On a 'U' shaped pond, do you core trench the entire dam?

I'm planning to hire this out, but I want to know what I'm talking about so that I can properly convey the message (without sounding like an idiot) to the contractor.

The property slopes gently from north to south, so everything except the northern shoreline will essentially be a dam.

Should all 600 feet of the dam be core trenched, or just the portion at the southern end that has 16 foot deep water pushing against it?


Side notes:

I'm planning to dig a 2:1 slope starting at the northern shoreline to a depth of 6 feet, and then the southern shoreline (dam) will have a 3:1 slope and it will be dug out enough to achieve a water depth of 16 feet.

I'm no pro, but I would say yes.

Hi David:

I'd try to engineer the pond with the smallest dam possible, might mean losing some pond size, but you save significant $$ as that size dam will be expensive. If you're committed to a 600' dam, per Bobbss, I strongly recommend having a core trench installed in it's entirety.

I'd ask for an estimate regrading the land and digging a pit pond or something with a much smaller dam. I'm curious if it may be less expensive than core trench install. Whatever you do, strongly encourage installing a high plasticity clay liner in 4-6" lifts from 18-24" to ensure your investment is successful. I work with leaking ponds every week and they end up costing far more to address than the original cost of engineering the pond correctly with a clay liner. You won't know you needed it until it's too late, sadly.

I would trench everywhere that I don’t water to leak under

In my inexperienced mind...coring a dam does a couple basic things...

1.) It allows for exploring the unknown of what type of earth is beneath the dam's location. If it's all good solid clay then there was less of a need to go there, but you'd never know otherwise. If you find sand/gravel veins or less desirable water holding materials...see #2.

2.) Coring allow the excavation of less desirable materials that can be replaced with good clay. Once layered and packed in, this ties the water holding clay "bowl" to the dam.

Some folks that live on the clay pans out here near the Midwest can often get away with scrapping off the topsoil, digging a hole and piling/packing good clay to form the dam. As Clint would say..."do you feel lucky...?".

If you get a hand auger and bore holes in the natural ground, and you have heavy clay from as deep as you can auger, up to the surface, there’s no reason to make coring a requirement. You are essentially replacing good clay with good clay. Dig holes along the centerline of the proposed dam and save some money. You can get a hand auger from Ben meadows or Foresty Supplier.

On the other hand, if you hit questionable material several feet down, then core it.

Don’t agree. Assure that you get a good core trench the first time.

I am not a dirt expert in any means but I have a pond like you described down to the ammount of dam there is. Only difference is mine is all dam excpt for the south side. I will say this though if you get it cored get the entire thing done. Mine has no leaks in the long dam part but there is a small leak in one of the side dams near where it comes back and molds into the hill. I have no clue if mine is cored or not though.

Adding:
3.) A properly compacted clay core, starting well below ground level and continuing to above water level, acts as a key to help hold the mass of the dam in place against the pressure of (16 ft?) of water attempting to push it downhill.