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Gibraltar Point Erosion Control Project

The Toronto and Region Conservation Authority (TRCA) is now interested in undertaking long-term remedial erosion control works along the southwestern tip of the Toronto Islands known as Gibraltar Point in the City of Toronto.

Project Update – January  15,  2015

Working in partnership with City of Toronto, TRCA continues to work to secure the funding required to proceed with implementation phase. As of Jan. 15, 2015, funding to construct the structures proposed in 2008 has not been secured and therefore, there is no confirmed construction start date. Funding is to come from the City of Toronto. Once construction funding has been confirmed (by City of Toronto), TRCA, in partner with the City of Toronto, will move forward with scheduling further public consultation and a construction timeline.

TRCA is working with the City of Toronto, regulatory stakeholders and a coastal engineer to further develop the design (i.e. size and amount of habitat compensation required) of structures proposed in 2008. This work is required in order to develop a cost estimate and feasibility of the construction phase.

For more information, please contact Ethan Griesbach, Project Manager II, Project Management Office, at or 416-625-6071

Project Background

Erosion has been documented at Gibraltar Point since 1879. In 1972, significant storm damage prompted the first of several studies recommending various long-term remedial solutions. Despite these recommendations, no major remedial actions were financially supported. Attempts were made rather to protect the Gibraltar Point shoreline with gabion baskets and rubble. These attempts had short-term success as they failed to address the large-scale coastal processes affecting the site.

A severe storm event in February 2004 caused significant damage to an existing washroom building and associated infrastructure, prompting the City of Toronto to request the assistance of the Toronto and Region Conservation Authority (TRCA). TRCA responded by immediately securing the shoreline adjacent to the washroom with emergency shoreline protection.

The Toronto and Region Conservation Authority (TRCA) is now interested in undertaking long-term remedial erosion control works along the southwestern tip of the Toronto Islands known as Gibraltar Point in the City of Toronto. The project study limits encompass approximately 3,500 metres of shoreline from the Western Channel in the west to Centre Island in the east.

 Location of Gibraltar Project
Figure 1 Location of Gibraltar Point Erosion Control Project.

Project Objectives

The objective of the project is to provide long-term protection against erosion by protecting the shore from wave energy, thereby reducing the risk to public safety and infrastructure.

Planning Mechanism for the Undertaking

TRCA must conduct its remedial flood and erosion control projects in accordance with the Environmental Assessment Act (EAA). Recognizing that common elements exist in addressing flood and erosion problems, a coordinated approach to environmental assessment was developed by Conservation Ontario for all conservation authorities known as the Class Environmental Assessment for Remedial Flood and Erosion Control Projects (Class EA).

In 2004, TRCA initiated the Gibraltar Point Erosion Control Project under the Class Environmental Assessment for Remedial Flood and Erosion Control Projects (2002). As part of the Class EA process, TRCA retained Shoreplan Engineering to complete a coastal analysis to determine the regional processes around Gibraltar Point and assist with the development of alternative long-term solutions to the shoreline erosion.

Results of Shoreplan's investigations determined that although erosion and deposition are occurring at various locations between the Western Gap and Gibraltar Point, there is an overall net loss of sand resulting in ongoing shoreline erosion. A comparison of hydrographic survey data shows a lowering of the lakebed in the nearshore area around Gibraltar Point, which is consistent with the undermining and eventual failure of previous local shoreline protection works. Furthermore, Shoreplan's findings indicated that over the next 100 years, a substantial loss of highly valuable recreational and ecological land is projected, ultimately resulting in the breaching of the Islands from Lake Ontario to the Inner Lagoons.

Prediction of shoreline erosion
Figure 2 Prediction of shoreline erosion after 100 years.
Source: Shoreplan Engineering Limited, 2007.

As part of the Class EA process, TRCA documented the decision making process and the value judgments made in selecting the preferred course of action in a report, including potential impacts of the project, a description of alternative designs for the undertaking and determining whether further assessment is necessary. The Environmental Study Report for the Gibraltar Point Erosion Control Project was made available to the public for comment on February 16, 2008, as advertised by TRCA in the Toronto Star. The project was granted approval under the Class EA process, on March 17, 2008. To view the report in full see:

Environmental Study Report - 21,446k

In addition to the Class EA process, TRCA recognizes that the Gibraltar Point Erosion Control Project will require an environmental screening under the Canadian Environmental Assessment Act (CEAA). CEAA may be triggered in response to the potential environmental impacts that the project will produce pursuant to subsection 35(2) under the federal Fisheries Act and section 5(1) of the federal Navigable Waters Protection Act. Under CEAA, A Responsible Authority will be identified to determine whether the impacts of the project are likely to cause significant environmental effects, taking into account mitigation measures.

Pending the approval of funding, TRCA will initiate the detailed analysis and design process, by assembling a planning team involving staff from TRCA, City of Toronto, Ministry of Natural Resources, Department of Fisheries and Oceans, as well as, experts to provide advice regarding dune ecology. This planning team will help set project targets that will direct the detailed modeling, analysis, and design process, and will assist in the preparation of a pre and post implementation monitoring plan.

Following completion of the detailed design process, the project will be screened through the Canadian Environmental Assessment Act. This screening will facilitate the necessary federal and provincial approvals that will be required to implement the project.

Public and Agency Consultation

The Class EA process provides that all views respecting a proposed remedial flood or erosion control project be taken into consideration during the planning and design of remedial flood and erosion control projects. The formation of a Community Liaison Committee (CLC) has allowed concerned citizens, local interest groups and non governmental organizations to voice issues of public concern as well as assisted in the planning and design process of the project.

