I've seen excavated ponds in my area on flat terrain that have filled in a year. Some of these ponds were created by the highway dept for the use of the dirt. Ofcourse, the soil type and annual rainfall are essential factors. Excavation projects can be costly though, usually requiring the use of an excavator and a dozer or bobtail, depending on what you plan to do with the excavated dirt. I recently had an excavation project completed, and was able to have the removed dirt spread with a dozer. I paid $105/hr for the excavator and $90/hr for the dozer. The total cost was $4600. Actual yards of dirt removed is difficult to estimate as bank area of an exsisting ponds was being removed. But, I'm guessing that enough dirt was removed to probably fill a 1/4 acre pond 6 feet deep.