Lethbridge County hears construction update on Chin Reservoir expansion

Chin Reservoir. Sunny South News file photo.

By Erika Mathieu
Sunny South News

Travis Geremia, of St. Mary River Irrigation District (SMRID), and Jeff Olitch of MPE Engineering, appeared as a delegation before Lethbridge County Council on April 6 to discuss the Chin Reservoir expansion project. Geremia is the structural engineer overseeing the project, and Olitch is the prime consultant of MPE overseeing project management.

The speakers shared updated schedules and timelines for the $133 million project.

The five stages of the complete project include relocation of the existing east dam, raising the reservoir, raising the west dam to accommodate raising of the full supply level (FSL), replacement of Chin conduits which were originally installed in 1951, and replacement of the Chin chute due to age and condition of infrastructure.

Olitch explained current reservoir storage is 154,000 acre-feet but, “raising of the FSL and expansion will increase storage by 103,000 acre-feet,” adding that enlarging the reservoir will increase the water storage by approximately 80 per cent.

“We actually have completed a lot of preliminary fieldwork and currently we are pretty much finished preliminary design on this (east dam) and we are ready to submit the Environmental Impact Assessment (EIA) and are waiting on comments on the Terms of Reference (TOR) on the EIA,” said Olitch.

“We have been going through all the regulatory (processes). We started this in 2021 and have gone through the submission for federal EIA,” adding the project was deemed to not require a federal EIA twice. The TOR was released to the public in late 2022, now the Alberta Environmental Protection Agency (EPA) is looking through those comments to amend the TOR if needed based on public feedback. Olitch said this is expected to come through, “any day now,” and be submitted sometime in April.  Based on the timelines of other EIAs, this process could take upwards of two years.

In the meantime, an EIA has been developed based on the existing TOR and the preliminary design was completed during that time as well. Olitch added the regulatory requirements are different for the west dam because it involves existing infrastructure and will be subject to regulation under the Water Act, and standards of dam safety, rather than an EIA.

Preliminary design for the West dam is currently under review, while preliminary design on the Chin chute is complete and final design has been started. Planning for some of the final design preparations such as the drilling program for east dam are underway.

“We may be in a holding pattern waiting for the EPA, however we are still moving forward on (the) other aspects we know we can.”

A construction tender is projected to go out in January 2025. Once ground breaks, the project may not be completed until as late as 2029 as dam construction will be reserved to the warmer months.

“We’re estimating three years, possibly three and a half, based off of preliminary design,” said Olitch, noting it could be up to four years. Given the scale of the project, significant settlement is anticipated, so spreading the construction out over several years will mitigate extreme end-of-project settlement.

The most recent dam constructed by the SMRID was the 40-Mile Reservoir near Foremost in 1986. It was built over the course of two years, but after the project was completed, settlement was so significant, “the dam actually visibly moved,” said Geremia, adding those considerations are being taken into the design of the Chin expansion to avoid a similar outcome.

The installation of the cofferdam (an enclosure built within a body of water to allow the enclosed area to be pumped out) is expected to take place between August – December 2024, and construction at the west dam will commence in 2025 and will take approximately two and a half years, while outlet structure construction and dam pre-loading will start in 2025-26. Dam backfilling will take place in 2026-2027, followed by removing the cofferdam in 2028, if all goes according to plan.

Olitch noted by putting the new Chin outlet structure in, the road across the dam will be compromised. The SMRID has submitted an application to Lethbridge County to close that road to public traffic and leave the construction access road for emergency vehicles only beginning sometime in 2025.

A funding agreement is in place between the Province, Canadian Infrastructure Bank and SMRID, which will see 30 per cent of the project cost dolled out upfront by the Province through grants, 20 per cent by SMRID upfront in cash, and the remaining 50 per cent will be funded by a low interest loan through the Canada Infrastructure Bank, to be payed back by SMRID and other partnering irrigation districts. The SMRID is currently in the process of releasing 15,000 acres of irrigation for uptake by irrigators to finance the loan portion of the expansion.

While the project notes indicate a timeline of two years to fill the reservoir upon completion, Olitch said filling the reservoir will be highly dependent on the availability of water. Furthermore, rapid filling of the reservoir isn’t advisable and would likely result in complications such as hydraulic fractures.

“If it is a drought year, there may not be a single drop of water going into that expansion area,” and could take ten years to fill the reservoir, concluded Olitch.