Friday, May 5, 2017

US-67 Bridges over Black River in Pocahontas, AR

(no 1986 Bridge Hunter, 1934 Bridge Hunter, several satellite views in the posting)

The left  satellite image is of the whole bridge; it spans a wide flood plane. The right image zooms down to the swing span over the normal river channel. Bridge Hunter talked about a swing span, but even after looking at the street view, I did not believe that was a swing span truss.But seeing the HAER photos show that it is a swing span even though it doesn't have the "tower" that is normally in the span where it sets on the pier. The new bridge was built in 1986, so obviously by then there was no need to swing the span since there was no room to do so. The old bridge was supposed to have be torn down after the new one was built, but traffic was heavy enough that they kept both bridges until 2016. In 2016 they closed the old bridge, blew it up, and started on a replacement bridge. In the flood video below you can see construction activity on the new bridge.


Street View
The HAER caption for this photo explicitly labels it as a turn span. They made the HAER record of this bridge after 1986 because you can see the piers for the new bridge. And I can see the underside of the new bridge so that I could determine that it has a steel-girder design.

HAER ARK,61-POCA,1--3 from LoC
I finally decided that the drone was over the normal channel, and the big white building is the Walmart Supercenter.
Screenshot from video
Looking at another satellite image, the city planners did keep development out of a flood plane, but the flood plane is not big enough to handle large runoffs. According to the comments on the video, flooding does occur rather frequently in this town.


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