Existing Conditions: Habitat

Aquatic habitats along the Toronto waterfront are the product of various combinations of physical conditions and processes.The three major controlling influences on the location, function, and attributes of shoreline habitats are: NEARSHORE GEOLOGY, METEOROLOGICAL CONDITIONS and CULTURAL INFLUENCES.


NEARSHORE GEOLOGY

  1. Post-Glacial Shorelines
  2. Western Lake Ontario Bathymetry
  3. Wave Zone Areas
  4. Toronto Waterfront Substrates and Features
  5. Shoreline Profiles


1. Post-Glacial Shorelines

The modern shoreline of Lake Ontario is situated between two post-glacial abandoned shorelines. The landward abandoned shoreline originally marked the edge of the higher post-glacial Lake Iroquois, resulting in a stranded shoreline bluff and abundant beach material along the present day tablelands.

The Lake Iroquois shoreline influences the morphology of modern streams and focusses the mid-reach recharge of ground water sources. However it has a minor effect on current aquatic habitats.

post glacial shorelines mapAn off-shore abandoned shoreline created by the lower post-glacial Admiralty Lake has a much greater effect on today’s shoreline.

The former Admiralty Lake shoreline has left a variety of submerged features including a prominent off-shore bluff known as the Toronto Scarp that runs parallel to the Toronto Islands and Scarborough shoreline. Admiralty Lake was also the source of relict sand and gravel deposits that can still be found in deep off-shore waters.

The most significant surficial geological features that affect and determine current shoreline conditions are found between the abandoned Admiralty Lake shore and the modern shoreline. Most current and historic habitats were created in this inundated area.

For example, historically, the dynamic movement of littoral material established the peninsula and lagoons of Toronto Bay. The bulk of this material was supplied from shoreline erosion of the significant deposits of sands found in the Scarborough Bluffs and re-worked beach deposits made available during rising water levels.

In addition, the Toronto Scarp at the shoreline of the former Admiralty Lake is an important area of congregation for Salmonid fish.

 

2. Western Lake Ontario Bathymetry

Lake Ontario bathymetry mapThe bathymetry of western Lake Ontario displays a number of features that affect aquatic habitats. Lake Ontario is a deep, cold, oligotrophic (nutrient-poor) lake with relatively steep shorelines, particularly on the northern shore. Shale bedrock is apparent along the shorelines of Niagara Region, Halton Region, Mississauga and Etobicoke. A major depositional zone exists at the Hamilton lakehead. There is an underwater bluff, similar to the Scarborough Bluffs, off the Niagara Region shoreline.

The Toronto area shoreline can be described in five zones:

  1. Etobicoke Shale Outcrop
  2. Humber Bay Depositional Area
  3. Toronto Scarp
  4. Scarborough Sand Plains
  5. Scarborough Boulder-Laden Till
Etobicoke shale outcrop map 1. Etobicoke Shale Outcrop
Along the western sector a thin till layer that originally covered the bedrock has been scoured off by glacial action leaving a prominent area of bedrock substrate that extends from the mouth of Mimico Creek westward to Burlington. This bedrock forms a convex shoreline profile consisting predominantly of broken shale boulders on top of bedrock extending into deep water.
Humber Bay depositional area map 2. Humber Bay Depositional Area
Along the western sector a thin till layer that originally covered the bedrock has been scoured off by glacial action leaving a prominent area of bedrock substrate that extends from the mouth of Mimico Creek westward to Burlington. This bedrock forms a convex shoreline profile consisting predominantly of broken shale boulders on top of bedrock extending into deep water.
map of Toronto Scarp 3. Toronto Scarp
The Toronto Scarp represents the former shoreline of Admiralty Lake about 5 km from the existing Lake Ontario shoreline. It is a prominent underwater bluff comprised of extensive sand deposits. The water depth increases abruptly at the edge of the shelf from about 20m to approximately 60m.
map of Scarborough Sand Plains 4. Scarborough Sand Plains
An extensive underwater sand plain occurs from the south shore of the Islands to the Toronto scarp and eastward to Bluffers Park. This material is a very thick deposit of sand that is most likely a glacial relict of flooded beaches and eroded material that originated from an interglacial river deposit of deltaic sands derived from the cathedral section of the Scarborough Bluffs. Within these sand substrates there are small pockets of gravels and cobbles, especially in the nearshore areas just west of Bluffers Park. This section of sand-dominated substrates displays a prominent concave shoreline profile .
map of Scarborough Till Scarborough Boulder-laden Till
From the east side of Bluffers Park to the East Point area there is a transition zone from sand to cobble, gravels and boulders. This coarser material originated from the high boulder content of adjacent tills that were eroded from the shore and re-worked as a boulder pavement. The headland created at East Point is a direct result of the high boulder and cobble content of the till, creating an area resistant to erosion. The boulder pavement provides an excellent example of unconsolidated material forming a convex shoreline profile. The extensive quantity of nearshore gravels is thought to provide a high degree of shoreline protection by attenuating waves and providing a dynamic equilibrium between erosion and accretion.

