Concern over the height of the new bridge over the Columbia River has been way overblown. There will certainly be an impact of any new bridge on Thompson Metal Fab, located just upstream of I-5. For the past few years they have been assembling barge loads of oil-drilling equipment produced by a number of regional fabricators that are sent each summer to Prudhoe Bay, Alaska. These barges are loaded to utilize the full height and width of the existing bridge lift span. Clearly this loading operation will have to be moved since there is no way a new bridge will have a lift opening or a clearance of 178 feet.
But most of us have no idea how much clearance is needed for a new bridge. A useful comparison would be the U.S. 190 bridge that crosses the Mississippi River at Baton Rouge, just north of New Orleans. This bridge does not have a lift span, and has a clearance of 113 feet during low water conditions. This clearance is often reduced to about 80 feet during high water spring flooding conditions. Since there is roughly 50 times as much tonnage passing under this bridge compared to the I-5 bridge, clearance isn’t a big problem.
Jim Windus
Vancouver
