Poe Dam

Located on California’s Feather River, the historic Poe Dam had four radial gates that needed their trunnion pins, gate arms, and other structural elements replaced. Following rehabilitation design, Pacific Gas and Electric (PG&E) retained a design-build team – of which Schnabel was a part – for the design, fabrication, and installation of a temporary bulkhead system to sequentially dewater the primary spillway gate bays during construction.

Challenges on the project included limited site access and a short construction season, which called for an easily maneuverable cofferdam. PG&E accepted Schnabel’s recommendation for a floating reverse needle beam system over a horizontal segmented bulkhead section.

Due to limited site access, the horizontal support beam and seven needles were floated to the dam from the reservoir. The upstream bulkhead system was designed for the full head of the reservoir plus seismic loading. The downstream system, consisting of timber lagging in a steel frame anchored to the spillway apron, was designed to be lowered from the access bridge above the spillway bays for full work area dewatering.

Upon the completion of this work, PG&E retained Schnabel to conduct an alternatives analysis for addressing deficiencies with the radial gate lifting chains. Alternatives included a site inspection of the existing chains and hoist operators, and a comprehensive analysis of using more corrosion-resistant materials for chain construction. Following the selection of an alternative by PG&E, Schnabel provided final engineering and design for replacing the chains and updating gate position sensor limit switches.