Pond Boss Forums POND CONSTRUCTION Soil questions Max Slope of Island Bank in Clay Dugout

I’d like to have an island in the pond I’m planning to dig. I’m thinking about what the slope of the banks should be. I know 3:1 is typically recommended for safety reasons but given it is an island I’d like to go as steep as possible to limit the amount of area available to vegetation.

The pond will be dug out of “near perfect clay” that has been sitting for eons, so structurally it holds really well. I’m wondering what you think the steepest is that I could go. Could I go 1:1 and still have it not slump? Steeper? Less steep? What do you think?

One question I would have is the proposed island existing dirt, virgin soil, that you will be cutting out from around it, or will this dirt be piled up to create an island?
Virgin soil if left undisturbed will hold up to steeper slopes then you will be able to maintain with dirt that has been worked.

I have found that islands are more trouble than they are worth for a pond, and you lose a LOT of water volume in the pond due to the island. Geese nest on it, catfish can dig holes in the bank and spawn, etc., etc.

But to answer your question, I wouldn't consider going steeper than 2:1 slope.

If you have any kind of wind wave action, you need to line it with rock. So you need a slope rock will stay on. Waves will wash a couple feet a year from your bank.

Thank you all for your thoughts. Gehajake, yes it will be cut out of virgin soil, so I'm wondering how steep.

Esshup I agree with you that islands can create a lot of headaches. I am hoping I can keep the geese off, as I would like to give the kids something to swim/boat "around". It is also a dugout so I don't have room for the extra soil anyways, so I won't lose any water volume that I could otherwise gain.

2:1 sounds reasonable. I was thinking I could maybe get away with 1:1, but maybe that is too aggressive. I don't think I should have any waves nehunter as you point out, as it is only 1.5 acres in total.

The steeper the banks are the harder it will be to get vegetation established, and once it is established, how will you mow or trim it? Set up a piece of 4x8 plywood at a 2:1 slope and try to walk on it. Think about if the water drops or does not stay at the same level that you think it will. Set it at 3:1 and check it again. You want the bank above the water line a gentle slope and I'd also make that slope continue down 3-4 foot water depth. Another reason for that is if the banks are too steep below the water line the fish will have no place to spawn. Think about habitat and cover for the fish too, how will you keep it in place if the banks are really steep?

A client has 3:1 slopes and they can't be mowed. The guy that dug the pond didn't know what he was doing and there is about 20-25 feet of 2:1 to 3:1 slope around the whole pond. Where the water level was, the water cut the bank and it's even steeper because it slid into the pond. The weeds are 4' high around the pond and it is unfishable unless you are in a boat, and you can't even see the water because the weeds are so high. Even in a 1/2 acre pond, you will have some wave action and the banks will get eroded.

Hey esshup, I should clarify that I only mean under water. Above water it will be much more gradual. There will be lots of other areas for spawning with more gradual underwater slopes, so it is really about just keeping cegwtqtion down around the island where nobody can really walk/mow/fish anyways.

Given this info do you still think 2:1 is steepest underwater slope? If it’s only the under water part could I go 1:1?

I would still make the slope 3:1 until at least 3' water depth, then go as steep as you dare and still not have the dirt slough off and fall to the deepest part of the pond - safety reasons. Fish spawning reasons too - sometimes the fish don't understand where you want them to spawn......