I recently stumbled across this forum and wish I would have seen it months ago. My family is in the process of designing a pond (approximately 1-acre of water) on our property. The area is quite hilly, and we've determined that we will put the pond on a flat which extends down the nose of a ridge. Significant design points are as follows:
1)Pond will have minimum surface water inflow due to topography (essentially no watershed--maybe 2 acres including pond area itself).
2)Water will be fed via a natural spring that we have already developed for water usage at a cabin. The spring produces approximately 80-100 gpm. We currently gather about 10 gpm at the cabin via a 1" water line. My calculations show that we should could pull the remainder with a 2" line given the elevation drop from the spring to the pond site.
3) Overflow system--still in question. I've enjoyed reading everyone's posts per overflow pipe/syphon system. Asthetically, the siphon system looks better to me. Overflow will be piped back to the creek bed where the spring originates. The pond will be located on a flat that is located on the ridge ABOVE the creekbed.
4) We have surveyed the site and I have built surfaces using CAD software to determine the amount of material to move. We are looking at around 6,000 yards of material to construct the dam. Several test pits have shown that the material is quite clayey--the test pits are currently holding approximately 3' of water from recent precipitation.
5) I've designed the pond to have 2:1 slopes on the outside of the dam and 3:1 slopes on the water side of the dam. I'm asssuming an 8' width at the top of the dam. I'm also assuming 2' of freeboard--I think this is ok because there is such minimal surface water flowing in--everyything will come from the spring and can be throttled.
5) Because we aren't daming a creek, the embankment will be horseshoe shaped. I have attached (or am attempting to attach) a map showing:
a) pond area b) current topo contours from survey c) cut/fill contours (red contours indicate a cut, blue contours indicate a fill for the dam) d) cross section depicting current surface and design surface used in volumetric calculations
6) I have access to Caterpillar's equipment handbook and estimate it will take approximately 2 weeks to move all the material with a 320 excavator and D6 dozer. (I'm a mining engineer and this sort of thing is right in line with my work, just on a MUCH SMALLER scale). Does this sound about right for 6,000 yards?
7) Several of my questions for you guys are below.
a) Compaction--do you recommend a vibratory compactor or will tracking with a dozer be sufficient? b) Drain systems--siphon vs overflow? c) Need for additional secondary spillway with such small watershed? d) Freeboard? 2' sufficient? e) Any other comments you can provide in terms of my dam layout, logistics, etc. We are currently clearing trees--we are about to start a large burning pile and start yanking stumps out.
Welcome to the forum. You are like most of us here, except you are slightly ahead of the curve. You found us before the pond is actually constructed.
I'll be relatively brief, and let others chime in on some of the points.
You will need a sheepsfoot roller or a pan scraper with multiple tires (full of dirt) to compact the soil. Tracks are on equipment to lessen the PSI of the equipment on the ground, something that you DON'T want for compaction. You might also need a water truck, you can't compact it properly if soil doesn't have enough moisture. Ideally compaction in 6" lifts, and roll it enough so the sheepsfoot walks up and out of the ground after a few passes.
Make sure you cut the core of the dam into good soil at the ends.
Do some more thinking on the backside of the dam slope. If you want to mow it, 3:1 is barely mowable - pucker factor keeps you in the seat.
Redundancy is good. I wouldn't rely on one system to divert excess water.
I'd recommend going to the Pond Boss store and ordering "Perfect Pond" and calling them to ask about the content of the Earthen Ponds books. At the very least, order the "Perfect Pond" book. http://www.pondboss.com/store.asp?c=8 Also, think about getting a subscription to the Pond Boss magazine.
One last thing. Think about contouring the ground in the pond to create structure (humps, channels, etc) and start looking at what to use for cover in the pond. It's MUCH easier to place cover in the pond before it fills with water.
This is a very comprehensive handbook that discusses alot of the engineering that goes into building a pond. Using it, I was able to calculate the volume of runoff that would enter my pond for 50 and 100-year storm events and then design an adequate emergency spillway.
