Manning Crevice Bridge Replacement, Riggins, ID


Atkins North America for the Federal Highway Administration – Western Federal Lands Highway Division

Manning Crevice Bridge is a 248-foot long one-lane suspension bridge with timber support towers crossing the Salmon River 13.5 miles from US 95.  The bridge was constructed in 1936 and the current sufficiency/load rating for the bridge has continued to degrade.   The project site is located in a steep, rocky section of the Salmon River Canyon.  White Shield provided survey services to support conceptual and preliminary design, hydraulic studies, and floodplain analysis for the new bridge.  Surveyors verified existing control on-site, tying to any control monuments near the project location, including one NGS monument, and one US Forest Service monument. Additional control monuments were set as necessary to perform a survey that included topographic and all cultural and natural features.  A medium-resolution High Definition Scan (HDS) of the project site was performed to facilitate topographic data collection and maintain the ability to “mine” data, as needed, for future specific design areas.  The HDS data captured elevations 200’ above grade to edge-of-water through the corridor to support future hydraulic modeling.  Mapping was provided in MicroStation V8 format (DGN) under FHWA WFLHD element placement standards.  Maps showed control, property and rights-of-way, and all cultural and natural features tied.  Contours were shown at 2’ intervals, and ASCII files were provided showing point numbers, northing, easting, elevation, and descriptors.

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