Belowground Stream pond

Hi Zach, nice to have you here. We (my girlfriend and I) have a small creek flowing in our land, and we would like to build a large pond. There are 2 options: putting a dam, or making a below ground pond. I prefer the second idea, I seems more natural to me. I can imagine something like this:

The construction process would be different than the one described here http://www.motherearthnews.com/diy/stream-pond-zmaz86mazgoe.aspx?PageId=1

Also I very like the natural (and slow) way to build it, I was planning to dig the pond, using the clay to build our house. The question is: how to best avoid erosion where the water falls into the pond? Indeed, I expect to create a 0.5 to 1 m high fall, and am a bit concerned about erosion problems. I was thinking to 1) put logs, like in the link above, and enjoy a waterfall 2) put a flow form or 3) avoid the fall by creating a gentle slope starting 5-10 meters upstream, with some kind of "stairs" in case the slope is still too steep.

What do you recommend? When it rains, the small creek can grow, but not too much, as the watershed is not that big and the soils quite good. By the way, I'd love to know what you would recommend if the creek could grow big, like in dry/arid places and destroy any logs or flowforms we put in.

thanks a lot!

greg

Hi Greg,

Great question, this one really made me think. This seems like a good technique to make a swimming hole, but I wouldn't really consider it a pond per say. A couple of thoughts.

From my training with Sepp I have been trained to be wary of any wood, debris, or roots being accidentally incorporated into a dam, as these will provide eventual failure points moving forward. That said for this type of swimming hole you are not creating a dam but rather a water fall that creates a swimming hole; I like the strategy if your primary goal is to make a deeper section in a creek to plunge into. It is also certainly great habitat as the article mentioned. This seems appropriate for swimming holes but I wouldn't consider this technique for a large pond with potentially serious consequences in the event of a failure. Here are my only concerns.

I would NOT use galvanized anything in a creek. It is pretty toxic stuff and I would never knowingly incorporate that into a stream system. But I am a purist when it comes to this type of thing.

I've heard that wood will not rot so long as it is constantly submerged in water. As there would be ample time when the top log is exposed to air it seems like this system would eventually fail over time. That said this could be a very long time with a species like black locust and the ramifications would not be too severe as you are talking about pretty small changes and a small amount of water being held behind this structure.

With this method don't you want erosion where the water enters the "pond." My understanding from the article is that this is the force you are using to make the deeper pool within the creek. Spillways armored with rock and replicating a stream bed is the best way to mitigate erosion that I know of.

It is important that you do calculations for the watershed of the creek to understand the water potential for the 24 and 36 hour 100 year rain event and feel confident that your system can handle the water from an even larger rain event. If I were in your shoes I would create a Holzer style water retention area with a keyway dam as this is what I understand will lead to the greatest benefit for the surrounding ecosystem. You will save many years of work on your back's sake with one day with an excavator. And when it comes down to it even if you only value your time at $10 an hour you will save a boatload of money by calling in the big guns for the heavy work. That's my 2 cents.

Sounds like a beautiful spot you guys have to steward, best of luck with this project!

Hi Zach,

thanks a lot for your detailed answer.

IMHO we should try to avoid putting dams in permanent creeks and rivers, as they can block wildlife. (agreed, with a good design and a well-placed spillway, this should not happen). This is why I like the idea of a belowground pond. Also, in case of a 100 year rain event, because there is no dam, then there is nothing that can be destroyed.

I wouldn't consider this technique for a large pond with potentially serious consequences in the event of a failure

mmh, what could be the serious consequences?

Then for the upstream part of the pond: if I use an excavator, then I would not be interested in the slow erosion process where the water enters the pond, maybe I would do a sort of backcut (to avoid the waterfall) so that any wildlife (fish) can continue to swim upstream. In other words, the water stream after the earthworks would continue as before, just passing through a pond that was not there before

Thanks you, again, and best greetings from Latin America,

greg

Greg Amos wrote: IMHO we should try to avoid putting dams in permanent creeks and rivers, as they can block wildlife.

I couldn't agree with you more Greg! Often times it is confusing for people when in "Desert of Paradise?" people see Sepp visiting a large reservoir and calling it an ecological catastrophe. The is the difference between decentralized natural water retention and man made reservoirs that actually steal the water from the surrounding land. With these Holzer style water retention areas the dam is made entirely of earth and the spillways does not impede wildlife, they actually enhance it similar to these waterfall swimming holes you shared. Most importantly the water is cycled by nature in accordance with her flows. These types of dams don't steal water, they just hold onto it for a little while.

A hydroelectric dam allows water to flood the creek when there is a need for power, not during the natural cycles. This can cause catastrophic damage for eggs and larvae of countless creek and river species. Not even to mention the need for fish ladders to even have a CHANCE of a wildlife corridor. And that is for the "Eco-Friendly" hydro-electric projects.

When I lived in Alaska I was quite near what was at one point the most productive river in the world. This was from the huge salmon spawns that used to travel the river each year. Today not a single salmon spawns up this river, with the city of Juneau built around it. Pretty surreal whenever I step back and think about that.

Greg Amos wrote: what could be the serious consequences?

If you are retaining a much large volume of water than the creek usually handles this much rushing down all at once can cause considerable damage downstream. Either via erosion, sediment flushing down the creek at an unusual time, or in the worst cases changes in stream course and catastrophic damage to downstream infrastructure. In Vermont one rain event cause millions and millions of dollars of damage because that large of an event had not been accounted for in much of the engineering.

Greg Amos wrote: the water stream after the earthworks would continue as before, just passing through a pond that was not there before

This is the ideal, nature always knows best and provides the answers to all questions.

Latin America is a stunningly beautiful place, sending my best to you down there!

Hi Zach,

great! I feel more confident now, thanks a lot for your support.

I'm looking forward to starting working on this!

all the best

greg