Key Study Components
The following studies will be conducted to identify the preferred alternative that will meet the project objective:
Aquatic Habitat Natural Heritage Study
The TRCA Coastal Ecology Unit has undertaken a study to determine the health of the aquatic ecosystem near the mouth of the Don River. The study developed inventories of the composition of waterfowl, fish and benthic invertebrate communities, habitat structure, and water quality. From this study, the potential environmental effects of the proposed naturalization and flood control options on the existing aquatic ecosystem can be evaluated, and recommendations can be developed to mitigate these effects or to include habitat improvement measures. In February 2007, the Coastal Ecology Unit prepared a Fish Community Study Update which will be included in this study.
Terrestrial Natural Heritage Study
The TRCA Terrestrial Natural Heritage Unit has conducted a study to determine the health of the terrestrial ecosystem within and adjacent to the project area. Inventories of vegetation and fauna (eg. birds, reptiles, amphibians, and mammals) have been compiled for species that occupy the area. The overall health of the terrestrial ecosystem can be derived from these inventories as a measure of the relative abundance of the species within the area, our understanding of their relative sensitivity to urban and other disturbed environments, and the physical features in which these species have been observed to occupy. Each naturalization and flood control alternative will undergo an assessment of the potential effects it will have on the existing terrestrial vegetation and fauna communities, and recommendations will be made to improve the terrestrial habitat conditions.
Cultural Heritage Study
The TRCA Cultural Heritage Unit has conducted a study to document the archaeological and historical record of the project area. Built or historical heritage resources within the area have been identified, and recommendations have been prepared to preserve and/or commemorate these resources as part of the flood control and naturalization options.
Additional studies may be required in order to select the preferred alternative for the EA.
The consulting team led by Gartner Lee Limited has been retained as part of their overall contract, to conduct the following preliminary studies:
Hydraulic Study
The consultant team will conduct a study to model the extent and severity of flooding within the project area over a range of discharges, up to and including the estimated discharge of the Don River if a storm the size of Hurricane Hazel was to occur over the Don watershed. The area of land inundated by water associated with such a storm is defined as being within the Regulatory Floodplain. Additional model runs will then determine how the various alternatives impact the extent and severity of flooding within and adjacent to the project area over the same range of discharges. Anticipated long-term climate change impacts on flow conveyance through the project area will also be examined.
Socioeconomic Study
The socioeconomic study will examine the existing and future socioeconomic conditions for the project area, and to assess whether the various naturalization and flood control alternatives are compatible with existing land uses and plans. The objectives of the socioeconomic study are to identify existing land use and socioeconomic patterns within the study area, and determine what impacts would occur to these components if the regulatory storm event were to occur in the Don watershed in the absence of flood protection. Furthermore, the study will assess how the various options will mitigate flood risk, and analyze how the various naturalization alternatives will influence land use, the local economy, and integration with services and infrastructure.
Rail Corridor Impact Assessment
This study will examine how incremental changes to exposure of flooding events and naturalization activities will impact the rail corridor. Key questions will include whether the rail corridor and spur lines will be located within or outside of the floodplain, and how rail infrastructure and activities will be impacted by any potential changes in flood frequency and magnitude within the area.
Any impacts to a rail corridor associated with an alternative will require review and approval from the rail corridor owner. Further, as GO Transit, CN and Toronto Terminals Railway will be directly involved with the TRCA as stakeholders affected by this work, the consultant team, under the direction of the TRCA, will be required to regularly liaise and coordinate with these and other affected rail corridor users.
West Nile Virus Risk Assessment
The public health study component will largely examine whether the various naturalization and flood control alternatives will increase breeding habitat conditions for Culex pipiens and Culex restuans. These are the two species of mosquitos identified as being the predominant transmitter of the West Nile Virus from birds to humans. Given this public health concern, it will be essential that the preferred alternative does not increase the public risk of exposure to West Nile Virus. Each design alternative will be assessed and evaluated for potential risks, as well as for design considerations that will reduce the risk. The effects of air quality and noise will also be examined.
Sediment Transport & Deposition
Since its construction between 1914 and 1922, the Keating Channel has been subject to heavy sediment loads, requiring regular dredging to maintain sufficient depths to allow for and maintain shipping activities at the mouth of the Don River. Between 1950 and 1970, widespread development throughout the Don Watershed and the construction of the Don Valley Parkway increased sedimentation rates by up to four times that of the pre-was era. After 1970, decreases in the number of new watershed disturbances and improved sediment control structures likely contributed to the decline in sedimentation in the Keating Channel to levels similar to the pre-war era.
A reduction in shipping activities within the Keating Channel, combined with restrictions on the open water disposal of dredgate imposed by the International Joint Commission (IJC) in 1974, resulted in a cessation of dredging in the Keating Channel. In the following five to six years, the Keating channel filled with sediment and debris to the point where it became visible under all but high lake levels, resulting in increased flood risk along the lower Don. By 1983, it was estimated that 300,000 m3 of sediment had accumulated in the Keating Channel. Prior to approval of the Keating Channel Environmental Assessment (EA), emergency measures were taken to remove 150,000 m3 of this material to reduce the flood hazard. Annual dredging and the deposit of dredgate in containment cells on the Leslie Street Spit was initiated in 1987 as part of the Keating Channel EA. From 1987 to 1991, large-scale dredging activities were conducted to remove new and older sediment deposits from the channel. Since 1992, regular dredging has been conducted to remove new sediment deposits in order to maintain the design flood risk stipulated in the Keating Channel EA. Sediment deposition rates in the Keating Channel are now similar in magnitude to those prior to the pre-war development boom at approximately 35,000 m3 per year.
A major component of this EA process will be to ensure that the preferred alternative is able to address the long-term management issue of heavy sediment loads to ensure that any naturalization and flood protection activities will not be undermined.
Groundwater and Soil Contamination Characterization Study
Toronto Waterfront Revitalization Corporation (TWRC) with the support of the City of Toronto and Toronto Economic Development Corporation (TEDCO) will undertake additional studies to characterize the existing groundwater and soil quality conditions within the project area. Information arising from this study will be used in the Don Mouth Naturalization and Port Lands Flood Protection EA process to identify potential sources of contaminated soils and groundwater within the area and their associated health hazards, and to determine whether the soils are structurally or environmentally sound for use in the various flood control options. Recommendations will be devised from this study to treat and/or dispose of any such contaminated soils, while ensuring that adjacent sources of untreated soils and groundwater are not able to re-contaminate the project area following the construction of the flood control structures.
