Raising Thirsk Dam provides 3100 million litres of drinking water capacity to the District of Summerland

Thirsk Reservoir Expansion wins Award of Excellence at
2008 Consulting Engineers of BC Awards

Associated Engineering received an Award of Excellence for our design of the Thirsk Reservoir Expansion at the Consulting Engineers of BC annual awards celebration in March. The annual awards recognize and celebrate excellence in consulting engineering.

Associated Engineering received the Award of Excellence for our design of upgrades to raise Thirsk Dam and provide additional storage capacity in Thirsk Reservoir. Located in Summerland, BC, Thirsk Reservoir is the District of Summerland’s main drinking water supply.

The District retained Associated Engineering to conduct a dam safety review on Thirsk Dam and its associated spillway, and evaluate options for providing additional water storage capacity in Thirsk Reservoir. After structural analysis, Associated Engineering recommended raising the dam to provide the additional water storage capacity and also to meet current seismic standards.

Accepting the Award of Excellence in the Municipal Engineering Category from CEBC President Francois Morton (left) and CEBC Executive Director Glenn Martin (right) are Greg Mealing from the District of Summerland and Associated Engineering’s Project Manager Ed Bird

The old 21.3 metre high dam is a very thin structure, only 0.76 metres wide at the crest. The unique design of the original dam made the project challenging. Project Manager Ed Bird reports, “The structure is an unreinforced, concrete arch-dam, one of only 14 such structures in Canada. The U.S. engineer who completed the original design was no longer available for consultation and no record drawings existed. Thus, the biggest challenge was the lack of information--we had little insight into dam’s actual construction or the rock encountered.”

Senior Structural Engineer, Dale Harrison, advises, “Without reinforcing steel, raising the dam could subject the structure to large thermal stresses during extreme seasonal temperatures, which could cause uncontrolled cracking. We developed a concept using thrust blocks and rock anchors to release stresses in the dam. The dam was reinforced by doweling into the downstream face of the dam and concrete was applied to thicken the structure and reduce stresses.”

Thirsk Dam was raised 5.3 metres, expanding Thirsk Reservoir by 3100 million litres. The expansion provides the District of Summerland with the water supply it needs to sustain growth and support agriculture in the community. The reservoir expansion provides a 96% increase in water capacity at a unit cost of less than 0.4 cents per litre. As an added benefit, water will be available to augment downstream Trout Creek, which will enhance fish habitat.