 

3. Wave Zone Areas

barrier beach at mouth of Highland CreekAlong the wave zone area bedload sediments from the major rivers have surcharged the shoreline with sand and helped to establish the barrier beaches associated with local coastal wetlands at the mouths of the Rouge and Highland Rivers.

The boulder-laden till also loaded the wave zone areas with a vast quantity of aggregates. Approximately 1 million cubic metres of stone were historically removed by stone-hooking for use in construction activities.

 

4. Toronto Waterfront Substrates and Features

In summary, as shown below, the key substrates along the Toronto waterfront are shale bedrock, sand, muds and clay, and boulder, cobble and gravel.

map of Toronto Waterfront substrates

 

5. Shoreline Profiles

The shoreline profiles vary considerably along the waterfront.

For example, in the vicinity of the Toronto islands (section 1 and section 2) the Toronto Scarp appears as a precipitous drop that varies from 15 – 60 metres to the deep lake, with the relatively shallow waters of Toronto Bay being sheltered by the islands.

In section 3, there is a gradual slope into the Lake from the base of the Leslie Street Spit, followed by a deep bluff formed by the Toronto Scarp.

In section 4, the effects of the Toronto Scarp have almost disappeared, and in section 5 there is the gradually sloping convex shoreline of the Scarborough boulder till.

map of Toronto Waterfront shoreline profiles

Toronto shoreline profile cross-section Toronto shoreline profile cross-section
Toronto shoreline profile cross-section Toronto shoreline profile cross-section
Toronto shoreline profile cross-section


METEOROLOGICAL CONDITIONS

Meteorological conditions — wind, nearshore wave climate, regional climatic conditions, solar heating, and thermal characteristics — have considerable influence on shoreline conditions and aquatic habitats.

    1. Wind and Waves
    2. Littoral Transport
    3. Thermal Conditions
    4. Hypolimnetic Upwellings
    5. Water Levels

 

1. Wind and Waves

stormy conditions on Toronto WaterfrontWinds, in combination with over-water fetch lengths, determine wave conditions across the Toronto waterfront.

A high percentage of lake currents and most nearshore waves are induced by wind conditions. Winds are responsible for the lake-wide circulation patterns that create the west-to-east ambient currents throughout the Toronto Waterfront.

Although prevailing winds are generally from the west, the much longer eastern fetches produce far more wave energy coming from the east.

In the eastern sector of the Toronto Waterfront the predominant eastern wave energy is partially balanced by wave energy from the southwest. By contrast, in the western sector the southwest waves provide less energy because of the much shorter fetches to the southwest.

 

2. Littoral Transport

Balances in the wave energy are important because breaking waves are the driving force that moves sediment and other materials along the shore. This littoral transport is the main mechanism that established the Toronto Islands. It also sorted and piled a variety of aggregates in the wave zone and moved historic and recent deltaic sediments to create our beaches.

Sediment eroded from the north shore of Lake Ontario was transported into the Toronto Islands because the net wave energy is directed westward. Changes in net wave energy directions, which can be caused by shoreline features, frequently define the boundaries of littoral cells.

Littoral cells are sections of the shoreline defined so that no input or outflow of sediments take place across their boundaries (see image above). They are important shoreline features because actions taken on the shoreline can have consequences anywhere within their littoral cell but seldom effect the shoreline in other cells.

