otto,
To some extent... I am in louisiana and everything holds water.. ha ha.. But really I am in "hills" north of baton rouge.
The few ponds near me are old and poorly build with little water shed and all loose 2-3 feet of water during the dry periods.
One test hole I dug was 4 feet deep by 3 feet in diameter. It completely all but 8 inches with ground water, after a rain completely filled then dropped back to that 8 inch level. However it is directly "up stream" of an old pond that I cut the dam to drain that had nearly completely silted in. There had been ( and continues to be) a continous influx of water seeping from the ground thru the old pond bed and out thru the dam where I cut it.
My dam at this site will be 10 feet total height from current ground level with some excavation to about 15 feet in places. and I am going to have to plan to dig at least 3-4 feet in most areas to achieve depths of 3-6 feet thru the entire pond bottom.
I know no dirt guy around..