Toronto Island Park were estimated to be $8 million for the 2017 event. In 2019, water levels rose even higher than in 2017, though preventative measures helped to keep the islands open. In 2019, the newly reached record levels were maintained for nearly four weeks. A full accounting of damages from the 2019 levels is still underway.

On August 8, 2018, a highly localized “ninja” storm dumped over 100 millimetres of rain in less than two hours. This storm was not forecast and was so localized that its track evaded detection by TRCA’s real-time precipitation gauges. Flows in Black Creek in the Rockcliffe neighbourhood, a highly flood vulnerable area, rose over two metres in 75 minutes, spilling into nearby properties and stranding two men in an elevator when they attempted to retrieve their vehicles from underground parking. They were rescued by first responders just in time.

On March 15, 2019, as late winter rainfall and snowmelt raised flows in rivers, an ice jam developed in the Town of Caledon, spilling into the Bolton Core neighbourhood. As floodwaters rose through the evening, over 80 homes were evacuated, of which 30 experienced direct flood impacts. The jammed ice had to be manually removed using excavators.

4.8.2 Recent flood events in the Grand River watershed

The Grand River lies at the heart of one of the fastest growing regions in Ontario; however, the watershed faces challenges brought on by intensive population growth, extensive agriculture and climate change. Warmer air and water temperatures, bigger rainstorms and dramatic changes in weather patterns pose new challenges in managing floods, improving water quality and securing water supplies for municipalities, farmers, industry and the natural environment.

Flooding in the Grand River watershed has many causes including:

  • Rapid snowmelt over a short period of time;
  • Combined rainfall and snowmelt;
  • Localized ice jam flooding;
  • Moderate rainfall on saturated or frozen ground;
  • Extreme localized rain (severe cellular storms, convective thunderstorms or lake breeze events);
  • Severe widespread rain (tropical storm remnants or large low pressure systems); and
  • Lake Erie surge (shoreline).

While there is seasonality associated with certain types of flooding in the watershed, the risk of riverine flooding remains relatively consistent throughout the year. Compounding challenges associated with riverine flooding, Lake Erie presents additional challenges through lake surge flooding, shoreline erosion and the influence of lake breezes (wind blowing from the water to the shore).

Large floods tend to happen on a cyclical basis in the watershed and trends show they occur in clusters. Data indicates there were clusters of large floods in the late 1940s, mid-1970s, early 2000s, late 2000s, and more recently 2017 and 2018.

In June of 2017, an unforecasted rainfall event caused significant flooding in the communities of Grand Valley, Drayton, West Montrose, Conestogo Cambridge-Preston and Glen Morris. More than 125 millimetres of rain fell across the northern portion of the watershed in the span of a few hours, resulting in the highest flows seen in the Grand River through Cambridge since the May 1974 benchmark flood event. Reports (unconfirmed) of several million dollars in damage resulted from this event.

The highest single-day rainfall event ever recorded in the Grand River watershed occurred in February 2018 and resulted in near floods of record that were further complicated by major ice jams in multiple communities. More than 5,000 residents in Brantford were evacuated due to overtopping of the dike system due to ice jams in that community. Dams owned and managed by the Grand River Conservation Authority helped reduce flows in the order of 40 to 50% downstream of the major reservoirs; however, significant transportation disruptions (road/bridge closures) still occurred due to ice impact. Municipal flood damages in Cambridge and Brantford associated with this event were reported to be in excess of $5 million. Damage incurred by individual property owners and businesses is unknown.

Snowmelt and ice jams in February 2019 resulted in the second highest community ice jam (West Montrose) identified in records dating back to 1967. This event was only exceeded by an event in February 1981.