One of the interesting aspects of littoral transport along the Toronto waterfront is that the potential for material to be moved along the shoreline is limited by sediment supply, as shown in the Potential and Actual Sediment Transport maps below.

map of potential littoral transport map of actual littoral transport
Potential Sediment Transport Map Actual Sediment Transport Map

The volume of littoral drift produced through erosion of the shoreline is less than could actually be carried by the available wave energy. For example, between Bluffers Park and East Point the available wave energy could transport 120,000 cubic metres of sand per year but now only 15,000 cubic metres per year, on average, is produced through erosion.

Historically, about 45,000 cubic metres were produced annually, before significant artificial armouring of the shoreline began in the 1970s. In contrast, stonehooking between 1850 and 1910 increased sand supply through higher toe erosion by removing the stones that naturally armoured the lakebed.

 

3. Thermal Conditions

Daily and seasonal weather conditions, especially solar heating, play a critical role in the ecology of Lake Ontario. The lake waters stratify according to temperature in the summer and winter. The amount and intensity of solar heating defines the scope and extent of this thermal stratification and the subsequent aquatic habitat conditions.

Two additional temperature-induced conditions that dramatically affect nearshore habitats are the formation of a thermal bar and hypolimnetic upwellings.

thermal conditions diagramEarly in the spring the nearshore waters of the lake heat up and form a band of warm water that is held in place by a thermal bar consisting of colder, denser off-shore water (water is at its maximum density at 4 degrees Celsius; represented by the light blue band on the diagram).

The warmer water (shown in yellow and red) builds in depth and concentrates warm water discharges from rivers, creeks and storm drains within the nearshore area. This phenomenon typically lasts until mid June, and surcharges the nearshore area with warm, nutrient-rich water.

The early season influx of nutrients has a profound effect on aquatic life by promoting primary production and accelerating the establishment of warm, eutrophic conditions along the shoreline of the oligotrophic Lake Ontario.

The thermal bar dissipates into full stratification in the early summer and under the appropriate wind conditions is vulnerable to hypolimnetic upwellings of deep cold lake water.

 

4. Hypolimnetic Upwelling

upwelling chartThe prevailing north-west winds and the location of the Toronto waterfront on the north-west coast of Lake Ontario make this area vulnerable to the displacement of relatively warm surface water by cold hypolimnetic upwellings. Dramatic temperature changes occur quickly during an upwelling event and can be lethal to fish.

Upwellings have the opposite affect of the thermal bar in that they can reduce productivity, limit the growth and survival of aquatic organisms, and disperse offshore the warmer water associated with river discharges and point sources.

Alewife, a relatively new species to Lake Ontario, has not adapted to hypolimnetic upwellings and is prone to massive die-off each spring because of the dramatic change in water temperatures.

 

5. Water Levels

As the last in the chain of Great Lakes, the amount of water flowing into Lake Ontario, and hence the water levels, are greatly influenced by precipitation and evaporation throughout the Great Lakes Basin. Water level fluctuations, both seasonally and from year to year, are a normal occurrence in the Great Lakes.

Over the decades, historical records show that Great Lakes water levels tend to follow an irregular cyclical pattern, as shown below. The pattern of annual fluctuations has been dampened since lake-wide regulation of water levels was introduced in the Great Lakes in 1958.

Lake Ontario water levels diagram

Fluctuating water levels play an important role in the development and maintenance of diverse shoreline ecosystems. They affect currents, wave action, turbidity, pH, temperature and nutrients. Wetland plants and animals are generally adapted to these changes and in many cases depend on them for certain functions (such as germination of seeds from sediments exposed by low water levels).

The Great Lakes system experienced extremely high water levels in the 1870s, early 1950s, early 1970s, mid-1980s and mid-1990s. Extremely low water levels were experienced in the late 1920s, mid-1930s, mid-1960s, and in the late 1990s leading up to today.

The recent decline in water levels is due mostly to evaporation during the warmer-than-usual temperatures of the past three years, a series of mild winters, and below-average snowpack in the Lake Superior basin.


CULTURAL INFLUENCES

Prior to settlement of the Toronto area, the shoreline was very different from the one we know today.