Through a series of CLC meetings, the range of solutions developed by Shoreplan were considered, ranging from traditional solutions such as breakwaters to more innovative approaches such as sand augmentation. In addition to providing feedback on technical and economic considerations, the members provided great insight into the importance of preserving the adjacent sand dunes, woodlots and beaches. The CLC provided valuable input into the planning and design process until a preferred alternative was selected and modified until all parties were satisfied that the impacts of the project are acceptable given its merits.

The Project

The preferred concept is a sand management plan that recognizes that some level of offshore protection may be required to ensure that the project is technically and economically feasible. The main purposes of the sand management plan are to provide a level of shoreline protection and to maintain the natural dynamic backshore processes that require a continuous supply of sand. Without a sand management plan, the existing dunes along the western facing shore will eventually degrade, as they require a continuous supply of fine sand.

The sand management plan attempts to replicate the natural sediment transport processes that have been altered over the last 100 years, resulting in a nearly complete loss of sand supply to the Toronto Islands. The Western Gap and the Eastern Channel define the Toronto Islands littoral cell. Sand moves within this cell but not across its lateral boundaries. To replicate the historic sediment transport processes the sand management plan will involve placing sand along the beach and nearshore of Gibraltar Point. The sand will then be moved by wind and wave action through the littoral cell towards the littoral cell boundaries. The sand deposited at the end of the littoral cell boundaries will then be dredged and placed back at Gibraltar Point, allowing the process to continue.

Based on the sediment transport analyses carried out to date it is anticipated that the desired sand supply could be up to 20,000 m³ per year. The majority of that sand will be produced from a backpassing operation, which will involve removing sand from the depositional area (offshore of Hanlan's Point Beach and the Western Gap) and relocating it updrift of Gibraltar Point in the vicinity of Centre Island Beach. It may also be economically feasible to utilize sand generated from local dredging operations that regularly occur, such as at Ashbridge's Bay and the Eastern Channel. Once the backpassing operation is established it is anticipated that sediment retained by the breakwaters and sill will also serve as a backpassing source. Any sand that is placed at Gibraltar Point must meet Ministry of Environment (MOE) guidelines for open water disposal. Recent tests carried out by the Toronto Port Authority as part of their dredging work have shown that the sand in the Western Gap to be of acceptable quality for open water placement.

The detailed design process will determine the annual sand requirements that produce the most efficient design, while achieving the project objective of managing erosion and preserving the dynamic nature of the shoreline. It has been determined that offshore protection will reduce the volume and frequency of sand that is required to be placed updrift of Gibraltar Point (e.g. more protection, less sand) as part of the sand management plan. As such, the detailed design process will utilize a physical model and/or computer model to examine a number of offshore protection options, in conjunction with different volumes of sand supply.

Five possible options for implementing the preferred alternative will be modeled. Three of these options will include different breakwater lengths and cross-sections (see Figures 3 and 4) in conjunction with varying levels of sand management. The fourth option will investigate an emergent breakwater with little to no sand management and the fifth option will investigate a sand management plan without offshore protection. The main purpose for considering these options is to test the cost sensitivity of different levels of sand management and to determine the possible environmental affects. A number of model setups will be tested to establish the level of erosion protection provided by the combination of different breakwater configurations with different volumes of sediment supply.

The four offshore protection options that will be modeled consist of different lengths of emergent (surface piercing) segmented breakwaters connected with submerged breakwaters (sills), in conjunction with different levels of sand management. The modeling will also help to determine the exact dimensions and spacing of the breakwaters. An overall length of 930 m for the breakwaters and sills was selected as a reasonable approximation of the longest length likely to be required in order to produce conservative cost estimates. It must be stated, however, that it is possible that the modeling could show that a longer length of breakwater may be more effective. For comparison we note that the shorter and longer breakwaters considered for Concept 3 were 750 m and 900 m, respectively. The 930 m long breakwater, extending further to the north would provide a greater level of protection to the southern end of Hanlan's Point, which was identified as an area of severe erosion experienced in 2006. A typical representation of these three options, is shown in Figure 2.

Representation of the offshore protection
Figure 2. Representation of the offshore protection to be explored during the detailed design process, showing emergent breakwaters connected by an underwater sill.
Source: Shoreplan Engineering Limited, 2007.

Figure 3 shows a typical cross-section for the sill. It has a maximum crest elevation of 2 m below chart datum so that it does not interfere with small craft navigation. The lakeward toe of the sill would be constructed down to a depth of 6 m below chart datum to allow for future downcutting of the lakebed profile as previously discussed. It is anticipated that the toe area would be excavated with a hydraulic dredge. Toe excavation and sill stone placement would occur in tandem with the stone placement following closely behind the dredging. This would allow the toe trench to be artificially backfilled with dredged sand rather than native sand from the lakebed in front of the sill. The landward toe of the sill would be constructed on the existing lakebed. The sill consists of randomly placed rip rap and small armourstone.

Typical sill cross-section
Figure 3. Typical sill cross-section.
Source: Shoreplan Engineering Limited, 2007.

Figure 4 shows a typical breakwater cross-section. The breakwaters would be constructed by placing armourstone on top of a modified sill cross-section. The sill cross-section is modified by extending the toe approximately 8 m lakeward to provide a stable base for the armour. The crest of the breakwater is about 2 m above chart datum, which is above the 100-year water level described previously.

Typical breakwater cross-section
Figure 4. Typical breakwater cross-section.
Source: Shoreplan Engineering Limited, 2007.

For more information, please contact Ethan Griesbach, Project Manager II, Project Management Office, at or 416-625-6071