Chronology of the Millbrook Dam Reconstruction Project

Pictured above is the Millbrook Dam – photo taken in October of last year (2016).


June 22,2017: Otonabee Conservation hosts an Open House in Millbrook to preview a revised design for the Millbrook Dam. In a letter to the community, Dan Marinigh, CAO, explains that the new design takes into consideration the comments from the community received at the Open House of January 26th, 2017.



February 2, 2017: Otonabee Conservation shares a letter to the community respecting the comments heard during the Open House of January 26,2017.


January 26, 2017: Otonabee Conservation hosted an Open House to present the design of the new Millbrook Dam.





January 13, 2017: Otonabee Conservation undertook remedial actions at the Millbrook Dam to ensure the structural integrity of the dam. The work involved the construction of a cofferdam in the mill pond in front of the existing penstock pipe and the strengthening of the toe berm.


August 29, 2016: The Board of Directors of Otonabee Conservation awarded a contract to the engineering firm, HATCH, for the design and procurement of construction services for the reconstruction of the Millbrook Dam.

February 25, 2016: Otonabee Conservation completed the planning process in accordance with the Environmental Assessment Act in the Class Environmental Assessment for Remedial Flood and Erosion Control Projects.

The Notice of Project Approval was issued.

The preferred option for the Millbrook Dam is the reconstruction of the spillway and enhancement of the earthen embankment to ensure integrity of the dam during periods of high flood events. Public access across the dam via a foot bridge and other amenities are also incorporated in this option and reflect the community values for the site as expressed throughout the consultation process. The Authority will now proceed with implementing the preferred option.

January 21, 2016: Otonabee Conservation opened a 15-day public comment period respecting the Addendum to the Environmental Study Report for Remedial Flood Control Works for the Millbrook Dam. The Addendum Report may be viewed online or may be downloaded (if downloading, please be aware that the file is large and it may take a few minutes to complete the download).

October 20, 2015: Otonabee Conservation hosted a public information centre to provide information to all interested parties and answer questions.  Staff and representatives from the consulting firm, HATCH, presented information about the purpose of the Addendum, a description of the Addendum process, the alternatives considered and a description of the updated preferred solution – Spillway Reconstruction with Headpond Retention.



July 2015: Otonabee Conservation received funding for upgrades to the Millbrook Dam thanks to the financial support from the Governments of Canada and Ontario through the Small Communities Fund. The Government of Canada will provide up to $1,119,363 through the Fund; the Province of Ontario will contribute up to $1,199,362 to this project; and the Conservation Authority will be responsible for all remaining costs.




June 2015: Otonabee Conservation hosted a Public Information Session at the municipal office of the Township of Cavan Monaghan. The formal presentation provided an update on the project work undertaken to date, the approach moving forward to ensure completion of the Class EA for the Millbrook Dam and Authority staff answered questions of those in attendance. A Fact Sheet was made available, summarizing the presentation.

June 2015: The Authority Board of Directors approves the awarding of the contract to HATCH to revise the Environmental Assessment for the Millbrook Dam is initiated.

May 2015: Otonabee Conservation issued a Request for Proposals to undertake the revision of the draft Environmental Assessment Report for the Millbrook Dam, with a closing date of June 12, 2015.

April 2015: The Board of Directors approved a staff recommendation to revise the draft Environmental Assessment Report for the Millbrook Dam to incorporate the new regulatory requirement dealing with inflow design. The report concluded that the dam must safely pass a volume of water equal to 181 cubic meters per second. In preparing the EA study, a design value of 100 cubic meters per second was used; the regulatory requirement is for a flow equal to 181 cubic meters per second. This change requires that alternative means of increasing the hydraulic capacity of the dam be investigated.

February 2015: The completed Millbrook Dam – Dam Safety Assessment Update Report was presented by D.M. Wills to the Board of Directors of Otonabee Conservation and the key findings of the report were adopted.

September 2014: Otonabee Conservation staff determined that there was a need to reconfirm the hydrological analysis that the IBI Group had undertaken, and that the results of this analysis and the earlier work undertaken by D.M. Wills be consolidated into a single report, whereby one author could validate all inputs, assumptions and findings/conclusions.

May 2014: D.M. Wills Associates was contracted by Otonabee Conservation to re-calculate the incremental analysis of the Inflow Design Flood. The resulting calculation doubled the Inflow Design Flood valve from 100 cms to 201 cms.

April 2014: Owing to subsurface seepage erosion, a sinkhole developed in the Millbrook earth embankment dam. Otonabee Conservation undertook remedial measures to mitigate the threat to the structural integrity of the Millbrook Dam to protect the public against possible harm. The site restoration and the installation of public safety measures resulted in public access to the site being restored in December 2014.

December 2013: Otonabee Conservation contracted D.M. Wills to review and update the dam safety assessment previously completed by the IBI Group in 2008 to ensure that the dam safety assessment satisfied the requirements of the new dam safety guidelines issued by the Ministry of Natural Resources and Forestry (MNRF). In addition, D.M. Wills was contracted to update and improve the accuracy of downstream inundation mapping, which also involved detailed topographical surveys to support the mapping.

April 2013: New dam safety guidelines established by the MNRF came into effect, requiring an applicant to demonstrate that the design of a dam meets the new safety guidelines. The guidelines also changed the formula for determining the Inflow Design Flood value.

2012-2013: Otonabee Conservation undertook a Class Environmental Assessment for the Millbrook Dam to determine a preferred solution to the problem of incremental flooding caused by the potential failure of the dam. The preferred solution documented in the draft Class EA study was to construct a new weir capable of passing an Inflow Design Flood value of 100 cms. It was not in the scope of the Class EA contract to re-assess the hydrology or the incremental analysis.

2008: The IBI Group was contracted to complete a dam safety assessment for the Millbrook Dam in accordance with the 1999 Draft Ontario Dam Safety Guideline. In the final analysis, the IBI Group undertook the incremental analysis and concluded that the Inflow Design Flood value of 100 cms was sufficient to control the risk due to dam failure.