The rivers and creeks supplied clear, cool water and provided habitats for river-spawning fish such as salmon. Nutrient-rich estuaries supported wetlands teeming with wildlife. Sandy spits provided protection from winds and wave action. Sheltered stretches of shoreline were lined with lush stands of emergent vegetation. Much of the nearshore was covered with sand, gravel and stone.

Cultural influences that have affected shoreline habitats:

  1. Forest Clearing
  2. Sawmills and Gristmills
  3. Stonehooking
  4. Shoreline Alterations
  5. Toronto and Region Area of Concern
  6. Wet Weather Flow Management Master
  7. Invasive Species
  8. Lakefilling
  9. Dredging Activities
  10. Shoreline Regeneration Initiatives

 

1. Forest Clearing

illustration of early settlement in Toronto areaColonization of the Toronto watersheds in the late 1700s and early 1800s resulted in profound changes to physical conditions in the rivers and creeks, which in turn affected waterfront habitats, fish and wildlife.

These changes began with extensive clearing of the dense forest cover that originally blanketed the uplands. As the forest trees and understory plants were removed, and land contours altered by grading, water and sediment runoff to the creeks and rivers increased, resulting in increased flooding and bank erosion downstream. Estuaries and rivermouth wetlands were choked by excessive inputs of sediments.

 

2. Sawmills and Gristmills

Numerous sawmills and gristmills were built along the banks of the creeks and rivers. They discharged their wastes directly into the watercourses, resulting in water pollution and siltation of fish spawning grounds. The millponds increased water temperatures, trapped sediments and altered flow regimes. The dams created barriers to fish moving upstream. The native salmon populations that were once plentiful in this area declined rapidly, with the last recorded catch in Toronto Bay occurring in 1874.

 

3. Stonehooking

chart of stonehooking records from 1850 to 1910From 1850-1910, stonehooking — the removal of aggregate materials from the lake bottom for use in construction — was a major force in changing physical conditions and shoreline processes.

During this time period, 1 million cubic metres of materials were removed from Toronto Harbour alone — enough to cover the entire waterfront from Etobicoke Creek to the Rouge River with a layer 1 metre thick and extending 25 metres offshore.

As a consequence of the loss of aggregate materials, large amounts of valuable aquatic habitat disappeared, and the shoreline was exposed to accelerated erosion.

In areas that still have an abundant supply of stone material (eg Northumberland County), it is an important component of the physical structure of the shoreline. The movement of stone material along the shoreline forms bays, points and bars which are critical elements of aquatic habitats.

 

4. Shoreline Alterations

Other early shoreline alterations included weed removal, filling of wetlands and small streams, hardening of the shoreline, and channelization of watercourses.

Starting in the 1790s, aquatic plants were frequently removed from Toronto Bay because they impeded navigation. A map of Toronto Bay in 1813 (below) shows early shoreline modifications in the form of docks, jetties and filling of small creeks.

By 1913, further alterations included navigable channels such as the Western and Eastern Gaps and the Keating Cut. Ashbridge’s Bay at the mouth of the Don River became severely polluted by wastes from the growing Town of York, the Gooderham and Worts Distillery, and associated cattle byres.

1813 map of Toronto shoreline 1913 map of Toronto shoreline
Alterations to Toronto Bay, 1813 Alterations to Toronto Bay, 1913

 

5. Toronto and Region Area of Concern

satellite photograph of Toronto waterfrontBy 1987, environmental conditions were so badly impaired that the Toronto waterfront was included on the International Joint Commission’s list of 42 Areas of Concern around the Great Lakes requiring remedial action.

The impairments noted for Toronto’s waterfront were:

  • Restrictions on fish and wildlife consumption
  • Degradation of benthos
  • Restrictions on dredging
  • Eutrophication and undesirable algae
  • Beach closures
  • Degradation of aesthetics
  • Degradation of fish and wildlife populations
  • Loss of fish and wildlife habitat

The key factors contributing to these problems are combined sewer overflows, contaminated stormwater, loss of habitats, and degradation of natural landscapes.

Over the past 25 years, eutrophication has been reduced, sediment quality has improved, and habitat availability and diversity have both been increased. Nevertheless, Toronto remains on the list of Areas of Concern.

