Rufus Laggren wrote:Travis
Happy New Year!
The wood dam looks interesting. Seems like something worth pursuing. A couple thoughts come.
First and the one I'm least detailed about is the undermining. Not sure about anything here - I don't have any PE creds. It seems to me that weight of the structure may have a bearing on how well it "sticks" in place. Also how well it resists lifting. I _think_ the wood structure may be considerably lighter than most dams. Then there's the question of soil permeability in the immediate dam area - how much "ground water" would you create with the pond, moving how fast, how deep? Would that impact the footings of dam significantly?
Second what is the life cycle of the dam? How does it evolve over 1,2,5,10 years with possible silt, erosion, wood decay? Since the life cycle is probably much shorter than that of a concrete dam, maybe it should be a very specific part of the design.
Third, what are the failure modes? Well designed engineering fails gracefully. Ie., it fails slowly, with multiple layered warnings and in manageable ways and locations. Because there are doubtless properties not to far downstream and possibly even work areas, habitations and such, this might be the most important consideration.
Oh, and fourth, how much would depend on fasteners? Metal fasteners don't have the great a working life in water. Fresh is much better than salt, but seems like it might need planning for.
Rufus Laggren wrote:Sounds like you have a safe test area. Sounds like maybe try it out? Possibly start low, 3-4' and see what happens. 50% of the knowledge and gain for (probably) 25% of the cost.
Thinking about it, resistance to the water weight still looks really iffy. Consider concrete forms and the need for whalers - fluid weight applies a _lot_ of horizontal force. I don't think a sloped face will change that force much - just maybe allow more down force. Which may not be enough to hold the thing in place w/out multiple _structural_, not hydraulic, keys. The more I think about the more it looks like "low" and "short term" may be the defining characteristics. And that would point to the question of how much benefit such a thing would provide you. Viable life span figures pretty important when trying to price out the ROI.
Another thought: If a small dam would cause enough sediment buildup quick enough, maybe it would effectively "grow" and maintain some effect even after it begins to fail.
Here are two links I dug out from another life. They are just random pages, examples - neither addresses the question here. But I think the sites themselves can be mined for good info on this type of project so I pass them along.
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