Monday, January 2, 2017

RK/L&N/MC&L Bridge over Cumberland River in Clarksville, TN

(Bridge Hunter, no Historic Bridges, satellite is below)
20161216 6969, upstream elevation
I saved a copy of the satellite image because it caught the RK/L&N/MC&L span is partially open.

Satellite
Satellite
It must be closing because you can see a towboat delivering a barge to Ingram Materials in the upper-left corner of this second satellite image.

+40+40, downstream elevation
The river must have been a lot higher when the satellite images were taken than when I took my pictures because the clearance was over 50 feet. I would think that would be plenty for a towboat.

Note the material handling operation under the left side of the swing span in my telescope closeup of the swing span.

Once again I've learned that having the sun at your back is not necessarily a good thing when taking pictures of a bridge. As the caption indicates, I cranked up the brightness and contrast of the closeup of the swing span. Below is another downstream elevation view, but I did not post process it except for cropping.

downstream elevation overview
Note the piers are stone except the concrete one on the right (west) side of the swing span.

downstream elevation
Greg Biggs comments on Bridge Hunter page explain: "The stone piers were built in 1859-1860 for the original wooden swing bridge built to cross the Cumberland River for the Memphis, Clarksville & Louisville RR. A few years ago a barge did a hit and run on one of the original piers and it was rebuilt" Echo Anderson observed that this was one of the few bridges that survived the flood of 2010.

I took pictures of the downstream elevation from the boat launch and a river side park, but they all turned out to be quite disappointing like the "downstream elevation overview" picture above from the boat launch. Fortunately, my wife took a bunch of "grab shots" as I drove along the river. Especially when we saw how long the wooden approach trestle was on the west side.

upsteam elevation

Also note the huge guard pier they have upstream of the center pier for the swing pier. I imagine it is easy to control the direction of a tow going upstream because the relative speed of the water past the rudder would be high when the towboat is pushing against the current. But for downstream tows that are flowing with the current, the relative flow of water past the rudder would be low. I'm sure the towboats have twin screws so that the throttles of the two engines can help steer the tow. But that big guard pier indicates that twin screws can have limited control.

Update: A 3D Satellite image shows the length of the trestle over the flood plain.

3D Satellite

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