Dam Safety

Mayfield and Mossyrock dams were engineered and built with a commitment to strength and safety. Special monitoring equipment installed in and near the dams monitor for any changes or movement.

Tacoma Power's dam safety program consists of many facets. Each dam is inspected every working day by trained on-site hydroelectric personnel. More detailed mechanical, electrical, and facility inspections occur weekly and monthly. During weekends and holidays security personnel also inspect the dams and embankments daily for any signs of distress or leakage.

Survey crews and site personnel take readings of control points, drainage weirs and other instrumentation devices on schedules that vary from a couple weeks to semi-annually. Plots of these readings are prepared for review by Tacoma Power's dam safety engineers.

The Federal Energy Regulatory Commission (FERC) conducts annual inspections with Tacoma Power engineers, and review dam safety records. In addition, independent engineering specialists conduct a thorough examination of the dams every five years. During this review, which takes approximately one year to complete, thorough examination of all previous structural, hydraulic and geotechnical studies are made to insure compliance with current standards.

Assuring dam safety is one of Tacoma Power's and FERC's highest priorities. The Cowlitz River Project dams continuously demonstrate high performance in meeting FERC's stringent requirements.