I didn't have much of a dam as mine is a hole. I pumped it out with a 2" trash pump that my excavator guy gave me to use. It took over a week! The excavator guy got in there and cleaned out half the pond, and said he would be back early the next day which was Friday. As you can guess, we had a localized rain event that knocked down giant oak trees and dumped 6" of rain filling the pond to overflow. I went out and got a 3" pump and used that as much as I could, but we didn't have 250' of flat hose to reach the ditch, so back to the 2" pump. 10 days later he got back in there and finished. We didn't get anymore than 8' deep because we had water coming in from the bottom. Pond filled to 6' deep in a few days with no rain at all. It is my third, and the forth pond that has been built on my street. No one can get more than 8' because the water comes in like a fire hose not to mention it pretty much rains, or snows here every day. One of those benefits of living in the middle of the rain/snowbelt of Lake Erie. We laugh at winters that don't produce at least 10 feet of snow. 20" of rain so far this spring and more coming this week!
