Monday, May 11, 2015

Los Angeles County, California Bridges: Hyperion and Glendale Bridges across the Los Angeles River (4)

August 1999 (34.1138 Degrees, -118.2654 Degrees) Los Angeles River Bridges
Standing on the deck of the Glendale Bridge and looking at the strange cutwaters facing downstream. The transmission lines cross the river south of the bridge where a big electrical substation is located. The Fletcher Drive Bridge, a seven span T girder bridge built in 1927, sits beside the substation on a large skew on a bend in the river. As we approach downtown L.A. the reinforced concrete bridges become more attractive.
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Los Angeles County, California Bridges: Hyperion and Glendale Bridges across the Los Angeles River (4) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.


Alan said...

The turbulence downstream of the piers of the bridge you are on would have caused problems at the piers of the old electric railway bridge you are looking at, -- scouring and/or hydraulic damming at the downstream piers, so continuous barriers were installed between. Those look newer, perhaps even postdating removal of the railway bridge, and since the bottom here appears to be concrete, scouring should not have been a problem, so I am wondering if they aren't actually a response to a hydraulic damming problem that actually developed.

I think they would properly be considered cutwaters upstream of the downstream piers, not downstream of the upstream bridge. ;)

Mark Yashinsky said...

Dear Alan,
I just realized that those tall structures downstream are actually the piers of a bridge (the electric railway bridge you mentioned) that used to sit there. The walls between those piers and the Glendale Bridge remain a mystery to me, unless they used to support another structure?

Alan said...

A google image search for "pacific electric bridge glendale" turned up pictures with both rail and road bridges (and PE train :) both before and after the barriers were built. Continued searching turned up a few more. All the before pictures showed the natural riverbed, all the after showed the concrete riverbed. It would be interesting to know all the dates, and to see pictures during construction, to see if they really were the same project.

Note that the PE bridge is at an angle to the channel and to the road bridge, so that the distances between the corresponding piers for the two bridges is different in each case. This could have set up some fascinating turbulence effects during floods, potentially raising the water level at the right bank dramatically, along with some extreme scouring conditions just about anywhere across the width of the river.

Googling "glendale bridge flood" turns up some interesting pictures from 1938. Though I didn't see anything specifically showing these bridges, it wouldn't surprise me if this was the incident that led to the channel (and "cutwater") work.

You must know some engineers involved in bridge pier footing design, I would think bringing the issues of scouring and hydraulic damming up with some of them could be fascinating.

My own interest in this narrower aspect of bridges (I have long had a more general interest in bridges) has been boosted by seeing some dramatic downstream rock sculpting carved by the ice age glacial outburst Missoula Floods channels, below pier-like obstructions. That was reinforced by the I-5 Skagit River bridge collapse of a couple of years ago, when I wondered what potential impact the dropped spans might have on scouring around the piers.