Tetra Tech INCA provided urban roadway design and construction
services for widening 2.8 miles of 228th Avenue SE in the City of Sammamish. The project resulted in a to a four-lane urban arterial with a planted median for access control, and left-turn lanes at major intersections. Roadway improvements, such as illumination, landscaping, sidewalk widening, and a meandering walkway near the future site of the Sammamish City Hall, were determined through an urban design/public works workshop and consensus building with the public and interested stakeholders.

This project included traffic control at major intersections, pedestrian lighting, storm drainage, stormwater management and treatment, coordination with various utilities, and preparation of right-of-way.

Tetra Tech INCA provided civil/site and structural engineering services for small bridges, drainage, and traffic for this trail extension. The extension of existing trail system provided a natural, safe level trail connection between the Madison Park and Montlake/University communities and between the existing Lake Washington Boulevard bicycle route and the Burke-Gilman Trail.

The trail is a vital link in the city-wide and regional trail systems. It connects the Burke-Gilman Trail with an I-90 path and Lake Washington Boulevard Route. The trail now traverses wetlands adjacent to the Broadmoor Golf Course, which serves as a buffer between the golf course and Foster Island. The trail in sensitive areas is mounted on timber piles above the wetted surface of the wetlands to minimize impacts.

Tetra Tech INCA was selected to design flood gates at the Old Bayou Segnette Pump Station and at the entrance to Company Canal. Initially, approximately 1,200 feet of structural flood wall was designed to protect the distance between the two gates.

At Old Bayou Segnette Pump Station, INCA designed a 30-foot-wide vertical lift gate. The gate will be powered electrically and controlled from three operating stations and has a manual back up lowering system.

At Company Canal, INCA designed a barge gate with a 45 feet clear opening, sill elevation at -8.00 and still water level at elevation 9.00. The barge is approximately 15 feet wide and 47 feet long. During storm threats, the barge will be floated into the closed position from the stored position via a powered windlass and then ballasted down for potential flood events.

Bluestone Dam is a flood control dam located in southwest West Virginia that has a continuing problem of drift and debris loading in the upstream reservoir. To identify options for alleviating this problem, the Huntington District performed a study that recommended construction of a multi-level gated intake tower and tunnel through the dam, to pass the drift and debris.

Tetra Tech INCA was selected to:

• Evaluate the finite element analysis performed by WES
• Prepare a Seismic Response Spectrum finite element analysis of the Intake Tower
• Prepare a Seismic Time History finite element analysis of the Intake Tower and dam monolith
• Optimize the Intake Tower structural form and prepare construction documents
• Provide engineering support during construction

The tower is 116-feet tall and the operating deck was designed for 37 feet of submergence. The tower walls were designed for a total head differential of 106 feet.

The corner collector entrance gate and piping system project included detailed design, contract plans, and specifications for a 15-foot wide by 28-foot high entrance wheel gate for a surface collection system to enhance downstream migration of juvenile fish past the Second Powerhouse at Bonneville. The design included provisions to supply flushing water to fish transport channel and modifications for relocating the powerhouse unwatering pump discharge pipe in the conveyance channel.

Tetra Tech INCA prepared plans and specifications for the entrance gate and associated storage systems; design of piping systems which included relocating the unwatering pump discharge in the conveyance channel and piping for flushing water system; and design coordination with hydraulic and biological work.