 

6. Wet Weather Flow Management Master Plan

The City of Toronto’s 2002 Wet Weather Flow Management Master Plan (WWFMMP) provides important direction for ongoing improvements. The plan proposes a program totalling $1 billion over 25 years, including public education, municipal operations, shoreline management, stream restoration, and control measures at the end-of-pipe, during conveyance, and at the source.

The shoreline management proposals include structures at the waterfront, near the mouths of Etobicoke Creek and the Humber River, to deflect ongoing inputs of pollutants away from waterfront beaches. These are proposed because the WWFMMP is limited to the City of Toronto, and there will be continued contributions of bacteria, nutrients and sediments into the watercourses from the “905” municipalities north of the City of Toronto.

Over 25 years, implementation of the WWFMMP will improve waterfront aquatic habitats by reducing inputs of nutrients, sediments and chemical pollutants to the watercourses and Lake Ontario. It will also improve habitat conditions in the rivers and creeks, with benefits to aquatic species that migrate upstream from the Lake and estuaries.

 

7. Invasive Species

Invasive species have also been responsible for major alterations in aquatic communities. Since the 1800s, more than 140 exotic aquatic organisms of all types — including plants, fish, algae and mollusks — have become established in the Great Lakes.

One of the most dramatic recent invasions has been the zebra mussel, which colonizes rocky substrates and other hard surfaces. Zebra mussels are highly efficient filter feeders, removing substantial amounts of phytoplankton and zooplankton from the food chain. They have caused significant increases in water clarity, which in turn is increasing the diversity and productivity of aquatic plants in the nearshore zone.

 

8. Lakefilling

During the industrial period from 1900-1960, extensive lakefilling transformed the 826-hectare Ashbridge’s Bay wetland complex, most of the central waterfront south of Front Street, portions of the Toronto Islands including the airport, the Leslie Street Spit, Ontario Place and the Western Beaches, as seen below.

In the 1970’s, the Metro Toronto and Region Conservation Authority began to develop a series of lakefill parks along the waterfront (Colonel Sam Smith, Humber Bay, Ashbridge’s Bay, and Bluffers Parks) to provide recreation opportunities for a rapidly increasing urban population.

map of alterations to Toronto Bay

 

9. Dredging Activities

The Toronto Port Authority undertakes dredging in the Keating Channel, Inner Harbour, East Gap, Western Channel, Coatsworth Cut and Ashbridges Bay.

aerial image of dredged areas in Toronto Harbour

Each year, 35,000 to 40,000 cubic metres of sediment settle in the Keating Channel. The material originates from run-off and erosion upstream in the Don River. Annual dredging is undertaken in the channel for flood protection and maintenance of navigable water.

The channel is dredged to a depth of 5.8 metres below chart datum and the dredged material is transported by tug and barge to the Toronto Port Authority’s Confined Disposal Facility (CDF) within the Leslie Street Endikement.

The project is subject to ongoing environmental monitoring by the Port and Conservation Authorities. The dredging operation is jointly funded by the City of Toronto, Toronto and Region Conservation (TRCA) and the Toronto Port Authority.

Although the majority of sediment from the Don watershed is captured in the Keating Channel, aerial photographs plainly show a plume of sediment that makes its way further, into the Inner Harbour. When needed, small quantities of material are dredged at berths to maintain the required depth for shipping.

Quantities in the order of 3,000 cubic metres are dredged every three to five years. Similar to the Keating Channel dredgate, the material is transported to the Toronto Port Authority’s CDF.

In general, Berth Nos. 275, 352 and 353 are dredged to 8.2 metres below chart datum while Berth Nos. 243 and 245 are dredged to 5.8 metres below chart datum.

The East Gap represents a portion of the main shipping channel into Toronto Harbour. Prior to the construction of the Leslie Street Spit, regular dredging of the Gap was required to maintain the navigation depth of 8.2 metres below chart datum.

Some sediment continues to intrude into the Gap from western littoral drift and erosion off the Centre Islands. The quantity of this sediment is in the order of 3,500 cubic metres per year. The Toronto Port Authority is currently undertaking a five-year program to remove approximately 60,000 cubic metres of material from the Gap.

