Muskoseepi Reservoir Dam (photo by Shaun Penner)

By Liam Verster

Structure and Safety Study of Muskoseepi Dam

Muskoseepi Reservoir Dam in good, safe condition: report

Apr 14, 2021 | 12:13 PM

A recent report from a Dam Safety Review of the Muskoseepi Reservoir Dam shows the infrastructure is in good, safe working condition.

The City of Grande Prairie initiated the study of the dam in 2020 to determine the condition of the structure and the impact of the spillway on properties.

Michael Harvard, the Development Engineer for the City’s Engineering Services department, says the study, which took just over 12 months, shows the structure is in satisfactory condition, and there’s no critical deficiencies that require immediate action.

“Based on the site inspection, and the safety assessment completed, the dam and spillway are safe and stable under normal operating conditions,” says Harvard.

“The review of the reservoir, which is the body of water just upstream of the dam, indicated that there’s adequate capacity during a designed storm event, so there’s no need for additional overflow structures.

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“The structural analysis concluded that the spillway concrete structure meets all the stability criteria set forth by the Canadian Dam Association guidelines.”

Harvard adds the zone of influence, which is the area impacted by the dam’s operations, only reaches as far as 825 metres upstream during a 1-in-5 year storm event. In a 1-in-100 year storm event, the effects of the operations can stretch as far as three kilometres, which is near Royal Oaks Drive.

He says the last 1-in-5 year storm event was recorded in 2016, when the City saw continued rainfall over a long period of time. These kinds of storms usually bring with them higher water levels in the river and storm ponds taking on a little bit of water.

“A 1-in-5 year event is still quite a small event in the grand scheme of things. You don’t necessarily see a massive sign of anything going on, it’s still routine operations.”

The study also found the operation of the spillway gates does not influence water flows upstream of the 108 Street bridge during normal weather conditions.

While the condition of the infrastructure meets all the requirements and guidelines, Harvard does say the report makes some recommendations for routine maintenance work.

“There will be some concrete repairs and some repairs to the riprap adjacent to the concrete structure, some erosion repair, and just other general maintenance that we will be undertaking over the next couple years.”

One final part of the inspection has been delayed while the City awaits regulatory approval. That involves removing the water from the spillway and conducting a structural analysis of the concrete. It’s expected that this part of the review will be completed sometime in the upcoming summer or fall.

Harvard says he doesn’t know what the cost of these jobs will be, but does say they will look for any available grants before doing the work.

The safety of the dam needs to be reviewed every decade and meet the provincial standards in order for the City to maintain it’s operator status. The City also has to routinely inspect the dam and have plans in place in order to ensure it’s kept up to that safety standard.

The study was presented to the City’s Infrastructure and Economic Development Committee on Tuesday, where it was received for information.