My long term goals have always included a healthy farm pond. I would like to capture the water at the top of my West-south-west sloping site, and I would really prefer to capture the water above the large fenced garden for future irrigation. If I use a 16:1 ratio, there is enough catchment area 'up hill of the proposed 0.1 acrepond to provide adequate water and the prior landowners have created a diversion ditch/stream along the NE corner of the plot.
But here is my concern: the actual pond would end up 30'-45' above the ground level of my home, and if there were a dam failure, the pond would come rushing down into my home & basement. Anyone else have a 1/10th acre pond (or larger) elevated behind their home? How did you handle it? Could I focus my earth-works on making sure that the trails/paths are also drainage ditches in case of an emergency, to guide water down around the house?
Pond questions continued: The area I have in mind for the pond is 'wooded' with scrub pine. Should I have those trees chopped now, then start the slow process of uprooting the stumps and excavating (via wheel barrel & lawntractor) topsoil away from the area of the future pond for other uses around my homestead? Or should I wait and have the whole thing done at once (trees downed, stumps excavated, and pond detention wall created) by experienced machine operators at some point in the future?
The soil maps say that there is a fragipan layer (water impermeable compressed clay & sand) between 10"-22" down into the soil... and I believe them. When I walked around the site on a normal moisture day, there were still soft & squishy areas on the slope. Can use the fragipan layer as a pond bottom? Could I excavate the fragipan from elsewhere around my land to use as a pond liner? Permies bonus -- removing/puncturing the fragipan should improve drainage on the site.
You have not given enough specifics about overall property for a good designer to start making recommendations. That being said, I'll point you in the direction of PA Yeoman there's lots of references and more modern equivalences but this is really where our design parameters originate when it comes to water design. Understanding keyline design, key points, contour swales for water harvesting and productive trees, and even zone configurations will really give you the information you need to begin to evaluate your plans.
My own preference would be to look at the overall farm, all the other uses and possible storages of water, slopes, and then come up with a complete main frame water design for the property. Then any individual element you install will fit in with the rest of the design as you get the pieces ready. You will probably want to be there at least for a full year, and go out and play in the rain often, watching water flows (if you haven't already).
I prefer to install the higher water storages first, since they will start the land hydrating and as they mature, more water will be available farther down for other features.
The house can have slightly above it compacted clay banks /terraces/paths/ slanted slightly back into the hill and sloped slightly downhill to either or both sides of the house. If you have paths already in the right place they could be developed to serve that function. Not so much to avoid dam wall rupture, since a properly designed and executed pond /dam will be good for a thousand years, but more just to generally keep the house and foundation drier and more stable as the landscape around it becomes more hydrated.
As far as machine vs hand labor. I live with compacted clay and rock as my topsoil, so digging by hand is done with a pick or steel bar. I'm tired of breaking my back and a backhoe doing everything at once is most appealing. Often just getting the backhoe there is most of the expense, so having more projects than just a single pond is the best use of the money- But everyone has to do their own evaluation of labor at home vs labor for others and just how much time and trouble a backhoe might save them. When I rented a backhoe the first time it took me quite a while to find where the key went, but by the end of that week rental I had installed a septic tank and drainfield and saved myself about three thousand dollars. --Just a thought
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