New Design for Millbrook Dam Spillway

On January 26th, 2017, Otonabee Conservation held an Information Centre at the Cavan Monaghan Municipal Office in Millbrook to share with the public the latest design for the reconstruction of the Millbrook Dam spillway.

We received a lot of positive feedback about the spillway design and the proposed finishing features. At that time, we also committed to continue to explore ways of further reducing the width of the spillway structure and ameliorating the visual impacts of the western half of the spillway that would be dry for most of the year.

Based on the input received and in further consideration of some geo-technical issues with the site, Otonabee Conservation’s consultatnts undertook a complete review of the design and concluded that a different design may be warranted. Our consultants were then asked to prepare a new design.

Below is a rendering of the new design for the spillway. The key changes are as follows:

  • The floor of the spillway has changed completely to deal with the geo-technical issues on site. These changes are below ground and underwater. They will not be visible to the viewer.
  • The weir has been changed from a straight 26-meter-wide weir to a u-shaped weir with outside wall dimensions of 5 meters by 16 meters by 5 meters.
  • The spillway is now 12 meters wide versus 26 meters in the original design.

  • There is now a new approach for the care of the water. A single coffer dam will direct water through a channel to be built where the steel penstock is presently situated. Construction of the spillway will occur in a single phase. In the earlier design sheet piling was to be used to divert the water during construction and construction would have been undertaken in two phases.
  • The plan for hardening the earthen berm remains unchanged as do the proposed finishing features for the bridge (public walkway) and walls of the spillway.

Overall this design is very similar to what exists today. The new 12-meter-wide spillway will replace the existing 7-meter-wide spillway. The weir will be the same u-shape. The size and water level of the mill pond will remain the same and the waterfall sights and sounds will be very similar to existing conditions.

Construction is anticipated to commence by the end of September, 2017.

Otonabee Conservation staff will be available to the public at the Cavan Monaghan Municipal Office on Thursday, June 22, 2017 from 4:00 p.m. to 7:00 p.m. to answer any questions.