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?