Inspections, performance evaluation and design of power pedestals and seepage monitoring system for a Saskatchewan earthfill dam
Morrison Dam is an 1,830 m long, 17-m high earthfill dam on the East Poplar River, approximately 4 km north of the Canada-USA border in Saskatchewan. Owned and operated by SaskPower and built between 1975 and 1977, the dam creates Cookson Reservoir which stores about 41,000 m3 of water and has a surface area of 680 ha at its full supply level. The reservoir primarily provides cooling water to the adjacent Poplar River thermal power plant.
The dam has experienced significant seepage throughout its history resulting in deterioration of the concrete spillway. In addition, the combined capacity of the flow control structures was determined to be inadequate based on Canadian Dam Association (CDA) guidelines. To address these issues, SaskPower undertook a rehabilitation program to demolish and replace a significant portion of the spillway structure, upgrade the remaining monoliths, refurbish the radial gates, and replace the underdrainage and seepage collection system. The dam is now protected from overtopping by a service spillway equipped with radial gates, and an auxiliary spillway channel. In addition, a low-level outlet structure is used to provide riparian and apportionment flows.
KCB was the prime consultant for the annual inspection of the dam, its related structures and instrumentation, and for evaluating the performance of the seepage monitoring system. We completed a structural review of the spillway gates and designed net gate trunnions and supports. In addition, the auxiliary spillway and riparian outlet structures were modified to improve their performance and increase capacity.
SaskPower also required a new power supply to operate the low-level outlet structure and the spillway radial gates using a “drill-pak”. We worked with the local utility to design the electrical system, including the layout of power meters, distribution panels and cables, and specified the cable sizes and other equipment.
The Morrison Dam now provides the ability to handle large floods in a manner that meets the CDA’s requirements.