Wednesday, January 17, 2018

Trail/US-66 Chain of Rocks Bridge over the Mississippi river north of St. Louis


Some comments indicate that you should park on the Illinois side, not the Missouri side. On the Missouri side, car windows have been smashed and items stolen, frequently. And it sounds like even on the Illinois side you should make sure that anything valuable is hidden in a spare tire or something quite clever. Just putting something in the trunk won't stop the thieves. It is probably best to leave a window rolled down so that they won't have to smash it.

William A. Shaffer posted
Chain of Rocks Bridge - St. Louis, MO
(Photo by William A. Shaffer)
If you're from the St. Louis Area, chances are you drove over this bridge once or twice. St. Louis has many bridges that span the Mississippi River, but only one with this terrible curve in it!
Steve Porter Great picture of The Curve. Imagine two trucks trying to navigate it from different directions.
William A. Shaffer I think the trailers were shorter back then, but it would still be a tight fit. I remember orange flashing lights somewhere around this spot, too.
William A. Shaffer Steve Porter, I believe I was shooting toward the Missouri side.
Both the strange 22-degree turn in the bridge and the Chain of Rocks owe their existence to glaciers. During the last ice age, the Mississippi River was re-routed from its original channel in soft river sediment (farther to the east in present day Illinois) to its present channel over resistant (mainly limestone) bedrock. The river has yet to wear down the bedrock and this feature is still a rough spot in the river. If the bridge had been built straight, the engineers would have had to choose between two problematic routes. One route would have put the bridge in a location where it couldn’t have been solidly founded on bedrock. The other route would have posed problems to river navigation by not allowing barges to line up with the current, possibly causing them to collide with the bridge. Although this bend was troublesome for motor traffic, it served as a compromise between geological and navigational concerns.
If a bridge were built in a similar location today, the extra expense to make the bridge straight would certainly be spent. In the day of the Old Chain of Rocks Bridge, cars were narrower, slower, and traffic was less of a concern. Today’s foundation piers can also be driven more efficiently and to deeper depths. The old bridge is still structurally sound after all its years. The unusual the bend in the fifteen-span bridge definitely adds character and doesn’t give pedestrians or cyclists any grief.
[conorw]
John has an alternative explanation for the bend:
The interesting feature of the Chain Of Rocks Bridge is the 24 degree bend about halfway across the river. The promoters had purchased land on each side of the river, but the parcels were not directly across the river from each other. The plan was to build the bridge on a diagonal to the river. The US Army Corps of Engineers objected to having a bridge cross the navigation channel at an angle. As a result, the section of the bridge crossing the navigation channel was built straight across the river, and then the remaining part of the bridge was built on the diagonal to meet up with the Missouri shore. The result is the 24 degree bend where the straight and diagonal sections meet.
[WeeksBridge]

In the satellite image, you can see a ripple just downstream from the bridge. More on that later.
3D Satellite
3D Satellite
This is a closeup of the upstream tower. These are water intake towers for a filtration plant. The sources conflict on weather or not they are still in service. These intakes are similar to Chicago's water cribs.


Street View
Street View
I zoomed in so that you can better see the two towers. Also note that you can see a ripple in the water.
U.S. Army Corps of Engineers (source link was broken)
Satellite
The "water ripple" is caused by Dam #27. It raises the water level for the intake to the bypass canal on the east side of the river. At the end of the canal is Lock #27. "Locks #27 are the busiest locks on the Mississippi River given that they are located south of the convergence with the Missouri River, so these locks handle the combined cargo flow from the Mississippi River, Missouri River, and Illinois River." [WeeksLock]
Satellite
(new window)



Forgotten Railways, Roads, and Places posted
William A. Shaffer posted two photos with the comment:
The Chain of Rocks Bridge at St. Louis, MO and the actual Chain of Rocks, for which the bridge is named.(All Photos by William A. Shaffer)I remember as a kid going over the Chain of Rocks Bridge. It had the bend as shown in one of these photographs. What I had forgotten what how narrow the bridge actually was. A couple of years ago, I walked across the bridge. The bridge has been closed to vehicular traffic for years. It really was built to accommodate Model T's!

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