Thanks for the posts, gents. A little more information. The pond is being built in a wooded area, so the watershed of about 7 - 10 acres should provide a good clean runoff through undisturbed woodland. The dam will be built across a natural draw, and will measure approx 50 yards across by 15 ft high. The spillway will overflow across an undisturbed ridge on one side of the damed up draw. Hopefully we will have some natural woodland vegetation covering the spillway, but I'm leaning toward a nice shot rock rip-rapped look at the mouth of the spillway. Our plan is to have the spillway wide enough where it will carry the water flow in a heavy rain to a depth of no more thantwo to three inches. Another feature my contractor suggests is digging a 12 to 15 foot basin where the watershed empties into the pond and then coming up to a 6 to 7 foot level and then a gradual deepening to approx 15 feet at the dam. He says this will act as a "sendiment pond" within the pond and should increase the life of the pond.