Sounds like the best possible site, no damn is probably the safest structure of all, in fact I heard there are legal requirements as to damns, and pond size...but if there is no damn, then I think it is possible to have up to 1 acre pond without any govt. permitting...subject to your
local law requirements of
course! As for silt, that is why ya dig it down deep first, because silt is going to get in there somehow. If you prepare for & immediately put in erosion control plants like ferns, bushes, or whatever, that stops erosion pretty well... gather those early from the site before you dig an save some money.
Hay bales are good but they look like hay bales & grass seed may not be the kind you want.
James Beam