Pond Boss Forums POND CONSTRUCTION Building a dam irregular shaped dam

I've got a question that's been on my mind and haven't been able to find any discussions on it. I, like many others I've seen on here, prefer the aesthetics of an irregular shaped pond; giving it a more natural look to the shoreline. I was wondering if anyone has gone out of their way to build a dam that wasn't straight. This is really just an aesthetics thing. You can always tell a man made pond from a natural one because of the dam. Even if the dam was just curved it'd look better IMO.

Are there any downsides from a structural standpoint? I would expect it to cost a little more but are there any other negatives?

Both of my dams are C-shaped with the inside of the C pointing uphill, and the spillway coming out of one corner. They don't look a bit natural, though. Many of the ponds around here are the same. I don't see many piped spillways, and not very many totally excavated ponds.

With the spillway on one corner do you get good circulation?

The dam on my bigger pond is curved on purpose to look natural with the concave side facing the pond. Many folks think it a natural pond.

The older one has only been over the spillway once. Newer one not close to full yet. Both are ovals. I get good circulation when I pump water into them nearly parallel to the bank.

You sound like my wife. I spent an extra day on the dozer so our pond shape would have "character" as she called it.

It is only time and money. Given enough of both, you can shape it many ways.

Well good to hear. I was imagining there may be forces concentrated on certain points as opposed to spread evenly across the entire dam if it were straight. Overthinking things again.

Force is proportional to the depth of water against the dam. On a typical excavated and dammed pond, that seldom exceeds a few psi. More of the water pressure will be in the excavated portion, and not affect the dam. If a gully or draw is dammed, then there is more pressure on the actual dam.

Probably not over thinking. I'm no engineer, but logic would seem to indicate an irregular shaped dam would require more reinforcement than a semi-circular one.

Imagine a round plastic tub compared to a rectangular one. When filled with water the rectangular one sides will tend to bulge, all other things of construction integrity being equal.

So I think your concern is valid. But from a practical standpoint it is more a matter of cost than design limitations. A longer curvy dam is going to take more dirt to construct but it can be made sound throuh proper design.

If the sides of a pond were made of solid material that provided tensile strength, then the physics would be similar. In this case, it depends on what is behind the inside of the dam (dam width and profile), not its shape specifically. A dam that is convex toward the pond works to be stronger because of compression against what is behind it (think of how an arch works in buildings). Not sure I am using the engineering terms correctly because its been a long time since I took a physics course. As a practical matter, almost all earthen dams fail due to water going over the top of them or through them, not from the weight of the water. Flowing water erodes them.

https://www.bayt.com/en/specialties/q/148146/what-are-the-causes-of-failure-of-earthen-dams/

Very solid points RAH and it definitely sounds like you know what you're talking about. And that's half the battle usually.

I'm thinking a bonus of a curved dam is that it would be a good way to use up some additional dirt excavated from the pond. It might take a little more time to construct the dam but it might be a wash if it prevents having to truck dirt offsite.

Thanks for the discussion everyone.

I went concave and am happy with the result. BTW - Unless you are selling the dirt, it is usually a lot cheaper to use it on site. Putting as much as you can behind the dam (or to increase free-board) is good insurance, along with an over-sized well-built emergency spillway.

That looks amazing RAH. It's so green. Love the boulders and the touch of lilies. I'd love to have some boulders around and in the pond but I doubt I'll find any in this part of the country and the cost to bring them in might hurt.

The rocks were found during excavation as you probably surmised. It is important to plant the things you want soon after the pond fills so that they out-compete less desirable plants (but some removal of invasives, especially at the beginning, is usually required).