Beneath the Surface
From the Toronto Aquatic Habitat meeting on May 2003
The following key points are highlights from a Toronto Aquatic Habitat report to help better understand the shoreline of Lake Ontario in the Scarborough Bluffs region. The document is presented by Dr. Doug Dodge (retired, Ministry of Natural Resources) from the Aquatic Habitat Advisory Committee and Gord McPherson from the TRCA.
Nearshore Geology – Post-glacial Shorelines (page 9)
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. An 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 still 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 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.
Nearshore Geology – Western Lake Ontario Bathymetry (page 10)
The 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.
Scarborough Sand Plains (page 12)
An extensive underwater sand plain occurs from the south shore of the Islands to the Toronto scarp and eastward to Bluffers Park. This very thick deposit of sand 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.
Scarborough Boulder-laden Till (page 13)
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 provides a degree of shoreline protection by attenuating waves and providing a dynamic equilibrium between erosion and accretion.
Nearshore Geology – Toronto Waterfront Habitats: Substrates and Features (page 14)
In summary, shown below are the major substrates along the Toronto waterfront: shale bedrock, sand, muds and clay, and boulder, cobble and gravel.
Nearshore Geology – Shoreline Profiles (page 15)
The shoreline profiles vary considerably along the waterfront, as shown in the cross sections 1 through 5, below. 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.
Meteorological Conditions – Littoral Transport (page 17)
The energy in breaking waves is the driving force that moves sediment and other materials along the shore. This littoral transport is the main mechanism that established the Toronto Islands. Littoral transport also sorted and piled a variety of aggregates in the wave zone and moved historic and recent deltaic sediments to create 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, define the boundaries of littoral cells.
Littoral Cells (page 18)
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 affect the shoreline in other cells. Along the Toronto waterfront the potential for material to be moved along the shoreline is limited by sediment supply (see Potential and Actual Sediment Transport maps). 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 shoreline erosion by removing the stones that naturally armoured the lakebed.
Cultural Influences – Forest Clearing (page 23)
Colonization 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 (EMCWTF, 2002). 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.
Cultural Influences – Stonehooking (page 23)
From 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, large amounts of valuable aquatic habitat disappeared, and the shoreline was exposed to accelerated erosion from waves and currents. Some areas, for example Northumberland County, still have an abundant supply of stone material, 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. (See photos.)
Cultural Influences – Shoreline Alterations (page 24)
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 removed from Toronto Bay because they impeded navigation. A map of Toronto Bay in 1813 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. Ashbridges 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.
Fish – Waterfront Fish Communities by Habitat Type – 4a) Open Coast (page 49)
Open coast habitats occur across most of the Toronto waterfront. In sharp contrast to sheltered embayments, coastal wetlands and estuaries, the open coast has much colder water, and is exposed to extensive wind and wave action, resulting in a relatively hostile environment for littoral vegetation and animals. Hypolimnetic upwellings of cold sub-surface waters are common, resulting in temperature fluctuations of as much as 12 Celsius degrees and reduced survival of warmwater fish in these areas. Open coast habitats with bedrock or cobble/boulder substrates and convex profiles are particularly suited to coldwater fish, since species such as lake trout and lake whitefish often rely on these substrates with nearby steep drop-offs for reproduction. Headlands, where the greatest aggregations of boulders occur, provide high quality coldwater spawning habitats. Open coast habitats associated with concave profiles (eg Scarborough Bluffs) and shifting lakebeds associated with dynamic beaches are suited to species which broadcast their eggs in water, such as lake herring, emerald shiner, alewife and smelt. These fish provide an important forage base for other species, including most sport fish. Many fish, for example, salmon species, also use open coast habitats as corridors during seasonal movements.
