I am looking for advice on building an embankment pond in a primary valley keypoint at my homestead. The existing slope is 25% and according to the USDA soil survey site info, the soil is mostly a well-draining, fine sandy loam with 12-16% clay, down to 80"+ and then, eventually, weathered bedrock. This link -- Pond Site -- is a KMZ file that you can open in Google Earth to see the proposed pond location with the property lines and some 5' and 1' contours added.
Is this site a good location? How can I construct a stable dam with this soil type? What equipment should I use? If you have recommended local contractors, who could help with this project that would also be appreciated.
The soil surveys are pretty general. I would recommend auguring a hole to look at the soil first hand. If you moisten it and give it the ol' ribbon test, and get about a 2" ribbon or more, you might be in luck. The weathered bedrock reference is generally not good. If you hit bedrock, it will likely be very hard to seal. A very small crack can cause the pond to leak.
In looking at the aerial pic, it looks like the drain's side slopes are going to be pretty steep. That being the case, it would likely be hard to have an adequately sized emergency spillway without a bunch of dirtwork.
Looks to me like you could go down the drain into that open field and have a better pond site and an easier to build emergency spillway as well. With the steep channel slope up on that mountainside, the pond surface area doesn't look like it would be very big anyway.
Thanks for the reply! Good point about the spillway. What is the ideal slope for an emergency spillway? In the "worst but not best case scenario" of having a poor ribbon test, but at least not hitting bedrock.. is a secure dam still feasible? While the obvious answer would be a pond further down the hill, the "open field" is livestock pasture and the further up I can build a pond, the better gravity feed potential I have for irrigation use, etc. Ideally, I would also like to construct a second pond on the east property line, where there is a gully forming in that valley from a spring that is flowing down the channel and causing erosion. This second dam would have to stretch across the property line onto the neighbor's land, but it might one day be possible. Assuming I could get these two ponds to a fairly decent size, I would then want to wrap thin, long ponds around the hillside on contour with interconnecting swales and terraces for growing various crops and trees. That is my fantasy, at least.
The google Earth image is great, really helps to visualize the situation. Few thoughts....
The drainage you have the proposed pond in is really steep. I would be very concerned about a dam blowout, which looks like it would do some real damage to your road and maybe house. The amount of earthmoving needed would be enormous, and still I would be very concerned about a heavy rain event.
The bedrock problem could be mitigated with a liner. If thats what you need, then thats what you need. Not a huge problem, adds some cost, but also gives you some certainty about water holding, especially in dry times.
Looking at the site, and reading your objectives, my thought is to install a diversion in the drainage at about the location of your proposed pond. Then run a ditch on contour to move the water to the East, along the hillside. Locate your pond in the small uppermost portion of your field, fairly close to your east property line.
Reasons for this is that if (when) you do have a blowout in the drainage, it would be much easier to repair a diversion than a pond. You could bring the water on contour around the hillside creating habitat. Your pond would still be much higher than the majority of your fields, so still useful for irrigation. That field still has a really steep slope, so you are going to need to move a TON of dirt to get a good sized pond there. Your dam will be enormous. Consider restrictions on maximum dam height before needing special permits, because you will likely be pushing those limits.
Definitely get a well respected local with hundreds of successful ponds to come out to your site. This wont be an easy job, but it still may be feasable. Good luck!
Hmm.. I like the diversion idea. I am definitely concerned about designing for high rain events. I am also allured by the designs of Sepp Holzer, which have similar grade slopes to mine. You can see his land by searching Google Earth for "Krameterhof - Josef Holzer". It is also viewable at this link: http://wiki.worldflicks.org/krameterhof.html He has over 60 small ponds on a mountainside in the Alps, which he uses to irrigate and to keep many kinds of fish. Attached is a closer aerial photo of a few of the ponds. Pretty amazing ideas that I would like to try and emulate, if they don't end up breaking the bank and also the dam.
