Urban Pond to Dam or not to Dam, Damn it......?

Hi,
I'm Brand spanking new to the forums, well long time lurker first time poster just set up a real account.

So I am going to build a pond in the backyard and I need some advice.

The decision it comes down to is whether or not to use a pond liner or build a miniature dam and seal the pond holzer style with manual labor, rock bars tampers etc.

Location:
Austin Texas

Soil:
Clay soil lightly expanding

The conditions:
The back yard is sloped to the back SW corner with an overall drop of 2.5 feet and a run of ~80ft from corner of the house to the opposite corner of the yard. The yard itself is rectangular 80X50ft. All the runoff from the roof flows into the back corner eventually as well as the runoff from the front yard which travels around the house into the backyard. The area the pond will go in was the site of an old shed. The dogs dug under the shed a foot or so and made a depression.

Design Goal:
I want to enhance this depression by using it as the deep zone for a 3 foot deep pond with steps at 2ft, 1ft, and 1/2ft. The pond would be ovalish and about 10-13ft wide at its shallowest zones. There would be a 2ft walkway around the back in between it and the fence.
I want to use manual labor to dig out the pond and then seal it by doing "the pigs work" using rock bars tamps and lots of people jumping up and down in sync. I would have a deep zone of about 3 ft about 4ft around at the back where I would like to put a dam key in. The pond would have a 10ft long finger coming off to use as a level spillway into the neighbor's yard on the other side of the fence.

Question?
Could this be done at all and or is it too dangerous for the neighbors if it fails or makes a mud puddle of their yard?
How deep, how wide, and how long would my impermeable layer or key have to be and would it need to wrap around the back corner?
How do I know if the clay content is high enough to seal and also to create the impermeable layer?
If I don't have high enough clay continent what do I ask supply companies for to get high clay dirt?

Or am I just overthinking the issue.

Resources I have:
Lots of people (this will be done at a permablitz)
Lots of rock bars and tampers plus 20-40 pairs of feet

Please any questions comments recommendations or criticisms Thanks,
Bryce

It certainly would not hurt to try the "natural way" first, At worst, the water will just seep away and you will have to find a better way to seal it.
You could also add some bentonite clay to help it seal.

I'm not sure what the necessity of the spillway going to the neighbor's is? Is that the lowest point?


You should test the soil to determine the clay content, here is a good way:
http://preparednessmama.com/jar-soil-test/

one way to test how leak-proof your pond will be is to dig out a sample of soil, and build your ideal pond in miniature. Tamp it down, see how well it holds water. Also, make it overflow and see how the water flows.

I'm not really sure why you want to dump all the excess water onto your neighbor's property though - can you create a network of swales you can feed through the rest of your property? If you can rent or borrow a BCS walk-behind tractor with a rotary plow, you can make quick work of small swales:

https://www.youtube.com/watch?v=VvKDadSiVd0

Thank you both for the thoughts.

As for the finger overflow. The pond will be at the lowest point in the yard and if it does over flow I want it level and flat and long so it moves aa a sheet into my neighbors yard as opposed to something more concentrated like a small spillway. The pond will be the last stop for water first moving through two swales and along a hugelkultur with wildflower patches next to it before ending up in the pond. The flow from the back roof will go first in to a tiny "naturally formed" swale, feeding the largest fig tree I've ever seen in texas. Then it will overflow into a small more scalloped or boomerang type swale and then into the main sawale before traveling along a hugelkultur mound and through a small wildflower area bordered by the hugel to which runs N by NE to SW and the swale to the north with a small strip of native wetland border plants and then into the first 1/2 depth of the pond which will be a very gradual transition.

I will do the soil test this weekend and post the results.

So if this seems feasible then I guess my next question is how do I make the Damn Key.

How deep should it be?

Does it need to go all the way down to the impermeable layer or can I get away with only going a few feet deeper than the pond.

I dont need but the deepest three layers to seal the 1/2ft zone can leak a bit to hydrate the area. Is that an unrealistic way to go about this?


Thanks for any imput.

It sounds like you have a lot of variables, the good thing is that you can't really screw it up, I've found my ponds are more of a continual development than a project that has
a beginning and end.
The main point is to slow/stop and make use of your natural water source- rain. Anything you do that keeps it from just rolling down hill to somewhere else is success.
(so don't worry!)


One "pond" I dug just will not hold water, so now its a deep swale that I've planted bamboo into.

"The pond would have a 10ft long finger coming off to use as a level spillway into the neighbor's yard on the other side of the fence.

Question?
Could this be done at all and or is it too dangerous for the neighbors if it fails or makes a mud puddle of their yard?"

What you do to the drainage system affects your neighbor. A cautionary tale...
My neighbor decided his property would sell easier without a pond, and filled his in. He ruined a well designed pond based drainage system. Big pond A overflowed into a pipe running under our street. This pipe fed another pond B which had a underground pipe feeding his tiny pond, C. His overflow was also directed underground into my larger pond, D. My pond overflows into a drainage ditch which joins the water shed traveling to the river a couple miles away.
The owner of pond B spent some funds to raise the walls of his pond higher, eventually after several blow outs, spending more money, putting in an overflow pipe that simply drains over some gravel he had to purchase, which has become a ditch, off of his property. He did what he could to fix his own land.
Pond C no longer exists, soooo... Now there is a lovely V shaped groove that carries all the run off across that yard, over mine, into the pond. This V deepens as the years progress. During the rainy seasons, I often have a river up to ten feet wide dividing my property. My pond is significantly more shallow now. Erosion. Delightful.
How do you get along with your neighbors? Are they litigous? We aren't. In your case, you wish to add a pond, perhaps reducing a seasonal flood in their backyard. They may end up grateful. It may be wise to bury a french drain nudging any overflow toward an additional swale?
I do hope your plans bear good fruit.