The Toronto Islands Flood Characterization and Risk Assessment Project was conducted to assist the City of Toronto and Toronto and Region Conservation Authority (TRCA) to respond to and plan for future flood conditions.
PLEASE NOTE: This page has been revised to include updated analyses using 2019 water levels. View addendum (Date: October 3, 2019)
Background
In the spring of 2017, water levels in Lake Ontario reached levels higher than had been measured since record keeping began in 1918.
The effect of the high water levels and associated flooding was significant on the Toronto Islands, where more than 800 residents, almost 30 businesses, and two schools were forced to adapt to rising waters and service disruptions. The island parks also experienced significant shoreline erosion, damage and debris accumulation.
In response to the 2017 flood conditions, TRCA and the City of Toronto deployed more than 45,000 sandbags, 1,000 metre bags, and more than a dozen industrial pumps to mitigate the effects of the rising water.
These assets were positioned throughout the islands, leveraging GIS maps with LiDAR imagery that identified areas and infrastructure that were threatened by the flood conditions. Mapping also identified the most strategic and effective locations to deploy the industrial pumps.
In 2018, TRCA worked with the City of Toronto to repair damaged areas and install naturalized berms and sumps to protect strategic areas from potential future flooding. The large metre bags were removed but the sand was left in place, forming berms that were planted with native grasses. Most of the sand from the smaller sandbags was deposited in a central area for future use.
The installation of 10 sumps was completed to collect surface flooding and drain low-lying and saturated areas with a series of weeper tiles. The City also made significant alterations to the ferry docks, allowing for safe passenger embarkation and debarkation for a wider range of lake levels.
About the Project
In 2018, TRCA in collaboration with the City of Toronto undertook the Toronto Islands Flood Characterization and Risk Assessment Project.
As of June 2019, Lake Ontario water levels have exceeded the previous records of 2017. While the Toronto Islands Flood Characterization and Risk Assessment project is based on the 2017 event, the utility of this project has already been demonstrated during the current high Lake Ontario water level event.
The project provides TRCA and the City of Toronto with an improved understanding of flood scenarios and community and infrastructure vulnerabilities and risks.
It also provides direction on future flood mitigation investments, where TRCA’s experience in implementing shoreline and flood protection measures throughout the Toronto waterfront areas could be leveraged in the delivery of flood protection measures.
View the Study
Flood Characterization Report
This report describes the conditions that led to the 2017 Lake Ontario high water levels; proposes updated return period water levels in Toronto; evaluates the impacts of Plan 2014 (the regulation for the St. Lawrence Seaway and Lake Ontario) to regulate water levels on Lake Ontario; and reviews recent climate change research related to future Lake Ontario water levels.
Flood Risk Assessment Report
This study was commissioned to inform TRCA and the City of Toronto in identifying and understanding risk to property and infrastructure on the Toronto Islands. It quantifies the financial costs and other impacts to Toronto Island residents, businesses, and the City of Toronto for the different return period flood events under existing conditions.
Development of Flood Maps
A series of Toronto Islands flood depth maps were developed, indicating areas of inundation with varying water levels.
Flood Mitigation Alternatives Report
This report identifies flood mitigation alternatives for the areas most affected by the 2017 flood. It presents the conceptual designs, estimated quantities and high-level budgetary cost estimates for the flood mitigation alternatives for six key areas.
Updated Analyses Using 2019 Water Levels
TRCA’s consultant completed an addendum to the reports, to estimate the return period lake levels taking into account the 2019 water levels and also to re-calculate the annualized damage estimates.