Hole in a swale

Hi guys

in one of my client's property, there is a hole in a swale, emptying a large proportion of the water that the swale holds. It is a deep hole, and looks like a collapsing or like it has been dug by an animal.
The hole is at least 1 meter (3 feet) deep and 60 cm (2 feet) wide.

I am about to fill it with clay, compact it, and plant it with trees. But I am curious what strategy you would adopt?

Thanks

I can't envision the structure very well, but I discovered that swales need spillways, and I really like rip-rap or cobbles for constructing spillways.

I don't know where you are, but we have a sinkhole in our back yard - not quite bottomless, but close, LOL! My nephew dropped one of my old galvanized feed cans (30 gallon garbage can) down the hole to stop it up somewhat because we had young critters in the yard (puppies, goats, calves at the time). Unfortunately, he put the can in the hole right side up, it then filled up with water, and can't be removed. So that's one way NOT to do it!

What you have planned sounds like it should work, as long as your hole isn't the bottomless kind.