Inspired by a link from Professor Bogdanski showing a water bridge over a river -- a bridge that carries a ship canal over a river -- I have solved the Columbia River Crossing problem. Pictures of the bridge itself are here, at Amusing Planet.
The problem of the bridges themselves is not that their lanes are narrow -- they aren't -- nor that they don't have enough lanes. The current bridges have just as many lanes as the freeways to the north and south; they're choke points only because so many entrances feed into them on both sides without enough room for merging. Besides this problem, the existing bridges pose another problem: they are drawbridges, and they are lifted 425 times a year to make way for river traffic, or just to keep the machinery working. With more clearance over the water, they would have to be lifted less often, or not at all if they are replaced with fixed bridges.
So far the highway people at ODOT and WSDOT, being highway people, have limited their concrete solutions (sorry) to plans to replace the bridges with a new and higher bridge, in effect, to raise the freeway. The Magdeburg Water Bridge of Professor Bogdanski's post suggests another and cheaper way to solve this problem. Instead of raising the bridges, lower the water.
"Huh?" I think I heard you say, possibly spewing coffee over your keyboard. No fooling: let's lower the water to provide more clearance. Here's how: Build a lock underneath the bridges, with a chamber a little more than twice as long as the longest ship or barge tow that now requires the bridges to be lifted. Extend the lock, possibly, underneath the railroad bridge. The lock does not have to cross the entire river, but only the space between two of the bridge supports. (Fish and small craft can still use the rest of the river without going through the locks.)
Dredge out about another forty feet or so , reinforcing the bridge supports as necessary. Again, the dredging is just in the lock chamber, not across the entire river. Barge tows will then be able to enter the lock at one end and wait while the water is pumped out to lower the tow as far as necessary to clear the bridge. When the water is lowered sufficiently, the barge tow will cross beneath the bridge to the other side. The lock operator will then raise the water level and open the gates so that the barge tow can proceed upstream or downstream, as the case may be.
The result? No more bridge lifts, no ridiculous reworking of the ramps, no destruction on Hayden Island. Light rail, if it should ever go to Vancouver, can use the railroad bridge.
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