Garden Hill Dam Class Environmental Assessment

The Garden Hill Dam was constructed in 1959 in association with improvements to Northumberland County Road 9.

The dam and head pond have historically supported water management, recreation, and wildlife habitat functions. Current objectives emphasize wildlife habitat, recreation, emergency fire response, and low-flow augmentation. Due to the small catchment upstream the dam does not provide a major flood-protection function.

The dam structure is owned by the GRCA. A portion of the dam embankment and the connecting culvert is within Ganaraska Road / County Road 9, which is owned by Northumberland County.

Yes, the GRCA has completed the following repairs / maintenance:

• Regular inspections
• Gantry improvements
• Wingwall fencing
• Safety signage
• Safety booms
• Vegetation control – tree removal
• Drainage improvements to handle runoff from the roadway

The County maintains CR9 and the culvert. Any restoration work on the dam and culvert will be coordinated between the County and the GRCA to make effective use of resources.

In its current configuration, removal and replacement of the dam’s stoplogs is a significant undertaking.

The dam control structure is not equipped with gains upstream of the stoplogs, meaning any temporary removal of stoplogs will result in a full drawdown of the entire reservoir upstream and the release of flows and sediment downstream.

In 2023, the GRCA initiated a temporary drawdown of the pond to facilitate inspection of the structure by removing 7 of the 19 stoplogs in each gate. The drawdown was undertaken over several days and only involved roughly 1/3 of the logs.

While a temporary cofferdam could be constructed upstream of the dam to facilitate the replacement of the logs, its construction would also result in impacts to the reservoir and river and would not necessarily address other issues with the structure which are being considered as part of the EA.

As part of the EA, the relationship between the reservoir and the surrounding hydrogeology is being examined and will be considered in the analysis of options. It is understood from surrounding property owners that impacts to their wells and water supply is of significant concern.

The dam is nearing the end of its design life and increasing maintenance requirements as well as meeting evolving regulatory and dam safety standards present an increasing challenge. It is becoming increasingly difficult for the CA to support these requirements without additional funding support from the municipality. GRCA is taking a comprehensive look at all options through the EA process to determine the best course of action. The Class EA provides a decision-making framework for consideration of multiple alternatives, including but not limited to do nothing, repair, and decommissioning of the structure.

It is expected that anticipated impacts will vary based on the proposed alternative. Assessments are currently being conducted to inform the Environmental Assessment to document existing conditions and evaluate potential impacts of proposed alternatives on the natural environment.

The reservoir pond upstream of the dam provides water for firefighting via a dry hydrant on the east bank along Mill Street. The CA is engaged with the Port Hope to review potential impacts to the dry hydrant and how to maintain water supply for firefighting through the EA process.

Prior to provincial funding cuts in 1997, CAs had received provincial funding to support capital projects, including maintenance of dams, flood control channels, etc. These cuts downloaded maintenance costs and responsibilities to municipalities.

Prior to provincial funding cuts in 1997, CAs had received provincial funding to support capital projects, including maintenance of dams, flood control channels, etc. These cuts downloaded maintenance costs and responsibilities to municipalities.

WECI stands for Water and Erosion Control Infrastructure, which is an annual Ontario Ministry of Natural Resources (MNR) fund to assist CAs and municipalities with high-priority maintenance, repairs or technical studies on aging flood control structures.

Upon approval, the MNR provides 50 per cent of funds for the project, matching municipal and CA funds through a cost-sharing approach. Applications are accepted annually and reviewed by a committee of peers for project eligibility and ranking.

In Ontario, the Environmental Assessment Act (EAA) requires that certain types of projects follow a planning and decision-making process to evaluate the potential environmental, social, economic, and cultural effects. Under the EAA, a Class Environmental Assessment is a process sets out a standardized planning process for similar classes or groups of activities. It applies to projects that are carried out routinely and have predictable environmental effects that can be readily managed.

As a water control infrastructure project being carried out by the GRCA the applicable Class EA process is the Class Environmental Assessment for Remedial Flood and Erosion Control Projects which has been developed by Conservation Ontario to evaluate projects that are carried out by 36 Conservation Authorities across Ontario.

The Class EA sets out procedures and environmental planning principles for Conservation Authorities to follow to plan, design, evaluate, implement and monitor a project so that environmental effects are considered as required.

To review a copy of the Class Environmental Assessment for Remedial Flood and Erosion Control Projects please see the following links:

• Conservation Ontario:Conservation Authority led remedial projects protect people and property
• Class Environmental Assessment for Remedial Flood and Erosion Control Projects

The Class EA sets process and environmental planning requirements for the Conservation Authority to plan, design, evaluate, implement, and monitor projects so that environmental effects are considered in a balanced and comprehensive fashion. It also provides a venue for public review and input into the process so that concerns and questions can be addressed and their feedback considered as part of the evaluation.

As a project being carried out by the GRCA, the applicable Class EA process is the Class EA for Remedial Flood and Erosion Control Projects. (https://conservationontario.ca/fileadmin/Class_EA_for_Remedial_Flood_and_Erosion_Control_Projects__February_2024_.pdf)

No. The Class EA framework provides an effective approach to evaluating the potential environmental, social, economic, and cultural effects of various alternatives and GRCA will be guided by this process in supporting a preferred alternative.