Hello! First post. Let me introduce myself...My name is Eric. I live in southwest Missouri and own 10 acres. We average 43 inches of rain here a year and its a zone 6 climate. Hot humid summers and cold wet winters. I'm a certified permaculture designer and took my permaculture design course, reading the landscape and earthworks course through Geoff Lawtons online design class last year. I am currently implementing my permaculture design. There is a lot to my plan and my story so I'm going to give you some back ground before I get into the pond question if you don't mind.
This is the contour map of my property and my neighbors property right below it. Mine is at the top in yellow.
Here is the satelite image of the same property.
And as a reference here is my permaculture design as I would like to implement, but i'm making some changes, its all fluid at this point and not set in stone.
I purchased a transit level and surveyed all the property and studied the patterns of the landscape quite closely over the period of three years. I've had a well drilled into the top of the ridgeline, its a "simple pump" brand well pump, I can drive it all off of the solar system I am installing.
I had a building pad built and built a 40x50x12 all steel building on top of the well and will build a house on one end and my shop on the other. Cooled from what I hope to be geothermal from the well. A few pics
n
Now on to the pond! The things we all love! I was excited for the building but I'm more excited for the pond. I have the perfect landscape to create a ridgepoint dam. A place that no one ever thinks to put a pond because it has zero catchment. In permaculture they teach us that everything must have at least 3 uses. My goals for the pond are, one, To use the light reflecting off of the pond to help me gain more solar energy, both in my solar panels and heat gain in the winter, two provide irrigation for my gardens and tree growing systems, and three I would like to use it grow fish to feed my family. I intend to fill the pond from three sources. one, the building itself, in 1 inch of rain I can expect approximately 1700 gallons. Two Giant swales will be cut on contour all around the property that will collect water and run it into the pond, and three, I can pump water out of the well, all day long, as long as the sun is shining.
Due to it being a ridgepoint dam and not in a valley, it will naturally take on a kidney bean shape as the land is higher in the middle of the ridge then the points. I have surveyed it out and its going to wrap entirely around the buildings SE and E sides. I'm shooting for a .25 acre pond with a depth of 8-12 feet according to the nrcs.
Here's the area the pond will be, i've been moving my 3 years of accumulated junk to make room for it
[img]
http://s6.postimg.org/4czthxsmp/20151101_101454.jpg[/img]
The giant hole in my front yard was where they robbed clay to build the pad. Bieng Im on a ridge and constructing a ridge point dam I have an abundance of material. I performed a soil same and I'm very close to pure clay in alot of parts, so the ponds a go this weekend.
[img]
http://s6.postimg.org/lqwma4pwx/20150905_123744.jpg[/img]
[img]
http://s6.postimg.org/bi454b1v5/20150907_125731.jpg[/img]
Here is my question. How deep should I dig the keyway or core trench. At each corner of the dam, the bank will be 3 foot 4 inches higher then original ground level and 1 foot higher in the center of the ridge then original ground level. The dam wall itself, will become the driveway to the shop and approx 12 feet wide at the top with a 3 to 1 slope into the pond and most likely the same or a little steeper on the back slope. the back slope will be planted in bamboo to lock the dam into the landscape and for ease of maintenance. "Plus" i can cut bamboo stakes for use in the gardens and tree markers, but you guys already knew I had a third reason
I know I was taught to build core trenches in my earthworks class below the bottom of the pond, and that makes sense to us for common valley dams, the most common type of pond, as you need to "LOCK" the dam into the landscape and prevent seepage.
But I was not taught about core trenches on a ridgepoint dam, as they are not common at all due to the zero catchment. So should I take the core trench all the way below water level, even though 80% of the dam is going to be below original ground level? I almost bet I really only need to go probably 6 feet down or so to act as the mechanical lock and then just compact and compact layers and layers of clay. Opinions? Even if it seeps a touch I can correct that easily with ducks.
Im so excited. If I get this right, since sediment cannot build up in this pond, if I get these earthworks correct, I will have a pond and swale combination that could be here for hundreds of years repairing the earth around it. Thanks for looking at my post!
