Ok kiddo, have you ever seen a dock before? It's like a platform that you can stand on that goes out into the water. Well, a floating dock is just like that but it's made with materials that help it float on top of the water.
Now, sometimes people might want to have a floating dock in a small area of water, like a pond or a lake. To do this, they create a space in the water where the dock can sit by building walls or barriers around it. This is called an impounded floating dock.
The walls around the dock keep the water from flowing in and out of the space. It's kind of like putting a fence around a backyard. The impounded dock is like the little yard inside the fence.
This can be really helpful if you want to keep your floating dock in one place and make sure it doesn't float away with the current. It also gives you more control over the water, so you can keep it clean and free from debris.
So there you have it, a floating dock (impounded) is just a special kind of dock that sits in a little area in the water that is enclosed by walls or barriers.