Beamish Lake, sometimes called Mountain Lake, located in the Hollow Glen area of the Municipality of Chelsea, is the centre of a residential neighbourhood. Several municipal roads along the lake run in the east—west direction and there are some lakefront houses with lacustrine equipment. Beamish Lake, supplied on the east by the Kelly Dam outlet, which is the property of the City of Gatineau, is retained on the west by the Hollow Glen Dam, which is the property of the Municipality of Chelsea, regularized by Beamish Dam, which is the property of the Lyle Beamish estate, and bordered on the northeast by Chemin Hollow Glen, which is the property of the Municipality of Chelsea.
A dam typical of the year it was built in—1960—it was a 180-m long and 9.64-m high earthen dyke. With a retention height of 8.09 m and a surface area of 18.15 ha., the dam could hold 1,468,335 m3 of water. Initially, it was a class A high-capacity dam and its consequence level in case of failure was “very high.”
In 2012, it was shown during a safety assessment by two independent firms that Hollow Glen Dam, built in 1960, did not comply with minimal safety standards with regard to stability and flooding. The municipality therefore had to take action to ensure compliance with the terms of the Dam Safety Act.
On April 16, 2013, resolution 101-13 was passed to authorize contracting professional engineering services for the design and oversight of Hollow Glen Dam repairs on Beamish Lake. After examining five proposals, the CIMA+ firm of experts was awarded the contract. The management of Hollow Glen Dam had been assigned to the municipality in an intermunicipal agreement signed on April 9, 2013, with the Collines-de-l ’Outaouais RCM.
Here is the list of corrections made to the dam by the contractor Charex as part of its 2014 repair contract:
Historic operation level: 102.95 m
Expected normal operation level: 103.0 m
Maximum operation level (in spate): 103.6 m
Crest level: 104.2 m
Minimal acceptable freeboard: 0.6 m
Design flood water (recurrence): 1,000 years
Design flood water (max. inflow) 29.2 m3/s
Verification flood water (recurrence): 10,000 years
Verification flood water (max. inflow) 45.9 m3/s
Beamish Lake’s drainage basin has two distinct zones. In the north, Gatineau Park is home to the Eardley Escarpment. This is a steep slope with a plateau on top. This zone is mostly wooded. The edge of the lake and the south of the drainage basin are found on a flat plain. This is a mainly agricultural zone. The drainage basin has a total surface area of 17.5 km2.
Since the final acceptance of repairs in July 2016, the operation and maintenance of the plant are controlled by the municipality. Two inspections are carried out every year to ensure the proper functioning of the dam. Until 2018, CIMA+ was in charge of inspections. Upcoming inspections will be carried out by the municipality.
The dam currently functions automatically to maintain a safe water level of 103.0 m except for periods of flooding when the manual function may be employed to lower the upstream water level.