Mammals (page 53)
One indicator of good ecological health is a well balanced, self-sustaining mammal population. The distribution of mammal species can vary greatly and are usually regulated by several environmental factors. The factors can be grouped into four major categories: weather/ climate, food, other animals and disease, habitat. (Dobbyn,1994). The complex of aquatic, wetland and terrestrial habitats currently found along the waterfront should attract a wide range of mammal species. However, currently waterfront sites support relatively low numbers of mammal species in comparison with less urban sites. Smaller, less mobile species such as the rodents are more likely to remain isolated in small pockets of habitats and are physically unable to disperse do to development barriers, roads, houses etc. The lack of connecting corridors between habitat blocks is one major factor. Larger more mobile species such as coyote and raccoons move more freely through developed areas and use all types of natural blocks, parks, brown fields and habitat nodes for foraging and habitation. Habitat quality is impacted by invasive species, chemical contamination and urban population influences. Waterfront aquatic and near-shore terrestrial habitats could, through enhancement, provide areas for resident wildlife while connecting corridors between isolated habitats located along the waterfront and those running north south along watershed green space. Mammals commonly found on the Toronto waterfront include several species of bat, red fox, eastern cottontail, groundhog, eastern grey squirrel, meadow vole, raccoon, opossum, mink, weasel species, striped skunk, red squirrel, eastern chipmunk, shrews, mole, white footed mouse and muskrat. Less common are beaver, coyote and white- tailed deer. (Dobbyn, 1994) Small mammals perform a notable role in wetland, nearshore and terrestrial ecosystems and are considered keystones to these systems while serving as a food source to larger mammals (eg coyote) and predatory birds (eg owls and hawks).
Page 56-101 has some many diagram showing restoration techniques. The restoration drawings are wonderful and some could be considered as alternatives. but it's important to point out that while 'habitat restoration' is an important aspect of shoreline health, that we are also a city of over 4 million people that deserve a natural connection to the shoreline, so why should fish habitat take priority the needs of the public?
Page 109-118 Meeting Notes - Overview of Aquatic Habitat Restoration Strategy Process
IMPORTANT meeting note about the construction debris (page 109)
Question: the amount of material removed from the shoreline by stone-hooking is incredible! Where do you expect that we can obtain enough material to put back on the waterfront?
Answer: there are several potential sources, including waste materials from quarries, constructions wastes including brick and concrete rubble, and rocks removed from green-field construction sites.
Page 105-108 has some Glossary Terms and I have selected the most relevant ones:
Backshore – the part of the shoreline that is usually dry, above the average water level, and bounded inland by the limit of storm run-up.
Bathymetry – the science of measuring water depth to understand the topography of the lake floor.
Benthic – on the bottom of a body of water.
Benthos – organisms that live on the bottom of a body of water.
Breakwater – a barrier built out into the lake to protect the shoreline from the force of waves.
Embayment – a natural or constructed area of sheltered water.
Estuary – the lower reach of a river or stream that is influenced by lake levels. Eutrophic – high in nutrients.
Fetch – line of continuous open water from point to point.
Groyne – a low wall or barrier built out into the lake to reduce erosion and littoral drift.
Hypolimnetic upwelling – the upwelling of cold water from a deep layer in a thermally stratified water body.
Littoral – pertaining to or along the shore.
Littoral cells – sections of the shoreline defined so that no input or outflow of sediment takes place across their boundaries.
Littoral transport – the movement of materials in the water along the shoreline.
Native species – species that are indigenous to Toronto ecosystems (eg lake trout).
Naturalized species – species that are not native to Toronto ecosystems but have become an integral part of the ecosystem (eg Pacific salmon).
Nearshore – zone that extends lake-ward from the average water level, where wave action and currents directly influence the shoreline.
Onshore – the part of the shore that is land-ward of the limit of storm run-up.
Riparian – bordering a lake or watercourse.
Thermal bar – a column of relatively cold, dense, off-shore water that holds a band of warm water in the nearshore zone in early spring.
Turbidity – the degree of cloudiness of water due to suspended silt or organic matter. Salmonid – fish of the salmon and trout group.
Spit – a peninsula or extension of land from the shoreline that is almost surrounded by water.
Stonehooking - the removal of aggregate materials from the lake bottom for use in construction. Most stonehooking along the Toronto waterfront occurred from approximately 1850-1910.
Storm run-up – the water that reaches inland during a storm, higher than the average water level, as a result of wind and wave action.
Submergents – aquatic plants that grow below the water surface.