Saturday, January 28, 2023

1911 River Mill Dam and 25mw Hydropower on Clackamas River at Estacada, OR

(Satellite)

Clark Niewendorp posted
The River Mill Dam, a hydroelectric dam and powerhouse just north of Estacada, Oregon, on the Clackamas River was built in 1911. It is an example of an Ambursen-type dam, a concrete-slab-and-buttress dam design. Only three dams of this design were built west of the Mississippi, and the only one to survive.

I noticed that the dam has a fish ladder dug into the north bank of the river. I also noticed the pipe that was added to spray water into the river. Since the pipe's inlet is near the top of the lake, the purpose is not to add cold water to the river. Is the purpose to oxygenate the water or to create a flow in the river near the fish ladder and away from the hydro plant discharge? Or both? Or something else?
Satellite

This peak through the trees shows more of the fish ladder.
Sing PaPa, Aug 2022

HydroReview
25mw

Sing PaPa, Aug 2022, cropped

Sing PaPa, Aug 2022, cropped
 
They evidently still use the original five horizontal-shaft generators.
HydroReview

This dam does not look like a buttress dam to me. I expected to see a bunch of triangular walls that are perpendicular to the face of the dam. For example:
Roseland Dam via Structurae.net

I do see a bunch of parallel white lines in today's spillway. Did they fill in the spaces between the buttresses? 
No. In addition to the usual upstream slabs for a buttress dam, I think they added slabs on the downstream side to form a spillway. In other words, the dam has more void space than concrete on the inside. [HydroReview]
Satellite

Another photo that shows that it was important to wall off the buttresses to create a spillway.
OSU Special Collections & Archives : Commons, No restrictions, via Wikimedia Commons

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