Using the Old to Build the New

The old Flower Creek Dam was completed in 1946 and was a thin-arch concrete structure that used the compressive forces of the arch and the compressive strength of the bedrock abutments to maintain structural integrity. Prior to construction, a geotechnical investigation revealed a limited amount of competent bedrock, a condition that would not support the same kind of structure as current dam-safety standards. As a result, Morrison-Maierle created an entirely different design that accommodated the lack of competent bedrock in the abutments and concrete samples of the previous dam that showed excessive hydration causing them to fall apart upon extraction. As a result, the new dam design included mass-concrete elements that relied on the sheer volume of concrete to resist sliding, overturn, and uplift forces.

Morrison-Maierle also developed a strategy to save the city a significant amount of money while building the new dam. In today’s projects, a large cost of replacing dams is the construction of cofferdams, typically on both the upstream and downstream sides of the project. The geotechnical investigation of this project showed that there was sufficient bedrock immediately downstream of the old dam. This allowed the design to incorporate the old dam as the upstream cofferdam which eliminated the need for a downstream cofferdam. After the project was completed, the old dam was then dismantled prior to filling the reservoir.

The city staff is able to control the level of the Flower Creek Reservoir by operating a single 36-inch outlet valve. This allows them to keep minimal flows going over the primary spillway while allowing higher cold-water flows to pass through the dam. This meets regulatory requirements for downstream fish habitats and provides a simplified operation for the owner.