Evaluation of timber crib dams

[GeotechPE]

My firm is preparing a proposal to provide engineering services to investigate and rehab (if applicable) an existing timber crib dam. I am looking for any references on the design and analysis of timber crib dams.

Thanks for the help.

 

[blueoak]

FERC is the best with:

http://www.ferc.gov/industries/hydropower/safety/guidelines/eng-guide/chap10.pdf

Very short description in older handbooks:
Low Dams,1938 by National Resources Committee
Engineering for Dams, 1947, Creager, Justin and Hinds

You might also try stream bank protection methods. Timber cribs are considered temporary and in new texts it is typically ignored. I only see it in stream bank protection handbooks, but be careful because these designs are typically allowed to fail during large storms.

Rehab for a timber crib is not ideal especially if it is above a town. Massachussetts recently accomplished it, but NY had a failure. The only time I run across timber cribs is in reports of dam failures back in the 20's through 30's. This is also back when the US govnment published handbooks on building dams with 6 mule teams and sheep.

 

[GeotechPE]

blueoak:

Thanks for the references.

The 14 foot high structure in question was constructed in 1842. Thats 164 years of services. For timber crib that is impressive. The structure has been concrete capped, had sheet pile added up stream and who knows what else over the decades.

We can not just recommend that the structure be abandoned becuase intuition says so. We need to provided some rational analysis to base our recommendations on. I anticipate replacement of the structure so I can sleep at night.

I did not know that the dam & earth retention forum existed. Do you think I should post this question in that forum also?

Thanks again.

geotechpe

 

[PEinc]

If FERC is involved, good luck. I was involved with a wood dam, about 22 feet high by several hundred feet long. The dam was hollow, but built upon a concrete base slab. FERC made the dam owner tear down the dam because no one could prove that the treated wood and connections were still OK after many years. I had to drain the 110 acre lake and then remove the dam.

 

[blueoak]

I haven't seen much in the dam forum.

The problem with these structures is that they are fine during normal operations, but get a flood event and they suddenly start to disintegrate. It seems like a lot are still in the east on large rivers with big populations. So you have downstream flooding occuring, no good way to drain the dam and then your structure suddenly fails sending a surge down the river overwhelming downstream flood protections.

As a retrofit you might consider replacing a section with obermeyer gates. You could potentially evacuate most of the reservoir prior to flood water reaching the dam. As for the dam, it sounds pretty ugly, I would check the history on it to see how many times it has failed. I have seen 80 yr old dams that have been completely rebuilt 4 times(but somehow people only remember the 80 yrs not the 4 failures). I guess it is like a ship, so long as a single timber remains it keeps the same name.

 

[GeotechPE]

PEinc, blueoak:

thanks for you input.