The Polk Trestle structure is an abandoned railroad trestle located over Little Sandy Creek in Polk, Pennsylvania. Polk Trestle features a 60-foot wide concrete arch with a concrete slab that lines the stream channel. A concrete weir/obstruction is located at the downstream end of the concrete slab that creates a 4-foot vertical drop from the concrete slab to the downstream pool level. The trestle structure is located on property belonging to the Commonwealth of Pennsylvania and removal is being overseen by Pennsylvania Fish and Boat Commission (PFBC). Polk Trestle demolition design was executed as a design-build project with AK Hydro supporting the contractor’s engineer (Honor Engineer Co.). AK Hydro was responsible for the hydrologic and hydraulic analysis, stream restoration design and analysis, and permitting support.

The existing trestle structure and weir/obstruction has created a significant scour/plunge pool downstream of the obstruction. To ensure long-term stability of Little Sandy Creek, rock cross vanes and constructed pools have been designed within the vicinity of the existing trestle. The cross vanes create a step pool configuration that would allow fish to navigate the structures and connect the upstream and downstream reaches that were previously disconnected by the trestle. In addition, the stream structures provide countermeasures against potential headcutting that could destabilize the upstream reach and impact upstream pools and fish habitat established by PFBC. After the trestle structure is removed, the trestle embankment will be cut to a stable slope and the toe of the embankment will be stabilized with riprap.

AK Hydro developed final design documents for the stream restoration design based on the results of the HEC-RAS hydraulic model. The final design documents included the development of a stream stabilization plan, proposed stream profile, stream cross sections, and typical stream and streambank stabilization details. The stream restoration design documents were coordinated with the contractor and the final design accounted for the recycling of existing concrete into the stream restoration features to offset construction costs. AK Hydro participated in an initial and periodic review meetings with Pennsylvania Department of Environmental Protection (DEP) to expedite the permitting processes.