First off love the forum and all of the information.

I am looking to have a pond built in the next year or so on my property in upstate New York, southern tier.

I will be a dammed up ravine with a spring at the top of the ravine along with runoff water. Pond is at lower portion of slanted property. Looking to make it about a 1/4 to 1/3 of an acre 8 to 10 feet deep, counting depth of ravine and overall height of sides. I would get the dam would be maybe 8 feet tall.

With a pond that size how wide should the dam be and how wide should the core be. Dont need overkill.

Thanks in advance for all info

I have a 1/4 acre pond (10 foot deep) that was built into a ravine. The dam at the water line is about 100 feet long. The adjacent two shorelines are 170' each (triangle shape). But, the top of my dam is much longer due to the 2 - 3 foot of freeboard. Freebaord is the height of the dam above fullpool level (where the outlet pipe is located on the pond side). This is very important to my pond as it holds alot of water once the overflow pipe is flooded and keeps it from flooding my front yard. It acts like a holding basin and yields good flash flood protection. I have excess watershed that tends to flush the pond a few times a year.

I can't really advise you with respect to pond construction design, but there are two books that get recommended here very regularly to those building a pond...

"Just Add Water"

"Perfect Pond...Want One?"

Found Here...

https://www.pondboss.com/store?c=8

Welcome back and it's good to hear that your startig the process!

The core (keyway) should extend into each side of the natural soil.

Agree with Noel on the books. Just Add Water and Perfect pond are/is is about dam design and construction. It will answer questions that you don’t know to ask.

We built our 3rd pond on our own 2 years back right at 1/2 acre. My advice is to aim for overkill on the core and dam. I have good clay but found a sand lens down about 5-7 feet that had to be cut by a solid core on 3 sides of the pond. Water coming into the pond through this lens required a bottom drain be installed during construction (valve closed at pond bottom after completion). I also built the u-shaped core and dam using good clay compacted with a sheep-foot roller in 6-8" lifts and it is at least 25 feet wide at water level everywhere. Also have over 5' of freeboard everywhere. Pond has held water like a drum since filling. Dam could be considered overkill, but I don't stress over its durability. I also have an earthen emergency spillway, but it has not yet been used. I actually built a berm on the upside to stop surface water in my small watershed from running directly into the pond (must filter down and through soil. Biggest issue so far is low fertility, but there is a treeline a ways below the dam that adds leaves each year when we get strong southern winds in Fall. Just letting the FHM and LCS forage base build now, and my emergent plant spread along with a lotus that is struggling with the low fertility. Best of luck to you! Find a pond expert, not a dirt digger.

Thanks for the responses. I have already purchased Otto's book but it wont be here for a couple weeks.

I guess I wasn't clear enough with my question. When I stated width of the dam, I meant wide of the core. not from shore to shore but from water to the outer part of the dam. Like 4 feet, 6 feet.. I would just like to get some education before it is actually done as I will feel better knowing in advance before the project begins then trying to learn on the fly.

I don't think there is an exact answer because the core trench size depends on many factors. Just like many things for ponds.

Also your dam is going to have be in the 10-15' range in height if you want a depth of 8-10'. I worry about that depth in the NY winters. What are your goals for the pond?

Not that my comments below are the right answer for you pond location, but, for an example, my pond was originally built in the late 60's/early 70's and the top of the dam (with 2 foot of freeboard) was about 6 feet wide. I don't really know if it had a legitimate core.

I had the pond renovated a few years ago and the muck was pushed to the back side of the dam and dressed out. It is now basically 20 feet across at the top and so much nicer to mow and hang out on.

The real concern is if you think your pond will overflow the dam. If so, the wider the better. My emergency overflow area is more like 40 feet across. A narrow dam will wash out much faster if/when your through pipe is overtaken and the water flows over the dam.

Just food for thought really,

The core width is typically determined by the blade width on the dozer for small ponds.

I’m also talking about the width of the core. You core instead of just dumping and packing dirt on the sides to tie both sides together. It prevents a seam at the bottom and sides. Seams leak.

And possible the width of the sheep's foot roller or whatever you compact the core with.

My sheep's foot is only 4' wide so I had to make multiple passes.