Garnet Bridge Over Mill Creek Replacement
Location
Garnet Street at Mill Creek, Mentone Area
City or County Responsible for Project
County of San Bernardino
Category
Bridge: Efficient and Sustainable Bridge Maintenance, Construction and Reconstruction Projects
Author
Sundaramoorthy (Sri) Srirajan, M.S., P.E.
County of San Bernardino Department of Public Works
825 E. 3rd Street, Room 143, San Bernardino, CA 92415-0835
(909) 387-8166
Project Description
The project replaced the existing Garnet Street Bridge that traverses the Mill Creek Wash in the community of Mentone. The bridge was constructed in 1925 and placed in its current location in 1941. The original bridge was a metal truss structure atop concrete footings built as part of a concrete and rock abutment on the north and south sides of the wash and was 159 feet long with a width of only 17 feet, 10 inches from rail-to-rail. Average Daily Traffic for Garnet Street in the project location is 2,610 vehicles per day. To improve safety and community access, while ensuring low maintenance costs and increased efficiency, the replacement bridge was constructed as a two lane 200’ long and interim 52’ wide concrete box girder bridge with bike path and sidewalks in both directions. The new bridge was designed and constructed to accommodate future bridge widening to add an additional two lanes, as well as withstand a 100-year storm event. The project is located in an environmentally sensitive area of Santa Ana River region. Approximately 0.84 acres of critical species habitat is impacted by the project. Rather than buying credits from a mitigation bank, the County provided compensatory mitigation by partnering with the Redlands Conservancy, a local non-profit conservation agency, to fund the long-term management of over 100 acres of wilderness area adjacent to the project. This provided a public benefit by ensuring the long-term management of a large section of critical habitat within the same upper Santa Ana River Watershed and saved $150,000 in taxpayer dollars at the same time. The County also collaborated with the City of Redlands to relocate an existing city waterline and with Verizon for their utility pole relocation. Taking full advantage of the seasonal nature of water flow within the creek, a shoo-fly access road through the creek was opened to commuters during peak hours, instead of a typical shoo-fly detour bridge. The creek-bed shoo-fly required extensive coordination with the Santa Ana Regional Water Quality Control Board to develop environmental mitigation measures and ensure habitat protection. The temporary detour road was removed after construction. The cost-efficient approach of constructing the bridge to accommodate future growth, partnership with the Redlands Conservancy, and the creative method of constructing a shoo-fly on the creek bed, rather than a detour bridge, reduced the amount of funding needed for the project significantly. Total cost to design and construct the bridge was $6.1 million, which was funded 80% with federal Highway Bridge Program funds and 20% County funds.
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