This material consists of clean sand suitable for open water disposal in accordance with MOE guidelines. The Port Authority has worked with TRCA to use the clean material in Embayment “A” of Tommy Thompson Park to improve aquatic habitat conditions and develop an emergent vegetation wetland area.

Similar to the East Gap, erosion of the shoreline of the Toronto Islands results in transportation of material into the Western Channel and restricts navigation.

Preliminary work is currently underway to assess possible alternatives for the disposal of the dredged material. An environmental assessment will be undertaken and dredging will probably commence within the next two years. The current design depth of the channel is 8.2 metres below chart datum, but may be reduced as a result of the environmental assessment.

Maintenance dredging is required in the Coatsworth Cut channel in Ashbridge’s Bay every two or three years. The design depth of the channel is 1.8 metres below chart datum. The Toronto Port Authority has permitted this dredge material to be transported and disposed in the Toronto Port Authority’s Confined Disposal Facility. This dredging is funded by the City and coordinated by TRCA.

 

10. Shoreline Regeneration Initiatives

Cultural modifications of the shoreline changed dramatically with the advent of the 1967 Waterfront Plan developed by Metro Toronto.

Lakefilling activities were directed away from creating port and industrial lands and focused on creating a series of regional waterfront recreational parks. The parks provided waterfront access, local greenspace, boating facilities, and — most important to this strategy — aquatic habitats.

The following is a summary of the key projects.

Sam Smith Waterfront Park incorporates many successful habitat creation projects, including wetlands, coastal meadows, shoals and reefs.

Humber Bay Park is the site of a range of intensive habitat restoration works. They include a Ministry of Natural Resources habitat project that placed extensive amounts of woody debris in a sheltered embayment.

Test scale wetlands were established in the estuary of Mimico Creek in 1995 and additional wetlands were created in association with the pedestrian bridge over the Creek. The estuary now provides an excellent opportunity to recreate a coastal wetland estuary complex.

As part of the development of the Humber Bay Shores area, habitat islands, beaches and shoals have been strategically built along the east side of Humber Bay Park, including one of the largest wetland creation projects to date.

The Toronto Bay area was the focus of a study by the Toronto Bay Initiative (A Living Place: Opportunities for Habitat Regeneration in Toronto Bay) that outlines many habitat opportunities. The wetland project and pike spawning habitat at Spadina Quay is an excellent example of created habitats within the harbour and is a useful design template for larger initiatives.

The restoration of the lower Don River and the wetland at the mouth of the Don River is one of the largest proposed restoration schemes for the Toronto Waterfront.

Within the Toronto Islands at the trout pond, a large wetland complex was enhanced and reconnected to the lagoons. This lacustrine marsh provides critical habitat functions for the fish and wildlife community of the islands.

Works undertaken in the mid 1990s on the islands focused on repairing vertical seawalls with a variety of shoals and riparian improvements. Of particular interest is the wetland shoreline that was created at the Queens City Yacht Club that provides vegetated shorelines and improved public access.

aerial view of Colonel Sam Smith Park aerial view of Humber Bay area aerial view of Lower Don River
Sam Smith Waterfront Park Humber Bay area Mouth of the Don River

The potential for Tommy Thompson Park to act as an aquatic habitat catalyst for the waterfront is based on the habitat opportunities in the 160 hectares of lagoons and bays associated with the park.

The Cell One wetland capping project is the single largest wetland gain to date on the waterfront. Additional wetland creation projects in the Park include Triangle Pond, Embayment A, and Embayment C.

Ashbridge’s Bay and Bluffer’s Parks are the location of two of the very first shoal and reef features within a boat basin on Toronto’s waterfront. Both parks have tremendous potential for additional habitats works.

East of Ashbridge’s Bay, the open coast shoreline is characterized by groynes and headland features. Overall these structures function well as aquatic habitat with the best example being the recent headland structure west of the RC Harris Water Filtration Plant.

East of Bluffer’s Park, the Sylvan Avenue project is an outstanding example of integrating aquatic habitats into the form and function of an erosion control project. The Port Union Road shoreline improvement project is another example of the integration of aquatic habitats into a shoreline management structure.

aerial view of Tommy Thompson Park aerial view of Bluffers Park aerial view of Sylvan Avenue project
Tommy Thompson Park Bluffer’s Park Sylvan Avenue project