Big Quilcene Diversion Dam Repair

The Big Quilcene River is the primary source of drinking water for the City of Port Townsend and industrial process water for the Port Townsend Paper Corporation. The municipal water diversion is located within the Olympic National Forrest, the structure directs water to a pipeline which then flows via gravity to City Lake 20 miles north of the diversion.

Constructed in 1928, the Big Quilcene municipal diversion is a 55-foot long timber crib structure backfilled with rock and gravel. The timbers consist of cedar logs placed in alternating directions and pinned together using 1-inch diameter steel pins. Wood planks cover the downstream face and crest surface. In the 1950’s the timber intake and flue were replaced with concrete and the original wooden pipeline was replaced with a steel pipeline. A concrete apron, which protects the diversion footing, replaced the log apron in 1986.

Inspections have revealed deterioration in some of the tie-back logs. Several logs need to be repaired and re-pinned and in addition, some voids have developed within the timber crib structure and need to be refilled. Upper spikes attaching to the face logs are in poor, corroded condition as are the upstream face boards and the concrete apron has exposed the upper rebar mat which will require resurfacing or replacement.

The repair of the diversion dam is proposed to be an in-kind repair that will maintain the character, scope (i.e., footprint), purpose and functionality. The onsite repairs are planned for Summer of 2018 and is expected to last approximately 15 weeks, with 6-8 weeks for in-river work. The exact timing will be determined based on stream flows and weather forecasts.

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